Accession Number : ADA019119

Title :   Sustained Venoconstriction in Man Supplemented with CO2 at High Altitude,


Personal Author(s) : Cruz,Julio C. ; Grover,Robert F. ; Reeves,John T. ; Maher,John T. ; Cymerman,Allen

Report Date : MAY 1975

Pagination or Media Count : 25

Abstract : Five male subjects were exposed to simulated high altitude (4000-4400 m) with supplemental CO2 in a hypobaric chamber for four days. Similar alveolar O2 tensions were obtained in four control subjects exposed to an altitude of 3500-4100 m without CO2. Thus both groups had comparable hypoxic levels, but one was nearly normocapnic and the other became spontaneously hypocapnic. A water-filled plethysmograph was used to determine forearm flow and venous compliance. Systemic blood pressure was measured with the cuff procedure. Catecholamines were measured in 24-hour urine collections. Venous compliance fell in both groups and was less (p < 0.01) than control values after 2, 48 and 72 h at high altitude. No significant difference was observed between the groups. Forearm flow and resistance were unaltered at altitude in the group with CO2, supplementation while forearm flow decreased and resistance increased in the hypocapnic group at 72 h of exposure. Urinary catecholamines increased in the group with CO2 and remained unaltered in the hypocapnic group. It is concluded that hypoxia is responsible for decreasing venous compliance, and hypocapnia for increasing resistance and decreasing flow. Group differences observed in urinary catecholamines may be explained by differences in arterial pH.

Descriptors :   *Vasoconstricting, *Carbon dioxide, *High altitude, Exposure(Physiology), Hypoxia, Plethysmography, Catecholamines, Blood flow, Simulation, Hypobaric chambers, Deformation, pH factor, Urine, Blood pressure, Oxygen, Resistance(Biology), Males, Human body, Military medicine

Subject Categories : Stress Physiology

Distribution Statement : APPROVED FOR PUBLIC RELEASE