Stress measurement from wearable photoplethysmographic sensor using heart rate variability data

In this paper we try to explore the concepts of Heart Rate Variability using Photoplethysmographic (PPG) optical sensor. During this process we also try to detect the stress level of the subject from the HRV data. Our nervous system is very tightly connected with our heart. A normal person while resting will have heart rate from 60 to 90 beats per minute. But when a person is stressed the time duration between each beat becomes random when compared to a steady non stressed person. So in this paper we find out how to obtain the HRV from a PPG signal and find out the areas under different frequency regions. Normally we will divide the heart rate into three frequency regions that is VLF, LF and HF which corresponds to very low frequency, low frequency and high frequency respectively. Then we find the periodogram for each of the frequency regions and from those periodograms we find out the area under curve for each frequency region and also the peak frequency in that region. Based on these values we will calculate the LF/HF ratio which is a measure of stress of a person. For stress level calculations we have collected data from persons in rest position with variable breathing rates in order to simulate stress.