Physiological adjustments of women to prolonged work during acute hypoxia

Five women (23-32 yr) performed bicycle work in a hypobaric chamber for 2 h at 41% of their respective altitude maximal oxygen uptakes (VO2) at 758, 586, 523, and 446 Torr barometric pressures (PB). Steady-state VO2 was achieved within 5 min work at all altitudes. Pulmonary ventilation (29.2 +/- 1.9 (mean +/- SE) 1/min, BTPS), respiratory rate (22 +/- 2 breaths/min), cardiac output (8.5 +/- 1.4 1/min), heart rate (115 +/- 6 beats/min), and stroke volume (75 +/- 13 ml) were similar at all altitudes, but time-related changes differed with altitude. Blood lactates did not change with work duration and were similar at 758 and 586 Torr PB but progressively elevated at 523 and 446 Torr. Blood norepinephrine, measured only at 758 and 446 Torr PB, increased with work but not altitude; epinephrine increased only at altitude. Norepinephrine levels and respiratory, cardiovascular, and thermoregulatory functions were essentially dependent on relative work load; blood lactates and epinephrine levels were not. Many physiological functions in these women performing sustained light work during acute altitude exposure were remarkably stable in contrast to previously reported studies on men.