A Proposal for a Correction Method to Obtain Photoplethysmographic Amplitude from a Smartwatch

Abstract

In recent years, the number of patients with mental illness due to mental stress has been increasing. Therefore, the evaluation of mental stress in daily life is necessary to prevent a mental illness. Conventional evaluation of mental stress uses biological information such as respiration, heart rate, saliva, and photoplethysmography (PPG). Among them, PPG is measurable by a daily smartwatch. Therefore, we examined the possibility of evaluating mental stress using PPG obtained from a smartwatch. In the mental stress evaluation, we focused on the photoplethysmographic amplitude (PPGA), which is the characteristic point of PPG. PPGA can be used to evaluate mental stress even with intermittent data. This is suitable for mental stress evaluation when the data from smartwatches may not be procured due to body movements. In contrast, the accuracy of acquiring PPGA from a smartwatch might be low owing to various factors such as changes in blood flow or skin temperature. Hence, in this research, we proposed a correction method to obtain a stable and accurate PPGA. In our experiment, the effectiveness of this method was examined by comparing the photoplethysmograph data and corrected data of the smartwatch after measuring with the photoplethysmograph and smartwatch simultaneously. Our results confirmed that the proposed method procures the PPGA with high accuracy.