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(Hypertension. 1996;27:1079-1089.)
© 1996 American Heart Association, Inc.

Articles

Wave Propagation in Coupled Left Ventricle–Arterial System

Implications for Aortic Pressure

David S. Berger; Kimberly A. Robinson; Sanjeev G. Shroff

From the Cardiology Section, Department of Medicine, University of Chicago (Ill).

Correspondence to Sanjeev G. Shroff, PhD, University of Chicago Medical Center, Room M-507, MC-5084, 5841 S Maryland Ave, Chicago, IL 60637. E-mail sshroff@medicine.bsd.uchicago.edu.

Abstract The objective of this study was to examine the effects of wave propagation properties (global reflection coefficient, _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_ao) 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 _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 _G, biphasic with c_ph, and increasing with Z_o. There was an interaction between _G and c_ph such that _G effects on P_m and P_d were augmented at 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-tube configuration. Our data do not support the prevailing hypothesis that P_s (and therefore ventricular load) can be selectively and significantly altered by manipulating _G, c_ph, and/or Z_o.

Key Words: pulse wave, propagation • pulse wave, velocity • blood pressure • rabbit • heart • ventricular function • compliance

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