Diaphragm mechanics in dogs with unilateral emphysema

We studied dogs with unilateral papain-induced emphysema to answer two questions: (1) Do emphysema lung-apposed hemidiaphragm (Di_E) and normal lung-apposed hemidiaphragm (Di_N) have equal capacities for lowering lung surface pressure? and (2) Are side-to-side differences in intrathoracic pressure the result of unequal force outputs by Di_E and Di_N or are they caused by differences in their mechanical efficiency as pressure generators? After the airways of the emphysematous and normal lungs were intubated with a dual lumen endotracheal tube, both phrenic nerves were maximally stimulated at rates between 1 and 50 Hz and the changes in airway occlusion pressure (ΔPao_E,N) and diaphragm length (sonomicrometry) were recorded. In all animals, ΔPao_N exceeded ΔPao_E. Differences in pressure ranged from 1.2±0.6 cm H₂O during a twitch to 6.0±2.9 cm H₂O during a 50-Hz tetanus. Midcostal bundles of DiE shortened less than corresponding bundles of Di_N, but both reached the same active length relative to their optimal lengths, which were measured in vitro. There was no significant difference in fiber type distribution, fiber cross-sectional area, or maximal isometric tetanic tensions among midcostal regions of Di_E and Di_N. We conclude that unilateral hyperinflation impairs the mechanical efficiency of the apposing hemidiaphragm as a pressure generator.