“…The relevance of the study of the photoplethysmogram low-frequency oscillation rhythms of less than 0.5 Hz is due to the fact that the corresponding spectral components can characterize changes in the vascular tone determined by the influence of various physiological mechanisms of regulation such as: endothelial, neurogenic, myogenic, and respiratory. Thus, e.g., a decrease in the amplitude of the PPGI signal spectral components in the neurogenic, myogenic, and respiratory ranges was found in a group of patients with diabetes mellitus [ 98 ]. In [ 99 ], a decrease in the amplitude of the vasomotion with a frequency of about 0.1 Hz in the presence of allergy was recorded with the PPGI.…”