Aortic input impedance in infants and children

Abstract

Flow and pressure measurements were performed in the ascending aortas of six pediatric patients ranging in age from 1 to 4 yr and in weight from 7.2 to 16.4 kg. From these measurements, input impedance was calculated. It was found that total vascular resistance decreased with increasing patient weight and was approximately one to three times higher than those of adults. Conductance per unit weight was relatively constant but was approximately three 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 four-element lumped-parameter models, the model with characteristic aortic resistor (R(c)) and inertance in series followed by parallel peripheral resistor (R(p)) and compliance fitted the data best. R(p) decreased with increasing patient weight and was one to three times higher than in adults, and R(c) decreased 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. adults. The results suggested that R(p) developed more rapidly with patient weight than did R(c). Compliance values increased with increasing patient weight and were 3 to 16 times lower than adult values.

Extraction of Pulmonary Vascular Compliance, Pulmonary Vascular Resistance, and Right Ventricular Work From Single-Pressure and Doppler Flow Measurements in Children With Pulmonary Hypertension: a New Method for Evaluating Reactivity

“…Previous investigators, using more invasive cuff-type flow probes, have identified these as useful parameters of vascular function. [23][24][25][26][27][28] …”

The arterial Windkessel

“…Other investigators have introduced an inertance in series with the characteristic impedance [4,5,7,25,32,57]. This series inertance does not affect the arterial input impedance at low frequencies but at high frequencies.…”

Downstream from the Heart Left Ventricle

“…Unreliability of arterial inertance representation can explain why the W4P fell short when applied by Sharp et al [17] to interpret pressureÀflow relationships in infants and children, who show aortic impedance data with much stronger inertial character than adults. Better impedance approximation was obtained by these authors from an alternative four-element model derived from the W3 by connecting L in series with R c (W4S model, Figure 21.4).…”

“…Better impedance approximation was obtained by these authors from an alternative four-element model derived from the W3 by connecting L in series with R c (W4S model, Figure 21.4). From W4S parameter estimates, Sharp et al [17] inferred that significant changes are in progress during vascular development from infancy to adulthood. In particular, a significant difference was observed in the development rate of R c and R p , such that a rapid reduction characterized the R c /R p ratio during early development.…”