Coronary and myocardial adaptations to high altitude in dogs.

The objective of this study was to determine whether exposure to high altitude (hypoxic hypoxemia) induces coronary and/or collateral growth. Fourteen mongrel dogs were maintained at a simulated altitude of 18,000 ft for 1 mo and 7 dogs maintained for 3 mo. Within 2 days after their sojourn, the following data were obtained at ambient pressure: pulmonary, right heart chamber, and wedge pressures as well as cardiac output. On an isolated heart preparation, coronary and collateral flows were determined; each vessel was injected with a different color tracer; and the heart was sliced, separated by perfusion territories, and examined for myocardial hypertrophy. We found that pulmonary artery pressures in altitude-adapted animals were higher compared with controls, and coronary flow per gram was increased after 1 mo of exposure but not different from control after 3 mo. Collateral flows were not significantly different from that of control animals, and biventricular hypertrophy occurred with right ventricular dominance. Comparing these results with those that we obtained previously from anemic animals, we favor the hypothesis that oxygen availability rather than blood flow velocity is most likely linked to vascular growth.