Ultrastructural effects of +Gz stress on swine cardiac muscle.

Miniature swine were subjected to 9 +Gz acceleration for 60-120s. Within 2 h following the +Gz force, the anterior papillary muscle was removed and prepared for scanning and electron microscopy. Ultrastructural changes observed in the cardiac myocytes included cellular redistribution of mitochondria and nuclei. Tears in the contractile fibers, bizarre profiles or nuclei, and peculiar membrane-bounded bodies in the cytoplasm also were observed. Hemorrhagic areas were localized around the Purkinje fibers. The T system and plasma membrane appeared unperturbed. The conclusion was drawn that, following high +Gz levels of acceleration, damage to myocardial ultrastructure ensues.