Compromised Resting Cerebral Metabolism After Sport-Related Concussion: A Calibrated MRI Study

Abstract

Use calibrated MRI to model baseline cerebrovascular physiology parameters and investigate whether changes in resting cerebral blood flow (CBF0) following sport-related concussion (SRC) are concordant with changes in resting and dynamic cerebral physiologic markers, within two weeks of the injury. Altered CBF0 in the acute phase post-concussion may contribute to neurobehavioral deficiencies, often reported weeks after the injury. However, in addition to changes in CBF0, little is known about other physiologic mechanisms that may be disturbed within the cerebrovasculature. The aim of this study was to assess whether changes in baseline perfusion following SRC were co-localized with changes in cerebral metabolic demand. Forty-two subjects (15 SRC patients 8.0 ± 4.6 days post-injury and 27 age-matched healthy control athletes) were studied cross-sectionally. CBF0, cerebrovascular reactivity (CVR), resting oxygen extraction (OEF0) and cerebral metabolic rate of oxygen consumption (CMRO2|0) were measured using a combination of hypercapnic and hyperoxic breathing protocols, and the biophysical model developed in calibrated MRI. Blood Oxygenation Level Dependent and Arterial Spin Labelling data were acquired simultaneously using a dual-echo arterial spin labelling sequence. SRC patients showed significant decreases in CBF0 spread across the grey-matter (p < 0.05, corrected), and these differences were also confounded by the effects of baseline end-tidal CO2 (p < 0.0001). Lower perfusion was co-localized with reductions in regional CMRO2|0 (p = 0.006) post-SRC, despite finding no group-differences in OEF0 (p = 0.800). Higher CVR within voxels showing differences in CBF0 was also observed in the SRC group (p = 0.001), compared to controls. Reductions in metabolic demand despite no significant changes in OEF0 suggests that hypoperfusion post-SRC may reflect compromised metabolic function after the injury. These results provide novel insight about the possible pathophysiologic mechanisms underlying concussion that may affect the clinical recovery of athletes after sport-related head injuries.