Two cases are presented of Canadian Forces pilots who experienced inflight bradycardia during 15 s of -1 Gz acceleration. The bradycardia was characterized by rapid cardio-deceleration, stable bradycardia, then cardio-acceleration during recovery following the -Gz exposure that was slower than the cardio-deceleration. Vagally mediated bradycardia in humans subjected to -Gz acceleration stress has been previously documented in laboratory studies. This bradycardia may be operationally significant since it signifies the presence of other physiological effects that predispose aviators to reduced subsequent +Gz tolerance. Research to investigate the implications of reduced +Gz tolerance following -Gz acceleration is warranted.
Aerospace Medicine Gravitation