<title>Spontaneous low-frequency fluctuations in finger blood volume, measured by photoplethysmography</title>

Several parameters of the cardiovascular system such as heart rate, arterial blood pressure and blood flow fluctuate spontaneously. These fluctuations are related to the autonomic nervous system activity. In particular the low frequency fluctuations are mediated by the sympathetic nervous system. In the cuttent study, the low frequency fluctuations of the tissue blood volume and the blood volume pulse in the fingertips of healthy subjects were investigated using 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. minus 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 but in some examinations the two parameters were inversely correlated. PPG measurements performed in near infrared radiation, showed better correlation between BV and AM than for red light PPG. The results show that several mechanisms are involved in the low frequency fluctuations in the tissue blood volume. The analysis of the PPG signal provides, therefore, a potential tool for studying the mechanism of the regulation of the microcirculation by the sympathetic nerves.