An analysis of the risk of human cardiac damage during +Gz stress: a review.

The available information concerning the subendocardial hemorrhage, myofibrillar degeneration, and necrosis observed in miniature swine after acute +Gz exposure, is reviewed and evaluated for any possible occurrence of similar pathology in humans. It is concluded that +Gz exposure poses no significant risk for cardiac damage in humans. Three primary considerations lead to this conclusion: 1) The lesions in swine probably result from very high (toxic) levels of both sympathetic adrenergic tone to the heart and circulating plasma catecholamines acting on the cardiac cells. Most of these catecholamines appear to be released as a result of the overall stress involved in exposing conscious miniature swine to +Gz on the centrifuge, and not directly as the result of the +Gz per se. Thus, the lesions in miniature swine appear to develop as a consequence of a somewhat unique form of the porcine stress syndrome. 2) +Gz exposure is not as psychologically stressful for humans. Therefore, humans would not be expected to have, and do not appear to have, catecholamine levels (cardiac or systemic) as high as those observed in miniature swine during +Gz stress. This conclusion is supported by direct comparisons of the heart rate and plasma catecholamine levels in men and miniature swine during +Gz exposure. 3) Although a large amount of clinical cardiologic data exists from humans who have been exposed to +Gz stress, none of these data indicates any degree of cardiac damage. Even more conclusive is the absence of any cardiac damage in the heart of a human subject who had many significant +Gz exposures over a 2-year period. Thus, the pathology in miniature swine does not appear to be an acceleration phenomenon, and probably does not occur in humans exposed to +Gz stress.