Simultaneous measurement of the photoplethysmographic signal variability in the right and left hands

The photoplethysmographic (PPG) signal, which is a measure of the systolic oscillations in the tissue blood volume, spontaneously fluctuates in the re spiration rate and in lower frequencies similar to the heart rate fluctuati ons. In the current study, the low frequency fluctuations, which are attrib uted to the sympathetic nervous system activity, were obtained from PPG exa minations simultaneously performed on the right and the left hands of healt hy subjects and hemiplegic patients. For normal subjects, the fluctuations in the two hands were found to be correlated, demonstrating their central o rigin. For some of the hemiplegic patients, the coefficient of correlation between the right and the left hands was significantly lower than the norma l range. The simultaneous measurement of the PPG signal fluctuations in bot h hands provides information on the adequate function of the autonomic nerv ous system.