Assessing prefrontal cortex oxygenation after sport concussion with near-infrared spectroscopy

Bishop SA, Neary JP. Clin Physiol Funct Imaging. 2017 Jun 18. doi: 10.1111/cpf.12447.

Take Home Message: Near-infrared spectroscopy, which can measure blood-oxygen levels, may provide an objective method to assess concussion within days of initial trauma but it is not ready for clinical roll out just yet.

Neurocognitive tests provide a marker of concussion recovery, but may not detect changes in the underlying physiology. An objective measure of physiological changes associated with concussion may assist clinicians in determining if individuals have fully recovered before returning to sport. The authors of this study assessed if near infrared spectroscopy (NIRS), a noninvasive and portable method to measure blood-oxygen levels at the brain’s surface, may be a biomarker of concussion. NIRS can detect changes in neural activity via blood metabolism and blood flow: oxyhemoglobin (increased blood flow) and deoxyhemoglobin (increase oxygen use). The authors recruited and baseline tested 147 collegiate and junior level football and hockey players. 33 individuals experienced concussions and were tested at 1-3 days (14 athletes), 4-6 days (8 athletes), or 7-14 days (11 athletes) after injury. The NIRS device was placed over the participant’s forehead above the eyes to measure frontal cortex activity. The participants then completed 5 minutes of normal breathing and then 5 hypercapnic sessions, which consisted of 20-seconds breath hold and 40-seconds of normal breathing. There were no differences in hemoglobin-oxygen levels between concussed individuals and controls. However, those assessed 7 to 14 days post concussion had lower hemoglobin-oxygen levels than those tested between 1 to 3 days or 4 to 6 days. Also, those assessed at 1 to 3 or 4 to 6 days post concussion had less hemoglobin-oxygen variability from rest to breath holding compared with controls.

The authors observed no differences in concentration at rest or during breath holds between concussed individuals versus controls, but found differences in hemoglobin variability. The findings suggest that centers in the brain, which are responsible for blood flow regulation to respiratory challenge (breath holding), may be altered following concussion, but are restored within a week of injury. The decreased hemoglobin-oxygen variability among concussed patients may suggest a reduced capacity to regulate responses to diverse conditions or challenges compared with healthy controls. The lack of group differences may be due to small sample size, use of a respiratory task as opposed to a cognitive task, or that NIRS can only measure the superficial cortex (whereas previous fMRI work measured the whole brain). Furthermore, it is difficult to determine if NIRS can assess recovery because there was no follow-up on when these individuals returned to activity. While NIRS seems to show potential to measure physiologic dysfunction inherent to concussion, it still requires more research before integrating into a standard concussion evaluation. In the meantime, clinicians can use these findings to explain to patients the possible changes that are occurring in the brain after a concussion.

Questions for Discussion: Do you think physiological markers will be the new standard for concussion evaluation in the future? 

Written by: Cody Criss & Dustin Grooms
Reviewed by: Jeffrey Driban

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