The novel noninvasive method to diagnose microvascular lesions has been developed using time constants obtained from a radial artery pulse (RAPW) and photoplethysmogram (PPG) utilizing the Windkessel model. There are two methods for measuring RAPW : The first is reflectance photoelectric and the second is air conduction. The purpose of this study is to investigate which method was better. Time constants were calculated from each frequency component, with fixtures attached to the palm and forearm. Pressure applied to the RAPW sensor was varied 6 points. Furthermore, the time constant calculability rate and variation rate calculated when the optical and air conduction sensor were used. The maximum value of the calculability rate for the former and latter were 88% and 100%, respectively. The minimum value of variability of the time constant was 18% and 11% for the former and latter, respectively. The results demonstrate that air conduction was the superior method.
