Assessment of Autonomic Regulatory Function using Pulse Volume of the Finger Photo-plethysmogram

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Normalized pulse volume (NPV) was advocated as a new measure for the assessment of finger vascular tone. Based on the optical model in the finger tip expressed by Lambert-Beer's law, NPV is expressed as ΔIィイD2aィエD2. Here, ΔIィイD2aィエD2 is the intensity of pulsatile component superimposed on the transmitted light (I). From a theoretical point of view, NPV seems to be superior to the conventional pulse volume (PV; corresponding to ΔIィイD2aィエD2). First, NPV is in direct proportion to ΔIィイD2aィエD2, which is the pulsatile to ΔVィイD2aィエD2. On the contrary, PV is only roughly in direct proportion to ΔVィイD2aィエD2. Relatedly, NPV can be processed as if it is an absolute value. Second, sensitivity of NPV against stressful stimulation is expected to be higher than that of PV. These theoretical expectations were supported experimentally using thirteen male students. First, the correlation between cutaneous vascular resistance in the finger tip (CVR) and NPV was higher than that between CVR and PV. Second, NPV decreased much more than PV during stressful tasks (mental arithmetic and mirror drawing). Some limitations of the present study were addressed, including which factors can violate the direct proportional relationship of NPV and PV to ΔVィイD2aィエD2.