Abstract
Aim: This study investigated cerebral hemodynamic responses to a neurovascular coupling (NVC) test in retired contact athletes with a history of repeated mild traumatic brain injury (mTBI) and in controls with no history of mTBI.Methods: Twenty-one retired rugby players (47.7 ± 12.9 year old; age at retirement: 38.5 ± 8.9 year; number of years playing rugby: 12.7 ± 3.7 year) with a history of three or more diagnosed concussions (8.9 ± 7.9 concussions per player) and 23 controls with no history of mTBI (46.5 ± 12.8 year old) performed a NVC test to detect task-orientated cerebral hemodynamic changes using functional near-infrared spectroscopy (fNIRS).Results: The NVC showed a statistically significant reduction in the cerebral hemodynamic response in comparison to the control group which had a greater relative increase of oxyhemoglobin (O2Hb). There were reductions in left middle frontal gyrus (MFG) O2Hb (−0.015 ± 0.258 μM) and relative increases in deoxyhemoglobin (HHb; −0.004 ± 0.159 μM) in the same region for the mTBI group in comparison to the control group (−0.160 ± 0.311 μM; −0.121 ± 0.076 μM for O2Hb and HHb, respectively). The mTBI group induced a greater rate of oxygen extraction compared to the control group.Conclusion: This was the first study to examine cerebral hemodynamic changes in retired rugby players in response to a NVC test, and we found reduced cerebral hemodynamic responses in participants with a history of mTBI compared to controls. These results suggest altered cerebral metabolic demands in participants with a history of multiple head injuries. Further research is needed to ascertain an understanding of the changes in hemodynamics from playing into retirement.
Highlights
Concussion or mild traumatic brain injury arises from a sudden movement of the brain within the cranium, with rapid angular or linear acceleration, deceleration or rotational force (Jordan, 2013)
The purpose of this study was to investigate neurovascular coupling (NVC) responses in a cohort of former rugby players who had a history of sport-related concussion, compared with a control group who had no history of concussion
The mild traumatic brain injury (mTBI) group had their left caudal PFC as the strongest O2Hb signal. This coincides with literature (Oudegeest-Sander et al, 2014; Hirose et al, 2016) as they both measured hemodynamics and reported tHb will be greater at baseline for the control group as mTBI individuals will have overcompensation of HHb from a lack of O2Hb, which may be indicative of conditions such as ischemia
Summary
Concussion or mild traumatic brain injury (mTBI) arises from a sudden movement of the brain within the cranium, with rapid angular or linear acceleration, deceleration or rotational force (Jordan, 2013). Over the course of one competitive season, rugby players have been reported to encounter 600–800 body impacts and around 50 to over 100 direct head impacts (King et al, 2017). This has resulted in urgent calls for research to improve the understanding of risks, methods for diagnosis, and long-term brain consequences for those athletes affected (Lipnick et al, 2018). It has been suggested that repetitive concussive injuries increase the risk of neurodegenerative problems in later life ranging from mild cognitive deficits to neurological disease such as Alzheimer’s (McKee et al, 2009; Johnson et al, 2010; Omalu et al, 2011)
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