THE VARIABILITY OF THE PHOTOPLETHYSMOGRAPHIC SIGNAL - A POTENTIAL METHOD FOR THE EVALUATION OF THE AUTONOMIC NERVOUS-SYSTEM

The heart rate variability is composed of low- and high-frequency fluc tuations, which are mediated by the sympathetic and the parasympatheti c nervous systems. The baseline and the amplitude of the photoplethysm ographic (PPG) signal also show fluctuations in the same frequencies. In the current study, PPG examinations were performed on the fingers o f normal subjects and diabetic patients, and three parameters were der ived from each PPG pulse: the baseline of the pulse, its amplitude and its period (which is equal to the heart period). The level of the var iability of each PPG pulse parameter was measured by the ratio of the standard deviation of the parameter to its mean value. The level of th e low-frequency fluctuations for the PPG amplitude and for the heart c ycle period did not differ between males and females, but was lower fo r diabetic patients, indicating lower activity of the autonomic nervou s system. The curves of the baseline and the amplitude of the PPG sign al for the non-diabetic subjects showed high correlation between the l eft and the right hands. For most of the diabetic patients the right-l eft correlation coefficients were significantly lower than those for t he non-diabetic subjects. Our initial results have shown that the vari ability of the PPG parameters shows promise for the assessment of the function of the autonomic nervous system.