THE CIRCULATION IN REST AND WORK ON MOUNT EVANS (4,300 M.)

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Abstract
Two subjects were studied in rest and work during a sojourn of 15 days at the summit of Mt. Evans, Colorado (elev. 4,300 m.). In both subjects an increase in the resting cardiac output of about 100% occurred during the first 4-5 days, later followed by a return to values still well above sea-level values. The blood vol. decreased considerably the first 3 or 4 days, then increased to a level still below the sea-level values. The % O2-capacity was increased already the first day, presumably as a result of withdrawal of fluid from the blood. Detns. of the total Oa-capacity showed that an increased formation of red cells first occurred after a latency of 4-5 days. In work the cardiac output was considerably higher the first days than later on, but even then it was still higher than at sea-level. The decline in cardiac output after about a wk. at high altitude is presumably related to the concomitant increase in blood vol. and total O2-capacity. The chemosensible reflexes were active during the whole sojourn at Mt. Evans. If the acclimatized subjects breathed an air mixture enriched with O2, the cardiac output both in rest and during work fell to values lower than the corresponding sea-level values.

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