In previous work (Weisman IM, Zeballos RJ, Johnson BD: Cardiopulmonary and gas exchange responses to acute strenuous exercise at 1,270 meters in sickle cell trait. Am J Med 1988; 84: 377-383), no significant differences in cardiopulmonary and gas exchange responses to acute, strenuous exercise were observed between volunteers with sickle cell trait (SCT) and control subjects at an altitude of 1,270 meters. The current study was designed to evaluate the effect of a greater hypoxic stimulus on the response of healthy, black male basic recruits, 11 with SCT (HbAS) and 11 control subjects, to acute strenuous exercise. Simulated 2,300-meter and simulated sea-level conditions were achieved by adjustment of the fraction of inspired oxygen (simulated condition of 2,300 meters equal to 18 percent; simulated sea-level condition equal to 24 percent) at the same barometric pressure (656 mm Hg). For each simulated condition, the subjects performed an incremental exercise test to exhaustion on a cycle ergometer. One steady-state exercise test with radial arterial access for arterial blood gases was performed under each condition on Day 2. Peak incremental exercise values for oxygen consumption (2.9 versus 2.81 liters/minute), heart rate (189 versus 187 beats/minute), oxygen pulse (15.4 versus 15.1 ml/beat), and anaerobic threshold (1.59 versus 1.62 liters/minute), at the simulated 2,300-meter height revealed no significant differences between men with SCT and control subjects, respectively. A 5 to 9 percent decrement in exercise performance at the simulated 2,300-meter level compared with exercise performance at the simulated sea-level condition was noted for both groups. Steady-state exercise values for arterial oxygen tension (64 versus 65 mm Hg), arterial oxygen saturation (90 versus 90 percent), alveolar-arterial oxygen pressure difference (22 versus 21 mm Hg), and physiologic dead space to tidal volume ratio (12 versus 11) at the simulated condition of 2,300 meters were similar for the SCT and control groups, respectively. It is concluded that in a moderate hypoxic environment, the cardiopulmonary and gas exchange responses of persons with SCT during brief episodes of exhaustive exercise were comparable to those of control subjects.
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