Failure of cholinergic blockade to prevent bronchodilatation following deep inspiration

The role of the cholinergic system in the phenomenon of bronchodilatation following a deep inspiration (BDFI) in humans has not been well established, although animal studies have suggested the cholinergic system to be of prime importance. We therefore induced cholinergic blockade with inhaled ipratropium bromide (Sch-1000) in five asymptomatic subjects and then assessed whether BDFI had been abolished. Since BDFI is only evident where there is normal or increased bronchomotor tone, prostaglandin F2 alpha (PGF2 alpha), a noncholinergic bronchoconstrictor, was used to re-establish bronchomotor tone in the presence of cholinergic blockade. At each stage the presence or absence of BDFI was assessed by comparing flows from a partial forced expiratory maneuver started at approximately 60% of vital capacity (Vmaxp) with flows from a forced expiratory maneuver started at lung capacity (Vmaxc). Flows were measured at the last 40% of vital capacity. The percent ratio of Vmaxp/Vmaxc was used as an indicator of BDFI. In the presence of cholinergic blockade and with reestablishment of bronchomotor tone with PGF2 alpha, BDFI could still be demonstrated (Vmaxp/Vmaxc percent ratio: control 110.3 +/- 10.6, after Sch-1000 129.4 +/- 10.3, after Sch-1000 and PGF2 alpha 59.4 +/- 6.9; P = 0.001). We conclude that there is not an essential role for the cholinergic system in the phenomenon of BDFI in healthy individuals.