Partial pressure of oxygen over substances. The effect of low partial pressure of oxygen in the air on the body and adaptation processes. Helium and other gases

Hypoxia is most clearly detected during stay in a rarefied space, when the partial pressure of oxygen drops.

In an experiment, oxygen starvation can occur at relatively normal atmospheric pressure, but with a low oxygen content in the surrounding atmosphere, for example, when an animal is in a confined space with a low oxygen content. The phenomena of oxygen starvation can be observed when climbing mountains, rising in an airplane to a high altitude - mountain and altitude sickness(Fig. 116).

The first signs of acute mountain sickness can often be observed already at an altitude of 2500 - 3000 m. For most people, they appear when climbing to 4000 m and above. The partial pressure of oxygen in the air, equal (at atmospheric pressure 760 mm Hg) to 159 mm, drops at this altitude (430 mm atmospheric pressure) to 89 mm. At the same time, arterial blood oxygen saturation begins to decrease. Symptoms of hypoxia usually appear when arterial oxygen saturation is around 85%, and death can occur when arterial oxygen saturation falls below 50%.

Climbing a mountain is accompanied by characteristic phenomena also due to temperature conditions, wind and muscle activity performed during the ascent. The more the metabolism increases due to muscle tension or a decrease in air temperature, the sooner signs of illness appear.

Disorders that arise during ascent to altitude develop more strongly the faster the ascent occurs. Training is of great importance in this regard.

Oxygen starvation when ascending in an airplane to a high altitude has some peculiarities. Climbing the mountain is slow and requires intense muscle work. Airplanes can reach altitude within a very short time. A pilot's stay at an altitude of 5000 m in the absence of sufficient training is accompanied by sensations of headache, dizziness, heaviness in the chest, palpitations, expansion of gases in the intestines, as a result of which the diaphragm is pushed upward, and breathing becomes even more difficult. The use of oxygen devices eliminates many of these phenomena (Fig. 117).

The effect on the body of low oxygen content in the air is expressed in disorders of the nervous system, breathing and circulation.

Some excitement is followed by fatigue, apathy, drowsiness, heaviness in the head, mental disorders in the form of irritability followed by depression, some loss of orientation, motor function disorders, and disorders of higher nervous activity. At medium altitudes, a weakening of internal inhibition develops in the cerebral cortex, and at higher altitudes, diffuse inhibition develops. Disorders of autonomic functions also develop in the form of shortness of breath, increased heart activity, changes in blood circulation and digestive disorders.

With acute oxygen starvation, the breath. It becomes superficial and frequent, which is the result of stimulation of the respiratory center. Sometimes a peculiar, intermittent, so-called periodic breathing (Cheyne-Stokes type) occurs. In this case, pulmonary ventilation noticeably suffers. With the gradual onset of oxygen starvation, breathing becomes frequent and deep, air circulation in the alveoli improves noticeably, but the carbon dioxide content and its tension in the alveolar air drop, i.e., hypocapnia develops, complicating the course of hypoxia. Impaired breathing may cause loss of consciousness.

Acceleration and intensification of the activity of the heart arise due to an increase in the function of its accelerating and amplifying nerves, as well as a decrease in the function of the vagus nerves. Therefore, increased heart rate during oxygen starvation is one of the indicators of the reaction of the nervous system that regulates blood circulation.

At high altitudes, a number of other circulatory disorders also occur. Blood pressure initially increases, but then begins to decrease in accordance with the state of the vasomotor centers. With a sharp decrease in the oxygen content in the inhaled air (up to 7 - 6%), the activity of the heart noticeably weakens, blood pressure drops, and venous pressure rises, cyanosis and arrhythmia develop.

Sometimes it is also observed bleeding from the mucous membranes of the nose, mouth, conjunctiva, respiratory tract, and gastrointestinal tract. Great importance in the occurrence of such bleeding is attached to the expansion of superficial blood vessels and disruption of their permeability. These changes occur partly due to the action of toxic metabolic products on the capillaries.

Dysfunction of the nervous system from being in a rarefied space also manifests itself gastrointestinal disorders usually in the form of lack of appetite, inhibition of the digestive glands, diarrhea and vomiting.

During high altitude hypoxia, the metabolism. Oxygen consumption initially increases, and then, with severe oxygen starvation, it decreases, the specific dynamic effect of protein decreases, and the nitrogen balance becomes negative. Residual nitrogen in the blood increases, ketone bodies accumulate, especially acetone, which is excreted in the urine.

A decrease in the oxygen content in the air to a certain limit has little effect on the formation of oxyhemoglobin. However, later, when the oxygen content in the air decreases to 12%, the oxygen saturation of the blood becomes about 75%, and when the oxygen content in the air is 6 - 7%, it is 50 - 35% of normal. The oxygen tension in capillary blood is especially reduced, which significantly affects its diffusion into the tissue.

Increased pulmonary ventilation and an increase in the tidal volume of the lungs during hypoxia cause depletion of alveolar air and blood in carbon dioxide (hypocapnia) and the occurrence of relative alkalosis, as a result of which the excitability of the respiratory center can be temporarily inhibited and the activity of the heart is weakened. Therefore, inhalation of carbon dioxide at altitudes, causing an increase in the excitability of the respiratory center, helps to increase the oxygen content in the blood and thereby improves the condition of the body.

However, the continuing decrease in the partial pressure of oxygen during ascent to altitude contributes to the further development of hypoxemia and hypoxia. The phenomena of insufficiency of oxidative processes are increasing. Alkalosis is again replaced by acidosis, which is again somewhat weakened due to an increase in the respiratory rate, a decrease in oxidative processes and the partial pressure of carbon dioxide.

Noticeably changed when rising to altitude and heat exchange. Heat transfer at high altitude increases mainly due to the evaporation of water by the surface of the body and through the lungs. Heat production gradually lags behind heat loss, as a result of which body temperature, which initially increases slightly, then decreases.

The onset of signs of oxygen starvation largely depends on the characteristics of the body, the state of its nervous system, lungs, heart and blood vessels, which determine the body’s ability to tolerate a rarefied atmosphere.

The nature of the action of rarefied air also depends on the rate of development of oxygen starvation. In acute oxygen starvation, dysfunction of the nervous system comes to the fore, while in chronic oxygen starvation, due to the gradual development of compensatory processes, pathological phenomena from the nervous system are not detected for a long time.

A healthy person generally copes satisfactorily with lowering barometric pressure and partial pressure of oxygen to a certain limit, and the better the slower the ascent and the easier the body adapts. The limit for a person can be considered a decrease in atmospheric pressure to one third of normal, i.e., up to 250 mm Hg. Art., which corresponds to an altitude of 8000 - 8500 m and an oxygen content in the air of 4 - 5%.

It has been established that during stay at heights there occurs device body, or its acclimatization, providing compensation for breathing disorders. Residents of mountainous areas and trained climbers may not develop mountain sickness when climbing to an altitude of 4000 - 5000 m. Highly trained pilots can fly without an oxygen apparatus at an altitude of 6000 - 7000 m and even higher.

Even people far from mountaineering and diving know that breathing in certain conditions becomes difficult for a person. This phenomenon is associated with a change in the partial pressure of oxygen in the environment, and, as a consequence, in the blood of the person himself.

Altitude sickness

When a resident of a flat area comes to the mountains on vacation, it seems that the air there is especially clean and it is simply impossible to breathe it.

In fact, such reflex urges to breathe frequently and deeply are caused by hypoxia. In order for a person to equalize the partial pressure of oxygen in the alveolar air, he needs to ventilate his own lungs as best as possible at first. Of course, after staying in the mountains for several days or weeks, the body begins to get used to the new conditions by adjusting the functioning of the internal organs. This is how the situation is saved by the kidneys, which begin to secrete bicarbonate to enhance ventilation of the lungs and increase the number of red blood cells in the blood that can carry more oxygen.

Thus, residents of mountainous areas always have higher hemoglobin levels than those living in lowlands.

Acute form

Depending on the characteristics of the body, the norm of partial pressure of oxygen may differ for each person at a certain age, state of health, or simply depending on the ability to acclimatize. That is why not everyone is destined to conquer the peaks, because even with a great desire, a person is not able to completely subjugate his body and force it to work differently.

Very often, untrained climbers may develop various symptoms of hypoxia during high-speed ascent. At an altitude of less than 4.5 km, they are manifested by headaches, nausea, fatigue and sudden changes in mood, since the lack of oxygen in the blood greatly affects the functioning of the nervous system. If such symptoms are ignored, cerebral or pulmonary edema subsequently develops, each of which can lead to death.

Thus, it is strictly prohibited to ignore changes in the partial pressure of oxygen in the environment, because it always affects the performance of the entire human body.

Diving underwater

When a diver dives into conditions where the atmospheric pressure is lower than usual, his body also faces a kind of acclimatization. The partial pressure of oxygen at sea level is an average value and also changes with immersion, but nitrogen is of particular danger to humans in this case. On the surface of the earth in flat areas, it does not affect people, but after every 10 meters of immersion it gradually contracts and provokes various degrees of anesthesia in the diver’s body. The first signs of such a violation may appear after 37 meters under water, especially if a person spends a long time at depth.

When atmospheric pressure exceeds 8 atmospheres, and this figure is reached after 70 meters under water, divers begin to feel nitrogen narcosis. This phenomenon is manifested by a feeling of alcoholic intoxication, which disrupts the submariner’s coordination and attentiveness.

To avoid consequences

In cases where the partial pressure of oxygen and other gases in the blood is abnormal and the diver begins to feel signs of intoxication, it is very important to ascend as slowly as possible. This is due to the fact that with a sharp change in pressure, the diffusion of nitrogen provokes the appearance of bubbles with this substance in the blood. In simple terms, the blood seems to boil, and the person begins to feel severe pain in the joints. In the future, he may develop disturbances in vision, hearing and the functioning of the nervous system, which is called decompression sickness. To avoid this phenomenon, the diver should be lifted very slowly or the nitrogen in his breathing mixture should be replaced with helium. This gas is less soluble, has lower mass and density, so costs are reduced.

If such a situation occurs, then the person must be immediately placed back into the high-pressure environment and wait for gradual decompression, which can last up to several days.

In order for the gas composition of the blood to change, it is not necessary to conquer peaks or descend to the seabed. Various pathologies of the cardiovascular, urinary and respiratory systems can also affect changes in gas pressure in the main fluid of the human body.

To accurately determine the diagnosis, appropriate tests are taken from patients. Most often, doctors are interested in the partial pressure of oxygen and carbon dioxide, since they ensure proper breathing of all human organs.

Pressure in this case is a process of dissolution of gases, which shows how efficiently oxygen works in the body and whether its indicators correspond to standards.

The slightest deviations indicate that the patient has deviations that affect the ability to use the gases entering the body to the maximum.

Pressure standards

The rate of partial pressure of oxygen in the blood is a relative concept, since it can vary depending on many factors. In order to correctly determine your diagnosis and receive treatment, you must contact a specialist with test results who can take into account all the individual characteristics of the patient. Of course, there are also reference standards that are considered ideal for a healthy adult. So, in the patient’s blood without abnormalities there is:

• carbon dioxide in the amount of 44.5-52.5%;
• its pressure is 35-45 mm Hg. Art.;
• liquid oxygen saturation 95-100%;
• O 2 in an amount of 10.5-14.5%;
• partial pressure of oxygen in the blood is 80-110 mm Hg. Art.

In order for the results to correspond to reality during the analysis, it is necessary to take into account a number of factors that can affect their correctness.

Causes of deviation from the norm, depending on the patient

The partial pressure of oxygen in arterial blood can change very quickly depending on various circumstances, therefore, in order for the test result to be as accurate as possible, the following features should be taken into account:

• the pressure rate always decreases with increasing age of the patient;
• during hypothermia, oxygen pressure and carbon dioxide pressure decrease, and the pH level increases;
• when overheating the situation is reversed;
• the actual partial pressure of gases will only be visible when blood is taken from a patient with a body temperature within the normal range (36.6-37 degrees).

Reasons for deviations from the norm depending on health workers

In addition to taking into account such characteristics of the patient’s body, specialists must also comply with certain standards to ensure correct results. First of all, the partial pressure of oxygen is affected by the presence of air bubbles in the syringe. In general, any contact of the analysis with ambient air can change the results. It is also important, after collecting blood, to carefully mix it in a container so that red blood cells do not settle at the bottom of the tube, which can also affect the test results showing hemoglobin levels.

It is very important to adhere to the time standards allotted for the analysis. According to the rules, all actions must be carried out within a quarter of an hour after collection, and if this time is not enough, then the container with blood must be placed in ice water. This is the only way to stop the process of oxygen consumption by blood cells.

Specialists should also calibrate the analyzer in a timely manner and take tests only with syringes containing dry heparin, which is electrolytically balanced and does not affect the acidity of the sample.

Test results

As is already clear, the partial pressure of oxygen in the air can have a noticeable effect on the human body, but the level of gas pressure in the blood can be disturbed for other reasons. To determine them correctly, decoding should be trusted only to an experienced specialist who can take into account all the characteristics of each patient.

In any case, hypoxia will be indicated by a decrease in oxygen pressure. Changes in blood pH levels, as well as carbon dioxide pressure or changes in bicarbonate levels, may indicate acidosis or alkalosis.

Acidosis is a process of acidification of the blood and is characterized by an increase in carbon dioxide pressure, a decrease in blood pH and bicarbonate levels. In the latter case, the diagnosis will be announced as metabolic acidosis.

Alkalosis is an increase in blood alkalinity. This will be indicated by an increased pressure of carbon dioxide, an increase in the number of bicarbonates, and, consequently, a change in the pH level of the blood.

Conclusion

The performance of the body is influenced not only by high-quality nutrition and physical activity. Each person gets used to certain climatic living conditions in which he feels most comfortable. Their change provokes not only poor health, but also a complete change in certain blood parameters. To determine a diagnosis based on them, you should carefully select a specialist and ensure compliance with all standards for taking tests.

The gases that make up the breathing air affect the human body depending on the value of their partial (partial) pressure:

where Pg is the partial gas pressure” kgf/cm², mm Hg. st or kPa;

Pa - absolute air pressure, kgf/cm², mmHg. Art. or kPa.

Example 1.2. Atmospheric air contains 78% nitrogen by volume. 21% oxygen and 0.03% carbon dioxide. Determine the partial pressure of these gases on the surface and at a depth of 40 m. Take atmospheric air pressure equal to 1 kgf/cm².

Solution: 1) absolute pressure of compressed air at a depth of 40 m according to (1.2)

2) partial pressure of nitrogen according to (1.3) on the surface
at a depth of 40 m
3) partial pressure of oxygen on the surface
at a depth of 40 m
4) partial pressure of carbon dioxide on the surface
at a depth of 40 m
Consequently, the partial pressure of gases included in the breathing air at a depth of 40 m increased 5 times.

Example 1.3. Based on the data in Example 1.2, determine what percentage of gases should be at a depth of 40 m so that their partial pressure corresponds to normal conditions on the surface.

Solution: 1) nitrogen content in the air at a depth of 40 m, corresponding to the partial pressure on the surface, according to (1.3)

2) oxygen content under the same conditions

3) carbon dioxide content under the same conditions

Consequently, the physiological effect on the body of the gases that make up the breathing air at a depth of 40 m will be the same as on the surface, provided that their percentage content decreases by 5 times.

Nitrogen air begins to have a toxic effect almost at a partial pressure of 5.5 kgf/cm² (550 kPa). Since atmospheric air contains approximately 78% nitrogen, the indicated partial pressure of nitrogen according to (1.3) corresponds to an absolute air pressure of 7 kgf/cm² (immersion depth - 60 m). At this depth, the swimmer becomes agitated, ability to work and attentiveness decrease, orientation becomes difficult, and sometimes dizziness occurs. At great depths (80...100 m), visual and auditory hallucinations often develop. Almost at depths of 80...90 m, a swimmer becomes unable to work, and descent to these depths while breathing air is only possible for a short time.

Oxygen in high concentrations, even under atmospheric pressure, it has a toxic effect on the body. Thus, at a partial pressure of oxygen of 1 kgf/cm² (breathing pure oxygen in atmospheric conditions), inflammatory phenomena develop in the lungs after 72 hours of breathing. When the partial pressure of oxygen is more than 3 kgf/cm², after 15...30 minutes, convulsions occur and the person loses consciousness. Factors predisposing to the occurrence of oxygen poisoning: the content of carbon dioxide in the inhaled air, strenuous physical work, hypothermia or overheating.

With a low partial pressure of oxygen in the inhaled air (below 0.16 kgf/cm²), the blood flowing through the lungs is not completely saturated with oxygen, which leads to a decrease in performance, and in cases of acute oxygen starvation - to loss of consciousness.

Carbon dioxide. Maintaining normal carbon dioxide levels in the body is regulated by the central nervous system, which is very sensitive to its concentration. An increased content of carbon dioxide in the body leads to poisoning, a decreased content leads to a decrease in the breathing rate and stops it (apnea). Under normal conditions, the partial pressure of carbon dioxide in atmospheric air is 0.0003 kgf/cm² (~30 Pa). If the partial pressure of carbon dioxide in the inhaled air increases by more than 0.03 kgf/cm² (-3 kPa), the body will no longer cope with the removal of this gas through increased breathing and blood circulation and severe disorders may occur.

It should be borne in mind that according to (1.3), a partial pressure of 0.03 kgf/cm² on the surface corresponds to a carbon dioxide concentration of 3%, and at a depth of 40 m (absolute pressure 5 kgf/cm²) - 0.6%. An increased content of carbon dioxide in the inhaled air enhances the toxic effect of nitrogen, which can already appear at a depth of 45 m. That is why it is necessary to strictly monitor the content of carbon dioxide in the inhaled air.

Saturation of the body with gases. Being under high pressure entails saturation of the body with gases that dissolve in tissues and organs. At atmospheric pressure on the surface in a human body weighing 70 kg, about 1 liter of nitrogen is dissolved. With increasing pressure, the ability of body tissues to dissolve gases increases in proportion to the absolute air pressure. So, at a depth of 10 m (absolute air pressure for breathing 2 kgf/cm²) 2 liters of nitrogen can already be dissolved in the body, at a depth of 20 m (3 kgf/cm²) - 3 liters of nitrogen, etc.

The degree of saturation of the body with gases depends on their partial pressure, the time spent under pressure, as well as on the speed of blood flow and pulmonary ventilation.

During physical work, the frequency and depth of breathing, as well as the speed of blood flow, increase, so the saturation of the body with gases is directly dependent on the intensity of the submarine swimmer’s physical activity. With the same physical activity, the speed of blood flow and pulmonary ventilation in a trained person increase to a lesser extent than in an untrained person, and the saturation of the body with gases will be different. Therefore, it is necessary to pay attention to increasing the level of physical fitness and the stable functional state of the cardiovascular and respiratory systems.

A decrease in pressure (decompression) causes desaturation of the body from indifferent gas (nitrogen). In this case, excess dissolved gas enters the bloodstream from the tissues and is carried by the blood stream into the lungs, from where it is removed into the environment by diffusion. If you ascend too quickly, gas dissolved in the tissues forms bubbles of various sizes. They can be carried throughout the body by blood flow and cause blockage of blood vessels, which leads to decompression sickness.

Gases formed in the intestines of a submariner while he is under pressure expand upon ascent, which can lead to pain in the abdomen (flatulence). Therefore, it is necessary to ascend from depth to the surface slowly, and in case of a long stay at depth - with stops in accordance with the decompression tables (Appendix 11.8).

(The last column shows the O 2 content, from which the corresponding partial pressure at sea level can be reproduced (100 mm Hg = 13.3 kPa)

Height, m	Air pressure, mm Hg. Art.	Partial pressure of O 2 in inspired air, mm Hg. Art.	Partial pressure of O 2 in alveolar air, mm Hg. Art.	Equivalent fraction O 2
				0,2095
				0,164
				0,145
				0,127
				0,112
				0,098
				0,085
				0,074
				0,055
				0,029
		0,4		0,014

Rice. 4. Zones of influence of oxygen deficiency during ascent to altitude

3. Zone of incomplete compensation (danger zone). It is implemented at altitudes from 4000 m to 7000 m. Unadapted people experience various disorders. When the safety limit (threshold of violations) is exceeded, physical performance drops significantly, the ability to make decisions weakens, blood pressure decreases, and consciousness gradually weakens; muscle twitching is possible. These changes are reversible.

4. Critical zone. Starts from 7000 m and above. P A O 2 gets lower critical threshold – those. its lowest value at which tissue respiration can still occur. According to various authors, the value of this indicator varies between 27 and 33 mm Hg. Art. (V.B. Malkin, 1979). Potentially lethal central nervous system disorders occur in the form of inhibition of the respiratory and vasomotor centers, the development of unconsciousness and convulsions. In the critical zone, the duration of oxygen deficiency is decisive for the preservation of life. A rapid increase in PO 2 in the inhaled air can prevent death.

Thus, the effect on the body of a reduced partial pressure of oxygen in the inhaled air under conditions of a drop in barometric pressure is not realized immediately, but upon reaching a certain reaction threshold corresponding to an altitude of about 2000 m. This situation is facilitated by the peculiarities of the interaction of oxygen with hemoglobin, which is graphically displayed by the oxyhemoglobin dissociation curve (Fig. 5).

Fig.5. Dissociation curves of oxyhemoglobin (Hb) and oxymyoglobin (Mb)

S-shaped the configuration of this curve due to binding of one hemoglobin molecule to four oxygen molecules is important in terms of oxygen transport in the blood. During the absorption of oxygen by the blood, PaO 2 approaches 90-95 mm Hg, at which the saturation of hemoglobin with oxygen is about 97%. Moreover, since the oxyhemoglobin dissociation curve in its right part is almost horizontal, when PaO 2 falls in the range from 90 to 60 mm Hg. Art. hemoglobin oxygen saturation does not decrease much: from 97 to 90%. Thus, thanks to this feature, a drop in PaO 2 in the specified range (90-60 mm Hg) will only slightly affect blood oxygen saturation, i.e. on the development of hypoxemia. The latter will increase after PaO 2 overcomes the lower limit of 60 mm Hg. Art., when the oxyhemoglobin dissociation curve moves from a horizontal position to a vertical one. At an altitude of 2000 m, PaO 2 is 76 mm Hg. Art. (10.1 kPa).

In addition, the drop in PaO 2 and the violation of hemoglobin oxygen saturation will be partially compensated by increased ventilation, increased blood flow speed, mobilization of deposited blood, and the use of the oxygen reserve of the blood.

A feature of hypobaric hypoxic hypoxia that develops during ascent in the mountains is not only hypoxemia, but also hypocapnia (a consequence of compensatory hyperventilation of the alveoli). The latter determines the formation gas alkalosis with appropriate shift of the oxyhemoglobin dissociation curve to the left . Those. there is an increase in the affinity of hemoglobin for oxygen, which reduces the supply of the latter to the tissues. In addition, respiratory alkalosis leads to ischemic hypoxia of the brain (spasm of cerebral vessels), as well as an increase in intravascular capacity (dilatation of somatic arterioles). The result of such dilatation is pathological deposition of blood in the periphery, accompanied by a violation of systemic (decrease in blood volume and cardiac output) and organ (impaired microcirculation) blood flow. Thus, exogenous mechanism of hypobaric hypoxic hypoxia, caused by a decrease in the partial pressure of oxygen in the inhaled air, will be supplemented endogenous (hemic and circulatory) mechanisms of hypoxia, which will determine the subsequent development of metabolic acidosis(Fig. 6).

A decrease in the partial pressure of oxygen in the inhaled air leads to an even lower level in the alveoli and outflowing blood. If plains dwellers climb mountains, hypoxia increases their ventilation by stimulating arterial chemoreceptors. The body responds with adaptive reactions, the purpose of which is to improve the supply of O2 to tissues. Changes in breathing during high-altitude hypoxia vary from person to person. The external respiration reactions that occur in all cases are determined by a number of factors: 1) the speed with which hypoxia develops; 2) degree of O2 consumption (rest or physical activity); 3) duration of hypoxic exposure.

The most important compensatory reaction to hypoxia is hyperventilation. The initial hypoxic stimulation of respiration, which occurs when rising to altitude, leads to the leaching of CO 2 from the blood and the development of respiratory alkalosis. This in turn causes an increase in the pH of the extracellular fluid of the brain. Central chemoreceptors respond to such a pH shift in the cerebrospinal fluid of the brain by a sharp decrease in their activity, which inhibits the neurons of the respiratory center so much that it becomes insensitive to stimuli emanating from peripheral chemoreceptors. Quite quickly, hyperpnea gives way to involuntary hypoventilation, despite persistent hypoxemia. Such a decrease in the function of the respiratory center increases the degree of hypoxic state of the body, which is extremely dangerous, primarily for the neurons of the cerebral cortex.

With acclimatization to high-altitude conditions, physiological mechanisms adapt to hypoxia. After staying for several days or weeks at altitude, as a rule, respiratory alkalosis is compensated by the release of HCO 3 by the kidneys, due to which part of the inhibitory effect on alveolar hyperventilation disappears and hyperventilation intensifies. Acclimatization also causes an increase in hemoglobin concentration due to increased hypoxic stimulation of erythropoietin by the kidneys. Thus, among Andean residents who constantly live at an altitude of 5000 m, the concentration of hemoglobin in the blood is 200 g/l. The main means of adaptation to hypoxia are: 1) a significant increase in pulmonary ventilation; 2) increase in the number of red blood cells; 3) increase in the diffusion capacity of the lungs; 4) increased vascularization of peripheral tissues; 5) increasing the ability of tissue cells to use oxygen, despite low pO 2.

Some people develop an acute pathological condition when rapidly ascending to high altitudes ( acute mountain sickness and high-altitude pulmonary edema). Since the central nervous system has the highest sensitivity to hypoxia of all organs, neurological disorders are the first to occur when climbing to high altitudes. When rising to altitude, symptoms such as headache, fatigue, and nausea may develop acutely. Pulmonary edema often occurs. Below 4500 m, such severe disturbances occur less frequently, although minor functional deviations occur. Depending on the individual characteristics of the body and its ability to acclimatize, a person is able to reach great heights.

Control questions

1. How do the parameters of barometric pressure and partial pressure of oxygen change with increasing altitude?

2. What adaptive reactions occur when rising to a height?

3. How does acclimatization to high mountain conditions occur?

4. How does acute mountain sickness manifest?

Breathing when diving to depth

When performing underwater work, a diver breathes under pressure 1 atm higher than atmospheric pressure. for every 10 m of dive. About 4/5 of the air is nitrogen. At sea level pressure, nitrogen has no significant effect on the body, but at high pressure it can cause varying degrees of narcosis. The first signs of mild anesthesia appear at a depth of about 37 m, if the diver remains at depth for an hour or more and breathes compressed air. With a long stay at a depth of more than 76 m (pressure 8.5 atm.), nitrogen narcosis usually develops, the manifestations of which are similar to alcohol intoxication. If a person inhales air of normal composition, then nitrogen dissolves in adipose tissue. Diffusion of nitrogen from tissue occurs slowly, so the diver's ascent to the surface must be very slow. Otherwise, intravascular formation of nitrogen bubbles is possible (the blood “boils”) with severe damage to the central nervous system, organs of vision, hearing, and severe pain in the joints. There is a so-called decompression sickness. To treat the victim, it is necessary to place him back in a high-pressure environment. Gradual decompression may last several hours or days.

The likelihood of decompression sickness can be significantly reduced by breathing special gas mixtures, such as an oxygen-helium mixture. This is due to the fact that the solubility of helium is less than that of nitrogen, and it diffuses faster from tissues, since its molecular weight is 7 times less than that of nitrogen. In addition, this mixture has a lower density, so the work spent on external respiration is reduced.

Control questions

5. How do barometric pressure and partial pressure of oxygen change with increasing altitude?

6. What adaptive reactions occur when rising to a height?

7. How does acclimatization to high mountain conditions occur?

8. How does acute mountain sickness manifest?

7.3 Test tasks and situational task

Choose one correct answer.

41. IF A PERSON DIVES WITHOUT SPECIAL EQUIPMENT WITH PRELIMINARY HYPERVENTILATION, THE CAUSE OF SUDDEN LOSS OF CONSCIOUSNESS MAY BE INCREASING

1) asphyxia

2) hypoxia

3) hyperoxia

4) hypercapnia

42. WHEN DIVING UNDER WATER WITH A MASK AND SNORKEL, YOU CANNOT INCREASE THE LENGTH OF THE STANDARD TUBE (30-35 cm) BECAUSE

1) the occurrence of a pressure gradient between air pressure in the alveoli and water pressure on the chest

2) the danger of hypercapnia

3) danger of hypoxia

4) increasing the volume of dead space

Situational task 8

Champion divers dive to depths of up to 100 m without scuba gear and return to the surface in 4-5 minutes. Why don't they get decompression sickness?

8. Standards of answers to test tasks and situational tasks

Sample answers to test tasks:

Standard answers to situational problems:

Solution to situational problem No. 1:

If we are talking about natural breathing, then the first one is right. The breathing mechanism is suction. But, if we mean artificial respiration, then the second one is right, since the mechanism here is a pressure one.

Solution to situational problem No. 2:

For effective gas exchange, a certain ratio between ventilation and blood flow in the vessels of the lungs is necessary. Consequently, these people had differences in blood flow values.

Solution to situational problem No. 3:

In the blood, oxygen exists in two states: physically dissolved and bound to hemoglobin. If hemoglobin does not work well, then only dissolved oxygen remains. But there is very little of it. This means it is necessary to increase its quantity. This is achieved through hyperbaric oxygen therapy (the patient is placed in a chamber with high oxygen pressure).

Solution to situational problem No. 4:

Malate is oxidized by the NAD-dependent enzyme malate dehydrogenase (mitochondrial fraction). Moreover, during the oxidation of one malate molecule, one NADH·H + molecule is formed, which enters the complete electron transfer chain with the formation of three ATP molecules from three ADP molecules. As you know, ADP is an activator of the respiratory chain, and ATP is an inhibitor. ADP in relation to malate is obviously in short supply. This leads to the fact that the activator (ADP) disappears from the system and the inhibitor (ATP) appears, which, in turn, leads to the stop of the respiratory chain and the absorption of oxygen. Hexokinase catalyzes the transfer of a phosphate group from ATP to glucose to form glucose-6-phosphate and ADP. Thus, when this enzyme operates in the system, the inhibitor (ATP) is consumed and the activator (ADP) appears, so the respiratory chain resumes its work.

Solution to situational problem No. 5:

The enzyme succinate dehydrogenase, which catalyzes the oxidation of succinate, belongs to FAD-dependent dehydrogenases. As you know, FADN 2 ensures the supply of hydrogen to the shortened electron transport chain, during which 2 ATP molecules are formed. Amobarbital blocks the respiratory chain at the level of the 1st coupling of respiration and phosphorylation and does not affect the oxidation of succinate.

Solution to situational problem No. 6:

If the umbilical cord is clamped very slowly, the carbon dioxide content in the blood will correspondingly increase very slowly and the neurons of the respiratory center will not be able to excite. The first breath will never happen.

Solution to situational problem No. 7:

Carbon dioxide plays a leading role in excitation of neurons of the respiratory center. In an agonal state, the excitability of the neurons of the respiratory center sharply decreases and therefore they cannot be excited by the action of normal amounts of carbon dioxide. After several respiratory cycles, a pause occurs, during which significant amounts of carbon dioxide accumulate. Now they can already excite the respiratory center. Several inhalations and exhalations occur, the amount of carbon dioxide decreases, a pause occurs again, etc. If the patient's condition cannot be improved, death is inevitable.

Solution to situational problem No. 8:

A diver at great depths breathes high-pressure air. Therefore, the solubility of gases in the blood increases significantly. Nitrogen is not consumed in the body. Therefore, when it rises quickly, its increased pressure quickly decreases, and it is rapidly released from the blood in the form of bubbles, which leads to embolism. The diver does not breathe at all during the dive. When raised quickly, nothing bad happens.

Annex 1

Table 1

Name of pulmonary ventilation indicators in Russian and English

Name of the indicator in Russian	Accepted abbreviation	Indicator name in English	Accepted abbreviation
Vital capacity of the lungs	vital capacity	Vital capacity	V.C.
Tidal volume	BEFORE	Tidal volume	TV
Inspiratory reserve volume	District Department of Internal Affairs	Inspiratory reserve volume	IRV
Expiratory reserve volume	ROvyd	Expiratory reserve volume	ERV
Maximum ventilation	MVL	Maximum voluntary ventilation	M.W.
Forced vital capacity	FVC	Forced vital capacity	FVC
Forced expiratory volume in the first second	FEV1	Forced expiratory volume 1 sec	FEV1
Tiffno index	IT, or FEV1/VC%		FEV1% = FEV1/VC%
Maximum flow rate at the moment of exhalation 25% FVC remaining in the lungs	MOS25	Maximum expiratory flow 25% FVC	MEF25
	Forced expiratory flow 75% FVC	FEF75
Maximum flow rate at the moment of exhalation of 50% FVC remaining in the lungs	MOS50	Maximum expiratory flow 50% FVC	MEF50
	Forced expiratory flow 50% FVC	FEF50
Maximum flow rate at the moment of exhalation 75% FVC remaining in the lungs	MOS75	Maximum expiratory flow 75% FVC	MEF75
	Forced expiratory flow 25% FVC	FEF25
Average expiratory volumetric flow rate in the range from 25% to 75% FVC	SOS25-75	Maximum expiratory flow 25-75% FVC	MEF25-75
	Forced expiratory flow 25-75% FVC	FEF25-75

Appendix 2

BASIC BREATHING PARAMETERS

Vital Capacity (VC = Vital Capacity) - vital capacity of the lungs(the volume of air that leaves the lungs when exhaling as deeply as possible after inhaling as deeply as possible)

IRV (IRV = inspiratory reserve volume) - inspiratory reserve volume(extra air) is the volume of air that can be inhaled during a maximum inhalation after a normal inhalation

ROvyd (ERV = Expiratory Reserve Volume) - expiratory reserve volume(reserve air) is the volume of air that can be exhaled during a maximum exhalation after a normal exhalation

EB (IC = inspiratory capacity) - inhalation capacity- actual sum of tidal volume and inspiratory reserve volume (EB = DO + ROvd)

FOEL (FRC = functional residual capacity) - functional residual capacity of the lungs. This is the volume of air in the lungs of a patient at rest, in a position where normal exhalation is completed and the glottis is open. FOEL is the sum of the expiratory reserve volume and residual air (FOEL = ROV + OB). This parameter can be measured using one of two methods: helium dilution or body plethysmography. Spirometry does not measure FUEL, so the value of this parameter must be entered manually.

OV (RV = residual volume) - residual air(another name is RVL, residual lung volume) is the volume of air that remains in the lungs after maximum exhalation. Residual volume cannot be determined using spirometry alone; this requires additional measurements of lung volume (using the helium dilution method or body plethysmography).

TLC (TLC = total lung capacity) - total lung capacity(the volume of air in the lungs after taking the deepest breath possible). VEL = vital capacity + ov