Normalized pulse volume (NPV) derived photo-plethysmographically as a morevalid measure of the finger vascular tone

Normalized pulse volume (NPV) was advocated as a more valid measure for the assessment of finger vascular tone. Based on the optical model in the fing er tip expressed by Lambert-Beer's law, NPV is expressed as DeltaI(a)/I. He re, DeltaI(a) is the intensity of pulsatile component superimposed on the t ransmitted light (I). Theoretically, NPV seems to be superior to the conven tional pulse volume (PV; corresponding to DeltaI(a)). Firstly, NPV is in di rect proportion to DeltaV(a), which is the pulsatile component of the arter ial blood volume, in a more exact manner. Relatedly, NPV can be processed a s if it is an absolute value. Secondly, the sensitivity of NPV during stres sful stimulations is expected to be higher. These expectations were support ed experimentally using 13 male students. Firstly, the correlation between cutaneous vascular resistance in the finger tip (CVR) and NPV was higher th an that between CVR and PV among all the subjects, although there was not m uch difference between these correlations within each subject. Secondly, NP V decreased much more than PV during mental stress. Some limitations of the present study were addressed, including the point that certain factors can violate the direct proportional relationship of NPV and PV to DeltaV(a). ( C) 2001 Elsevier Science B.V. All rights reserved.