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 experienced by fighter pilots represent an extreme form of orthostatic challenge. G-induced loss of consciousness (G-LOC) represents a failure of the baroreflex system to maintain the appropriate level of cerebral perfusion. The anecdotal experience of fighter pilots is that their cardiovascular systems adapt to frequent exposure to high +Gz levels. Hypothesis: The purpose of this study was to demonstrate that the baroreflex-mediated cardiovascular response of a group of 8 fighter pilots to a mild accelerative stimulus differs from that of a group of 12 non-pilots. Methods: Arterial pressures and heart rate responses to rapid head-up tilting to +75°were compared between the two groups. Five variables were examined: systolic, diastolic, mean arterial and pulse pressures, and heart rate. Results: The cardiovascular responses of the groups were fundamentally different. In response to tilt, the non-pilots showed little change in systolic and mean arterial pressures, diastolic pressure increased slightly and pulse pressure decreased significantly. In the pilot group, however, significant increases were observed in systolic, diastolic and mean arterial pressures (p < 0.05), whereas pulse pressure did not change. Between groups there were significant differences observed in terms of arterial pressures (p < 0.05), but not heart rate. Conclusion: The baroreflex of a fighter pilot is capable of adapting to +Gz, becoming a more sensitive and effective BP control system as a result. This adaptation affords the pilot greater protection against G-LOC.