ABSTRACT
BACKGROUND: One of the key factors in maintaining optimal cognitive performance in the high-G environment is the adequate delivery of oxygen to the cerebral tissue. As eye-level blood pressure is compromised at 22 mmHg x G(-1), perfusion to the peripheral cerebral tissues (cerebral cortex) may not be adequate to support the mental demands of flight. This study measured the effect of closed-loop flight simulations (3 min) on cerebral oxygen saturation changes (rSO2), arterial oxygen saturation (SAO2), and heart rate (HR), in both rested (8 h of rest) and sleepless (24 h without sleep) conditions. METHODS: Subjects (16; 8 males and 8 females) were subjected to G-exposures via closed-loop flight simulations in a series of four 3-min sorties flown by subjects on the Dynamic Environment Simulator (centrifuge) in either a rested or a sleepless state. Prior to the centrifuge flight, subjects were instrumented with sensors for measurement of arterial oxygen saturation (SAO2) and regional cerebral tissue oxygenation (rSO2). Subjects wore the standard flight suit, boots, CSU-13B/P anti-G suit, and the COMBAT EDGE positive-pressure breathing for G-protection system. RESULTS: Significant changes in cerebral and arterial oxygen saturation were observed within groups when comparing pretest baselines and minimum values during the test and pre- and post-G rSO2, SAO2, and HR in both the rested and sleepless state, (p # 0.01), respectively, for each group. Comparisons between groups showed women to have significantly smaller regional cerebral cortex oxygen decreases than men (p # 0.01). No significant changes in SAO2, however, were observed between groups. Both men and women showed a slow recovery of rSO2 values to the prebaseline levels. CONCLUSIONS: Sleeplessness had no effect on the rSO2, SAO2, and HR compared with the rested condition. During acceleration, regional cerebral tissue oxygen decreased 13% in men compared with 9% in women. The recovery of cerebral tissue oxygen levels to prebaseline values was retarded somewhat when compared with the recovery response of arterial oxygen saturation.
Subject(s)
Aerospace Medicine , Hypergravity/adverse effects , Hypoxia, Brain/etiology , Hypoxia, Brain/metabolism , Military Personnel , Oxygen/metabolism , Sex Characteristics , Adult , Brain Chemistry , Cerebral Cortex/metabolism , Female , Gravity Suits , Heart Rate/physiology , Humans , Hypoxia, Brain/physiopathology , Hypoxia, Brain/prevention & control , Male , Oximetry , Regression Analysis , Rest/physiology , Sleep Deprivation/physiology , Valsalva ManeuverABSTRACT
BACKGROUND: Disease of the major vessels in the neck can disrupt autoregulation and lead to changes in the cerebral blood flow and cerebral autoregulation. These changes can be reflected by means of cerebral oxygen saturation. METHODS: We measured cerebral oxygen saturation in 20 patients with atherosclerotic disease of the carotid and vertebral arteries and compared results with 10 normal subjects. Saturation was measured using a noninvasive near-infrared device, the transcranial cerebral oximeter. RESULTS: There were marked decreases in cerebral oxygen saturation in patients with carotid-vertebral artery disease when the position of the patient was changed, from supine to erect. CONCLUSION: Changes in regional cerebral oxygen saturation inpatients with carotid-vertebral artery disease may reflect disruption of cerebral autoregulation.
