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A review of methods to determine the functional arterial parameters stiffness and resistance

Westerhof, Nico; Westerhof, Berend E.

doi: 10.1097/HJH.0b013e3283633589
REVIEW
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Objectives: In treatment of hypertension not only the pressure response is of interest, but also the effect on arterial parameters, for example, stiffness and resistance, is essential. We therefore reviewed what quantitative information on arterial stiffness can be obtained from pressure wave analysis.

Methods: Using data from published large cohort studies, we derived relations between stiffness and the pressure-derived variables systolic pressure, pulse pressure, augmentation index (AIx), return time of reflected wave and reflection magnitude.

Results: All pressure-derived variables give limited information on arterial function in terms of stiffness and resistance, except AIx (in low stiffness range only). Input impedance as a comprehensive description of the arterial system is too complex to derive and interpret in practice, but is accurately described by three parameters: systemic vascular resistance, total arterial stiffness, and aortic characteristic impedance (outflow tract size and proximal aortic stiffness). These parameters predict aortic pressure well in terms of magnitude and shape: with measured flow the predicted (p) and measured (m) systolic, Ps, and diastolic, Pd pressures relate as Ps,p = 0.997Ps,m − 1.63 and Pd,p = 1.03Pd,m − 3.12 mmHg (n = 17). Therefore, methods should be developed to determine, preferably noninvasively, these three arterial parameters.

Conclusion: Variables derived from pressure wave shape alone (e.g. inflection point, AIx among others), and wave separation (e.g. reflection magnitude), while predicting cardiovascular events, give little information on arterial function. We propose to develop new, and improve existing, noninvasive methods to determine systemic vascular resistance, total arterial stiffness, and aortic characteristic impedance. This will allow quantifying the response of arterial function to treatment.

aDepartment of Pulmonary Diseases, Institute for Cardiovascular Research, ICaR-VU, VU University Medical Center

bEdwards Lifesciences BMEYE, Amsterdam

cHeart Failure Research Center, Academic Medical Center Amsterdam, The Netherlands

Correspondence to Nico Westerhof, PhD, VU University Medical Center, Department of Pulmonary Diseases, De Boelelaan 1117 1081 HV, Amsterdam, The Netherlands. Tel: +31 20 444 1887; fax: +31 20 44 44 328; e-mail: n.westerhof@vumc.nl

Abbreviations: ρ, blood density, 1.06 g/cm3; A, cross-sectional area; AIx, augmentation index, augmented pressure over pulse pressure; CA and EA, area compliance and area stiffness, EA = 1/CA = dP/dA; CT and ET, total arterial compliance and total arterial stiffness, ET = 1/CT; Pm,Pf,Pb, measured forward and backward (reflected) pressure; PP, pulse pressure; Ps,Pd, systolic, diastolic pressure; PWV, pulse wave velocity; SVR, systemic vascular resistance; tsho,tinfl; time of shoulder point and inflection point; Zc, characteristic impedance

Received 20 February, 2013

Revised 4 April, 2013

Accepted 14 May, 2013

Copyright © 2013 Wolters Kluwer Health, Inc. All rights reserved.