The cardiovascular system during physical activity increases its requirements. The oxygen demand of active muscles increases dramatically, more nutrients are used, metabolic processes are accelerated, and therefore the amount of decay products increases. With prolonged exercise, as well as when performing physical activity in conditions of high temperature, body temperature rises. With intense exercise, the concentration of hydrogen ions in the muscles and blood increases, which causes a decrease in blood pH.
During exercise, numerous changes occur in the cardiovascular system. All of them are aimed at fulfilling the same task: to allow the system to meet the increased needs, ensuring the maximum efficiency of its functioning. To better understand the changes that are taking place, we need to take a closer look at certain functions of the cardiovascular system. We will study the changes in all components of the system, paying special attention to the heart rate; systolic blood volume; cardiac output; blood flow; arterial pressure; blood.
HEART RATE. Frequency - heart rate - the simplest and most informative parameter of the cardiovascular system. Measuring it involves determining the pulse, usually in the area of the wrist or carotid artery. Heart rate reflects the amount of work that the heart must do to meet the increased demands of the body when it is involved in physical activity. To better understand, let's compare heart rate at rest and during exercise. Resting heart rate. The average heart rate at rest is 60-80 beats per minute. In middle-aged people, those who are sedentary and those who do not engage in muscular activity, the heart rate at rest can exceed 100 beats per minute. In well-trained athletes involved in endurance sports, resting heart rate is 28-40 beats per minute. Heart rate usually decreases with age. The heart rate is also influenced by environmental factors, for example, it increases in conditions of high temperature and high altitude. Already before the start of the exercise, the heart rate, as a rule, exceeds the usual rate at rest. This is the so-called pre-launch reaction. It occurs due to the release of the neurotransmitter norepinephrine from the sympathetic nervous system and the hormone adrenaline from the adrenal glands. Apparently, the vagal tone also decreases. Since the heart rate is usually elevated before exercise, it should only be determined at rest in conditions of complete relaxation, for example, in the morning, before getting out of bed after a restful sleep. The heart rate before exercise cannot be read as resting heart rate.
Heart rate during exercise.
When you start exercising, your heart rate rises rapidly in proportion to the intensity of the exercise. When work intensity is precisely controlled and measured (for example, on a bicycle ergometer), oxygen consumption can be predicted. Therefore, the expression of the intensity of physical work or exercise in terms of oxygen consumption is not only accurate, but also the most appropriate when examining both different people and the same person in different conditions.
Maximum heart rate. Heart rate increases in proportion to the increase in the intensity of physical activity almost until the moment of extreme fatigue (exhaustion). As this moment approaches, the heart rate begins to stabilize. This means that the maximum heart rate has been reached. Maximum heart rate - the maximum rate achieved with maximum effort before the moment of extreme fatigue. This is a very reliable indicator that remains constant from day to day and only changes slightly with age from year to year.
The maximum heart rate can be determined taking into account age, since it decreases by about one beat per year, starting from the age of 10-15 years. Subtracting age from 220 gives you an approximate average of your maximum heart rate. It should be noted, however, that individual maximum heart rates may differ quite significantly from the average thus obtained. For example, a 40-year-old person would have an average maximum heart rate of 180 beats per minute.
However, of all 40-year-olds, 68% will have a maximum heart rate in the range of 168-192 beats per minute, and in 95% this indicator will fluctuate in the range of 156-204 beats per minute. This example demonstrates the potential for error in estimating a person's maximum heart rate.
Steady heart rate. At constant submaximal levels of physical activity, heart rate increases relatively quickly until it reaches a plateau - a stable heart rate that is optimal to meet the needs of blood circulation at a given intensity of work. With each subsequent increase in intensity, the heart rate reaches a new stable indicator within 1-2 minutes. However, the higher the intensity of the load, the longer it takes to achieve this indicator.
The concept of heart rate stability formed the basis of a number of tests developed to assess physical fitness. In one of these tests, subjects were placed on a bicycle ergometer-type device and worked at two to three standardized intensities. Those with better physical fitness, based on their cardio-respiratory endurance, had lower rates of sustained heart rate at a given intensity of work compared to less physically fit. Thus, this indicator is an effective indicator of the performance of the heart: a lower heart rate indicates a more productive heart.
When the exercise is performed at a constant intensity for a long time, especially in conditions of high air temperature, the heart rate rises, instead of demonstrating a steady rate. This reaction is part of a phenomenon called cardio - vascular shift.
SYSTOLIC BLOOD VOLUME.
Systolic blood volume also increases during exercise, allowing the heart to work more efficiently. It is well known that at almost maximum and maximum intensity of the load, systolic volume is the main indicator of cardio-respiratory endurance. Let's take a look at what underlies this.
Systolic volume is determined by four factors:
1) the volume of venous blood returned to the heart;
2) ventricular distensibility or their ability to increase;
3) contractility of the ventricles;
4) pressure in the aorta or pressure in the pulmonary artery (pressure that must overcome the resistance of the ventricles in the process of contraction).
The first two factors affect the ability of the ventricles to fill with blood, determining how much blood is available to fill them, as well as how easily they fill at a given pressure. The last two factors affect the ability to expel from the ventricles, determining the force with which the blood is ejected, as well as the pressure that it must overcome, moving through the arteries. These four factors directly control changes in systolic volume due to increased exercise intensity.
Increase in systolic volume with exercise.
Scientists agreed that the value of systolic volume during exercise exceeds that at rest. At the same time, there are very conflicting data on the change in systolic volume during the transition from work of very low intensity to work of maximum intensity or to work until the onset of extreme fatigue. Most scientists believe that systolic volume increases with increasing work intensity, but only up to 40-60% of the maximum. It is believed that at the indicated intensity, the systolic blood volume indicator shows a plateau and does not change even when the moment of extreme fatigue is reached.
When the body is in an upright position, the systolic volume of blood almost doubles compared to that at rest, reaching maximum values during muscle activity. For example, in physically active but untrained people, it increases from 50-60 ml at rest to 100-120 ml at maximum load. In well-trained athletes involved in endurance sports, the systolic volume index can increase from 80-110 ml at rest to 160-200 ml at maximum load. When performing an exercise in the supination position (for example, swimming), the systolic volume also increases, but not so pronounced - by 20-40%. Why is there such a difference due to different positions of the body?
When the body is in the supination position, blood does not accumulate in the lower extremities. It returns to the heart faster, which leads to higher systolic volume at rest in a horizontal position (supination). Therefore, the increase in systolic volume at maximum load is not as large in the horizontal position of the body compared to the vertical one. Interestingly, the maximum systolic volume that can be achieved when exercising in an upright position is only slightly higher than in a horizontal position. The increase in systolic volume at low or moderate intensity of work is mainly aimed at compensating for gravity.
Explanation of increased systolic blood volume.
It is well known that systolic blood volume increases during the transition from rest to exercise, but until recently the mechanism of this increase has not been studied. One of the possible mechanisms may be the Frank-Starling law, according to which the main factor regulating systolic blood volume is the degree of ventricular distensibility: the more the ventricle is stretched, the more forcefully it contracts.
Some of the newer cardiovascular function diagnostic devices can accurately determine changes in systolic volume during exercise. The echocardiography method and the radionuclide method have been successfully used to determine how the chambers of the heart respond to increased oxygen demand during exercise. Both methods provide a constant image of the heart at rest, as well as at near maximum exercise intensities.
To implement the Frank-Starling mechanism, it is necessary that the volume of blood entering the ventricle increases. For this to happen, venous return to the heart must increase. This can quickly come about with redistribution of blood due to sympathetic activation of arteries and arterioles in inactive areas of the body and general sympathetic activation of the venous system. In addition, during exercise, the muscles are more active, so their pumping action is also increased. In addition, breathing becomes more intense, therefore intrathoracic and intra-abdominal pressure increases. All these changes enhance venous return.
During exercise, cardiac output increases, mainly to meet the increased oxygen demand of working muscles.
BLOOD FLOW.
The cardiovascular system is even more efficient in terms of supplying blood to those areas that need it. Recall that the vascular system is able to redistribute blood, supplying it with the most needy areas. Consider changes in blood flow during exercise.
Redistribution of blood during exercise. During the transition from the state of rest to the performance of physical activity, the structure of the blood flow changes markedly. Under the influence of the sympathetic nervous system, blood is diverted from areas where its presence is not necessary, and is sent to areas that are actively involved in the exercise. At rest, cardiac output in the muscles is only 15-20%, and during intense physical exertion - 80-85%. The blood flow in the muscles increases mainly due to a decrease in the blood supply to the kidneys, liver, stomach and intestines.
As body temperature rises due to exercise or high air temperature, much more blood is sent to the skin to transfer heat from the depths of the body to the periphery, from where heat is released into the external environment. An increase in skin blood flow means that the blood supply to the muscles is reduced. This, by the way, explains the lower results in most sports that require endurance in hot weather.
With the beginning of the exercise, active skeletal muscles begin to experience an increasing need for blood flow, which is satisfied by general sympathetic stimulation of the vessels of those areas in which the blood flow is to be limited. The vessels in these areas narrow and the blood flow is directed to the skeletal muscles, which are in need of additional blood. In skeletal muscle, the sympathetic stimulation of the narrowing walls of the vessels of the fibers weakens, and the sympathetic stimulation of the vasodilating fibers increases. Thus, the vessels dilate and more blood enters the active muscles.
Cardiovascular shift.
With a prolonged load, as well as performing work in conditions of elevated air temperature, the volume of blood decreases due to the loss of fluid by the body due to sweating and the general movement of fluid from the blood to the tissues. This is swelling. With a gradual decrease in total blood volume as the duration of exercise increases and more blood moves to the periphery to cool, cardiac filling pressure decreases. This reduces venous return to the right side of the heart, which in turn reduces systolic volume. Reduced systolic volume is compensated by an increase in heart rate, aimed at maintaining the value of cardiac output.
These changes represent a so-called cardio-vascular shift, allowing you to continue with low- or moderate-intensity exercise. At the same time, the body is unable to fully compensate for the reduced systolic volume at high exercise intensities, since the maximum heart rate is reached earlier, thereby limiting the maximum muscle activity.
ARTERIAL PRESSURE.
During physical exertion that requires the manifestation of endurance, systolic blood pressure increases in proportion to the increase in the intensity of the load. Elevated systolic blood pressure is the result of increased cardiac output that accompanies increased work intensity. It ensures the rapid movement of blood through the vessels. In addition, blood pressure determines the amount of fluid leaving the capillaries to the tissues, transporting the necessary nutrients. Thus, increased systolic pressure contributes to the implementation of the optimal process of transport. During muscular activity that requires the manifestation of endurance, diastolic pressure practically does not change, regardless of the intensity of the load.
Diastolic pressure reflects the pressure in the arteries while the heart is at rest. None of the changes we've looked at affect this pressure to a significant extent, so there's no reason to expect it to increase.
Arterial pressure reaches stable values during submaximal exercise, requiring the manifestation of endurance, constant intensity. With an increase in the intensity of the load, systolic pressure also increases. With prolonged exercise of constant intensity, systolic pressure may gradually decrease, but diastolic pressure remains unchanged.
With upper body loads requiring high intensity, the blood pressure response is even more evident. Apparently, this is due to less muscle mass and fewer vessels in the upper body compared to the lower. This difference causes greater resistance to blood flow and, consequently, increased blood pressure to overcome the resistance.
Differences in systolic blood pressure response between the upper and lower body are of particular importance to the heart. Myocardial oxygen utilization and myocardial blood flow are directly related to the product of heart rate and systolic blood pressure. When performing static, dynamic strength or upper body exercises, the double product increases, indicating an increase in the load on the heart.
Plasma volume. With the onset of muscle activity, the transition of blood plasma into the interstitial space is almost instantly observed. An increase in blood pressure causes an increase in hydrostatic pressure in the capillaries. Therefore, an increase in blood pressure pushes fluid out of the vessel into the intercellular space. In addition, due to the accumulation of decay products in the active muscle, intramuscular osmotic pressure increases, attracting fluid to the muscle.
If exercise intensity or environmental factors cause sweating, additional plasma volume losses can be expected. The main source of fluid for the formation of sweat is the interstitial fluid, the amount of which decreases as the sweating process continues.
With a load lasting several minutes, changes in the amount of fluid, as well as thermoregulation, have practically no effect, however, with an increase in the duration of the load, their importance for ensuring effective activity increases .. Changes in the cardiovascular system during physical work.
At rest, the minute volume of the heart fluctuates between 3.5-5.5 liters, with muscular work it reaches 30-40 liters. Between the value of the minute volume of the heart, the power of muscle work and oxygen consumption, there is a linear relationship, but only if there is a steady state of oxygen consumption. This can be seen from the data given in Table. eight.
An increase in cardiac output occurs due to an increase in contractions and an increase in stroke (systolic) volume of the heart. The systolic volume of the heart at rest ranges from 60-80 ml; during work, it can double or more, which depends on the functional state of the heart, the conditions for filling it with blood, training. In a well-trained person, the systolic volume can reach high values (up to 200 ml) at a moderate pulse rate.
The new level of activity of the cardiovascular system, which is established in connection with work, is provided mainly due to nervous and, to a lesser extent, humoral influences. At the same time, the formation of conditioned reflex connections contributes to the establishment of this new level even before the start of work. During work, further changes in the activity of the cardiovascular system occur.
The flow of blood to the heart is determined by venous inflow and the duration of diastole. Venous flow increases during work. Reflex action on proprioceptors causes vasodilatation of muscles and superficial vessels and at the same time constriction of internal vessels - the "celiac reflex". Blood from the muscles is distilled into the veins and the heart, and the speed of blood movement is proportional to the number of muscle movements (the action of the "muscle pump"). The movement of the diaphragm has the same effect.
The duration of diastole during work is shortened. The shortening mechanism is reflex - through baroreceptors in the mouths of the vena cava and proprioceptors of the working muscles. The overall result is an increase in heart rate.
Optimal conditions for the work of the heart are created when the rate of diastolic filling and the duration of diastole correspond to each other. With insufficient or excessive blood supply, the heart is forced to work due to increased contractions.
The efficiency of the heart depends not only on its functional state, muscle power, nutritional status, nervous regulation, but also on the ability to develop contraction force depending on diastolic filling. The magnitude of the stroke volume is thus proportional to the magnitude of the venous inflow.
The rhythm of cardiac activity can be determined by the pulse rate. To characterize muscular work, both the heart rate during work and the rate of its recovery after work are taken into account. Both of these functions depend on the intensity and duration of work. Moderate work is characterized by a more or less constant pulse rate; with hard work, its continuous growth is observed. The rate of recovery of the pulse rate depends on the intensity of work (Table 9).
In a trained person, the pulse rate, ceteris paribus, is always less than that of an untrained person. The blood supply to the working organs depends on the state of the cardiovascular system. The regulation of the vascular system is conditionally unconditioned reflex and local humoral. At the same time, metabolic products (histamine, adenylic acid, acetylcholine), especially histamine, which greatly expands small vessels, play a special role in vascular regulation. A large role in the regulation of blood vessels belongs to the products of the endocrine glands - adrenaline, which narrows the vessels of the internal organs, and vasopressin (a hormone of the cerebral appendage), acting on arterioles and capillaries. Humoral regulation can be carried out directly by acting on the muscular wall of blood vessels and reflexively through interoreceptors.
The nervous regulation of the vascular system is very sensitive, and this explains the great mobility of the blood supply to the organs. Due to the conditioned-unconditioned reflex and humoral mechanisms, during work, blood is redistributed from the internal organs to the working muscles and at the same time the volume of the vascular bed of capillaries increases (Table 10).
As can be seen from Table. 10, during operation, the number of open capillaries, their diameter and capacity increase significantly. At the same time, it should be noted that the reaction of the vessels is not differentiated (a feature of the central nervous regulation). So, for example, when working with one hand, the concomitant vascular reaction extends to all limbs.
Of great importance for assessing the functional state of the body during work is blood pressure, which is influenced by three factors: the amount of emptying of the heart, the intensity of the celiac reflex and vascular tone.
Systolic (maximum) pressure is a measure of the energy expended by the heart and is related to systole volume; at the same time, it characterizes the reaction of the vascular walls to the pressure of the blood wave. An increase in systolic blood pressure during work is an indicator of increased heart activity.
Diastolic (minimum) pressure is an indicator of vascular tone, the degree of vasodilation and depends on the vasomotor mechanism. During operation, the minimum pressure changes little. Its decrease indicates an expansion of the vascular bed and a decrease in peripheral resistance to blood flow.
Due to the increase in the maximum pressure during work, the pulse pressure increases, which characterizes the volume of blood supply to the working organs.
Minute volume, pulse rate and blood pressure return to baseline after exercise much later than other functions. Often, the indicators of minute volume, pulse and blood pressure in some segments of the recovery period are lower than the initial ones, which indicates that the recovery process has not yet been completed (Table 11).
| min | Pulse rate a minute | Arterial pressure, mm Hg Art. | Pulse pressure, mm Hg Art. | Minute volume of blood, ml | |
| maximum | minimum | ||||
| Up to load | |||||
| After load | |||||
| 1st | 110 | 145 | 40 | 105 | 12 486,1 |
| 2nd | 80 | 126 | 52 | 74 | 6 651,2 |
| 3rd | 67 | 112 | 58 | 54 | 4 256,6 |
| 4th | 61 | 108 | 60 | 48 | 8 485,5 |
| 5th | 63 | 106 | 62 | 44 | 3 299,9 |
| 5th | 65 | 98 | 64 | 34 | 2 728,11 |
| 7th | 70 | 102 | 60 | 42 | 3 629,5 |
| 8th | 72 | 108 | 62 | 46 | 3 896,5 |
| 9th | 72 | 108 | 62 | 48 | 4 114.1 |
The frequency and strength of heart contractions during muscular work increase significantly. Muscular work while lying down speeds up the pulse less than sitting or standing.
The maximum blood pressure increases to 200 mm Hg. and more. An increase in blood pressure occurs in the first 3-5 minutes from the start of work, and then in strong trained people with prolonged and intense muscular work, it is kept at a relatively constant level due to the training of reflex self-regulation. In weak and untrained people, blood pressure begins to fall already during work due to lack of training or insufficient training of reflex self-regulation, which leads to disability due to a decrease in blood supply to the brain, heart, muscles and other organs.
In people trained for muscular work, the number of heart contractions at rest is less than in untrained people, and, as a rule, no more than 50-60 per minute, and in especially trained people - even 40-42. It can be assumed that this decrease in heart rate is due to the pronounced in those involved in physical exercises that develop endurance. With a rare rhythm of heartbeats, the duration of the phase of isometric contraction and diastole is increased. The duration of the ejection phase is almost unchanged.
Resting systolic volume in trained is the same as in untrained, but as training increases, it decreases. Consequently, their minute volume also decreases at rest. However, in trained systolic volume at rest, as in untrained, it is combined with an increase in ventricular cavities. It should be noted that the cavity of the ventricle contains: 1) systolic volume, which is ejected during its contraction, 2) reserve volume, which is used during muscle activity and other conditions associated with increased blood supply, and 3) residual volume, which is almost not used even during the most intense work of the heart. In contrast to the untrained, the trained have a particularly increased reserve volume, and the systolic and residual volumes are almost the same. A large reserve volume in trained people allows you to immediately increase the systolic blood output at the beginning of work. Bradycardia, lengthening of the isometric tension phase, a decrease in systolic volume, and other changes indicate the economical activity of the heart at rest, which is referred to as controlled myocardial hypodynamia. During the transition from rest to muscular activity, the trained immediately manifest hyperdynamia of the heart, which consists in an increase in heart rate, an increase in systole, a shortening or even disappearance of the isometric contraction phase.
The minute volume of blood after training increases, which depends on the increase in systolic volume and the strength of cardiac contraction, the development of the heart muscle and the improvement of its nutrition.
During muscular work and in proportion to its value, the minute volume of the heart in a person increases to 25-30 dm 3 , and in exceptional cases up to 40-50 dm 3 . This increase in minute volume occurs (especially in trained people) mainly due to systolic volume, which in humans can reach 200-220 cm 3 . A less significant role in the increase in minute volume in adults is played by an increase in heart rate, which especially increases when systolic volume reaches the limit. The more fitness, the relatively more powerful work a person can perform with an optimal increase in heart rate up to 170-180 in 1 min. An increase in the pulse above this level makes it difficult for the heart to fill with blood and its blood supply through the coronary vessels. With the most intense work in a trained person, the heart rate can reach up to 260-280 per minute.
An increase in blood pressure in the aortic arch and carotid sinus reflexively dilates the coronary vessels. The coronary vessels expand the fibers of the sympathetic nerves of the heart, excited both by adrenaline and acetylcholine.
In trained people, heart mass increases in direct proportion to the development of their skeletal muscles. In trained men, the volume of the heart is greater than that of untrained men, 100-300 cm 3, and in women - by 100 cm 3 or more.
During muscular work, the minute volume increases and blood pressure increases, and therefore the work of the heart is 9.8-24.5 kJ per hour. If a person performs muscular work for 8 hours a day, then the heart during the day produces work of approximately 196-588 kJ. In other words, the heart per day performs work equal to that which a person weighing 70 kg expends when climbing 250-300 meters. The performance of the heart increases during muscular activity, not only due to an increase in systolic ejection and an increase in heart rate, but also a greater acceleration of blood circulation, since the rate of systolic ejection increases by 4 times or more.
The increase and increase in the work of the heart and the narrowing of blood vessels during muscular work occurs reflexively due to irritation of the receptors of the skeletal muscles during their contractions.
People who lead an active lifestyle have a high chance of not being at risk of developing cardiovascular disease. Even the lightest exercises are effective: they have a good effect on blood circulation, reduce the level of deposits of cholesterol plaques on the walls of blood vessels, strengthen the heart muscle and maintain the elasticity of blood vessels. If the patient also adheres to a proper diet and at the same time exercises, then this is the best medicine to support the heart and blood vessels in great shape.What kind of physical activity can be used for people at high risk of developing heart disease?
Before starting training, patients of the "risk" group should consult with their doctor in order not to harm their health.
People suffering from the following diseases should avoid strenuous exercise and strenuous exercise:
- diabetes
- hypertension;
- angina pectoris
- ischemic heart disease;
- heart failure.
What effect does sport have on the heart?
Sports can affect the heart in different ways, both strengthen its muscles and lead to serious diseases. In the presence of cardiovascular pathologies, sometimes manifested in the form of chest pain, it is necessary to consult a cardiologist.It's no secret that athletes often suffer from heart disease due to influence big physical stress on the heart. That is why they are advised to include training before a serious load in the regime. This will serve as such a "warm-up" of the muscles of the heart, balance the pulse. In no case should you abruptly quit training, the heart is used to moderate loads, if they don’t, hypertrophy of the heart muscles can occur.
The influence of professions on the work of the heart
Conflicts, stress, lack of normal rest negatively affects the work of the heart. A list of professions that negatively affect the heart was compiled: athletes take the first place, politicians the second; the third is teachers.Professions can be divided into two groups according to their influence on the work of the most important organ - the heart:
- Professions are associated with an inactive lifestyle, physical activity is practically absent.
- Work with increased psycho-emotional and physical stress.
