High altitude tolerance of normal dogs and dogs with myocardial infarcts

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Abstract
Normal dogs, sham-operated dogs and dogs with large myocardial infarcts produced by coronary artery ligation were exposed to simulated altitudes of 34,000–38,000 feet for 3–3 1/2 hours. Twelve of thirteen normal dogs and all eight dogs with 3–14-day infarcts survived exposure to 34,000 feet. Five of six dogs with 2-day infarcts and three of six sham-operated dogs died during an exposure to 34,000 feet. There were no deaths among eight normal dogs and two deaths among four dogs with 7–18-day infarcts during exposure to 38,000 feet. Respiratory and heart rates increased markedly in all dogs at high altitudes. Throughout the exposures, ectopic ventricular beats were recorded frequently in most of the dogs with infarcts, less frequently in sham-operated dogs and rarely in normal dogs. Deaths among normal and sham-operated dogs and some of the deaths among dogs with infarcts were from respiratory failure. Two deaths from ventricular fibrillation were recorded in dogs with infarcts. Exposure to high altitudes did not modify significantly either the gross or histologic appearance of the infarcts.