Acute Adolescent Concussion: Cerebrovascular Reactivity, Symptom Burden, And Exercise Response

Cerebral vasoreactivity (CVR) disruptions have been observed following concussion, which may exacerbate concussion-related symptoms. These CVR disruptions may also influence the cerebral blood flow (CBF) responses during aerobic exercise and thus limit exercise capacity post-concussion. PURPOSE: To examine the relationships between concussion-related symptoms, cerebral vasculature’s ability to respond to changes in CO2 (vasoreactivity), and CBF responses during sub-maximal aerobic exercise in adolescents post-concussion. METHODS: : Adolescents less than two weeks post-concussion completed the Post-Concussive Symptom Checklist (PCSC), cerebral vascular assessments, and a modified YMCA exercise protocol. CVR at rest was estimated from the slope (cm/s/mmHg) of the relationship between the increases in breath-by-breath end-tidal CO2 and responses of CBF velocity during an air rebreathing task (i.e., increasing end-tidal CO2). CBF velocity was measured via transcranial Doppler ultrasonography at the M1 segment of the middle cerebral artery unilaterally during the air rebreathing task and during the aerobic exercise test. Only physical and vestibular-related symptoms were included in analysis: headache, nausea, balance problems, dizziness, fatigue, and % activity level. Two stepwise linear regressions were conducted to test (1) if concussion symptoms are related to CVR and (2) if CVR predicted relative change in CBF velocity during the aerobic exercise test. RESULTS: The majority of the variance in CVR was explained by symptoms of nausea, dizziness, as well as current physical activity levels. Age, sex, resting heart rate, balance, and fatigue also contributed to a lesser degree. Exercise caused a significant increase in MCA blood flow (p<0.001). This exercise induced increase in CBF was largely explained by CVR and estimated VO2peak, with resting heart rate, prior concussion(s), and time since injury also contributing. CONCLUSIONS: Our findings suggests that symptom burden is related to disruptions in CVR in adolescents in the early weeks after a concussion. In turn, the cerebral blood flow response to exercise was related to both CVR and aerobic capacity, suggesting that disruptions in CVR may impact exercise tolerance post-concussion.