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

Periodic fluctuations in pressure throughout the day are commonplace and depend on a number of factors. With constant monitoring of indicators blood pressure, measurement rules must be followed. The change in this indicator depends on the time of day, psychological state patient and age, so if the measurements are high, this may be due to the influence external factors and not because of illness.

How it changes blood pressure in humans within 24 hours?

A person does not always feel that the blood pressure value is too high, without realizing that a deviation has formed. Hypertension, if not properly treated, causes associated chronic diseases when symptoms become more active. Hypertension is diagnosed on early stages, if you periodically monitor the pressure values. Blood pressure readings during the day depend on many factors: body position during measurement, the person’s condition and time of day. In order for 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 body’s biorhythms adapt to them.

Blood pressure changes due to a number of factors:

Enter your pressure

Move the sliders

• the value increases 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 rests quietly, blood pressure drops.

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

Causes of strong surges in blood pressure

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

Reasons for changes in blood pressure in humans during the day:

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

Stress, fatigue, lack of sleep, worries and excessive loads At work - common reasons changes in blood pressure and hypertensive crises. This is typical for women - they are more emotional and unstable compared to men. Chronic stress, constant pressure surges over time provoke the development of the primary form of hypertension, which requires drug treatment.

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

The indicators can be affected by excitement, impatience, constipation or freezing in a standing position. 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 the person takes several deep breaths before taking the measurement.

In the evening the readings rise, and at night the pressure drops. This should be taken into account both when measuring and when taking antihypertensive medications.

Measuring and monitoring indicators

Daily blood pressure monitoring will help identify a hidden threat and select the right drug.

To receive exact values Blood pressure, you must adhere to certain measurement rules. Blood pressure fluctuates throughout the day, and in hypertensive patients these fluctuations are much higher. If necessary, blood pressure is monitored calm state, in motion, after physical or emotional stress. Measuring blood pressure at rest allows you to evaluate the effect on blood pressure medicines. It is better to monitor blood pressure on both arms, as the values ​​​​differ. 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 exercise.
• Take measurements while sitting or lying down, after relaxing for 5 minutes.
• In a sitting position, lean on the back of the chair, since holding your back on your own leads to slight increase HELL.
• If a person is lying down, the arm is located along the body, then a cushion is placed under the elbow so that the arm is at the level of the thoracic region.
• You cannot 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 slightly loosened.

Blood pressure and health

Among the many health problems experienced 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 types of high (low) blood pressure - true high blood pressure, which occurs even without a specific cause, for example, 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 problems associated with hypertension and is caused, in part, by congenital predisposition.
  If symptomatic high blood pressure occurs, it is necessary to be treated for the disease that caused it.
• Among the factors that cause high blood pressure are the consumption of too much large quantity salt, overeating, alcohol abuse, smoking, lack physical 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.

High 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. Blood pressure may become higher than usual if you are in a condition nervous tension or feel awkward, especially in the presence of a doctor. Sufferers should monitor daily changes in their blood pressure throughout the day and seek advice from a doctor.

Fluctuations in blood pressure

Blood pressure is constantly changing - You should not be too concerned or happy about the readings obtained from one or two measurements.
Blood pressure varies both during the day and throughout the month; it is influenced by the time of year and temperature. The graph below shows the increase and decrease in blood pressure over the course of a day.
If you want to measure blood pressure correctly, you should know that it changes along with atmospheric pressure even in healthy people both during the day and throughout short periods time depending on physical activity, emotional excitability, diet, not to mention the influence of medications taken, smoking and drinking alcohol. For example, many people's blood pressure may change due to anxiety associated with the procedure of measuring it. The difference in readings in healthy people fluctuates when the “upper” (systolic) pressure changes within a range of up to 30 mm Hg. Art. and “lower” (diastolic) within the range of up to 10 mm Hg. Art.
Please try to have a clear picture of your blood pressure. To do this, you need to take measurements regularly throughout the day and keep clear records of your results.

Blood pressure measurement and health monitoring

A person's blood pressure changes significantly throughout the day depending on his emotional and physical state.
If a measurement shows that blood pressure is high, this does not necessarily indicate that the person is sick.
It is very dangerous to worry or make assumptions about a person's health without having the necessary information and only having the results of one or two measurements.
Monitor changes in blood pressure when you 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 your doctor and consult with him. There is nothing surprising in the fact that in this way you can monitor your mental and physical state on a daily basis.

The relationship between blood pressure values ​​during “office” measurements and daily monitoring

Circadian rhythm of blood pressure

In healthy people

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

IN evening time Blood pressure usually decreases and reaches a minimum from 2.00 to 4.00 at night. Then 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 blood pressure reduction at night, patients are divided into four groups. The first group includes patients whose blood pressure curve at night has a bucket-shaped depression. Such patients are called “dipper” type hypertensives (from English dipper – “bucket, scoop”). If blood pressure does not fall sufficiently at night and the bucket-shaped depression on the blood pressure graph is small, then such patients are classified as a “non-dipper” group (second group). This condition is typical in some pathological conditions (secondary hypertension, severe primary arterial hypertension), in the elderly. Among patients in this group, there is a high risk of target organ damage (including strokes and heart attacks).

Patients with an excessive drop in blood pressure (a very large depression on the graph) are classified as a group called “over-dipper” or “hyper-dipper” (third group). In such patients there is greatest number cases of asymptomatic brain damage such as stroke.

If blood pressure readings at night exceed those during the day, 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 of conduct daily monitoring HELL

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

When measuring blood pressure, the arm with the cuff should be extended along the body and relaxed.

Intensive ones are excluded physical activity and exercise on the day of blood pressure monitoring.

If blood pressure measurement begins while walking, then you need to stop, lower your arm along your body and wait until the measurement is completed.

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 24-hour blood pressure monitoring.

At night, the patient should sleep and not think about the operation of the recording device, otherwise the values ​​of night 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.

Important to know!!!

Without pedantic keeping of a diary indicating time and type active actions, time of taking medications, duration of rest, deciphering the monitoring results is impossible!

Options for 24-hour blood pressure monitoring

Depending on the goals of researchers, several monitoring options are possible:

1) during normal working hours;

2) on weekends;

3) under moderate physical and psychological stress;

4) in a regime of sharply limited physical and psychological stress;

5) under the maximum possible physical and psychological stress.

DAILY VARIATIONS IN BLOOD PRESSURE
AND CHOICE OF OPTIMAL ANTIHYPERTENSIVE THERAPY

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

Daily, or circadian, fluctuations in blood pressure (BP) are a relatively little-studied physiological phenomenon that certain situations may play a role in causing fatal cardiovascular diseases. It is well known that the incidence of heart attacks, strokes and sudden cardiac death is highest in the morning hours, 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 daily blood pressure fluctuations, which is assessed using the method of non-invasive 24-hour blood pressure monitoring (ABPM). Therefore, consideration of methods for assessing circadian blood pressure fluctuations and their role in the selection of antihypertensive therapy deserves attention.

METHODS OF ASSESSMENT AND TYPES OF CIRCADIAN 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 therefore 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 sufficient high levels In AD, no organ lesions typical of hypertension were detected. At the same time, in many patients with hypertension, blood pressure levels increase both during the day and at night. Often, in patients with a “mild” increase in blood pressure during the day, it is “night” 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, specifically in morning time(from 6 to 12 am). Similar to the recognized method for assessing variability heart rate The attention of researchers is also drawn to the degree of daily 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 blood supply disorders to vital important organs and be an independent predictor of risk various complications AG. Required component diagnostic conclusion when carrying out ABPM is also the “daily blood pressure index” - a decrease in blood pressure expressed as a percentage in non-day active period days (during sleep) compared to the period of daytime activity. Normal this indicator is 10–20%.

According to the latest European recommendations on the diagnosis and treatment of hypertension (2003), the blood pressure level when measured in a doctor’s office is 140/90 mm Hg. Art. approximately corresponds to the average daily blood pressure level of 125/80 mm Hg. Art. The average blood pressure level during the active period of the day is higher than that during the inactive period. The recommendations of the Ukrainian Society of Cardiology (2004) suggest that intermediate 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 pattern of daily blood pressure fluctuations in patients with normo- and hypertension (Fig. 1):

• BP levels are highest after 10 a.m., peak at noon, and may plateau until 6 p.m.
• Most healthy individuals and patients with hypertension experience an increase in blood pressure immediately after waking up (approximately 6 a.m.) by 20/15 mmHg. Art.
• Late in the evening, blood pressure levels normally decrease by 10–20% compared to the active period (the “deeper” type profile, that is, optimal); The minimum blood pressure is recorded at approximately 3 am.

Rice. 1. Diagram of systolic blood pressure fluctuations over 24 hours in individuals with normal blood pressure (lower curve) and hypertension (upper curve). The period of maximum risk of cardiovascular events is highlighted by a rectangle, and the “non-deeper” profile (without adequate nighttime blood pressure reduction) is indicated by 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). Some patients with hypertension may experience the following features of the daily blood pressure profile:

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

Rice. 2. Graphic representation of ABPM results and changes in heart rate (dashed line below) in patient K., 56 years old. The abscissa axis reflects the time of day, the ordinate axis shows blood pressure levels and heart rate. Daily blood pressure profile of the “diper” type (daily blood pressure index 15/19 mm Hg) with a persistent increase in blood pressure of the 2nd–3rd degree, pronounced fluctuations in systolic blood pressure (SD 17/12 mm Hg) and a significant increase in blood pressure 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 the pronounced morning rise in blood pressure.

There is still no consensus on the normal amplitude of blood pressure fluctuations throughout the day. The recommendations of the Russian Cardiology Research 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 blood pressure fluctuations (SD): for systolic blood pressure - 15 mm Hg. Art. in active and 15 mm Hg. Art. - during the inactive period of the day, for diastolic blood pressure - 14 and 12 mm Hg, respectively. Art. If any of these four indicators increases, a conclusion is made about excessive fluctuations in blood pressure. In this case, it is especially important to select antihypertensive drugs with a long-lasting and persistent pharmacological effect.

In addition to lifestyle, the pattern of daily blood pressure fluctuations depends on many factors, such as age, gender and ethnicity. For example, the nocturnal decrease in blood pressure is less pronounced in older people, men, and black patients. In addition, insufficient reduction of 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 CIRCADIAN FLUCTUATIONS IN BP 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 daily fluctuations in hemodynamic parameters decreases with age. Previous results suggest that the use of exogenous melatonin contributes to some extent to lower blood pressure levels.

More convincing are the data regarding 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 simultaneously. This is not strange, since stimulation of adrenergic receptors in the kidneys promotes the synthesis of renin. At the same time, the modulator of the secretion of some hormonal substances may actually be changes in blood pressure. Obviously, the peak activity of renin is observed around 8 am, angiotensin II and aldosterone - somewhat later. It is also known that fluctuations in renin activity occur during sleep, with maximum levels being reached during the slow-wave sleep phase. However, the significance of circadian changes in these parameters in the pathogenesis of essential hypertension has not been fully established. Obviously, the morning peak in 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 EFFECTIVENESS OF ANTIHYPERTENSIVE DRUGS

Existing ideas about circadianity and the degree of daily 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 during the passive period of the day and the morning risk hours 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 levels during sleep. In patients with daily blood pressure profiles of the “non-deeper” and “night-peaker” types, to achieve this goal, the blood pressure level should be selectively corrected at night.
• Another goal of antihypertensive therapy is to prevent excessive increases in blood pressure in the morning. Therefore, the key property of an optimal antihypertensive drug may be the long-term preservation of the antihypertensive effect, which makes it possible to “override” the morning hours with a single morning or evening dose of medication. It is this aspect of pharmacotherapy for hypertension that has become the main driving force for the development of many modern long-acting drugs.
• In patients with a persistent increase in blood pressure throughout the day (Fig. 3), the goal of treatment is not only to reduce average blood pressure values, 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. Graphic representation of ABPM results in patient B., 44 years old. Daily blood pressure profile of the “non-deeper” type (daily blood pressure index 9/5 mm Hg) with a persistent increase in blood pressure of the 3rd degree and normal fluctuations in systolic blood pressure (SD 13 /9 mmHg). These features indicate a high probability of symptomatic hypertension.

One of the most important characteristics of modern antihypertensive drugs is maintaining their concentrations in the blood 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 medications may last until your next dose. But at the same time, at the peak concentration of the drug, an excessive decrease in blood pressure levels may be observed. In order to assess fluctuations in 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 optimally should exceed 50–60%.

A high T/R ratio indicates a long-lasting 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 “withdrawal syndrome” in case of accidental missing the next dose. In addition, an adequate level of T/P 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/R 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 treating hypertensive crises, but with long-term maintenance therapy they can even increase the amplitude of blood pressure fluctuations. At the same time, 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 makes patients less willing to undergo long-term treatment of hypertension compared to a single dose.

To date, there is insufficient research on the effectiveness of hypertension treatment depending on the daily blood pressure profile. 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 blood pressure control over 24 hours. However, their use does not always prevent the morning rise in blood pressure. Most often, single-dose antihypertensive drugs 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, which combine drugs with varying durations of hypotensive effect in adequate doses. As a rule, such combination drugs contain a diuretic component, which induces more persistent vasodilation, potentiates the effect of drugs from other groups and contributes to a longer preservation of the 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, taking into account the mechanisms of circadian blood pressure fluctuations.
• Do not limit yourself to taking medications once a day and prescribe another drug to be taken late in the evening in order to reliably control blood pressure after 6-8 hours, that is, early in the morning. For example, if Enap-HL (10 mg enalapril + 12.5 mg hydrochlorothiazide) was taken in the morning, you can add a calcium antagonist (amlodipine) or an alpha-blocker (doxazosin) in the evening. This approach is especially indicated for patients with daily blood pressure profiles of the “non-deeper” or “night-peaker” type. Note that fixed combinations of antihypertensive drugs containing a diuretic 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 lowering blood pressure is partially achieved when taking the drug Enap-HL, it is advisable not to double the dose of both components of the combination by prescribing a 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 stage 2 or 3 hypertension and an optimal daily blood pressure 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 forms of drugs that can be administered once a day, with a slow release of the active substance, or choose drugs with a high T/R ratio. 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, when using telmisartan, which is considered a promising drug that prevents morning increases in blood pressure). Note that this approach is not always advisable in patients with a daily blood pressure profile of the “hyper-deep” type, since it may lead to an excessive decrease in blood pressure levels at night.

Thus, the nature and amplitude of circadian blood pressure fluctuations 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 during certain periods of the day.

Blood pressure is a fairly important criterion for the vital functions 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 readings make it possible to notice the development of various critical conditions in time and stop them. There are several options for determining blood pressure levels. Thus, arterial oscillography is used for long-term recording of blood pressure levels. It allows you to see fluctuations in blood pressure of 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 records three types of blood pressure fluctuations:

Systolic waves of the first order;
- respiratory waves of the 2nd order;
- vascular waves of the third order.

1st order pressure fluctuations

These indicators are determined by the systole (contraction) of the ventricles of the heart. During the period of expulsion of blood from the cardiac ventricles, an increase in pressure is observed in the aorta, as well as in the pulmonary artery. It rises and reaches a maximum level of 140 and 40 mmHg. This pressure is maximum or systolic, it is recorded by the letter combination DM.

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

The difference between systolic and diastolic pressure is the pulse pressure, which is what ensures the appearance of the systolic wave (first-order wave) on the kymogram. Usually the pulse pressure is 30-40 mmHg. 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 the level of pulse pressure will be.

Pulse pressure reaches its maximum value 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 metabolic processes that occur between the blood passing through the capillaries and the tissues surrounding them.

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

Blood pressure fluctuations of 2 orders

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

Each wave of the 2nd order consists of several waves of the 1st 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 circle. This is explained by an increase in the capacity of the pulmonary vessels, as well as a slight decrease in their resistance to blood flow, and a greater 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 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 intestines and liver.

The described mechanisms create conditions for storing blood in the pulmonary vessels and reducing the volume of its release 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 increases.

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

In addition, fluctuations in blood flow volumes can also secondary provoke an increase or decrease in blood pressure, as vascular reflexogenic zones are activated.
Blood pressure fluctuations of 3 orders

As for waves of the 3rd order, they represent an even slower increase and decrease in pressure indicators. Each of them covers several respiratory waves of the 2nd order. Such fluctuations arise due to periodic changes in the tone of the vasomotor centers. Waves of the third order often appear due to insufficient oxygen supply to the brain (high-altitude hypoxia), after blood loss or poisoning by several poisons.

Thus, measuring 1st, 2nd and 3rd order blood pressure fluctuations is sometimes an important diagnostic procedure necessary for identifying and treating various pathological conditions associated with the activity of the cardiovascular system.