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We determined regional (Vr) and overall lung volumes in six head-up anesthetized dogs before and after the stepwise introduction of saline into the right pleural space. Functional residual capacity (FRC), as determined by He dilution, and total lung capacity (TLC) decreased by one-third and chest wall volume increased by two-thirds the saline volume added. Pressure-volume curves showed an apparent increase in lung elastic recoil and a decrease in chest wall elastic recoil with added saline, but the validity of esophageal pressure measurements in these head-up dogs is questionable. Vr was determined from the positions of intraparenchymal markers. Lower lobe TLC and FRC decreased with added saline. The decrease in upper lobe volume was less than that of lower lobe volume at FRC and was minimal at TLC. Saline increased the normal Vr gradient at FRC and created a gradient at TLC. During deflation from TLC to FRC before saline was added, the decrease in lung volume was accompanied by a shape change of the lung, with greatest distortion in the transverse (ribs to mediastinum) direction. After saline additions, deflation was associated with deformation of the lung in the cephalocaudal and transverse directions. The deformation with saline may be a result of upward displacement of the lungs into a smaller cross-sectional area of the thoracic cavity.

Lobar functional residual capacity-to-total lung capacity ratios (FRC/TLC) and strains in five supine anesthetized dogs were determined from volumes and side lengths of tetrahedra formed by multiple intraparenchymal markers whose positions were determined roentgenographically. Strain is related to fractional changes in length of elements in a Cartesian coordinate system and was used to describe parenchymal distortion. Volumes and strain patterns were compared in three states: intact dogs, after transection of forelimb structures to relieve traction on the chest wall, and in dogs' excised lungs. Removing traction (NT) decreased the plethysmographically determined FRC and the upper-to-lower lobe ratio (UL/LL) for FRC/TLC. The ratio in the NT state was more like the ratio in the excised lungs (UL/LL approximately equal to 1) than in the intact dog (UL/LL greater than 1). Strain patterns were similar between the intact and the NT states, indicating no lobar shape change at FRC between these two states. Strain in the excised lungs differed greatly from strains in the intact and NT states. We conclude that forelimb traction alters volume distribution between lobes and that lung-chest wall interactions are important in determining volume and strain patterns.