Influence of mental stress on the arterial stiffness parameters detected from photoplethysmographic signal waveform

In order to improve the planning decisions of the urban environment and consider the well-being of the residents, an objective assessment of mental stress in the urban environment is needed. The aim of this study was to investigate the changes in the photoplethysmographic (PPG) and second derivative of PPG (SDPPG) signal parameters related to arterial stiffness during the mental stress assessment. The study was carried out on 15 female and 13 male subjects between the age of 25 and 60 years. The finger PPG signal was recorded with a transmission mode sensor during the subject's inactive state, followed by an arithmetic stress test. The PPG signals were post-processed and the statistically significant increases in an augmentation index related parameter PPGAI, in ‘aging index’ AGI, and in the SDPPG amplitude ratios b/a and decreases in d/a and the slope of the ascending waveform front due to induced mental stress were found ( $p<0.05$ ). The results indicate that the arterial stiffness was increased during the stress test. In summary, the PPG waveform parameters related to arterial stiffness could be considered for the mental stress assessment.