Cardiorespiratory response to exercise before and after acute beta-adrenoreceptor blockade in nonsmokers and chronic smokers

Abstract

To evaluate the effects of chronic smoking on exercise performance we studied 5 smokers and 7 nonsmokers of comparable age and physical characteristics. The resting heart rate in smokers (75 +/- 3 beats/min; mean +/- SD) was significantly (P less than 0.01) higher than in nonsmokers (64 +/- 5). During exercise on a bicycle ergometer the heart rate remained significantly (P less than 0.01) higher in smokers than in nonsmokers. After exercise, the heart rate in nonsmokers settled to 78 +/- 9 beats/min at 10 minutes compared with 105 +/- 11 (P less than 0.01) in smokers. Oxygen consumption was similar in both groups throughout. Beta-adrenergic blockade reduced the exercise tachycardia in both groups but the heart rate for the same workload remained significantly (P less than 0.01) higher in smokers. Beta-blockade significantly reduced (P less than 0.05) oxygen consumption in nonsmokers but not in smokers who also incurred a significantly (P less than 0.05) greater oxygen debt and had higher serum lactate levels. These differences were attributed mainly to carboxyhaemoglobinaemia and partly to the effect of prolonged smoking on the heart and on intermediary metabolism.