Heart-lung interactions determined by electron beam X-ray CT in laterally recumbent rabbits

Electron beam X-ray computed tomography (CT) was used to measure lung air content and its distribution within the lung as well as lung shape and heart position in rabbits in right and left lateral recumbency. Sham-operated control (S) rabbits and left-pneumonectomized rabbits with wax plombage were studied at functional residual capacity (FRC) and total lung capacity. Results were obtained for both lungs and for the right lung only of S rabbits. FRC of both lungs and the right lung only of the S rabbits and of the remaining right lung of the pneumonectomized rabbits was smaller in rabbits in right lateral recumbency than in those in left lateral recumbency. The reduction in right lung volume at FRC was accompanied by an overall reduction in lung size, although the lung shape remained similar, and was accompanied by movement of the heart centroid toward the dependent chest and spine. Application of a positive tracheal pressure of 25 cmH2O increased lung volume and reduced the dependency of lung volume and shape on posture. Lung inflation in the right lateral position was accompanied by movement of the heart centroid away from the dependent chest and spine. Gravitational gradients in regional air content did not differ between the cranial half of the lung, which was in contact with the heart, and the caudal half of the right lung, which was not in contact with the heart. Likewise, the cephalocaudal gradient in regional air content was similar when the right lung was dependent and nondependent. The location of the heart in the cranial half of the thorax does not appear to induce differences in regional air content between the cranial and caudal lung halves.