) measurements. Methods 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). Results 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. Conclusions 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....

Primary objective: To assess and compare the parasympathetic state of individuals in healthy vs concussion groups, by measuring cardiovascular metrics under resting and baroreflex conditions using a squat-stand manoeuvre. Research design: This was a retrospective mixed-method study, with participants who sustained a medically diagnosed sport concussion (n = 12), being tested within 72-hours post-injury. Methods and procedures: Participant’s heart rate (Electrocardiogram, ECG) and blood pressure (finger plethysmography) data was collected during rest and during 10-second squat-stands (10SS, 0.05 Hz). Blood pressure and heart rate standard deviation data was analysed in the 0–5 seconds and 6–10 seconds periods of squatting and standing. Resting and baroreflex ECG data were analysed via Fourier Transformations for %Low Frequency and %High Frequency (%LF and %HF). Results: The control group alleviated more pressure and had a significantly higher standard deviation of heart rate during the 6–10 seconds of squatting (p < 0.05). Overall heart rate standard deviation in the concussion group was significantly lower than healthy controls when standing (p < 0.05). There were no differences in %LF and % HF between groups or between rest and 10SS. Conclusion: This study provides preliminary evidence that autonomic function is dysregulated following mTBI within the initial 72 hours of injury.

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.