STRUCTURAL-CHANGES UNDERLYING COMPENSATORY INCREASE OF DIFFUSING-CAPACITY AFTER LEFT PNEUMONECTOMY IN ADULT DOGS

To determine if the functional compensation in diffusing capacity of t he remaining lung following pneumonectomy is due to structural growth, we performed morphometric analysis of the right lung in three adult f oxhounds approximately 2 yr after left pneumonectomy (removal of 42% o f lung) and compared the results to those in normal adult dogs previou sly studied by the same techniques. Diffusing capacity was calculated by an established morphometric model and compared to physiologic estim ates at peak exercise in the same dogs after pneumonectomy. The major structural changes after left pneumonectomy are hyperinflation of the right lung, alveolar enlargement, and thinning of the alveolar-capilla ry tissue barrier. These changes confer significant functional compens ation for gas exchange by reducing the overall resistance to O2 diffus ion. The magnitude of compensation in diffusing capacity estimated eit her morphometrically or physiologically is similar. In spite of morpho metric and physiologic evidence of functional compensation, there is n o evidence of significant growth of structural components. After pneum onectomy, morphometric estimates of diffusing capacity are on average 23% higher than physiologic estimates in the same dogs at peak exercis e. We conclude that the previously reported large differences between morphometric and physiologic estimates of diffusing capacity reflects the presence of large physiologic reserves available for recruitment.