Evaluating Cerebrovascular Reactivity during the Early Symptomatic Phase of Sport Concussion.

Cerebrovascular reactivity (CVR) indexes the ability of blood vessels to respond to vasoactive stimuli and may be a sensitive biomarker of concussion. However, alterations in whole-brain CVR remain poorly understood during the early symptomatic phase of injury. In this study, CVR was assessed using blood-oxygenation-level dependent functional magnetic resonance imaging (BOLD fMRI) combined with a respiratory challenge paradigm; resting cerebral blood flow (CBF) was also evaluated using arterial spin labeling (ASL). Imaging data were collected for 77 university-level athletes, including 56 athletic uninjured controls and 21 concussed athletes scanned in the early symptomatic phase of injury (≤7 days post-injury). The normal response to respiratory challenge was assessed in the athletic control group, in which a robust whole-brain response was observed. The concussed athletes were then compared to a matched subset of controls. Concussion was associated with greater reductions in BOLD activity during the early phase of the respiratory task, localized primarily in frontal and pre-frontal areas, whereas no significant effects on resting global CBF were observed. In addition, greater symptom severity was associated with greater reductions in BOLD response, with effects distributed throughout the brain. This study establishes fMRI with respiratory challenge as a robust method for assessing acute concussion-related alterations in CVR. Moreover, it highlights the importance of examining neurovascular response to physiological stressors after a concussion.