Effects of three kinds of hypoxias on vigilance performance.

The consequences for vigilance performance of inhaling carbon monoxide at altitude were examined. In addition, the effects of altitude and CO at an equivalent reduction in O2-carrying capacity were compared. Ten subjects performed a visual vigilance task under four atmospheric conditions. Physiological measures included heart rate, blood pressure, and ventilation. Blood hemoglobin and CO levels were measured directly from blood samples drawn after 0,50 and 120 min of exposure. The physiological variables measured and subjective responses of subjects showed no changes attributable to the atmospheric conditions. A statistically significant change in vigilance performance as measured by precentage of signals detected, was found between control and low oxygen; however, performance under CO and the combination of CO and low oxygen was not different from control. The lack of deterioration in performance under the combination of CO and low oxygen suggested that the increased severity of the stress resulted in activation of compensatory mechanisms which counterbalanced the decreased O2 available to the tissues.