Instantaneous venous oxygenation estimation using the Photoplethysmograph (PPG) waveform

In this study oesophageal photoplethysmograph data from eight patients under positive pressure ventilation were analysed in order to test the hypothesis that the modulations created by the ventilation in the AC Photoplethysmograph (PPG) signal could be used to estimate venous oxygen saturation. In order to estimate the instantaneous arterial and venous oxygen saturation Smoothed-pseudo Wigner-Ville Distribution (SPWVD) was utilised. The result from this study showed that there was no significant different in the conventional (time domain) arterial saturation and the instantaneous arterial saturation. However, the instantaneous venous oxygen saturation estimated with the ventilator modulation were significantly lower then the conventional arterial saturation (P = 0.008) and also from the instantaneous arterial saturation (P = 0.008).