Arterial hemodynamics in a rabbit model of atherosclerosis

Although atherosclerosis significantly alters the structural characteristics of the arterial tree, its effect on arterial impedance, which is a means of quantifying the functional characteristics of the arterial system, has not been characterized. To assess how one type of atherosclerosis affects impedance, we studied arterial impedance in New Zealand White rabbits after 11 wk on a 2% cholesterol diet. From open-chest aortic pressures and flows, impedance data were obtained from spectral analysis of randomly paced and Fourier analysis of nonpaced beats. Compliance was calculated from the low-frequency impedance moduli by assuming a windkessel model for the arterial system. Under base-line conditions, the atherosclerotic impedance phase spectrum in the low-frequency range remained negative for higher values of frequency than in controls. There was no difference between the groups in mean arterial blood pressure, impedance modulus spectrum, characteristic impedance, compliance, or total peripheral resistance. Wave reflections were, however, increased in the atherosclerotic animals. The differences between the two groups in phase and wave reflection were completely abolished after phenylephrine (3 micrograms.kg-1.min-1). Thus this study demonstrates that under base-line conditions atherosclerosis increases wave reflection at the input to the arterial system in the absence of an alteration in global arterial compliance, total peripheral resistance, or mean blood pressure. This increase is presumably secondary to atherosclerotic changes at arterial sites, which produce local impedance mismatching.