Partitioning of pulmonary function in rabbits during cholinergic stimulation.

Our goal was to partition whole lung resistance (RL) and cholinergic reactivity in rabbits into central airway, peripheral airway, and alveolar tissue (Rt) resistances by using forced oscillation (2 Hz), a retrograde catheter, and an alveolar capsule. Central and peripheral airway resistances accounted for approximately 80% of the baseline RL. However, immediately after acetylcholine challenge, Rt was negative. Bilateral vagal stimulation made Rt negative when the capsule was located on the left lung and not on the right lung. Stimulating either vagus produced a negative Rt in the lung ipsilateral to the stimulated nerve. Partial occlusion of the right main-stem bronchus with a balloon also made Rt negative. These results suggest that heterogeneous airflow exists at the level of the alveolar capsule during bronchoconstriction. Phase relationships between tracheal flow and retrograde catheter pressure suggest that flow at the level of the catheter was homogeneous. Thus, using only tracheal and retrograde catheter pressures, we repartitioned RL into its central airway and peripheral lung components. We conclude that cholinergic reactivity resides predominantly in the peripheral lung and that its peripheral location may be due largely to the development of heterogeneous airflow in peripheral airways.