Effects on body position and cholinergic blockade on mechanics of collateral ventilation

We studied the effects of position and cholinergic blockade on the mechanics of collateral ventilation in anesthetized paralyzed dogs. Resistance to collateral flow (Rcoll) is higher when an obstructed segment is dependent than when it is nondependent. Decreases of Rcoll in response to the local infusion of low oxygen mixtures are greater in dependent regions. We conclude that 1) changes in position affect Rcoll directly through local changes in lung volume related to the gradient of pleural pressure; 2) responses of collateral channels to local concentrations of CO2 and O2 are determined by ventilation perfusion relationships, which vary at different heights in the lung; and 3) resting cholinergic tone in the anesthetized dog varies at different heights in the lung.