Noninvasive quantification of heterogeneous lung growth following extensive lung resection by high-resolution computed tomography

To quantify the in vivo magnitude and distribution of regional compensatory lung growth following extensive lung resection, we performed high-resolution computed tomography at 15- and 30-cmH₂O transpulmonary pressures and measured air and tissue (including microvascular blood) volumes within and among lobes in six adult male foxhounds, before and after balanced 65% lung resection (∼32% removed from each side). Each lobe was identified from lobar fissures. Intralobar gradients in air and tissue volumes were expressed along standardized x,y,z-coordinate axes. Fractional tissue volume (FTV) was calculated as the volume ratio of tissue/(tissue + air). Following resection compared with before, lobar air and tissue volumes increased 1.8- to 3.5-fold, and whole lung air and tissue volumes were 67 and 90% of normal, respectively. Lobar-specific compliance doubled post-resection, and whole lung-specific compliance normalized. These results are consistent with vigorous compensatory growth in all remaining lobes. Compared with pre-resection, post-resection interlobar heterogeneity of FTV, assessed from the coefficient of variation, decreased at submaximal inflation, but was unchanged at maximal inflation. The coefficient of variation of intralobar FTV gradients changed variably due to the patchy development of thickened pleura and alveolar septa, with elevated alveolar septal density and connective tissue content in posterior-caudal and peripheral regions of the remaining lobes; these areas likely experienced disproportional mechanical stress. We conclude that HRCT can noninvasively and quantitatively assess the magnitude and spatial distribution of compensatory lung growth. Following extensive resection, heterogeneous regional mechanical lung strain may exceed the level that could be sustained solely by existing connective tissue elements.