Cerebrovascular reactivity impairment after sport-induced concussion
Following a head impact there are several systemic secondary effects, such as decreased cerebral blood flow and altered heart rate variability, which can be objectively assessed. Unfortunately, return-to-play guidelines do not include any objective measurements. The purpose of this study was to evaluate cerebrovascular reactivity after a sport-induced concussion by monitoring the middle cerebral artery blood velocity, based on transcranial Doppler ultrasonography, and end tidal carbon dioxide (PETCO2) measurements, based on an expired gas analyzing system. Thirty-one athletes were placed into 2 groups: 21 healthy athletes and 10 athletes that had a concussion within the last seven days. After measurements at rest, the athletes were instructed to hold their breath or hyperventilate (5 trials each) and the researchers measured the middle cerebral artery blood velocity and PETCO2. At rest there were no significant differences between groups. After trials 3, 4, and 5 of holding their breath concussed athletes’ middle cerebral artery blood velocity did not return to normal. In contrast, the control group’s middle cerebral artery blood velocity returned to normal after each trial. While the concussed athletes showed a different response to breath holding than the control participants these differences were not significant between groups. There were also no significant differences in mean PETCO2 after each breath hold between groups. Both control and concussed athletes showed significant decreases in middle cerebral artery velocity and PETCO2 following hyperventilation trials.
This study represents an interesting first step towards the potential use of transcranial Doppler ultrasonography and/or expired gas measurements as an objective way to assess concussed athletes. Furthermore, these results may provide insight to the cerebrovascular pathology following a concussion. The authors found that concussed athletes during a hyperventilation-stressed state have lower middle cerebral artery velocity compared to healthy athletes, which suggests that it may be an indicator of delayed physiological responses to mild traumatic brain injuries but larger studies are needed to verify this. These data suggest that normal cerebral vascular reactivity may be disrupted in the days immediately after occurrence of mild traumatic brain injuries. Transcranial Doppler ultrasonography combined with expired gas measurements may provide a useful method for assessing cerebral vascular reactivity impairment after mild traumatic brain injuries. Further research, including serial monitoring after mild traumatic brain injuries and analysis of cerebral vascular reactivity response to exercise, is warranted before any firm conclusions can be drawn. This study provides insight to how the brain reacts to stress and research like this may lead to better return-to-play guidelines. Future studies should incorporate serial monitoring and more variables (e.g., heart rate, blood pressure). Do you monitor heart rate or blood pressure among your concussed patients?
Written by: Jane McDevitt, MS, ATC, CSCS
Len TK, Neary JP, Asmundson GJ, Goodman DG, Bjornson B, & Bhambhani YN (2011). Cerebrovascular reactivity impairment after sport-induced concussion. Medicine and Science in Sports and Exercise, 43 (12), 2241-8 PMID: 21606867