Changes of cerebral oxygen saturation under lower body negative pressure

The purpose of this study was to observe and analyse the changes of regional cerebral oxygen saturation (SrO2) under lower body negative pressure (LBNP). 12 healthy young subjects were tested in an LBNP chamber in sitting position. Incremental negative pressure was used and end points of test were onset of presyncopal symptoms or completion of the 15min test. The results were: (1) SrO2 showed a significant decrease under LBNP; (2) The magnitude of decrease of SaO2 showed significant differences among subjects with different reactions at the termination of LBNP; (3) Under LBNP the arterial oxygen saturation (SrO2) kept constant. The changes of SrO2 correlated strongly with the percentage changes of superaorbitalis arterial blood flow (r = 0.59-0.86, P < 0.05 or 0.01). It was suggested that the changes of SrO2 were related to the decrease of cerebral blood flow under LBNP. It was possible to use SrO2 to detect presyncopal and syncopal symptoms. So the monitoring of SrO2 could be used in studies of G-LOC.