Effects of unilateral hyperinflation on the interpulmonary distribution of pleural pressure

Motivated by single lung transplantation, we studied the mechanics of the chest wall during single lung inflations in recumbent dogs and baboons and determined how pleural pressure (Ppl) is coupled between the hemithoraces. In one set of experiments, the distribution of Ppl was inferred from known volumes and elastic properties of each lung. In a second set of experiments, costal pleural liquid pressure (Ppl(cos)) was measured with rib capsules. Both methods revealed that the increase in Ppl over the ipsilateral or inflated lung (ΔPpl(i)) is greater than that over the contralateral or noninflated lung (ΔPpl(c)). Mean d(ΔPpl(c))/d(ΔPpl(i)) and its 95% confidence interval was 0.7 ± 0.1 in dogs and 0.5 ± 0.1 in baboons. In a third set of experiments in three dogs and three baboons, we prevented sternal displacement and exposed the abdominal diaphragm to atmospheric pressure during unilateral lung inflation. These interventions had no significant effect on Ppl coupling between the hemithoraces. We conclude that lungs of unequal size and mechanical properties need not be exposed to the same surface pressure, because thoracic midline structures and the lungs themselves resist displacement and deformation.