Effect of adrenergic and vagal blockade on the normal human airway response to exercise

Ten normal, non-asthmatic subjects performed an 18 min graduated exercise test on a static exercise bicycle on 3 separate days. They received either no medication, or propranolol 80 mg orally 2 h before, or ipratropium bromide 0.216 mg by inhalation 30 min before, the start of exercise. With no medication, transpulmonary index (TPI), a measure of airway resistance, fell linearly during exercise from a resting value of 0.269 +/- 0.024 to 0.170 +/- 0.014 kPa X 1(-1) X s by the end of exercise. This returned to baseline between 2 and 4 min after stopping exercise. Propranolol elevated baseline TPI slightly from 0.270 +/- 0.024 to 0.294 +/- 0.024 before exercise and during exercise this fell linearly to 0.185 +/- 0.016 kPa X 1(-1) X s. The fall in TPI during exercise after propranolol was not significantly different from the fall seen with no medication. Six minutes after exercise stopped TPI rose to 0.336 +/- 0.035 kPa X 1(-1) X s after propranolol. All values for TPI from 4 min to 16 min after exercise were significantly higher after propranolol than the corresponding values found after no medication (P less than 0.05). Ipratropium bromide decreased baseline TPI from 0.264 +/- 0.024 to 0.163 +/- 0.013 kPa X 1(-1) X s (P less than 0.001) and this did not change significantly further either during or after exercise. Normal subjects show considerable airway dilatation during exercise and this appears to result from inhibition of resting vagal tone. The sympathetic system does not appear to mediate the airway dilatation during exercise, but it may be important in protecting against post-exercise bronchoconstriction.