Postural changes in pulmonary blood flow in pulmonary hypertension: A noninvasive technique using ventilation-perfusion scans

Abstract

To determine whether postural changes in ratio of upper to lower (U:L) zone pulmonary blood flow reflect pulmonary arterial pressures, we used pulmonary perfusion photoscintigraphy to study 12 normal subjects and 10 patients with precapillary pulmonary hypertension (eight classified as 'primary' and two as thromboembolic). All patients underwent right-heart catheterization and measurement of pulmonary arterial systolic, diastolic, mean and capillary (wedge) pressures. The distribution of perfusion was then assessed in the supine and erect positions after i.v. injection of technetium-99m-labeled, macroaggregated albumin. Perfusion distribution was corrected for lung volume by zenon-133 equilibrium ventilation scans. In normal subjects, the U:L lung zone perfusion ratio decreased by 70.7 ± 12.2% with the change in position. The patient group differed (p <0.0001) from normal subjects in that there was only a 19 ± 17.4% shift of U:L ratio with the postural change. The mean pulmonary arterial pressure in the patient groups was 50 ± 24.2 mm Hg. The postural change in U:L zone ratio correlated significantly with the mean pulmonary arterial pressure (r = -0.84, p <0.01) pulmonary arterial systolic (r = -0.83, p <0.01) and diastolic pressures (r = -0.72, p <0.05) and with the pulmonary vascular resistance (r = -0.74, p <0.02). No correlation was found with other hemodynamic, spirometric or blood gas data. We conclude that the postural shift in U:L ratiowarrents further exploration as a noninvasive approach for detecting and quantifying pulmonary hypertension.