Comparison of Left and Right Fingertip PPG Signals Using Signal Power Estimates and Poincare Indexes

Photoplethysmography (PPG) is a non-invasive method to measure the relative blood volume change in blood vessels used in a wide range of medical applications. PPG signals can be recorded from different body regions such as fingertips, forehead and earlobes. In this study, information content of PPG signals of the left and the right index fingertips are processed and analyzed. PPG recordings are performed from ten healthy volunteers. Prior to recordings, all volunteers take rest for five minutes. Using a dedicated measurement system, signals are recorded from the left and the right fingertips of each volunteer simultaneously for 60 seconds with a sampling frequency of 50Hz, digitized with 10-bit resolution and stored in a personal computer. Signal average power and Poincare indexes of the signals are estimated and statistically analyzed. There are no systematic differences between the signal power estimated from the left and right fingertip signals (P>0.5). The signal power estimates for the left and the right fingertips show moderate correlations of 0.78, 0.80 and 0.68 for 0-4Hz, 0-2Hz and 2-4Hz frequency bands, respectively. When Poincare indexes SD1 and SD1/SD2 are considered, there are no systematic differences between the left and right fingertip signals (P > 0.5) however a systematic difference exists between the SD2 estimates (P=0.15). SD1 and SD1/SD2 estimates for the left and the right fingertips show high positive correlations of 1.00 and 0.99, respectively. However, a correlation of -0.30 exits for the left and the right fingertips when SD2 estimate is considered.