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. S ham-operated control (S) rabbits and left-pneumonectomized rabbits wit h 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 onl y of the S rabbits and of the remaining right lung of the pneumonectom ized rabbits was smaller in rabbits in right lateral recumbency than i n 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 t he heart centroid toward the dependent chest and spine. Application of a positive tracheal pressure of 25 cmH(2)O increased lung volume and reduced the dependency of lung volume and shape on posture. Lung infla tion 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 h alf of the lung, which was in contact with the heart, and the caudal h alf of the right lung, which was not in contact with the heart. Likewi se, the cephalocaudal gradient in regional air content was similar whe n the right lung was dependent and nondependent. The location of the h eart in the cranial half of the thorax does not appear to induce diffe rences in regional air content between the cranial and caudal lung hal ves.