Assessing Pre-Frontal Cortex Oxygenation After Sport Concussion With Near Infrared Spectroscopy

Abstract

Clinicians typically rely on neuropsychological and balance tests to track concussion recovery. These balance and neuropsychological tests only imply impairments that are based on performance – the tests do not directly measure (or reliably track) brain physiology throughout concussion recovery. Because of these issues, there has been a call to find an objective biomarker that can index both severity and the timeline for recovery. An additional problem is that, with the amount of concussions occurring at a recreational activity level, an effective biomarker must be cost effective, easily applied, and easily interpreted for lay people.

To address these issues, non-invasive near infrared spectroscopy (NIRS) was used to assess pre-frontal cortex oxygenation, by measuring relative changes in oxy- (HbO2 ) and deoxy-hemoglobin (HHb), and the associated standard deviations. Resting hemoglobin, and hemoglobin changes in response to increases in CO2 (induced by 20s breath-holds), were measured in all participants. Data were aggregated into healthy baselines (n = 115), and concussed participants on days 1-3 (n =14), 4-6 (n = 8), and 7-14 (n = 11). The data were statistically compared using 1 x 4 ANOVAs.

Results showed that resting HbO2 values progressively lowered from days 1-3 to 7-14 (with no differences compared to controls). This is a similar statistical trend to a previous functional magnetic resonance imaging study that focused on concussions (Meier et al., 2015). The second major finding showed that hypercapnic HbO2 standard deviation was lower than resting values in days 1-3 and 4-6, but reversed back towards the healthy control group as the injury abated. Monitoring pre-frontal cortex oxygenation changes is a viable biomarker to assess the physiological state of the brain following concussion.

Keywords: concussion, pathophysiology, near-infrared spectroscopy, hypercapnia