Vascular Responses to Manual PC6 Acupuncture in Nonsmokers and Smokers Assessed by the Second Derivative of the Finger Photoplethysmogram Waveform

Representative traces of the digital volume pulse (DVP; top) and its first and second derivative (d2DVP/dt2; bottom). The a, b, c, d and e waves are defined as the positive and negatives peaks of the d2DVP/dt2 waveform. The aging index was defined as (b – c – d – e)/a, the B:A ratio was calculated as the ratio of the absolute value for the height of the b wave (B) to that of the a wave (A), and the D:A ratio was calculated as the ratio of the absolute value for the height of the d wave (D) to a wave (A).