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Frank orthogonal vectorcardiograms (VCGs) were recorded from 10 subjects prior to, during, and for 15 min after exposures to +3Gz , +5Gz, and +7Gz. The order of acceleration exposure was randomized, with the individual exposures separated by at least 1 week. Standard USAF anti-G suits were worn by all subjects. Detailed analysis of the scalar lead electrocardiograms revealed no abnormalities. There were no consistent signs of conduction disturbances or ischemic ST-T segment changes. The QRS axis of the VCG demonstrated posterior rotation in the sagittal plane and counterclockwise rotation in the transverse plane during +Gz stress. The changes in the VCGs recorded during +Gz stress appeared to be related to rotational changes of the heart due to mechanical stress and/or motion within the thorax. There were no ECG or VCG changes indicative of myocardial ischemia and/or damage during or after +Gz stress.

Four female adult miniature swine were acceleration conditioned for a period of 1 month using repeated acute exposure to simulated aerial combat maneuver profiles which exposed the animals to an average of +4.5G, for 106s. This period of conditioning produced adaptation as evidenced by decreased maximal heart rates during +Gz and by the absence of any +Gz induced gross cardiac pathology. Coronary blood flow was measured in these conditioned animals with the radiolabeled microsphere technique. Blood flows were measured under resting conditions, during 60s exposures to +3Gz and +5Gz and 10 min after +5Gz exposure. Coronary flow was increased 2-3 fold during +3Gz and +5Gz. The regional distribution of coronary blood flow during +Gz was similar to that under resting control conditions. There were no significant differences between coronary blood flows during +Gz in these conditioned animals and the values previously reported from the initial exposure of miniature swine to similar levels of +Gz. These results indicate that 1 month of acceleration conditioning of the types used in these studies has no significant effect on the response of coronary blood flow to +3Gz and +5Gz stress.