Pulse Waveform and Pulse Amplitude Analysis During Lower Body Negative Pressure

The use of lower body negative pressure (LENP) as an acceleration pre-conditioning technique for space applications was investigated. The purpose of this study was to evaluate changes in cephalic blood flow during LBNP. The intent was to see if detection or warning of impending syncope was possible, and to simulate effects which occur under exposure to + Gz. Ten subjects underwent the following LBNP profile while in a standing position: Five minutes of baseline at ambient pressure, followed by increments of -10 mm Hg every three minutes to a minimum of -50 mm Hg. They remained at -50 mm Hg for a maximum of twenty minutes or until presyncopal symptoms occurred. An additional five minutes of post-LBNP baseline data were collected. The analog pulse waveform signals were obtained from a pulse oximeter sensor located approximately at eye level on the subject's ear lobe. The pulse waveform analysis included pulse area, amplitude, and duration. Six of the ten subjects experienced presyncopal symptoms during the LBNP profile. Significant changes were observed in several variables at the presyncopal endpoint and included: pulse waveform area (P =0.0048), pulse waveform amplitude (P =0.0236). In the non-presyncopal group, pulse waveform area (P =0.0208), amplitude (P=0.0070), and duration (P=0.0030) demonstrated significant changes compared to baseline values after exposure to LBNP.