Regional lung expansion at total lung capacity in intact vs. excised canine lungs

A computer-based biplane videoroentgenographic recording technique that determines the spatial coordinates of radiopaque lung parenchymal markers was used to compare regional lung expansion at total lung capacity (TLC) in the intact dog (prone and supine) and after removal from the chest. The reproducibility of the technique was examined by repeated determinations of intermarker distances at various static lung volumes during stepwise inflation and deflation of the lungs. Most of the variability in repeated determinations of intermarker distances at any lung volume was due to cardiogenic motion. When marker positions were determined repeatedly at the same phase of the cardiac cycle, the maximum coefficient of variation was less than 3% for a marker pair separated by 16.5 mm. At TLC, distances between all intralobar marker pairs in the intact thorax (prone and supine) and excised were highly linearly related (r = 0.96-0.99), whereas distances between interlobar marker pairs did not correlate as well (r = 0.77-0.86). We conclude that at TLC 1) the intact thorax does not distort the shape of the individual lobes from the state of isotropic expansion, and 2) in different body positions, overall lung shape may be different due to displacementof lobes relative to each other, but individual lobes remain uniformly expanded.