Research methods and indicators of external respiration. Assessment of the severity of the disease

The earliest and most pronounced changes in respiratory function in patients with asthma, they are observed in the ventilation link, which affects bronchial patency and the structure of lung volumes. These changes increase depending on the phase and severity of BA. Even with a mild course of BA in the phase of exacerbation of the disease, there is a significant deterioration in bronchial patency with its improvement in the remission phase, but without complete normalization. The greatest violations are observed in patients at the height of an attack of BA and, especially, in asthmatic status (Raw reaches more than 20 cm of water column, SGaw is less than 0.01 cm of water column, and FEV is less than 15% of due). Raw in BA increases both during inhalation and exhalation, which does not allow a clear differentiation of BA from COB. The most characteristic feature of BA should be considered not so much the transient nature of obstruction as its lability, which manifests itself both during the day and in seasonal fluctuations.

Bronchial obstruction are usually combined with a change in the OEL and its structure. This is manifested by a shift in the level of functional residual capacity (FRC) to the inspiratory area, a slight increase in the RCL and a regular increase in the RCL, which sometimes reaches 300-400% of the proper value during exacerbation of BA. In the early stages of the disease, VC does not change, but with the development of pronounced changes, it clearly decreases, and then TOL/TOL can reach 75% or more.

When using bronchodilators there was a clear dynamics of the studied parameters with their almost complete normalization in the remission phase, which indicates a decrease in bronchomotor tone.

In patients with BA more often than in other lung pathologies, both in the interictal period and in the remission phase, general alveolar hyperventilation is observed with clear signs of its uneven distribution and inadequacy to pulmonary blood flow. This hyperventilation is associated with excessive stimulation of the respiratory center from the cortex and subcortical structures, irritant and mechanoreceptors of the lungs and respiratory muscles, due to impaired control of bronchial tone and respiratory mechanics in patients with asthma. First of all, there is an increase in the ventilation of the functional dead space. Alveolar hypoventilation is more often observed with severe attacks of suffocation, it is usually accompanied by severe hypoxemia and hypercapnia. The latter can reach 92.1 + 7.5 mm Hg. at stage III of asthmatic status.

With absence signs of development of pneumofibrosis and emphysema of the lungs in patients with asthma, there is no decrease in the diffusion capacity of the lungs and its components (according to the breath-holding method according to CO) either during an asthma attack or in the interictal period. After the use of bronchodilators, against the background of a significant improvement in the state of bronchial patency and the structure of the RFE, a decrease in the diffusion capacity of the lungs, an increase in ventilation-perfusion unevenness and hypoxemia are often observed due to the inclusion of a larger number of hypoventilated alveoli in ventilation.

FVD has its own characteristics in patients with chronic suppurative lung diseases, the outcome of which is to some extent pronounced destructive changes in the lungs. Chronic suppurative lung diseases include bronchiectasis, chronic abscesses, cystic hypoplasia of the lungs. The development of bronchiectasis, as a rule, is facilitated by a violation of bronchial patency and inflammation of the bronchi. The presence of a focus of infection inevitably leads to the development of bronchitis, and therefore violations of respiratory function are largely associated. Moreover, the severity of ventilation disorders directly depends on the volume of bronchial damage. The most characteristic functional changes in bronchiectasis are mixed or obstructive. Restrictive violations occur in only 15-20% of cases. In the pathogenesis of violations of bronchial patency, the main role is played by edematous-inflammatory changes in the bronchial tree: edema, hypertrophy of the mucosa, accumulation of pathological contents in the bronchi. In about half of the patients, bronchospasm also plays a role. With a combination of bronchiectasis with pneumosclerosis, emphysema, pleural adhesions, changes in the mechanics of breathing become even more heterogeneous. Lung compliance is often reduced. There is an increase in OOL and the ratio of OOL / OEL. Increasing uneven ventilation. More than half of the patients have impaired lung diffusion, and the severity of hypoxemia at the onset of the disease is low. The acid-base state usually corresponds to metabolic acidosis.

In chronic abscess violations of respiratory function practically do not differ from respiratory disorders in bronchiectasis.

With cystic underdevelopment of the bronchi more pronounced violations of bronchial patency and a lesser severity of diffusion disorders are revealed than with acquired bronchiectasis, which indicates a good compensation for this defect and the limited nature of the inflammatory process.

PHYSIOLOGY OF RESPIRATION

Breathing is one of the most important physiological functions. This is gas exchange between the external environment and the body, in which oxygen is consumed, carbon dioxide is released and the necessary energy is generated. It includes external (pulmonary) respiration, transport of gases by the blood and gas exchange in tissues (tissue or internal respiration). External respiration, in turn, consists of 3 stages: ventilation - air exchange between the environment and the alveoli, diffusion of gases through the alveolar-capillary membrane and blood perfusion in the pulmonary capillaries.

Biochemical methods are used to study tissue respiration, for example, the determination of lactate in venous blood, electrochemical blood gas analyzers, and the polarography method.

The transport of gases in the blood can be assessed using oximeters (pulse oximeters). Normally, hemoglobin is 96-98% saturated with oxygen. To assess lung perfusion, isotopic methods are used (introduction of albumin labeled with a gamma-emitting isotope into a vein) and radiopaque techniques. Diffusion ability is determined by inhalation of a small concentration of carbon monoxide by the rate of its entry into the blood.

Due to the complexity of the appropriate equipment, the diffusion capacity of the lungs and the features of hemodynamics are rarely determined even in the largest specialized clinics, while the ventilation function of the lungs is easily accessible for examination by widely used devices and methods. It is primarily characterized by static, dynamic and derived lung volumes and respiratory rates.

1.1. Lung volumes and capacities

Under lung volumes understand the amount of air contained in the lungs in different phases of respiration. Allocate and lung capacity - the sum of several volumes. Static volumes are determined with calm breathing, and dynamic volumes with forced breathing. Derived volumes are usually calculated using formulas.

There are the following static volumes and capacities:

OEL (TLC) - total lung capacity - all the air in the lungs at the height of maximum inspiration;

VC (VC) - vital capacity - the largest amount of air that can be exhaled after a maximum breath. VC, obtained during inspiration after a full exhalation, is somewhat larger, since there is no blocking of air in the smallest bronchi (the phenomenon of "air trap");

OOL (R.V.) - residual lung volume - air remaining in the lungs after maximum expiration;

BEFORE (VT) - tidal volume - the air that passes through the lungs with a calm inhalation and exhalation, on average - about 500 ml;

ROVD (vyd) (IRV, ERV) - inspiratory and expiratory reserve volumes - this is the air that can be additionally inhaled or exhaled after a calm inhalation or exhalation;

Evd(IC) - inspiratory capacity - sum BEFORE And ROVD;

FFU (FRC) - functional residual capacity - the air remaining in the lungs after a quiet exhalation, the sum OOL And RO vyd.

In a routine study OEL, OOL And FFU not available for measurement. They are determined using gas analyzers, studying the change in the composition of gas mixtures during breathing in a closed circuit (the content of helium, nitrogen, radioactive xenon), or with general plethysmography, when the subject is in a sealed cabin and pressure fluctuations are measured in it during his breathing.

The part of the air in the airways and alveoli that is not involved in gas exchange is called dead space (MP). Anatomical dead space - part of the air that does not reach the alveoli on inspiration, and does not go out into the atmosphere on exhalation, functional dead space - the air of non-perfused alveoli. The air of the dead space and the residual volume is involved in the warming and moistening of the inhaled gas to provide the necessary conditions for the vital activity of the alveoli.

The amount of dead space is determined in the same way as the residual volumes. Fine MP is 140 ml in women and 150 ml in men, mainly due to anatomical dead space. Under the minute volume of breathing understand the amount of air passing through the lungs per minute, it is determined by the formula MOD \u003d BH x DO, Where BH- respiratory rate, normally 12 - 20, an average of 16 per minute. Having accepted BEFORE for 500 ml, we get the average MAUD- 8 l.

Considering the presence MP, then only a part of this air, which is called alveolar ventilation, is involved in gas exchange and is AB \u003d (DO - MP) x BH. about 70% MAUD. With deep breathing, the ratio AB/MOD increases, at superficial - decreases.

The amount of oxygen consumed in 1 minute ( IGO 2) is easily determined spirographically. Based on it, you can determine the value of the main exchange ( OO), knowing the energy value of oxygen, taking into account the respiratory coefficient. For this IPC multiply by 7.07 (the number of minutes in a day X average caloric equivalent of oxygen):

OO \u003d IPC x 7.07(kcal/day).

1.2. Forced breathing tests

In addition to static volumes, dynamic volumes are of great clinical importance, determined during forced (most rapid and complete) breathing, especially during exhalation, since inspiration is a more arbitrary act, and therefore less constant. Their use in clinical practice contributes to clarifying the level of bronchial obstruction and diagnosing early manifestations of bronchopulmonary changes in the form of impaired patency of small bronchi.

A quick and complete expiration test is carried out from the position of maximum inspiration, i.e. FZhEL (FVC) - expiratory forced vital capacity. FZhEL less VC by 200 - 400 ml due to the decline at the end of the accelerated exhalation of a part of the small bronchioles (expiratory collapse). If there is their pathology, the phenomenon of "air capture" is observed, when FZhEL less VC 1 liter or more. At the same time, the speed of forced inspiration (test of inspiratory FZhEL) will be greater than exhalation.

Cases when FZhEL greater than or equal VC, should be considered as an incorrectly performed test. All indicators must be determined at least 3 times and take the highest value of each. In addition, the forced expiratory volume in the first second is determined ( FEV1 = FEV 10), which is compared either with the proper value, or with VC or FZhEL.

Tiffno index \u003d (FEV / VC)x100%, normal 70-80%

It decreases with obstructive processes and may increase with "clean" restriction, when VC reduced, and the expiratory rate did not decrease. However, the defeat of only small bronchi often does not lead to a change FEV1 therefore, the Tiffno test cannot serve as an early sign of obstruction. When decreasing VC and preserved bronchial patency, this indicator may slightly increase, and with mixed obstructive-restrictive processes, its value loses its diagnostic value. Then calculate the ratio FEV1 not to the actual, but to the proper VC.

When determining the Tiffno index, two separate studies are required - with calm breathing ( VC) and during forced exhalation, which reduces the accuracy of the result. More reliable can be considered the Gensler index, performed in one go:

Gensler index \u003d (FEV1 / FVC) x 100%, normal 85-90%

Note that FEV, FZhEL And VC taken directly from the system ATPS without recalculation.

For a more subtle and accurate characterization of respiratory apparatus disorders, the expiratory rate is determined at its various moments, as well as the peak expiratory volumetric velocity ( PIC vyd), or the highest rate for the entire expiration time.

Abroad, the forced expiratory volumes are also often determined in 0.5, 2 and 3 s, the time to reach the maximum expiratory rate, the half-expiratory time VC etc. Compared with the Tiffno and Gensler tests, instantaneous expiratory volumetric velocities are more informative ( ISO = FEV in the US system), measured at expiratory points 25, 50, 75 and 85% VC (MOS 25, MOS 50 etc.), characterizing the state of large, medium and small bronchi, respectively, and the average volumetric velocities in the areas of expiration 25 - 50, 50 - 75, 75 - 80% VC (SOS 25 _ 50 etc.).

In another, European, notation, the countdown is based on the proportion VC, remaining in the lungs, then these instantaneous expiratory velocities ( MEF) are denoted, respectively, MSV 75, MSV 50, MSV 25, MSV 25 _ 75 And PSV(peak expiratory flow).

Important information about the functional reserves of the external respiration apparatus is given by the test of maximum ventilation of the lungs ( MVL). Maximum ventilation is the volume of air passing through the lungs per minute of the most frequent and deep breathing.

Typically, the test is carried out for 10 - 15 s, and the result is given in 1 min. Fine MVL 8-20 times more MAUD and reaches 150 - 180 liters. A close correlation of changes has been established MVL And FEV1, so some authors restrict themselves to defining only FEV1.

Additional information can be provided by the shape of the maximum ventilation curve, which shifts upward with obstruction due to air entrapment (increase FFU and decrease RO vd).

1.3. Systems of physical conditions in which gas volumes can be located during spirography

When analyzing tidal volumes, it is necessary to take into account their dependence on changes in pressure, temperature and humidity. In the lungs, the air is in alveolar conditions, i.e. at t = 37 ° C, relative air humidity of 100% and a pressure approximately equal to atmospheric pressure. Under the same conditions, the proper values \u200b\u200bare given in tables and formulas (less often - in standard ones). When air exits the lungs into the external environment or into the spirograph circuit, it quickly cools to room temperature, and excess moisture condenses, while the relative humidity remains 100% (for room temperature), and the pressure does not change. Such conditions are called atmospheric.

The measured oxygen consumption is usually reduced to standard conditions - 0 ° C, zero humidity, pressure 760 mm Hg. Art. These three systems of conditions are abbreviated as BTPS(alveolar conditions - Body temperature, Pressure, Saturated), ATPS(atmospheric - Ambient Temperature, Pressure, Saturated) and STPD(standard - Standard Temperature. Pressure, Dry). The values obtained by spirography (under atmospheric conditions) lead to alveolar and standard conditions. For such recalculations, tables and nomograms have been developed in which, taking into account temperature, pressure and sometimes humidity, the corresponding coefficients are found (Table 1).

Table 1

Approximate conversion factors to BTPS and STRD (at atmospheric pressure 740 - 780 mmHg)

In mass studies, it is permissible to use a coefficient of 1.1 to convert to BTPS and 0.9 - to STRD. Volumes should not be recalculated if they are used in any formula based on the division of two indicators obtained in the same system of conditions (for example, the Tiffno index, Table 2).

table 2

The degree of violation of the ventilation function of the lungs according to N.N. Kanaev

1.4. Research standardization

To obtain stable results of the study, spirography is carried out under the same conditions, as close as possible to the main exchange. The data obtained are compared with the norms (proper values) calculated on the basis of the results of a survey of large groups of healthy people, tabulated, standardized by sex, age and height, or according to formulas obtained on the basis of tables. An indicator that differs from the tabular one by no more than 15–20% is considered normal.

When evaluating the results of a study of lung ventilation function, it is necessary to take into account the reproducibility and repeatability of indicators.

Reproducibility is the allowable fluctuation of the measured values during repeated examination during the day. For VC it is +150 ml.

Repeatability - the limit of fluctuations when repeating the study several times during the year. For VC repeatability is +380 ml. For FEV1 fluctuations within +15% are allowed.

1.5. Lateral test

If it is necessary to detect unilateral lung damage, the lateral (spiroplanimetric) Bergan test, or the lateral position test, is used. To do this, a curve of calm breathing is recorded in the supine position with a raised head (place a high pillow), then the patient is asked to turn on his right side, pressing his outstretched right arm to the body. Due to the displacement of air from the compressed lung, the curve rises horizontally. Next, the spirogram is recorded again in the prone position, and then in the same way, but in the position on the left side. Measure the rise of the curve above the initial level in millimeters when turning to the right and left side (hpr and hleft) and determine the function of the right and left lung according to the formula:

Normally, the function of the right lung is 55 - 57%, the left - 43 - 45%.

Rice. 1. Principles of lateral test analysis

2. METHODS FOR STUDYING THE RESPIRATORY FUNCTION

Spirometry is a method for measuring lung volumes, spirography is a graphical recording of their changes over time. The curve obtained by writing on paper, in the coordinates "volume - time", is called a spirogram. The inspiratory and expiratory rate can be indirectly measured by a spirogram or directly determined using pneumotachometry and pneumotachography.

Spirometry, spirography and pneumotachometry are the most commonly used methods for studying the ventilation function of the lungs. They are non-invasive, cheap, require relatively little time and with satisfactory accuracy allow to establish the presence, nature and severity of ventilation disorders.

There are open and closed type spirographs. The latter can be with or without compensation for the consumed oxygen. In open-type devices, atmospheric air is breathed without taking into account oxygen consumption, which simplifies the study and maintenance of devices. In closed-type spirographs, the subject breathes air from a sealed breathing circuit, which requires the mandatory use of a chemical carbon dioxide absorber, but allows determining the minute oxygen consumption. In this case, the curve of the spirogram gradually shifts due to a decrease in the volume of gas.

To increase the study time on closed-type spirographs, it is possible to gradually add oxygen to the respiratory system as it is consumed, and the main curve will be horizontal, and the amount of added gas is recorded as an additional line on the spirogram.

2.1. Method of spirographic research

Spirometry and spirographic studies in full and in a simplified version (with registration of only the main indicators) are carried out in conditions close to the main metabolism, usually in a sitting position, in the first half of the day, on an empty stomach or not earlier than 1 - 1.5 hours after eating . In the afternoon, a longer rest is needed.

The study of gas exchange indicators is carried out in the morning, in the supine position, 12-13 hours after eating. No pre-training required. The subject is explained the purpose of the study and the respiratory maneuvers that he has to perform.

Unlike ECG spirography has contraindications. It is not recommended to perform it on febrile and infectious patients, people suffering from severe angina pectoris or high unstable arterial hypertension, severe heart failure and other serious illnesses, patients with mental disorders who are not able to properly perform the study, and elderly people for whom regulatory quantities.

Connection to a spirometer or spirograph is made through a sterile mouthpiece (mouthpiece). A disinfected clamp is applied to the nose. Connection to open-type devices is carried out without taking into account the phase of breathing, and to closed-type devices - at the level of calm exhalation.

Respiratory volumes are determined using the formula:

Where LV- line length, S- sensitivity of the device, equal to 25 mm/l.

At a tape speed of 50 mm / min, one minute corresponds to a segment of 5 cm, and 600 mm / min - 1 cm = 1 sec (to determine FEV1. Convenient to use special calculation rulers, marked on such a scale. To determine the proper indicators of respiration and basal metabolism, tables and nomograms are included in the device kit. Taking into account the measurement error (not less than 50 ml), all obtained values of lung volumes should be rounded up to the correct numbers (up to 0.05 l).

A complete spirographic study begins with registration BH, BEFORE And software 2 at rest, not less than 3 - 5 minutes (until steady state). During registration BH, BEFORE And software 2 the subject is offered to breathe calmly, without fixing attention on breathing. Then, after a short break (1 - 2 minutes) with disconnection from the apparatus of a closed type, register VC, FEV 1 or forced expiratory curve ( FZhEL) And MVL. Each of these indicators is recorded at least 3 times until the maximum values are obtained.

During registration VC It is recommended to take the deepest breath and the most complete calm exhalation. Carry out a two-stage test VC when, against the background of calm breathing, they are asked to take only one deep breath, and after a while - only the maximum exhalation. The distance between the tops of these teeth somewhat (by 100 - 200 ml) exceeds the one-time VC. To assess the correctness of the respiratory maneuver, it is necessary to pay attention to the shape of the curve vertices VC. When a truly maximum inhalation and exhalation is reached, the curves are somewhat rounded at the upper and lower points (inspiratory and expiratory apnea).

During registration FEV, And FZhEL it is necessary to inhale as deeply as possible and after a short pause (1 - 2 s) exhale as quickly and as completely as possible, when registering MVL- breathe as often as possible and at the same time as deeply as possible.

Before registering MVL it is useful to demonstrate the pattern of breathing by performing this breathing maneuver with several forced breaths. Registration time MVL- no more than 10 - 15 s. Duration of intervals between individual measurements VC, FEV,, FZhEL And MVL without disconnection from the open-type apparatus and with disconnection from the closed-type apparatus, if the subject easily copes with the necessary breathing maneuvers, does not exceed 1 min.

When fatigue and shortness of breath occur, which is most often observed after a short but tiring registration MVL, the intervals between individual measurements are increased to 2 - 3 or more minutes. When recording indicators of pulmonary ventilation at rest ( BH, BEFORE), software 2 And VC The spirograph paper moves at a speed of 50 mm/min. FZhEL And MVL– 600 - 1200 mm/min.

Loop flow - volume

An important diagnostic value is the analysis of the volume-flow loop of maximum forced expiration and inspiration. This loop is formed as a result of superimposing the flow velocity graph along the vertical axis, and the lung volume value along the horizontal axis. This loop is built by modern computer spirographs in automatic mode (Fig. 2). On this loop, the main indicators of the spirogram are highlighted.

Rice. 2. Loop flow - volume

According to the shape of the loop and changes in its parameters, it is possible to distinguish the norm and the main types of respiratory failure: obstructive, restrictive and mixed.

Normal spirogram. In a healthy person, the conclusion of the study of respiratory function usually indicates that there are no disorders. The table shows a list of indicators of the function of the respiratory system and their normal values. Most of the values of the indicators are expressed as a percentage of the so-called "proper" values. These are values characteristic of a healthy person, male or female, age, weight and height. Conventionally, this can be considered "normal" values.

Rice. 3. Loop flow - volume is normal.

The normal flow-expiratory volume loop (Figure 3) has a fast peak in maximum expiratory flow ( pic) and a gradual decline in the flow to zero, and it has a linear section - MOS50vyd. The inspiratory loop on the negative part of the flow axis is quite deep, convex, and often symmetrical. MOS50vd > MOS50vyd.

Table 3

The main indicators of spirography:

Abbreviations	Notation	Indicators	Normal values in%% to the due (D)
VC	vital capacity	VC - vital capacity of the lungs	> 80%
FVC	forced vital capacity	FVC - forced vital capacity	.> 80%
MVV	maximal voluntary ventilation	MVL - the volume of maximum ventilation of the lungs	> 80%
R.V.	residual volume	ROL - residual lung volume
FEV1	forced expiration volume in 1 sec (liter)	FEV1 - forced expiratory volume in 1 second (l)	> 75%
FEV/ FVC %	forced expiratory volume in 1 s as percentage of FVC	FEV1/FVC - forced expiratory volume in %% of FVC	> 75%
FEV 25-75%	mean forced expiratory flow during the middle of FVC	MOS25-75% - forced expiratory flow rate in the range of 25-75% FVC	> 75%
PEF	peak expiratory flow	POS - peak volume forced expiratory flow	> 80%
FEF (MEF)25%	mean forced expiratory flow during the 25% of FVC	MOS25% - forced expiratory flow rate in the range of 25% FVC	> 80%
FEF (MEF)50%	mean forced expiratory flow during the 50% of FVC	MOS50% - forced expiratory flow rate in the range of 50% FVC	> 80%
FEF (MEF)75%	mean forced expiratory flow during the 75% of FVC	MOS75% - forced expiratory flow rate in the range of 75% FVC	> 80%

Fine FEV1, FZhEL, FEV1/FVC exceed 80% of standard indicators. If these indicators are less than 70% of the norm, this is a sign of pathology (Table 3).

The range from 80% to 70% due is interpreted individually. In older age groups, such indicators may be normal, in young and middle-aged people they may indicate the initial signs of obstruction. In such cases, it is necessary to deepen the examination, conduct a test with β2-adrenergic receptor agonists.

For the diagnosis of respiratory failure, a number of modern research methods are used, which make it possible to get an idea of the specific causes, mechanisms and severity of the course of respiratory failure, concomitant functional and organic changes in internal organs, the state of hemodynamics, acid-base state, etc. For this purpose, the function of external respiration, blood gas composition, respiratory and minute ventilation volumes, hemoglobin and hematocrit levels, blood oxygen saturation, arterial and central venous pressure, heart rate, ECG, if necessary, pulmonary artery wedge pressure (PWLA) are determined, echocardiography is performed. and others (A.P. Zilber).

Assessment of respiratory function

The most important method for diagnosing respiratory failure is the assessment of the respiratory function of the respiratory function), the main tasks of which can be formulated as follows:

Diagnosis of violations of the function of external respiration and an objective assessment of the severity of respiratory failure.
Differential diagnosis of obstructive and restrictive disorders of pulmonary ventilation.
Substantiation of pathogenetic therapy of respiratory failure.
Evaluation of the effectiveness of the treatment.

These tasks are solved using a number of instrumental and laboratory methods: pyrometry, spirography, pneumotachometry, tests for the diffusion capacity of the lungs, impaired ventilation-perfusion relations, etc. The volume of examinations is determined by many factors, including the severity of the patient's condition and the possibility (and expediency!) a full and comprehensive study of FVD.

The most common methods for studying the function of external respiration are spirometry and spirography. Spirography provides not only a measurement, but a graphical recording of the main indicators of ventilation during calm and shaped breathing, physical activity, and pharmacological tests. In recent years, the use of computer spirographic systems has greatly simplified and accelerated the examination and, most importantly, made it possible to measure the volumetric velocity of inspiratory and expiratory air flows as a function of lung volume, i.e. analyze the flow-volume loop. Such computer systems include, for example, spirographs manufactured by Fukuda (Japan) and Erich Eger (Germany) and others.

Research methodology. The simplest spirograph consists of a double cylinder filled with air, immersed in a container of water and connected to a device to be registered (for example, a drum calibrated and rotating at a certain speed, on which the readings of the spirograph are recorded). The patient in a sitting position breathes through a tube connected to an air cylinder. Changes in lung volume during respiration are recorded by a change in the volume of a cylinder connected to a rotating drum. The study is usually carried out in two modes:

In the conditions of the main exchange - in the early morning hours, on an empty stomach, after a 1-hour rest in the supine position; 12-24 hours before the study, medication should be stopped.
In conditions of relative rest - in the morning or afternoon, on an empty stomach or not earlier than 2 hours after a light breakfast; before the study, rest for 15 minutes in a sitting position is necessary.

The study is carried out in a separate dimly lit room with an air temperature of 18-24 C, after familiarizing the patient with the procedure. When conducting a study, it is important to achieve full contact with the patient, since his negative attitude towards the procedure and the lack of necessary skills can significantly change the results and lead to an inadequate assessment of the data obtained.

The main indicators of pulmonary ventilation

Classical spirography allows you to determine:

the value of most lung volumes and capacities,
main indicators of pulmonary ventilation,
oxygen consumption by the body and ventilation efficiency.

There are 4 primary lung volumes and 4 containers. The latter include two or more primary volumes.

lung volumes

Tidal volume (TO, or VT - tidal volume) is the volume of gas inhaled and exhaled during quiet breathing.
Inspiratory reserve volume (RO vd, or IRV - inspiratory reserve volume) - the maximum amount of gas that can be additionally inhaled after a quiet breath.
Expiratory reserve volume (RO vyd, or ERV - expiratory reserve volume) - the maximum amount of gas that can be additionally exhaled after a quiet exhalation.
Residual lung volume (OOJI, or RV - residual volume) - the volume of reptile remaining in the lungs after maximum exhalation.

lung capacity

The vital capacity of the lungs (VC, or VC - vital capacity) is the sum of TO, RO vd and RO vyd, i.e. the maximum volume of gas that can be exhaled after a maximum deep breath.
Inspiratory capacity (Evd, or 1C - inspiratory capacity) is the sum of TO and RO vd, i.e. the maximum volume of gas that can be inhaled after a quiet exhalation. This capacity characterizes the ability of lung tissue to stretch.
Functional residual capacity (FRC, or FRC - functional residual capacity) is the sum of OOL and PO vyd i.e. the amount of gas remaining in the lungs after a quiet exhalation.
The total lung capacity (TLC, or TLC - total lung capacity) is the total amount of gas contained in the lungs after a maximum breath.

Conventional spirographs, widely used in clinical practice, allow you to determine only 5 lung volumes and capacities: TO, RO vd, RO vyd. VC, Evd (or, respectively, VT, IRV, ERV, VC and 1C). To find the most important indicator of lung ventilation - functional residual capacity (FRC, or FRC) and calculate the residual lung volume (ROL, or RV) and total lung capacity (TLC, or TLC), it is necessary to apply special techniques, in particular, helium dilution methods, flushing nitrogen or whole body plethysmography (see below).

The main indicator in the traditional method of spirography is the vital capacity of the lungs (VC, or VC). To measure VC, the patient, after a period of quiet breathing (TO), first takes a maximum breath, and then, possibly, a full exhalation. In this case, it is advisable to evaluate not only the integral value of VC) and inspiratory and expiratory vital capacity (VCin, VCex, respectively), i.e. the maximum volume of air that can be inhaled or exhaled.

The second obligatory method used in traditional spirography is a test with the determination of forced (expiratory) vital capacity of the lungs OGEL, or FVC - forced vital capacity expiratory), which allows you to determine the most (formative speed indicators of pulmonary ventilation during forced exhalation, characterizing, in particular, the degree Intrapulmonary airway obstruction As with the VC test, the patient inhales as deeply as possible, and then, in contrast to the VC determination, exhales the air as fast as possible (forced expiration), which registers a gradually flattening exponential curve. Evaluating the spirogram of this expiratory maneuver, several indicators are calculated:

Forced expiratory volume in one second (FEV1, or FEV1 - forced expiratory volume after 1 second) - the amount of air removed from the lungs in the first second of exhalation. This indicator decreases both with airway obstruction (due to an increase in bronchial resistance) and with restrictive disorders (due to a decrease in all lung volumes).
Tiffno index (FEV1 / FVC,%) - the ratio of forced expiratory volume in the first second (FEV1 or FEV1) to forced vital capacity (FVC, or FVC). This is the main indicator of the expiratory maneuver with forced exhalation. It significantly decreases in broncho-obstructive syndrome, since the slowing of exhalation due to bronchial obstruction is accompanied by a decrease in forced expiratory volume in 1 s (FEV1 or FEV1) in the absence or slight decrease in the total FVC value. With restrictive disorders, the Tiffno index practically does not change, since FEV1 (FEV1) and FVC (FVC) decrease almost to the same extent.
Maximum expiratory flow at 25%, 50% and 75% of forced vital capacity . These indicators are calculated by dividing the corresponding forced expiratory volumes (in liters) (at the level of 25%, 50% and 75% of total FVC) by the time to reach these volumes during forced exhalation (in seconds).
Mean expiratory flow rate at 25~75% of FVC (COC25-75% or FEF25-75). This indicator is less dependent on the patient's voluntary effort and more objectively reflects bronchial patency.
Peak volumetric forced expiratory flow rate (POS vyd, or PEF - peak expiratory flow) - the maximum volumetric forced expiratory flow rate.

Based on the results of the spirographic study, the following are also calculated:

the number of respiratory movements during quiet breathing (RR, or BF - breathing freguency) and
minute volume of breathing (MOD, or MV - minute volume) - the amount of total ventilation of the lungs per minute with calm breathing.

Investigation of the flow-volume relationship

Computer spirography

Modern computer spirographic systems allow you to automatically analyze not only the above spirographic indicators, but also the flow-volume ratio, i.e. dependence of the volume flow rate of air during inhalation and exhalation on the value of lung volume. Automatic computer analysis of the inspiratory and expiratory flow-volume loop is the most promising method for quantifying pulmonary ventilation disorders. Although the flow-volume loop itself contains much of the same information as a simple spirogram, the visibility of the relationship between volumetric airflow rate and lung volume allows a more detailed study of the functional characteristics of both the upper and lower airways.

The main element of all modern spirographic computer systems is a pneumotachographic sensor that registers the volumetric air flow rate. The sensor is a wide tube through which the patient breathes freely. In this case, as a result of a small, previously known, aerodynamic resistance of the tube between its beginning and end, a certain pressure difference is created, which is directly proportional to the volumetric air flow rate. Thus, it is possible to register changes in the volumetric flow rate of air during inhalation and exhalation - pneumotachogram.

Automatic integration of this signal also makes it possible to obtain traditional spirographic indicators - lung volume values in liters. Thus, at each moment of time, information about the volumetric air flow rate and about the volume of the lungs at a given moment of time simultaneously enters the computer's memory device. This allows a flow-volume curve to be plotted on the monitor screen. A significant advantage of this method is that the device operates in an open system, i.e. the subject breathes through the tube along an open circuit, without experiencing additional resistance to breathing, as in conventional spirography.

The procedure for performing breathing maneuvers when registering a flow-volume curve is similar to writing a normal coroutine. After a period of compound breathing, the patient delivers a maximum breath, resulting in the inspiratory portion of the flow-volume curve being recorded. The volume of the lung at point "3" corresponds to the total lung capacity (TLC, or TLC). Following this, the patient performs a forced expiration, and the expiratory part of the flow-volume curve (“3-4-5-1” curve) is recorded on the monitor screen. reaching a peak (peak volumetric velocity - POS vyd, or PEF), and then decreases linearly until the end of the forced exhalation, when the forced exhalation curve returns to its original position.

In a healthy person, the shape of the inspiratory and expiratory parts of the flow-volume curve differ significantly from each other: the maximum volumetric flow rate during inspiration is reached at about 50% VC (MOS50%inspiration > or MIF50), while during forced expiration, the peak expiratory flow ( POSvyd or PEF) occurs very early. The maximum inspiratory flow (MOS50% of inspiration, or MIF50) is about 1.5 times the maximum expiratory flow at mid-vital capacity (Vmax50%).

The described flow-volume curve test is carried out several times until a concurrence of results is obtained. In most modern instruments, the procedure for collecting the best curve for further processing of the material is carried out automatically. The flow-volume curve is printed along with multiple pulmonary ventilation measurements.

Using a pneumotochographic sensor, the curve of the volumetric air flow rate is recorded. Automatic integration of this curve makes it possible to obtain a tidal volume curve.

Evaluation of the results of the study

Most lung volumes and capacities, both in healthy patients and in patients with lung disease, depend on a number of factors, including age, sex, chest size, body position, fitness level, and the like. For example, the vital capacity of the lungs (VC, or VC) in healthy people decreases with age, while the residual volume of the lungs (ROL, or RV) increases, and the total lung capacity (TLC, or TLC) practically does not change. VC is proportional to the size of the chest and, accordingly, the height of the patient. In women, VC is on average 25% lower than in men.

Therefore, from a practical point of view, it is not advisable to compare the values of lung volumes and capacities obtained during a spirographic study: with single “standards”, the fluctuations in the values \u200b\u200bof which due to the influence of the above and other factors are very significant (for example, VC normally can range from 3 to 6 l) .

The most acceptable way to evaluate the spirographic indicators obtained during the study is to compare them with the so-called due values, which were obtained when examining large groups of healthy people, taking into account their age, sex and height.

Proper values of ventilation indicators are determined by special formulas or tables. In modern computer spirographs, they are calculated automatically. For each indicator, the boundaries of normal values in percentage are given in relation to the calculated due value. For example, VC (VC) or FVC (FVC) is considered reduced if its actual value is less than 85% of the calculated proper value. A decrease in FEV1 (FEV1) is stated if the actual value of this indicator is less than 75% of the due value, and a decrease in FEV1 / FVC (FEV1 / FVC) - if the actual value is less than 65% of the due value.

Limits of normal values of the main spirographic indicators (as a percentage in relation to the calculated proper value).

Indicators	Conditional rate	Deviations
		Moderate	Significant


FEV1/FVC

In addition, when evaluating the results of spirography, it is necessary to take into account some additional conditions under which the study was carried out: the levels of atmospheric pressure, temperature and humidity of the surrounding air. Indeed, the volume of air exhaled by the patient usually turns out to be somewhat less than that which the same air occupied in the lungs, since its temperature and humidity, as a rule, are higher than those of the surrounding air. To exclude differences in the measured values associated with the conditions of the study, all lung volumes, both due (calculated) and actual (measured in this patient), are given for conditions corresponding to their values at a body temperature of 37 ° C and full saturation with water. in pairs (BTPS system - Body Temperature, Pressure, Saturated). In modern computer spirographs, such a correction and recalculation of lung volumes in the BTPS system are performed automatically.

Interpretation of results

The practitioner should have a good idea of the true possibilities of the spirographic research method, which are usually limited by the lack of information about the values of the residual lung volume (RLV), functional residual capacity (FRC) and total lung capacity (TLC), which does not allow a full analysis of the REL structure. At the same time, spirography makes it possible to get a general idea of the state of external respiration, in particular:

identify a decrease in lung capacity (VC);
identify violations of tracheobronchial patency, and using modern computer analysis of the flow-volume loop - at the earliest stages of the development of obstructive syndrome;
identify the presence of restrictive disorders of pulmonary ventilation in cases where they are not combined with impaired bronchial patency.

Modern computer spirography allows obtaining reliable and complete information about the presence of broncho-obstructive syndrome. More or less reliable detection of restrictive ventilation disorders using the spirographic method (without the use of gas-analytical methods for assessing the structure of the TEL) is possible only in relatively simple, classic cases of impaired lung compliance, when they are not combined with impaired bronchial patency.

Diagnosis of obstructive syndrome

The main spirographic sign of obstructive syndrome is the slowing down of forced exhalation due to an increase in airway resistance. When registering a classic spirogram, the forced expiratory curve becomes stretched, such indicators as FEV1 and the Tiffno index (FEV1 / FVC, or FEV, / FVC) decrease. VC (VC) at the same time either does not change, or slightly decreases.

A more reliable sign of broncho-obstructive syndrome is a decrease in the Tiffno index (FEV1 / FVC, or FEV1 / FVC), since the absolute value of FEV1 (FEV1) can decrease not only with bronchial obstruction, but also with restrictive disorders due to a proportional decrease in all lung volumes and capacities, including FEV1 (FEV1) and FVC (FVC).

Already in the early stages of the development of an obstructive syndrome, the calculated indicator of the average volumetric velocity decreases at the level of 25-75% of FVC (SOS25-75%) - O "is the most sensitive spirographic indicator, indicating an increase in airway resistance earlier than others. However, its calculation requires sufficient accurate manual measurements of the descending knee of the FVC curve, which is not always possible according to the classical spirogram.

More accurate and more accurate data can be obtained by analyzing the flow-volume loop using modern computerized spirographic systems. Obstructive disorders are accompanied by changes predominantly in the expiratory part of the flow-volume loop. If in most healthy people this part of the loop resembles a triangle with an almost linear decrease in the volumetric air flow rate during expiration, then in patients with impaired bronchial patency, a kind of “sagging” of the expiratory part of the loop and a decrease in the volumetric airflow rate are observed at all values of lung volume. Often, due to an increase in lung volume, the expiratory part of the loop is shifted to the left.

Reduced spirographic indicators such as FEV1 (FEV1), FEV1 / FVC (FEV1 / FVC), peak expiratory volume flow (POS vyd, or PEF), MOS25% (MEF25), MOS50% (MEF50), MOC75% (MEF75) and COC25-75% (FEF25-75).

Vital capacity (VC) may remain unchanged or decrease even in the absence of concomitant restrictive disorders. At the same time, it is also important to assess the value of the expiratory reserve volume (ERV), which naturally decreases in obstructive syndrome, especially when early expiratory closure (collapse) of the bronchi occurs.

According to some researchers, a quantitative analysis of the expiratory part of the flow-volume loop also makes it possible to get an idea of the predominant narrowing of large or small bronchi. It is believed that obstruction of the large bronchi is characterized by a decrease in forced expiratory volume velocity, mainly in the initial part of the loop, and therefore such indicators as peak volume velocity (PFR) and maximum volume velocity at the level of 25% of FVC (MOV25%) are sharply reduced or MEF25). At the same time, the volume flow rate of air in the middle and end of expiration (MOC50% and MOC75%) also decreases, but to a lesser extent than POS vyd and MOS25%. On the contrary, with obstruction of small bronchi, a decrease in MOC50% is predominantly detected. MOS75%, while MOSvyd is normal or slightly reduced, and MOS25% is moderately reduced.

However, it should be emphasized that these provisions are currently quite controversial and cannot be recommended for use in general clinical practice. In any case, there are more reasons to believe that the uneven decrease in the volumetric flow rate of air during forced expiration reflects the degree of bronchial obstruction rather than its localization. The early stages of bronchial constriction are accompanied by a slowdown in the expiratory air flow at the end and middle of expiration (decrease in MOS50%, MOS75%, SOS25-75% with little changed values of MOS25%, FEV1 / FVC and POS), whereas with severe bronchial obstruction, a relatively proportional decrease in all speed indicators, including the Tiffno index (FEV1 / FVC), POS and MOS25%.

Of interest is the diagnosis of obstruction of the upper airways (larynx, trachea) using computer spirographs. There are three types of such obstruction:

fixed obstruction;
variable extrathoracic obstruction;
variable intrathoracic obstruction.

An example of a fixed obstruction of the upper airways is deer stenosis due to the presence of a tracheostomy. In these cases, breathing is carried out through a rigid, relatively narrow tube, the lumen of which does not change during inhalation and exhalation. This fixed obstruction limits the flow of air both inspiratory and expiratory. Therefore, the expiratory part of the curve resembles the inspiratory part in shape; volumetric inspiratory and expiratory velocities are significantly reduced and almost equal to each other.

In the clinic, however, more often one has to deal with two variants of variable obstruction of the upper airways, when the lumen of the larynx or trachea changes the time of inhalation or exhalation, which leads to selective restriction of inspiratory or expiratory air flows, respectively.

Variable extrathoracic obstruction is observed with various kinds of stenosis of the larynx (edema of the vocal cords, swelling, etc.). As is known, during respiratory movements, the lumen of the extrathoracic airways, especially narrowed ones, depends on the ratio of intratracheal and atmospheric pressures. During inspiration, the pressure in the trachea (as well as the intraalveolar and intrapleural pressure) becomes negative, i.e. below atmospheric. This contributes to the narrowing of the lumen of the extrathoracic airways and a significant limitation of the inspiratory air flow and a decrease (flattening) of the inspiratory part of the flow-volume loop. During forced exhalation, intratracheal pressure becomes significantly higher than atmospheric pressure, and therefore the diameter of the airways approaches normal, and the expiratory part of the flow-volume loop changes little. Variable intrathoracic obstruction of the upper airways is also observed in tumors of the trachea and dyskinesia of the membranous part of the trachea. The diameter of the thoracic airways is largely determined by the ratio of intratracheal and intrapleural pressures. With forced exhalation, when intrapleural pressure increases significantly, exceeding the pressure in the trachea, the intrathoracic airways narrow, and their obstruction develops. During inspiration, the pressure in the trachea slightly exceeds the negative intrapleural pressure, and the degree of narrowing of the trachea decreases.

Thus, with variable intrathoracic obstruction of the upper airways, there is a selective limitation of the air flow on exhalation and flattening of the inspiratory part of the loop. Its inspiratory part remains almost unchanged.

With variable extrathoracic obstruction of the upper airways, selective restriction of the volumetric airflow rate is observed mainly on inspiration, with intrathoracic obstruction - on expiration.

It should also be noted that in clinical practice, cases are quite rare when the narrowing of the lumen of the upper airways is accompanied by flattening of only the inspiratory or only the expiratory part of the loop. Usually reveals airflow limitation in both phases of breathing, although during one of them this process is much more pronounced.

Diagnosis of restrictive disorders

Restrictive disorders of pulmonary ventilation are accompanied by a limitation of filling the lungs with air due to a decrease in the respiratory surface of the lung, exclusion of a part of the lung from breathing, a decrease in the elastic properties of the lung and chest, as well as the ability of the lung tissue to stretch (inflammatory or hemodynamic pulmonary edema, massive pneumonia, pneumoconiosis, pneumosclerosis and so-called). At the same time, if restrictive disorders are not combined with the violations of bronchial patency described above, airway resistance usually does not increase.

The main consequence of restrictive (restrictive) ventilation disorders detected by classical spirography is an almost proportional decrease in most lung volumes and capacities: TO, VC, RO ind, RO vy, FEV, FEV1, etc. It is important that, unlike the obstructive syndrome, a decrease in FEV1 is not accompanied by a decrease in the FEV1/FVC ratio. This indicator remains within the normal range or even slightly increases due to a more significant decrease in VC.

In computed spirography, the flow-volume curve is a reduced copy of the normal curve, shifted to the right due to a general decrease in lung volume. Peak volumetric flow rate (PFR) of expiratory flow FEV1 is reduced, although the FEV1/FVC ratio is normal or increased. Due to the limitation of lung expansion and, accordingly, a decrease in its elastic traction, flow rates (for example, COC25-75%, MOC50%, MOC75%) in some cases can also be reduced even in the absence of airway obstruction.

The most important diagnostic criteria for restrictive ventilation disorders, which make it possible to reliably distinguish them from obstructive disorders, are:

an almost proportional decrease in lung volumes and capacities measured by spirography, as well as flow indicators and, accordingly, a normal or slightly changed shape of the curve of the flow-volume loop, shifted to the right;
normal or even increased value of the Tiffno index (FEV1 / FVC);
the decrease in inspiratory reserve volume (RIV) is almost proportional to the expiratory reserve volume (ROV).

It should be emphasized once again that for the diagnosis of even “pure” restrictive ventilation disorders, it is impossible to focus only on a decrease in VC, since the sweat rate in severe obstructive syndrome can also significantly decrease. More reliable differential diagnostic signs are the absence of changes in the shape of the expiratory part of the flow-volume curve (in particular, normal or increased values of FB1 / FVC), as well as a proportional decrease in RO ind and RO vy.

Determination of the structure of total lung capacity (TLC, or TLC)

As mentioned above, the methods of classical spirography, as well as computer processing of the flow-volume curve, make it possible to get an idea of the changes in only five of the eight lung volumes and capacities (TO, RVD, ROV, VC, EVD, or, respectively - VT, IRV, ERV , VC and 1C), which makes it possible to assess predominantly the degree of obstructive pulmonary ventilation disorders. Restrictive disorders can be reliably diagnosed only if they are not combined with a violation of bronchial patency, i.e. in the absence of mixed disorders of pulmonary ventilation. Nevertheless, in the practice of a doctor, such mixed disorders are most often encountered (for example, in chronic obstructive bronchitis or bronchial asthma, complicated by emphysema and pneumosclerosis, etc.). In these cases, the mechanisms of impaired pulmonary ventilation can only be identified by analyzing the structure of the RFE.

To solve this problem, it is necessary to use additional methods for determining functional residual capacity (FRC, or FRC) and calculate indicators of residual lung volume (ROL, or RV) and total lung capacity (TLC, or TLC). Since FRC is the amount of air remaining in the lungs after maximum expiration, it is measured only by indirect methods (gas analysis or using whole body plethysmography).

The principle of gas analysis methods is that the lungs are either injected with an inert gas helium (dilution method), or the nitrogen contained in the alveolar air is washed out, forcing the patient to breathe pure oxygen. In both cases, the FRC is calculated from the final gas concentration (R.F. Schmidt, G. Thews).

Helium dilution method. Helium, as is known, is an inert and harmless gas for the body, which practically does not pass through the alveolar-capillary membrane and does not participate in gas exchange.

The dilution method is based on measuring the helium concentration in the closed container of the spirometer before and after mixing the gas with the lung volume. A covered spirometer with a known volume (V cn) is filled with a gas mixture consisting of oxygen and helium. At the same time, the volume occupied by helium (V cn) and its initial concentration (FHe1) are also known. After a quiet exhalation, the patient begins to breathe from the spirometer, and helium is evenly distributed between the volume of the lungs (FOE, or FRC) and the volume of the spirometer (V cn). After a few minutes, the helium concentration in the general system (“spirometer-lungs”) decreases (FHe 2).

Nitrogen washout method. In this method, the spirometer is filled with oxygen. The patient breathes into the closed circuit of the spirometer for several minutes, while measuring the volume of exhaled air (gas), the initial content of nitrogen in the lungs and its final content in the spirometer. The FRC (FRC) is calculated using an equation similar to that of the helium dilution method.

The accuracy of both of the above methods for determining the FRC (RR) depends on the completeness of the mixing of gases in the lungs, which in healthy people occurs within a few minutes. However, in some diseases accompanied by a pronounced uneven ventilation (for example, with obstructive pulmonary pathology), balancing the concentration of gases takes a long time. In these cases, the measurement of FRC (FRC) by the methods described may be inaccurate. These shortcomings are devoid of the more technically complex method of whole body plethysmography.

Whole body plethysmography. The method of whole body plethysmography is one of the most informative and complex research methods used in pulmonology to determine lung volumes, tracheobronchial resistance, elastic properties of lung tissue and chest, as well as to evaluate some other parameters of pulmonary ventilation.

The integral plethysmograph is a hermetically sealed chamber with a volume of 800 liters, in which the patient is freely placed. The subject breathes through a pneumotachograph tube connected to a hose open to the atmosphere. The hose has a flap that allows you to automatically shut off the air flow at the right time. Special barometric sensors measure the pressure in the chamber (Pcam) and in the oral cavity (Prot). the latter, with the valve of the hose closed, is equal to the alveolar pressure inside. The pneumotachograph allows you to determine the air flow (V).

The principle of operation of the integral plethysmograph is based on Boyle Moriosht's law, according to which, at a constant temperature, the relationship between pressure (P) and gas volume (V) remains constant:

P1xV1 = P2xV2, where P1 is the initial gas pressure, V1 is the initial gas volume, P2 is the pressure after changing the gas volume, V2 is the volume after changing the gas pressure.

The patient inside the plethysmograph chamber inhales and exhales calmly, after which (at the FRC level, or FRC) the hose flap is closed, and the subject makes an attempt to “inhale” and “exhale” (the “breathing” maneuver) With this “breathing” maneuver intra-alveolar pressure changes, and the pressure in the closed chamber of the plethysmograph changes inversely proportional to it. When you try to "inhale" with a closed valve, the volume of the chest increases, which leads, on the one hand, to a decrease in intra-alveolar pressure, and on the other hand, to a corresponding increase in pressure in the plethysmograph chamber (Pcam). On the contrary, when you try to "exhale" the alveolar pressure increases, and the volume of the chest and the pressure in the chamber decrease.

Thus, the whole body plethysmography method makes it possible to calculate intrathoracic gas volume (IGO) with high accuracy, which in healthy individuals quite accurately corresponds to the value of functional residual lung capacity (FRC, or CS); the difference between VGO and FOB usually does not exceed 200 ml. However, it should be remembered that in case of impaired bronchial patency and some other pathological conditions, VGO can significantly exceed the value of the true FOB due to an increase in the number of unventilated and poorly ventilated alveoli. In these cases, it is advisable to combine a study using gas analytical methods of the whole body plethysmography method. By the way, the difference between VOG and FOB is one of the important indicators of uneven ventilation of the lungs.

Interpretation of results

The main criterion for the presence of restrictive disorders of pulmonary ventilation is a significant decrease in the TEL. With a "pure" restriction (without a combination of bronchial obstruction), the structure of the TEL does not change significantly, or a slight decrease in the ratio of TOL/TEL was observed. If restrictive disorders occur against the background of bronchial patency disorders (mixed type of ventilation disorders), along with a clear decrease in the TFR, a significant change in its structure is observed, which is characteristic of broncho-obstructive syndrome: an increase in TRL/TRL (more than 35%) and FFU/TEL (more than 50% ). In both variants of restrictive disorders, VC is significantly reduced.

Thus, the analysis of the structure of the REL makes it possible to differentiate all three variants of ventilation disorders (obstructive, restrictive, and mixed), while the assessment of only spirographic parameters does not make it possible to reliably distinguish the mixed variant from the obstructive variant, accompanied by a decrease in VC).

The main criterion for the obstructive syndrome is a change in the structure of the REL, in particular, an increase in the ROL / TEL (more than 35%) and FFU / TEL (more than 50%). For "pure" restrictive disorders (without a combination with obstruction), the most characteristic is a decrease in the TEL without changing its structure. The mixed type of ventilation disturbances is characterized by a significant decrease in the TRL and an increase in the ratios of TOL/TEL and FFU/TEL.

Determination of uneven ventilation of the lungs

In a healthy person, there is a certain physiological uneven ventilation of different parts of the lungs, due to differences in the mechanical properties of the airways and lung tissue, as well as the presence of the so-called vertical pleural pressure gradient. If the patient is in an upright position, at the end of exhalation, pleural pressure in the upper lung is more negative than in the lower (basal) sections. The difference can reach 8 cm of water column. Therefore, before the start of the next breath, the alveoli of the tops of the lungs are stretched more than the alveoli of the lower basal regions. In this regard, during inspiration, a larger volume of air enters the alveoli of the basal regions.

The alveoli of the lower basal sections of the lungs are normally better ventilated than the areas of the apexes, which is associated with the presence of a vertical intrapleural pressure gradient. However, normally, such uneven ventilation is not accompanied by a noticeable disturbance of gas exchange, since the blood flow in the lungs is also uneven: the basal sections are better perfused than the apical ones.

In some diseases of the respiratory system, the degree of uneven ventilation can increase significantly. The most common causes of such pathological uneven ventilation are:

Diseases accompanied by an uneven increase in airway resistance (chronic bronchitis, bronchial asthma).
Diseases with unequal regional extensibility of lung tissue (pulmonary emphysema, pneumosclerosis).
Inflammation of the lung tissue (focal pneumonia).
Diseases and syndromes, combined with local restriction of expansion of the alveoli (restrictive) - exudative pleurisy, hydrothorax, pneumosclerosis, etc.

Often different causes are combined. For example, in chronic obstructive bronchitis complicated by emphysema and pneumosclerosis, regional disorders of bronchial patency and extensibility of the lung tissue develop.

With uneven ventilation, the physiological dead space increases significantly, gas exchange in which does not occur or is weakened. This is one of the reasons for the development of respiratory failure.

To assess the unevenness of pulmonary ventilation, gas analytical and barometric methods are more often used. Thus, a general idea of the uneven ventilation of the lungs can be obtained, for example, by analyzing the curves of helium mixing (dilution) or nitrogen leaching, which are used to measure FRC.

In healthy people, mixing helium with alveolar air or washing out nitrogen from it occurs within three minutes. With violations of bronchial patency, the number (volume) of poorly ventilated alveoli increases dramatically, and therefore the mixing (or washing out) time increases significantly (up to 10-15 minutes), which is an indicator of uneven pulmonary ventilation.

More accurate data can be obtained using a nitrogen leaching test with a single breath of oxygen. The patient exhales as much as possible, and then inhales pure oxygen as deeply as possible. Then he slowly exhales into a closed system of a spirograph equipped with a device for determining the concentration of nitrogen (azotograph). Throughout the exhalation, the volume of the exhaled gas mixture is continuously measured, and the changing concentration of nitrogen in the exhaled gas mixture containing nitrogen of the alveolar air is also determined.

The nitrogen leaching curve consists of 4 phases. At the very beginning of exhalation, air enters the spirograph from the upper airways, which is 100% p. oxygen that filled them during the previous breath. The nitrogen content in this portion of exhaled gas is zero.

The second phase is characterized by a sharp increase in the concentration of nitrogen, which is due to the leaching of this gas from the anatomical dead space.

During the long third phase, the nitrogen concentration of the alveolar air is recorded. In healthy people, this phase of the curve is flat - in the form of a plateau (alveolar plateau). If there is uneven ventilation during this phase, the nitrogen concentration increases due to the gas being washed out from the poorly ventilated alveoli, which are emptied last. Thus, the greater the rise in the nitrogen washout curve at the end of the third phase, the more pronounced is the unevenness of pulmonary ventilation.

The fourth phase of the nitrogen washout curve is associated with the expiratory closure of the small airways of the basal parts of the lungs and the inflow of air mainly from the apical parts of the lungs, the alveolar air in which contains nitrogen of a higher concentration.

Assessment of the ventilation-perfusion ratio

Gas exchange in the lungs depends not only on the level of general ventilation and the degree of its unevenness in various parts of the organ, but also on the ratio of ventilation and perfusion at the level of the alveoli. Therefore, the value of the ventilation-perfusion ratio (VPO) is one of the most important functional characteristics of the respiratory organs, which ultimately determines the level of gas exchange.

Normal VPO for the lung as a whole is 0.8-1.0. With a decrease in VPO below 1.0, perfusion of poorly ventilated areas of the lungs leads to hypoxemia (decrease in oxygenation of arterial blood). An increase in VPO greater than 1.0 is observed with preserved or excessive ventilation of zones, the perfusion of which is significantly reduced, which can lead to impaired CO2 excretion - hypercapnia.

Causes of HPE violation:

All diseases and syndromes that cause uneven ventilation of the lungs.
The presence of anatomical and physiological shunts.
Thromboembolism of small branches of the pulmonary artery.
Violation of microcirculation and thrombosis in the vessels of the small circle.

Capnography. Several methods have been proposed to detect violations of HPV, of which one of the simplest and most accessible is the capnography method. It is based on the continuous registration of CO2 content in the exhaled mixture of gases using special gas analyzers. These instruments measure the absorption of infrared rays by carbon dioxide as it passes through an exhaled gas cuvette.

When analyzing a capnogram, three indicators are usually calculated:

slope of the alveolar phase of the curve (segment BC),
the value of CO2 concentration at the end of exhalation (at point C),
the ratio of functional dead space (MP) to tidal volume (TO) - MP / DO.

Determination of diffusion of gases

Diffusion of gases through the alveolar-capillary membrane obeys Fick's law, according to which the diffusion rate is directly proportional to:

partial pressure gradient of gases (O2 and CO2) on both sides of the membrane (P1 - P2) and
diffusion capacity of the alveolar-caillary membrane (Dm):

VG \u003d Dm x (P1 - P2), where VG is the gas transfer rate (C) through the alveolar-capillary membrane, Dm is the diffusion capacity of the membrane, P1 - P2 is the partial pressure gradient of gases on both sides of the membrane.

To calculate the diffusion capacity of light POs for oxygen, it is necessary to measure the 62 (VO 2 ) uptake and the average O 2 partial pressure gradient. VO 2 values are measured using an open or closed type spirograph. To determine the oxygen partial pressure gradient (P 1 - P 2), more complex gas analytical methods are used, since in clinical conditions it is difficult to measure the partial pressure of O 2 in the pulmonary capillaries.

The most commonly used definition of the diffusion capacity of light is ne for O 2, but for carbon monoxide (CO). Since CO binds 200 times more actively with hemoglobin than oxygen, its concentration in the blood of the pulmonary capillaries can be neglected. Then, to determine DlCO, it is sufficient to measure the rate of passage of CO through the alveolar-capillary membrane and the gas pressure in the alveolar air.

The single-breath method is most widely used in the clinic. The subject inhales a gas mixture with a small content of CO and helium, and at the height of a deep breath for 10 seconds holds his breath. After that, the composition of the exhaled gas is determined by measuring the concentration of CO and helium, and the diffusion capacity of the lungs for CO is calculated.

Normally, DlCO, reduced to body area, is 18 ml/min/mm Hg. st./m2. The diffusion capacity of the lungs for oxygen (DlO2) is calculated by multiplying DlCO by a factor of 1.23.

The following diseases most often cause a decrease in the diffusion capacity of the lungs.

Emphysema of the lungs (due to a decrease in the surface area of the alveolar-capillary contact and the volume of capillary blood).
Diseases and syndromes accompanied by diffuse lesions of the lung parenchyma and thickening of the alveolar-capillary membrane (massive pneumonia, inflammatory or hemodynamic pulmonary edema, diffuse pneumosclerosis, alveolitis, pneumoconiosis, cystic fibrosis, etc.).
Diseases accompanied by damage to the capillary bed of the lungs (vasculitis, embolism of small branches of the pulmonary artery, etc.).

For the correct interpretation of changes in the diffusion capacity of the lungs, it is necessary to take into account the hematocrit index. An increase in hematocrit in polycythemia and secondary erythrocytosis is accompanied by an increase, and its decrease in anemia is accompanied by a decrease in the diffusion capacity of the lungs.

Airway resistance measurement

Measurement of airway resistance is a diagnostically important parameter of pulmonary ventilation. Aspirated air moves through the airways under the action of a pressure gradient between the oral cavity and the alveoli. During inspiration, expansion of the chest leads to a decrease in viutripleural and, accordingly, intra-alveolar pressure, which becomes lower than the pressure in the oral cavity (atmospheric). As a result, the air flow is directed into the lungs. During expiration, the action of the elastic recoil of the lungs and chest is aimed at increasing the intra-alveolar pressure, which becomes higher than the pressure in the oral cavity, resulting in a reverse flow of air. Thus, the pressure gradient (∆P) is the main force that ensures the transport of air through the airways.

The second factor that determines the amount of gas flow through the airways is the aerodynamic drag (Raw), which, in turn, depends on the clearance and length of the airways, as well as on the viscosity of the gas.

The value of the volumetric air flow rate obeys the Poiseuille law: V = ∆P / Raw, where

V is the volumetric velocity of the laminar air flow;
∆P - pressure gradient in the oral cavity and alveoli;
Raw - aerodynamic resistance of the airways.

It follows that in order to calculate the aerodynamic resistance of the airways, it is necessary to simultaneously measure the difference between the pressure in the oral cavity in the alveoli (∆P), as well as the volumetric air flow rate.

There are several methods for determining Raw based on this principle:

whole body plethysmography method;
airflow blocking method.

Determination of blood gases and acid-base status

The main method for diagnosing acute respiratory failure is the study of arterial blood gases, which includes the measurement of PaO2, PaCO2 and pH. You can also measure the saturation of hemoglobin with oxygen (oxygen saturation) and some other parameters, in particular the content of buffer bases (BB), standard bicarbonate (SB) and the amount of excess (deficit) of bases (BE).

The parameters PaO2 and PaCO2 most accurately characterize the ability of the lungs to saturate the blood with oxygen (oxygenation) and remove carbon dioxide (ventilation). The latter function is also determined from the pH and BE values.

To determine the gas composition of the blood in patients with acute respiratory failure in intensive care units, a complex invasive technique for obtaining arterial blood is used by puncturing a large artery. More often, a puncture of the radial artery is performed, since the risk of developing complications is lower. The hand has a good collateral blood flow, which is carried out by the ulnar artery. Therefore, even if the radial artery is damaged during puncture or operation of the arterial catheter, the blood supply to the hand is preserved.

Indications for puncture of the radial artery and placement of an arterial catheter are:

the need for frequent measurement of arterial blood gases;
severe hemodynamic instability against the background of acute respiratory failure and the need for constant monitoring of hemodynamic parameters.

A negative Allen test is a contraindication to catheter insertion. For the test, the ulnar and radial arteries are pinched with fingers so as to turn the arterial blood flow; the hand turns pale after a while. After that, the ulnar artery is released, continuing to compress the radial. Usually the color of the brush is quickly (within 5 seconds) restored. If this does not happen, then the hand remains pale, ulnar artery occlusion is diagnosed, the test result is considered negative, and the radial artery is not punctured.

In the case of a positive test result, the palm and forearm of the patient are fixed. After preparing the surgical field in the distal parts of the radial artery, the guests palpate the pulse on the radial artery, perform anesthesia in this place, and puncture the artery at an angle of 45°. The catheter is advanced until blood appears in the needle. The needle is removed, leaving the catheter in the artery. To prevent excessive bleeding, the proximal part of the radial artery is pressed with a finger for 5 minutes. The catheter is fixed to the skin with silk sutures and covered with a sterile dressing.

Complications (bleeding, arterial occlusion by a thrombus, and infection) during catheter placement are relatively rare.

It is preferable to draw blood for research into a glass rather than a plastic syringe. It is important that the blood sample does not come into contact with the surrounding air, i.e. collection and transport of blood should be carried out under anaerobic conditions. Otherwise, exposure to the blood sample of ambient air leads to the determination of the level of PaO2.

Determination of blood gases should be carried out no later than 10 minutes after arterial blood sampling. Otherwise, ongoing metabolic processes in the blood sample (initiated mainly by the activity of leukocytes) significantly change the results of the determination of blood gases, reducing the level of PaO2 and pH, and increasing PaCO2. Especially pronounced changes are observed in leukemia and in severe leukocytosis.

Methods for assessing the acid-base state

Measurement of blood pH

The pH value of blood plasma can be determined by two methods:

The indicator method is based on the property of some weak acids or bases, used as indicators, to dissociate at certain pH values, thus changing the color.
The pH-metry method makes it possible to more accurately and quickly determine the concentration of hydrogen ions using special polarographic electrodes, on the surface of which, when immersed in a solution, a potential difference is created that depends on the pH of the medium under study.

One of the electrodes - active, or measuring, is made of a noble metal (platinum or gold). The other (reference) serves as a reference electrode. The platinum electrode is separated from the rest of the system by a glass membrane permeable only to hydrogen ions (H+). Inside the electrode is filled with a buffer solution.

The electrodes are immersed in the test solution (for example, blood) and polarized from a current source. As a result, a current appears in a closed electrical circuit. Since the platinum (active) electrode is additionally separated from the electrolyte solution by a glass membrane permeable only to H + ions, the pressure on both surfaces of this membrane is proportional to blood pH.

Most often, the acid-base state is assessed by the Astrup method on the microAstrup apparatus. Determine the indicators of BB, BE and PaCO2. Two portions of the studied arterial blood are brought into equilibrium with two gas mixtures of known composition, differing in the partial pressure of CO2. pH is measured in each portion of blood. The pH and PaCO2 values in each portion of blood are plotted as two points on a nomogram. Through 2 points marked on the nomogram, a straight line is drawn to the intersection with the standard graphs of BB and BE and the actual values of these indicators are determined. Then measure the pH of the blood under study and find on the resulting straight point corresponding to this measured pH value. The projection of this point onto the y-axis determines the actual pressure of CO2 in the blood (PaCO2).

Direct measurement of CO2 pressure (PaCO2)

In recent years, for direct measurement of PaCO2 in a small volume, a modification of polarographic electrodes designed to measure pH has been used. Both electrodes (active and reference) are immersed in an electrolyte solution, which is separated from the blood by another membrane, permeable only to gases, but not to hydrogen ions. CO2 molecules, diffusing through this membrane from the blood, change the pH of the solution. As mentioned above, the active electrode is additionally separated from the NaHCO3 solution by a glass membrane permeable only to H + ions. After the electrodes are immersed in the test solution (for example, blood), the pressure on both surfaces of this membrane is proportional to the pH of the electrolyte (NaHCO3). In turn, the pH of the NaHCO3 solution depends on the concentration of CO2 in the blood. Thus, the magnitude of the pressure in the circuit is proportional to the PaCO2 of the blood.

The polarographic method is also used to determine PaO2 in arterial blood.

Determination of BE from the results of direct measurement of pH and PaCO2

Direct determination of pH and PaCO2 of the blood makes it possible to significantly simplify the procedure for determining the third indicator of the acid-base state - the excess of bases (BE). The latter indicator can be determined by special nomograms. After direct measurement of pH and PaCO2, the actual values of these indicators are plotted on the corresponding nomogram scales. The points are connected by a straight line and continue it until it intersects with the BE scale.

This method of determining the main indicators of the acid-base state does not require balancing the blood with a gas mixture, as when using the classical Astrup method.

Interpretation of results

Partial pressure of O2 and CO2 in arterial blood

The values of PaO2 and PaCO2 serve as the main objective indicators of respiratory failure. In a healthy adult breathing room air with an oxygen concentration of 21% (FiO 2 \u003d 0.21) and normal atmospheric pressure (760 mm Hg), PaO 2 is 90-95 mm Hg. Art. With a change in barometric pressure, ambient temperature and some other conditions, PaO2 in a healthy person can reach 80 mm Hg. Art.

Lower values of PaO2 (less than 80 mm Hg) can be considered the initial manifestation of hypoxemia, especially against the background of acute or chronic damage to the lungs, chest, respiratory muscles, or the central regulation of respiration. Reducing PaO2 to 70 mm Hg. Art. in most cases, it indicates compensated respiratory failure and, as a rule, is accompanied by clinical signs of a decrease in the functionality of the external respiratory system:

slight tachycardia;
shortness of breath, respiratory discomfort, appearing mainly during physical exertion, although at rest the respiratory rate does not exceed 20-22 per minute;
a noticeable decrease in exercise tolerance;
participation in breathing of the auxiliary respiratory muscles, etc.

At first glance, these criteria for arterial hypoxemia contradict the definition of respiratory failure by E. Campbell: “respiratory failure is characterized by a decrease in PaO2 below 60 mm Hg. st ... ". However, as already noted, this definition refers to decompensated respiratory failure, manifested by a large number of clinical and instrumental signs. Indeed, a decrease in PaO2 below 60 mm Hg. Art., as a rule, indicates severe decompensated respiratory failure, and is accompanied by shortness of breath at rest, an increase in the number of respiratory movements up to 24-30 per minute, cyanosis, tachycardia, significant pressure of the respiratory muscles, etc. Neurological disorders and signs of hypoxia in other organs usually develop when PaO2 is below 40-45 mm Hg. Art.

PaO2 from 80 to 61 mm Hg. Art., especially against the background of acute or chronic damage to the lungs and the respiratory apparatus, should be regarded as the initial manifestation of arterial hypoxemia. In most cases, it indicates the formation of mild compensated respiratory failure. Reducing PaO 2 below 60 mm Hg. Art. indicates moderate or severe pre-compensated respiratory failure, the clinical manifestations of which are pronounced.

Normally, the pressure of CO2 in arterial blood (PaCO 2) is 35-45 mm Hg. Hypercapia is diagnosed when PaCO2 rises above 45 mm Hg. Art. PaCO2 values are greater than 50 mm Hg. Art. usually correspond to the clinical picture of severe ventilation (or mixed) respiratory failure, and above 60 mm Hg. Art. - serve as an indication for mechanical ventilation, aimed at restoring the minute volume of breathing.

Diagnosis of various forms of respiratory failure (ventilation, parenchymal, etc.) is based on the results of a comprehensive examination of patients - the clinical picture of the disease, the results of determining the function of external respiration, chest X-ray, laboratory tests, including the assessment of blood gas composition.

Above, some features of the change in PaO 2 and PaCO 2 in ventilation and parenchymal respiratory failure have already been noted. Recall that for ventilation respiratory failure, in which the process of releasing CO 2 from the body is disturbed in the lungs, hypercapnia is characteristic (PaCO 2 is more than 45-50 mm Hg), often accompanied by compensated or decompensated respiratory acidosis. At the same time, progressive hypoventilation of the alveoli naturally leads to a decrease in the oxygenation of the alveolar air and the pressure of O 2 in arterial blood (PaO 2), resulting in the development of hypoxemia. Thus, a detailed picture of ventilation respiratory failure is accompanied by both hypercapnia and increasing hypoxemia.

The early stages of parenchymal respiratory failure are characterized by a decrease in PaO 2 (hypoxemia), in most cases combined with severe hyperventilation of the alveoli (tachypnea) and developing in connection with this hypocapnia and respiratory alkalosis. If this condition cannot be stopped, signs of a progressive total decrease in ventilation, minute respiratory volume and hypercapnia gradually appear (PaCO 2 is more than 45-50 mm Hg). This indicates the accession of ventilation respiratory failure due to fatigue of the respiratory muscles, a pronounced obstruction of the airways, or a critical drop in the volume of functioning alveoli. Thus, the later stages of parenchymal respiratory failure are characterized by a progressive decrease in PaO 2 (hypoxemia) in combination with hypercapnia.

Depending on the individual characteristics of the development of the disease and the predominance of certain pathophysiological mechanisms of respiratory failure, other combinations of hypoxemia and hypercapnia are possible, which are discussed in subsequent chapters.

Acid-base disorders

In most cases, to accurately diagnose respiratory and non-respiratory acidosis and alkalosis, as well as to assess the degree of compensation for these disorders, it is quite sufficient to determine blood pH, pCO2, BE, and SB.

During the period of decompensation, a decrease in blood pH is observed, and in alkalosis, it is quite simple to determine the values of the acid-base state: with acidego, an increase. It is also easy to determine the respiratory and non-respiratory types of these disorders by laboratory parameters: changes in pCO 2 and BE in each of these two types are multidirectional.

The situation is more complicated with the assessment of the parameters of the acid-base state during the period of compensation for its violations, when the pH of the blood is not changed. Thus, a decrease in pCO 2 and BE can be observed both in non-respiratory (metabolic) acidosis and in respiratory alkalosis. In these cases, an assessment of the overall clinical situation helps to understand whether the corresponding changes in pCO 2 or BE are primary or secondary (compensatory).

Compensated respiratory alkalosis is characterized by a primary increase in PaCO2, which is essentially the cause of this acid-base disorder; in these cases, the corresponding changes in BE are secondary, that is, they reflect the inclusion of various compensatory mechanisms aimed at reducing the concentration of bases. On the contrary, for compensated metabolic acidosis, changes in BE are primary, and shifts in pCO2 reflect compensatory hyperventilation of the lungs (if it is possible).

Thus, comparison of the parameters of acid-base disorders with the clinical picture of the disease in most cases makes it possible to reliably diagnose the nature of these disorders even during the period of their compensation. Establishing the correct diagnosis in these cases can also help evaluate changes in the electrolyte composition of the blood. In respiratory and metabolic acidosis, hypernatremia (or normal concentration of Na +) and hyperkalemia are often observed, and in respiratory alkalosis, hypo- (or normo) natremia and hypokalemia

Pulse oximetry

The supply of oxygen to peripheral organs and tissues depends not only on the absolute values of D2 pressure in arterial blood, but also on the ability of hemoglobin to bind oxygen in the lungs and release it in the tissues. This ability is described by an S-shaped oxyhemoglobin dissociation curve. The biological meaning of this shape of the dissociation curve is that the region of high values of O2 pressure corresponds to the horizontal section of this curve. Therefore, even with fluctuations in oxygen pressure in arterial blood from 95 to 60-70 mm Hg. Art. saturation (saturation) of hemoglobin with oxygen (SaO 2) remains at a sufficiently high level. So, in a healthy young man with PaO 2 \u003d 95 mm Hg. Art. saturation of hemoglobin with oxygen is 97%, and at PaO 2 = 60 mm Hg. Art. - 90%. The steep slope of the middle section of the oxyhemoglobin dissociation curve indicates very favorable conditions for the release of oxygen in the tissues.

Under the influence of some factors (temperature increase, hypercapnia, acidosis), the dissociation curve shifts to the right, which indicates a decrease in the affinity of hemoglobin for oxygen and the possibility of its easier release in tissues. the same level requires more PaO 2 .

The shift of the oxyhemoglobin dissociation curve to the left indicates an increased affinity of hemoglobin for O 2 and its lower release in tissues. This shift occurs due to the action of hypocapnia, alkalosis and lower temperatures. In these cases, a high saturation of hemoglobin with oxygen is maintained even at lower values of PaO 2

Thus, the value of saturation of hemoglobin with oxygen in respiratory failure acquires an independent value for characterizing the provision of peripheral tissues with oxygen. The most common non-invasive method for determining this indicator is pulse oximetry.

Modern pulse oximeters contain a microprocessor connected to a sensor containing a light emitting diode and a light sensitive sensor located opposite the light emitting diode). Usually 2 wavelengths of radiation are used: 660 nm (red light) and 940 nm (infrared). Oxygen saturation is determined by the absorption of red and infrared light, respectively, by reduced hemoglobin (Hb) and oxyhemoglobin (HbJ 2 ). The result is displayed as SaO2 (saturation obtained from pulse oximetry).

Normal oxygen saturation is over 90%. This indicator decreases with hypoxemia and a decrease in PaO 2 less than 60 mm Hg. Art.

When evaluating the results of pulse oximetry, one should bear in mind a rather large error of the method, reaching ± 4-5%. It should also be remembered that the results of an indirect determination of oxygen saturation depend on many other factors. For example, from the presence on the nails of the examined varnish. The varnish absorbs part of the radiation from the anode with a wavelength of 660 nm, thereby underestimating the values of the SaO 2 index.

The readings of the pulse oximeter are affected by a shift in the hemoglobin dissociation curve that occurs under the influence of various factors (temperature, blood pH, PaCO2 level), skin pigmentation, anemia at a hemoglobin level below 50-60 g/l, etc. For example, small pH fluctuations lead to significant changes indicator SaO2, with alkalosis (for example, respiratory, developed against the background of hyperventilation), SaO2 is overestimated, with acidosis - underestimated.

In addition, this technique does not allow taking into account the appearance in the peripheral blood of pathological varieties of hemoglobin - carboxyhemoglobin and methemoglobin, which absorb light of the same wavelength as oxyhemoglobin, which leads to an overestimation of SaO2 values.

Nevertheless, at present, pulse oximetry is widely used in clinical practice, in particular, in intensive care units and intensive care units for a simple approximate dynamic monitoring of the state of hemoglobin saturation with oxygen.

Assessment of hemodynamic parameters

For a complete analysis of the clinical situation in acute respiratory failure, it is necessary to dynamically determine a number of hemodynamic parameters:

blood pressure;
heart rate (HR);
central venous pressure (CVP);
pulmonary artery wedge pressure (PWP);
cardiac output;
ECG monitoring (including for the timely detection of arrhythmias).

Many of these parameters (BP, heart rate, SaO2, ECG, etc.) make it possible to determine modern monitoring equipment in intensive care and resuscitation departments. In severely ill patients, it is advisable to catheterize the right heart with the installation of a temporary floating intracardiac catheter to determine CVP and PLA.

The whole complex process can be divided into three main stages: external respiration; and internal (tissue) respiration.

external respiration- gas exchange between the body and the surrounding atmospheric air. External respiration involves the exchange of gases between atmospheric and alveolar air, and between pulmonary capillaries and alveolar air.

This breathing is carried out as a result of periodic changes in the volume of the chest cavity. An increase in its volume provides inhalation (inspiration), a decrease - exhalation (expiration). The phases of inhalation and the exhalation following it are . During inhalation, atmospheric air enters the lungs through the airways, and during exhalation, part of the air leaves them.

Conditions necessary for external respiration:

tightness of the chest;
free communication of the lungs with the environment;
elasticity of lung tissue.

An adult makes 15-20 breaths per minute. The breathing of physically trained people is rarer (up to 8-12 breaths per minute) and deep.

The most common methods for examining external respiration

Methods for assessing the respiratory function of the lungs:

Pneumography
Spirometry
Spirography
Pneumotachometry
Radiography
X-ray computed tomography
Ultrasonography
Magnetic resonance imaging
Bronchography
Bronchoscopy
Radionuclide methods
Gas dilution method

Spirometry- a method for measuring the volume of exhaled air using a spirometer device. Various types of spirometers with a turbimetric sensor are used, as well as water ones, in which the exhaled air is collected under the spirometer bell placed in water. The volume of exhaled air is determined by the rise of the bell. Recently, sensors that are sensitive to changes in the volumetric velocity of the air flow, connected to a computer system, have been widely used. In particular, a computer system such as "Spirometer MAS-1" of Belarusian production, etc., works on this principle. Such systems allow not only spirometry, but also spirography, as well as pneumotachography).

Spirography - method of continuous recording of volumes of inhaled and exhaled air. The resulting graphic curve is called the spirofamma. According to the spirogram, it is possible to determine the vital capacity of the lungs and respiratory volumes, respiratory rate and arbitrary maximum ventilation of the lungs.

Pneumotachography - method of continuous registration of the volumetric flow rate of inhaled and exhaled air.

There are many other methods for examining the respiratory system. Among them are chest plethysmography, listening to sounds that occur when air passes through the respiratory tract and lungs, fluoroscopy and radiography, determining the oxygen and carbon dioxide content in the exhaled air stream, etc. Some of these methods are discussed below.

Volumetric indicators of external respiration

The ratio of lung volumes and capacities is shown in fig. 1.

In the study of external respiration, the following indicators and their abbreviation are used.

Total lung capacity (TLC)- the volume of air in the lungs after the deepest breath (4-9 l).

Rice. 1. Average values of lung volumes and capacities

Vital capacity of the lungs

Vital capacity (VC)- the volume of air that can be exhaled by a person with the deepest slow exhalation made after the maximum inhalation.

The value of the vital capacity of human lungs is 3-6 liters. Recently, in connection with the introduction of pneumotachographic technology, the so-called forced vital capacity(FZhEL). When determining FVC, the subject must, after the deepest possible breath, make the deepest forced exhalation. In this case, the exhalation should be carried out with an effort aimed at achieving the maximum volumetric velocity of the exhaled air flow throughout the entire exhalation. Computer analysis of such a forced expiration allows you to calculate dozens of indicators of external respiration.

The individual normal value of VC is called proper lung capacity(JEL). It is calculated in liters according to formulas and tables based on height, body weight, age and gender. For women 18-25 years of age, the calculation can be carried out according to the formula

JEL \u003d 3.8 * P + 0.029 * B - 3.190; for men of the same age

Residual volume

JEL \u003d 5.8 * P + 0.085 * B - 6.908, where P - height; B - age (years).

The value of the measured VC is considered reduced if this decrease is more than 20% of the VC level.

If the name “capacity” is used for the indicator of external respiration, then this means that such a capacity includes smaller units called volumes. For example, the OEL consists of four volumes, the VC consists of three volumes.

Tidal volume (TO) is the volume of air that enters and leaves the lungs in one breath. This indicator is also called the depth of breathing. At rest in an adult, DO is 300-800 ml (15-20% of the VC value); monthly child - 30 ml; one year old - 70 ml; ten-year-old - 230 ml. If the depth of breathing is greater than normal, then such breathing is called hyperpnea- excessive, deep breathing, if DO is less than normal, then breathing is called oligopnea- Insufficient, shallow breathing. At normal depth and breathing rate, it is called eupnea- normal, sufficient breathing. The normal resting respiratory rate in adults is 8-20 breaths per minute; monthly child - about 50; one-year-old - 35; ten years - 20 cycles per minute.

Inspiratory reserve volume (RIV)- the volume of air that a person can inhale with the deepest breath taken after a quiet breath. The value of RO vd in the norm is 50-60% of the value of VC (2-3 l).

Expiratory reserve volume (RO vyd)- the volume of air that a person can exhale with the deepest exhalation made after a quiet exhalation. Normally, the value of RO vyd is 20-35% of the VC (1-1.5 liters).

Residual lung volume (RLV)- the air remaining in the airways and lungs after a maximum deep exhalation. Its value is 1-1.5 liters (20-30% of the TRL). In old age, the value of the TRL increases due to a decrease in the elastic recoil of the lungs, bronchial patency, a decrease in the strength of the respiratory muscles and chest mobility. At the age of 60, it already makes up about 45% of the TRL.

Functional residual capacity (FRC) The air remaining in the lungs after a quiet exhalation. This capacity consists of the residual lung volume (RLV) and the expiratory reserve volume (ERV).

Not all atmospheric air entering the respiratory system during inhalation takes part in gas exchange, but only that which reaches the alveoli, which have a sufficient level of blood flow in the capillaries surrounding them. In this regard, there is a so-called dead space.

Anatomical dead space (AMP)- this is the volume of air in the respiratory tract to the level of the respiratory bronchioles (there are already alveoli on these bronchioles and gas exchange is possible). The value of AMP is 140-260 ml and depends on the characteristics of the human constitution (when solving problems in which it is necessary to take into account AMP, and its value is not indicated, the volume of AMP is taken equal to 150 ml).

Physiological Dead Space (PDM)- the volume of air entering the respiratory tract and lungs and not taking part in gas exchange. FMP is larger than the anatomical dead space, as it includes it as an integral part. In addition to the air in the respiratory tract, the FMF includes air that enters the pulmonary alveoli, but does not exchange gases with the blood due to the absence or decrease in blood flow in these alveoli (the name is sometimes used for this air alveolar dead space). Normally, the functional dead space is 20-35% of the tidal volume. An increase in this value over 35% may indicate the presence of certain diseases.

Table 1. Indicators of pulmonary ventilation

In medical practice, it is important to take into account the dead space factor when designing breathing devices (high-altitude flights, scuba diving, gas masks), and carrying out a number of diagnostic and resuscitation measures. When breathing through tubes, masks, hoses, additional dead space is connected to the human respiratory system and, despite an increase in the depth of breathing, ventilation of the alveoli with atmospheric air may become insufficient.

Minute breathing volume

Minute respiratory volume (MOD)- the volume of air ventilated through the lungs and respiratory tract in 1 min. To determine the MOD, it is enough to know the depth, or tidal volume (TO), and respiratory rate (RR):

MOD \u003d TO * BH.

In mowing, the MOD is 4-6 l/min. This indicator is often also called lung ventilation (distinguish from alveolar ventilation).

Alveolar ventilation

Alveolar ventilation (AVL)- the volume of atmospheric air passing through the pulmonary alveoli in 1 min. To calculate alveolar ventilation, you need to know the value of AMP. If it is not determined experimentally, then for calculation the volume of AMP is taken equal to 150 ml. To calculate alveolar ventilation, you can use the formula

AVL \u003d (DO - AMP). BH.

For example, if the depth of breathing in a person is 650 ml, and the respiratory rate is 12, then the AVL is 6000 ml (650-150). 12.

AB \u003d (DO - OMP) * BH \u003d TO alf * BH

AB - alveolar ventilation;
TO alv — tidal volume of alveolar ventilation;
RR - respiratory rate

Maximum lung ventilation (MVL)- the maximum volume of air that can be ventilated through the lungs of a person in 1 minute. MVL can be determined with arbitrary hyperventilation at rest (breathing as deeply as possible and often no more than 15 seconds is permissible during mowing). With the help of special equipment, MVL can be determined during intensive physical work performed by a person. Depending on the constitution and age of a person, the MVL norm is in the range of 40-170 l / min. In athletes, MVL can reach 200 l / min.

Flow indicators of external respiration

In addition to lung volumes and capacities, the so-called flow indicators of external respiration. The simplest method for determining one of these, peak expiratory volume flow, is peak flowmetry. Peak flow meters are simple and quite affordable devices for use at home.

Peak expiratory volume flow(POS) - the maximum volumetric flow rate of exhaled air, achieved in the process of forced exhalation.

With the help of a pneumotachometer device, it is possible to determine not only the peak volumetric expiratory flow rate, but also inhalation.

In a medical hospital, pneumotachograph devices with computer processing of the information received are becoming more widespread. Devices of this type make it possible, on the basis of continuous registration of the volumetric velocity of the air flow created during the exhalation of the forced vital capacity of the lungs, to calculate dozens of indicators of external respiration. Most often, POS and maximum (instantaneous) volumetric air flow rates at the moment of exhalation are determined 25, 50, 75% FVC. They are called indicators ISO 25, ISO 50, ISO 75, respectively. Also popular is the definition of FVC 1 - forced expiratory volume for a time equal to 1 e. Based on this indicator, the Tiffno index (indicator) is calculated - the ratio of FVC 1 to FVC expressed as a percentage. A curve is also recorded, reflecting the change in the volumetric velocity of the air flow during forced exhalation (Fig. 2.4). At the same time, the volumetric velocity (l/s) is displayed on the vertical axis, and the percentage of exhaled FVC is displayed on the horizontal axis.

In the above graph (Fig. 2, upper curve), the peak indicates the PIC value, the projection of the moment of expiration of 25% FVC on the curve characterizes the MOS 25 , the projection of 50% and 75% FVC corresponds to the MOS 50 and MOS 75 values. Not only the flow rates at individual points, but also the entire course of the curve, are of diagnostic significance. Its part, corresponding to 0-25% of the exhaled FVC, reflects the air permeability of the large bronchi, trachea and, the area from 50 to 85% of the FVC - the permeability of the small bronchi and bronchioles. The deflection on the downward section of the lower curve in the expiratory region of 75-85% FVC indicates a decrease in the patency of the small bronchi and bronchioles.

Rice. 2. Flow indicators of respiration. Curves of notes - the volume of a healthy person (upper), a patient with obstructive violations of the patency of small bronchi (lower)

The determination of the listed volumetric and flow indicators is used in diagnosing the state of the external respiration system. To characterize the function of external respiration in the clinic, four types of conclusions are used: normal, obstructive disorders, restrictive disorders, mixed disorders (combination of obstructive and restrictive disorders).

For most flow and volume indicators of external respiration, deviations of their value from the due (calculated) value by more than 20% are considered to be outside the norm.

Obstructive disorders- these are violations of the airway patency, leading to an increase in their aerodynamic resistance. Such disorders can develop as a result of an increase in the tone of the smooth muscles of the lower respiratory tract, with hypertrophy or edema of the mucous membranes (for example, with acute respiratory viral infections), accumulation of mucus, purulent discharge, in the presence of a tumor or foreign body, dysregulation of the patency of the upper respiratory tract and other cases.

The presence of obstructive changes in the respiratory tract is judged by a decrease in POS, FVC 1 , MOS 25 , MOS 50 , MOS 75 , MOS 25-75 , MOS 75-85 , the value of the Tiffno test index and MVL. The Tiffno test indicator is normally 70-85%, its decrease to 60% is regarded as a sign of a moderate violation, and up to 40% - a pronounced violation of bronchial patency. In addition, with obstructive disorders, indicators such as residual volume, functional residual capacity and total lung capacity increase.

Restrictive violations- this is a decrease in the expansion of the lungs during inspiration, a decrease in respiratory excursions of the lungs. These disorders can develop due to a decrease in lung compliance, with chest injuries, the presence of adhesions, accumulation of fluid in the pleural cavity, purulent contents, blood, weakness of the respiratory muscles, impaired transmission of excitation in neuromuscular synapses and other reasons.

The presence of restrictive changes in the lungs is determined by a decrease in VC (at least 20% of the expected value) and a decrease in MVL (non-specific indicator), as well as a decrease in lung compliance and, in some cases, by an increase in the Tiffno test (more than 85%). In restrictive disorders, total lung capacity, functional residual capacity, and residual volume are reduced.

The conclusion about mixed (obstructive and restrictive) disorders of the external respiration system is made with the simultaneous presence of changes in the above flow and volume indicators.

Lung volumes and capacities

Tidal volume - this is the volume of air that a person inhales and exhales in a calm state; in an adult, it is 500 ml.

Inspiratory reserve volume is the maximum volume of air that a person can inhale after a quiet breath; its value is 1.5-1.8 liters.

Expiratory reserve volume - This is the maximum volume of air that a person can exhale after a quiet exhalation; this volume is 1-1.5 liters.

Residual volume - is the volume of air that remains in the lungs after maximum exhalation; the value of the residual volume is 1-1.5 liters.

Rice. 3. Change in tidal volume, pleural and alveolar pressure during lung ventilation

Vital capacity of the lungs(VC) is the maximum volume of air that a person can exhale after taking the deepest breath possible. The VC includes inspiratory reserve volume, tidal volume, and expiratory reserve volume. The vital capacity of the lungs is determined by a spirometer, and the method of its determination is called spirometry. VC in men is 4-5.5 liters, and in women - 3-4.5 liters. It is more in a standing position than in a sitting or lying position. Physical training leads to an increase in VC (Fig. 4).

Rice. 4. Spirogram of lung volumes and capacities

Functional residual capacity(FOE) - the volume of air in the lungs after a quiet exhalation. FRC is the sum of expiratory reserve volume and residual volume and is equal to 2.5 liters.

Total lung capacity(TEL) - the volume of air in the lungs at the end of a full breath. The TRL includes the residual volume and vital capacity of the lungs.

Dead space forms air that is in the airways and does not participate in gas exchange. When inhaling, the last portions of atmospheric air enter the dead space and, without changing their composition, leave it when exhaling. The dead space volume is about 150 ml, or about 1/3 of the tidal volume during quiet breathing. This means that out of 500 ml of inhaled air, only 350 ml enters the alveoli. In the alveoli, by the end of a calm expiration, there is about 2500 ml of air (FFU), therefore, with each calm breath, only 1/7 of the alveolar air is renewed.

The total lung capacity of an adult male is on average 5-6 liters, but during normal breathing only a small part of this volume is used. With calm breathing, a person performs about 12-16 respiratory cycles, inhaling and exhaling about 500 ml of air in each cycle. This volume of air is called the respiratory volume. With a deep breath, you can additionally inhale 1.5-2 liters of air - this is the reserve volume of inspiration. The volume of air that remains in the lungs after maximum expiration is 1.2-1.5 liters - this is the residual volume of the lungs.

Measurement of lung volumes

Under the term measurement of lung volumes commonly understood as the measurement of total lung capacity (TLC), residual lung volume (RRL), functional residual capacity (FRC) of the lungs and vital capacity (VC). These indicators play a significant role in the analysis of the ventilation capacity of the lungs, they are indispensable in the diagnosis of restrictive ventilation disorders and help evaluate the effectiveness of the therapeutic intervention. The measurement of lung volumes can be divided into two main stages: the measurement of the FRC and the performance of a spirometry study.

To determine the FRC, one of the three most common methods is used:

gas dilution method (gas dilution method);
body plethysmographic;
radiological.

Lung volumes and capacities

Usually, four lung volumes are distinguished - inspiratory reserve volume (IRV), tidal volume (TO), expiratory reserve volume (ERV) and residual lung volume (ROL) and the following capacities: vital capacity (VC), inspiratory capacity (Evd), functional residual capacity (FRC) and total lung capacity (TLC).

The total lung capacity can be represented as the sum of several lung volumes and capacities. Lung capacity is the sum of two or more lung volumes.

Tidal volume (TO) is the volume of gas that is inhaled and exhaled during a respiratory cycle during quiet breathing. DO should be calculated as an average after recording at least six respiratory cycles. The end of the inspiratory phase is called the end-inspiratory level, the end of the exhalation phase is called the end-expiratory level.

Inspiratory reserve volume (IRV) is the maximum volume of air that can be inhaled after a normal average quiet breath (end-inspiratory level).

Expiratory reserve volume (ERV) is the maximum volume of air that can be exhaled after a quiet exhalation (end-expiratory level).

Residual lung volume (RLV) is the volume of air that remains in the lungs after a full exhalation. TRL cannot be measured directly, it is calculated by subtracting the EV from the FRC: OOL \u003d FOE - ROvyd or OOL \u003d OEL - VC. Preference is given to the latter method.

Vital capacity (VC) - the volume of air that can be exhaled during a full exhalation after a maximum inspiration. With a forced exhalation, this volume is called the forced vital capacity of the lungs (FVC), with a calm maximum (inhalation) exhalation - the vital capacity of the lungs of inhalation (exhalation) - FVC (VC). ZhEL includes DO, ROVD and ROVID. The VC is normally approximately 70% of the TRL.

Inspiratory capacity (EVD) - the maximum volume that can be inhaled after a quiet exhalation (from the end-expiratory level). EVD is equal to the sum of DO and ROVD and normally is usually 60-70% VC.

Functional residual capacity (FRC) is the volume of air in the lungs and airways after a quiet exhalation. The FRC is also referred to as the final expiratory volume. FFU includes ROvyd and OOL. Measurement of FRC is a defining step in assessing lung volumes.

Total lung capacity (TLC) is the volume of air in the lungs at the end of a full breath. The REL is calculated in two ways: OEL \u003d OOL + VC or OEL \u003d FOE + Evd. The latter method is preferable.

Measurement of the total lung capacity and its components is widely used in various diseases and provides significant assistance in the diagnostic process. For example, with emphysema, there is usually a decrease in FVC and FEV1, the FEV1 / FVC ratio is also reduced. A decrease in FVC and FEV1 is also noted in patients with restrictive disorders, but the FEV1/FVC ratio is not reduced.

Despite this, the FEV1/FVC ratio is not a key parameter in the differential diagnosis of obstructive and restrictive disorders. For the differential diagnosis of these ventilation disorders, it is necessary to measure the RFE and its components. With restrictive violations, there is a decrease in the TRL and all its components. In obstructive and combined obstructive-restrictive disorders, some components of the REL are reduced, some are increased.

The FRC measurement is one of the two main steps in the measurement of the RFE. FRC can be measured by gas dilution methods, body plethysmography or radiography. In healthy individuals, all three methods allow obtaining close results. The coefficient of variation of repeated measurements in the same subject is usually below 10%.

The gas dilution method is widely used because of the simplicity of the technique and the relative cheapness of the equipment. However, in patients with severe bronchial conduction disorders or emphysema, the true TEL value measured by this method is underestimated because the inhaled gas does not penetrate into hypoventilated and unventilated spaces.

The body plethysmography method allows you to determine the intrathoracic volume (VGO) of gas. Thus, FRC measured by body plethysmography includes both ventilated and non-ventilated lung regions. In this regard, in patients with pulmonary cysts and air traps, this method gives higher rates compared to the method of diluting gases. Body plethysmography is a more expensive method, technically more difficult and requires more effort and cooperation from the patient compared to the gas dilution method. Nevertheless, the body plethysmography method is preferable, since it allows a more accurate assessment of the FRC.

The difference between the values obtained using these two methods provides important information about the presence of unventilated air space in the chest. With severe bronchial obstruction, the method of general plethysmography may overestimate the FRC.

Based on the materials of A.G. Chuchalin