MR Based Quantification of Global Cerebral Metabolic Rate of Oxygen Consumption during Hypercapnia

Introduction: Hypercapnia is a common occurrence in pathophysiologic conditions (e.g. cardio-respiratory disease processes) [1]. Carbon dioxide is a potent cerebral vasodilator. Hypercapnia induced hyper-perfusion is often used as a diagnostic tool to measure cerebral vascular reactivity (CVR) to assess the integrity of cerebral circulation which can be altered in pathophysiological states [2]. While the vascular effects of hypercapnia on cerebral blood flow have been well documented, there is no general consensus on its metabolic effects [3]. A recent paper suggested therapeutic effects of hypercapnia in neonates with congenital heart disease (CHD) at risk for hypoxic ischemic injury secondary to hypoperfusion. However, quantification of cerebral metabolic activity during hypercapnia in such a population remains inadequate [4]. Additionally, from a neuroscience research perspective, assumption of constant cerebral metabolic rate of oxygen consumption (CMRO2) during hypercapnia is used for calibrating blood oxygen-level dependent (BOLD) response in functional magnetic resonance imaging (fMRI), yet verification is pending [5]. Here, we present a robust and reliable method for quantifying CMRO2 during hypercapnia by simultaneously measuring total cerebral blood flow (tCBF) and venous oxygen saturation (SvO2) in the major cerebral supply and drainage vessels with a temporal resolution of ~30s.