The oscillometric method of measuring blood pressure has disadvantages. Methods for measuring blood pressure: advantages and disadvantages

The diagnosis of arterial hypertension is made based on the results obtained from repeated blood pressure measurements. With a persistent increase in its indicators, there is a risk of developing a heart attack or stroke. To avoid such consequences, it is very important to monitor your condition using existing methods of measuring pressure.

The standard site for measuring blood pressure is the brachial artery. But when using devices to determine its indicators on the wrist and fingers, it is important to understand that systolic and diastolic pressure vary significantly in different parts of the arterial tree. Therefore, all existing methods remain relevant today.

Oscillometric measurement method

To monitor blood pressure at home, the patient must measure it with a tonometer several times a day. The obtained values ​​must be recorded for further transmission to the doctor during treatment. Automatic or electronic blood pressure monitors are especially popular. Their work is carried out according to the principle of the oscillometric method. This technology involves placing a device cuff on the patient's upper limb. The most effective method of measuring blood pressure on the shoulder is considered.

The principle of the oscillometric method is to process human pressure fluctuations in the cuff of a special device. Its indicators can be determined by the passage of blood through the compressed area of ​​the artery, resulting in pulsation. This requires the use of a sphygmomanometric cuff with an electronic sensor. It is thanks to him that the occurring fluctuations are assessed. The obtained results are converted using special algorithms into digital indicators. The oscillometric method is highly accurate.

Who invented it?

For the first time, such methods for studying blood pressure began to be used in 1876, when it was proposed by the French physiologist and inventor Etienne-Jules Marais in 1876. He is one of the founders of modern cardiology and circulatory physiology, who made a significant contribution to the development of these areas. But the oscillometric approach to measurement, which the scientist proposed, remained unclaimed for a long time, because there were certain difficulties in performing this research.

Today this technique is very popular and has already been thoroughly studied. When measuring, the obtained indicators are processed by a special program, after which digital values ​​appear on the monitor. The technology itself is kept strictly secret by manufacturing companies. At the same time, they are constantly modernizing it, trying to cope with the main flaw of the oscillometric method, which is the error of the results due to the movement of the patient at the time of the measurement procedure.

What is its essence?

Arterial oscillography detects fluctuations at the moment of dosed compression of a blood vessel. The compression effect of the limb where the artery passes is achieved through a cuff. At the same time, its inner surface acts as a sensor, thanks to which changes occurring are recorded.

Information is sent to the device via the cable. After it is processed by a microprocessor and a special calculation program, pressure indicators are displayed on the display. Pulse fluctuations may be irregular if there is a rhythm disorder. This is also recorded with an ultra-sensitive cuff. A premature or missed heartbeat may be reported by the device as arrhythmia or hypertension.

The design of the cuff is designed so that air flows into it in a dosed manner and then comes out. The first phase involves contraction of the upper limb (compression), followed by the second phase, relaxation or decompression.

Once the cuff is fixed on the patient's arm, it is compressed using a pump, which can be either manual or automatic. The compression should be at a level slightly higher than the upper pressure at the brachial artery site. After this, it is necessary to ensure a smooth decrease in pressure under the cuff. When there is a sharp jump in oscillations in the cuff, the upper blood pressure is determined, and when it stops, the lower blood pressure is determined.

Decoding the results

The duration of the measurement procedure using the oscillometric method is about 30 seconds. In the first phase, the values ​​of the pulse wave are analyzed, namely:

• individual impacts are assessed;
• the cycle period is determined;
• The duration of systole and diastole is measured.

Once the results are obtained, they can be compared with the values ​​​​in the table presented, which shows the levels of arterial hypertension.

As a rule, using the method of studying arterial hypertension, patients are not at rest. This affects the results, which may differ from the original values ​​when the procedure is repeated. This does not happen due to the inaccuracy of the tonometer. The reason for this is the physiological variability of human blood pressure.

Due to the fact that pressure can change dynamically, you should not rely on the readings of one test. Only after repeated measurements taken in a row (with an interval of 20 minutes) can the exact value of blood pressure be determined.

All measurement methods have their own nuances. The advantages of the oscillometric approach include:

• no need for special skills when working with the device;
• the ability to control your condition at home;
• the ability to measure pressure even with barely noticeable Korotkoff sounds;
• the ability to record blood pressure readings in the presence of a thin layer of clothing;
• determination of results for “endless tone” and “auscultation failure”;
• resistance to extraneous noise and the possibility of its use in situations with increased noise load (for example, on an airplane);
• the results do not depend on the movement of the cuff or its rotation.

The only disadvantages that can be identified are errors in the movement of the patient's hand.

In order to obtain correct indicators, the measurement must be carried out in a calm environment.

Half an hour before this, it is advisable to give up smoking, tonic drinks, alcohol and eliminate physical activity. Blood pressure should be measured at different times of the day.

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The oscillometric method was proposed by Marey in 1876. It was not widely used in the clinic due to the complexity of its implementation. However, the method turned out to be very convenient for use in automatic blood pressure meters. Therefore, this method is now a very common method for measuring blood pressure in automatic blood pressure detectors.

The main essence of the method is as follows. A pneumatic cuff is placed on the patient's shoulder and air is inflated to a pressure greater than systolic blood pressure. The air is then gradually released from the cuff (either continuously or in steps). In this case, weak (up to 5 mmHg) pressure pulsations appear in the cuff, associated with pulsations of blood pressure in the artery passing under the cuff. These small measurements, called "oscillometer pulse", are recorded over the entire cuff pressure range. The dependence of cuff pressure on time is shown in Fig. 42.

Rice. 42. Recording cuff pressure. The stepwise nature of decompression and marked pulsations are visible

To determine blood pressure, a graph of the dependence of the amplitudes of the “oscillometer pulse” on the pressure in the cuff is plotted (Fig. 43). This graph is called the "oscillometer curve" or "bell". The pressure in the cuff is plotted along the horizontal axis (from left to right in the direction of decrease), and the corresponding values ​​of pulsation amplitudes are plotted along the vertical axis. The "bell" shape, although it varies from patient to patient (and sometimes within a patient from minute to minute), appears to be an extremely accurate indicator of blood pressure levels.

Under correct measurement conditions, the “bell” has a single, clearly defined maximum. Mean hemodynamic blood pressure is defined as the pressure in the cuff at which the maximum amplitude of the “oscillometer pulse” was recorded (i.e., according to the position of the maximum “bell”). Next, based on the obtained value of average hemodynamic blood pressure, using special analysis algorithms, systolic blood pressure is determined on the left side of the “bell”, and diastolic blood pressure on the right side.

Rice. 43. "Bell" amplitude of pulsations. There is a single, clearly defined maximum. Vertical lines correspond to systolic, mean and diastolic blood pressure (from left to right).

Thus, in addition to systolic and diastolic blood pressure, the oscillometric method allows you to directly determine the average hemodynamic blood pressure (unlike the auscultatory method).

Methodology for measuring blood pressure (from the report of Russian experts on the study of arterial hypertension - DAG-1, 2000)

1. Preparation for blood pressure measurement. Blood pressure should be measured in a quiet, calm and comfortable environment at a comfortable room temperature. The patient should sit in a straight-backed chair located next to the examining table. To measure blood pressure in a standing position, use a special stand with an adjustable height and a supporting surface for the arm and tonometer.

Blood pressure should be measured 1-2 hours after eating; The patient must rest for at least 5 minutes before measurement. The patient should not smoke or drink coffee for 2 hours before measurement. Talking during the procedure is not recommended.

2. Cuff position. The cuff is placed on the bare shoulder. To avoid distortion of blood pressure readings, the width of the cuff should be at least 40% of the shoulder circumference (on average 12-14 cm) with the length of the chamber at least 80% of the shoulder circumference. The use of a narrow or short cuff leads to a significant false increase in blood pressure (for example, in obese individuals). The middle of the cuff balloon should be positioned exactly above the palpable artery, with the lower edge of the cuff being 2.5 cm above the cubital fossa. Between the cuff and the surface of the shoulder, it is necessary to leave a free space equal to the thickness of one finger.

3. To what level should air be inflated into the cuff? To answer this question, first assess the level of systolic blood pressure by palpation: while controlling the pulse on the radial artery with one hand, quickly pump air into the cuff until the pulse on the radial artery disappears. For example, the pulse disappeared when the pressure gauge read 120 mmHg. We add another 30 mm Hg to the resulting pressure gauge reading. In our example, the maximum level of air injection into the cuff should be 120+30=150 mmHg. This procedure is necessary to accurately determine systolic blood pressure with minimal discomfort for the patient, and also avoids errors caused by the appearance of an auscultatory dip - a silent interval between systolic and diastolic blood pressure.

4. Position of the stethoscope. The head of the stethoscope is placed strictly above the point of maximum pulsation of the brachial artery, determined by palpation.

In emergency cases, when searching for an artery is difficult, proceed as follows: mentally draw a line through the middle of the ulnar fossa and place the head of the stethoscope next to this line, closer to the medial condyle. You should not touch the cuff and tubes with the stethoscope, as ringing from contact with them can distort the perception of Korotkoff sounds.

5. Rate of air inflation and cuff decompression. Air is pumped into the cuff to the maximum level quickly. Slow pumping leads to disruption of venous outflow, increased pain and blurred sound. Air is released from the cuff at a rate of 2 mmHg. per second until Korotkoff sounds appear, then at a speed of 2 mmHg. from tone to tone. The higher the decompression rate, the lower the measurement accuracy. Usually it is enough to measure blood pressure with an accuracy of 5 mm. Hg Art., although nowadays they increasingly prefer to do this within 2 mm. Hg Art.

6. General rule for measuring blood pressure. At the first meeting with the patient, it is recommended to measure blood pressure in both arms to find out on which arm it is higher (differences of less than 10 mm Hg are most often associated with physiological fluctuations in blood pressure). The true value of blood pressure is determined by higher values ​​determined on the left or right arm.

7. Repeated blood pressure measurements. Blood pressure levels may fluctuate from minute to minute. Therefore, the average value of two or more measurements taken on one arm more accurately reflects the level of blood pressure than a single measurement. Repeated blood pressure measurements are performed 1-2 minutes after complete decompression of the cuff. Additional blood pressure measurement is especially indicated for severe cardiac arrhythmias.

8. Systolic and diastolic blood pressure. As already noted, systolic blood pressure is determined when the first phase of sounds appears (according to Korotkov) according to the nearest scale division (rounded within 2 mmHg). When phase I appears between two minimum divisions on the pressure gauge scale, the blood pressure corresponding to the higher level is considered systolic.

The level at which the last distinct tone is heard corresponds to diastolic blood pressure. When Korotkoff sounds continue to very low values ​​or to zero, the level of diastolic blood pressure corresponding to the beginning of phase IV is recorded. When diastolic blood pressure is above 90 mmHg. Auscultation should be continued for another 40 mmHg, in other cases 10-20 mmHg. after the last tone disappears. This will avoid the detection of falsely elevated diastolic blood pressure when sounds resume after auscultatory failure.

9. Measuring blood pressure in other positions. At the patient’s first visit to the doctor, it is recommended to measure blood pressure not only in a sitting position, but also in a lying and standing position. In this case, a tendency to orthostatic arterial hypotension may be detected (maintenance of systolic blood pressure reduced by 20 mmHg or more 1-3 minutes after transferring the patient from a lying position to a standing position).

10. Measurement of blood pressure in the lower extremities. If coarctation of the aorta (congenital narrowing of the aorta in the descending section) is suspected, it is necessary to measure blood pressure in the lower extremities. To do this, it is recommended to use a wide, long thigh cuff (18x42 cm). Place it on the middle of the thigh. If possible, the patient should lie on his stomach. With the patient lying on his back, one leg should be slightly bent so that the foot rests on the couch. In both options, Korotkoff sounds are heard in the popliteal fossa. Normally, blood pressure in the legs is approximately 10 mmHg. higher than on the hands. Sometimes equal values ​​are detected, but after physical activity blood pressure in the legs increases. With coarctation of the aorta, blood pressure in the lower extremities may be significantly lower.

11. Special situations that arise when measuring blood pressure:

Auscultatory failure. It should be borne in mind that in the period between systole and diastole, a moment is possible when the sounds completely disappear - a period of temporary absence of sound between phases I and II of Korotkoff sounds. Its duration can reach 40 mmHg; auscultatory failure is most often observed with high systolic blood pressure. In this regard, incorrect assessment of true systolic blood pressure is possible.

Absence of phase V of Korotkoff sounds (the “infinite tone” phenomenon). This is possible in situations accompanied by high cardiac output (thyrotoxicosis, fever, aortic insufficiency, in pregnant women). In this case, Korotkoff sounds are listened to the zero division of the scale. In these cases, the beginning of phase IV of Korotkoff sounds is taken as diastolic blood pressure.

In some healthy individuals, barely audible tones of phase IV are detected before the pressure in the cuff decreases to zero (i.e., phase V is absent). In such cases, the moment of a sharp decrease in the volume of tones is also taken as diastolic blood pressure, i.e. the beginning of phase IV of Korotkoff sounds.

Features of blood pressure measurement in the elderly. With age, the walls of the brachial artery thicken and harden, and it becomes rigid. To achieve compression of a stiff artery, a higher level of pressure in the cuff is required, as a result of which doctors diagnose pseudohypertension (a false increase in blood pressure). Pseudohypertension can be recognized by palpation of the pulse on the radial artery - when the pressure in the cuff exceeds systolic blood pressure, the pulse continues to be detected. In this case, only direct invasive blood pressure measurement can determine the patient's true blood pressure.

Very large shoulder circumference. In patients with an upper arm circumference greater than 41 cm or with a tapered upper arm, accurate blood pressure measurement may not be possible due to incorrect cuff position. In such cases, the palpation (pulse) method of determining blood pressure more accurately reflects its true value.

The oscillometric method is one of the successfully used non-invasive methods for measuring blood pressure. It is mainly used in semi-automatic and automatic devices for measuring pressure - tonometers, as well as devices for long-term recording of indicators - blood pressure monitors.

It was first proposed by the French physiologist Marey in 1876, but for a long time the method was not in demand due to the complexity of performing the study.

Now this technique has been very well studied; the obtained indicators are analyzed using special programs and converted into numbers that we see on the monitor. Manufacturers keep these programs secret and constantly improve them, trying to get rid of the main drawback that the oscillometric method has - the dependence of the accuracy of the readings on the patient’s movement during the measurement.

Principle of the method

Arterial oscillography records changes in tissue volume under conditions of dosed compression and decompression of a blood vessel. This change in volume is associated with an increase in arterial blood supply to the tissue during the pulse impulse. Compression and decompression of the limb in which the artery passes is carried out using a cuff.

In this case, the inner surface of the cuff becomes the sensor that registers changes in the volume of the limb, imperceptible to the eye. The change in pressure in the cuff is the main indicator that this method analyzes. Through the cable, the information is transmitted to the device, which processes it using an analog-to-digital converter and a microprocessor with a program for calculating indicators and turns it into an image - pressure numbers on the display.

If the rhythm is disturbed, the pulse fluctuations become irregular, which is also detected by the sensitive cuff. Information about a missed or premature heartbeat is perceived and reflected on the display as an arrhythmia.

It is clear that oscillography also records the pulse, the measurement results of which are also visible on the tonometer screen.

How is the measurement carried out?

The blood pressure cuff is designed in such a way that air can be injected into it in measured doses and then released. In the first phase, compression (compression) of the limb occurs, and in the second phase, relaxation (decompression) occurs. The oscillometric method assumes that it simultaneously serves as a receiver of pulse oscillations (unlike the Korotkov method).

The cuff is placed and fixed on the shoulder. The compression in it, using an automatic or manual pump, is raised to a level slightly higher than the systolic pressure in the brachial artery. In automatic blood pressure monitors, the required compression in the cuff is determined automatically. In semi-automatic devices, the patient himself orients himself to the desired degree of compression of the limb. After this, a smooth stepwise decrease in pressure in the cuff is performed - decompression.

In the very first arterial oscilloscopes, all measurements were made on paper tape. During decompression, when the pressure in the cuff became equal to systolic, an abrupt increase in oscillations, that is, deviations of the recording from a straight line, appeared on the arterial oscillogram. Oscillations stopped at the moment when the level of compression in the cuff became equal to diastolic. The cuff stopped detecting changes in shoulder volume during pulse waves.

The blood pressure measurement method used in modern machines is based on the same principle. At each stage of decompression, the device determines how pronounced the vibrations inside the cuff are. When these fluctuations sharply increase, systolic pressure is recorded, and when they stop, diastolic pressure is recorded.

The method determines the pressure, which is usually slightly higher than when using Korotkoff sounds, listened to with a phonendoscope. However, these indicators differ slightly, and in arterial hypertension they are almost equal.

Advantages and disadvantages

The main disadvantage of the oscillometric method is the need for immobility of the limb during measurement.

The method also has advantages over measuring blood pressure using Korotkoff sounds:

• the accuracy of the results does not depend on the person conducting the research;
• the ability to correctly measure with weak tones, an “endless” tone or an “auscultatory failure”, when the usual sound characteristics are changed using a phonendoscope;
• the ability to apply the cuff to a thin layer of clothing;
• unnecessary special training.

The oscillometry method is also used in devices for analyzing arterial and peripheral vascular resistance, stroke and cardiac output and other characteristics of blood circulation.

Advantages: a) relatively resistant to noise loads, which allows it to be used in situations with high noise levels (up to the helicopter cabin); b) allows for determination of blood pressure in cases that pose a problem for the auscultatory method - with a pronounced auscultatory failure, “endless tone”, weak Korotkoff sounds; c) pressure values ​​are practically independent of the rotation of the cuff on the arm and little dependent on its movements along the arm (until the cuff reaches the elbow); d) allows you to measure blood pressure without loss of accuracy through thin clothing; e) operational practice shows that this method, as a rule, provides a lower percentage of unsuccessful measurements in the 24-hour monitoring mode than the auscultatory method.

Disadvantages: a) relatively low resistance to hand movements: for example, the SL90202 device did not provide blood pressure measurements during a bicycle ergometer test in 82% of measurements; b) in a small number of patients (about 5%) it gives stable and significant differences from blood pressure values ​​using the Korotkoff method, which makes it difficult to interpret the results.

The ultrasound method of recording blood pressure is based on recording the appearance of minimal blood flow in the artery after the pressure created by the cuff becomes lower than the blood pressure at the site of compression of the vessel. Using Doppler ultrasound, only the systolic level of regional blood pressure is determined.

The urgent need for cuffless means for monitoring non-invasive blood pressure control stimulates ongoing attempts to create such equipment. Experimental developments in this area are based on studies of the possibilities of using certain functional dependencies that could connect the value of blood pressure with any physiological parameter recorded non-invasively. To date, attempts have been made to use the following parameters or phenomena: 1) the amplitude of pulse pressure waves recorded on the surface of the skin in the area where the artery exits the surface; 2) blood flow speed in the artery; 3) the phenomenon of cavitation in liquid under the influence of ultrasound; 4) the speed of propagation of the pulse wave.

Continuous measurement of the amplitude of the pulse wave recorded on the surface of the skin underlies the tonometric method for determining blood pressure. Its idea is to, by applying pressure from the outside, compensate for the pressure exerted on the blood by the arterial wall itself, while the instantaneous value of the recorded fluctuations becomes proportional to the value of blood pressure. Although the tonometric method involves an external force, usually generated by a cuff, it is essentially a non-cuff method, since the cuff is not used to occlude the artery. Tonometers require preliminary calibration, since the compensating effect is applied not only to the artery, but also to the surrounding tissue. When correctly installed and properly calibrated, the tonometer determines the instantaneous blood pressure value without causing virtually any inconvenience to the patient. Such, for example, is the ML-105 tonometer with a built-in microprocessor ZET-80.

A big disadvantage of tonometers is their high “criticality” to the accuracy of the location of the tonometric sensor in relation to the artery, and therefore their handling requires professional skill. To overcome this drawback, it is planned to develop a tonometric sensor of a special design in combination with a microprocessor for processing its signal. The sensor is a matrix of point pressure sensors that reliably covers the area where the artery is located. The microprocessor determines which sensor is located correctly and also automatically adjusts the pressing force. The developers of the tonometer believe that in the future devices of this type will occupy a dominant place among devices for measuring blood pressure.

The speed of blood flow in the artery can be determined using ultrasound location. An attempt was made to connect this parameter with the value of blood pressure and, on the basis of this, to carry out continuous cuffless blood pressure recording. The method consists in preliminary establishing for a patient whose pressure is to be monitored the relationship between blood pressure and blood flow velocity in a certain artery by simultaneously measuring these two parameters at rest and at different levels of physical activity. In this case, pressure is measured in the usual way, but blood flow speed? ultrasonic Doppler sensor. Subsequently, blood pressure measurements are made by continuously determining the blood flow velocity based on a previously obtained ratio. The device is portable and is intended for monitoring blood pressure in conditions of free patient behavior. The complexity of installing and securely fixing the sensor, as well as calibration, precludes the use of the described procedure on a wide scale.

The phenomenon of cavitation in liquid under the influence of ultrasound has been used by Japanese researchers for continuous non-invasive determination of blood pressure. Cavitation in the blood, for example in the left ventricle of the heart, occurs under the influence of a high-power ultrasonic wave. Provided that other parameters of the liquid (temperature, gas concentration in it) are constant, the formation of cavitation nuclei depends on the absolute pressure in this liquid, called critical pressure. When an ultrasonic wave acts on the blood, this pressure is the sum of the ultrasound pressure, blood pressure and atmospheric pressure. Knowing the parameters of the ultrasonic wave, the value of atmospheric pressure, as well as the critical pressure for a given liquid, it is possible to determine the pressure in it.

The occurrence of cavitation is also recorded using ultrasound, but with a frequency an order of magnitude higher than that used to initiate cavitation. To do this, the measurement area is probed with an ultrasonic beam, which begins to be strongly reflected from cavitation nuclei when they occur, when the pressure in the measurement area becomes equal to critical. To reduce the power of exciting radiation and, therefore, to reduce the damaging effect of ultrasound on blood elements, it is proposed to pre-saturate the blood with an inert gas, such as helium, which significantly reduces the critical pressure.

The speed of propagation of mechanical vibrations in any medium depends on the elastic properties of this medium. In particular, the velocity of pulse wave propagation (PWV) along the artery? from the elasticity of its wall. With unchanged elastic-viscous properties of the vessel, PWV is determined by the magnitude of the stress in it when interacting with blood pressure. This property was used to develop a method for cuffless continuous blood pressure monitoring. The method is based on an almost linear dependence of PWV on blood pressure in the physiological range of pressure values. In practice, pulse wave propagation time (PWT) is measured, defined as the interval between pulse waves recorded at different points in the arterial system, or as the interval between the ECG signal and the pulse wave at a point distant from the heart. For example, a micro-design device is described, consisting of a photoelectric pulse wave sensor located on the wrist of an ECG unit, a display timer pressure unit and a power source. The pressure is determined by the value of the interval between the R wave of the ECT and any stable point on the pulse wave curve based on from the ratio

where is R? average pressure mmHg Art.; T? VRPV s.

The calculation formula is based on the assumption that the normal average pressure is 100 mm Hg. Art. corresponds to a RTW of 0.2 s. This calibration of the device is conditional and is intended for the convenience of the consumer, since in most cases it is required to know not the absolute value of blood pressure, but its dynamics. If necessary, the device can be calibrated for a specific patient.

Let us evaluate the possibility of using the presented methods of cuffless blood pressure control for the purposes that were formulated above.

The most unique method for determining blood pressure is based on the phenomenon of cavitation. However, this method is in its infancy and is far from practical application in clinical settings. In addition, the need for precise adjustment of ultrasonic sensors will eliminate any movement of the patient. The issue of the permissible duration of continuous observation is problematic, since cavitation bubbles can pose a threat to microembolism of the capillary network. In addition, strong ultrasonic exposure in itself may be unfavorable. This technically very complex method is more suitable for diagnostic purposes, as it makes it possible to determine blood pressure in any part of the cardiovascular system where ultrasound penetrates.

Determining blood flow speed depending on blood pressure requires a preliminary establishment of the relationship between two parameters, which is hardly feasible in an intensive care unit. The use of the method is justified in complex research work, where the costs of conducting the study are recouped by the information subsequently obtained.

Are further choices limited to two methods? tonometric and method based on the measurement of VRPV. Let us analyze the advantages and disadvantages of these methods for each point of the requirements for a device for monitoring blood pressure in an intensive care unit.

1. Disturbing influence of the measurement procedure

The tonometry method requires an external influence on the artery to compensate for the intrinsic tension of its wall.

The VRPV method does not require any impact on the vascular system, using processes that constantly occur in the human body.

2. Obtaining data on system blood pressure

The tonometry method provides information about the pressure at the point where the sensor is applied, usually on the arm where the arteries exit to the surface.

The VRPV method provides information about the pressure in the entire artery through which the pulse wave propagates, in particular in the aorta and femoral artery.

3. Obtaining absolute blood pressure numbers

The tonometry method requires preliminary calibration, after which it gives absolute numbers of systolic, diastolic and average pressure.

The VRPV method requires preliminary calibration, after which it gives absolute numbers of average blood pressure.

4 Criticality of sensor placement accuracy

The tonometry method is extremely sensitive to the accuracy of the sensor location; in case of inaccurate installation, the amplitude characteristics of the pulse signal, which are a source of information about the value of blood pressure, are distorted.

The VRPV method is not critical to the accuracy of the sensor layout; it is only important that the pulse wave is recorded. When using this method, information about pressure is carried not by the amplitude of the wave, but by its phase.

5 Noise immunity

The tonometry method, being amplitude, is subject to the influence of mechanical interference associated with the patient’s movements.

The VRPV method, being a phase method, is much less subject to amplitude interference associated with the patient’s movements.

A comparison of the two methods shows that the method of determining blood pressure by VRPV is more effective in an intensive care unit. This is an even more correct conclusion, since it is known that when transmitting information, preference is given to phase modulation methods. The analogy in this case is not artificial, since in the tonometric method, blood pressure modulates the amplitude of the output signal of the pulse sensor, and in the VRPV method, pressure changes the time relationships in a series of successive pulse wave pulses.

The analysis carried out gives the right to conclude that among the currently available methods of non-invasive cuffless determination of blood pressure, only one of them can be used to implement monitor control? method of control based on the value of VRPV. Based on this relatively simple method, a compact, reliable device can be developed that can be used to solve the following clinical problems: 1) monitoring blood pressure in the intensive care unit; 2) monitoring the dynamics of blood pressure during diagnostic or therapeutic intervention; 3) control of blood pressure during sleep in patients at risk of developing a hypertensive crisis.