• Trevor K Len, J Patrick Neary, Gordon J G Asmundson, Darren G Candow, David G Goodman, Bruce Bjornson, and Yagesh N Bhambhani.
• Faculty of Kinesiology and Health Studies, University of Regina, Saskatchewan, Canada.
• Brain Inj. 2013 Jan 1;27(3):346-53.

Primary ObjectiveThis study examined the effects of mild traumatic brain injury (mTBI) on cerebrovascular reactivity (CVR).Research DesignA repeated measures design was used to examine serial changes in CVR.Methods And ProceduresTwenty subjects who recently suffered a mTBI were subjected to a respiratory challenge consisting of repeated 20 s breath-holds (BH) and hyperventilations (HV). Testing occurred on days 2 (D2), 4 (D4) and 8 (D8) post-injury as well as a baseline (BASE) assessment (after return-to-play). Transcranial Doppler was used to assess mean cerebral blood velocity (vMCA) and expired gas analysis provided end-tidal carbon dioxide (PETCO2) levels.ResultsThere was no significant difference in resting vMCA across all testing days for mTBI. No significant differences in PETCO2 were found throughout the testing protocol. A significant effect (p < 0.001) of testing day on vMCA was found during BH and HV challenges for mTBI. Post-hoc analysis revealed significant differences (p < 0.05) in vMCA between D2 and the other testing days.ConclusionsThese data suggest that, following mTBI: (1) CVR is not impaired at rest; (2) CVR is impaired in response to respiratory stress; and (3) the impairment may be resolved as early as 4 days post-injury.

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