Hypertension is a major risk factor for cardiovascular and cerebrovascular disease. Essential hypertension is characterised by chronically elevated sympathetic nerve activity (SNA), which is controlled in large part by the brainstem. It has been suggested that impaired blood flow to the brainstem and thus impaired reactivity of brainstem blood vessels may be a common, but hitherto little investigated, source of hypertension in humans.
Compared with the cerebral cortex the brainstem has been the focus of comparatively little functional magnetic resonance imaging (fMRI) research. This arises principally from the technical challenges of imaging this small structure which lies close to air spaces in the head and which are a source of magnetic field inhomogeneity.
We propose to develop a quantitative fMRI toolkit to map vascular function in the human brainstem. This will be implemented on Cardiff University Brain Research Imaging Centre's (CUBRIC) research dedicated 3T MRI system in a collaboration between imaging scientists in Cardiff and physiologists in Bristol. We will optimise MRI acquisition and post-processing to permit quantitation of brainstem blood flow and we will design, implement and evaluate a robust protocol for mapping brainstem cerebrovascular reactivity using hypercapnic (carbon dioxide) challenges. This will pave the way for quantitative study of blood pressure control and hypertension in humans.