Using time-frequency analysis of the photoplethysmographic waveform to detect the withdrawal of 900 mL of blood.

Background: We designed this study to determine if 900 mL of blood withdrawal during spontaneous breathing in healthy volunteers could be detected by examining the time-varying spectral amplitude of the photoplethysmographic (PPG) waveform in the heart rate frequency band and/or in the breathing rate frequency band before significant changes occurred in heart rate or arterial blood pressure. We also identified the best PPG probe site for early detection of blood volume loss by testing ear, finger, and forehead sites.

Methods: Eight subjects had 900 mL of blood withdrawn followed by reinfusion of 900 mL of blood.