Effect of an inhaled atropinelike agent on normal airway function

Ten normal subjects inhaled 80 microgram ipratropium or placebo. Body plethysmograph studies showed that ipratropium increased specific conductance (0.14-0.21 s-1.cmH2O-1) and increased flow rates during both maximal and partial forced expiratory maneuvers at all volumes from 50 to 10% vital capacity (P less than 0.01). Ipratropium produced no change in quasi-static or dynamic compliance, closing volume, or the slope of phase III of the closing volume trace, but there was an increase in the height of phase IV (P less than 0.01). Specific conductance reflects central airways caliber, whereas flow rates at low lung volumes in the absence of alteration in static recoil pressure may reflect the caliber of more peripheral airways. We conclude that inhibition of vagal tone results in dilatation of large and small airways. Analysis of the flow volume results on the equal pressure point model suggests that the bronchodilatation normally resulting from the inhalation to total lung capacity is not solely due to inhibition of vagal tone.