Analysis of i-PPG signals acquired using smartphones for the calculation of pulse transit time and oxygen saturation

Image-based photoplethysmography (i-PPG) is one of the blooming research fields which make use of videos of individuals to obtain photoplethysmography (PPG) signals. Vital parameters such as SPO
2
and a correlation to blood pressure (BP) were obtained from i-PPG. Videos are taken from the fingertips of 3 healthy individuals and are analyzed for calculating oxygen saturation and pulse transit time (PTT). To calculate the oxygen saturation (SPO
2
), each video is divided into five-second segments. The values found are compared with those calculated from other segments and with reference values obtained from the standard pulse oximeter. To calculate PTT, each frame of the video is divided into four vertical sections of the equal size. Frome these rectangles, PTT is calculated. The results show that the calculated SPO
2
values have mean absolute error and standard deviation between 0.09 and 1, and± 0.571 respectively. An inverse relationship is observed between the calculated PTT values and reference BP values. The correlation between diastolic BP and PTT is found to be good which makes it a suitable parameter for calculating the same.