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Reflectance photoplethysmography as an adjunct to assessment of gravitational acceleration tolerance: preliminary findings.

We have examined the feasibility of using reflectance photoplethysmography to assess Gz acceleration tolerance. Reflectance plethysmograms recorded using a sensor placed on the region of the superficial temporal artery were analysed along with the mean value and the pulsatile component of the Doppler velocity recorded from the opposite temporal artery. The photoplethysmogram signal and pulsatile and mean Doppler velocities were examined as predictors of impending peripheral light loss (PLL) during the experiments. Photoplethysmography correctly predicted a large percentage of the PLL runs (80.5%) and non-PLL runs (98.3%). Mean Doppler velocity predicted a higher percentage of PLL runs (88.1%), but with an unacceptably low rate of non-PLL runs (77.2%). The pulsatile Doppler velocity yielded only 50.7% correct prediction of PLL runs. The results of this preliminary study indicate that, with an improved design of the sensor and the electronics, it may be possible to use reflectance photoplethysmography in acceleration tolerance experiments as a reliable predictor of impending peripheral light loss.