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Neurometabolite changes in College Hockey Players Correlated with Repetitive Head Impacts1Radiology, Brigham and Women's Hospital, Boston, MA, United States, 2Neurotrauma Research Laboratory, Michigan Concussion Center, University of Michigan, Ann Arbor, MI, United States, 3Department of Kinesiology & Applied Physiology, University of Delaware, Newark, DE, United States, 4Department of Physical Therapy & Athletic Training, Northern Arizona University, Flagstaff, AZ, United States
Synopsis
Repetitive head impacts can lead to long-term cognitive deficits and neurodegenerative diseases such as chronic traumatic encephalopathy. To further understand the effects of repetitive subconcussive head impacts, this study aimed to measure neurochemical concentrations throughout a season of collegiate hockey and examine the relation between subconcussive impacts and neurochemical changes using telemetry and MRS data. As seen in previous studies, players experienced an increase in N-acetyl aspartate and choline. Interestingly, post season NAA was negatively correlated with some telemetry metrics.
Intro
Repetitive head impacts (RHI) can lead to long-term cognitive deficits and neurodegenerative diseases such as chronic traumatic encephalopathy [1,2]. Interestingly, even subconcussive impacts – such as heading a soccer ball – that may not produce any concussion can lead to metabolic changes in the brain as detected by Magnetic Resonance Spectroscopy (MRS) [3]. To further understand the effects of subconcussive head impacts, this study aimed to measure neurochemical concentrations throughout a season of collegiate hockey and examine the relation between subconcussive impacts and neurochemical changes.Methods
Twenty two collegiate ice hockey players (age 20.3 ±0.8 years) were studied across two seasons (Year 1: n = 9, all male; Year 2 = 13, 8 male, 5 female). The male athletes were outfitted with a head impact telemetry system (Triax Technologies, Norwalk, CT) that measured the number, location, and magnitude of head impacts throughout all home practices and games. Prior to analysis, head impact data was cleaned by eliminating impacts occurring outside the time of play, eliminating impacts of 16 g or less, and utilizing a impact waveform classifier to discard incidental impacts. Outcome metrics of cumulative peak linear acceleration (PLA), cumulative peak rotational acceleration (PRA), cumulative number of impacts, and daily impact density were calculated. Daily impact density is the summation of the magnitude of a given impact (either PLA or PRA) divided by the time from the previous hits for each of the impacts sustained by an individual over one day [4]. One Year 1 participant was removed from the results because they suffered a concussion during the season. Additionally, MR imaging sessions were performed on all the subjects before, during, and after the season. Using a Siemens 3T Prisma, each scan included single voxel PRESS (TE = 30ms, TR = 2000ms, 20x20x20 mm, 128 averages, 64 channels) sequences of the posterior cingulate gyrus (PCG), the dorsolateral prefrontal cortex (DLPFC), and the primary motor cortex (M1). The MRS results were pre-processed using OpenMRSLab to frequency correct, water suppress, and phase correct the data then post-processed using LC Model.Results
In comparing the pre and post season MRS results for all subjects, for M1 there was a significant increase in the total N-acetylasparatate (tNAA/tCr; p = 0.0107) and total choline (tCho/tCr; p = 0.0105) ratio to total creatine. A choline increase was also seen in the DLPFC (p = 0.0139). Additionally, there was an increase pre to post season in the glutathione ratio (GSH/tCr) for the DLPFC (p = 0.0484). In comparing the pre and post season MRS results for only the male athletes, the M1 tNAA/tCho increased (p = 0.0289) and the DLPFC tCh/tCr increased (p = 0.0224). In correlating the MRS and telemetry Year 1 data, there was a correlation of M1 tNAA concentration with the mean PLA daily impact density (p = 0.076, r = -0.707) and with the mean PRA daily impact density (p = 0.082, r = -0.697) although not statistically significant.Discussion
These findings may suggest there is a threshold of RHIs that leads to neurochemical changes in the brain as proposed by Bari et al (2018) [5]. The increase in DLPFC tCho/tCr is consistent with previous findings in both female soccer players and male football players [2,5,6]. This choline increase may be explained by membrane turnover and repair due to injury. Furthermore, the increase in M1 tNAA/tCr found post season is particularly interesting, as it was not seen in the two previous football studies [5,6]. However, the nearly significant negative correlations of post-season tNAA with PLA and PRA are similar to correlations based on severity of hits and tNAA in the DLPFC [6]. The differences in brain regions could be explained by differences in the characteristics of and amount of subconcussives hits in hockey compared to football. The increase in M1 tNAA/tCr may also be explained by the role of aerobic activity on brain chemistry as has been found in other studies [7,8]. A set of non-contact athlete controls in this study would have helped draw further comparisons.Further research into the relationships of the quantity and intensity of RHIs and neurochemical changes is necessary to understand the effects of subconcussive impacts.Acknowledgements
We would like to acknowledge funding from the Delaware Economic Development Office Grant, State of Delaware Federal Research and Development Grant Program, and the Office of Naval Research ( N00014-18-1-2018).References
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