Association between Aortic Stiffness and Cerebral Pulsatility is Modestly Influenced by Augmentation Index

James Pearson,Laura J Watkeys,James M Coulson,Zachary J Schlader,Craig G Crandall,John R Cockcroft,Carmel M Mceniery,Barry J Mcdonnell

doi:10.2991/artres.k.191212.001

Abstract

Central Pulse Pressure (CPP) and Aortic Pulse Wave Velocity (aPWV) share a positive relationship with cerebral pulsatility and are associated with cerebrovascular disorders including stroke. Our aim was to examine the influence of Augmentation Index (AIx) upon this relationship, first by using a cross sectional design across a wide range of CPP and aPWV in healthy individuals and second, following administration of Glyceryl Trinitrate (GTN) to acutely change AIx. We measured CPP, aPWV, AIx and Middle Cerebral Artery Pulsatility Index (MCAPI) in 99 healthy individuals (54 females). In all individuals, after accounting for the effect of age and gender, MCAPI shared an independent inverse relationship with AIx (β = −0.515, R2 = 0.109; p = 0.001), and a positive relationship with CPP (β = 0.570, R2 = 0.093; p = 0.003) but not aPWV (p > 0.05). GTN was administered to 25 of these participants (14 females). Following GTN, AIx75 decreased in all participants relative to baseline (12 ± 19 to 5 ± 16%; p = 0.0001). In the 20 min following GTN administration, CPP shared a positive relationship with MCAPI (β = 0.305, R2 = 0.042; p = 0.002) while AIx, adjusted for heart rate (AIx75), shared an inverse relationship with MCAPI (β = −0.320, R2 = 0.019; p = 0.031). These findings indicate that the positive relationship between CPP and MCAPI may be somewhat modified by AIx. This suggests that an increased AIx may weakly attenuate increases in MCAPI that are associated with aortic stiffening in a healthy population at rest, but also following acute reductions in AIx75 after administration of GTN.

Highlights

Aortic stiffness, as measured by Aortic Pulse Wave Velocity and Central Pulse Pressure (CPP), increase with healthy aging [1,2] and independently predict cardiovascular mortality, including stroke [3,4,5]
Large artery stiffness is associated with increased cerebral blood flow pulsatility [6,7,8,9,10] which likely increases the mechanical insult delivered into the cerebral microvasculature [11] and may help to explain the increased frequency of white matter lesions observed in individuals with increased large artery stiffness [12,13]
Univariate regression analysis indicated that Middle Cerebral Artery Pulsatility Index (MCAPI) shared a relationship with age (R2 = 0.057, b = 0.239; p = 0.018), CPP (R2 = 0.161, b = 0.401; p = 0.0001, Figure 1) and Aortic Pulse Wave Velocity (aPWV) (R2 = 0.053, b = 0.230; p = 0.028)

Summary

Introduction

As measured by Aortic Pulse Wave Velocity (aPWV) and Central Pulse Pressure (CPP), increase with healthy aging [1,2] and independently predict cardiovascular mortality, including stroke [3,4,5]. Large artery stiffness is associated with increased cerebral blood flow pulsatility [6,7,8,9,10] which likely increases the mechanical insult delivered into the cerebral microvasculature [11] and may help to explain the increased frequency of white matter lesions observed in individuals with increased large artery stiffness [12,13]. As the forward-travelling pressure wave propagates throughout the arterial tree it encounters bifurcations and sites of impedance mismatch that result in a proportion of this pressure wave being reflected back to the aorta. An increased AIx has been hypothesised to dampen the transmission of highly pulsatile forces travelling from the aorta into the end organ those with a low resistance to flow (e.g. the brain and kidney) [6,19,28]

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