Accumulated mental stress study using the meridians of traditional chinese medicine with photoplethysmography

Objectives: To investigate accumulated mental stress according to the concept of the meridians of Traditional Chinese Medicine (TCM). This stress was quantified by using pulse spectrum analysis of finger-tip photoplethysmography (PPG). Stress accumulation is one of the main causes of cardiovascular disease and depression in humans, resulting in chronic physiologic malfunctions; however, few studies have thoroughly assessed the quantitative evaluation of accumulative stress using the concept of TCM. Design: This study investigated accumulated mental stress from the perspective of TCM based on an 8-day experiment. The theory of organ resonance was integrated into the proposed PPG sensing instrument to capture the nine harmonics of TCM. Participants were given daily mental arithmetic tasks over 1 week to simulate stress accumulation, and trends in the proportion of the nine harmonics of TCM were extracted over several days and analyzed to identify the affective factors related to cumulative stress. Results: The experimental results showed that the kidney harmonic proportion (C₂) and stomach harmonic proportion (C₅) were significant only on the first few days because of a physiologic phenomenon of temporary stimulation. Most important, the trend of the liver harmonic proportion (C₁) from days 3 to 8 dramatically increased and became gradually saturated because of the influence of accumulated mental stress. Conclusions: The results strongly suggest that pulse spectrum analysis of the PPG signal provides physiologically and pathologically important information on accumulated mental stress and can be useful for TCM analysis.