Lavrenjuk А., Chernetchenko D., Botsva N., Pustova K.

Oles Honchar Dnipro National University, Ukraine

Blood pressure monitoring

Blood pressure in the arteries - one of the main indicators of the cardiovascular system. Persistently raised blood pressure is one of the major risk factors for diseases such as myocardial infarction and stroke. Uncontrolled hypertension is also associated with high rates of mortality, particularly in middle and high-income countries [1]. Therefore, equipment for measuring blood pressure parameters is a part of practically all modern multichannel monitor systems.

There are several methods for measuring blood pressure, which include palpation, arterial tonometry, Doppler, auscultation, oscillometry and plethysmography. Non-invasive monitors with combination of auscultative and oscillometric channels allows the implementation of flexible algorithms for determining the parameters of arterial pressure – values of systolic, diastolic, and mean pressure, and thus improve the accuracy and reliability of measurements. The search for simple, non-invasive and informative tests is a key step to predict the risk of complications and progression of cardiovascular disease.

One of the important morphological characteristics of the vessels is the rigidity of the vascular wall, which is mainly measured by the velocity of the pulse wave propagation. This method, proposed in the 1950's, is undergoing a revival, due to the development of a new generation of devices integrated with computer systems [2,3].

To determine the propagation velocity of a pulse wave, the Moens–Korteweg equation is used:

E – the elastic modulus of the vessel wall, h – the wall thickness of the vessel; d – the diameter of the vessel, p – the density of the blood.

With increasing rigidity E vessels, increasing the thickness of its walls and with a decrease in diameter, the velocity of the pulse wave increases. Also, the degradation of vessels walls ways to decreasing pulse wave velocity variability during systolic and diastolic cycles. The frequency and duration of the pulse wave depends on the characteristics of the heart, and the magnitude and shape of its peaks – on the state of the vascular system.

The form of pulse oscillations and their characteristics reflect the work of the heart and the state of the vascular system, therefore, their registration in different parts of the vascular system and further analysis have a diagnostic value.

The beginning of systole occurs earlier than the beginning of an increase in blood flow to the investigated area of the vessel. Need some time Δt for proliferation of the pressure wave on the vascular system. Using the anatomical distance (L) from the heart to the area under study, the wave propagation velocity can be calculated:

At any point in the vascular system, blood pressure can be defined as:

P₀ – the atmospheric pressure (in the right atrium); pgh – the hydrostatic pressure; R - the pressure created by the heart.

To obtain raw data for further processing and determination of pressure parameters, it is necessary to measure pressure by a mechanical tonometer at the beginning of the experiment and at the end. The next step is the synchronous measurement of the electrocardiogram and pulse rate and processing of the obtained data using the Matlab software package. Using the original program code data collected and processed.

After recording the ECG and heart rate, the delay between the R peaks of the ECG and the maximum slope of the pulse wave is considered; it allows to obtain the propagation time of the pulse wave equal to the value of pulse transit time (PTT). The calculations also use the approximate distance of the vessels from the heart to the wrist equal to half the height value. With PTT and the length of the vessels, it is possible to calculate the speed of the pulse wave propagation (Fig.1), and then from the Moens–Korteweg equation we can find the relationship between wave propagation and arterial pressure and obtain numerical values for systolic and diastolic pressure.

Fig. 1. ECG, pulse and wave propagation velocity: the upper chart – electrocardiographic data, average one- the pulse rate (synchronized with ECG),

the lower one – rate of pulse wave propagation.

In order to calculate the pressure factors more accurately, it is necessary to conduct a series of measurements for different people and in different states. Based on this, can obtain compliance for systolic and diastolic pressure and teach the program to recalculate values and output data almost instantly.

The results of the work can be useful in carrying out automated medical and biological research.

References

1. Manzella D., Grella R. et all. Blood pressure and cardiac autonomic nervous system in obese type 2 diabetic patients: effect of metformin administration // American Journal of Hypertension. 2004. 17(3), 223–227.

2. H'juston M. Sosudistaja biologija v klinicheskoj praktike. – L'vov, 2007.

3. Radchenko, G.D. Vpliv trivaloї kombіnovanoї antigіpertenzivnoї terapії na zhorstkіst' arterіj elastichnogo ta m’jazovogo tipіv u pacієntіv z tjazhkoju arterіal'noju gіpertenzієju/G.D. Radchenko i dr.//Ukraїns'kij kardіologіchnij zhurnal. 2009. 2, 109–128.