EFFECTS OF HIGH ALTITUDE ON PULMONARY AND SYSTEMIC BLOOD PRESSURES IN UNANESTHETIZED MONKEYS.

Aortic, pulmonary and left atrial blood pressures were recorded by means of chronically implanted catheters in two pig-tailed monkeys Macaca nemistrina for periods of approximately two weeks at sea-level pre-altitude, four weeks at an altitude of 3,800 meters altitude, then two more weeks upon return to sea-level post-altitude. Aortic and venous pressures were recorded in three additional monkeys at sea-level only. After one week at altitude aortic pressures had approached 125 per cent of the pre-altitude average. The aortic pressure then declined steadily throughout the altitude stay, reaching pre-altitude values during the last week at altitude. In the post-altitude phase aortic pressure dropped below pre-altitude values, reaching a low of 60 to 70 per cent of per-altitude averages, then gradually approaching 100 per cent. Mean pulmonary blood pressures were elevated throughout the altitude stay, with a range of from 142 per cent to 260 per cent of pre-altitude averages. Pulmonary arterial pressures dropped upon return to sealevel, but remained above pre-altitude averages in a range of 100 to 210 per cent. Changes in left atrial pressures were inconclusive. Results of the present study are compared with those of previous high altitude studies on various experimental animals or on humans. It was concluded that the response to altitude of the subhuman primate preparation used in the present study closely parallels that of man, and that therefore such a preparation is to be preferred over other species commonly employed in such studies.