Regional lung strain in dogs during deflation from total lung capacity

Regional lung distortion during deflation from total lung capacity to functional residual capacity (FRC) in intact supine and prone anesthetized dogs was determined from the displacement of multiple metallic markers embedded in the lung parenchyma. Distortion was expressed as strain (ε), which is related to fractional length changes. In the supine position, transverse strain (ε(yy)) was larger than vertical strain (ε(xx)) and cephalocaudal strain (ε(zz)) in the upper lobe. The FRC of the lower lobe was smaller than FRC of the upper lobe and all strains were larger, but ε(zz) increased most and became equal to ε(yy). In the prone position, ε(yy) was largest in all upper lobes and in three of four lower lobes. Strains and volumes of the upper and lower lobes were similar. The upper and lower lobes rotated slightly around different axes, indicating that interpleural fissures allow additional degrees of freedom for the lungs to conform to the thoracic cavity. In the prone position, there were no consistent gradients of strain or volume. These results indicate that, in determining the regional distribution of FRC in the recumbent dog, in addition to the effect of gravity on the lung, there are important interactions between lung and thoracic cavity shapes.