Maximal O₂ Uptake Limitation in Contracting Skeletal Muscle During Carbon Monoxide Hypoxia

Abstract

Previous studies have shown that at levels of approximately 20% carboxyhemoglobin (COHb), O₂ uptake (VO₂) during maximal exercise in humans, was preserved at normoxic levels (Ekblom and Huot, 1972; Pirnay et al., 1971; Vogel and Gleser, 1972). However, when severe carbon monoxide hypoxia (COH) (COHb-60%) was superimposed on submaximal contractions of the canine gastrocnemius muscle preparation, VO₂ fell below normoxic levels (King et al., 1987). Maximal O₂ uptake (MVO₂) is limited even at levels as low as 7% COHb (Horvath et al., 1975). At levels of 20% COHb, MVO₂ has been shown to be reduced by approximately 20% in both exercising humans (Ekblom and Huot, 1972; Pirnay et al., 1971; Vogel and Gleser, 1972) and dogs (Horst-man et al., 1974). It would appear that the limitation of VO₂ during COH is dependent upon both the magnitude of the O₂ demnd (%MVO₂) and severity of COH. The purpose of the present experiments, therefore, was to define the mechanisms of the VO₂ responses of the canine gastrocnemius muscle at rest, submaximal, and maximal contractions during normoxia and COH.