What is the minute volume of breathing at rest? External respiration and lung volumes

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 the subject is able to 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 ROvyd 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).

To assess the quality of lung function, it examines tidal volumes (using special devices - spirometers).

Tidal volume (TV) is the amount of air that a person inhales and exhales during quiet breathing in one cycle. Normal = 400-500 ml.

Minute respiration volume (MRV) is the volume of air passing through the lungs in 1 minute (MRV = DO x RR). Normal = 8-9 liters per minute; about 500 l per hour; 12000-13000 liters per day. With increasing physical activity, MOD increases.

Not all inhaled air participates in alveolar ventilation (gas exchange), because some of it does not reach the acini and remains in the respiratory tract, where there is no opportunity for diffusion. The volume of such airways is called “respiratory dead space”. Normally for an adult = 140-150 ml, i.e. 1/3 TO.

Inspiratory reserve volume (IRV) is the amount of air that a person can inhale during the strongest maximum inhalation after a quiet inhalation, i.e. over DO. Normal = 1500-3000 ml.

Expiratory reserve volume (ERV) is the amount of air that a person can additionally exhale after a quiet exhalation. Normal = 700-1000 ml.

Vital capacity of the lungs (VC) is the amount of air that a person can maximally exhale after the deepest inhalation (VC=DO+ROVd+ROVd = 3500-4500 ml).

Residual lung volume (RLV) is the amount of air remaining in the lungs after maximum exhalation. Normal = 100-1500 ml.

Total lung capacity (TLC) is the maximum amount of air that can be held in the lungs. TEL=VEL+TOL = 4500-6000 ml.

DIFFUSION OF GASES

Composition of inhaled air: oxygen - 21%, carbon dioxide - 0.03%.

Composition of exhaled air: oxygen - 17%, carbon dioxide - 4%.

The composition of the air contained in the alveoli: oxygen - 14%, carbon dioxide -5.6%.

As you exhale, the alveolar air is mixed with the air in the respiratory tract (in the “dead space”), which causes the indicated difference in air composition.

The transition of gases through the air-hematic barrier is due to the difference in concentrations on both sides of the membrane.

Partial pressure is that part of the pressure that falls on a given gas. At an atmospheric pressure of 760 mm Hg, the partial pressure of oxygen is 160 mm Hg. (i.e. 21% of 760), in the alveolar air the partial pressure of oxygen is 100 mm Hg, and carbon dioxide is 40 mm Hg.

Gas voltage is the partial pressure in a liquid. Oxygen tension in venous blood is 40 mm Hg. Due to the pressure gradient between alveolar air and blood - 60 mm Hg. (100 mm Hg and 40 mm Hg), oxygen diffuses into the blood, where it binds to hemoglobin, converting it into oxyhemoglobin. Blood containing a large amount of oxyhemoglobin is called arterial. 100 ml of arterial blood contains 20 ml of oxygen, 100 ml of venous blood contains 13-15 ml of oxygen. Also, along the pressure gradient, carbon dioxide enters the blood (since it is contained in large quantities in the tissues) and carbhemoglobin is formed. In addition, carbon dioxide reacts with water, forming carbonic acid (the reaction catalyst is the enzyme carbonic anhydrase, found in red blood cells), which breaks down into a hydrogen proton and bicarbonate ion. CO 2 tension in venous blood is 46 mm Hg; in alveolar air – 40 mm Hg. (pressure gradient = 6 mm Hg). Diffusion of CO 2 occurs from the blood into the external environment.

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

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

1. 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 breathing 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 rate - the number of inhalations and exhalations per unit of time. An adult makes an average of 15-17 breathing movements per minute. Training is of great importance. In trained people, respiratory movements occur more slowly and amount to 6-8 breaths per minute. Thus, in newborns, RR depends on a number of factors. When standing, the RR is greater than when sitting or lying down. During sleep, breathing is less frequent (by about 1/5).

During muscular work, breathing increases 2-3 times, reaching 40-45 cycles per minute or more in some types of sports exercises. The respiratory rate is affected by ambient temperature, emotions, and mental work.

Depth of breathing or tidal volume - the amount of air that a person inhales and exhales during quiet breathing. During each breathing movement, 300-800 ml of air in the lungs is exchanged. Tidal volume (TV) decreases with increasing respiratory rate.

Minute breathing volume- the amount of air that passes through the lungs per minute. It is determined by the product of the amount of inhaled air and the number of respiratory movements in 1 minute: MOD = DO x RR.

In an adult, the MOD is 5-6 liters. Age-related changes in external respiration parameters are presented in Table. 27.

Table 27. Indicators of external respiration (according to: Khripkova, 1990)

A newborn baby's breathing is rapid and shallow and subject to significant fluctuations. With age, there is a decrease in respiratory rate, an increase in tidal volume and pulmonary ventilation. Due to the higher respiratory rate, children have a significantly higher minute breathing volume (calculated per 1 kg of weight) than adults.

Ventilation may vary depending on the child's behavior. In the first months of life, anxiety, crying, and screaming increase ventilation by 2-3 times, mainly due to an increase in the depth of breathing.

Muscular work increases the minute volume of respiration in proportion to the magnitude of the load. The older children are, the more intense muscular work they can do and the more their ventilation increases. However, under the influence of training, the same work can be performed with a smaller increase in ventilation. At the same time, trained children are able to increase their minute volume of breathing when working to a higher level than their peers who do not engage in physical exercise (quoted from: Markosyan, 1969). With age, the effect of training is more pronounced, and in adolescents 14-15 years old, training causes the same significant changes in pulmonary ventilation as in adults.

Vital capacity of the lungs- the greatest amount of air that can be exhaled after a maximum inhalation. Vital capacity (VC) is an important functional characteristic of breathing and is composed of tidal volume, inspiratory reserve volume and expiratory reserve volume.

At rest, tidal volume is small compared to the total volume of air in the lungs. Therefore, a person can both inhale and exhale a large additional volume. Inspiratory reserve volume(RO ind) - the amount of air that a person can additionally inhale after a normal inhalation and is 1500-2000 ml. Expiratory reserve volume(RO exhalation) - the amount of air that a person can additionally exhale after a quiet exhalation; its size is 1000-1500 ml.

Even after the deepest exhalation, a certain amount of air remains in the alveoli and airways of the lungs - this residual volume(OO). However, during quiet breathing, significantly more air remains in the lungs than the residual volume. The amount of air remaining in the lungs after a quiet exhalation is called functional residual capacity(FOE). It consists of residual lung volume and expiratory reserve volume.

The largest amount of air that completely fills the lungs is called total lung capacity (TLC). It includes residual air volume and vital capacity of the lungs. The relationship between lung volumes and capacities is presented in Fig. 8 (Atl., p. 169). Vital capacity changes with age (Table 28). Since measuring the vital capacity of the lungs requires the active and conscious participation of the child himself, it is measured in children from 4-5 years of age.

By the age of 16-17 years, the vital capacity of the lungs reaches values ​​characteristic of an adult. Lung vital capacity is an important indicator of physical development.

Table 28. Average vital capacity of the lungs, ml (according to: Khripkova, 1990)

From childhood until the age of 18-19, the vital capacity of the lungs increases, from 18 to 35 years it remains at a constant level, and after 40 it decreases. This is due to a decrease in the elasticity of the lungs and the mobility of the chest.

The vital capacity of the lungs depends on a number of factors, in particular body length, weight and gender. To assess vital capacity, the proper value is calculated using special formulas:

for men:

VC should = [(height, cm∙ 0.052)] - [(age, years ∙ 0,022)] - 3,60;

for women:

VC should = [(height, cm∙ 0.041)] - [(age, years ∙ 0,018)] - 2,68;

for boys 8-10 years old:

VC should = [(height, cm∙ 0.052)] - [(age, years ∙ 0,022)] - 4,6;

for boys 13-16 years old:

VC should = [(height, cm∙ 0.052)] - [(age, years ∙ 0,022)] - 4,2

for girls 8-16 years old:

VC should = [(height, cm∙ 0.041)] - [(age, years ∙ 0,018)] - 3,7

Women have vital capacity 25% less than men; in trained people it is greater than in untrained people. It is especially high when playing sports such as swimming, running, skiing, rowing, etc. So, for example, for rowers it is 5,500 ml, for swimmers - 4,900 ml, gymnasts - 4,300 ml, football players - 4 200 ml, weightlifters - about 4,000 ml. To determine the vital capacity of the lungs, a spirometer device (spirometry method) is used. It consists of a vessel with water and another vessel with a capacity of at least 6 liters placed upside down in it, containing air. A system of tubes is connected to the bottom of this second vessel. The subject breathes through these tubes, so that the air in his lungs and in the vessel forms a single system.

Gas exchange

Content of gases in the alveoli. During the act of inhalation and exhalation, a person constantly ventilates the lungs, maintaining the gas composition in the alveoli. A person inhales atmospheric air with a high content of oxygen (20.9%) and a low content of carbon dioxide (0.03%). Exhaled air contains 16.3% oxygen and 4% carbon dioxide. When you inhale, out of 450 ml of inhaled atmospheric air, only about 300 ml enters the lungs, and approximately 150 ml remains in the airways and does not participate in gas exchange. When you exhale, which follows inhalation, this air is expelled unchanged, that is, it does not differ in composition from atmospheric air. That's why it's called air dead, or harmful, space. The air that reaches the lungs is mixed here with 3000 ml of air already in the alveoli. The gas mixture in the alveoli involved in gas exchange is called alveolar air. The incoming portion of air is small compared to the volume to which it is added, so complete renewal of all the air in the lungs is a slow and intermittent process. The exchange between atmospheric and alveolar air has little effect on the alveolar air, and its composition remains practically constant, as can be seen from Table. 29.

Table 29. Composition of inhaled, alveolar and exhaled air, in%

When comparing the composition of alveolar air with the composition of inhaled and exhaled air, it is clear that the body retains one fifth of the incoming oxygen for its needs, while the amount of CO 2 in the exhaled air is 100 times greater than the amount that enters the body during inhalation. Compared to inhaled air, it contains less oxygen, but more CO 2. Alveolar air comes into close contact with the blood, and the gas composition of arterial blood depends on its composition.

Children have a different composition of both exhaled and alveolar air: the younger the children, the lower their percentage of carbon dioxide and the higher the percentage of oxygen in exhaled and alveolar air, respectively, the lower the percentage of oxygen used (Table 30). Consequently, children have low efficiency of pulmonary ventilation. Therefore, for the same volume of oxygen consumed and carbon dioxide released, a child needs to ventilate his lungs more than adults.

Table 30. Composition of exhaled and alveolar air
(average data for: Shalkov, 1957; comp. By: Markosyan, 1969)

Since small children breathe frequently and shallowly, a large proportion of the tidal volume is the volume of “dead” space. As a result, the exhaled air consists more of atmospheric air, and has a lower percentage of carbon dioxide and a lower percentage of oxygen used from a given volume of breathing. As a result, the efficiency of ventilation in children is low. Despite the increased percentage of oxygen in the alveolar air compared to adults in children, it is not significant, since 14-15% of oxygen in the alveoli is sufficient to completely saturate the hemoglobin in the blood. More oxygen than is bound by hemoglobin cannot pass into arterial blood. The low level of carbon dioxide in the alveolar air in children indicates its lower content in the arterial blood compared to adults.

Exchange of gases in the lungs. Gas exchange in the lungs occurs as a result of the diffusion of oxygen from the alveolar air into the blood and carbon dioxide from the blood into the alveolar air. Diffusion occurs due to the difference in the partial pressure of these gases in the alveolar air and their saturation in the blood.

Partial pressure- this is the part of the total pressure that accounts for the share of a given gas in the gas mixture. The partial pressure of oxygen in the alveoli (100 mmHg) is significantly higher than the O2 tension in the venous blood entering the capillaries of the lungs (40 mmHg). The partial pressure parameters for CO 2 have the opposite value - 46 mm Hg. Art. at the beginning of the pulmonary capillaries and 40 mm Hg. Art. in the alveoli. The partial pressure and tension of oxygen and carbon dioxide in the lungs are given in table. 31.

Table 31. Partial pressure and tension of oxygen and carbon dioxide in the lungs, mmHg. Art.

These pressure gradients (differences) are the driving force for the diffusion of O 2 and CO 2, that is, gas exchange in the lungs.

The diffusion capacity of the lungs for oxygen is very high. This is due to the large number of alveoli (hundreds of millions), their large gas exchange surface (about 100 m2), as well as the small thickness (about 1 micron) of the alveolar membrane. The diffusion capacity of the lungs for oxygen in humans is about 25 ml/min per 1 mmHg. Art. For carbon dioxide, due to its high solubility in the pulmonary membrane, the diffusion capacity is 24 times higher.

Oxygen diffusion is ensured by a partial pressure difference of about 60 mmHg. Art., and carbon dioxide - only about 6 mm Hg. Art. The time for blood to flow through the capillaries of the small circle (about 0.8 s) is enough to completely equalize the partial pressure and tension of gases: oxygen dissolves in the blood, and carbon dioxide passes into the alveolar air. The transition of carbon dioxide into the alveolar air at a relatively small pressure difference is explained by the high diffusion capacity for this gas (Atl., Fig. 7, p. 168).

Thus, a constant exchange of oxygen and carbon dioxide takes place in the pulmonary capillaries. As a result of this exchange, the blood is saturated with oxygen and freed from carbon dioxide.