Study of the cardiovascular effects of clenbuterol in exercise-induced asthma.

The protective effect of clenbuterol on exercise-induced asthma was studied in 14 patients with aspecific bronchial hyperreactivity. The selectivity of clenbuterol for beta 2-receptors was also studied. Patients were selected according to spirometric criteria: reduced dynamic indexes of respiratory function after exercise and, particularly, forced expiratory volume at 1 s (FEV1) decreased by at least 20% compared with initial values. A polycardiographic study was simultaneously carried out for the evaluation of systolic time intervals and polycardiographic indexes (Weissler index, Blumberger index and QT/QS2 index). After the preliminary measurements (C1), oral clenbuterol was started (0.02 mg X 2/day) and measurements were repeated after 30 (CII) and 60 days (CIII) of therapy. During treatment, physical exercise did not significantly influence the indexes of respiratory function (FEV1 decreased by 4.7 +/- 5.8 and 9.8 +/- 10.5% in CII and CIII with respect to initial values). Similarly systolic time intervals and polycardiographic indexes did not change significantly with respect to the initial values. A small increase in heart rate at rest was observed in CII (+ 7%, p less than 0.05): however, no significant changes were recorded in CIII compared with the initial values. Clenbuterol thus seems to offer an effective protection against exercise-induced asthma without the negative effects on the cardiovascular system which may arise from activation of beta 1-adrenergic receptors.