Changes in blood circulation during physical activity. Topic of the lecture: “Regulation of blood circulation. The effect of physical training and physical inactivity on hemodynamics
Exercise greatly improves the pumping function of the heart. One of the most important effects of training is slowing the resting heart rate. This is a sign of lower myocardial oxygen consumption, i.e. increased protection from coronary disease hearts. Adaptation of the peripheral circulatory system includes a number of vascular and tissue changes. Muscle blood flow during exercise increases significantly and can increase by 100 times, which requires increased heart function. In trained muscles, capillary density increases. An increase in the arteriovenous oxygen difference occurs due to an increase in muscle mitochondria and the number of capillaries, as well as more efficient shunting of blood from non-working muscles and abdominal organs. The activity of oxidative enzymes increases. These changes reduce the amount of blood the muscles need to work. An increase in the oxygen transport capacity of the blood and the ability of erythrocytes to give oxygen further increases the arteriovenous difference.
Thus, the most significant changes during training, there is an increase in the oxidative potential of muscles and regional blood flow, economization of the work of the heart at rest and at moderate loads.
As a result of training, the reaction is significantly reduced blood pressure under various loads.
An important protective role is played by a change in fibrinolytic activity (a decrease in viscosity) of the blood and a decrease in adhesion (deformation) of platelets. Under load, blood clotting increases, but at the same time blood viscosity decreases, which leads to a normalization of the ratio of these two processes. During exercise, a 6-fold increase in blood fibrinolytic activity was registered.
Summarizing the available information, we can say that physical activity:
- - reduces the risk of developing coronary heart disease, reducing the work of the heart at rest, and myocardial oxygen demand;
- - reduces blood pressure,
- - reduces heart rate and tendency to arrhythmias.
- - Simultaneously increase: coronary blood flow, peripheral circulation efficiency, myocardial contractility, circulating blood volume and erythrocyte volume, resistance to stress.
Hypertension (AH) is the main risk factor among diseases of the circulatory system. A prerequisite for the practical use of physical training in hypertension is the reduction of blood pressure under the influence of systematic training. Well known over low level BP in highly skilled athletes. According to observations, among physically active contingents, the incidence of GB is significantly lower than among sedentary groups of the population. Various training programs are used, but the most common are dynamic exercises, including walking, running, cycling, i.e. exercises involving large muscle groups. The complex programs include other types of exercises (general developmental, gymnastic, etc.), sport games. The intensity, duration and frequency of classes, although they vary, provide a training effect. physical education should not be carried out during any acute illness, including colds, and during periods of exacerbation of chronic diseases. Great importance in the process of training is given to self-control. It is also necessary to diagnose the state of the blood during physical education. The number of leukocytes, erythrocytes and hemoglobin in athletes at rest, as a rule, does not differ from their number in people who are not involved in sports. The detection of a decrease in these indicators in some of them cannot be assessed as a pathological sign, because this is due to an increase in the volume of circulating plasma, which leads to a relative decrease in the formed elements per unit volume of blood. Athletes show an increase in the number of lymphocytes (up to 37%) and eosinophils (up to 5%) and a decrease in the number of neutrophils (up to 5%). This indicates the state of adaptation of the body to physical stress and the body's defense system as a whole.
During muscle activity, the need for oxygen is increased, which means that the amount of oxygen that the blood must deliver to the tissues must also be greater. There are two ways to meet this increased demand: increasing the volume of blood pumped by the heart (cardiac output), and increasing the amount of oxygen delivered by a given volume of blood. The arterial blood is already completely saturated and can no longer absorb oxygen, but the oxygen content in the venous blood is normally more than half of that in the arterial blood. Increasing the release of oxygen from the blood is an obvious way to get more O2 from each of its volumes.
Consider first the process of increasing the extraction of oxygen from the blood. The entire muscle mass of a lean person, which is almost half of his weight, consumes about 50 ml of 02 per 1 min. This amount of oxygen is delivered by a blood stream with a volume of approximately 1 liter (i.e., when arterial blood turns into venous blood, the oxygen content in it decreases from 200 ml per 1 liter to 150 ml per 1 liter). Since a quarter of the oxygen is extracted from the arterial blood, we say that the extraction is 25%. With a strong physical load, the blood flow in the muscles in a healthy person can be 20 liters per 1 minute (in well-trained athletes - even more), and the oxygen extraction in the muscles increases to 80 or 90%; in other words, very little oxygen remains in the venous blood coming from the hard working muscles (Folkow and Neil, 1971).
The second way to increase oxygen delivery is to increase cardiac output. It can be achieved by increasing heart rate and stroke volume. Due to the interest associated with medicine and sports, there is much more information about humans than about other mammals. At rest, the human heart beats at a rate of about 70 beats per minute, and the stroke volume is about 70 ml (for each side), so the minute volume is about 5 liters. With great physical exertion, the work of the heart can easily increase by a factor of five or more (if, moreover, oxygen extraction is tripled, this will correspond to a 15-fold increase in oxygen delivery). Most of the increase in cardiac output is associated with an increase in heart rate, which can rise to 200 beats per minute, but the volume also increases, which can exceed 100 ml.
B
Rice. 4.16. Distribution of total blood flow (minute volume) (A) and oxygen consumption (B) between muscles (shaded areas of bars) and other parts of the body (light areas). Data are given for a person at rest (I), for an average person with heavy muscle loading (II), and for a high-class athlete with heavy loading (III). (Folkow and Neil, 1971.)
On fig. 4.16 shows the distribution of blood flow in humans at rest and during exercise. In an athlete, blood flow to the muscles in extreme conditions can increase by 25-30 times; blood flow to the rest of the body is slightly reduced. An athlete's muscle oxygen consumption can increase 100 times; this is only possible due to an approximately threefold increase in oxygen extraction.
More on the topic BLOOD CIRCULATION DURING PHYSICAL LOAD:
- EXAMINATION OF ANIMALS WHEN PROVIDING OBSTETRIC CARE IN PERINATAL PATHOLOGY AND GYNECOLOGICAL DISEASES
Exercise greatly improves the pumping function of the heart. One of the most important effects of training is slowing the resting heart rate. This is a sign of lower myocardial oxygen consumption, i.e. increased protection against coronary heart disease. Adaptation of the peripheral circulatory system includes a number of vascular and tissue changes. Muscle blood flow during exercise increases significantly and can increase by 100 times, which requires increased heart function. In trained muscles, capillary density increases. An increase in the arteriovenous oxygen difference occurs due to an increase in muscle mitochondria and the number of capillaries, as well as more efficient shunting of blood from non-working muscles and abdominal organs. The activity of oxidative enzymes increases. These changes reduce the amount of blood the muscles need to work. An increase in the oxygen transport capacity of the blood and the ability of erythrocytes to give oxygen further increases the arteriovenous difference.
Thus, the most significant changes during training are an increase in the oxidative potential of muscles and regional blood flow, economization of the work of the heart at rest and during moderate exercise.
As a result of training, the response of blood pressure to various loads is significantly reduced.
Under load, blood clotting increases, but at the same time blood viscosity decreases, which leads to a normalization of the ratio of these two processes. During exercise, a 6-fold increase in blood fibrinolytic activity was registered.
Summarizing the available data, we can say that physical activity:
reduces the risk of developing coronary heart disease by reducing the work of the heart at rest, and myocardial oxygen demand;
lowers blood pressure,
reduces heart rate and tendency to arrhythmias.
At the same time increase:
coronary circulation,
efficiency of peripheral circulation,
myocardial contractility,
circulating blood volume and erythrocyte volume,
resistance to stress.
The second way of exposure is an indirect effect on risk factors, such as overweight, lipid (fat) metabolism, smoking, alcohol consumption.
Hypertension (AH) is the main risk factor among diseases of the circulatory system. A prerequisite for the practical use of physical training in hypertension is the reduction of blood pressure under the influence of systematic training. Lower blood pressure levels are well known in highly skilled athletes. According to observations, among physically active contingents, the incidence of GB is significantly lower than among sedentary groups of the population. Various training programs are used, but the most common are dynamic exercises, including walking, running, cycling, i.e. exercises involving large muscle groups. Complex programs also include other types of exercises (general developmental, gymnastic, etc.), sports games.
Physical activity is accompanied by one of the most natural adaptive reactions for the body, which requires good interaction of all parts of the circulatory system. The fact that skeletal muscles make up up to 40% of body weight, and the intensity of their activity can vary widely, puts them in a special position compared to other organs. In addition, it must be borne in mind that in nature, both the search for food and, sometimes, life itself depend on the functionality of skeletal muscles. Therefore, in the process of evolution, close relationships have been developed between muscle contractions and cardiovascular vascular system. They are aimed at creating, as far as possible, the maximum conditions for the blood supply to the muscles, even at the expense of reducing blood flow in other organs and systems. Given the importance of providing blood to the contractile muscles, in the process of evolution, an advanced level of regulation of hemodynamics from the motor parts of the CNS was formed. Due to them, conditioned reflex mechanisms of blood circulation regulation are formed, i.e. prestart reactions. Their significance lies in the mobilization of the cardiovascular system, due to which, even before the onset of muscle activity, heart contractions become more frequent, and pressure rises.
The sequence of inclusion of the cardiovascular system during physical labor can be traced during intense exercise. Muscles contract under the influence of impulses traveling in pyramidal tracts, which begin in the precentral twist. Descending to the muscles, next to the motor parts of the central nervous system, they also excite the respiratory and vasomotor centers of the medulla oblongata. From here, through the sympathetic nervous system, the activity of the heart increases and the vessels narrow. At the same time, catecholamines are released into the bloodstream from the adrenal glands, which constrict blood vessels. In functioning muscles, the vessels, on the contrary, expand dramatically. This is mainly due to the accumulation of metabolites such as H +, COT, K + 'adenosine like. As a result, a redistributive reaction of blood flow occurs: the more the number of muscles contracts, the more blood ejected by the heart enters them. Due to the fact that the previous IOC is no longer enough to meet the increased blood demand of the functioning muscles, the activity of the heart rapidly increases. At the same time, the IOC can increase by 5-6 times and reach 20-30 l / min. Of this volume, up to 80-85% enters the functioning skeletal muscles. If at rest 0.9-1.0 l / min (15-20% of the IOC in 5 l / min) of blood passes through the muscles, then during contraction the muscles can receive up to 20 l / min or more.
At the same time, it is muscle contraction that also affects blood flow. With intensive contraction as a result of vascular compression, blood access to the muscles decreases, but with relaxation it quickly increases. With a smaller force of contraction, blood access is increased during both contraction and relaxation phases. In addition, contracted muscles squeeze out the blood of the venous section, on the one hand, it is accompanied by an increase in venous return to the heart, and on the other hand, prerequisites are created for increasing blood access to the muscles during the relaxation phase.
The intensification of the activity of the heart during muscle contraction occurs against the background of a proportional increase in blood flow through the coronary vessels. Autonomous regulation ensures the preservation of cerebral blood flow for the same level. The blood supply to other organs depends on the load. If the muscle load is intense, then, despite the growth of the IOC, the access of blood to many internal organs may deteriorate. This is due to a sharp contraction of the afferent arteries under the influence of sympathetic vasoconstrictor impulses. A developed redistributive reaction can be expressed to such an extent that, for example, due to a decrease in renal blood flow, secretion almost completely stops.
The growth of the IOC leads to an increase in Rs. RD due to the expansion of muscle vessels can remain the same or even decrease. If a decrease in the bpore of the vascular part of the skeletal muscles does not compensate for the narrowing of other vascular zones, then Rd increases.
During exercise, excitation of vasomotor neurons is also facilitated by impulses from muscle proprioceptors and vascular chemoreceptors. Along with this, during muscular work, the adrenal system of the adrenal glands takes part in the regulation of blood flow. During work, other hormonal mechanisms for regulating blood flow (vasopressin, thyroxine, renin, atrial natriuretic hormone) are also activated.
During muscular work, the reflexes that control AT at rest are “cancelled”. Despite the increase in AT, reflexes from baroreceptors do not inhibit the activity of the heart. In this case, the influence of other regulatory mechanisms prevails.
In functioning muscles, an increase in AT during vasodilation also leads to changes in the conditions of water exchange. An increase in filtration pressure contributes to the retention of part of the fluid in the tissues. This causes an increase in hematocrit. An increase in the concentration of erythrocytes (sometimes by 0, § "1012 / l) is one of the expedient reactions of the body, since this increases the oxygen capacity of the blood.
The chapter deals with blood circulation at various levels of physical activity, lack and excess of oxygen, low and high ambient temperatures, and changes in gravity.
PHYSICAL ACTIVITY
Work can be dynamic, when resistance is overcome at a certain distance, and static, with isometric muscle contraction.
Dynamic work
Physical stress elicits immediate responses from various functional systems, including the muscular, circulatory, and respiratory systems. The severity of these reactions is determined by the adaptability of the body to physical stress and the severity of the work performed.
Heart rate. According to the nature of the change in heart rate, two forms of work can be distinguished: light, non-fatiguing work - with the achievement of a stationary state - and heavy, fatigue-causing work (Fig. 6-1).
Even after the end of the work, the heart rate changes depending on the voltage that has taken place. After light work, the heart rate returns to its original level within 3-5 minutes; after hard work, the recovery period is much longer - with extremely heavy loads, it can reach several hours.
With hard work, blood flow and metabolism in the working muscle increases by more than 20 times. The degree of changes in indicators of cardio- and hemodynamics during muscular activity depends on its power and physical fitness (adaptability) of the organism (Table 6-1).
Rice. 6-1.Changes in heart rate in individuals with average performance during light and heavy dynamic work of constant intensity
In persons trained for physical activity, myocardial hypertrophy occurs, capillary density and contractile characteristics of the myocardium increase.
The heart increases in size due to hypertrophy of cardiomyocytes. The weight of the heart in highly skilled athletes increases to 500 g (Fig. 6-2), the concentration of myoglobin in the myocardium increases, the heart cavities increase.
The density of capillaries per unit area in a trained heart increases significantly. Coronary blood flow and metabolic processes increase in accordance with the work of the heart.
Myocardial contractility (the maximum rate of increase in pressure and ejection fraction) is markedly increased in athletes due to the positive inotropic action of sympathetic nerves.
Table 6-1.Changes in physiological parameters during dynamic work of different power in people who do not go in for sports (top line) and in trained athletes (bottom line)
Nature of work | Easy | Medium | submaximal | Maximum |
Work power, W | 50-100 | 100-150 | 150-250 |
|
100-150 | 150-200 | 200-350 | 350-500 and> |
|
Heart rate, bpm | 120-140 | 140-160 | 160-170 | 170-190 |
90-120 | 120-140 | 140-180 | 180-210 |
|
Systolic blood volume, l/min | 80-100 | 100-120 | 120-130 | 130-150 |
80-100 | 100-140 | 140-170 | 170-200 |
|
Minute volume of blood, l/min | 10-12 | 12-15 | 15-20 | 20-25 |
8-10 | 10-15 | 15-30 | 30-40 |
|
Average blood pressure, mm Hg | 85-95 | 95-100 | 100-130 | 130-150 |
85-95 | 95-100 | 100-150 | 150-170 |
|
Oxygen consumption, l/min | 1,0-1,5 | 1,5-2,0 | 2,0-2,5 | 2,5-3,0 |
0,8-1,0 | 1,0-2,5 | 2,5-4,5 | 4,5-6,5 |
|
Blood lactate, mg per 100 ml | 20-30 | 30-40 | 40-60 | 60-100 |
10-20 | 20-50 | 50-150 | 150-300 |
During exercise, cardiac output increases due to an increase in heart rate and stroke volume, and changes in these values are purely individual. In healthy young people (with the exception of highly trained athletes), cardiac output rarely exceeds 25 l / min.
Regional blood flow. During physical exertion, regional blood flow changes significantly (Table 6-2). Increased blood flow in working muscles is associated not only with an increase in cardiac output and blood pressure, but also with the redistribution of BCC. With maximum dynamic work, blood flow in the muscles increases by 18-20 times, in the coronary vessels of the heart by 4-5 times, but decreases in the kidneys and abdominal organs.
In athletes, the end-diastolic volume of the heart naturally increases (3-4 times more than the stroke volume). For an ordinary person, this figure is only 2 times higher.
Rice. 6-2.Normal heart and athlete's heart. An increase in the size of the heart is associated with elongation and thickening of individual myocardial cells. In the adult heart, there is approximately one capillary for every muscle cell.
Table 6-2.Cardiac output and organ blood flow in humans at rest and during exercise of varying intensity
O absorption 2 , ml / (min * m 2) |
||||
peace | Easy | Medium | Maximum |
|
140 | 400 | 1200 | 2000 |
|
Region | Blood flow, ml/min |
|||
Skeletal muscles | 1200 | 4500 | 12 500 | 22 000 |
A heart | 1000 |
|||
Brain | ||||
Celiac | 1400 | 1100 | ||
renal | 1100 | |||
Leather | 1500 | 1900 | ||
Other organs | ||||
Cardiac output | 5800 | 9500 | 17 500 | 25 000 |
With muscle activity, myocardial excitability increases, the bioelectric activity of the heart changes, which is accompanied by a shortening of the PQ, QT intervals of the electrocardiogram. The greater the power of work and the lower the level of physical fitness of the body, the more the electrocardiogram parameters change.
With an increase in heart rate up to 200 per minute, the duration of diastole decreases to 0.10-0.11 s, i.e. more than 5 times in relation to this value at rest. The filling of the ventricles in this case occurs within 0.05-0.08 s.
Blood pressure in humans during muscular activity increases significantly. When running, causing an increase in heart rate up to 170-180 per minute, the following increases:
Systolic pressure on average from 130 to 250 mm Hg;
Average pressure - from 99 to 167 mm Hg;
Diastolic - from 78 to 100 mm Hg.
With intense and prolonged muscular activity, the stiffness of the main arteries increases due to the strengthening of the elastic framework and the increase in the tone of smooth muscle fibers. In the arteries of the muscular type, moderate hypertrophy of the muscle fibers can be observed.
The pressure in the central veins during muscular activity, as well as the central blood volume, increases. This is due to an increase in venous blood return with an increase in the tone of the walls of the veins. The working muscles act as an additional pump, which is referred to as the "muscle pump", providing an increased (adequate) blood flow to the right heart.
The total peripheral vascular resistance during dynamic work can decrease by 3-4 times compared with the initial, non-working state.
Oxygen consumption increases by an amount that depends on the load and the efficiency of the efforts expended.
With light work, a steady state is reached, when oxygen consumption and its utilization are equivalent, but this occurs only after 3-5 minutes, during which the blood flow and metabolism in the muscle adapt to the new requirements. Until a steady state is reached, the muscle depends on a small oxygen reserve,
which is provided by O 2 associated with myoglobin, and from the ability to extract oxygen from the blood.
With heavy muscular work, even if it is performed with constant effort, a stationary state does not occur; like heart rate, oxygen consumption is constantly increasing, reaching a maximum.
oxygen debt. With the start of work, the need for energy increases instantly, but it takes some time for blood flow and aerobic metabolism to adjust; Thus, there is an oxygen debt:
In light work, the oxygen debt remains constant after reaching a steady state;
With hard work, it grows until the very end of the work;
At the end of work, especially in the first minutes, the rate of oxygen consumption remains above the level of rest - there is a "payment" of oxygen debt.
A measure of physical stress. As the intensity of dynamic work increases, the heart rate increases, and the rate of oxygen consumption increases; the greater the load on the body, the greater this increase compared to the level at rest. Thus, heart rate and oxygen consumption serve as a measure of physical stress.
Ultimately, the adaptation of the organism to the action of high physical loads leads to an increase in the power and functional reserves of the cardiovascular system, since it is this system that limits the duration and intensity of the dynamic load.
HYPODYNAMIC
The release of a person from physical labor leads to physical detraining of the body, in particular, to a change in blood circulation. In such a situation, one would expect an increase in efficiency and a decrease in the intensity of the functions of the cardiovascular system. However, this does not happen - the economy, power and efficiency of blood circulation are reduced.
In the systemic circulation, a decrease in systolic, mean and pulse blood pressure is more often observed. In the pulmonary circulation, when hypokinesia is combined with a decrease in hydrostatic blood pressure (bed rest, weightless
bridge) increases blood flow to the lungs, increases pressure in the pulmonary artery.
At rest with hypokinesia:
Heart rate naturally increases;
Cardiac output and BCC decrease;
With prolonged bed rest, the size of the heart, the volume of its cavities, as well as the mass of the myocardium noticeably decrease.
The transition from hypokinesia to normal activity mode causes:
Pronounced increase in heart rate;
Increase in the minute volume of blood flow - IOC;
Decreased total peripheral resistance.
With the transition to intense muscular work, the functional reserves of the cardiovascular system decrease:
In response to a muscle load of even low intensity, the heart rate rapidly increases;
Shifts in blood circulation are achieved by including its less economical components;
At the same time, the IOC increases mainly due to an increase in heart rate.
Under conditions of hypokinesia, the phase structure of the cardiac cycle changes:
The phase of expulsion of blood and mechanical systole is reduced;
The duration of the phase of tension, isometric contraction and relaxation of the myocardium increases;
The initial rate of increase in intraventricular pressure decreases.
Myocardial hypodynamia. All of the above indicates the development of the phase syndrome of myocardial hypodynamia. This syndrome, as a rule, is observed in a healthy person against the background of a reduced return of blood to the heart during light physical exertion.
ECG changes.With hypokinesia, the electrocardiogram parameters change, which are expressed in positional changes, relative slowing of conduction, decrease in P and T waves, change in the ratio of T values in different leads, periodic displacement segment S-T, changing the process of repolarization. Hypokinetic changes in the electrocardiogram, regardless of the picture and severity, are always reversible.
Changes in the vascular system. With hypokinesia, a stable adaptation of the vascular system and regional blood flow to these conditions develops (Table 6-3).
Table 6-3.The main indicators of the cardiovascular system in humans under conditions of hypokinesia
Changes in the regulation of blood circulation. With hypokinesia, signs of the predominance of sympathetic influences over parasympathetic ones change the system of regulation of the activity of the heart:
The high activity of the hormonal link of the sympathoadrenal system indicates a high stress level of hypokinesia;
Increased excretion of catecholamines in the urine and their low content in tissues is realized by a violation hormonal regulation activity of cell membranes, in particular, cardiomyocytes.
Thus, the decrease in the functionality of the cardiovascular system during hypokinesia is determined by the duration of the latter and the degree of limitation of mobility.
CIRCULATION IN OXYGEN DEFICIENCY
As altitude increases, atmospheric pressure decreases, and the partial pressure of oxygen (PO 2 ) decreases in proportion to the decrease in atmospheric pressure. The reaction of the body (primarily the respiratory, circulatory and blood organs) to oxygen deficiency depends on its severity and duration.
For short-term reactions in high altitude conditions, only a few hours are required, for primary adaptation - several days and even months, and the stage of stable adaptation of migrants is acquired over the years. The most effective adaptive reactions are manifested in the indigenous population of high-mountain regions due to long-term natural adaptation.
Initial adaptation period
The movement of a person (migration) from the flat terrain to the mountains is accompanied by a pronounced change in the hemodynamics of the systemic and pulmonary circulation.
Tachycardia develops and the minute volume of blood flow (MOV) increases. Heart rate at an altitude of 6000 m in new arrivals at rest reaches 120 per minute. Physical activity causes more pronounced tachycardia and an increase in cardiac output than at sea level.
The stroke volume changes slightly (both an increase and a decrease can be observed), but the linear velocity of blood flow increases.
Systemic blood pressure in the first days of stay at heights increases slightly. The rise in systolic blood pressure is mainly caused by an increase in the IOC, and diastolic - by an increase in peripheral vascular resistance.
BCC increases due to the mobilization of blood from the depot.
Excitation of the sympathetic nervous system It is realized not only by tachycardia, but also by paradoxical dilatation of the veins of the systemic circulation, which leads to a decrease in venous pressure at altitudes of 3200 and 3600 m.
There is a redistribution of regional blood flow.
The blood supply to the brain increases due to the reduction of blood flow in the vessels of the skin, skeletal muscles, and the digestive tract. The brain is one of the first to respond
for oxygen deficiency. This is due to the special sensitivity of the cortex hemispheres to hypoxia due to the use of a significant amount of O 2 for metabolic needs (a brain weighing 1400 g consumes about 20% of the oxygen consumed by the body).
In the first days of alpine adaptation, the blood flow in the myocardium decreases.
The volume of blood in the lungs increases markedly. Primary high altitude arterial hypertension- an increase in blood pressure in the vessels of the lungs. The basis of the disease is an increase in the tone of small arteries and arterioles in response to hypoxia, usually pulmonary hypertension begins to develop at an altitude of 1600-2000 m above sea level, its value is directly proportional to the height and persists throughout the entire period of stay in the mountains.
An increase in pulmonary arterial blood pressure during ascent to a height occurs immediately, reaching its maximum in a day. On the 10th and 30th days, pulmonary BP gradually decreases, but does not reach the initial level.
The physiological role of pulmonary hypertension is to increase the volumetric perfusion of the pulmonary capillaries due to the inclusion of structural and functional reserves of the respiratory organs in gas exchange.
Inhalation of pure oxygen or a gas mixture enriched with oxygen high altitude leads to a decrease in blood pressure in the pulmonary circulation.
Pulmonary hypertension, together with an increase in the IOC and the central blood volume, place increased demands on the right ventricle of the heart. At high altitudes, if adaptive reactions are disrupted, altitude sickness or acute pulmonary edema may develop.
Effect thresholds
The effect of oxygen deficiency, depending on the height and degree of extremeness of the terrain, can be divided into four zones (Fig. 6-3), delimited from each other by effective thresholds (Ruf S., Strughold H., 1957).
Neutral zone. Up to an altitude of 2000 m, the ability for physical and mental activity suffers little or does not change at all.
zone of full compensation. At altitudes between 2000 and 4000 m, even at rest, heart rate, cardiac output and MOD increase. The increase in these indicators while working at such heights occurs to a greater extent.
degree than at sea level, so that both physical and mental performance are significantly reduced.
Zone of incomplete compensation (danger zone). At altitudes from 4000 to 7000 m, an unadapted person develops various disorders. Upon reaching the violation threshold (safety limit) at an altitude of 4000 m, physical performance drops sharply, and the ability to react and make decisions weakens. Muscle twitching occurs, blood pressure decreases, consciousness gradually becomes clouded. These changes are reversible.
Rice. 6-3.Influence of oxygen insufficiency when ascending to a height: the numbers on the left are the partial pressure of O 2 in the alveolar air at the corresponding height; the figures on the right are the oxygen content in gas mixtures, which gives the same effect at sea level
Critical zone. Starting from 7000 m and above, in the alveolar air it becomes below the critical threshold - 30-35 mm Hg. (4.0-4.7 kPa). Potentially lethal disorders of the central nervous system occur, accompanied by unconsciousness and convulsions. These disturbances can be reversible under the condition of a rapid increase in the inhaled air. In the critical zone, the duration of oxygen deficiency is of decisive importance. If hypoxia continues for too long,
violations occur in the regulatory links of the central nervous system and death occurs.
Long stay in the highlands
With a long stay of a person in high mountains at altitudes up to 5000 m, further adaptive changes in the cardiovascular system occur.
Heart rate, stroke volume and IOC stabilize and decrease to the initial values and even lower.
Pronounced hypertrophy of the right parts of the heart develops.
The density of blood capillaries in all organs and tissues increases.
BCC remains increased by 25-45% due to an increase in plasma volume and erythrocyte mass. In high altitude conditions, erythropoiesis increases, so the concentration of hemoglobin and the number of red blood cells increase.
Natural adaptation of highlanders
The dynamics of the main hemodynamic parameters in the natives of the highlands (highlanders) at an altitude of up to 5000 m remains the same as in the inhabitants of the lowlands at sea level. The main difference between "natural" and "acquired" adaptation to high altitude hypoxia lies in the degree of tissue vascularization, microcirculation activity and tissue respiration. For permanent residents of the highlands, these parameters are more pronounced. Despite the reduced regional blood flow in the brain and heart in the natives of the highlands, the minute oxygen consumption by these organs remains the same as in the inhabitants of the plains at sea level.
CIRCULATION WITH EXCESS OF OXYGEN
Prolonged exposure to hyperoxia leads to the development of toxic effects of oxygen and a decrease in the reliability of adaptive reactions of the cardiovascular system. An excess of oxygen in the tissues also leads to an increase in lipid peroxidation (LPO) and the depletion of endogenous antioxidant reserves (in particular, fat-soluble vitamins) and the antioxidant enzyme system. In this regard, the processes of catabolism and deenergization of cells are enhanced.
The heart rate decreases, the development of arrhythmias is possible.
With short-term hyperoxia (1-3 kg X sec/cm -2), electrocardiographic characteristics do not go beyond the physiological norm, but with many hours of exposure to hyperoxia, the P wave disappears in some subjects, which indicates the appearance of an atrioventricular rhythm.
Blood flow in the brain, heart, liver and other organs and tissues is reduced by 12-20%. In the lungs, blood flow can decrease, increase, and return to its original level.
Systemic blood pressure changes slightly. The diastolic pressure usually rises. Cardiac output significantly decreases, and total peripheral resistance increases. The rate of blood flow and BCC during breathing with a hyperoxic mixture is significantly reduced.
The pressure in the right ventricle of the heart and pulmonary artery with hyperoxia often decreases.
Bradycardia in hyperoxia is mainly due to increased vagal influences on the heart, as well as the direct action of oxygen on the myocardium.
The density of functioning capillaries in tissues decreases.
Vasoconstriction during hyperoxia is determined either by the direct action of oxygen on vascular smooth muscles, or indirectly through a change in the concentration of vasoactive substances.
Thus, if the human body responds to acute and chronic hypoxia with a complex and quite effective set of adaptive reactions that form the mechanisms of long-term adaptation, then the action of acute and chronic hyperoxia effective means the body has no protection.
CIRCULATION AT LOW EXTERNAL TEMPERATURES
There are at least four external factors that have a serious impact on human circulation in the Far North:
Sharp seasonal, inter- and intra-day changes in atmospheric pressure;
Cold exposure;
A sharp change in photoperiodicity (polar day and polar night);
fluctuations magnetic field Earth.
The complex of climatic and ecological factors of high latitudes imposes stringent requirements on the cardiovascular system. Adaptation to conditions of high latitudes is divided into three stages:
Adaptive voltage (up to 3-6 months);
Stabilization of functions (up to 3 years);
Adaptability (up to 3-15 years).
Primary northern arterial pulmonary hypertension - the most characteristic adaptive reaction. An increase in blood pressure in the pulmonary circulation occurs at sea level under conditions of normal barometric pressure and O 2 content in the air. At the heart of such hypertension is the increased resistance of small arteries and arterioles of the lungs. Northern pulmonary hypertension is ubiquitous among visitors and indigenous populations of the polar regions and occurs in adaptive and maladaptive forms.
The adaptive form is asymptomatic, equalizes the ventilation-perfusion relationship and optimizes the oxygen regime of the body. Systolic pressure in the pulmonary artery with hypertension rises to 40 mm Hg, the total pulmonary resistance increases slightly.
maladaptive form. Latent respiratory failure develops - "polar shortness of breath", working capacity decreases. Systolic pressure in the pulmonary artery reaches 65 mm Hg, and the total pulmonary resistance exceeds 200 dynes Hsek H cm -5 . At the same time, the trunk of the pulmonary artery expands, pronounced hypertrophy of the right ventricle of the heart develops, while the stroke and minute volumes of the heart decrease.
CIRCULATION UNDER EXPOSURE TO HIGH TEMPERATURES
Distinguish adaptation in arid and humid zones.
Human adaptation in arid zones
Arid zones are characterized by high temperatures and low relative humidity. The temperature conditions in these zones during the hot season and in the daytime are such that the heat input to the body through insolation and contact with hot air can be 10 times higher than heat generation in the body at rest. Similar heat stress in the absence
effective mechanisms of heat transfer quickly leads to overheating of the body.
The thermal states of the body under conditions of high external temperatures are classified as normothermia, compensated hyperthermia and uncompensated hyperthermia.
hyperthermia- a borderline state of the body, from which a transition to normothermia is possible or fatal outcome(thermal death). The critical body temperature at which thermal death occurs in humans corresponds to + 42-43? C.
Action high temperature air per person, not adapted to the heat, causes the following changes.
Expansion of peripheral vessels is the main reaction to heat in arid zones. Vasodilation, in turn, should be accompanied by an increase in BCC; if this does not happen, then a drop in systemic blood pressure occurs.
The volume of circulating blood (VCC) at the first stages of thermal exposure increases. With hyperthermia (due to evaporative heat transfer), the BCC decreases, which entails a decrease in central venous pressure.
Total peripheral vascular resistance. Initially (the first phase), with a slight increase in body temperature, systolic and diastolic blood pressure decreases. The main reason for the decrease in diastolic pressure is a decrease in total peripheral vascular resistance. During heat stress, when the body temperature rises to +38 °C, the total peripheral vascular resistance decreases by 40-55%. This is due to dilatation of peripheral vessels, primarily of the skin. A further increase in body temperature (second phase), on the contrary, may be accompanied by an increase in total peripheral vascular resistance and diastolic pressure with a pronounced decrease in systolic pressure.
The heart rate (HR) increases, especially in poorly trained and poorly adapted people. In a person at rest at a high external temperature, the increase in the number of heartbeats can reach 50-80%. In well-adapted people, heat does not cause an increase in heart rate until heat stress becomes too severe.
Central venous pressure increases with an increase in body temperature, but thermal exposure can also cause the opposite effect - a transient decrease in the central blood volume and a persistent decrease in pressure in the right atrium. The variability of indicators of central venous pressure is due to the difference in the activity of the heart and BCC.
Minute volume of blood circulation (MOV) increases. The stroke volume of the heart remains normal or slightly decreases, which is more common. The work of the right and left ventricles of the heart when exposed to high external temperatures (especially with hyperthermia) increases significantly.
A high external temperature, which practically excludes all heat transfer pathways in humans, except for the evaporation of sweat, requires a significant increase in skin blood flow. The growth of blood flow in the skin is provided mainly by an increase in the IOC and, to a lesser extent, by its regional redistribution: under heat load at rest, the blood flow in the celiac region, kidneys, and skeletal muscles decreases in a person, which “frees” up to 1 liter of blood/min; the rest of the increased cutaneous blood flow (up to 6-7 liters of blood / min) is provided by cardiac output.
Intense sweating ultimately leads to dehydration of the body, thickening of the blood and a decrease in BCC. This puts additional stress on the heart.
Adaptation of migrants in arid zones. In the newly arrived migrants in the arid zones of Central Asia, when performing heavy physical work, hyperthermia occurs 3-4 times more often than among the natives. By the end of the first month of stay in these conditions, the indicators of heat exchange and hemodynamics in migrants improve and approach those of local residents. By the end of the summer season, there is a relative stabilization of the functions of the cardiovascular system. Starting from the second year, the hemodynamic parameters of the migrants almost do not differ from those of the local residents.
Aborigines of arid zones. Aborigines of arid zones have seasonal fluctuations hemodynamic parameters, but to a lesser extent than in migrants. The skin of the natives is richly vascularized, has developed venous plexuses, in which blood moves 5-20 times slower than in the main veins.
The mucous membrane of the upper respiratory tract is also richly vascularized.
Human adaptation in humid zones
Human adaptation in the humid zones (tropics), where - in addition to elevated temperatures - the relative humidity of the air is high, proceeds similarly to arid zones. The tropics are characterized by a significant tension in the water and electrolyte balance. For permanent residents of the humid tropics, the difference between the temperature of the "core" and "shell" of the body, hands and feet is greater than that of migrants from Europe, which contributes to a better removal of heat from the body. In addition, among the natives of the humid tropics, the mechanisms for generating heat with sweat are more perfect than among visitors. In aborigines, in response to a temperature exceeding +27 °C, sweating begins faster and more intensely than among migrants from other climatic and geographical regions. For example, in Australian aborigines, the amount of sweat evaporated from the surface of the body is twice that of Europeans in identical conditions.
CIRCULATION UNDER ALTERED GRAVITY
The gravitational factor has a constant effect on blood circulation, especially in areas of low pressure, forming a hydrostatic component of blood pressure. Due to the low pressure in the pulmonary circulation, the blood flow in the lungs largely depends on the hydrostatic pressure, i.e. gravitational effect of blood.
The model of the gravitational distribution of pulmonary blood flow is shown in fig. 6-4. In an upright adult, the apices of the lungs are located about 15 cm above the base of the pulmonary artery, so the hydrostatic pressure in the upper sections of the lungs is approximately equal to the arterial pressure. In this regard, the capillaries of these departments are slightly perfused or not perfused at all. In the lower parts of the lungs, on the contrary, hydrostatic pressure is combined with arterial pressure, which leads to additional stretching of the vessels and their plethora.
These features of the hemodynamics of the pulmonary circulation are accompanied by a significant unevenness of blood flow in different parts of the lungs. This unevenness significantly depends on the position of the body and is reflected in the indicators of regional saturation.
Rice. 6-4.A model that relates the uneven distribution of pulmonary blood flow in a vertical position of the human body with the pressure acting on the capillaries: in zone 1 (apex), the alveolar pressure (P A) exceeds the pressure in the arterioles (P a), and the blood flow is limited. In zone 2, where P a > P A , the blood flow is greater than in zone 1. In zone 3, the blood flow is increased and is determined by the pressure difference in arterioles (P a) and pressure in venules (Ru). In the center of the lung diagram are the pulmonary capillaries; vertical tubes on the sides of the lung - manometers
blood with oxygen. However, despite these features, in a healthy person, the saturation of the blood of the pulmonary veins with oxygen is 96-98%.
With the development of aviation, rocketry and man's spacewalk, changes in systemic hemodynamics under conditions of gravitational overload and weightlessness acquire great importance. Changes in hemodynamics are determined by the type of gravitational loads: longitudinal (positive and negative) and transverse.
QUESTIONS FOR SELF-CHECKING
1. What types of work can be distinguished by changes in heart rate?
2. What changes in the myocardium and regional circulation are observed during physical exertion?
3. By what mechanisms is the regulation of blood circulation carried out during physical exertion?
4. How does oxygen consumption change during exercise?
5. What changes occur in the circulatory system during hypokinesia?
6. Name the types of hypoxia depending on the duration of action.
7. What changes in the circulatory system are observed during adaptation to high mountains?