Increased carbon monoxide clearance during exercise in humans.

PURPOSE

Hyperventilation increases the clearance of carbon monoxide (CO) from blood; thus, we hypothesized that CO elimination would be enhanced with exercise. Accordingly, this study examined the effect of exercise on the half-life of carboxyhemolobin elimination.

METHODS

Six healthy subjects (three males and three females) with mean ± SD ages of 23 ± 4 yr were exposed to CO sufficient to raise blood carboxyhemolobin concentration to 10-14% on five separate days. The half-life for CO elimination was measured breathing room air at rest and during exercise at three intensities.

RESULTS

Comparisons showed that the half-life decreased with exercise from that during rest in all subjects. The half-life was also measured during 100% oxygen breathing at the lowest exercise intensity of 63 ± 15 W and found to be the least of all measured (23 ± 4 min).

CONCLUSIONS

1. Exercise increased isocapnic ventilation, thereby decreasing the half-life of CO elimination. 2) The half-life of CO elimination represents a hyperbolic function of ventilation [y = y0 + (a / x)], and so increasing ventilation by exercise reaches a point of diminishing returns. 3) Breathing 100% oxygen during mild exercise is as effective in eliminating CO as treatment with hyperbaric oxygen. 4) Moderate exercise under room air conditions is as effective in eliminating CO as breathing oxygen at rest. Thus, the combination of mild exercise, hyperventilation, and normobaric hyperoxia (100% oxygen inhalation) may be considered the "triple therapy" for CO elimination in some patients.