Bilateral impact on the lung of hemidiaphragmatic paralysis in the dog

The present study was designed to test the hypothesis that the expansion of a particular lung during breathing is partly related to the action of the hemidiaphragm on the opposite side. Two endotracheal tubes were inserted in the right and left main stem bronchi of anesthetized dogs, and the changes in pleural pressure (DeltaPpl) over the two lungs were assessed separately, first before and then after section of one phrenic nerve, by measuring the changes in airway opening pressure (DeltaPao) in the two tubes during occluded breaths. After phrenic nerve section, DeltaPao in the ipsilateral lung decreased 28+/-2%, and DeltaPao in the contralateral lung decreased 16+/-2% (P<0.01 for both). Parasternal intercostal activity, however, increased 15% on either side of the chest (P<0.05), thus indicating that the neural inspiratory drive was greater. Analysis of the results also suggested that after phrenic section, the contralateral (intact) hemidiaphragm still contributed nearly a third of the DeltaPpl over the ipsilateral lung. These observations indicate, in agreement with the hypothesis, that hemidiaphragmatic paralysis in the dog has a direct detrimental effect on the expansion of both lungs. They may account for the fact that in patients with hemidiaphragmatic paralysis, ventilation is reduced in both lung bases.