The importance of myocardial perfusion in the pathogenesis of the cardiac pathology associated with +Gz exposure in miniature swine.

Minor cardiomyopathy has been associated with exposure of miniature swine to levels of high sustained +Gz which can be attained routinely in new USAF high-performance aircraft. One possible cause of these lesions is total or regional myocardial ischemia. To test this hypothesis, regional coronary blood flow was measured with the radiolabeled microsphere technique in chronically instrumented miniature swine during 60-s exposures to +3Gz, +5Gz, or +7Gz. Acceleration exposure resulted in detectable left ventricular subendocardial hemorrhage in 1 of 5 animals exposed to +3Gz, in 7 of 8 animals exposed to +5Gz and in all 8 animals exposed to +7Gz. All levels of +Gz stress caused 2-3 fold increases in coronary blood flow. The regional distribution of coronary blood flow during +Gz was similar to that under resting control conditions as long as aortic diastolic pressure was maintained. There was no clear evidence of total or regional myocardial ischemia during +Gz or of any relationship between regional coronary blood flow and the presence of subendocardial hemorrhage. It is concluded that myocardial ischemia is not a primary factor in the pathogenesis of the cardiac lesions associated with the exposure of miniature swine to +Gz stress.