DETERMINANTS OF AIRWAY SMOOTH-MUSCLE SHORTENING IN EXCISED CANINE LOBES

There is marked heterogeneity of airway narrowing in intraparenchymal airways in response to bronchoconstricting stimuli. We hypothesized th at this heterogeneity results from variations in the structure of the airway wall. Freshly excised dog lung lobes were inflated to transpulm onary pressures (PL) of between 5 and 15 cmH(2)O, and an aerosol conta ining a high concentration of carbachol was administered. The lobes we re fixed and processed for Light-microscopic examination and morphomet ric analysis of membranous airway dimensions. The relationships of smo oth muscle shortening to PL and airway dimensions were analyzed using multiple linear regression. The results show that airway smooth muscle shortening was greater at lower PL and in airways with larger interna l perimeter and a greater number of folds per internal perimeter and t hat it was less in airways with greater inner wall area. We conclude t hat the magnitude and variability of airway smooth muscle shortening a nd airway narrowing in response to maximal constricting stimuli are in fluenced by mechanical factors related to airway wall geometry.