This study evaluated cerebrovascular reactivity (CVR) after a sport-induced concussion, also called mild traumatic brain injury (mTBI), by monitoring middle cerebral artery blood velocity (vMCA) with transcranial Doppler ultrasonography and simultaneous end-tidal carbon dioxide (PETCO2) measurements.
Thirty-one athletes (16–25 yr old) participated in this study. The participants were divided into two groups—healthy (n = 21) and mTBI (n = 10). Participants in the mTBI group suffered an mTBI within the last 7 d (x─ = 4.5 ± 1.1 d). Outcome measures included vMCA and PETCO2 in response to breath holding (5 × 20 s, 40-s rest) and hyperventilation (5 × 20 s, 40-s rest).
Resting vMCA values between groups were not significantly different. Percentage change of vMCA was significantly different after the recovery period of the second hyperventilation (P = 0.034). mTBI subjects failed to return to resting levels after each breath hold. PETCO2 changes mirrored the vMCA changes.
These data suggest that normal CVR responses may be disrupted in the days immediately after occurrence of mTBI. Transcranial Doppler ultrasonography combined with expired gas measurements provides a useful method for assessing CVR impairment after mTBI. Further research, including serial monitoring after mTBI and analysis of CVR response to exercise, is warranted before any firm conclusions can be drawn.
1Faculty of Kinesiology and Health Studies, University of Regina, Regina, Saskatchewan, CANADA; 2Traumatic Stress Group, University of Regina, Regina, Saskatchewan, CANADA; 3Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, CANADA; 4Department of Pediatrics, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, CANADA; and 5Department of Occupational Therapy, University of Alberta, Edmonton, Alberta, CANADA
Address for correspondence: J. Patrick Neary, Ph.D., Faculty of Kinesiology and Health Studies, University of Regina, Regina, Saskatchewan, Canada S4S 0A2; E-mail: firstname.lastname@example.org.
Submitted for publication December 2010.
Accepted for publication May 2011.