Cerebral Blood Flow Based Computer Modeling of Gz-Induced Effects

BACKGROUND: There is continued interest in acceleration (G) effects in civil aviation, as G-induced loss of consciousness (G-LOC), impaired consciousness, and visual effects play a role in aerobatic, agricultural, and military aviation accidents. METHODS: A software model [the Civil Aerospace Medical Institute G-Effects Model (CGEM)] based on physical and physiological variables related to in-flight tissue resupply and using oxygen flow as a proxy for supply availability, was developed to evaluate risk of G-LOC and related phenomena in aeronauts. Aeronauts were modeled using several parameters, including sex, cardiovascular fitness, and other common modifiers such as G-suits, positive pressure breathing gear, anti-G straining, and other muscle tensing. The software was validated by comparison with experimental data from the peer-reviewed literature. RESULTS: CGEM predicted physiological effects of Gz exposure accurately, particularly for rapid onset rates. Predicted times to G-LOC and absolute incapacitation periods were consistently within 1 SD of pooled results obtained during centrifuge experiments using U.S. Navy (USN) and U.S. Air Force (USAF) pilots. Predictions of G tolerance based on visual effects onset also compared well with published data, as did evaluation of symptoms expected during a difficult aerobatic maneuver. DISCUSSION: CGEM is a new tool for civil and military aviation. Rather than providing a simple G tolerance number, flight surgeons, pilots, and accident investigators can gain insight into changes in risk-from factors such fatigue, medications, dehydration, and anti-G countermeasures used-through proper selection of parameters.