Slower adaptation of \(\dot V\)O2 to steady state of submaximal exercise with Β-blockade
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The kinetics of oxygen uptake (VO2) were assessed in 17 normal subjects with Β-blockade and placebo. Β-blockade was achieved with either 50 mg oral metoprolol or 40 mg oral propranolol, each twice per day. Tests were conducted on the cycle ergometer at work rates approximating 80% of the work rate at ventilatory anaerobic threshold. Work rate was initiated as a square wave starting from prior rest. Data obtained 48 h, 1 week, and 4 weeks after starting drug or placebo were pooled to increase the number of points for regression analysis of kinetic parameters. While there were no differences in the plateau values for \(\dot V\)O2 with and without Β-blockade, the rate of adaptation to steady state was significantly slower with Β-blockade than with placebo (p<0.05). This resulted in an increase of oxygen deficit by approximately 200 ml O2. Cardiac output measured by CO2 rebreathing was significantly reduced by Β-blockade (metoprolol by 4.1%, propranolol by 12.2%, both P<0.05). Blood lactate concentration was unaffected by Β-blockade. It was concluded that the influence of Β-blockade on the oxygen transport system was responsible for the significantly slower increase of \(\dot V\)O2 to steady state in submaximal exercise.
Key wordsΒ-adrenergic receptor blockade Oxygen uptake Oxygen deficit Exercise
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