A novel diagnostic method has been developed for microvascular lesions using time constants obtained from the peripheral Windkessel model (WK model). Since the time constant of the WK model reflects changes in resistance and vascular elasticity due to a decrease in the internal vessel diameter, an increase in surface roughness of intima, and an increase in blood viscosity, it was proposed to use it as an indicator for vascular evaluation. For noninvasive and easy measurement of the time constant, it is necessary to calculate from the frequency components of the arterial pressure pulse and phalangeal volume pulse. Therefore, it is necessary to establish each pulse wave measurement method and to consider the optimal combination. The fingertip photoplethysmograph was used because it is said to be proportional to the volume pulse of the fingertip. Owing to the difficulty of using the conventional air-conduction method for measuring the arterial pressure pulse, reflection photo and cuff pressure methods were considered. The probability of obtaining time constants and the fluctuation rate were compared across the three methods. The results demonstrated the superiority of the air-conduction method over the other two. The air-conduction method was considered to produce a waveform proportional to the arterial blood pressure pulse wave. The best pulse wave measurement method for measuring peripheral time constants were the air-conduction method for arterial pressure pulse and the transmission photo method for fingertip volume pulse.
