Wave propagation in coupled left ventricle-arterial system - Implications for aortic pressure

The objective of this study was to examine the effects of wave propagation properties (global reflection coefficient, Gamma(G); pulse wave velocity, C-ph; and characteristic impedance, Z(o)) on the mechanical performance of the coupled left ventricle-arterial system. Specifically, we sought to quantify effects on aortic pressure (P-av) and flow (Q(ao)) while keeping constant other determinants of P-ao and Q(ao) (left ventricular end-diastolic volume, V-ed, and contractility, heart rate, and peripheral resistance, R(s)). Isolated rabbit hearts were subjected to real-time, computer-controlled physiological loading. The arterial circulation was modeled with a lossless tube terminating in a complex load. The loading system allowed for precise and independent control of all arterial properties as evidenced by accurate reproduction of desired input impedances and computed left ventricular volume changes. While propagation phenomena affected P-ao and Q(ao) morphologies as expected, their effects on absolute P-ao values were often contrary to the current understanding. Diastolic (P-d) and mean (P-m) P-ao and stroke volume decreased monotonically with increases in Gamma(G), c(ph), or Z(o) over wide ranges. In contrast, these increases had variable effects on peak systolic P-ao (P-s): decreasing with Gamma(G), biphasic with c(ph), and increasing with Z(o). There was an interaction between Gamma(G) and c(ph) such that Gamma(G), effects on P-m and P-d were augmented al higher c(ph) and vice versa. Despite large changes in system parameters, effects on P-m and P-s were modest (<10% and <5%, respectively); effects on P-d were always two to four times greater. Similar results were obtained when the single-tube model of the arterial system was replaced by an asymmetrical T-lube configuration. Our data do not support the prevailing hypothesis that P-s (and therefore ventricular load) can be selectively and significantly altered by manipulating Gamma(G), c(ph), and/or Z(o).