PULMONARY BLOOD-FLOW DOES NOT REDISTRIBUTE IN DOGS WITH REPOSITION FROM SUPINE TO LEFT LATERAL POSITION

Background: Recent studies have questioned the classical gravitational model of pulmonary perfusion. Because the lateral position is commonl y used during surgery, the authors studied the redistribution of pulmo nary blood flow in the left lateral decubitus position using a high sp atial resolution technique. Methods: Distributions of pulmonary blood flow were measured using intravenously injected 15-mu m diameter radio active-labeled microspheres in eight halothane-anesthetized dogs, whic h were studied in the supine and left lateral decubitus positions in r andom order. Lungs flushed free of blood were air-dried at total lung capacity and sectioned into 1,498-2,336 (1.7 cm(3)) pieces per animal. Radioactivity was measured by a gamma counter, and signals were corre cted for piece weight and normalized to mean flow. Results: Blood flow to the dependent left lung did not increase, and blood flow to the no ndependent right lung did not decrease in the lateral position. The le ft lung received 39.3 +/- 7.0% and 39.2 +/- 8.8% (mean +/- SD) of perf usion in the supine and left lateral positions, respectively. Detailed assessment of the spatial distributions of pulmonary blood flow revea led the lack of a gravitational gradient of blood flow in the lateral position. The distributions of blood now did not differ in the supine and left lateral decubitus positions.Conclusions: Perfusion to each lu ng did not change with movement from the supine to the left lateral po sition. These findings contradict the prediction of increased dependen t lung and decreased nondependent lung blood flow based on the gravita tional model. It was concluded that the distribution of blood flow in the lateral position in dogs is dominated by pulmonary vascular struct ure.