EVIDENCE OF BAROREFLEX ADAPTATION TO REPETITIVE +GZ IN FIGHTER PILOTS

Background: The arterial baroreflex acts to maintain arterial pressure in the face of an orthostatic challenge. The high +Gz loads experienc ed by fighter pilots represent an extreme form of orthostatic challeng e. C-induced loss of consciousness (G-LOC) represents a failure of the baroreflex system to maintain the appropriate level of cerebral perfu sion. The anecdotal experience of fighter pilots is that their cardiov ascular systems adapt to frequent exposure to high +Gz levels. Hypothe sis: The purpose of this study was to demonstrate that the baroreflex- mediated cardiovascular response of a group of 8 fighter pilots to a m ild accelerative stimulus differs from that of a group of 12 non-pilot s. Methods: Arterial pressures and heart rate responses to rapid head- up tilting to +75 degrees were compared between the two groups. Five v ariables were examined: systolic, diastolic, mean arterial and pulse p ressures, and heart rate. Results: The cardiovascular responses of the groups were fundamentally different. In response to tilt, the non-pil ots showed little change in systolic and mean arterial pressures, dias tolic pressure increased slightly and pulse pressure decreased signifi cantly. In the pilot group, however, significant increases were observ ed in systolic, diastolic and mean arterial pressures (p < 0.05), wher eas pulse pressure did not change. Between groups there were significa nt differences observed in terms of arterial pressures (p < 0.05), but not heart rate. Conclusion: The baroreflex of a fighter pilot is capa ble of adapting to +Gz, becoming a more sensitive and effective BP con trol system as a result. This adaptation affords the pilot greater pro tection against G-LOC.