Factors determining lobar emptying during maximal and partial forced deflations in nonhomogeneous airway obstruction in dogs.

The partial expiratory flow-volume (PEFV) maneuver has been proposed as a sensitive test to detect nonuniform airway disease. We tested this hypothesis in seven dogs in an open-chest preparation in which the right upper lobe (RUL) bronchus was partially obstructed. Alveolar capsules were placed on the obstructed RUL and nonobstructed right lower lobe (RLL) to measure respective alveolar pressures (Palv) during PEFV and maximal expiratory flow-volume (MEFV) maneuvers. PEFV curves were initiated at about 75% of the whole-lung vital capacity (VC). A Pitot static tube was placed into the airway to identify sites of flow limitation (choke-points [CP]), frictional pressure losses to CP (Pfr), CP area (A*), and compliance (K*). Results were analyzed at 45% VC, where a central tracheal CP was identified, and at 29% VC, where lobar CP were identified. At both lung volumes, the results showed that during PEFV, Palv and flows of the obstructed RUL decreased, whereas Palv and flows of the RLL increased compared with values obtained during MEFV. However, total maximal expiratory flow (Vmax) did not change between maneuvers. At 45% VC, although Pfr decreased during PEFV, this decrease was not large enough to result in an increase in A* and hence total Vmax because CP were identified in the noncompliant trachea. At 29% VC, offsetting changes in lobar A* and flow occurred between maneuvers: during PEFV, RLL A* and flow relatively increased while RUL A* and flow decreased. This study describes the mechanisms that explain why the PEFV maneuver is not useful in the detection of nonhomogeneous airway obstruction.