The development of myocardial changes during intermittent high altitude hypoxia in rats.

The initial phase and the development of myocardial focal necroses were studied in 50 rats adapted successively to intermittent high altitude. The altitude hypoxia was produced in a low pressure chamber (7000 m, five days a week, four hours daily). First-minute myocardial changes detected by histochemical methods were found after 4 exposures at a level of 3000 m and distinct ones after 8 exposures at a level of 4500 m. Histologically, acute focal necroses were found after 11 exposures at a level of 6000 m. Hypoxia and stress are suggested to account for these myocardial focal changes. During further adaptation no further acute focal necroses were observed.