Maximal oxygen consumption rate in patients with bronchial asthma—the effect of β₂-adrenoreceptor stimulation

Abstract

Five young male patients with exercise-induced asthma (EIA) were subjected to graded bicycle exercise with work loads corresponding to 50%, 75% and 120% of the load necessary to elicit maximal oxygen uptake (Vo2 max). The exercise tests were performed after inhalation of salbutamol (Ventoline) as well as after inhalation of saline as control. Additionally two maximal work tests (bicycling and treadmill) were performed without inhalation on a work load corresponding to 100% Vo2 max. Oxygen uptake (Vo2) heart rate (HR), mean blood pressure (MBP), rating of perceived exertion (RPE) as well as arterial concentration of glucose and acid-base variables were measured. Vo2 max during bicycle exercise averaged 3.16 l/min and no significant difference was disclosed between the beta 2-stimulation and the control situations. The coefficient of variation of a single Vo2 max measurement was 4.7%. The maximal treadmill running revealed a significantly higher Vo2 max (3.42 l/min, P less than 0.05) than during bicycling; no EIA was provoked in any of the experiments. After beta 2-stimulation a higher HR and MBP in relation to Vo2 was observed than in the control experiment; however, the slope of HR/Vo2 and MBP/Vo2 relationships was not affected. Normal relationships were observed between Vo2 and work load, ventilation, RPE and acid-base data and these relations were unaffected of beta 2-stimulation. It is concluded, that Vo2 max seems to be within the normal range in asthmatics, provided they are free from attacks.