Cerebral Blood Flow Alterations in Acute Sport-Related Concussion

Sport Concussion and the Female Athlete

Sport concussion (SC) has emerged as a major health concern in the medical community and general public owing to increased research and media attention, which has primarily focused on male athletes. Female athletes have an equal, if not increased, susceptibility to SC. An ever-growing body of research continues to compare male and female athletes in terms of SC before and after an injury. Clinicians must be cognizant of this literature to make evidence-based clinical decision when providing care to female athletes and discern between dated and/or unsupported claims in terms of SC.

The modern landscape of sport-related concussion research: key achievements and future directions

The study of contact and collision sport athletes at risk for concussion began approximately three decades ago. Since then, sport-related concussion (SRC) research across several medical specialties has helped to develop consensus guidelines for clinical management through interdisciplinary efforts. The modern landscape of SRC research includes large-scale investigations to define the natural history of concussion and identify factors that should guide prevention, diagnosis, and treatment specific to the individual patient. We now know that the clinical and physiologic effects of concussion are related but independent constructs deserving further scientific exploration. This has sparked research that incorporates advanced neuroimaging, fluid biomarkers, biomechanics, and genomics, in addition to standard clinical outcomes. Additionally, translational research has informed our understanding of optimal rehabilitation strategies and led to a shift from the "complete rest" approach to earlier, active management interventions after concussion. Collectively, these advancements are likely to substantially improve patient outcomes after SRC and, ultimately, may prove beneficial for identifying and appropriately managing those at risk for longer-term difficulties associated with repetitive head impact exposure. The broader public health implications of improving sports safety and encouraging developmentally appropriate participation among youth and adolescents are a particularly important byproduct of continued research into SRC.

Concussion and the autonomic nervous system: An introduction to the field and the results of a systematic review

BACKGROUND

Recent evidence suggests that autonomic nervous dysfunction may be one of many potential factors contributing to persisting post-concussion symptoms.

OBJECTIVE

This is the first systematic review to explore the impact of concussion on multiple aspects of autonomic nervous system functioning.

METHODS

The methods employed are in compliance with the American Academy of Neurology (AAN) and PRISMA standards. Embase, MEDLINE, PsychINFO, and Science Citation Index literature searches were performed using relevant indexing terms for articles published prior to the end of December 2016. Data extraction was performed by two independent groups, including study quality indicators to determine potential risk for bias according to the 4-tiered classification scheme of the AAN.

RESULTS

Thirty-six articles qualified for inclusion in the analysis. Only three studies (one Class II and two Class IV) did not identify anomalies in measures of ANS functioning in concussed populations.

CONCLUSIONS

The evidence supports the conclusion that it is likely that concussion causes autonomic nervous system anomalies. An awareness of this relationship increases our understanding of the physical impact of concussion, partially explains the overlap of concussion symptoms with other medical conditions, presents opportunities for further research, and has the potential to powerfully inform treatment decisions.

Return to play following sports-related concussion

Returning a concussed athlete to practice and competition is an ever-evolving concept that has received considerable scientific and public attention during the past 20 years. Whereas there is now more international consensus regarding return to play, the decision to do so is clinically based with scant objective measures to guide decision making. To encapsulate the return-to-play process, this chapter will give a historic overview of the graded progression process, outline how rest can be both beneficial and detrimental in recovery, and how exercise is emerging as a management tool.

Early changes in cerebral autoregulation among youth hospitalized after sports-related traumatic brain injury

OBJECTIVE

To examine early cerebral haemodynamic changes among youth hospitalized with sports-related traumatic brain injury (TBI).

STUDY DESIGN

Youth 0-18 years admitted to a level one trauma centre with sports-related TBI were enrolled. Daily measures included clinical symptoms and Glasgow Coma Scale (GCS) score. Using Transcranial Doppler (TCD) ultrasonography and tilt testing, we measured middle cerebral artery flow velocity (Vmca) and cerebral autoregulation index (ARI).

RESULTS

Six previously healthy males age 14 (IQR 12-16) years with headache and abnormal head CT were admitted with median admission GCS 15. Six patients underwent 12 TCD examinations between hospital days 0-9. Low Vmca occurred in 3/6 patients and on the side of TBI, whereas high Vmca occurred in 2/6 patients. Five patients had at least one measurement of impaired and five patients had absent cerebral autoregulation of at least one hemisphere; all these five patients had GCS 15 and headache during TCD examinations. Three patients were discharged with absent cerebral autoregulation. Five (83%) patients were discharged to home and one patient was discharged to a rehabilitation facility.

CONCLUSION

Headache, abnormal Vmca and impaired cerebral autoregulation occur after sports-related TBI, despite normal GCS. Headache may signal underlying neurovascular abnormality in sports-related TBI.

Heart rate variability and implication for sport concussion

Finding sensitive and specific markers for sports-related concussion is both challenging and clinically important. Such biomarkers might be helpful in the management of patients with concussion (i.e. diagnosis, monitoring and risk prediction). Among many parameters, blood flow-pressure metrics and heart rate variability (HRV) have been used to gauge concussion outcomes. Reports on the relation between HRV and both acute and prolonged concussion recovery are conflicting. While some authors report on differences in the low-frequency (LF) component of HRV during postural manipulations and postexercise conditions, others observe no significant differences in various HRV measures. Despite the early success of using the HRV LF for concussion recovery, the interpretation of the LF is debated. Recent research suggests the LF power is a net effect of several intrinsic modulatory factors from both sympathetic and parasympathetic branches of the autonomic nervous system, vagally mediated baroreflex and even some respiratory influences at lower respiratory rate. There are only a few well-controlled concussion studies that specifically examine the contribution of the autonomic nervous system branches with HRV for concussion management. This study reviews the most recent HRV- concussion literature and the underlying HRV physiology. It also highlights cerebral blood flow studies related to concussion and the importance of multimodal assessment of various biological signals. It is hoped that a better understanding of the physiology behind HRV might generate cost-effective, repeatable and reliable protocols, all of which will improve the interpretation of HRV throughout concussion recovery.

White matter signal abnormalities in former National Football League players

Introduction

Later-life brain alterations in former tackle football players are poorly understood, particularly regarding their relationship with repetitive head impacts (RHIs) and clinical function. We examined white matter signal abnormalities (WMSAs) and their association with RHIs and clinical function in former National Football League (NFL) players.

Methods

Eighty-six clinically symptomatic former NFL players and 23 same-age reportedly asymptomatic controls without head trauma exposure underwent magnetic resonance imaging and neuropsychological testing. FreeSurfer calculated WMSAs. A cumulative head impact index quantified RHIs.

Results

In former NFL players, increased volume of WMSAs was associated with higher cumulative head impact index scores (P = .043) and worse psychomotor speed and executive function (P = .015). Although former NFL players had greater WMSA volume than controls (P = .046), these findings are inconclusive due to recruitment of controls based on lack of clinical symptoms and head trauma exposure.

Discussion

In former NFL players, WMSAs may reflect long-term microvascular and nonmicrovascular pathologies from RHIs that negatively impact cognition.

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Repetitive head impact exposure was positively associated with WMSAs in former NFL players.

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In former NFL players, greater WMSAs was associated with worse psychomotor speed and executive function.

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The pathologies of WMSAs may contribute to the clinical presentation of chronic traumatic encephalopathy.

A National Study on the Effects of Concussion in Collegiate Athletes and US Military Service Academy Members: The NCAA-DoD Concussion Assessment, Research and Education (CARE) Consortium Structure and Methods

BACKGROUND

The natural history of mild traumatic brain injury (TBI) or concussion remains poorly defined and no objective biomarker of physiological recovery exists for clinical use. The National Collegiate Athletic Association (NCAA) and the US Department of Defense (DoD) established the Concussion Assessment, Research and Education (CARE) Consortium to study the natural history of clinical and neurobiological recovery after concussion in the service of improved injury prevention, safety and medical care for student-athletes and military personnel.

OBJECTIVES

The objectives of this paper were to (i) describe the background and driving rationale for the CARE Consortium; (ii) outline the infrastructure of the Consortium policies, procedures, and governance; (iii) describe the longitudinal 6-month clinical and neurobiological study methodology; and (iv) characterize special considerations in the design and implementation of a multicenter trial.

METHODS

Beginning Fall 2014, CARE Consortium institutions have recruited and enrolled 23,533 student-athletes and military service academy students (approximately 90% of eligible student-athletes and cadets; 64.6% male, 35.4% female). A total of 1174 concussions have been diagnosed in participating subjects, with both concussion and baseline cases deposited in the Federal Interagency Traumatic Brain Injury Research (FITBIR) database.

CONCLUSIONS

Challenges have included coordinating regulatory issues across civilian and military institutions, operationalizing study procedures, neuroimaging protocol harmonization across sites and platforms, construction and maintenance of a relational database, and data quality and integrity monitoring. The NCAA-DoD CARE Consortium represents a comprehensive investigation of concussion in student-athletes and military service academy students. The richly characterized study sample and multidimensional approach provide an opportunity to advance the field of concussion science, not only among student athletes but in all populations at risk for mild TBI.

Concussion in pediatric surgical patients scheduled for time-sensitive surgical procedures

Background

Each year in the United States approximately three million individuals sustain sport or recreation-related concussion which may occur in the setting of orthopedic trauma requiring surgical intervention under general anesthesia. The effects of surgery and general anesthesia on brain recovery are currently unknown. The objective of this study was to determine the prevalence of recent sport concussion, recognized or not, in a preoperative, pediatric, surgical population.

Methods

The study involved administering a questionnaire to all eligible, consented patients in one of the following settings: Preoperative Clinic, Day Surgery Unit, Trauma Clinic, or inpatient floor. The questionnaire was designed to determine the occurrence and symptoms of a concussion. This study was conducted at an urban 395-bed comprehensive center for pediatric health, between May 2014 and April 2015. Inclusion criteria for study were age 5–21 years, presentation for surgical repair of orthopedic traumatic injury or nasal fracture, and precipitating injurious event occurring within four weeks of surgery.

Results

The prevalence of concussion in the setting of orthopedic trauma, either known or unknown at the time of presentation for surgery was 6%. The interval between surgery and injury was between three and 13 days. Prior education for recognition of concussion was present in 66% of patients.

Conclusions

The impact of surgery with general anesthesia in pediatric patients with a recent concussion is unknown. No changes in post-op disposition were noted in this patient population. However, our findings support the need to measure neurocognitive function before and after administration of operative procedures in a larger population with a recent concussion compared with controls.

The Pathophysiology of Concussion

Concussion is a significant issue in medicine and the media today. With growing interest on the long-term effects of sports participation, it is important to understand what occurs in the brain after an impact of any degree. While some of the basic pathophysiology has been elucidated, much is still unknown about what happens in the brain after traumatic brain injury, particularly with milder injuries where no damage can be seen at the structural level on standard neuroimaging. Understanding the chain of events from a cellular level using studies investigating more severe injuries can help to drive research efforts in understanding the symptomatology that is seen in the acute phase after concussion, as well as point to mechanisms that may underlie persistent post-concussive symptoms. This review discusses the basic neuropathology that occurs after traumatic brain injury at the cellular level. We also present the pathology of chronic traumatic encephalopathy and its similarities to other neurodegenerative diseases. We conclude with recent imaging and biomarker findings looking at changes that may occur after repeated subconcussive blows, which may help to guide efforts in understanding if cumulative subconcussive mechanical forces upon the brain are detrimental in the long term or if concussive symptoms mark the threshold for brain injury.

The effect of repetitive subconcussive collisions on brain integrity in collegiate football players over a single football season: A multi-modal neuroimaging study

The cumulative effect of repetitive subconcussive collisions on the structural and functional integrity of the brain remains largely unknown. Athletes in collision sports, like football, experience a large number of impacts across a single season of play. The majority of these impacts, however, are generally overlooked, and their long-term consequences remain poorly understood. This study sought to examine the effects of repetitive collisions across a single competitive season in NCAA Football Bowl Subdivision athletes using advanced neuroimaging approaches. Players were evaluated before and after the season using multiple MRI sequences, including T₁-weighted imaging, diffusion tensor imaging (DTI), arterial spin labeling (ASL), resting-state functional MRI (rs-fMRI), and susceptibility weighted imaging (SWI). While no significant differences were found between pre- and post-season for DTI metrics or cortical volumes, seed-based analysis of rs-fMRI revealed significant (p < 0.05) changes in functional connections to right isthmus of the cingulate cortex (ICC), left ICC, and left hippocampus. ASL data revealed significant (p < 0.05) increases in global cerebral blood flow (CBF), with a specific regional increase in right postcentral gyrus. SWI data revealed that 44% of the players exhibited outlier rates (p < 0.05) of regional decreases in SWI signal. Of key interest, athletes in whom changes in rs-fMRI, CBF and SWI were observed were more likely to have experienced high G impacts on a daily basis. These findings are indicative of potential pathophysiological changes in brain integrity arising from only a single season of participation in the NCAA Football Bowl Subdivision, even in the absence of clinical symptoms or a diagnosis of concussion. Whether these changes reflect compensatory adaptation to cumulative head impacts or more lasting alteration of brain integrity remains to be further explored.

Mapping the Connectome Following Traumatic Brain Injury

There is a paucity of accurate and reliable biomarkers to detect traumatic brain injury, grade its severity, and model post-traumatic brain injury (TBI) recovery. This gap could be addressed via advances in brain mapping which define injury signatures and enable tracking of post-injury trajectories at the individual level. Mapping of molecular and anatomical changes and of modifications in functional activation supports the conceptual paradigm of TBI as a disorder of large-scale neural connectivity. Imaging approaches with particular relevance are magnetic resonance techniques (diffusion weighted imaging, diffusion tensor imaging, susceptibility weighted imaging, magnetic resonance spectroscopy, functional magnetic resonance imaging, and positron emission tomographic methods including molecular neuroimaging). Inferences from mapping represent unique endophenotypes which have the potential to transform classification and treatment of patients with TBI. Limitations of these methods, as well as future research directions, are highlighted.

The potential for animal models to provide insight into mild traumatic brain injury: Translational challenges and strategies

Mild traumatic brain injury (mTBI) is a common health problem. There is tremendous variability and heterogeneity in human mTBI, including mechanisms of injury, biomechanical forces, injury severity, spatial and temporal pathophysiology, genetic factors, pre-injury vulnerability and resilience factors, and clinical outcomes. Animal models greatly reduce this variability and heterogeneity, and provide a means to study mTBI in a rigorous, controlled, and efficient manner. Rodent models, in particular, are time- and cost-efficient, and they allow researchers to measure morphological, cellular, molecular, and behavioral variables in a single study. However, inter-species differences in anatomy, morphology, metabolism, neurobiology, and lifespan create translational challenges. Although the term "mild" TBI is used often in the pre-clinical literature, clearly defined criteria for mild, moderate, and severe TBI in animal models have not been agreed upon. In this review, we introduce current issues facing the mTBI field, summarize the available research methodologies and previous studies in mTBI animal models, and discuss how a translational research approach may be useful in advancing our understanding and management of mTBI.

Multi-Disciplinary Management of Athletes with Post-Concussion Syndrome: An Evolving Pathophysiological Approach

Historically, patients with sports-related concussion (SRC) have been managed in a uniform fashion consisting mostly of prescribed physical and cognitive rest with the expectation that all symptoms will spontaneously resolve with time. Although this approach will result in successful return to school and sports activities in the majority of athletes, an important proportion will develop persistent concussion symptoms characteristic of post-concussion syndrome (PCS). Recent advances in exercise science, neuroimaging, and clinical research suggest that the clinical manifestations of PCS are mediated by unique pathophysiological processes that can be identified by features of the clinical history and physical examination as well as the use of graded aerobic treadmill testing. Athletes who develop PCS represent a unique population whose care must be individualized and must incorporate a rehabilitative strategy that promotes enhanced recovery of concussion-related symptoms while preventing physical deconditioning. In this review, we present our evolving evidence-based approach to evaluation and management of athletes with PCS that aims to identify the pathophysiological mechanisms mediating persistent concussion symptoms and guides the initiation of individually tailored rehabilitation programs that target these processes. In addition, we outline the important qualified roles that multi-disciplinary healthcare professionals can play in the management of this patient population, and discuss where future research efforts must be focused to further evaluate this evolving pathophysiological approach.

Longitudinal Brain Magnetic Resonance Imaging CO2 Stress Testing in Individual Adolescent Sports-Related Concussion Patients: A Pilot Study

Background

Advanced neuroimaging studies in concussion have been limited to detecting group differences between concussion patients and healthy controls. In this small pilot study, we used brain magnetic resonance imaging (MRI) CO₂ stress testing to longitudinally assess cerebrovascular responsiveness (CVR) in individual sports-related concussion (SRC) patients.

Methods

Six SRC patients (three males and three females; mean age = 15.7, range = 15–17 years) underwent longitudinal brain MRI CO₂ stress testing using blood oxygen level-dependent (BOLD) MRI and model-based prospective end-tidal CO₂ targeting under isoxic conditions. First-level and second-level comparisons were undertaken using statistical parametric mapping (SPM) to score the scans and compare them to an atlas of 24 healthy control subjects.

Results

All tests were well tolerated and without any serious adverse events. Anatomical MRI was normal in all study participants. The CO₂ stimulus was consistent between the SRC patients and control subjects and within SRC patients across the longitudinal study. Individual SRC patients demonstrated both quantitative and qualitative patient-specific alterations in CVR (p < 0.005) that correlated strongly with clinical findings, and that persisted beyond clinical recovery.

Conclusion

Standardized brain MRI CO₂ stress testing is capable of providing a longitudinal assessment of CVR in individual SRC patients. Consequently, larger prospective studies are needed to examine the utility of brain MRI CO₂ stress testing as a clinical tool to help guide the evaluation, classification, and longitudinal management of SRC patients.

Neuroimaging Assessment of Cerebrovascular Reactivity in Concussion: Current Concepts, Methodological Considerations, and Review of the Literature

Concussion is a form of traumatic brain injury (TBI) that presents with a wide spectrum of subjective symptoms and few objective clinical findings. Emerging research suggests that one of the processes that may contribute to concussion pathophysiology is dysregulation of cerebral blood flow (CBF) leading to a mismatch between CBF delivery and the metabolic needs of the injured brain. Cerebrovascular reactivity (CVR) is defined as the change in CBF in response to a measured vasoactive stimulus. Several magnetic resonance imaging (MRI) techniques can be used as a surrogate measure of CBF in clinical and laboratory studies. In order to provide an accurate assessment of CVR, these sequences must be combined with a reliable, reproducible vasoactive stimulus that can manipulate CBF. Although CVR imaging currently plays a crucial role in the diagnosis and management of many cerebrovascular diseases, only recently have studies begun to apply this assessment tool in patients with concussion. In order to evaluate the quality, reliability, and relevance of CVR studies in concussion, it is important that clinicians and researchers have a strong foundational understanding of the role of CBF regulation in health, concussion, and more severe forms of TBI, and an awareness of the advantages and limitations of currently available CVR measurement techniques. Accordingly, in this review, we (1) discuss the role of CVR in TBI and concussion, (2) examine methodological considerations for MRI-based measurement of CVR, and (3) provide an overview of published CVR studies in concussion patients.

The Sport Concussion Assessment Tool: a systematic review

OBJECTIVE

Over the last 2 decades, sport-related concussion (SRC) has garnered significant attention. Even with increased awareness and athlete education, sideline recognition and real-time diagnosis remain crucial. The need for an objective and standardized assessment of concussion led to the eventual development of the Sport Concussion Assessment Tool (SCAT) during the Second International Conference on Concussion in Sport in 2004, which is now in its third iteration (SCAT3). In an effort to update our understanding of the most well-known sideline concussion assessment, the authors conducted a systematic review of the SCAT and the evidence supporting its use to date.

METHODS

English-language titles and abstracts published between 1995 and October 2015 were searched systematically across 4 electronic databases and a review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines adapted for the review of a heterogeneous collection of study designs. Peer-reviewed journal articles were included if they reported quantitative data on any iteration of the SCAT, Standardized Assessment of Concussion (SAC), or modified Balance Error Scoring System (mBESS) data at baseline or following concussion in an exclusively athlete population with any portion older than 13 years of age. Studies that included nonathletes, only children less than 13 years old, exclusively BESS data, exclusively symptom scale data, or a non–SCAT-related assessment were excluded.

RESULTS

The database search process yielded 549 abstracts, and 105 full-text articles were reviewed with 36 meeting criteria for inclusion. Nineteen studies were associated with the SAC, 1 was associated with the mBESS exclusively, and 16 studies were associated with a full iteration of the SCAT. The majority of these studies (56%) were prospective cohort studies. Male football players were the most common athletes studied. An analysis of the studies focused on baseline differences associated with age, sex, concussion history, and the ability to detect an SRC.

CONCLUSIONS

Looking toward the upcoming Concussion in Sport Group meeting in fall 2016, one may expect further revision to the SCAT3. However, based on this systematic review, the authors propose further, in-depth study of an already comprehensive concussion test, with acute, diagnostic, as well as long-term use.