Information content of pulmonary perfusion scintigraphy

A scinticamera computer system was used to measure the distribution of blood flow in both upright and supine lungs sequentially with the same counting geometry. The counting ratio of the upper half to the lower half lung, and the difference of distribution indices between supine lung and upright lung which is the fraction of postural change from the supine upper half to upright lower half lung to total distribution of blood flow, were referred to as ''U/L ratio'' and postural ''Change of Distribution'' respectively. U/L ratio correlated well with left atrial mean pressure (r = 0.87, p < 0.001) with the regression equation and Change of Distribution correlated well with pulmonary artery mean pressure (PAm) (r = -0.88, p < 0.001) in cardiac diseases. The relationship between the Change of Distribution and PAm was investigated using various regression analyses and the best fit was obtained by logarithmic regression (r = -0.92) with the regression equation. This regression equation means that there is no change of distribution of pulmonary blood flow with pulmonary artery pressure over 58 mmHg and that entire pulmonary blood flow comes to the lower half lung when the pulmonary artery pressure decreases to zero level. Pulmonary parenchymal and vascular disorders including primary pulmonary hypertension also held the same relationship with PAm. The relationship between upright U/L ratio and postural Change of Distribution permitted differentiation between precapillary pulmonary hypertension and postcapillary pulmonary hypertension. (J.P.N.)