The American review of respiratory disease
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Am. Rev. Respir. Dis. · Jun 1989
Hypoxic, hypercapnic acidosis decreases tension and increases fatigue in hamster diaphragm muscle in vitro.
Hypoxia and hypercapnic acidosis have been shown to have a negative inotropic effect on diaphragmatic contractility. The effect of combined hypercapnia and hypoxia was studied in vitro using hamster diaphragm strips. A 12% CO2, 21% O2, and 67% N2 gas mixture was used to produce hypoxic, hypercapnic acidosis. ⋯ With repeated contractions, tension declined at a faster rate than in control, hypoxia alone, or hypercapnia alone. In the combined hypoxic, hypercapnic solution, the time constant of relaxation (tau) was increased prior to the start of the fatigue run compared to the control (tau = 35 +/- 6 versus 45 +/- 5 ms; p less than 0.001), and the tau increased at a faster rate than in control. These studies suggest that hypoxic, hypercapnic acidosis has a greater detrimental effect on the muscle than either abnormality alone and makes the muscle more susceptible to fatigue.