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Hardware-software complex for assessment of variability of heart rate and pulse wave velocity


Heart rate variability - express test system The heart rate variability (HRV) study is a method for assessing health status and the impact of stress on the human body. Heart rate variability is a small fluctuation in the duration of the heart cycle that changes as a person inhales and exhales, and from the complex interaction of hemodynamic, electrophysiological and chemical processes occurring in the body. An indicator of heart rate variability is the degree of change in heart rate over a certain period of time. The time intervals between consecutive heartbeats are called cardiointervals. The unit of measurement for cardiointervals is milliseconds (msec). If the intervals between heartbeats are relatively constant and vary slightly,then HRV is low. If their duration varies widely, then the HRV is high. A decrease in the degree of pulse variability in a healthy person is considered as a sign of stress regulatory processes.

Pulse sensor The heart rate variability (HRV) test system consists of a pulse sensor and software installed in the computer.
HRV test system is designed to assess a person's health status by analyzing a pulse wave registered by a special sensor.
The results of the analysis are complex estimation of functional systems and detection of irregularities in human health:
measuring the level of stress, spectral analysis of RR-intervals and conclusions about the state of health.
The design of the pulse sensor is made in the form of a clip and is a photometric sensor that records the pulsations of capillary
blood filling at the measurement point.
The pulse sensor is connected to the USB port of the computer using the analog-to-digital converter (ADC) module



Advantages:
- system is easy to use and special training is not required;
- information about pulsations of capillary blood filling is registered and displayed;
- there are no sticky electrodes or other electrodes, which are inconvenient for the patient;
- number of heartbeats for the breath cycle is determined;
- it is possible to visualize and study the primary pulse wave graph after recording is complete.

Example of pulse waves displayed on the monitor screen during recording




Examples of a software windows.

VISUALIZATION OF THE REAL PULSE WAVES AND THE INITIAL RHYTMOGRAMS
working window

A rhythmogram is a graphic representation of the duration of R-R intervals. When building a rhythmogram on the axis of the abscissus is postponed the recording time or number of pulse beats, and on the ordinate axis - the duration of each cardiointerval. In this case, the upper edge of the rhythmogram has a wavelike appearance. It is formed by changing the heart rhythm. The heart rhythm is determined by the property of specialized cells of the heart's conducting system to spontaneously activate, the so-called a property of cardiac automatism. Heart rate regulation is performed by the autonomic nervous system, the Central nervous system and a number of humoral and reflex effects.
When working in real time, the system can detect possible rhythm disturbances and extrasystoles.
Extrasystole is an extraordinary premature cardiac contraction, depolarization and contraction of the heart or its individual chambers, this is the most frequently recorded type of arrhythmia.
The presence of extrasystoles is one of the diagnostic signs. However, to analyze heart rate variability, possible extrasystoles must be removed from consideration, as well as recording artifacts.

RECALCULATED RHYTMOGRAM AND VISUALIZATION OF DATA DISTRIBUTION
Example of a rhythmogram saturated with different frequencies of changes in cardiointervals.


Geometric method rhythm analysis involves estimating the density of the RR interval distribution function using a histogram method and analyzing it. When building a histogram along the abscissus axis, the values of the RR intervals (in units of time) are deferred, and the entire range possible values are divided into N non-intersecting intervals. Each of the ranges is assigned the number of RR intervals, caught in this gap. These quantities are deposited along the ordinate axis, as shown above.
The wider the base distribution histogram of cardiointervals, the more different variants of R-R intervals and the higher the variability heart rate. The higher the top of the histogram, the greater the centralization of the rhythm.
Geometric methods also include a scatterogram. It reflects the interdependence of pairs of consecutive R-R intervals. A scatterogram (or scatter) is a graphical representation of pairs of R-R intervals (previous and subsequent) in a two-dimensional coordinate plane. In this case, the value R-R(n) is deposited along the abscissus axis, and the value R-R (n-1) is deposited along the ordinate axis.
Usually, a scatterogram has the shape of an ellipse stretched along the bisector. Scatterogram also possible to judge the heart rhythm variability. The closer the "cloud" of points, the less variability there is. With an elongated ellipse, the variability is high. A shift of the point cloud to the right along the coordinate axis reflects a rhythm deceleration, while a shift to the left reflects a faster rate. If the points are far away from the whole set, it is either artifacts, or rhythm disturbances, most often - extrasystoles. The absence of an ellipse on the rhythmogram is usually indicates a violation of the heart rhythm.

STATISTICAL ANALYSIS OF HEART RATE. ASSESSMENT OF STRESS LEVEL


SDNN - standard deviation of cardio intervals from the average value. Indicates how different the length of all R-R intervals is in General, from their average value. SDNN reflects all the cyclic components responsible for variability during the recording period. This is one of the main indicators of heart rate variability, which characterizes the state of regulation mechanisms.
RMSSD is the square root of the mean squares of the differences between adjacent cardio intervals. This indicator also reflects variability. However, unlike the previous indicator, it is used to evaluate high-frequency components of variability. Its growth reflects an increase in the activity of the parasympathetic regulation link when adapting to loads. This indicator-it reflects both variability and autonomization of the heart rate and correlates with the largest number of others characteristics of the heart rhythm wave structure .
HRV coefficient is an integral indicator of heart rate variability and reflects the state of the cardiovascular system according to several criteria.
Stress index or stress indicator reflects the level of psycho-emotional and physical stress.
This parameter characterizes cardiovascular system regulatory centers state. The index norm is an index value from 50 to 200. With physical exertion, chronic fatigue, and a decrease in the body's reserves with age, the index ranges from 150 to 500. With angina, psychophysiological fatigue, significant psychological and emotional stress, the stress index reaches values from 500 to 800. An index above 800 indicates a significant violation of regulatory mechanisms. The stress index of more than 900 units can be observed in the pre-infarction state of the patient.

HEART RHYTHM WAVE STRUCTURE ANALYSIS. SPECTRAL ANALYSIS OF HEART RATE


Spectral analysis of the pulse wave structure is used to identify characteristic periods in the dynamics of cardio intervals, assessment of the contribution of certain periodic components to the overall dynamics of changes in heart rate.
Spectral analysis allows us to distinguish periodic components in the heart rate fluctuations in the wave structure of the heart rate:
- fast or high-frequency vibrations (HF component) (frequency range from 0.15 to 0.4 Hz);
- slow or low-frequency vibrations (LF component) (frequency range from 0.04 to 0.15 Hz);
- very slow or very low frequency vibrations (VLF component) (frequency range from 0.04 to 0.015 Hz);

Spectral analysis evaluates the following indicators:

TR (total power spectrum, TF) - reflects the total effect of exposure to the heart rate of all levels of regulation. High values are typical for healthy people and reflect a good functional state of the cardiovascular system, A decrease in the total power of the spectrum is observed with a decrease in the adaptive capabilities of the cardiovascular system, low stress resistance of the body.

HF high frequency wave power-reflects the activity of the parasympathetic cardioinhibitory center of the medulla oblongata. Increase - at rest, during sleep, with frequent hyperventilation. Reduction - with physical activity, stress, various diseases.

LF low frequency wave power-reflects the activity of the sympathetic centers of the medulla oblongata (pacemaker and vasoconstrictor). High absolute values are observed in healthy people. Reduction - with physical activity, stress, various diseases.

VLF power of very low frequency waves-reflects the activity of Central ergotropic and humoral-metabolic mechanisms of heart rate regulation.

LF/HF (vagosympathetic balance coefficient) - the ratio of low-frequency wave power (LF) to high-frequency wave power (HF).
Increasing the coefficient - when activating the sympathetic nervous system.
A decrease in the coefficient occurs when the parasympathetic nervous system is activated.

Example of determining the ratio of respiratory rate and pulse rate.

DETERMINING THE RATIO OF RESPIRATION AND HEART RATE


The frequency of respiratory cycles is one of the main parameters for assessing the state of the entire body.
The algorithm of the respiratory evaluation module allows to get information about the respiratory rate after processing the full schedule of pulse wave recording.
The number of pulse beats per respiratory cycle is an important characteristic of the state of the body.

TOTAL ASSESSMENT OF REGULATORY SYSTEMS


Based on the results of a General assessment of the state of regulatory systems, the program prepares an interpretation of the diagnostic conclusion for help and decision-making by the doctor.


Pulse wave velocity measurement

Pulse wave velocity - express test system The vascular tone and elasticity of the vessel walls are determined by the Pulse Wave Movement Velocity. An increase in vascular stiffness leads to an increase in this rate. When measuring the difference in the time of pulse waves occurrence, so-called lag, simultaneous recording of two signals is used.
To measure the speed of the pulse wave, a two-sensor pulse sensor is used. A two-touch pulse sensor is connected to a computer via an analog - to-digital Converter (ADC) unit. The first sensor is a photometric element in the form of a clip that is attached to the patient's earlobe, as described above.
The second sensor is used as an acoustic transducer. The sensitive element is pressed against the projection of the radial artery in the specific point on the patient's wrist during the measurement process.

Acoustic sensorThe design of the acoustic transducer allows recording pulse waves act similar to that of a pulse diagnosis when using manual palpation of the pulse.
Acoustic sensor is designed to record vibrations of the radial artery wall in the form of twice differentiated analog signal corresponding to the vessel wall movements.



Scheme of the pulse wave speed test
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Scheme of the pulse wave speed test

During the test, the flow of information from both sensors is transmitted to the computer and processed by special software.

Example of displaying graphic information received from sensors on a computer screen.
Pulse waves graphs

The yellow graph shows the process of pulsation and blood filling in the tissues of the earlobe. The green graph is a doubly differentiated graph of radial artery wall oscillation.

Average graphs
The software calculates the Pulse Wave Transit Time using two averaged graphs obtained from both sensors.
To calculate the speed of pulse wave propagation, the program enters a parameter-the distance of the Pulse Wave, which is measured on the patient.
The propagation of the pulse wave inside the vessel is caused by the elasticity of the artery walls. The speed of the radial artery Pulse Wave is a parameter that can be used to judge the elasticity/stiffness of the vessel.
Determining the speed of pulse wave propagation and other parameters of vascular stiffness can reveal the beginning of cardiovascular system severe disorders development. This information allows to choose the right individual therapy. For young and middle-aged people, the pulse wave propagation speed is 5.5-8.0 m/s.
With age, the elasticity of the artery walls decreases and the speed of the pulse wave increases. The speed of the Pulse Wave increases with vascular atherosclerosis, hypertension, symptomatic hypertension and all pathological conditions when the vascular wall is compacted.
HRV diagnosis by modern digital technology, can reliably and objectively to evaluate the real status of functional systems of the body.

Lithuania Vilnius
e-mail:
aidas2000@mail.ru

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