Quantitative radiocardiography in patients with patent ductus arteriosus.

Analytical models of the analog computer simulation method of radiocardiogram (RCG) were revised to obtain quantitative hemodynamic evaluations in patent ductus arteriosus (PDA). The theoretical and technical aspects are herein outlined, and the effects of clinical application discussed. Twenty-six patients with a left-to-right PDA shunt were studied by the revised RCG models, and the results were compared with oxymetric or echocardiographic data. Between RCG and oxymetry, the systemic blood flow (SBF) findings agreed well (r = 0.91), but in oxymetry, the pulmonary blood flow (PBF) findings were generally seen greater than in RCG (r = 0.81), and the oxymetric shunts appeared larger than in RCG (r = 0.75). This is because oxymetry cannot avoid the direct effects of the uneven partition of shunt flow to the lungs, whereas RCG can, in addition, measure the mean PBFs and SBFs. RCG may thus be said to be superior to oxymetry in assessing PDA shunts. Furthermore, RCG can estimate the mean left and right heart volumes (LHV and RHV) at the same time; the RCG LHV was found to correspond to the echocardiographic left ventricular end-diastolic volume (LVEDV) (r = 0.89). Moreover, the obtained relation between the RHV/LHV (Y) and the shunt ratio (X) proved to be the same that calculated theoretically (Y = -X + 1.0) in uncomplicated patients. Patients not presenting this relation may be assumed to suffer some condition complicating the PDA. In effect, the analog computer simulation method of RCG is a unique non-invasive means of obtaining quantitative analyses in PDA and in other congenital shunt diseases as well.