Quantitative estimation by indicator-dilution technics of the contribution of blood from each lung to the left-to-right shunt in atrial septal defect.

A method based on the initial portion of indicator-dilution curves has been used to determine the proportion of blood from each lung which drains anomalously. The results obtained appear to substantiate the derivation and permit the expression, in numerical values, of the greater proportion of anomalous drainage of blood from the right lung in the usual case of atrial septal defect. The principal assumptions pertaining to the method are discussed in some detail. SYSTEMIC arterial dilution curves of T-1824 have been used to demonstrate the hemodynamic derangement of ''anomalous drainage" of pulmonary venous blood in certain forms of acyanotic congenital heart disease characterized by a left-to-right shunt.' In the usual case of atrial septal defect the proportion of blood from the right lung which drains anomalously is greater than from the left lung. This paper outlines a method for the estimation of the magnitude of the anomalous drainage from each lung. The principal features of dilution curves obtained following injection of an indicator into the right and into the left pulmonary arteries in the usual case of atrial septal defect are evident in the example given in figure 1. The initial peak of concentrations, which occurs at 10.4 sec. and 10.0 sec. after injections of dye into the right pulmonary artery and into the left pulmonary artery respectively, is due to indicator that drains normally to the left ven-tricle on the first circulation. The second peak of concentration, which occurs at 14.8 sec. and at approximately 14.5 sec. following injection of indicator at each of these respective sites, represents indicator that has drained anomalously to the right atrium, and has passed, principally by way of the left pulmonary artery, to the systemic circulation following its second passage through the lungs. 212 THEORETIC CONSIDERATIONS In the absence of mitral insufficiency, or of an interventricular or aortopulmonary communication , the cavity of the left ventricle may be regarded as a final common path, in that all of a substance which enters will pass, without delay, to the systemic circulation. For reasons that are made readily apparent in a later section , quantitative analysis which involves the determination of components of dye concentration is best confined to that part of the dilution which represents the curve of increasing concentration due to dye which passes to the systemic circulation on its first circulation. The calculation of the proportion of anomalous drainage that occurs from …