Aortic to brachial PWV ratio : le rôle hémodynamique des artères de conduction à prédominance musculaire par le gradient de rigidité artérielle

Authors: Fortier, Catherine
Advisor: Agharazii, MohsenMac-Way, Kai-Kock Fabrice
Abstract: Noninvasive determination of aortic stiffness has sparked considerable interest over the last four decades. Actually, increased aortic stiffness has emerged as an independent predictor of cardiovascular events and mortality, and as the main responsible of isolated systolic hypertension. However, the impacts of aortic stiffness on microcirculation and organ damages are best explained through the arterial stiffness gradient, in other words, with the interaction between soft aorta and adjacent stiff muscular arteries. Mechanical properties of muscular mid-caliber arteries (ex: brachial artery) are thought to be relatively stable over time, and then, do not significantly contribute to the lost and inversion of the arterial stiffness gradient with aging. In a longitudinal study with hemodialysis patients, we observed an annual decrease in brachial stiffness despite an accelerated increase in aortic stiffness. These observations let us hypothesize, first, that muscular arteries may not be as stable over time as it is expected and second, that arterial stiffness gradient may be a better predictor of mortality as both peripheral and central stiffness may change, at least in a high-risk population. The objectives of this thesis were to assess the combined effect of a reduced brachial stiffness and increased aortic stiffness on all-cause mortality by proposing a parameter of arterial stiffness gradient, the aortic-brachial PWV ratio (PWV ratio: cf-PWV/cr-PWV), to examine relationships between hemodynamic parameters, PWV ratio and its two PWV components, and to assess determinants of changes in brachial stiffness. In a dialysis cohort of patients, we demonstrated that PWV ratio was an independent predictor of all-cause mortality that performed better than aortic stiffness and other hemodynamic parameters. In contrast with aortic stiffness which is dependent on operational pressure, we demonstrated in a second study the pressure independence of PWV ratio in two different cohorts of patients. These results suggest that PWV ratio could be a new parameter of vascular aging with clinical interest above and beyond aortic stiffness. This study also a general regression of brachial stiffness in dialysis patients and over the sixth decade of age in the other cohort of patients. The regression of brachial stiffness, as presented in the first study of this thesis, was not explained by age, traditional risk factors, and mineral parameters. Baseline aortic stiffness was the only determinant of the decrease in brachial stiffness, which let us propose that muscular arteries may adapt to high aortic stiffness by becoming more compliant, dampening the ejected blood volume from the ventricular contraction instead of the aorta. This thesis also presents our last study on a new method of pulse wave analysis, the reservoir-wave approach, which reintroduces the importance of peripheral resistance and arterial compliance (reservoir pressure) in the comprehension of pressure curves. We observed that brachial stiffness was significantly associated with the reservoir pressure, but also with diastolic pressure. Finally, works presented in this thesis were conducted with the participation of chronic kidney disease patients, a very interesting population characterized by an early and accelerated vascular aging. Consequently, our results may not be reproducible in healthy or lower-risk populations.
Document Type: Thèse de doctorat
Issue Date: 2018
Open Access Date: 3 July 2018
Permalink: http://hdl.handle.net/20.500.11794/30268
Grantor: Université Laval
Collection:Thèses et mémoires

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