ARTERIAL WAVE-PROPAGATION PHENOMENA, VENTRICULAR WORK, AND POWER DISSIPATION

The effects of wave propagation phenomena, namely global reflection co efficient (Gamma(G)[omega]) and pulse wave velocity (c(ph)), are studi ed in a model of the coupled left ventricle/arterial system. The left ventricle consists of a time-varying elastance, while the arterial sys tem is modeled as a single, uniform, elastic tube terminating in a com plex load. Manipulation of model parameters allowed for the precise co ntrol of Gamma(G)(omega) and c(ph) independent of each other, peripher al resistance, and characteristic impedance. Reduction of Gamma(g)(ome ga) and c(ph) were achieved through increases in load compliance and t ube compliance, respectively. The equations describing the system were solved for left ventricular and aortic pressures and aortic flow. Fro m these, stroke volume (SV), left ventricular stroke work (SW), and st eady (W-s), oscillatory (W-o), and total power dissipation (W-t) in th e arterial system were calculated. An index of arterial system efficie ncy was the ratio W-o/W-t (%W-o), with lower values indicating higher efficiency. Reduction of Gamma(G)(omega) yielded initial increases in W-s, while W-o increased for the entire range of Gamma(G)(omega), resu lting in increased %W-o. This reduced efficiency is imposed on the ven tricle, resulting in increased SW without increased SV. On the other h and, decreased c(ph) yielded in a steady increase in W-s and a biphasi c response in W-o, resulting in reduced %W-o for most of the range of reduced c(ph). These results suggest that differential effects on arte rial system efficiency can result from reductions of Gamma(G)(omega) a nd c(ph). In terms of compliance, changes in arterial compliance can h ave different effects on efficiency, depending on where the compliance change takes place. Reasons for these results are suggested, and the role of distributed compliances is raised as a new problem.