After interruption of a constant flow (Vcoll) delivered through a bronchoscope into a wedged segment of lung, the pressure at the tip of the bronchoscope (Pb) often decays in a pattern seemingly indicative of two time constants. We tested the hypothesis that the initial more rapid component of the decay is associated with pressure equilibration across the bronchial resistance (Rb), separating bronchoscope tip from alveolus, and that the slower component is associated with pressure equilibration across the collateral pathways separating the wedged segment from surrounding regions. In eight open-chest mongrel dogs, we affixed an alveolar capsule to the segment subtended by the wedged bronchoscope and measured alveolar pressure (PA) and Pb during delivery of Vcoll into the segment and after its sudden interruption. Under both control conditions and after delivery of aerosolized histamine (1.0 or 10 mg/ml), we were unable to demonstrate a gradient between Pb and PA either during constant flow or after flow interruption. Whenever the decay of Pb was not monoexponential, neither was that of PA. Thus there was no evidence of an appreciable Rb, and the rapid component of the decay must be attributable to other factors. In a second protocol, we examined whether behavior departing from monoexponential decay was attributable to the presence of multicompartment behavior within the wedged segment or rather reflected the behavior of a single homogeneous but nonlinear compartment. In five closed-chest dogs, we systematically varied the initial Pb by changing Vcoll and recorded nonexponential pressure decay after flow interruption.(ABSTRACT TRUNCATED AT 250 WORDS)