Radiographic detection of mobilizable lung water: the gravitational shift test

A radiographic method for detecting excessive lung water in patients with pulmonary infiltrates of uncertain cause is described. The gravitational shift test uses bedside frontal films before and after prolonged lateral decubitus positioning. Excess lung water is identified by detecting a shift in infiltrate to the dependent lung while the opposite side clears or remains stable. The test was evaluated in 33 patients with infiltrates of well defined etiology. Twelve patients had heart failure or fluid overload (edema): 14 had pulmonary infection or parenchymal damage (inflammation); and seven had inflammation plus edema. Infiltrates shifted to the dependent lung in 85% of patients with lung edema, but did not shift in 78% of patients with inflammatory disease. The test also detected excess lung water in six of seven patients with underlying inflammatory disease. Each patient with a positive test showed clinical, physiologic, and radiographic improvement after therapy directed at mobilizing excessive lung water. When the differential diagnosis of a diffuse infiltrate is in question, a positive test represents a strong indication for a trial of diuretic therapy.