Serial distribution of bronchoconstriction induced by vagal stimulation or histamine

We compared the relative site of airway responses with histamine aerosol and electrical stimulation of the vagi in dogs that were anesthetized, vagotomized, mechanically ventilated, and treated with propranolol. We made measurements of pulmonary resistance by forced oscillations and of dead-space volume as indirect indicators of airway size. Direct measures of airway size were obtained from radiographic bronchograms and from acoustically equivalent airway areas as a function of distance, computed from pulse response data. During vagal stimulation there were marked increases in pulmonary resistance, decreases in dead space, and reduction in acoustic cross-sectional area at all distances. In contrast, after inhalation of enough aerosol histamine to increase pulmonary resistance approximately as much as it did during vagal stimulation, we observed little ro no reduction in dead space and reductions in acoustic cross-sectional area that were most marked in distal airways. The findings were confirmed by the radiographic bronchograms and are consistent with observations reported by others. These observations confirm previous data and demonstrate the utility of this technique for in vivo measurements.