Cerebral tissue oxygen status and psychomotor performance during lower body negative pressure (LBNP).
Cerebral oxygen sufficiency was studied noninvasively, using multiwavelength near-infrared spectrophotometry, in eight subjects exposed to lower body negative pressure (LBNP) of up to -90 mm Hg to induce presyncopal symptoms and signs. LBNP caused only small changes in the forebrain measures until the last 60 s of the exposures, whereupon oxyhemoglobin (HbO2) and oxidised cytochrome c oxidase fell, reduced hemoglobin (Hb) rose slightly, and the tissue blood volume (HbO2 + Hb) fell. In subjects showing presyncope, these changes anticipated the onset of a terminal bradycardia by some 20 s and may provide the trigger for cardiovascular decompensation, while the cessation of LBNP led to an overshoot in cerebral blood volume suggestive of a reactive hyperemia. Psychomotor testing showed a significant slowing of reaction time with LBNP, but only for the easiest component of a complex task, while saccadic latencies were found to be shortened following LBNP exposure.
Glaister
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Crew Technology Division, USAF School of Aerospace Medicine, Brooks AFB, TX.
Miller
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D000328:Adult; D001143:Arousal / Q000502:physiology; D001921:Brain / Q000378:metabolism*; D002560:Cerebrovascular Circulation / Q000502:physiology; D003072:Cognition Disorders / Q000503:physiopathology*; D003244:Consciousness Disorders / Q000503:physiopathology*; D003664:Decompression; D006112:Gravitation; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D008833:Microcirculation / Q000503:physiopathology; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D013055:Spectrophotometry, Infrared; D013575:Syncope / Q000503:physiopathology