Hypoxia, smoking history, and exercise.

Six nonsmokers and six cigarette smokers, 22-34 years old, performed bicycle work (53% sea level VO2 max) for 30 min in an altitude chamber under four conditions: SL, simulated sea level (PIO2 = 159 torr, PB = 523 torr) with 0.5% HbCO; SLCO, simulated sea level with 4.2% HbCO; and ACO, altitude with 4.2% HbCO. During work at altitude, heart rate (HR), minute ventilation and tidal volume increased and diastolic blood pressures decreased relative to SL. Cardiac output (Qc), stroke volume (SV), and arterial-mixed venous oxygen difference (a--vO2) were similar in smokers and nonsmokers at SL, SLCO, and A. At ACO, nonsmokers increased Qc and SV and decreased a--vO2, but these were not influenced in the smokers. Smokers showed a graded increase in HR when exposed to work in SLCO, A, and ACO. Their lower finger temperatures during A and ACO suggested vasoconstriction in the extremities. Cigarette smokers may be partially adapted to hypoxia.