Characterizing the relationship between flow-mediated vasodilation and radial artery tonometry in peripheral artery disease

Abstract

Background: Arterial stiffness, measured by the augmentation index (AIX) from radial artery tonometry, and endothelial dysfunction, measured by brachial-artery flow-mediated vasodilation (FMD), have each been associated with increased risk of cardiovascular events. However, their interrelationship in peripheral artery disease (PAD) patients is poorly understood.

Materials and methods: In a cross-sectional analysis of 123 vascular surgery outpatients, the association between FMD and AIX was examined in controls with atherosclerotic risk factors (n = 32) and patients with PAD (n = 91). PAD was defined as claudication symptoms with an ankle-brachial index of <0.9 or a history of revascularization for symptomatic PAD. Controls had an ankle-brachial index ≥0.9 and no history of atherosclerotic vascular disease.

Results: Compared to controls, patients with PAD had lower FMD (6.3 ± 3.8 versus 8.4 ± 3.7, P = 0.008), while central AIX normalized to 75 beats per minute (25.5 ± 9.0 versus 19.3 ± 8.6, P = 0.001) and peripheral AIX (91.3 ± 14.5 versus 81.3 ± 11.4, P = 0.001) were higher. FMD was not significantly correlated with either central or peripheral AIX (central AIX: P = 0.58; peripheral AIX: P = 0.89) across the entire cohort, or in either the patients with PAD (central AIX: P = 0.48; peripheral AIX: P = 0.23) or controls (central AIX: P = 0.43; peripheral AIX: P = 0.92). In a multivariate model including FMD, higher AIX remained independently associated with PAD.

Conclusions: In an analysis of vascular surgery outpatients, no correlation between FMD and AIX was detected. Larger prospective studies are needed to determine whether the inclusion of both parameters improves predictive models for the early identification and potential risk stratification of PAD patients.

Keywords: Arterial stiffness; Endothelial function; Flow-mediated vasodilation; Peripheral artery disease; Radial artery tonometry.

FIGURE 1. The Augmentation Index

A) In healthy arteries, the reflected wave returns late in diastole. B) In stiffer arteries, the reflected wave returns earlier in diastole, and C) augments the pressure of the combined waveform. The augmentation index (AIX) represents the augmented pressure as a percentage of the overall pulse pressure such that [augmented pressure/(systolic blood pressure – diastolic blood pressure) × 100]. Note: Figure was modified and reproduced with permission from AtCor Medical.

FIGURE 2

FMD and Tonometry Correlations