Effect of finger pressure on blood pressure measurement using photoplethysmography

Abstract

Photoplethysmography (PPG) is a technique that uses a light source by allowing light to pass through a fingertip and detect the reflection of light to obtain the PPG signal. The PPG signal can be used to monitor personal health and to determine the blood pressure (BP) value. However, it is difficult to obtain a reliable PPG signal due to various environmental factors. A pressure that a finger presses on the sensor during measurement is one of the main factor to obtain a wave-like PPG signal. In this work, effect of finger pressure on blood pressure measurement using PPG is intensively investigated in order to improve the reliability and accuracy. The BP prototype with a force sensor put at a location of fingertip next to the light sensor is developed in order to detect a finger pressure. An optimum condition of the fingertip pressure for the BP measurement is evaluated by using a maximum and minimum values of PPG signals from the IR light reflection. The calibration of the BP prototype is performed and back test with a commercial BP monitor. It is found that the optimum finger pressure is in medium region of 65-75 with the reliable wave-form. Moreover, the accuracy of our BP prototype is about +2.0 mmHg compared to the accuracy of commercial BP monitor of +3 mmHg and the accuracy of our previous work of +9.2 mmHg. Thus, our developed BP prototype with the control of the finger pressure exhibits an improvement of reliability and accuracy. This suggests a potential application for a commercial BP monitor without a cuff.