A novel non-invasive trans-reflectance photoplethysmographic probe for use in cases of low peripheral blood perfusion.

The acquisition of reliable and meaningful photo-plethysmographic (PPG) signals using conventional pulse oxime-try technology may be compromised by conditions of low tissue perfusion. We have developed a novel 'trans-reflectance' PPG measurement system which combines reflectance and transmit-tance together into a single mode. For comparison purposes the system also enables the independent display of reflectance and transmittance PPG signals simultaneously. Preliminary experiments were performed on volunteers to assess the performance of the probe, where, artificial hypoperfusion was created in individuals and data was recorded with the newly developed trans-reflectance photoplethysmographic mode, and the conventional transmittance and reflectance PPG modes. The PPG signals recorded during hypoperfusion using the trans-reflectance mode were of good quality with higher signal-to-noise ratio than those obtained from the transmittance and reflectance modes.