Photoplethysmographic variability: spontaneous fluctuations in the tissue blood volume and in the systolic blood volume increase

Several parameters of the cardiovascular system such as heart rate, arterial blood pressure and blood flow fluctuate spontaneously due to the autonomic nervous system activity. In the current study, the low frequency fluctuations of the tissue blood volume and the blood volume pulse in the fingertips of healthy subjects were investigated using transmission photoplethysmography (PPG). The baseline of the PPG signal (BL) is inversely related to tissue blood volume so that the parameter BV, defined by: BV equals Const.-BL is directly related to the blood volume. The amplitude (AM) is directly related to the systolic blood volume increase. For most of the examinations BV and AM show positive correlation, which is expected since BV depends on the tissue blood volume and AM depends on the compliance of the blood vessels, both of which decrease during vasoconstriction, which is caused by higher activity of the sympathetic nervous system. The analysis of the PPG signal provides, therefore, a potential tool for study in the mechanism of the regulation of the microcirculation by the sympathetic nerves.