Measurement of gastric oscillations from finger photoplethysmographic signal using autoregressive model

In this article we investigate the presence of gastric motility (GM) oscillation in the lower frequency range of photoplethysmography (PPG) signal. The objective of this article is to analyze the lower frequency oscillations of PPG signal using the novel autoregressive (AR) model and studying the presence of gastric motility (GM) rhythm in finger PPG. We acquired finger PPG and GM (measured using Electrogastrogram, EGG) signals at the sampling rate of 100 Hz simultaneously from 10 healthy subjects for 30 minutes duration in fasting and postprandial states. A lower frequency oscillation (≈ 0.05 Hz) called slow wave was extracted from PPG signal which looks similar to the slow wave of GM in both shape and frequency in the range (0 – 0.1953) Hz using discrete wavelet transform (DWT). In a previous study, we demonstrated that there is a good cross-correlation exists between slow waves on both PPG and EGG signals [Annals of Biomedical Engg. DOI: 10.1007/s10439-010-0113-4]. Here in this study, power spectral density (PSD) of PPG and EGG slow waves were estimated using AR spectral estimation method. Dominant frequencies of PPG and EGG slow wave were estimated and the results imply that finger PPG signal reveals GM related information.