Mechanism of lobar alveolar pressure decline during forced deflation in canine regional emphysema

Mink, S. N. Mechanism of lobar alveolar pressuredecline 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 toexamine the extent to which differences in alveolar pressures(PA) would develop between anemphysematous right lower lobe (RLL) and normal left lower lobe (LLL)during forced vital capacity (FVC) deflation. RLL and LLLPA(PA_RLL and PA_LLL,respectively) were measured by the alveolar capsule technique. Duringforced deflation, PA and lobarflows were determined between 95 and 20% FVC. A choke point common toboth lower lobes was observed at >40% FVC. The results showed thatdeflation compliance (C) was altered for the RLL such that <90%lobar vital capacity, C_RLL > C_LLL, whereas >90% lobar vitalcapacity, C_RLL < C_LLL. At 95 and 90% FVC, theinitial RLL PA decline wasgreater than that for the LLL (P < 0.05). However, large differences inPA were prevented because of theeffect of interdependence of regional expiratory flow (IREF). IREFcaused a relative decrease in RLL flows and increase in LLL flows thatlimited PA differences. Between 80 and 50% FVC, as C_RLL becamegreater than C_LLL, and because ofthe initial effect of IREF,PA_RLL was~PA_LLL.At 40% FVC, without IREF, lobar differences inPA widened. These findings indicate that IREF may affect the dynamics of flow limitation inregional lung disease.