Lung injury edema in dogs: influence of sympathetic ablation

Increased vascular permeability characterizes lung injury pulmonary edema and renders fluid balance in the injured lung especially sensitive to changes in hydrostatic pressure. Pulmonary edema is often associated with increased sympathetic nervous system activity which can lead to pulmonary venoconstriction. This postcapillary venoconstriction could raise microvascular pressure and might therefore increase edema in the injured lung. We produced lung injury edema in dogs with oleic acid and directly measured small (less than 2 mm) pulmonary vein pressure. We found that the small pulmonary vein pressure was increased from 9.8 +/- 0.5 mmHg to 12.6 +/- 0.5 mmHg (n = 10) by oleic acid injury edema. The increase was not due to a rise in left atrial pressure since the small pulmonary vein-left atrial pressure gradient also increased. To test if this increase in the postcapillary pressure gradient was sympathetically mediated, we either unilaterally ablated the stellate ganglion or produced unilateral alpha adrenergic blockade with phenoxybenzamine before giving oleic acid. Both of these "antisympathetic" interventions prevented the increase in pulmonary vein pressure caused by oleic acid edema in the protected lung but not in the intact contralateral lung. These interventions produced a 30 +/- 6.8% reduction in the amount of edema caused by oleic acid. Restoring the increase in small vein pressure by inflating a balloon in the left atrium of dogs with bilateral stellate ganglion ablations abolished the reduction in edema produced by antisympathetic treatment. However, the decrease in edema was not significantly correlated with the reduction in pulmonary vein pressure. Thus, the mechanism of the effects of these antisympathetic interventions remains unclear. We conclude that lung injury edema causes sympathetically mediated pulmonary venoconstriction and that antisympathetic interventions significantly reduce lung injury edema and microvascular pressure.