5.1 INERTIAL-VISCOELASTIC MINIMAL MODEL OF THE ARTERIAL SYSTEM RECONCILES ARTERIAL COMPLIANCE ESTIMATIONS

Abstract

Background: The arterial system is viscoelastic rather than purely elastic. There exist various methods to characterize the purely elastic nature of arterial compliance, each method yielding different values. The pulse pressure method (CPPM), estimating compliance by matching the pulse pressure (PP) of a two-element Windkessel to measured PP, yields consistently lower values than the pressure decay time method (Cdec) and diastolic area method (Carea). An alternative inertial-viscoelastic model (IVEMM) that is viscoelastic and frequency-dependent rather than purely elastic and constant has been shown in dogs to reconcile the various compliance estimation methods. We assessed the presumed merits of IVEMM compliance estimates in a clinically diverse human sample. Methods: Central pressure and flow were measured using carotid tonometry and phase-contrast MRI, respectively, in 226 subjects. Arterial compliance was estimated using (1) Cppm; (2) Cdec; (3) Carea; (4) CIVEMM(jω). Results: Cppm was nearly perfectly correlated with CIVEMM evaluated at frequency of heart rate (Pearson coefficient (ρ) = 0.99; slope (B) = 1.00; P < 0.001). Carea (ρ = 0.979; B = 0.928; P < 0.001) and Cdec (ρ = 0.974; B = 0.954; P < 0.001) were very strongly correlated with CIVEMM evaluated at 0 hertz (static compliance). Conclusion: CPPM is fit to PP defined in systole, when fast-acting phenomena are likely to elicit viscoelasticity of the arterial system. Its consistently lower values compared to Cdec and Carea are clarified by IVEMM to be the result of estimating viscoelastic compliance at frequency of heart rate. Cdec and Carea are estimates of static compliance. Consistent with dog studies, IVEMM appears to reconcile the three popular compliance estimation techniques.