Changes in blood pressure during the day. Daily rhythms of the cardiovascular and respiratory systems

Periodic fluctuations in pressure during the day is a common occurrence, depending on a number of factors. With constant monitoring of indicators blood pressure, you must follow the rules of measurement. The change in this indicator depends on the time of day, psychological state patient and age, so if the measurements are high, it may have happened under the influence external factors and not because of illness.

How is it changing human blood pressure within 24 hours?

A person does not always feel that the value of blood pressure is overestimated, not knowing about the formation of a deviation. Hypertension in the absence of proper treatment causes concomitant chronic diseases when the symptoms are more active. Hypertension is diagnosed on early stages if the pressure values ​​are periodically monitored. Blood pressure indicators during the day depend on many factors: the position of the body during the measurement, the state of the person and the time of day. In order for the measurements to be as accurate as possible, they are made at the same time of day, in a familiar environment. If the conditions are similar every day, the biorhythms of the body adapt to them.

Blood pressure changes due to a number of factors:

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• the value rises in the morning when the patient is in a horizontal position;
• during the day the pressure drops;
• in the evening the values ​​increase;
• at night, when a person is calmly resting, the pressure drops.

This explains why measurements must be taken at the same time, and it is pointless to compare morning and evening numbers. Sometimes there is an increase in pressure when measured in a hospital or clinic. This is due to nervousness, fear or stress in front of the “white coats”, and as a result, the pressure rises slightly.

Causes of strong jumps in blood pressure

Blood pressure is the most important indicator health, which reflects the work of the cardiovascular system.

Causes of blood pressure drops in a person during the day:

• excessive consumption of coffee, tea, alcohol;
• vegetative-vascular dystonia;
• overwork, stress;
• endocrine disorders;
• climate or weather change;
• pathology of the cervical vertebrae.

Stress, fatigue, lack of sleep, worries and excessive loads At work - common causes BP fluctuations and hypertensive crises. This is typical for women - more emotional and unstable compared to men. chronic stress, constant pressure surges over time provoke the development of a primary form of hypertension, which requires medical treatment.

Changes from endocrine system also cause BP fluctuations. Women are especially susceptible to this before menopause or menstruation. In the second part of the cycle, fluid in the body is retained, and excessive emotionality, characteristic of this period, also contributes to an increase in pressure. Unstable pressure arises as a result pathological changes in the adrenal glands.

Excitement, impatience, constipation or freezing in a standing position can affect the performance. The readings increase if the person needs to urinate or when the room is cold. Often the value is distorted under the influence of electromagnetic fields, so it is not recommended to keep the phone near the tonometer. The pressure should stabilize if a person takes a few deep breaths before measuring.

By evening, the indicators increase, and at night the pressure decreases. This should be taken into account both when measuring and when taking antihypertensive drugs.

Measuring and monitoring indicators

24-hour blood pressure monitoring will help identify a hidden threat, select the right drug.

For getting exact values Blood pressure, it is necessary to adhere to certain measurement rules. Blood pressure fluctuates throughout the day, and in hypertensive patients these differences are much higher. If necessary, blood pressure is monitored in calm state, in motion, after physical or emotional stress. Measurement of blood pressure at rest allows you to evaluate the effect on blood pressure medicines. Blood pressure is better controlled on both arms, as the values ​​​​are different. It is better to measure on the hand where the indicators are higher.

Conditions necessary to obtain the most accurate results:

• Half an hour before the measurement, do not eat, do not smoke, do not be exposed to hypothermia and do not play sports.
• Measurements should be made sitting or lying down, having previously relaxed for 5 minutes.
• In a sitting position, lean on the back of a chair, as self-holding the back leads to a slight increase HELL.
• If a person lies, the arm is located along the body, then a roller is placed under the elbow so that the arm is at the level of the thoracic region.
• Do not speak or move while taking measurements.
• When taking a series of measurements, pause between measurements for 15 seconds or longer, optimally - 1 minute.
• Between measurements, the cuff is loosened slightly.

Blood pressure and health

Among the many health problems faced by modern man, most often he faces problems related to blood pressure. It is widely known that high blood pressure causes diseases such as cerebral hemorrhage or heart disease. Deviations in blood pressure from the norm cause numerous diseases and complications.

High and low blood pressure

• There are two varieties of high (low) blood pressure - true high blood pressure, which occurs even without a specific cause, such as another disease, etc., and symptomatic high blood pressure, which is a consequence of diseases such as kidney disease, disorders metabolism, etc. True high blood pressure is responsible for more than 90% of the problems associated with hypertension, and is caused, in part, by a congenital predisposition.
  If there is symptomatic high blood pressure, it is necessary to treat the disease that caused it.
• Among the factors that cause high blood pressure are the use of too much a large number salt, overeating, alcohol abuse, smoking, lack of exercise, obesity, overwork and stress.
  It is important to take care of your health by regularly measuring your blood pressure with a blood pressure monitor and following the recommendations above.

Increased blood pressure caused by nervous tension

It is possible that the results of measuring blood pressure at home will differ significantly from those obtained in the presence of a doctor. Your blood pressure may become higher than usual if you are nervous tension or feel embarrassed, especially in the presence of a doctor. Those who suffer from this should monitor daily changes in their blood pressure during the day and seek the advice of a doctor.

fluctuations in blood pressure

Blood pressure is constantly changing - you should not be too worried or pleased with the readings obtained as a result of one or two measurements.
Blood pressure changes both during the day and during the month; it is affected by the time of year and temperature. The graph below shows the increase and decrease in blood pressure during the day.
If you want to measure blood pressure correctly, you should know that it changes with atmospheric pressure even in healthy people both during the day and throughout short intervals time depending on physical activity, emotional excitability, on the diet, not to mention the influence of medications taken, smoking and drinking alcohol. For example, for many, pressure can change due to the excitement associated with the very procedure for measuring it. The difference in readings in healthy people fluctuates with a change in the "upper" (systolic) pressure within the range of up to 30 mm Hg. Art. and "lower" (diastolic) up to 10 mm Hg. Art.
Please try to get a clear picture of your blood pressure. To do this, you need to make regular measurements throughout the day and keep clear records of the results.

Blood pressure measurement and health monitoring

A person's blood pressure changes significantly during the day, depending on his emotional and physical state.
If the measurement showed that the blood pressure is elevated, this does not necessarily indicate that the person is sick.
It is very dangerous to worry or draw conclusions about the state of a person's health without having the necessary information and having only the results of one or two measurements.
Monitor changes in blood pressure when your Everyday life events occur and try to find out when your blood pressure rises and/or falls. This is much more important than knowing your baseline blood pressure. Show the notes to the doctor and consult with him. There is nothing surprising in the fact that in this way you can monitor your mental and physical condition on a daily basis.

The ratio of blood pressure values ​​during "office" measurement and daily monitoring

circadian rhythm BP

In healthy people

The daily rhythm is characterized by two daily maxima: the first - from 9.00 to 11.00 and the second - from 18.00 to 19.00. Between these two peaks there is a plateau.

IN evening time Blood pressure usually decreases and reaches a minimum from 2.00 to 4.00 at night. Then the blood pressure begins to rise, and the rate of increase is maximum from 6.00 to 8.00 in the morning.

In hypertensive patients

According to the degree of decrease in blood pressure at night, patients are divided into four groups. The first group includes patients in whom the BP curve at night has a bucket-shaped depression. Such patients are called "dipper" hypertensives (from English dipper - "bucket, ladle"). If the blood pressure falls insufficiently at night and the bucket-like depression on the blood pressure graph is small, then such patients are referred to the “non-dipper” group (second group). This condition is typical for some pathological conditions (secondary hypertension, severe primary arterial hypertension), in the elderly. Among patients in this group, the risk of target organ damage (including strokes and heart attacks) is high.

Patients with an excessive drop in blood pressure (a very large depression in the graph) are classified as a group called "over-dipper" or "hyper-dipper" (third group). In such patients, there is largest number cases of asymptomatic brain lesions of the type of stroke.

If the blood pressure at night exceeds the daytime, then such patients are called "night-peaker". This is the most severe patients with the most high risk development of complications arterial hypertension, they form the fourth group.

Patient instruction, or rules for conducting daily monitoring HELL

During daily monitoring, it is necessary to follow certain rules, which significantly increases diagnostic value research and minimizes the number of erroneous measurements.

During the measurement of blood pressure, the arm with the cuff should be extended along the body and relaxed.

Intensive are excluded physical exercise and exercise on the day of BP monitoring.

If the measurement of blood pressure begins while walking, then you need to stop, lower your hand along the body and wait for the measurement to end.

The patient is not allowed to look at the readings of the device, as this provokes an alarming reaction in him, which can lead to distortion of the results and neutralize the main advantage of daily monitoring of blood pressure.

At night, the patient should sleep, and not think about the operation of the recording device, otherwise the values ​​​​of nighttime blood pressure will be unreliable.

During monitoring, it is necessary to keep a detailed diary in which the patient must reflect his actions and well-being.

It is important to know!!!

Without pedantic journaling with time and type active action, the time of taking medications, the duration of rest, it is impossible to decipher the results of monitoring!

Ambulatory blood pressure monitoring options

Depending on the goals that researchers face, several options for monitoring are possible:

1) during normal business hours;

2) in the weekend mode;

3) in the mode of moderate physical and psychological stress;

4) in the mode of sharply limited physical and psychological stress;

5) in the mode of the maximum possible physical and psychological stress.

DAILY VARIATIONS OF ARTERIAL PRESSURE
AND THE CHOICE OF THE OPTIMAL ANTIHYPERTENSIVE THERAPY

OH. Zharinov
National medical Academy postgraduate education them. P.L. shupika,
Department of Cardiology and Functional Diagnostics

Diurnal, or circadian fluctuations in blood pressure (BP) is a relatively little-studied physiological phenomenon, which in certain situations may play a role in the occurrence of fatal cardiovascular disease. It is well known that the incidence of heart attacks, strokes, and sudden cardiac death is highest in the morning, when blood pressure levels are highest. It is also assumed that a separate risk factor for complications of arterial hypertension (AH) may be the amplitude of diurnal fluctuations in blood pressure, which is assessed by the method of non-invasive 24-hour blood pressure monitoring (ABPM). Therefore, the consideration of methods for assessing circadian fluctuations in blood pressure and their role in the choice of antihypertensive therapy deserves attention.

METHODS OF ASSESSMENT AND TYPES OF CIRCADAL CHANGES IN BP

Implementation in clinical practice The ABPM method made it possible to record and evaluate changes in blood pressure over long periods of time, and, consequently, to deepen the understanding of many aspects of the risk of complications of hypertension and ways of differentiated selection of therapy. First of all, it was possible to prove the presence of “white collar hypertension” and find out why many patients with registered during a polyclinic examination have enough high levels BP did not reveal any organ lesions typical of AH. At the same time, in many patients with hypertension, the level of blood pressure rises both during the day and at night. Often, in patients with a “mild” increase in blood pressure during the daytime, it is “nighttime” hypertension that is a risk factor for severe organ damage, in particular, LV hypertrophy. On the other hand, a noticeable morning increase in blood pressure leads to an increase in the frequency acute complications hypertension, including myocardial infarction and stroke, morning time(from 6 am to 12 am). By analogy with the recognized method of estimating variability heart rate the attention of researchers is also attracted by the degree of diurnal fluctuations in blood pressure (SD), calculated using standard methods of variation statistics. Reflecting the amplitude of blood pressure fluctuations throughout the day from the average level, it may indicate the severity of circulatory disorders in vital important organs and be an independent risk predictor various complications AG. Mandatory component The diagnostic conclusion during ABPM is also the “daily blood pressure index” - a decrease in blood pressure expressed as a percentage in active period days (during sleep) compared to the period of daytime activity. Fine this indicator is 10–20%.

According to the latest European recommendations on the diagnosis and treatment of hypertension (2003) blood pressure level when measured in the doctor's office 140/90 mm Hg. Art. approximately corresponds to the average daily level of blood pressure 125/80 mm Hg. Art. The average level of blood pressure during the active period of the day is higher than that during inactive time. In the recommendations of the Ukrainian Society of Cardiology (2004), it is proposed to consider average level BP during the day<135/80 мм рт. ст., ночью <120/75 мм рт. ст. Следовательно, пограничные уровни АД в разные периоды суток отличаются. А это следует учитывать при программировании устройств для СМАД и интерпретации полученных результатов.

Studies conducted using the ABPM method indicate a similar nature of daily fluctuations in blood pressure in patients with normo- and hypertension (Fig. 1):

• BP levels are highest after 10 am, peak at noon, and may plateau until 6 pm.
• Most healthy individuals and patients with hypertension experience an increase in blood pressure immediately after waking up (approximately 6 a.m.) by 20/15 mm Hg. Art.
• Late in the evening, the level of blood pressure normally decreases by 10-20% compared to the active period (profile of the “diper” type, that is, optimal); the minimum arterial pressure is registered approximately at 3 o'clock in the morning.

Rice. 1. Scheme of fluctuations in systolic blood pressure over 24 hours in individuals with normal levels of blood pressure (lower curve) and arterial hypertension (upper curve). The period of maximum risk of cardiovascular events is marked with a rectangle, the non-deeper profile (without an adequate nighttime decrease in blood pressure) is marked with a dotted line.

The nature of daily fluctuations in blood pressure depends on the duration and timing of the active period of the day, the level of physical activity and anxiety (for example, with white-collar hypertension). In some patients with hypertension, the following features of the daily blood pressure profile may be observed:

• The absence of a nighttime decrease in blood pressure with a decrease of 0–10% (a “non-deep” profile, that is, an insufficient decrease in blood pressure) or even an increase in blood pressure in the passive period (a “night-picker” profile, that is, an increase in blood pressure at night). These types of diurnal BP fluctuations are associated with an increased risk of target organ damage (left ventricular hypertrophy, microalbuminuria) and cardiovascular events (hemorrhagic stroke).
• Decrease in blood pressure by more than 20% at night (hyper-deeper profile, i.e. excessive decrease in blood pressure). It is assumed that this type of circadian BP profile may be accompanied by an increased risk of ischemic stroke.
• Excessive morning increase in blood pressure (relative to the rate of growth and the achieved level of blood pressure) (Fig. 2). When choosing the optimal antihypertensive therapy, one should take into account the fact that the daily profile of BP of the “hyper-deep” type can be due to both an excessive decrease in BP at night and a significant increase in BP in the morning.

Rice. 2. Graphic representation of the results of ABPM and changes in heart rate (dashed line at the bottom) in patient K., 56 years old. The abscissa axis reflects the time of day, the ordinate axis - blood pressure levels and heart rate. Diurnal BP profile of the “diper” type (daily BP index 15/19 mm Hg) with a persistent increase in BP of the 2nd or 3rd degree, pronounced fluctuations in systolic BP (SD 17/12 mm Hg) and a significant increase in BP in the morning hours. In addition to the use of drugs with a persistent and powerful antihypertensive effect (probably fixed combinations), in this case, it is necessary to correct a pronounced morning rise in blood pressure.

So far, there is no consensus on the normal amplitude of blood pressure fluctuations throughout the day. The recommendations of the Russian Cardiology Scientific and Production Complex of the Ministry of Health of the Russian Federation, based on a large number of examinations of healthy individuals, indicate the following approximate figures for fluctuations in blood pressure (SD): for systolic blood pressure - 15 mm Hg. Art. in active and 15 mm Hg. Art. - in the inactive period of the day, for diastolic blood pressure - respectively 14 and 12 mm Hg. Art. With an increase in any of these four indicators, a conclusion is made about excessive fluctuations in blood pressure. In this case, it is especially important to select antihypertensive agents with a long and persistent pharmacological action.

In addition to lifestyle, the nature of daily fluctuations in blood pressure depends on many factors, such as age, gender and ethnicity. For example, the nighttime decrease in blood pressure is less pronounced in the elderly, men, black patients. In addition, an insufficient decrease in blood pressure at night is observed in many pathological conditions and diseases, for example, symptomatic hypertension (renovascular hypertension, primary aldosteronism, Cushing's syndrome, pheochromocytoma), obesity, diabetes mellitus, sleep disorders.

MECHANISMS OF CIRCADIAL OSCILLATIONS OF HELL LEVEL

The main “regulator” of circadian rhythms in the human body is located in the suprachiasmatic nucleus of the anterior hypothalamus, and the most important endocrine “messenger” is the pituitary hormone melatonin. Along with a decrease in melatonin levels, the amplitude of diurnal fluctuations in hemodynamic parameters decreases with age. Previous results suggest that the use of exogenous melatonin contributes to some extent to lowering blood pressure.

More convincing are the data on the role of the autonomic nervous system, as well as the renin-angiotensin-aldosterone system in the circadian levels of hemodynamic parameters. In particular, the activity of sympathetic impulses and the level of catecholamines increase at the moment of awakening or immediately after it, while the activity of the parasympathetic nervous system changes, on the contrary, with a peak at night. Changes in the activity of the renin-angiotensin and sympathetic nervous systems occur almost in parallel. This is not strange, since the excitation of adrenergic receptors in the kidneys promotes the synthesis of renin. At the same time, the modulator of the secretion of certain hormonal substances can be the actual changes in blood pressure. Obviously, the peak of renin activity is observed at about 8 am, angiotensin II and aldosterone - somewhat later. It is also known that fluctuations in renin activity are observed during sleep, with maximum levels being reached during non-REM sleep. However, the significance of circadian changes in these parameters in the pathogenesis of essential hypertension has not been fully established. Obviously, the morning peak of the risk of hypertension complications is also due to an increase in the activity of other neurohumoral substances (adrenocorticotropic hormone, cortisol, natriuretic peptides, opioids, endothelins), blood clotting factors, platelet activation and suppression of fibrinolysis. These mechanisms may be important specific targets for the prevention of cardiovascular complications of hypertension.

DAILY VARIATIONS IN THE EFFICACY OF ANTIHYPERTENSIVE MEDICINES

Existing ideas about the circadian pattern and the degree of diurnal fluctuations in blood pressure make it possible to substantiate some approaches to the differentiated selection of antihypertensive drugs. First of all, the need to take into account blood pressure levels in the passive period of the day and the morning hours of risk is obvious:

• The significant role of nocturnal blood pressure as a risk factor for severe complications of hypertension indicates the importance of normalizing blood pressure during sleep. In patients with non-deeper and night-picker circadian BP profiles, selective nighttime BP control should be used to achieve this goal.
• Another goal of antihypertensive therapy is to prevent an excessive increase in blood pressure in the morning. Therefore, the key property of the optimal antihypertensive drug may be the long-term preservation of the antihypertensive effect, which allows you to “block” the morning hours with a single morning or evening medication. It is this aspect of the pharmacotherapy of hypertension that has become the main leitmotif for the development of many modern drugs with prolonged action.
• In patients with a persistent increase in blood pressure throughout the day (Fig. 3), the goal of treatment is not only to reduce the average blood pressure, but also to restore the optimal daily blood pressure profile. Obviously, to solve this problem, specific “chronotherapeutic” approaches are needed to determine the optimal time for taking antihypertensive drugs.

Rice. 3. Graphical representation of the results of ABPM in patient B., 44 years old. Daily BP profile of the “non-deep” type (daily BP index 9/5 mmHg) with a persistent increase in BP of the 3rd degree and normal fluctuations in systolic BP (SD 13 /9 mmHg). These features indicate a high likelihood of symptomatic hypertension.

One of the most important characteristics of modern antihypertensive drugs is the maintenance of their blood concentrations and the effect of lowering blood pressure at the end of the interdose interval, that is, before taking the next dose. Many of the common short-acting drugs can work until the next dose. But at the same time, at the peak of the concentration of the drug, an excessive decrease in the level of blood pressure can be observed. In order to assess the fluctuation of the antihypertensive effect and avoid prescribing medications in high doses, a standard was introduced - the so-called minimum / maximum action ratio (trough / peak, T / P), which in the optimal case should exceed 50-60%.

A high T/P ratio indicates a long-term and persistent antihypertensive effect of the drug, which leads to a more favorable benefit / risk ratio in long-term treatment of hypertension compared to short-acting drugs, provides an effect throughout the day with a single dose and avoids the “withdrawal syndrome” in case of accidental skipping another dose. In addition, an adequate level of the T / P index helps to reduce the number of side effects of antihypertensive drugs and increase patient adherence to treatment. At the same time, drugs with a T / P ratio of up to 50%, that is, significant fluctuations in the effect of lowering blood pressure (for example, nifedipine and captopril), fully meet the needs of the treatment of hypertensive crises, however, with long-term maintenance therapy, they can even increase the amplitude of blood pressure fluctuations. In this case, the blood supply to vital organs often and significantly changes, and the undesirable effects of therapy may even outweigh the risk. Given the limited time to maintain the effect of lowering blood pressure, these drugs should be prescribed at least 3 times a day. In turn, this worsens the disposition of patients to long-term treatment of hypertension compared with a single dose.

To date, studies on the effectiveness of the treatment of hypertension depending on the daily profile of blood pressure are not enough. It is known that all groups of first-line antihypertensive drugs (diuretics, beta-blockers, calcium antagonists, angiotensin-converting enzyme inhibitors, angiotensin II receptor antagonists) include drugs that provide mild and stable control of blood pressure for 24 hours. However, their use does not always prevent the morning rise in blood pressure. Most often, antihypertensive drugs for a single dose are prescribed in the morning. The problem is that 24 hours after taking such drugs, the residual effect of lowering blood pressure remains, while for effective prevention of complications in the morning at this time of day, it is desirable to achieve the maximum antihypertensive effect of therapy. In clinical practice, various methods are used to solve the described problem:

• Prescribe fixed combinations of antihypertensive drugs that combine drugs with different duration of hypotensive effect in adequate doses. As a rule, such combined preparations contain a diuretic component that induces more stable vasodilation, potentiates the effect of drugs from other groups and contributes to a longer pharmacological effect. In Ukraine, fixed combinations of angiotensin-converting enzyme inhibitors or beta-blockers with diuretics are most often used. Note that the inclusion of neurohumoral modulators in antihypertensive therapy regimens is justified, given the mechanisms of circadian BP fluctuations.
• Go beyond once-daily medication and give another late-night drug to achieve reliable BP control 6-8 hours later, i.e. early in the morning. For example, if Enap-HL (10 mg enalapril + 12.5 mg hydrochlorothiazide) was taken in the morning, a calcium antagonist (amlodipine) or an alpha-blocker (doxazosin) can be added in the evening. This approach is particularly indicated for patients with diurnal non-deeper or night-picker BP profiles. Note that fixed combinations of diuretic-containing antihypertensive agents are usually prescribed in the morning, often before breakfast.
• Increase the dose of the non-diuretic component of the fixed combination. For example, if the effect of reducing blood pressure is partially achieved when taking Enap-HL, it is advisable not to double the dose of both components of the combination by prescribing the second Enap-HL tablet in the evening, but to increase only the dose of enalapril by switching to Enap 20-HL (20 mg enalapril + 12 .5 mg hydrochlorothiazide). This approach can be applied to many patients with 2nd or 3rd degree AH and an optimal 24-hour BP profile. Due to the fact that Enap-HL contains a therapeutic dose of hydrochlorothiazide (12.5 mg), increasing the dose of the diuretic component is not advisable. In addition, the use of a diuretic in the evening is not justified, including as a component of a fixed combination.
• Use once-daily, sustained-release formulations, or choose high T/P ratios. This route meets the requirements for the management of most patients with persistent hypertension, but is associated with a certain increase in treatment costs (for example, with the use of telmisartan, which is considered a promising drug to prevent morning BP increase). It should be noted that this approach is not always appropriate in patients with a diurnal BP profile of the “hyper-diper” type, since it may lead to an excessive decrease in BP levels at night.

Thus, the nature and amplitude of circadian fluctuations in blood pressure is a determining risk factor for many complications of hypertension. An informative method for clinical assessment of blood pressure fluctuations throughout the day is the ABPM method. Adequate selection of antihypertensive therapy should be carried out taking into account circadian fluctuations in blood pressure and may include selective correction of blood pressure levels at certain periods of the day.

Blood pressure is a rather important criterion for the vital activity of the body, because this indicator depends on the activity of many organs and can indicate a variety of disorders in their functioning. Sometimes blood pressure indicators allow you to notice the development of various critical conditions in time and stop them. There are several options for determining the level of blood pressure. So, arterial oscillography is used for long-term recording of blood pressure levels. It allows you to see fluctuations in blood pressure 1, 2, 3 orders.

Arterial oscillography allows you to graphically display the pulsations of large arteries when they are compressed by a cuff. This method captures three types of blood pressure fluctuations:

Systolic waves of the 1st order;
- respiratory waves of the II order;
- vascular waves of the III order.

Pressure fluctuations of the 1st order

These indicators are due to systole (contraction) of the ventricles of the heart. During the period of expulsion of blood from the cardiac ventricles, there is an increase in pressure in the aorta, as well as in the pulmonary artery. It rises and reaches a maximum mark - 140 and 40 mm Hg. This pressure is maximum or systolic, it is fixed by the letter combination SD.

During diastole (expansion of the cavities of the heart), the heart does not receive blood from the arterial system, only its outflow from the large arteries to the region of the capillaries occurs. Accordingly, at this moment, the pressure in the arteries decreases to a minimum, it is classified as minimal or diastolic, and is denoted by the letter combination DD. The level of this indicator largely depends on the lumen and vascular tone, and on average is 60-80 mm Hg.

The difference between the indicators of systolic and diastolic pressure is the pulse pressure, it is it that provides the appearance of a systolic wave (wave of the first order) on a kymogram. Usually the pulse pressure is 30-40mm Hg. This indicator is directly proportional to the stroke volume of the heart and indicates the strength of heart contractions, because the more blood the heart sends into systole, the greater will be the level of pulse pressure.

The maximum value of pulse pressure reaches in the vessels that are located near the heart, namely, in the aorta, as well as in large arteries. In small arteries, the interval between systolic and diastolic pressure is somewhat smoothed out, and in arterioles (as in capillaries), the pressure is constant and does not depend on systole and diastole. This feature of the body is important for the stability of the metabolic processes that occur between the blood passing through the capillaries and the tissues surrounding them.

The number of waves of the first order is equal to the heart rate (heart rate).

Arterial pressure fluctuations of the 2nd order

These are respiratory waves that reflect fluctuations in blood pressure associated with respiratory function. Their number is equal to the number of respiratory movements.

Each wave of the second order consists of several waves of the first order. They have a rather complex mechanism of occurrence: during inhalation, optimal conditions are created in our body to ensure the flow of blood from the systemic circulation into the small one. This is due to an increase in the capacity of the pulmonary vessels, as well as a slight decrease in their resistance to blood flow, a large flow of blood from the right ventricle of the heart to the lungs. In addition, this is facilitated by the presence of a pressure difference between the vessels in the abdominal cavity and the chest, this difference occurs when the negative pressure inside the pleural cavity increases and when the diaphragm lowers and squeezes out blood from the venous vessels in the intestine and liver.

The described mechanisms create conditions for storing blood in the pulmonary vessels and for reducing the volume of its exit from the lungs into the left half of the heart. Thus, at maximum inspiration, there is a decrease in blood flow to the heart and a natural decrease in blood pressure. And closer to the end of exhalation, blood pressure indicators increase.

These are mechanical factors that explain the formation of waves of the second order. But they also depend on nervous factors. Thus, a change in the activity of the respiratory center, which is observed during inspiration, leads to an increase in the activity of the vasomotor center, which increases the tone of the vessels in the systemic circulation.

In addition, fluctuations in blood flow volumes are also able to provoke a second increase or decrease in blood pressure, since vascular reflexogenic zones are activated.
Arterial pressure fluctuations of the 3rd order

As for the third-order waves, they represent an even slower increase and decrease in pressure indicators. Each of them covers several respiratory waves of the second order. Such fluctuations arise due to periodic changes in the tone of the vasomotor centers. Waves of the ІІІ order often appear due to insufficient supply of oxygen to the brain (altitude hypoxia), after suffering blood loss or poisoning with several poisons.

Thus, the measurement of blood pressure fluctuations of the 1st, 2nd and 3rd order is sometimes an important diagnostic manipulation necessary for the detection and treatment of various pathological conditions associated with the activity of the cardiovascular system.