Pulmonary vein blood flow velocity in pulsus paradoxus.

The effect of inspiration on pulmonary vein blood flow velocity and forward pressure gradient from pulmonary vein to left atrium was studied in seven patients with chronic constrictive pericarditis, five of whom had clinically obvious pulsus paradoxus. Compared to patients without pericardial disease, where inspiration produced no change, patients with pericardial disease showed an inspiratory fall in the forward pressure gradient and forward blood flow velocity in the pulmonary veins on inspiration. The mechanism of pulsus paradoxus in these patients can be explained by incomplete transmission of the inspiratory fall of intrathoracic pressure to the left atrium.