Tidal volume and minute volume of breathing (MRV), respiratory equivalent. Human lung volume - measuring lung volumes How to find tidal volume

During inhalation, the lungs are filled with a certain amount of air. This value is not constant and may change under different circumstances. The volume depends on external and internal factors.

What affects lung capacity?

The level of filling of the lungs with air is influenced by certain circumstances. Men have a larger average organ volume than women. In tall people with a large body constitution, the lungs can hold more air when inhaling than in short and thin people. With age, the amount of air inhaled decreases, which is a physiological norm.

Systematic smoking reduces lung capacity. Low filling capacity is typical for hypersthenics (short people with a rounded body and short, wide-boned limbs). Asthenics (narrow-shouldered, thin) are able to inhale more oxygen.

All people living high relative to sea level (mountainous areas) have reduced lung capacity. This is due to the fact that they breathe thin, low-density air.

Temporary changes in the respiratory system occur in pregnant women. The volume of each lung is reduced by 5-10%. The rapidly growing uterus increases in size and puts pressure on the diaphragm. This does not affect the woman’s general condition, since compensatory mechanisms are activated. Due to accelerated ventilation, they prevent the development of hypoxia.

Average lung volumes

Lung volume is measured in liters. Average values are calculated during normal breathing at rest, without deep inhalations and full exhalations.

The average figure is 3-4 liters. In physically developed men, the volume during moderate breathing can reach up to 6 liters. The normal number of respiratory acts is 16-20. With active physical activity and nervous strain, these numbers increase.

Vital capacity, or vital capacity of the lungs

The vital capacity is the greatest capacity of the lung during maximum inhalation and exhalation. In young, healthy men, the figure is 3500-4800 cm 3, in women – 3000-3500 cm 3. For athletes, these figures increase by 30% and amount to 4000-5000 cm 3. Swimmers have the largest lungs - up to 6200 cm 3.

Taking into account the phases of lung ventilation, the following types of volume are divided:

respiratory - air that circulates freely through the bronchopulmonary system at rest;
reserve during inhalation - air filled with the organ during maximum inhalation after a quiet exhalation;
exhalation reserve - the amount of air removed from the lungs during a sharp exhalation after a calm inhalation;
residual - air remaining in the chest after maximum exhalation.

Airway ventilation refers to gas exchange for 1 minute.

The formula for its definition:

tidal volume × number of breaths/minute = minute breathing volume.

Normally, an adult's ventilation is 6-8 l/min.

Table of indicators of the average lung volume:

The air that is located in such parts of the respiratory tract - the nasal passages, nasopharynx, larynx, trachea, central bronchi - does not participate in gas exchange. They constantly contain a gas mixture called “dead space”, which is 150-200 cm 3 .

Vital capacity measurement method

External respiratory function is examined using a special test - spirometry (spirography). The method records not only the capacity, but also the speed of air flow circulation.
For diagnostics, digital spirometers are used, which replaced mechanical ones. The device consists of two devices. A sensor for recording air flow and an electronic device that converts measurement indicators into a digital formula.

Spirometry is prescribed to patients with respiratory dysfunction and chronic bronchopulmonary diseases. Calm and forced breathing are assessed, and functional tests are performed with bronchodilators.

Digital data of vital fluid during spirography are distinguished by age, gender, anthropometric data, and the absence or presence of chronic diseases.

Formulas for calculating individual VC, where P is height, B is weight:

for men – 5.2×P – 0.029×B – 3.2;
for women – 4.9×P – 0.019×B – 3.76;
for boys from 4 to 17 years old with a height of up to 165 cm – 4.53×P – 3.9; with height over 165 cm – 10×P – 12.85;
for girls from 4 to 17 years old the swarm grows from 100 to 175 cm - 3.75×P - 3.15.

Measurement of vital capacity is not carried out for children under 4 years of age, patients with mental disorders, or with maxillofacial injuries. An absolute contraindication is acute contagious infection.

Diagnostics are not prescribed if it is physically impossible to carry out the test:

neuromuscular disease with rapid fatigue of the striated muscles of the face (myasthenia gravis);
postoperative period in maxillofacial surgery;
paresis, paralysis of the respiratory muscles;
severe pulmonary and heart failure.

Reasons for an increase or decrease in vital capacity indicators

Increased lung capacity is not a pathology. Individual values depend on the physical development of the person. In athletes, VC can exceed standard values by 30%.

Respiratory function is considered impaired if a person’s lung capacity is less than 80%. This is the first signal of insufficiency of the bronchopulmonary system.

External signs of pathology:

breathing problems during active movements;

change in chest amplitude.

Initially, it is difficult to determine violations, since compensatory mechanisms redistribute air in the structure of the total volume of the lungs. Therefore, spirometry is not always of diagnostic value, for example, in cases of pulmonary emphysema and bronchial asthma. During the course of the disease, swelling of the lungs is formed. Therefore, for diagnostic purposes, percussion is performed (low position of the diaphragm, specific “boxy” sound), chest X-ray (more transparent lung fields, expansion of boundaries).

Factors reducing vital capacity:

reduction in the volume of the pleural cavity due to the development of the cor pulmonale;
rigidity of the organ parenchyma (hardening, limited mobility);
high standing of the diaphragm with ascites (accumulation of fluid in the abdominal cavity), obesity;
pleural hydrothorax (effusion in the pleural cavity), pneumothorax (air in the pleural layers);
diseases of the pleura - tissue adhesions, mesothelioma (tumor of the inner lining);
kyphoscoliosis – curvature of the spine;
severe pathology of the respiratory system - sarcoidosis, fibrosis, pneumosclerosis, alveolitis;
after resection (removal of part of an organ).

Systematic monitoring of VC helps to track the dynamics of pathological changes and take timely measures to prevent the development of diseases of the respiratory system.

Lung volumes and capacities

During the process of pulmonary ventilation, the gas composition of the alveolar air is continuously updated. The amount of pulmonary ventilation is determined by the depth of breathing, or tidal volume, and the frequency of respiratory movements. During breathing movements, a person’s lungs are filled with inhaled air, the volume of which is part of the total volume of the lungs. To quantitatively describe pulmonary ventilation, total lung capacity was divided into several components or volumes. In this case, the pulmonary capacity is the sum of two or more volumes.

Lung volumes are divided into static and dynamic. Static pulmonary volumes are measured during completed respiratory movements without limiting their speed. Dynamic pulmonary volumes are measured during respiratory movements with a time limit for their implementation.

Lung volumes. The volume of air in the lungs and respiratory tract depends on the following indicators: 1) anthropometric individual characteristics of the person and the respiratory system; 2) properties of lung tissue; 3) surface tension of the alveoli; 4) the force developed by the respiratory muscles.

Tidal volume (TO)- the volume of air that a person inhales and exhales during quiet breathing. In an adult, DO is approximately 500 ml. The value of DO depends on the measurement conditions (rest, load, body position). DO is calculated as the average value after measuring approximately six quiet breathing movements.

Inspiratory reserve volume (IRV)- the maximum volume of air that a subject can inhale after a quiet breath. The size of the ROVD is 1.5-1.8 liters.

Expiratory reserve volume (ERV)- the maximum volume of air that a person can additionally exhale from the level of quiet exhalation. The value of POvyd is lower in a horizontal position than in a vertical position, and decreases with obesity. It is equal to an average of 1.0-1.4 liters.

Residual volume (VR)- the volume of air that remains in the lungs after maximum exhalation. The residual volume is 1.0-1.5 liters.

The study of dynamic lung volumes is of scientific and clinical interest, and their description goes beyond the scope of a normal physiology course.

Lung capacity. Vital capacity of the lungs (VC) includes tidal volume, inspiratory reserve volume, and expiratory reserve volume. In middle-aged men, vital capacity varies between 3.5-5.0 liters and more. For women, lower values are typical (3.0-4.0 l). Depending on the methodology for measuring vital capacity, a distinction is made between inhalation vital capacity, when after a complete exhalation a maximum deep breath is taken, and exhalation vital capacity, when after a full inhalation a maximum exhalation is made.

Inspiratory capacity (EIC) is equal to the sum of tidal volume and inspiratory reserve volume. In humans, EUD averages 2.0-2.3 liters.

Functional residual capacity (FRC) is the volume of air in the lungs after a quiet exhalation. FRC is the sum of expiratory reserve volume and residual volume. FRC is measured by gas dilution, or gas dilution, and plethysmography. The value of FRC is significantly influenced by the level of physical activity of a person and body position: FRC is smaller in a horizontal position of the body than in a sitting or standing position. FRC decreases in obesity due to a decrease in the overall compliance of the chest.

Total lung capacity (TLC) is the volume of air in the lungs at the end of a full inhalation. TEL is calculated in two ways: TEL - OO + VC or TEL - FRC + Evd. TLC can be measured using plethysmography or gas dilution.

Measurement of lung volumes and capacities is of clinical importance in the study of pulmonary function in healthy individuals and in the diagnosis of human lung disease. Measurement of lung volumes and capacities is usually carried out using spirometry, pneumotachometry with the integration of indicators, and body plethysmography. Static lung volumes may decrease under pathological conditions that lead to limited lung expansion. These include neuromuscular diseases, diseases of the chest, abdomen, pleural lesions that increase the rigidity of the lung tissue, and diseases that cause a decrease in the number of functioning alveoli (atelectasis, resection, scar changes in the lungs).

For comparability of the results of measurements of gas volumes and capacities, the data obtained must be correlated with the conditions in the lungs, where the temperature of the alveolar air corresponds to body temperature, the air is at a certain pressure and is saturated with water vapor. This state is called standard and is designated by the letters BTPS (body temperature, pressure, saturated).

4. Change in lung volume during inhalation and exhalation. Function of intrapleural pressure. Pleural space. Pneumothorax.
5. Breathing phases. Volume of the lung(s). Respiration rate. Depth of breathing. Pulmonary air volumes. Tidal volume. Reserve, residual volume. Lung capacity.
6. Factors influencing pulmonary volume during the inspiratory phase. Extensibility of the lungs (lung tissue). Hysteresis.
7. Alveoli. Surfactant. Surface tension of the fluid layer in the alveoli. Laplace's law.
8. Airway resistance. Lung resistance. Air flow. Laminar flow. Turbulent flow.
9. Flow-volume relationship in the lungs. Pressure in the airways during exhalation.
10. Work of the respiratory muscles during the respiratory cycle. The work of the respiratory muscles during deep breathing. Breathing phases. Volume of the lung(s). Respiration rate. Depth of breathing. Pulmonary air volumes. Tidal volume. Reserve, residual volume. Lung capacity.

External respiration process is caused by changes in the volume of air in the lungs during the inhalation and exhalation phases of the respiratory cycle. During quiet breathing, the ratio of the duration of inhalation to exhalation in the respiratory cycle is on average 1:1.3. External breathing of a person is characterized by the frequency and depth of respiratory movements. Respiration rate a person is measured by the number of respiratory cycles within 1 minute and its value at rest in an adult varies from 12 to 20 per 1 minute. This indicator of external respiration increases with physical work, increasing ambient temperature, and also changes with age. For example, in newborns the respiratory rate is 60-70 per 1 min, and in people aged 25-30 years - an average of 16 per 1 min. The depth of breathing is determined by the volume of inhaled and exhaled air during one respiratory cycle. The product of the frequency of respiratory movements and their depth characterizes the basic value of external respiration - ventilation. A quantitative measure of pulmonary ventilation is the minute volume of breathing - this is the volume of air that a person inhales and exhales in 1 minute. The minute volume of a person's breathing at rest varies between 6-8 liters. During physical work, a person's minute breathing volume can increase 7-10 times.

Rice. 10.5. Volumes and capacities of air in the human lungs and the curve (spirogram) of changes in air volume in the lungs during quiet breathing, deep inhalation and exhalation. FRC - functional residual capacity.

Pulmonary air volumes. IN respiratory physiology a unified nomenclature of pulmonary volumes in humans has been adopted, which fill the lungs during quiet and deep breathing during the inhalation and exhalation phases of the respiratory cycle (Fig. 10.5). The lung volume that is inhaled or exhaled by a person during quiet breathing is called tidal volume. Its value during quiet breathing averages 500 ml. The maximum amount of air that a person can inhale above the tidal volume is called inspiratory reserve volume(average 3000 ml). The maximum amount of air that a person can exhale after a quiet exhalation is called the expiratory reserve volume (on average 1100 ml). Finally, the amount of air that remains in the lungs after maximum exhalation is called the residual volume, its value is approximately 1200 ml.

The sum of two or more pulmonary volumes is called pulmonary capacity. Air volume in human lungs it is characterized by inspiratory lung capacity, vital lung capacity and functional residual lung capacity. Inspiratory capacity (3500 ml) is the sum of tidal volume and inspiratory reserve volume. Vital capacity of the lungs(4600 ml) includes tidal volume and inspiratory and expiratory reserve volumes. Functional residual lung capacity(1600 ml) is the sum of expiratory reserve volume and residual lung volume. Sum vital capacity of the lungs And residual volume is called the total lung capacity, the average value of which in humans is 5700 ml.

When inhaling, the human lungs due to contraction of the diaphragm and external intercostal muscles, they begin to increase their volume from the level, and its value during quiet breathing is tidal volume, and with deep breathing - reaches different values reserve volume inhale. When exhaling, the volume of the lungs returns to the original level of functional function. residual capacity passively, due to elastic traction of the lungs. If air begins to enter the volume of exhaled air functional residual capacity, which occurs during deep breathing, as well as when coughing or sneezing, then exhalation is carried out by contracting the muscles of the abdominal wall. In this case, the value of intrapleural pressure, as a rule, becomes higher than atmospheric pressure, which determines the highest speed of air flow in the respiratory tract.

Ventilator! If you understand it, it is equivalent to the appearance, as in the films, of a superhero (doctor) super weapons(if the doctor understands the intricacies of mechanical ventilation) against the death of the patient.

To understand mechanical ventilation you need basic knowledge: physiology = pathophysiology (obstruction or restriction) of breathing; main parts, structure of the ventilator; provision of gases (oxygen, atmospheric air, compressed gas) and dosing of gases; adsorbers; elimination of gases; breathing valves; breathing hoses; breathing bag; humidification system; breathing circuit (semi-closed, closed, semi-open, open), etc.

All ventilators provide ventilation by volume or pressure (no matter what they are called; depending on what mode the doctor has set). Basically, the doctor sets the mechanical ventilation mode for obstructive pulmonary diseases (or during anesthesia) by volume, during restriction by pressure.

The main types of ventilation are designated as follows:

CMV (Continuous mandatory ventilation) - Controlled (artificial) ventilation

VCV (Volume controlled ventilation) - volume controlled ventilation

PCV (Pressure controlled ventilation) - pressure controlled ventilation

IPPV (Intermittent positive pressure ventilation) - mechanical ventilation with intermittent positive pressure during inspiration

ZEEP (Zero endexpiratory pressure) - ventilation with pressure at the end of expiration equal to atmospheric

PEEP (Positive endexpiratory pressure) - Positive end expiratory pressure (PEEP)

CPPV (Continuous positive pressure ventilation) - mechanical ventilation with PDKV

IRV (Inversed ratio ventilation) - mechanical ventilation with a reverse (inverted) inhalation:exhalation ratio (from 2:1 to 4:1)

SIMV (Synchronized intermittent mandatory ventilation) - Synchronized intermittent mandatory ventilation = A combination of spontaneous and mechanical breathing, when, when the frequency of spontaneous breathing decreases to a certain value, with continued attempts to inhale, overcoming the level of the established trigger, mechanical breathing is synchronously activated

You should always look at the letters ..P.. or ..V.. If P (Pressure) means by distance, if V (Volume) by volume.

Vt – tidal volume,
f – respiratory rate, MV – minute ventilation
PEEP – PEEP = positive end expiratory pressure
Tinsp – inspiratory time;
Pmax - inspiratory pressure or maximum airway pressure.
Gas flow of oxygen and air.

Tidal volume(Vt, DO) set from 5 ml to 10 ml/kg (depending on the pathology, normal 7-8 ml per kg) = how much volume the patient should inhale at a time. But to do this, you need to find out the ideal (proper, predicted) body weight of a given patient using the formula (NB! remember):

Men: BMI (kg)=50+0.91 (height, cm – 152.4)

Women: BMI (kg)=45.5+0.91·(height, cm – 152.4).

Example: a man weighs 150 kg. This does not mean that we should set the tidal volume to 150kg·10ml= 1500 ml. First, we calculate BMI=50+0.91·(165cm-152.4)=50+0.91·12.6=50+11.466= 61,466 kg our patient should weigh. Imagine, oh allai deseishi! For a man weighing 150 kg and height 165 cm, we must set the tidal volume (TI) from 5 ml/kg (61.466·5=307.33 ml) to 10 ml/kg (61.466·10=614.66 ml) depending on pathology and extensibility of the lungs.

2. The second parameter that the doctor must set is respiration rate(f). The normal respiratory rate is 12 to 18 per minute at rest. And we don't know what frequency to set: 12 or 15, 18 or 13? To do this we must calculate due MOD (MV). Synonyms for minute breathing volume (MVR) = minute ventilation (MVL), maybe something else... This means how much air the patient needs (ml, l) per minute.

MOD=BMI kg:10+1

according to the Darbinyan formula (outdated formula, often leads to hyperventilation).

Or modern calculation: MOD=BMIkg·100.

(100%, or 120%-150% depending on the patient’s body temperature..., from the basal metabolism in short).

Example: The patient is a woman, weighs 82 kg, height is 176 cm. BMI = 45.5 + 0.91 (height, cm - 152.4) = 45.5 + 0.91 (176 cm - 152.4) = 45.5+0.91 23.6=45.5+21.476= 66,976 kg should weigh. MOD = 67 (rounded up immediately) 100 = 6700 ml or 6,7 liters per minute. Now only after these calculations can we find out the breathing frequency. f=MOD:UP TO=6700 ml: 536 ml=12.5 times per minute, which means 12 or 13 once.

3. Install REER. Normally (previously) 3-5 mbar. Now you can 8-10 mbar in patients with normal lungs.

4. The inhalation time in seconds is determined by the ratio of inhalation to exhalation: I: E=1:1,5-2 . In this parameter, knowledge about the respiratory cycle, ventilation-perfusion ratio, etc. will be useful.

5. Pmax, Pinsp peak pressure is set so as not to cause barotrauma or rupture the lungs. Normally, I think 16-25 mbar, depending on the elasticity of the lungs, the weight of the patient, the extensibility of the chest, etc. In my knowledge, lungs can rupture when Pinsp is more than 35-45 mbar.

6. The fraction of inhaled oxygen (FiO 2) should be no more than 55% in the inhaled respiratory mixture.

All calculations and knowledge are needed so that the patient has the following indicators: PaO 2 = 80-100 mm Hg; PaCO 2 =35-40 mm Hg. Just, oh allai deseishi!

Breathing volumes are determined spirometrically and should be considered among the most indicative ventilation values.

Minute breathing volume

This refers to the amount of air ventilated during quiet breathing per minute.

Method of determination. The subject, connected to a spirograph, is first given the opportunity for several minutes to get used to breathing that is not quite usual for him. After the hyperventilation that occurs initially in most cases gives way to calm breathing, the minute volume of breathing is determined by multiplying the volume of breathing during inhalation by the number of breaths per minute. In case of restless breathing, the volumes ventilated for each breath for a minute are measured and the results are added up.

Normal values. The proper minute volume of respiration is obtained by multiplying the proper basal metabolic rate (the proper number of calories in 24 hours compared to the total body surface area) by 4.73.

The resulting values will be in the range of 6-9 liters. They are influenced by the metabolic rate (intensity) (eg, thyrotoxicosis) and the amount of dead space ventilation. This makes it possible to sometimes attribute deviations from the norm to the pathology of one of these factors.

When replacing air breathing with oxygen breathing in healthy individuals, there is no change in the minute volume of breathing. On the contrary, with very severe respiratory failure, the minute volume when breathing oxygen decreases and at the same time the oxygen consumption per minute increases. “Calmation of breathing” occurs. This effect is explained by better arterialization of blood when breathing pure oxygen compared to breathing with atmospheric air. This attracts even more attention under load.

Compare with this what was said in the section on cardiopulmonary (cardiopulmonary) oxygen deficiency.

Test for maximum expiratory volume (Tiffno test)

The maximum expiratory volume is understood as the expiratory work of the lungs per second, i.e., the amount of air exhaled with force per second after the maximum inhalation.

The duration of exhalation in patients with emphysema is longer than in healthy individuals. This fact, first recorded on the Hutchinson spirometer, was later confirmed by Tiffeneau and Pinelli, who also pointed out its completely definite relationship with vital capacity.

In German literature, the amount of air exhaled in a sample per second is called “useful fraction of vital capacity”, the British speak of “timed capacity” (capacity for a certain period of time), in French literature the term “capacite pulmonaire utilisable a l'effort” is used ( pulmonary capacity, utilized with effort).

This test is of particular importance because it allows one to draw general conclusions about the width of the respiratory tract and, accordingly, about the amount of breathing resistance in the bronchial system, as well as about the elasticity of the lungs, the mobility of the chest and the strength of the respiratory muscles.

Normal values. The maximum expiratory volume is expressed as a percentage of vital capacity. In healthy people, it is equal to 70-80% of vital capacity. In this case, at least 55% of the available vital capacity must be expired in the first half of a second.

In healthy people, it takes 4 seconds to fully exhale after a deep inhalation. After 2 seconds, 94% of the vital capacity is exhaled, after 3 seconds - 97% of the vital capacity.

Expiratory volume decreases with age from 83% of vital capacity in youth to 69% in old age. This fact is confirmed by Gitter in his extensive research on more than 1,000 industrial workers. Tiffeneau considers normal the maximum expiratory volume in the first second, which is 83.3% of the true or actual capacity, Biicherl - 77.3% for men and 82.3% for women.

Execution method. A spirograph is used, the kymograph of which quickly moves the tape (at least 10 mm/sec). After recording the vital capacity in the usual way, the subject is asked to take a maximum breath again, hold his breath a little, then exhale quickly and as deeply as possible. Some simplification can be achieved if the so-called expirogram is recorded with the simultaneous determination of the vital capacity and the maximum volume of exhalation in one exhalation after the maximum inhalation.

Grade. The Tiffeneau test is considered a reliable criterion for recognizing obstructive bronchitis and the resulting emphysema. In these cases, with normal vital capacity, a significant decrease in the maximum expiratory volume is found, while with restrictive ventilation failure, although the vital capacity is reduced, the percentage of the maximum expiratory volume remains normal.

Since the cause of obstructive disorders, along with organically caused obstacles in the airways, can also be a functional spasm, a test with asthmamolysin is recommended for differential diagnostic identification of the true cause.

Asthmolysin test. After preliminary determination of vital capacity and maximum expiratory volume, 1 ml of asthmamolysin or histamine is injected subcutaneously and after 30 minutes the same values are re-determined. If the obtained ventilation values indicate a tendency towards normalization, then we are talking about the functional component of obstructive bronchitis.

The article was prepared and edited by: surgeon