A. Accuracy of Differential Estimation Using Single Mobile
The accuracy of the results relies entirely on the effective estimation of VTT from the graphs. Identification of the time instance of S1 sound from the audio was an easy task with proper filtering of the signal, but the selection of the corresponding peaks in the video intensity was difficult in some situations due to presence of flat peaks instead of a sharp for a systolic pulse in the video intensity plot. The flat peak pattern appears due to inappropriate pressure applied by the finger and misplacement of finger while placing on the camera. Fig. 9(a) shows a plot with sharp peaks and Fig. 9(b) shows a pattern of flat peaks. A sample data set was considered and the VTT was obtained using both sharp and flat peaked data points. Table II shows the values of VTT and Ps computed from data consisting of 1) ten sharp peaks (SP); 2) five sharp peaks and five flat peaks (SP + FP); and 3) ten flat peaks (FP). For verifying the Ps estimated using this method, we measured the blood pressure as 125 mmHg for a single subject using a commercial meter.From Table II,it was determined that the presence of sharp peaks in the data resulted in higher accuracy when compared to flat peaks. Hence, for an accurate measurement of blood pressure, the sharp peaks play an important role.