3T Bold MRI Measured Cerebrovascular Response to Hypercapnia and Hypocapnia: A Measure of Cerebral Vasodilatory and Vasoconstrictive Reserve

Cerebral autoregulation is an intrinsic physiological response that maintains a constant cerebral blood flow (CBF) despite dynamic changes in the systemic blood pressure. Autoregulation is achieved through changes in the resistance of the small blood vessels in the brain through reflexive vasodilatation and vasoconstriction. Cerebrovascular reactivity (CVR) is a measure of this response. CVR is defined as a change in CBF in response to a given vasodilatory stimulus. CVR therefore potentially reflects the vasodilatory reserve capacity of the cerebral vasculature to maintain a constant cerebral blood flow. A decrease in CVR (which is interpreted as a reduction in the vasodilatory reserve capacity) in the vascular territory downstream of a larger stenosed supply artery correlates strongly with the risk of a hemodynamic stroke. As a result, the use of CVR studies to evaluate the state of the cerebral autoregulatory capacity has clinical utility. Application of CVR studies in the clinical scenario depends on a thorough understanding of the normal response. The goal of this thesis therefore was to map CVR throughout the brain in normal healthy individuals using Blood Oxygen Level Dependant functional Magnetic Resonance Imaging (BOLD MRI) as an index to CBF and precisely controlled changes in end-tidal partial pressure of carbon dioxide (PETCO2) as the global flow stimulus.MAS