Impacts of systemic hemodynamic factors on cerebral and peripheral perfusion
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Changes in physiological factors involving modulation of hemodynamics such as baroreflex sensitivity (BRS), heart rate, and/or blood pressure influence blood flow to downstream tissues leading to changes in response and/or function of tissues. For example, a sufficient increase in heart rate elicits greater accumulative shear stimuli on a per minute basis leading to a greater vasodilatory response of endothelial cells and providing greater perfusion to skeletal muscle. The high-flow and low-impedance nature of the cerebral circulation leads to increased susceptibility to damage from considerable blood pressure fluctuations. For this reason, the cerebrovasculature holds a very narrow range of operation of cerebral autoregulation in response to changes in perfusion pressure. In a nondemented elderly population and patients with Alzheimer’s disease, impaired BRS has been linked with poor cognitive function and a link between high pulsatile components of blood pressure (i.e., pulse pressure) and impaired cognitive function has also been reported. Three research investigations were included in this dissertation study. The first study was to determine the association between heart rate at rest and endothelium-dependent vasodilation as assessed by flow-mediated dilation (FMD) of the brachial artery. The primary findings from study 1 revealed an indirect association between heart rate and FMD through shear stimuli. The studies 2 and 3 sought to determine the association of regional cerebral perfusion with cardiovagal BRS and blood pressure components. A link between cardiovagal BRS and regional cerebral perfusion of the hippocampus was demonstrated in the study 2. This finding may add mechanistic insight to the relationship between impaired BRS and cognitive dysfunction. The primary finding from the study 3 revealed a significant relationship between peripheral pulsatile blood pressure components and regional cerebral perfusion of the hippocampus as well as anterior white matter. This finding highlights the importance of pulsatile pressure on cerebral vascular beds. Taken together, the overall findings from this dissertation study indicate the potential impacts of systemic hemodynamic factors on cerebral and peripheral perfusion. Future longitudinal studies in nondemented elderly and individuals with Alzheimer’s disease are warranted to reveal the causality of these associations.