Mink, S. N. Mechanism of lobar alveolar pressure decline during forced deflation in canine regional emphysema. J. Appl. Physiol. 82(2): 632-643, 1997.A canine model of unilobar papain-induced emphysema was used to examine the extent to which differences in alveolar pressures (PA) would develop between an emphysematous right lower lobe (RLL) and normal left lower lobe (LLL) during forced vital capacity (FVC) deflation. RLL and LLL PA (PA_RLL and PA_LLL, respectively) were measured by the alveolar capsule technique. During forced deflation, PA and lobar flows were determined between 95 and 20% FVC. A choke point common to both lower lobes was observed at >40% FVC. The results showed that deflation compliance (C) was altered for the RLL such that <90% lobar vital capacity, C_RLL > C_LLL, whereas >90% lobar vital capacity, C_RLL < C_LLL. At 95 and 90% FVC, the initial RLL PA decline was greater than that for the LLL (P < 0.05). However, large differences in PA were prevented because of the effect of interdependence of regional expiratory flow (IREF). IREF caused a relative decrease in RLL flows and increase in LLL flows that limited PA differences. Between 80 and 50% FVC, as C_RLL became greater than C_LLL, and because of the initial effect of IREF, PA_RLL was ~PA_LLL. At 40% FVC, without IREF, lobar differences in PA widened. These findings indicate that IREF may affect the dynamics of flow limitation in regional lung disease.