Evaluation of flow-volume curves generated by forced-expiratory spirometry in anesthetized dogs

Positive-pressure plethysmography was used to generate partial and maximal flow-volume data in 10 anesthetized dogs. Acetylcholine (ACh) administered IV induced significant (P less than 0.05) changes in tidal breathing, as evidenced by decreased tidal volume, increased respiratory rate and dynamic resistance, and decreased dynamic compliance. Partial forced-expiratory spirometry-determined from end inspiratory capacity and functional residual capacity, revealed changes in flow and volume as a result of ACh treatment. These changes were not seen in maximal curves (determined from total lung capacity). Peak expiratory flows were limited by the presence of an endotracheal tube. Use of instantaneous time-constant variables to evaluate the concavity or convexity of the downslope of a flow-volume curve did not reveal differences after IV ACh administration. Seemingly, partial forced-expiratory spirometry was useful in detecting bronchoconstriction in anesthetized dogs. Accepted techniques of flow-volume curve analysis for the evaluation of small airway function were not sensitive enough to detect bronchoconstriction in the dog.