Am. J. Respir. Crit. Care Med., Vol 149, No. 5, May 1994, 1241-1247.
Factors determining lobar emptying during maximal and partial forced deflations in nonhomogeneous airway obstruction in dogs
D Georgopoulos, A Gomez and S Mink
Section of Respiratory Diseases, University of Manitoba, Winnipeg, Canada.
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.
