| Summary: | Background: Arterial compliance is pressure-dependent due to the nonhomogeneous composition of the arterial wall. Wall distending pressure varies within each cardiac cycle, thus arterial compliance is dynamic and time-varying within any given cycle. As compliance is a component of the pulsatile load presented by the arterial system (AS), its dynamic nature is expected to influence the phase of wave reflections. This phase modulation of wave reflection may influence left ventricular (LV) and AS coupling.
Methods: A time-varying elastance-resistance model the LV is coupled to a tube-load model of the AS. The tube, representing a segment of the aorta, is uniform and loss-free, terminating in a complex frequency-dependent load incorporating pressure-dependent compliance (C(P)). Aortic characteristic impedance, pulse wave velocity, and steady afterload were kept constant. In one set of experiments, the magnitude of C(P) was decreased while retaining its pressure-dependence, thus preserving compliance variations within any given cycle. In a second set, both the magnitude and pressure-dependence were progressively decreased, such that compliance became increasingly constant; mean compliance and reflection magnitude were pairwise matched to each case of the first set of experiments.
Results: When stiffening was accompanied by retained pressure-dependence, there was marked delaying of wave reflections compared to more constant compliance cases. Pressures and myocardial wall stress at end-systole were elevated, while stroke volume and ejection period were decreased.
Conclusion: The dynamic loading effects of pressure-dependent compliance can have complex effects on LV-AS coupling. Characterization of the complex changes of C(P) with age and disease deserves further investigation.
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