High-Resolution Time-Frequency Analysis Of Neurovascular Responses To Ischemic Challenges

DETECTION OF 900 ML BLOOD WITHDRAWAL BY AMPLITUDE MODULATION ANALYSIS OF THE PHOTOPLETHYSMOGRAPHIC WAVEFORM Christopher G. Scully, MS, Nandakumar Selvaraj, PhD, Frederick W. Romberg, MS, Richa Wardhan, MD, John Ryan, BA, John Florian, PhD, David G. Silverman, MD, Kirk H. Shelley, MD, PhD, and Ki H. Chon, PhD Department of Biomedical Engineering, Worcester Polytechnic Institute, Worcester, MA Department of Anesthesiology, Yale University, School of Medicine, New Haven, CT Department of Biomedical Research and Development, Navy Experimental Diving Unit, Panama City, FL Background: This study was designed 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 waveform in the heart rate frequency band and/or in the breathing rate frequency band prior to significant changes occurring in heart rate or blood pressure. We also identified the best photoplethysmographic probe site for early detection of blood volume loss by testing ear, finger and forehead sites. Methods: 8 subjects had 900 ml of blood withdrawn followed by reinfusion of 900 ml of blood. Physiological monitoring included photoplethysmographic waveforms from ear, finger and forehead probe sites, standard electrocardiogram, and standard blood pressure cuff measurements. The time-varying amplitude sequences in the heart rate frequency band and breathing rate frequency band present in the photoplethysmographic waveform were extracted from highresolution time-frequency spectra. These amplitudes were used as a parameter for blood loss detection. Results: Heart rate and blood pressure showed no significant changes during the protocol. The amplitude signal extracted at the frequency corresponding to the heart rate via timefrequency analysis of the photoplethysmographic waveform from ear, finger, and forehead probe sites significantly (P<0.05) decreased at 300, 600 and 900 ml blood withdrawal compared to baseline. The mean percent decrease in the amplitude of the heart rate component at 900 ml blood loss relative to baseline was 45.2%, 42.0%, and 42.3% for ear, finger and forehead probe sites,