Changes in clinical cardiologic measurements associated with high +Gz stress

Because of reports of subendocardial hemorrhage and myofibrillar degeneration in animals exposed to sustained high G loads (greater than +6 Gz for 15 s or more), questions have been raised regarding the safety of exposing pilots and human subjects to the similar G-stress levels likely to be encountered in the new high-performance fighter aircraft. Noninvasive clinical cardiologic data, including ECGs, vectorcardiograms, systolic time intervals, and maximal treadmill stress tests, were obtained from two groups of subjects before and at several times after exposure to high-G stress. The group exposed to the greater G stress (three 40-s runs at 8 G and two 40-s runs at 10 G, all in one day) developed moderate cutaneous petechiasis and had other minor physical findings after the G stress, but showed few significant changes in cardiologic data: serum total CPK and LDH levels rose, and preejection period shortened at 48 h poststress. The group exposed to the lesser G stress (one 100-s variable-G maneuver peaking twice at 8 G for 3 s, once a week for 3 weeks) had no symptoms following the G stress, but the vectorcardiograms revealed transient T-loop angle changes, and preejection period measured at 1 week poststress was significantly decreased. Because the serum enzyme changes were noncardiac in origin, and because the few other changes were not in a direction indicative of cardiac damage, we conclude that the G stresses imposed in these studies were not significantly injurious.