Aortic input impedance in infants and children

Flow and pressure measurements were performed in the ascending aortas of si x pediatric patients ranging in age from 1 to 4 yr and in weight from 7.2 t o 16.4 kg. From these measurements, input impedance was calculated. It was found that total vascular resistance decreased with increasing patient weig ht and was approximately one to three times higher than those of adults. Co nductance per unit weight was relatively constant but was approximately thr ee times higher than for adults. Strong inertial character was observed in the impedance of four of the six patients. Among a three-element and two fo ur-element lumped-parameter models, the model with characteristic aortic re sistor (R-c) and inertance in series followed by parallel peripheral resist or (R-p) and compliance fitted the data best. R, decreased with increasing patient weight and was one to three times higher than in adults, and R, dec reased with increasing patient weight and was 2 to 15 times higher. The R-p -to-R-c ratio differed significantly between infants and children vs. adult s. The results suggested that R, developed more rapidly with patient weight than did R,. Compliance values increased with increasing patient weight an d were 3 to 16 times lower than adult values.