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 reacts with adaptive reactions, the purpose of which is to improve the supply of O2 to tissues. Changes in breathing during high-altitude hypoxia in different people are different. 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 response 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 Given the body and its ability to acclimatize, a person is able to reach great heights.
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. Standard 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 molecule of malate, one molecule of NADH·H + is formed, which enters complete chain electron transfer to form 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 content will increase very slowly. carbon dioxide in the blood 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 | Name of indicator on English language | 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
1.8 Partial tension of oxygen in the blood
PaO2 is the partial tension of oxygen in arterial blood. This is the tension of physically distributed oxygen in arterial blood plasma under the influence of a partial pressure equal to 100 mm Hg (PaO2 = 100 mm Hg). Every 100 ml of plasma contains 0.3 ml of oxygen. The O2 content in the arterial blood of trained athletes under resting conditions does not differ from its content in non-athletes. During physical activity, an accelerated breakdown of oxyhemoglobin occurs in the arterial blood flowing to the muscles with the release of free O2, so PaO2 increases
PвO2 is the partial tension of oxygen in venous blood. This is the tension of physically dissolved oxygen in the plasma of venous blood flowing from the tissue (muscle). Characterizes the tissue's ability to utilize oxygen. At rest it is 40-50 mmHg. At maximum work, due to intensive utilization of O2 by working muscles, it decreases to 10-20 mmHg. Art.
The difference between PaO2 and PvO2 is the value of AVR-O2 - the arterial-venous difference in oxygen. Characterizes the tissue's ability to utilize oxygen. ABP-O2 is the difference between the oxygen content in arterial blood released into the systemic arteries from the left ventricle and in venous blood flowing to the right atrium.
With the development of aerobic endurance, pronounced sarcoplasmic hypertrophy of skeletal muscles occurs, which leads to a decrease in oxygen in the venous blood (PbO2), and a corresponding increase in ABP-O2. So, if at rest PbO2 in men and women is 30 mm Hg, then after endurance exercise in untrained men PbO2 = 13 mm Hg, in untrained women 14 mm Hg. Accordingly, in trained men and women - 10 and 11 mm Hg. In women, the content of hemoglobin, bcc and oxygen content in arterial blood is lower, therefore, with equal oxygen content in venous blood, the total systemic AVR-O2 in women is less. At rest, it is equal to 5.8 ml of O2 per 100 ml of blood, versus 6.5 in men. After completing the exercise, untrained women had ABP-O2 = 11.1 ml O2/100 ml of blood, versus 14 in untrained men. As a result of training, ABP-O2 increases in both women and men as a result of a decrease in the oxygen content in the venous blood (12.8 and 15.5, respectively).
According to Fick's formula (PO2(MPC) = SV*ABP-O2), the product of SV by AVR-O2 determines the maximum oxygen consumption and is an important indicator of aerobic endurance. Endurance athletes use their oxygen transport capabilities more efficiently because they use more oxygen contained in each milliliter of blood than untrained people.
1.9 The influence of health training on the hemodynamics of the body
As a result of health training, the functionality of the cardiovascular system increases. There is an economization of the work of the heart at rest and an increase in the reserve capabilities of the circulatory apparatus during muscle activity. One of the most important effects of physical training is a decrease in heart rate at rest (bradycardia) as a manifestation of economization of cardiac activity and lower myocardial oxygen demand. Increasing the duration of the diastole (relaxation) phase provides greater blood flow and a better supply of oxygen to the heart muscle. In people with bradycardia, cases of coronary heart disease (CHD) are detected much less frequently than in people with a rapid pulse. It is believed that an increase in heart rate at rest by 15 beats/min increases the risk of sudden death from a heart attack by 70%. The same pattern is observed with muscle activity.
When performing a standard load on a bicycle ergometer in trained men, the volume of coronary blood flow is almost 2 times less than in untrained men (140 versus 260 ml/min per 100 g of myocardial tissue), and the myocardial oxygen demand is correspondingly 2 times less (20 versus 40 ml /min per 100g tissue). Thus, with an increase in the level of training, the myocardial oxygen demand decreases both at rest and at submaximal loads, which indicates economization of cardiac activity. As training increases and myocardial oxygen demand decreases, the level of threshold load that the subject can perform without the threat of myocardial ischemia and an attack of angina increases.
The most pronounced increase in the reserve capabilities of the circulatory system during intense muscle activity: an increase in maximum heart rate, CO and VO2, AVR-O2, a decrease in total peripheral vascular resistance, which facilitates mechanical work heart and increases its performance. Adaptation of the peripheral blood circulation comes down to an increase in muscle blood flow under extreme loads (maximum 100 times), an arteriovenous difference in oxygen, the density of the capillary bed in working muscles, an increase in the concentration of myoglobin and an increase in the activity of oxidative enzymes.
An increase in fibrinolytic activity of the blood during health-improving training (maximum 6 times) and a decrease in the tone of the sympathetic nervous system also play a protective role in the prevention of cardiovascular diseases. As a result, the response to neurohormones decreases under conditions of emotional stress, i.e. The body's resistance to stress increases.
In addition to the pronounced increase in the body's reserve capabilities under the influence of health-improving training, its preventive effect is also extremely important. With increasing training (as the level of physical performance increases), there is a clear decrease in all the main risk factors: cholesterol in the blood, blood pressure and body weight. There are examples when, as UVC increased, the cholesterol content in the blood decreased from 280 to 210 mg, and triglycerides from 168 to 150 mg%. At any age, with the help of training, you can increase aerobic capacity and the level of endurance - indicators of the biological age of the body and its viability. For example, well-trained middle-aged runners have a maximum possible heart rate that is about 10 beats per minute higher than untrained runners. Physical exercises such as walking and running (3 hours per week) already after 10-12 weeks lead to an increase in VO2 max by 10-15%.
Thus, the health-improving effect of mass physical education is associated primarily with an increase in the aerobic capabilities of the body, the level of general endurance and physical performance. Increased performance is accompanied by a preventive effect against risk factors for cardiovascular diseases: a decrease in body weight and fat mass, cholesterol and triglycerides in the blood, a decrease in blood pressure and heart rate. In addition, regular physical training can significantly slow down the development of age-related changes in physiological functions, as well as degenerative changes in various organs and systems (including delay and reverse development of atherosclerosis). Performance physical exercise has a positive effect on all parts of the musculoskeletal system, preventing the development of degenerative changes associated with age and physical inactivity. Increases mineralization bone tissue and calcium content in the body, which prevents the development of osteoporosis. The flow of lymph to the articular cartilage and intervertebral discs increases, which is the best remedy prevention of arthrosis and osteochondrosis. All these data indicate the invaluable positive impact of health-improving physical education on the human body.
Conclusion
In this course work The main hemodynamic characteristics and their changes during physical activity were considered. Brief conclusions are summarized in Table 10.
Table10. Basic hemodynamic characteristics
| Definition | Characteristic. | Training effect | |
| Heart rate | Heart rate - heart rate contractions per minute (pulse rate). | Resting heart rate average. For men - 60 beats/min, for women - 75, for trained ones. husband. -55, for outstanding athletes - 50 beats/min. Minimum The recorded resting heart rate for athletes is 21 beats/min. Heart rate max avg. for men 200 beats/min, for trained ones - 195, for super athletes -190 beats/min (exercise max. aerobic power), 180 beats/m (max. anaerobic power), max heart rate for untrained women - 205 beats/min, for athletes - 195 beats/min. | A decrease in heart rate (bradycardia) is an effect of endurance training and leads to a decrease in myocardial oxygen demand. |
| CO | CO=SV/HR The amount of blood ejected by each ventricle of the heart during one contraction. | The CO2 of rest in untrained men is on average 70-80 ml, in trained men - 90 ml, in outstanding athletes - 100-120 ml. At maximum aerobic load, COmax in untrained young men is 120-130 ml, in trained ones - 150, in outstanding athletes - 190-210 ml. COmax for untrained women is 90 ml, for outstanding stayers it is 140-150 ml. | An increase in CO as a result of exercise is a sign of increased heart efficiency. |
| SV or MOK or Q | CO=CO*HR SV=PO2/AVR-O2 Amount of blood ejected by the heart in 1 minute IOC - Volume of blood passing through. through the bloodstream vessels per unit time Q=P/R- Blood flow | Resting SV for men = 4-5 l/min, for women 3-5 l/min. Average SV max for untrained men is 24 l/min, for super athletes (endurance training) and those with a large heart volume (1200-1300 ml) - more than 30 l/min - for skiers, SVmax = 38–42 l/min. In untrained women, SV-18l/min. For outstanding athletes, CBmax = 28-30. Basic equation of hemodynamics P-blood pressure, R-vascular resistance. | One of the main effects of endurance training is an increase in CBmax. The increase in CO is not due to heart rate, but due to CO |
| HELL | SBP - SystolicBP - maximum blood pressure on the aortic wall achieved at the moment of SV DBP-DiastolicBP the pressure of the blood with which it returns to the atrium in diastole. | Standards BP-100-129 mm Hg. for max. and 60-79 mm Hg. for the minimum for persons under 39 years of age The upper limit of normal systolic pressure from 21 to 60 years of age is 140 mm Hg, for diastolic pressure is 90 mm Hg. With little physical activity, BPmax increases to 130-140 mmHg, with moderate exercise to 140-170, with heavy exercise to 180-200. Administrator, usually with physical the load decreases. For hypertension and physical activity, SADmax = 250 mm Hg. An increase in blood pressure is associated with an increase in R and CO. | Exercising helps lower blood pressure, but blood pressure does not go beyond normal limits. Dynamic loads (endurance exercise) help lower blood pressure, statistical loads (strength exercise) help to raise blood pressure. |
| R | 3.14*R^4-Vascular or peripheral. resistant | Depends on L-length of the vessel, n-blood viscosity, R-radius of the vessel; 3.14 is the number Pi. | Redistribution of blood flow, increased capillarization, slowing down the speed of blood flow in highly trained athletes. |
| BCC | BCC - Circulating blood volume - the total amount of blood located in the blood vessels. | It makes up 5-8% of weight, at rest in women - 4.3 l, in men - 5.5 l. During exercise, the bcc first increases and then decreases by 0.2-0.3 l due to the outflow of part of the plasma from the capillaries into the intercellular space. In women at max. work BCC average = 4 l, for men - 5.2 l. With a load of maximum aerobic power in trained men, BCCavg = 6.42 l. | Increase in blood volume during endurance training. |
| PaO2, PвO2 | PaO2, PвO2 - Partial tension of oxygen in arterial or venous blood. Partial pressure. PaO2-PвO2 =АВР-О2 arterial-venous difference in oxygen | PaO2-100mmHg.PbO2pok-40-50mmHg.PbO2max.work=10-20mmHg. If PbO2 at rest in men and women is 30 mm Hg, then after endurance exercise in untrained men PbO2 = 13 mm Hg, women 14 mm Hg. Accordingly, in trained men and women - 10 and 11 mm Hg. AVR-O2 at rest = 5.8 mlO2/100 ml of blood, versus 6.5 in men. After exercise, in untrained women, AVR-O2 = 11.1 mlO2/100 ml of blood, versus 14 in men. As a result of training, ABP-O2 in women was 12.8, in men - 15.51 ml O2 / 100 ml of blood. | Sarcoplasmic hypertrophy of skeletal muscles leads to a decrease in the oxygen content in the venous blood PvO2 and an increase in ABP-O2. Consequently, the BMD increases. |
In column 3 it is given a brief description of studied quantities and their limiting values.
The degree of change in hemodynamic parameters during physical activity depends on the initial values at rest. Physical activity requires a significant increase in the functions of the cardiovascular, respiratory and circulatory systems. Providing working muscles with a sufficient amount of oxygen and removing carbon dioxide from tissues depends on this. The cardiovascular system has a number of mechanisms that allow it to deliver as much blood as possible to the periphery. First of all, these are hemodynamic factors: an increase in heart rate, CO, blood volume, acceleration of blood flow, changes in blood pressure. These indicators vary among representatives various types sports. (According to sports specialization, sprinters train speed, stayers train endurance, weightlifters train strength.)
The use of echocardiography in sports medicine has made it possible to establish differences in the ways of heart adaptation depending on the direction of the training process. In athletes training endurance, cardiac adaptation occurs primarily due to dilatation with slight hypertrophy, and in athletes training strength - due to true myocardial hypertrophy and slight dilatation. With intense physical work, cardiac activity increases. The heart should be trained gradually according to age.
A hemodynamic factor such as changes in blood pressure is very important. The direction of the training process affects blood pressure. Physical loads of a dynamic nature help to reduce it, while statistical loads help to increase it. Hypertension can be caused by physical and emotional stress. A low level of systolic pressure in the pulmonary artery is an indicator of the high state of the cardiovascular system of endurance athletes. It characterizes the potential readiness of the body, in particular hemodynamics, for large and prolonged physical exertion.
The physiological changes in the body caused by endurance training are the same in women as in men. Thus, in the oxygen transport system, maximum indicators (LVmax, SVmax, COmax), lactate concentration at maximum work increase, and HRmax decreases due to increased parasympathetic influences. All this indicates an increase in efficiency and economy, as well as an increase in the reserve capabilities of the oxygen transport system.
The state of the body, both at rest and during exercise, depends on many reasons: external conditions, specific sports (swimming, winter sports, etc.), hereditary factors, gender, age, etc.
The limit to the growth of training effects in each person is genetically predetermined. Even systematic intense physical training cannot increase the body's functional capabilities beyond the limit determined by the genotype. Resting heart rate, heart size, left ventricular wall thickness, myocardial capillarization, and coronary artery wall thickness are influenced by hereditary factors.
It must be borne in mind that physical exercise helps improve health, improve the biological mechanisms of protective and adaptive reactions, and increase nonspecific resistance to various harmful influences. environment, only under the obligatory condition that the degree of physical activity in these classes is optimal for this particular person. Only the optimal degree of physical activity, corresponding to the capabilities of the person performing it, ensures improved health, physical improvement, prevents the occurrence of a number of diseases and helps to increase life expectancy. Physical activity less than optimal does not give the desired effect, above optimal it becomes excessive, and excessive activity instead of healing effect can cause various diseases and even sudden death from cardiac overstrain. Sports achievements should increase due to improved health.
Special mention should be made of the impact of health physical culture on an aging body. Physical education is the main means of delaying age-related deterioration of physical qualities and a decrease in the adaptive abilities of the body in general and the cardiovascular system in particular. Changes in the circulatory system and a decrease in cardiac performance entail a pronounced decrease in the maximum aerobic capabilities of the body, a decrease in the level of physical performance and endurance. The rate of age-related decrease in MOC in the period from 20 to 65 years in untrained men averages 0.5 ml/min/kg, in women - 0.3 ml/min/kg per year. In the period from 20 to 70 years, maximum aerobic performance decreases by almost 2 times - from 45 to 25 ml/kg (or by 10% per decade). Adequate physical training and health-improving physical education classes can significantly stop age-related changes in various functions. Physical labor, physical education and outdoor sports are especially beneficial, while smoking and alcohol abuse are especially harmful to the cardiovascular system.
The above material traces the patterns of changes in the basic hemodynamic characteristics of the body. Simultaneously increasing the level of health and functional state of a person is impossible without the active, widespread and comprehensive use of physical education and sports.
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...) and relative (with significant dilatation of the left ventricle with expansion of the aortic opening) insufficiency of the aortic valve. Etiology 1) RL; 2) FROM; 3) syphilitic aortitis; 4) diffuse connective tissue diseases; 5) atherosclerosis of the aorta; 6) injuries; 7) congenital defect. Pathogenesis and changes in hemodynamics. The main pathological process leads to wrinkling (rheumatism,...
Literary data on the issue being studied; 2) assess morphofunctional indicators in participants of groups of various training orientations at the initial stage; 3) determine the influence of aerobic and anaerobic physical exercises on the morphofunctional capabilities of those involved; 4) carry out comparative analysis indicators studied among group participants in the dynamics of the training process. 2.2...
We did not find an electrocardiographic technique mainly for identifying physiological and pathological changes in the heart, while we did not find any work that would use ECG indicators to determine fitness and the effect of physical activity on changes in heart rate and blood pressure.”12 The analysis of the ECG showed , that at rest the studied values are for gymnasts 15-16 years old...
(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).
Under normal conditions, a person breathes ordinary air, which has a relatively constant composition (Table 1). There is always less oxygen and more carbon dioxide in the exhaled air. Alveolar air contains the least oxygen and the most carbon dioxide. The difference in the composition of alveolar and exhaled air is explained by the fact that the latter is a mixture of dead space air and alveolar air.
Alveolar air is the internal gas environment of the body. The gas composition of arterial blood depends on its composition. Regulatory mechanisms maintain the constancy of the composition of alveolar air. The composition of alveolar air during quiet breathing depends little on the phases of inhalation and exhalation. For example, the carbon dioxide content at the end of inhalation is only 0.2-0.3% less than at the end of exhalation, since with each inhalation only 1/7 of the alveolar air is renewed. In addition, it occurs continuously during inhalation and exhalation, which helps to equalize the composition of alveolar air. With deep breathing, the dependence of the composition of alveolar air on inhalation and exhalation increases.
Table 1. Air composition (in%)
Gas exchange in the lungs occurs as a result of the diffusion of oxygen from the alveolar air into the blood (about 500 liters per day) and carbon dioxide from the blood into the alveolar air (about 430 liters per day). Diffusion occurs due to the difference in the partial pressure of these gases in the alveolar air and their tension in the blood.
Gas partial pressure: concept and formula
Gas partial pressure in a gas mixture is proportional to the percentage of gas and the total pressure of the mixture:
For air: P atmospheric = 760 mm Hg. Art.; C oxygen = 20.95%.
It depends on the nature of the gas. The entire gas mixture atmospheric air taken as 100%, she has a pressure of 760 mm Hg. Art., and part of the gas (oxygen - 20.95%) is taken as X. From here partial pressure oxygen in the air mixture is 159 mm Hg. Art. When calculating the partial pressure of gases in the alveolar air, it is necessary to take into account that it is saturated with water vapor, the pressure of which is 47 mm Hg. Art. Consequently, the proportion of the gas mixture that is part of the alveolar air does not account for a pressure of 760 mm Hg. Art., and 760 - 47 = 713 mm Hg. Art. This pressure is taken as 100%. From here it is easy to calculate that the partial pressure of oxygen, which is contained in the alveolar air in the amount of 14.3%, will be equal to 102 mm Hg. Art.; Accordingly, the calculation of the partial pressure of carbon dioxide shows that it is equal to 40 mm Hg. Art.
The partial pressure of oxygen and carbon dioxide in the alveolar air is the force with which the molecules of these gases strive to penetrate the alveolar membrane into the blood.
Diffusion of gases through a barrier obeys Fick's law; Since the membrane thickness and diffusion area are the same, diffusion depends on the diffusion coefficient and pressure gradient:
Gas Q- volume of gas passing through the tissue per unit time; S - fabric area; DK - gas diffusion coefficient; (P 1, - P 2) - gas partial pressure gradient; T is the thickness of the tissue barrier.
Considering that in the alveolar blood flowing to the lungs, the partial oxygen tension is 40 mmHg. Art., and carbon dioxide - 46-48 mm Hg. Art., then the pressure gradient determining the diffusion of gases in the lungs will be: for oxygen 102 - 40 = 62 mm Hg. Art.; for carbon dioxide 40 - 46(48) = minus 6 - minus 8 mm Hg. Art. Since the diffusion coefficient of carbon dioxide is 25 times greater than that of oxygen, carbon dioxide moves more actively from the capillaries into the alveoli than oxygen in the opposite direction.
In the blood, gases are in a dissolved (free) and chemically bound state. Only dissolved gas molecules participate in diffusion. The amount of gas dissolving in a liquid depends on:
- on the composition of the liquid;
- volume and pressure of gas in liquid;
- liquid temperature;
- nature of the gas under study.
The higher the pressure and temperature of a given gas, the more gas dissolves in the liquid. At a pressure of 760 mm Hg. Art. and a temperature of 38 °C, 2.2% oxygen and 5.1% carbon dioxide dissolve in 1 ml of blood.
The dissolution of a gas in a liquid continues until a dynamic equilibrium occurs between the number of gas molecules dissolving and escaping into the gaseous medium. The force with which molecules of a dissolved gas tend to escape into a gaseous medium is called tension of gas in liquid. Thus, at equilibrium, the gas tension is equal to the partial pressure of the gas in the liquid.
If the partial pressure of a gas is higher than its voltage, then the gas will dissolve. If the partial pressure of a gas is lower than its voltage, then the gas will leave the solution into the gaseous environment.
The partial pressure and tension of oxygen and carbon dioxide in the lungs are given in table. 2.
Table 2. Partial pressure and tension of oxygen and carbon dioxide in the lungs (mm Hg)
Oxygen diffusion is ensured by the difference in partial pressures in the alveoli and blood, which is equal to 62 mm Hg. Art., and for carbon dioxide it is only about 6 mm Hg. Art. The time of blood flow through the capillaries of the small circle (on average 0.7 s) is sufficient for almost complete equalization of the partial pressure and tension of gases: oxygen dissolves in the blood, and carbon dioxide passes into the alveolar air. The transition of carbon dioxide into the alveolar air at a relatively small pressure difference is explained by the high diffusion capacity of the lungs for this gas.
I would like to summarize information about the principles of diving regarding breathing gases in keynotes format, i.e. when understanding a few principles eliminates the need to memorize many facts.
So, breathing underwater requires gas. The simplest option is air supply, which is a mixture of oxygen (∼21%), nitrogen (∼78%) and other gases (∼1%).
The main factor is environmental pressure. Of all the possible pressure units, we will use "absolute technical atmosphere" or ATA. The surface pressure is ∼1 ATA, every 10 meters of immersion in water adds ∼1 ATA to it.
For further analysis, it is important to understand what partial pressure is, i.e. pressure of an individual component of a gas mixture. The total pressure of a gas mixture is the sum of the partial pressures of its components. Partial pressure and the dissolution of gases in liquids are described by Dalton's laws and are directly related to diving, since most of a person consists of liquid. Although partial pressure is proportional to the molar ratio of gases in a mixture, for air the partial pressure can be calculated by volume or weight concentration, the error will be less than 10%.
When diving, pressure affects us comprehensively. The regulator maintains the air pressure in the breathing system approximately equal to the ambient pressure, less exactly by the amount required for “inhalation”. So, at a depth of 10 meters, the air inhaled from the cylinder has a pressure of about 2 ATA. Similar absolute pressure will be observed throughout our body. Thus, the partial pressure of oxygen at this depth will be ∼0.42 ATA, nitrogen ∼1.56 ATA
The impact of pressure on the body consists of the following key factors.
1. Mechanical impact on organs and systems
We will not consider it in detail, in short - the human body has a number of air-filled cavities and a sharp change in pressure in any direction causes stress on tissues, membranes and organs, up to mechanical damage - barotrauma.
2. Saturation of tissues with gases
When diving (increasing pressure), the partial pressure of gases in the respiratory tract is higher than in the tissues. Thus, gases saturate the blood, and through the bloodstream all tissues of the body are saturated. The rate of saturation varies for different tissues and is characterized by a “half-saturation period,” i.e. the time during which, at constant gas pressure, the difference in the partial pressures of gas and tissue is halved. The reverse process is called “desaturation” and occurs upon ascent (pressure decrease). In this case, the partial pressure of gases in the tissues is higher than the pressure in the gases in the lungs, the reverse process occurs - gas is released from the blood in the lungs, blood with a lower partial pressure circulates throughout the body, gases pass from the tissues into the blood and again in a circle. Gas always moves from higher to lower partial pressure.
It is fundamentally important that different gases have different saturation/desaturation rates due to their physical properties.
The higher the pressure, the greater the solubility of gases in liquids. If the amount of dissolved gas is greater than the solubility limit at a given pressure, gas evolution occurs, including concentration in the form of bubbles. We see this every time we open a bottle of sparkling water. Since the rate of gas removal (tissue desaturation) is limited physical laws and gas exchange through the blood, too rapid a drop in pressure (rapid ascent) can lead to the formation of gas bubbles directly in the tissues, vessels and cavities of the body, disrupting its functioning even to death. If the pressure drops slowly, then the body has time to remove the “excess” gas due to the difference in partial pressures.
To calculate these processes, mathematical models of body tissues are used, the most popular is the Albert Bühlmann model, which takes into account 16 types of tissues (compartments) with a half-saturation/half-desaturation time from 4 to 635 minutes.
The greatest danger is posed by an inert gas that has the highest absolute pressure, most often it is nitrogen, which forms the basis of air and does not participate in metabolism. For this reason, the main calculations in mass diving are carried out using nitrogen, because the effect of oxygen in terms of saturation is orders of magnitude less, while the concept of “nitrogen load” is used, i.e. residual amount of nitrogen dissolved in tissues.
Thus, tissue saturation depends on the composition of the gas mixture, pressure and duration of its exposure. For initial levels of diving, restrictions are practiced on the depth, duration of the dive and the minimum time between dives, which obviously do not allow tissue saturation to dangerous levels under any circumstances, i.e. no-decompression dives, and even then it is customary to perform "safety stops".
“Advanced” divers use dive computers that dynamically calculate saturation using models depending on gas and pressure, including calculating the “compression ceiling” - the depth above which ascent is potentially dangerous based on the current saturation. During complex dives, computers are duplicated, not to mention the fact that single dives are usually not practiced.
3. Biochemical effects of gases
Our body is maximally adapted to air at atmospheric pressure. As pressure increases, gases, even those not involved in metabolism, affect the body in a variety of ways, and the effect depends on the partial pressure of a particular gas. Each gas has its own safety limits.
Oxygen
As a key participant in our metabolism, oxygen is the only gas that has not only an upper, but also a lower safety limit.
Normal oxygen partial pressure is ∼0.21 ATA. Oxygen requirement strongly depends on the state of the body and physical activity, the theoretical minimum required level to maintain vital functions healthy body in a state of complete rest is estimated at ∼0.08 ATA, practical - at ∼0.14 ATA. A decrease in oxygen levels from “nominal” primarily affects the ability to perform physical activity and can cause hypoxia, or oxygen starvation.
At the same time, high oxygen partial pressure causes a wide range of negative consequences- oxygen poisoning or hyperoxia. A particular danger during immersion is its convulsive form, which is expressed in damage to the nervous system and convulsions, which entails the risk of drowning.
For practical diving purposes, it is generally accepted that the safety limit is ∼1.4 ATA, and the moderate risk limit is ∼1.6 ATA. At pressures above ∼2.4 ATA for a long time, the probability of oxygen poisoning tends to unity.
Thus, by simply dividing the maximum oxygen level of 1.4 ATA by the partial pressure of oxygen in the mixture, you can determine the maximum safe pressure of the environment and establish that it is absolutely safe to breathe pure oxygen (100%, 1 ATA) at depths of up to ∼4 meters (!! !), compressed air (21%, 0.21 ATA) - up to ∼57 meters, standard “nitrox-32” with an oxygen content of 32% (0.32 ATA) - up to ∼34 meters. Similarly, you can calculate the limits for moderate risk.
They say that it is to this phenomenon that “nitrox” owes its name, since initially this word meant breathing gases with reduced oxygen content for working at great depths, “nitrogen enriched”, and only then it began to be deciphered as “nitrogen-oxigen” and denote mixtures with elevated oxygen content.
It must be taken into account that increased partial pressure of oxygen in any case has an effect on nervous system and light, and these are different types of exposure. In addition, exposure tends to accumulate over a series of dives. To take into account the impact on the central nervous system, the concept of “oxygen limit” is used as a calculation unit, with the help of which safe limits are determined for one-time and daily exposure. You can familiarize yourself with the tables and calculations in detail.
In addition, increased oxygen pressure negatively affects the lungs; to account for this phenomenon, “oxygen endurance units” are used, which are calculated using special tables that correlate the partial pressure of oxygen and the number of “units per minute”. For example, 1.2 ATA gives us 1.32 OTUs per minute. The recognized safety limit is 1425 units per day.
From the above, in particular, it should be clear that for a safe stay at great depths, a mixture with a reduced oxygen content is required, which is unsuitable for breathing at lower pressures. For example, at a depth of 100 meters (11 ATA), the oxygen concentration in the mixture should not exceed 12%, and in practice it will be even lower. It is impossible to breathe such a mixture on the surface.
Nitrogen
Nitrogen is not metabolized by the body and has no lower limit. With high blood pressure, nitrogen has a toxic effect on the nervous system, similar to a narcotic or alcohol intoxication, known as “nitrogen narcosis.”
The mechanisms of influence have not been precisely clarified; the limits of influence are purely individual and depend both on the characteristics of the organism and on its condition. Thus, it is known that the effects of fatigue, hangover, all types of depressed state of the body such as colds, etc. enhance the effect.
Minor manifestations in the form of a state comparable to mild intoxication are possible at any depth; the empirical “martini rule” applies, according to which the effect of nitrogen is comparable to a glass of dry martini on an empty stomach for every 10 meters of depth, which is not dangerous and adds a good mood. Nitrogen accumulated during regular diving also affects the psyche, similar to soft drugs and alcohol, which the author himself is a witness and participant. It manifests itself in vivid and “narcotic” dreams, in particular, it acts within a few hours. And yes, divers are a bit of drug addicts. Nitrogen.
The danger is represented by strong manifestations, which are characterized by a rapid increase up to a complete loss of adequacy, orientation in space and time, hallucinations, which can lead to death. A person can easily rush to the depths because it’s cool there or he allegedly saw something there, forget that he is under water and “take a deep breath,” spitting out the mouthpiece, etc. Exposure to nitrogen in itself is not lethal or even harmful, but the consequences in diving conditions can be tragic. It is characteristic that when the pressure decreases, these manifestations pass just as quickly; sometimes it is enough to rise only 2..3 meters to “sober up sharply.”
Probability of strong manifestation at depths accepted for recreational diving entry level(up to 18 m, ∼2.2 ATA) is assessed as very low. According to available statistics, cases of severe poisoning become quite likely from 30 meters of depth (∼3.2 ATA), and then the probability increases as pressure increases. At the same time, people with individual stability may not experience problems even at much greater depths.
The only way to counteract this is constant self-monitoring and the monitoring of a partner, with an immediate reduction in depth in case of suspected nitrogen poisoning. The use of "nitrox" reduces the likelihood of nitrogen poisoning, of course, within the depth limits imposed by oxygen.
Helium and other gases
In technical and professional diving, other gases are also used, in particular helium. There are examples of the use of hydrogen and even neon in deep mixtures. These gases have a high saturation/desaturation rate; the toxic effects of helium are observed at pressures of more than 12 ATA and can, paradoxically, be compensated for by nitrogen. However wide application they do not have a high cost, so it is virtually impossible for an average diver to encounter them, and if the reader is really interested in such questions, then he should use professional literature, and not this modest review.
When using any mixtures, the calculation logic remains the same as described above, only limits and parameters specific to each gas are used, and for deep technical dives several different compositions are usually used: for breathing on the way down, working at the bottom and a gradual way up with decompression, the compositions of these gases are optimized based on the logic of their movement in the body described above.
Practical conclusion
Understanding these theses makes it possible to give meaning to many of the restrictions and rules given in the courses, which is absolutely necessary for both further development, and for their correct violation.
Nitrox is recommended for use during normal diving because it reduces the nitrogen load on the body even if you remain completely within the limits of recreational diving, which means better health, more fun, and easier consequences. However, if you are going to dive deep and often, you need to remember not only its advantages, but also the possible oxygen intoxication. Always check your oxygen levels yourself and determine your limits.
Nitrogen poisoning is the most likely problem you will encounter, always be aware of yourself and your partner.
Separately, I would like to draw your attention to the fact that reading this text does not mean that the reader has mastered the full set of information for understanding working with gases during complex dives. For practical application this is absolutely not enough. This is just a starting point and a basic understanding, nothing more.