Photoplethysmogram Signal Morphology-Based Stress Assessment

Stress is a healthy natural response to a perceived or actual threat. However, when stress is persistent, it may decrease work productivity, increase the risk of diseases, and affect the quality of life. Stress is reflected in physiological variables, such as heart rate, blood pressure, and pulse wave velocity among others. A photoplethys-mogram (PPG) contains information related to pulse rate and blood pressure. This study analyses parameters derived from PPG signal morphology for mental stress assessment.A low-complexity algorithm is designed using bandpass filtered higher-order derivatives of the PPG signal for estimation of six morphological parameters: the forward pulse wave amplitude A
1
, the systole and diastole durations T
1
and T
d
, the time delays of reflected waves T
12
and T
13
from the renal and iliac sites in the central arteries, and the pulse duration T
p
. The parameters were investigated on a set of 18 healthy subjects by using a modified Trier Social Stress Test.The results show that the most sensitive PPG morphology parameters to mental stress are the amplitude of forward wave A
1
, the duration of diastole T
d
, the time delay of the reflected wave T
13
, and the pulse-to-pulse interval T
p
.