Posture and regional cerebrovascular reactivity; technological advancements with positional MRI

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With the advancement of magnetic resonance imaging (MRI) techniques, an exciting time has emerged for research in the field of cerebral anatomy and physiology. The basis of this proposal is to employ a one of a kind imaging technique to drive forward our basic understanding of regional blood flow regulation in the human brain. The circulation of brain blood flow is profoundly influenced by the local prevailing pH (acid-base balance). An increased pH (reduced acidity) of cerebral extra-vascular tissue reduces blood flow, while a decreased pH (increased acidity) increases the cerebral blood flow. Changes in cerebral extra-vascular pH occur daily - determined in large part from variations in breathing frequency (and in turn changes in arterial partial pressure of CO2). The natural 'reactivity' of the cerebral vessels to changes in pH appear to be a surrogate for cerebral health. That is, the more the blood flow changes for a given change in pH, the 'healthier' they are. Indeed, those with lower reactivity are at higher risk of cerebrovascular disease. Currently, the regional variations in cerebral reactivity across separate brain regions remains poorly studied (requiring expensive imaging techniques), while the regional reactivity to changes in pH during changes in posture remain completely undetermined. Understanding these basic cerebrovascular responses is particularly important for determining brain regions that may have an increased risk for ischemic stroke. Humans spend the majority of life in the upright position; it is therefore prudent to describe the 'natural' (healthy) cerebrovascular response to changes in pH while both supine and upright. Before these data are acquired, cerebrovascular disease pathology potentially exacerbated in the upright position cannot be quantified. The Welcome Back MRI and Pain Management Centre in Kamloops, BC, currently possess the only upright MRI in Canada with the potential capacity to image the cerebral vessels. The goal of this collaborative research proposal is to take advantage of this unique measurement tool and quantify the natural regional cerebral blood flow response to changes in pH while in the supine AND upright posture in healthy humans.