Serial monitoring of CO₂ reactivity following sport concussion using hypocapnia and hypercapnia

Abstract

Primary objective: This study examined the effects of mild traumatic brain injury (mTBI) on cerebrovascular reactivity (CVR).

Research design: A repeated measures design was used to examine serial changes in CVR.

Methods and procedures: Twenty 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.

Results: There 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.

Conclusions: These 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.

• Transcranial Doppler
• mild traumatic brain injury
• cerebral blood flow
• breath holding
• hyperventilation
• cerebrovascular reactivity

Acknowledgements

The authors would like to thank the University of Regina men's and women's hockey teams as well as the Athol Murray College of Notre Dame for their participation in this study. We would also like to thank Dr Michael Gaetz for his editorial review and helpful comments of our manuscript.

Declaration of Interest: This study was supported in part by grants received from the Canadian Institutes of Health Research (JPN), Heart & Stroke Foundation of Saskatchewan (TKL), and the Saskatchewan Health Research Foundation (JPN). The authors report no conflicts of interest.