What is the volume of dead space. minute ventilation. Anatomical and functional dead space

More on Dead Space Ventilation:

1. Features of ventilation in newborns and young children Indications for ventilatory support and basic principles of mechanical ventilation in newborns and children

The term "physiological dead space" is used to refer to all the air in the respiratory tract that does not participate in gas exchange. It includes the anatomical dead space plus the volume of the alveoli where blood does not come into contact with air. Thus, these alveoli with incomplete capillary blood supply (for example, in pulmonary thrombosis) or distended and therefore containing excess air (for example, in emphysema) are included in the physiological dead space, provided that they remain ventilated with excessive perfusion. It should be noted that the bullae are often hypoventilated.

Anatomical dead space is determined by continuous analysis of the nitrogen concentration in the exhaled air with simultaneous measurement of the expiratory volume flow rate. Nitrogen is used because it does not participate in gas exchange. Using a nitrometer, data are recorded after a single breath of pure oxygen (Fig. 5). The first part of the record at the beginning of exhalation refers to the dead space proper gas, which is free of nitrogen, followed by a short phase of rapidly increasing nitrogen concentration, which refers to the mixed dead space and alveolar air, and finally the alveolar proper data, which reflects the degree of dilution alveolar nitrogen with oxygen. If there were no mixing of alveolar gas and dead space gas, then the increase in nitrogen concentration would occur abruptly, with a straight front, and the volume of anatomical dead space would be equal to the volume exhaled before the appearance of alveolar gas. This hypothetical situation of a straight front can be evaluated by the Fowler method, in which the ascending segment of the curve is divided into two equal parts and the anatomical dead space is obtained.

Rice. 5. Determination of dead space by the single breath method. Modified by Comroe et al.

Physiological dead space can be calculated using the Bohr equation, based on the fact that exhaled gas is the sum of the gases in the anatomical dead space and in the alveoli. Alveolar gas can come from alveoli with sufficient ventilation and perfusion, as well as from those in which the ventilation-perfusion ratio is disturbed:

where PaCO 2 is the partial pressure of carbon dioxide in arterial blood (it is assumed that it is equal to the "ideal" alveolar pressure of CO 2); PECO 2 - pressure of carbon dioxide in the mixed exhaled air; YT - tidal volume. This method requires a simple analysis of exhaled air in arterial blood. It expresses the ratio of dead space (Vd) to tidal volume (Vt), as if the lung were physiologically composed of two parts: one normal in terms of ventilation and perfusion, and the other with undetermined ventilation and no perfusion.

Inhaled air contains such a small amount of carbon dioxide that it can be neglected. Thus, all carbon dioxide enters the exhaled gas from the alveoli, where it enters from the capillaries of the pulmonary circulation. During exhalation, the alveolar gas "loaded" with carbon dioxide is diluted with dead space gas. This leads to a drop in the concentration of carbon dioxide in the exhaled gas compared to that in the alveolar (dead space is understood here as physiological, and not anatomical).

Rice. 3-2. Types of dead space. (A) L patom and h its braids. In both units, the blood flow corresponds to the distribution) of ventilation. The only areas where gas exchange does not occur are the conductive EPs (shaded). Hence, all dead space in this model is anatomical. The blood of the pulmonary veins is fully oxygenated. (B) Physiological. In one unit ventilation is associated with blood flow (right unit), in the other unit (left unit) there is no blood flow. In this model, the physiological dead space includes the anatomical and infusing region of the lung. The blood of the pulmonary veins is partially oxygenated.

Knowing a simple mass equilibrium equation, one can calculate the ratio of physiological dead space to tidal volume, Vl)/vt.

The total amount of carbon dioxide (CO 2 ) in the respiratory system at any given time is the product of the initial volume that contained CO 2 (alveolar volume) and the concentration of CO 2 in the alveoli.

The alveoli contain a mixture of gases, including O 2 , CO 2 , N 2 and water vapor. Each of them has kinetic energy, thereby creating pressure (partial pressure). The alveolar CO 2 concentration is calculated as the partial pressure of alveolar CO 2 divided by the sum of the partial pressures of gases and water vapor in the alveoli (Chapter 9). Since the sum of the partial pressures in the alveoli is equal to the barometric pressure, the alveolar content CO 2 can be calculated as:

raso Alveolar content of CO 2 = vax------- 2 - ,

where: va - alveolar volume,

PASO 2 - partial pressure of CO 2 in the alveoli, Pb - barometric pressure.

The total amount of CO 2 remains the same after the alveolar CO 2 mixes with the dead space gas. Therefore, the amount of CO 2 released with each exhalation can be calculated as:

Vrx^L-VAx*^,

where: РЁСО 2 is the average partial pressure of CO 2 in the exhaled gas. The equation can be written more simply as:

VT x PYOCO? = VA x PAC0 2 .

The equation shows that the amount of CO 2> released with each exhalation and defined as the product of the tidal volume and the partial pressure of CO 2 in the exhaled gas is equal to the amount of CO 2 in the alveoli. CO 2 is not lost or added to the gas entering the alveoli from the pulmonary circulation; just the partial pressure of CO 2 in the exhaled air (Pic() 2) is set at a new level as a result of the dilution of the physiological dead space by the gas. Replacing VT in the equation with (VD + va), we get:

(VD + va) x РЁСО 2 \u003d va x Rdso 2.

Transforming the equation by replacing Yd by (Ym - Y D) gives:

UR \u003d UTH RAS ° * - PYOS ° *. GZ-8]

The equation can be expressed more generally:

vd PASO 2 - PYoso 2

= -----^----------l

Equation known like the Bohr equation, shows that the ratio of dead space to tidal volume can be calculated as the quotient of the difference between alveolar and exhaled gases PC() 2 divided by alveolar PC() 2 . Since the alveolar PC() 2 practically coincides with the arterial Pco 2 (PaC() 2), Vo/Vm can be calculated by simultaneously measuring Pco 2 in arterial blood and exhaled gas samples.

As an example for calculation, consider the data of a healthy person whose minute ventilation (6 L/min) was achieved with a tidal volume of 0.6 L and a respiratory rate of 10 breaths/min. In the arterial blood sample, PaS() 2 was 40 mm Hg. Art., and in the sample of exhaled gas RESO - 28 mm Hg. Art. Introducing these quantities into the equation , we obtain:

U°L°_--?v = 0.30 VT 40

dead space

Hence Y D is (0.30 x 600 ml) or 180 ml, and Y A is (600 iv./i 180 ml) or 420 ml. In any adult healthy person, U 0 / U "G ranges from 0.30 to 0.35.

Influence of the fan pattern on vd/vt

In the previous example, the tidal volume and respiratory rate were accurately indicated, allowing VD and VA to be calculated after the VD/VT value was determined. Consider what happens when a healthy 70 kg person "kicks" three different breathing patterns to maintain the same top minute ventilation (Figure 3-3).

On fig. 3-FOR VE is 6 L/min, Ut is 600 ml, and f is 10 resp/min. A person weighing 70 kg has a dead space volume of approximately 150 ml. Kate was noted earlier, 1 ml of dead space is accounted for by one pound of body weight. Hence VI) equals 1500 ml (150x10), va -4500 ml (450x10), and VD/VT- 150/600 or 0.25.

The subject increased the respiratory rate to 20 breaths/min (Figure 3-3B). Nsln \ "M was maintained at the same level of 6 l / min, then Ut will be equal to 300 ml. P;> and V g> b 150 ml vd and UA reach 3000 ml / min. UD/UT will increase to 150/300 or 0.5. This d frequent shallow breathing pattern appears to be ineffective With toch

Rice. 3-3. Influence of the respiratory pattern on the volume of dead space, the non-mass of alnesppyarpoi ineptilation and Vn / V "r. The dead space is indicated by the shaded area!") In each case, the minute ventilation is 6 l / min; the respiratory system showed i> koip.e idg.ha. (A) Tidal volume is 600 ml, respiratory rate is 10 breaths/min. (B) The tidal volume is reduced and the respiratory rate is doubled. (C) The tidal volume is doubled and the frequency is<ч

11..,..,.,.,^, .,., ., m.g, 4 Mitii\rrii4u kpim and MvnilHI OGTLGKM CONSTANT, OT".

ki vision inference CO 2 because half of each breath ventilates the dead space.

Finally, VT increased to 1200 ml and the respiratory rate decreased to 5 breaths/min (Fig. 3-3B).

Relationship between alveolar ventilation and CO2 production rate

The rate of formation of CO 2 (Vco 2) in a healthy person weighing 70 kg at rest is about 200 ml per 1 min. The respiratory control system is "set" to maintain PaS() 2 at 40 mm Hg. Art. (ch. 16). At steady state, the rate at which CO 2 excreted from the body is equal to the rate of its formation. The relationship between PaC() 2 , VCO 2 and VA is given below:

VA = Kx-^-l

where: K is a constant equal to 0.863; VA is expressed in the BTPS system, and Vco 2 in the STPD system (Appendix 1, p. 306).

The equation shows that at a constant rate of carbon dioxide formation, PaCO- changes inversely with alveolar ventilation (Fig. 3-4). The dependence of RLS() 2 , and hence PaS() 2 (the identity of which is discussed in Chapters 9 and 13) on va can be estimated using Fig. 3-4. In fact, changes in Pco 2 (alveolar silt and arterial) are determined by the ratio between \/d and vk,t. e. value VD/VT (section "Calculation of the volume of physiological dead space"). The higher VD/VT, the greater Vi<; необходима для измене­ния Уд и РаСО;,.

Relationship between alveolar ventilation, alveolar Po 2 and alveolar Pco 2

Just as Plso 2 is determined by the balance between CO 2 production and alveolar ventilation, alveolar P () 2 (P / \ () 2) is a function of the rate of oxygen uptake through the alveolar-capillary membrane (ch. 9) and alveolar-

Rice. 3-4. Relationship between alveolar ventilation and alveolar Rsh,. Alveolar Pco is inversely related to alveolar ventilation. The degree of change in purulent ventilation to alveolar Pc: o, :; apmsite from the relationship between dead space ventilation and general ventilation. The ratio for a person of average build with a stable normal formation rate (. "O, - (about 200 m h / mip)

sing ventilation.

The sum of the partial pressures of O 2 , CO 2 , N: > and water vapor in the alveoli is equal to the barometric pressure. Since the partial pressures of nitrogen and water vapor are constant, the partial pressures of O 2 or CO^ can be calculated if one of them is known. The calculation is based on alveolar gas equation:

rao? = Ryu? - Rdso 2 (Fio 2 + ---),

where: Ryu 2 - Po 2 in the inhaled gas,

FlO 2 - fractional concentration of O 2 in the inhaled gas,

R is the respiratory gas exchange ratio.

R, respiratory gas exchange ratio, expresses the rate of release of CO ^ relative to the rate of absorption of O 2 (V () 2), i.e. e. R \u003d Vco 2 / V (\u003e 2. In a steady state of the body, the respiratory gas exchange ratio is equal to respiratory coefficient(RQ), which describes the ratio of carbon dioxide production to oxygen consumption at the cellular level. This ratio depends on what is mainly used in the body as energy sources - carbohydrates or fats. In the process of metabolism, 1 g of carbohydrates is released more CO2.

In accordance with the alveolar gas equation, RL() 2 can be calculated as the partial pressure of O 2 in the inhaled gas (PIO 2) minus a value that includes RLSO 2 and a factor that takes into account the change in the total gas volume if oxygen uptake differs from carbon dioxide emission: [ Fl() 2 + (1 -- Fl() 2)/RJ. In a healthy adult with an average body size at rest, V() 2 is about 250 ml/min; VCO 2 - approximately 200 ml/min. R is thus equal to 200/250 or 0.8. Note that the value of IFlO, + (1 - FlO 2)/RJ decreases to 1.2 when FlOz ^ 0.21, and to 1.0 when FlOa» 1.0 (if in each case R = 0.8).

As an example for calculating RLS() 2 , consider a healthy person who breathes room air and whose PaS() 2 (approximately equal to RLS() 2) is 40 mmHg. Art. We take the barometric pressure equal to 760 mm Hg. Art. and water vapor pressure - 47 mm Hg. Art. (the inhaled air is completely saturated with water at normal body temperature). Pyu 2 is calculated as the product of the total partial pressure of "dry" gases in the alveoli and the fractional concentration of oxygen: i.e. Pyu 2 = (760 - 47) x 0.21. Hence Plo 2 = [(760 - 47) x 0.21 J -40 = 149-48 = 101 mm. rt. Art.

Rice. 3-5. The ratio between alveolar ventilation and alveolar Po, Alveolar 1 ) () 2 increases with increasing alveolar ventilation until reaching a plateau

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
• Ultrasound procedure
• 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. one.

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, FMP 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 value of 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 respiratory 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: norm, 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.

Anatomical dead space is the volume of the conducting airways. Normally, it is about 150 ml, increasing with a deep breath, as the bronchi are stretched by the lung parenchyma surrounding them. The amount of dead space also depends on the size of the body and posture. There is an approximate rule according to which, in a seated person, it is approximately equal in milliliters to body weight in pounds (1 pound - 453.6 g).

A. After inhaling from a container with pure oxygen, the subject exhales, and the concentration of N 2 in the exhaled air first increases, and then remains almost constant (the curve practically reaches a plateau corresponding to pure alveolar air). B. Dependence of concentration on exhaled volume. The volume of dead space is determined by the point of intersection of the abscissa axis with a vertical dotted line drawn in such a way that the areas L and B are equal.

Anatomical dead space volume can be measured using the Fowler method. In this case, the subject breathes through a valve system and the nitrogen content is continuously measured using a high-speed analyzer that takes air from a tube starting at the mouth. When a person exhales after inhaling 100% O 2 , the N 2 content gradually increases as dead space air is replaced by alveolar air.

At the end of exhalation, an almost constant nitrogen concentration is recorded, which corresponds to pure alveolar air. This section of the curve is often called the alveolar "plateau", although even in healthy people it is not completely horizontal, and in patients with lung lesions it can go up steeply. With this method, the volume of exhaled air is also recorded.

To determine the volume of dead space build a graph linking the content of N 2 with exhaled volume. Then, a vertical line is drawn on this graph so that area A is equal to area B. The volume of dead space corresponds to the point of intersection of this line with the x-axis. In fact, this method gives the volume of the conducting airways up to the "midpoint" of the transition from dead space to alveolar air.

"Physiology of Respiration", J. West

This and the next two chapters discuss how inhaled air enters the alveoli, how gases pass through the alveolar-capillary barrier, and how they are removed from the lungs in the bloodstream. These three processes are provided respectively by ventilation, diffusion and blood flow. Typical values ​​of volumes and flow rates of air and blood are given. In practice, these values ​​vary significantly (according to J….

Before moving on to dynamic ventilation rates, it is useful to briefly review "static" lung volumes. Some of these can be measured with a spirometer. During exhalation, the bell of the spirometer rises and the pen of the recorder falls. The amplitude of oscillations recorded during quiet breathing corresponds to the tidal volume. If the subject takes the deepest possible breath, and then - as deep as possible ...

Functional residual capacity (FRC) can also be measured using a general plethysmograph. It is a large hermetic chamber, resembling a pay phone booth, with the subject inside. At the end of a normal exhalation, with the help of a plug, the mouthpiece through which the subject breathes is closed, and he is asked to make several respiratory movements. When you try to inhale, the gas mixture in his lungs expands, their volume increases, ...