Correlation of PPG and Accelerometer Signals

Accelerometers are being used in biomedical applications for assessing the functioning of the heart by measuring the vibrations created due to pulses. They are being used in smartphones and smart watches to find heart rates. A pulse sensor is an optical sensor which takes optical input and requires a photodiode to absorb the output radiations, whereas accelerometers require only vibrations as input. So pulse sensors can be replaced by compact and more sensitive accelerometers. The signals were acquired using the SEN-11574 pulse sensor and ADXL335 accelerometer from 10 volunteers. The main peaks and secondary peaks of the accelerometer signals and the main peaks and secondary peaks of the PPG signals were found. The time difference between the peaks was calculated for both the signals. This peak to peak time intervals are indicators of heart rate. The coefficient of correlation between PPG and accelerometer signals was found for each sample, and the average coefficient of correlation for the acquired ten samples was found to be 0.9912, which implies a strong positive correlation between the signals.