Application of finger arterial compliance-blood pressure function for an evaluation of the sympathetically mediated vascular tone

Normalized pulse volume (NPV, Sawada, Tanaka, & Yamakoshi, 2001) was calculated on a beat-to-beat basis by dividing the ac component by the dc component in near-infrared finger photoplethysmogram. Finger arterial compliance index (CI) was obtained by dividing NPV by the respective pulse pressure. Twelve female subjects underwent immersions of the contralateral hand in water at two different temperatures (44°C, 22°C). During the last 3 min of each of the 8-min resting and immersion conditions, CI was measured for the finger position at heart level, 15 cm, and 30 cm below the heart for 1 min each. Results indicated that a negatively linear regression could be applied to the beat-to-beat data on log CI and mean blood pressure (MBP) over the three finger position (whole regression). CI calculated at 90 mmHg (CI 90) was arbitrarily chosen as a reference point for comparing compliance among conditions. CI 90 decreased significantly during the 22°C condition. In conclusion, CI seemed more valid as an index of the finger arterial vascular tone through the removal of MBP influence.