From Big Medical Encyclopedia

GAS EXCHANGE — set of processes of exchange of gases between a human body or an animal and the environment; consists in consumption by an organism of oxygen, release of carbon dioxide gas and insignificant amounts of light-end products and water vapor. Final utilization of nutrients and use of their energy for life activity of an organism, formation of heat and maintenance of constant body temperature at hematothermal animals and the person are impossible without constantly made.

G.'s studying at the person is important for assessment of dynamics of a disease, efficiency of its treatment and extent of compensation. Researches G. are widely conducted also at healthy people; on the basis of the obtained data develop diets for persons of different professions, norms of a cubic capacity and ventilation of tight rooms, etc.

Pilot studies of G. at animals are conducted for the purpose of studying of many of the general and special biol, problems (ecology, evolutionary development, a metamorphosis, hibernations, shock, etc.). Researches G. in pharmacology and endocrinology allow to find out impact of different substances on intensity of oxidizing processes; they found broad application in many special fields of medicine (anesthesiology, air, space, underwater medicine etc.). Due to the prevention of decompressive frustration great interest represents studying of exchange of nitrogen between an organism and the environment.

The basis of modern ideas of G. is made by the law of perdurability of matter and energy opened by M. V. Lomonosov in 1748, and the systematic research G. began with A. Lavoisier's works (1777). In Russia classical researches of a number of questions of G. are begun by I. M. Sechenov (the doctrine about blood gases, about structure of an alveolar air) and his pupils. A. A. Likhachev's works (1893, etc.) who established coincidence of the results received at a direct calorimetry and a research G. (an indirect calorimetry) after confirmed in the USA with Benedict (F. Benedict, 1894) and in Germany M. Rubner were of great importance (1894). The received results served the final statement of the law of energy conservation in the annex to a human body. I. M. Sechenov and M. N. Sh and rubbed nicknames (1901) were pioneers in development of methods of studying of G. and its measurements at muscular activity.

The doctrine about G. was by K. Foyt (1875), M. Pettenkofer (1863) and E. Pflyuger's works the basis for physiology and hygiene of food. A big contribution to development of the theory and practicians G. brought the Soviet scientific B. E. V otchat, E. M. Krep, etc.

Depending on the l which developed in fi about - and ontogenesis anatomo-fiziol. and ekol. features of an organism of G. it is carried out in the different ways: at the elementary and nek-ry multicellular — by diffusion of gases directly through a body surface; at high-organized animals and the person through skin also went. - kish. the path occurs only insignificant part G., and its main part is provided with systems of breath and blood circulation.

Mechanisms G. at the person come down to external, or pulmonary, to breath (see), providing exchange of gases between a fresh and alveolar air and between an alveolar air and blood; to binding of gases blood and to their transfer to fabrics with the subsequent diffusion between blood and an interintercellular lymph; to tissue respiration (see. biological oxidation ). External respiration provides active ventilation of alveoluses and maintenance of almost constant partial pressure of carbon dioxide gas (pCO 2 ) and oxygen (pO 2 ) in an alveolar air. A difference between pO 2 in an alveolar air (100 mm of mercury.) and tension of oxygen in the blood inflowing to capillaries of a small circle of blood circulation (40 mm of mercury.), provides bystry transition of oxygen from alveoluses in blood; owing to high diffusion capacity of easy pO 2 in the blood flowing from pulmonary capillaries approaches alveolar pO 2 .

G.'s intensity changes depending on conditions of the environment. At the person in quite wide interval of ambient temperature (from about 15 to 25 °) G.'s intensity almost does not change (a so-called zone of indifference). At lower temperature of G. increases; at intensive cooling when thermal control is insufficient and body temperature goes down, G. long enough remains high, but then begins to decrease according to decrease in body temperature. At temperature increase of the environment G.'s intensity decreases. However at further temperature increase when there comes the hyperthermia, G.'s intensity increases.

In the course of evolution at the person and animals ability to maintain relative constancy of speed of oxygen consumption (vO was developed 2 ) with the broad range of changes of contents it in inhaled air. Inhalation of pure oxygen at the healthy person does not increase vO 2 . However at very low pO 2 , when systems of breath and blood circulation are not able to provide receipts of enough oxygen to fabrics any more, its consumption sharply falls.

At the person and animals investigate in the conditions of absolute rest, at a temperature of comfort (18 — 23 °), on an empty stomach. The amount of the oxygen consumed at the same time and the released energy characterizes level standard metabolism (see), to-ry depends on the surface area of a body, age and a floor.

Fluctuations in G.'s intensity are connected by hl. obr. with changes in activity of an organism in general, its separate bodies and fabrics, and also with nek-ry qualitative features of tissue respiration. G.'s increase (so-called effect of specific dynamic action) occurs after meal, protein-rich. This phenomenon can be explained with increase in vO 2 the bodies which are actively participating in digestion. Muscle performance is followed by strengthening G. Tak, the trained athletes have vO 2 can increase from 200 to 5000 ml in 1 min. (so-called maximum oxygen consumption — MPK, or O 2 - ceiling). During the long work of average intensity there is a bystry increase of vO in the beginning 2 and vCO 2 (speed of release of carbon dioxide gas), reaching by 3 — 6 min. a fixed level (so-called work with a stable state). At high-intensity loadings delivery of oxygen to fabrics lags behind an oxygen request of an organism owing to what the big oxygen debt which is expressed in that is formed as after completion of work high vO value remains 2 , only gradually returned to initial level. Also change of vCO is characteristic 2 , leading to increase it is (higher than 1,0) respiratory coefficients (i.e. the attitudes of volume of the emitted carbon dioxide gas towards amount of the consumed oxygen: CO 2 / O 2 ) in operating time and to decrease it (lower than 0,7) after work (see. Respiratory coefficient ). Excess vCO 2 in operating time it is connected with replacement of carbonic acid from buffer connections owing to the strengthened formation and accumulation of acid metabolic products. Upon termination of work in an organism there is oxygen consumption, bigger in comparison with release of carbonic acid. It causes decrease in a respiratory coefficient. During the moderate work the respiratory coefficient is close to 1,0 that is connected with preferential use of carbohydrates. During very long work on a measure of exhaustion in an organism of reserves of carbohydrates the respiratory coefficient gradually decreases, indicating increase in a share of use of fats in a metabolism. Thus, vO 2 , vCO 2 and the released energy depend on many factors: sizes of standard metabolism, heating environments, specific and dynamic influence of food and first of all from muscle performance. Therefore daily oxygen consumption is ranging from 300 l (at the bed patient) to 1000 l and above (at persons, the engaged physical. work and sport); power consumption at the same time makes 1500 — 5000 kcal and more. Respectively there are shifts of a respiratory coefficient connected with change of a metabolism (see the Metabolism and energy), acid-base equilibrium (see) and lung ventilation (see).

Totally reflects intensity of the oxidation-reduction processes happening in all bodies and fabrics and is under control of a nervous system. Numerous researches on animals and the person showed great importance of uslovnoreflektorny regulation of. The nervous system regulates G.'s intensity as directly, and through endocrine system. In particular, the nervous influences stimulating secretion of thyroxine provide increase in intensity of oxidizing processes, characteristic of this hormone.

Diffusion of blood gases (transition of gases from alveoluses in blood, from blood in cells of fabrics and back) is carried out through membranes and cytoplasm of cells on a concentration gradient — from places with higher concentration in the field of more low concentration. Due to this process in alveoluses of lungs for fractions of a second there is an alignment of partial pressures of various gases in an alveolar air and blood.

the Scheme of diffusion of blood gases through an alveolar and capillary partition: 1 — a molecular layer of liquid; 2 — a layer of cells of an epithelium of alveoluses; 3 — intercellular liquid; 4 — a layer of cells of an endothelium of capillaries; 5 — a blood plasma; 6 — a cover of an erythrocyte. Figures specified pressure (in mm of mercury.), corresponding to the partial pressure of oxygen and carbon dioxide gas in alveoluses and in blood.

Diffusion of gases through an alveolar and capillary partition begins with diffusion through a thin coat of liquid on a surface of cells of an alveolar epithelium (fig). Diffusion rate in liquid is lower than diffusion rate in air since the diffusion coefficient is inversely proportional viscosity of the environment. Diffusion rate of various gases in liquid depends also on their solubility (absorption) in this liquid. On the surface of liquid tension of gas same, as well as in a gaseous fluid, but in the depth of liquid it is lower. The solubility of gas, the more concentration gradient between surface and deep layers of liquid is better and the diffusion rate is higher. Diffusion rate is determined by a formula v = by a / √ M, where v — diffusion rate, and — coefficient of absorption, M — a pier. weight of gas. The size of relative diffusion rate of two various gases is determined by the relation of speeds of their diffusion: vCO 2 / vO 2 , in particular for carbon dioxide gas and oxygen it makes 20,7. Thus, molecules of carbon dioxide gas diffuse in water, intercellular liquid, a blood plasma by nearly 21 times quicker, than molecules of oxygen.

Due to diffusion the continuous stream of gases through fabric partitions is supported. Its size is defined by the Fick's law:

J = DS dp/dt,

where J — a gas flow, D — a diffusion coefficient, S — the area of diffusion, dp/dt a gradient of partial

pressure of gas. As diffusion of gas in liquid depends on absorption of gas in this liquid, enter coefficient of absorption (a), an instead of a pressure gradient into a formula — a difference of pressure on both sides of a partition (P1 — P2). Calculation is carried out on the simplified formula:

J = (Da/760) of S(P1-P2).

At a difference of partial pressures, equal 35 mm of mercury., through an alveolar and capillary partition of lungs can diffuse St. 6 d oxygen in 1 min. Carbon dioxide gas owing to more high speed of diffusion diffuses approximately in the same quantity at a difference of partial pressures, a component of only 6 mm of mercury.

Respiratory function of blood

of an organism plays an Important role in G. the blood providing binding of oxygen of air in capillaries of lungs, delivery to its fabrics and removal from an organism of the carbonic acid formed in the course of a metabolism. Except these gases, in blood there are a nitrogen, argon, helium, etc. Amount of the gas dissolved in blood (in ml or about. %) calculate by a formula: a×p/760 where and — a solubility coefficient of gas, r — the partial pressure of gas. The solubility coefficient characterizes amount of the gas dissolved in

1 ml of liquid at this temperature and pressure equal to 760 mm of mercury. For whole blood at t ° 38 ° the solubility coefficient of oxygen is equal 0,022, carbon dioxide gas 0,511, nitrogen 0,011. The amount of the nitrogen dissolved in blood is small (apprx. 1,2 about. %). Though fiziol, value of nitrogen is not established, however in nek-ry cases, napr, at a caisson disease (see. Compressed-air disease ), it is necessary to consider changes of its concentration.

In normal conditions in blood not enough oxygen and carbon dioxide gas is dissolved to satisfy the need of an organism for oxygen and to provide process of removal of carbonic acid. At pO 2 in alveoluses of lungs, equal 100 mm of mercury., in the dissolved look contains in an arterial blood 0,30 about. %, and in the mixed venous blood during the falling of pO 2 to 37 mm of mercury. contains 0,11 about. % of oxygen. The amount of the dissolved carbonic acid with other things being equal is more: contains in an arterial blood 2,6 about. % of carbonic acid (partial voltage is 40 mm of mercury.), and in the mixed blue blood 2,9 about. % (partial voltage is 45 mm of mercury.). These sizes make an insignificant part of total quantity of oxygen (19 about. % in an arterial blood and 12,1 about. % in venous) and carbonic acids (52 about. % in an arterial blood and 58 about. % in venous), transported by blood.

Chemical binding of oxygen is provided contained in erythrocytes hemoglobin (see). Connecting to oxygen, hemoglobin turns into easily dissociating oxyhemoglobin. The amount of oxygen, a cut can be connected by blood after full saturation of hemoglobin of blood oxygen, is called the oxygen capacity of blood. The size of oxygen capacity of blood normal at the person fluctuates within 16,0 — 24,0 about. % at t ° 0 ° and pressure of 760 mm of mercury.; it is slightly higher at men and is lower at women. The clinic defines the saturation rate of an arterial blood oxygen representing percentage of the oxygen content in blood (a) to its oxygen capacity (And): a/A×100. At an arterial anoxemia (stay in mountains, hypostasis of a lung, pneumonia) saturation rate of an arterial blood oxygen decreases (see. Hypoxia ). The venous anoxemia is noted at a circulatory unefficiency when at the normal oxygen content and carbonic acids in an arterial blood saturation rate is lowered by oxygen of a venous blood and it contains a large amount of carbonic acid. The anemic anoxemia is characterized by the low oxygen capacity of blood (to 5 about. %) at normal saturation rate of an arterial blood oxygen and the lowered saturation value of a venous blood. In these cases owing to low sizes of oxygen capacity arteriovenous distinctions will be insignificant. At researches of origins of various forms of anemias studying of so-called transport properties of hemoglobin is of interest. Full ability to connect oxygen at all four gem of a molecule of hemoglobin is identical, but this ability changes not in proportion to change of partial pressure, i.e. it is various at different ratios of hemoglobin and oxyhemoglobin. After oxygenation to the first of gem affinity of hemoglobin to oxygen increases and the subsequent oxygenation accelerates. For plotting of binding of oxygen or curves of dissociation of oxyhemoglobin of a blood sample in special saturexes saturate with gas mixtures with the increasing partial pressures of oxygen and determine its quantity in blood and a gaseous fluid of the saturex or saturation rate of blood by oxygen and pO 2 in the saturex. Saturation rate of blood oxygen (in %) or the oxygen content (in about. %) postpone on ordinate axis, and on abscissa axis — the partial pressure of oxygen (there are devices which are writing down these curves automatically). At low pO 2 blood contains insignificant amount of oxyhemoglobin. Sharp raising of a curve is noted in the range of pressure of 20 — 45 mm of mercury.; further speed of response is slowed down, and at pO 2 , making 96 — 100 mm of mercury., the limit of saturation is reached.

The dissociation rate of oxyhemoglobin on oxygen and hemoglobin depends not only on the partial pressure of oxygen, but also on other factors. At increase in tension of carbonic acid in blood affinity of hemoglobin to oxygen decreases and dissociation of oxyhemoglobin is facilitated. Also change of pH of blood in the acid party has similar effect — the curve of dissociation of oxyhemoglobin moves to the right and down. Influence of pH in the field of low partial pressures of oxygen is especially accurately expressed. Temperature increase also shifts a curve of dissociation of oxyhemoglobin to the right. At decrease in temperature affinity of hemoglobin to oxygen increases, and return of oxygen oxyhemoglobin at average and pO high values 2 decreases.

Transfer of carbonic acid blood is closely connected with transport of oxygen hemoglobin and erythrocytes. In the dissolved form only the insignificant amount of carbonic acid is transferred, its most part chemically contacts in the form of bicarbonates of plasma and erythrocytes, and also proteins of plasma and hemoglobin. Carbon dioxide gas in capillaries of fabrics diffuses in a blood plasma, then in erythrocytes. Under the influence of enzyme of a karboangidraza carbon dioxide gas turns in coal to - that: CO 2 + H 2 <>O-H 2 CO 3 <-> H + + HCO 3 - . Coal to - that in the form of an ion of bicarbonate partially diffuses back in plasma, being replaced according to the law of an ionic Donnan equilibrium (see. Membrane equilibrium ) in erythrocytes ions of chlorine. The ions of HCO which remained in erythrocytes 3 - 1 and the ions of chlorine which entered erythrocytes connect to potassium ions and hemoglobin. The blood enriched in erythrocytes of KHCO 3 and sodium bicarbonate in plasma, comes to lungs where there are same processes, however in the opposite direction: ions of HCO 3 - 1 in erythrocytes break up, and the formed carbon dioxide gas quickly diffuses in plasma and from there in alveoluses. To release of CO 2 transformations of hemoglobin into oxyhemoglobin promote. The last, having more expressed acid properties, it is capable to translate bicarbonates in coal to - that, edges under the influence of a karboangidraza it is split with formation of CO 2 .

Preservation of a difference of ion concentration of potassium and sodium in and out of erythrocytes is provided with the energy received during the splitting of ATP by the corresponding ATP-ase. In transport of CO 2 hemoglobin can participate and directly — by education in capillaries of fabrics of carbohaemoglobin (HbCO 2 ). In lungs (pulmonary capillaries) owing to decrease in pCO 2 to 40 mm of mercury. carbohaemoglobin dissociates on hemoglobin and free CO 2  ; the last leaves with expired air.

It is considered to be that about 80% of all quantity coal to - you are transferred from fabrics to lungs in the form of bicarbonates, 10 — 15% — in the form of carbamic connections, 6 — 7% — in the form of the free dissolved carbonic acid. As hemoglobin has buffer properties (see. Buffer systems ), transport of carbonic acid occurs practically without change of pH of blood.

Disturbances in oxidizing processes in fabrics and hemodynamic frustration can cause deviations in buffer effect of hemoglobin and a blood plasma and to lead to acidosis (pH lower than 6,5) or to an alkalosis (increase in pH to 8,0). At not gas acidosis (see) the content of carbonic acid in an arterial blood it is lowered because ability of blood to connect carbonic acid is reduced and the curve of binding of carbonic acid is shifted to the right and down (at diseases of kidneys, lungs). At alkalosis (see) ability of blood to connect carbonic acid increases — the curve of binding is shifted to the left and up (at a hyperventilation, rise uphill, tetanies).

Gas exchange at advanced and senile age

Idiosyncrasy of aging is the decrease in intensity of tissue respiration leading to reduction of standard metabolism and oxygen consumption that is connected with reduction of number of active cellular elements owing to fibrous and sclerous changes, dehydration of fabrics, reduction of amount of substrates of oxidation, decrease of the activity of respiratory enzymes, etc. Partial pressure of oxygen in an alveolar air at elderly and old people remains at the same level, as at young age. At the same time oxygen saturation of an arterial blood decreases that leads to increase in an alveolyarnoarterialny gradient of oxygen. Loss by pulmonary fabric of elasticity, emergence of atelectatic sites in lungs cause difficulty of lung ventilation. In turn age and atherosclerotic changes of vessels of a small circle of blood circulation lead to the fact that disturbance of uniformity of lung ventilation is followed diskoordinatsiy ventilation and a blood-groove. During the aging diffusion capacity of lungs goes down that is caused by reduction of a surface of diffusion because of decrease in quantity of alveoluses and capillaries, functionally connected with each other. The tendency to increase in content of carbonic acid in an arterial blood is observed that is caused by anatomic and functional shunting in lungs. The arteriovenous difference on oxygen as a result of delay of a blood-groove and development of a circulator hypoxia increases.

At elderly and old people at physical. to loading imperfection of the systems participating in providing and regulation of especially clearly comes to light. Compensatory shifts develop in G. slowly, oxygen «cost» of work, oxygen «debt» increases, the recovery period is extended.

Pathology of gas exchange

G.'s Disturbances at a number of diseases and patol, states are an essential symptom or the main pathogenetic substrate of a disease and have independent a wedge. value. Can be the reasons of such disturbances of G.: 1) change of structure or partial pressure of gases in inhaled air; 2) pathology of system of external respiration and its regulation; 3) disturbance of transport and distribution function of systems of blood and blood circulation; 4) disturbance of oxidation-reduction processes in fabrics (oppression of cellular respiration).

G.'s increase due to the increased power consumption and oxygen consumption is observed at thyrotoxicosis (see) that is used for its diagnosis, at hron, infectious intoxications (e.g., tuberculosis), at increase in a metabolism in connection with diseases of c. N of page, adrenal glands, gonads (see. Metabolism and energy ), at overdose adrenomimetichesky means (see), and also at neurosises. The syndrome of a hyperventilation, i.e. excess removal from an organism of CO can be a consequence of disturbances of regulation of G. at neurosises 2 due to increase in ventilation of alveoluses at frequent and deep breath (see. Lung ventilation ); decrease in concentration of CO 2 in blood — hypocapny (see) — leads to reduction of a brain blood-groove and can be the cause faint (see).

G.'s decrease accompanies reduction of exchange of energy in the course of an artificial hypothermia (see. hypothermia artificial ), at a myxedema (see. Hypothyroidism ), nutritional dystrophy (see) it is also observed also at nek-ry types of shock (see).

Patol, the states caused by change of structure and pressure of inhaled air are observed at breath in the conditions of a tenuous atmosphere. More rare the wrong use of artificial respiratory mixes, breath in loop systems without sufficient stabilization of amount of the exchanging gas, etc. is the reason of pathology.

The leading place in G.'s pathology belongs to states, at to-rykh the hypoxia — the deficit of oxygen in fabrics most often connected with reduction of the oxygen content in blood i.e. an anoxemia develops (see. Hypoxia ). In the conditions of a tenuous atmosphere, napr, at rise on height more than 3000 m, where pO 2 in air it is considerably reduced, primary arterial anoxemia and a hypocapny is observed (see. Hypobaropathy , Mountain disease ). It is caused by primary decrease in pO 2 in an alveolar air in this connection saturation of blood oxygen in pulmonary capillaries decreases, its partial pressure and contents in an arterial blood falls. Decrease in pO 2 stimulates work of a respiratory center, leading to increase in minute volume of breath and removal of carbon dioxide gas. A hypocapny and gas developing under its influence alkalosis (see) promote increase in anchoring strength of hemoglobin with oxygen that in the conditions of a hypoxia complicates intake of oxygen from blood in fabric.

G.'s disturbances at pathology of external respiration can be caused by decrease in permeability for gases of alveolocapillary membranes, insufficient exchange of air in lungs at hypoventilation and uneven ventilation of alveoluses, and also disturbance of the ventilating and perfused relations. All listed types of disturbances are characterized by an anoxemia, but exchange of carbon dioxide gas at them changes not equally that is used in clinic for differential diagnosis.

The anoxemia in combination with a hypocapny is observed at disturbances of G. caused by defeat of membranes of air cells therefore solubility of oxygen in substance of an alveolar membrane and diffusion of oxygen from alveoluses in blood (the alveolar and capillary block) is at a loss. At the same time the stimulation of breath caused by an anoxemia leads to a hyperventilation of alveoluses, the edge is practically not increased by transition of oxygen to blood, but promotes excess removal of carbon dioxide gas, diffusion rate to-rogo in relation to oxygen is more than 20 times higher. Degree of an anoxemia in these cases is very considerable and is clinically expressed diffusion cyanosis (see), sharply accruing even at small physical. to loading — in proportion to increase in concentration in blood recovered hemoglobin (see). Such disturbance of G. is characteristic of diffusion pulmonary fibroses and granulomatoses of various etiology, napr, at a berylliosis (see. Beryllium ), sarcoidosis (see), Hammen's syndrome — Rich (see. Hammena-Rich syndrome ), it is also observed also at nek-ry pneumoconiosis (see), sometimes at cancer limfangiit e of lungs (see. Lungs , tumors).

Combination of an anoxemia to a delay of release of carbon dioxide gas and increase in pCO 2 in a blood plasma — hypercapnia (see) it is in most cases caused by hypoventilation of air cells. At this pO 2 in an alveolar air falls, pCO 2 also the gradient of partial pressure necessary for diffusion of gases through an alveolocapillary membrane increases, it is created due to decrease in pO 2 and increases in pCO 2 blood plasma.

The leading place among the reasons of alveolar hypoventilation is taken by disturbances of bronchial passability and change of functional pulmonary volumes, first of all the volume of a minimal air. They create the main a wedge, types respiratory insufficiency (see) at such widespread diseases, as bronchial asthma (see), bronchiolitis (see), bronchitis (see), pneumosclerosis (see), emphysema of lungs (see). Also central disorders of regulation of breath along with disturbances of a lipometabolism can be the cause of alveolar hypoventilation (see. Pikkviksky syndrome ), disturbance of activity of a respiratory center at organic lesions of c. N of page, poisonings barbiturates (see), drugs opium (see), and also defeat of motor nerves, skeletal muscles, diaphragms, pleura and thorax.

The special type of disturbance of G. arises at uneven damage of bronchial tubes and lungs patol, process, at Krom in lungs sites hypo - and hyperventilations coexist. At a hyperventilation of alveoluses when the amount of oxygen in them is not enough for elimination of the anoxemia connected with hypoventilation of other sites, release of carbon dioxide gas from an organism can be provided due to high speed of its diffusion in zones of a hyperventilation. In some cases it complicates distinguishing of this type of disturbances with the alveolocapillary block. Unlike the last, at patients with the anoxemia caused by irregularity of alveolar ventilation physical. loading does not increase degree of cyanosis, and in some cases cyanosis even decreases because of improvement of ventilation in zones where it was reduced (due to forcing of breath at loading, elimination of a local bronchospasm, etc.).

At hypoventilation of alveoluses and diffusion disturbances oxygen therapy (see) significantly or completely eliminates deficit of oxygen in blood. However at decrease in reaction of a respiratory center to carbonic acid (at the expressed hypercapnia, organic lesions of c. the N of page, cerebral atherosclerosis at persons of advanced and senile age etc.) can lead use of oxygen to an apnoea, regulation to-rogo in such cases is carried out through the carotid chemoceptors sensitive to an anoxemia. One of indicators of possible approach of an apnoea (see. Breath ) disturbance of a respiratory rhythm is, e.g. Cheyna-Stokes breath (see).

At the majority of bronchopulmonary diseases of disturbance of G. have difficult genesis since disorders of ventilation are usually combined with disturbance of diffusion of gases from lungs in blood and disturbance of a pulmonary blood-groove.

(E.g., at a thromboembolism of pulmonary arteries) disorders of pulmonary blood circulation can be the leading reason of disturbances of G., but more often they play a role of an accessory pathogenetic factor at disturbances of lung ventilation. Crucial importance at the same time has disturbance of uniformity of ventilation of alveoluses and their perfusion by blood. The relation of the minute volume of alveolar ventilation (V) averaging at rest 4 — 5 l to the minute volume of perfusion of lungs (P), equal about 5 l/min is normal, is in limits 0,8 — 1.

Ratio distortion between ventilation and perfusion can happen in separate alveoluses, segments, segments and even the whole lung owing to emergence as the hypoventilated sites to the kept perfusion (at asthma, peri-and intra bronchial defeats with partial obstruction of bronchial tubes, an atelectasis, etc.), and the hypoperfused zones, ventilation in to-rykh is kept or is even strengthened (at an embolism of branches of a pulmonary artery, involvement of branches of a pulmonary artery in inflammatory process). At the first type of changes the relation< of V/P 0,8, and at the second V/P> 1. The disproportion between ventilation and a blood-groove in lungs leads to a hypoxia. In separate options dominance of ventilation over a blood-groove can cause a syndrome of a hyperventilation with a hypocapny, at Krom dissociation of oxyhemoglobin is at a loss (shift of curve dissociation up and to the left). At a hypoxia with a hypercapnia dissociation of oxyhemoglobin is facilitated, but oxygenation of blood in lungs is at a loss.

G.'s pathology in connection with disturbance of transport of gases between lungs and cells of an organism is observed at reduction of gas capacity of blood owing to a shortcoming or qualitative changes of hemoglobin, and also at decrease in rate of volume flow of a blood-groove in fabrics.

At anemias the oxygen capacity of blood decreases in proportion to decrease in concentration of hemoglobin. Reduction of intake of oxygen in fabric from unit volume of blood can partially be compensated by acceleration of a blood-groove. Also transport of carbonic acid from fabrics to lungs since at reduction of content in blood of erythrocytes there is a deficit of the bicarbonates which are contained in them is broken. Capacity of blood concerning carbon dioxide gas is as a result limited and its exit from fabrics is at a loss. Decrease in concentration of hemoglobin at anemias limits transport of carbonic acid in the form of carboxyhaemoglobin.

Disturbance of transport of oxygen arises also at an inactivation of a part of molecules of hemoglobin due to oxidation of iron in structure their gem, i.e. due to transformation of hemoglobin into a methemoglobin, to-ry loses ability to attach oxygen and worsens dissociation of oxyhemoglobin (see. Methemoglobinemia ).

The inactivation of hemoglobin occurs also owing to formation of carboxyhaemoglobin (HbCO) in the presence in inhaled air of impurity of carbon monoxide since communication between hemoglobin and carbon monoxide rather stronger, than between hemoglobin and oxygen. Besides, existence in blood of carboxyhaemoglobin worsens dissociation of oxyhemoglobin. Therefore the inactivation of 50% of Hb due to its transformation into HbCO is followed by much heavier disturbance of G., than, e.g., loss of 50% of Hb at bleeding.

G.'s disturbance owing to reduction of rate of volume flow of a blood-groove in capillaries takes place at disturbance of the central mechanisms of regulation of a hemodynamics, an acute heart failure, hron, cardiovascular insufficiency, etc.

Local development of developments of stagnation in separate bodies and fabrics develops at regional disturbances of a tone of vessels, a local staz, ischemia and inflammatory processes.

In the conditions of stagnation of blood transition of oxygen from blood of fabric capillaries relatively increases (the arteriovenous difference on oxygen increases). Diffusion of gas happens at the same time against the background of gradual decrease in its partial pressure below characteristic of fabric capillaries that, in turn, can break the course of oxidizing processes in fabrics.

Increase of concentration of the recovered hemoglobin in capillary blood of body parts, remote from heart, where the blood stream is slowed most down, is clinically shown Crocq's disease (see).

At G.'s pathology only due to disorders of pulmonary blood circulation or disturbance of transport of gases usual oxygen therapy significantly does not improve oxygenation) fabrics. At separate types of such disturbances the oxygenobarotherapy is effective (see. Hyperbaric oxygenation ).

Primary disturbance of G. at the level of cells is observed by hl. obr. at influence of the poisons blocking respiratory enzymes (see). As a result of a cell lose ability to utilize oxygen (the arteriovenous difference on oxygen at the same time falls since a venous blood is rich with oxygen) and the sharp fabric hypoxia develops. Can promote disturbance of cellular respiration vitamin deficiency (see), napr, a vitamin deficiency of B2 (see. Riboflavinum ), PP (see. Niacin ), being coenzymes (or their predecessors) oxidation-reduction fermental systems of a cell.

Disturbance of receipt, transport and transition to fabrics of oxygen is followed by insufficiency of intracellular oxidation and causes disturbance of the structural organization of subcellular and cellular elements, up to a necrosis.

For diagnosis of types and extent of disturbances of G. use complex methods of its studying and investigate functions of external respiration. For determination of amount of oxygen and carbonic acid in blood samples use manometrical devices of Van-Slayka (see. Van-Slayka methods ), Barkrofta (see. Mikrorespirometra ), Skolandera-Rafton's syringe and his modifications — Mishurov's device, gas chromatographs (see. Chromatography , devices).

Measurement of partial pressure and concentration of oxygen in small volumes of blood and directly in an intact organism make by means of oxygen electrodes (membrane electrodes of Clark, electrodes catheters, all-glass electrodes of Glaykhmana-Lyubers, ultramicroelectrodes) and gas analyzers, the design to-rykh is based on the polyarografichesky principle of measurement of oxygen, and also by means of gas analyzers with ion-selective electrodes (see). Membrane electrodes and ultramicroelectrodes differ in the minimum time of response, and their indications do not depend on a blood-groove. Definition of saturation rate of blood oxygen is made by spektrofotometrichesk (see. Oksigemografiya .)

At a research G. in the course of breath measure rate of volume flow of oxygen consumption and release of carbon dioxide gas by means of volume (the closed type) and gas-analytical (open type) devices. Disturbances of diffusion permeability of alveolocapillary membranes objectively come to light with the help mass spectrometry (see) and special diffuziometr on a basis gasometry (see). Disturbances of bronchial passability and change of functional pulmonary volumes are studied by means of spirometry, the spirography (see), pneumotachometry, pnevmotakhografiya (see) with use of functional tests (see. Votchala-Tiffno test , Vital capacity of lungs ). Degree of irregularity of alveolar ventilation is determined by lengthening of time of cultivation of nitrogen, helium or other indicator gases in a total amount of lungs by means of spirocounts (see. Spirography , devices), equipped with special gas analyzers (see).

About irregularity of distribution of the ventilating and perfused relations in lungs judge also indirectly — by the relation of so-called functional dead space to respiratory volume. At assessment of extent of disturbances of G. consider also changes acid-base equilibrium (see).

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L. R. Iseev; L. A. Isaakyan (biochemical), O. V. Korkushko (mister.), V. P. Zhmurkin, H. N. Lapteva (patol.), V. P. Shmelyov (diffusion of gases).