Measurement of the variability of the skin blood volume using dynamic spectroscopy

The light incident on the skin is subject to scattering and absorption by the tissue itself and by the blood. The measurement of the transmitted or reflected light from the tissue — photoplethysmography — shows oscillation in the heart rate due to tissue blood volume increase during the systolic heart contraction period. In the current study, two parameters were derived from the photoplethysmographic signal: BV which is related to the total absorbed light in the tissue and AM, the amplitude of the pulsatile signal, which is related to the systolic blood volume increase. Both parameters fluctuate due to the activity of the autonomic nervous system, and in particular fluctuate in low frequency — below 0.05 Hz which is attributed to the sympathetic nervous system activity. The spontaneous fluctuations in BV and AM are more correlated for infrared than for red light, due to difference between their absorption constants for oxygenated and reduced hemoglobin. The dynamic spectroscopy of the skin provides information on the autonomic nervous regulation of the tissue blood flow.