Variability of Lung Scans Following Pulmonary Embolization

A concept of functional pulmonary ischemia secondary to physiologic shifts of perfusion in the lungs is presented as an explanation of sequential changes in perfusion scans. Three cases of pulmonary embolism and one of congestive heart failure are presented as examples. One patient showed a new perfusion and ventilation defect in the left lower lobe during clinical recovery from pulmonary embolism. Pulmonary arteriogram disclosed patent arterial branches to this region but showed evidence of slightly increased vascular resistance. The anatomically patent but functionally occluded pulmonary arteries and airways did not open after administration of either vaso- or bronchodilator drugs, but they became functionally patent when the scan procedures were performed with the ischemic area in the most dependent position. Three patients showed intrapulmonary perfusion shifts from already perfused areas to previously nonperfused areas resulting in new ischemic regions in previously well perfused lung. Shifts of perf...