The value of exercise in testing beta blockade and airway reactivity in asthmatic patients

On separate days, in double-blind fashion, 23 subjects with mild or moderate asthma were injected intravenously with a placebo or 0.4 mg pindolol. Plethysmographic and spirometric measurements were performed before and after injection and repeatedly after exhausting incremental bicycle ergometer exercise. The mean reduction in maximal exercise heart rate of 26 bpm after pindolol compared to placebo confirmed significant cardiovascular beta blockade. Baseline 1-second vital capacity (FEV1) values and other flow rates were similar in both trials. There were similar reductions in FEV1 (median of 1% to 2% and mean of 3% to 5%) and other flow rates immediately after injection of placebo or pindolol. Exercise-induced bronchospasm (EIB) occurred in 34 of 46 trials and tended to be more severe in subjects with more baseline airway obstruction. Minimal EIB (FEV1 to 80% to 90% of baseline values) developed in eight after taking placebo and in seven after taking pindolol; mild EIB (FEV1 to 60% to 79% of baseline) developed in the five after placebo and six after pindolol and moderate EIB (FEV1 to 40% to 59% of baseline) developed in three after placebo and five after pindolol. In five subjects, FEV1 was reduced to a greater extent after placebo than after pindolol (median of 6%), whereas in 13 subjects, FEV1 was reduced to a greater extent after pindolol than after placebo (median of 10%). These small differences in FEV1 between placebo and pindolol were significant by the t test after exercise but not before exercise. Thus, exercise appears to increase the sensitivity in evaluating airway reactivity in asthmatic patients and also tests the effectiveness of cardiovascular beta blockade.