4.3 Whole-Body vs. Regional Arterial Stiffness: Implications for a Single Windkessel Model of the Circulation

Abstract

Introduction

We questioned whether a single Windkessel (WK) adequately describes the circulation by estimating the radial arterial diastolic pressure-decay constant (tau) and combining this with systemic hemodynamic and arterial stiffness measurements.

Methods

In the non-invasive cardiac laboratory, we performed echocardiography with simultaneous cuff BP, heart-femoral [hf] and femoral-ankle [fa] PWV (Colin VP1000), and radial tonometry (Sphygmocor). Tau was calculated by photo-digitizing the radial pulse contour and fitting pressures (at 20 ms intervals) to: P = A + ([systolic BP]-A)*exp(-(t-t0)/tau), where P = pressure, A = modeled minimum diastolic BP, and t0 = mono-exponential decay start time. Systemic vascular resistance (SVR) = mean pressure/[cardiac output]; WK stiffness (1/[WK capacitance]) = SVR/tau; central and peripheral arterial stiffness = hfPWV 2 and faPWV 2 , respectively; and estimated wall/ lumen ratio (W/L) = PWV 2/(central pulse pressure/stroke volume).

Results

In 76 individuals (mean age 55 years, weight 84 kg, BP 138/79 mmHg, resting HR 67; 45% female), WK stiffness was negatively correlated with age(p<0.05) but not with BP, hfPWV² or faPWV². In contrast, hfPWV²and faPWV² were positively correlated with age (p<0.0001 and p<0.01, respectively) but neither was correlated with tau or WK stiffness. Using 6 multilinear stepwise backward regression models for WK stiffness, the major contributing factors were: SVR (p<10⁻⁶), t0 (p<10⁻⁶), heart rate (p<10⁻⁵), and W/L (p=0.01).

Conclusion

We identified SVR, heart rate, timing of pressure decay, and vessel geometry as correlates of WK stiffness but the lack of relationship between PWV-based arterial stiffness and stiffness derived from the WK model mitigates against a single arterial WK.