Spectral characteristics of photoplethysmographic indicators of human peripheral vascular tone.
Frequently observed neurocirculatory disorders of peripheral hemodynamics, leading to the emergence of juvenile hypertension, make the problem of early diagnosis of peripheral hemodynamic disorders in young people urgent.
Features of natural quasiperiodic fluctuations of regional vascular tone and blood filling are due to changes in the activity of the central and autonomous circuits of regulation of cardiohemodynamics in healthy individuals and in those examined with disorders of the functional state of the cardiovascular system. These features can be investigated by the method of harmonic analysis of long-term recorded photoplethysmograms.
We have proposed an analysis of the spectral characteristics of the main indicators of the contour analysis of photoplethysmograms recorded synchronously with expiratory spirograms. Such an analysis makes it possible to establish a different degree of influence of the autonomous and central circuits of hemodynamic regulation on the tone of arteries of various diameters. The main indicators of the contour analysis of digital photoplethysmograms are the amplitude of the pulse wave, which characterizes the total pulse blood flow to the region through the large distribution arteries and their tone and pulse cycle duration (the time interval between the minima of the photoplethysmogram).
It was found that the spirogram spectrum has several harmonics. The lowest frequency harmonic of the spirogram is observed at a frequency of about 0.09 Hz and corresponds to a period of respiratory excursions of about 11 s. Three more harmonics are observed at multiples of frequencies 0.18, 0.30, 0.40 Hz.
The duration of the pulse cycles is informationally similar to the RR-intervals of the electrocardiogram. The analysis of the spectra of the heart rate index, determined by the photoplethysmogram, made it possible to clearly identify the dominant respiratory harmonic at a frequency of 0.09 Hz. In addition to the respiratory harmonics, the spectrum of this indicator contains less powerful low-frequency harmonics at frequencies of about 0.02 Hz and approximately 0.002 Hz. The harmonic of 0.02 Hz is possibly due to a periodic change in the activity of sympathoadrenal influences on the heart rhythm, and the harmonic of 0.002 Hz is due to changes in the activity of the subcortical nerve centers.
Three fundamental harmonics are observed in the spectra of the pulse wave amplitude: a pronounced respiratory harmonic at a frequency of 0.09 Hz, a harmonic at a frequency of about 0.18 Hz, corresponding to the second harmonic of a spirogram, and, finally, a low-frequency harmonic at a frequency of 0.02 Hz, apparently characterizing the influence of the central circuit of regulation on the tone of large arteries and their pulse blood supply. It is important to note that in the absence of synchronous registration of a spirogram, the harmonic at a frequency of 0.18 Hz can be mistaken for a respiratory harmonic, which significantly distorts the interpretation of the results.
A differentiated approach to determining the quantitative spectral characteristics of each indicator of the contour analysis of photoplethysmogram allows determining the ratio of the effects of the central and autonomous circuits of blood circulation regulation on the main effector links of the peripheral vascular bed: total pulse blood filling of large arteries of a human limb, tone of regional arteries of large diameter, tone of peripheral arteries of small diameter and arterioles.
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