Impaired Cerebral Vasoreactivity Despite Symptom Resolution in Sports-Related Concussion

Transcranial Doppler Ultrasound and Concussion-Supplemental Symptoms with Physiology: A Systematic Review

Sport-related concussion (SRC) can impair the cerebrovasculature both acutely and chronically. Transcranial Doppler (TCD) ultrasound assessment has the potential to illuminate the mechanisms of impairment and provide an objective evaluation of SRC. The current systematic review investigated studies employing TCD ultrasound assessment of intracranial arteries across three broad categories of cerebrovascular regulation: neurovascular coupling (NVC), cerebrovascular reactivity (CVR), and dynamic cerebral autoregulation (dCA). The current review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) database (CRD42021275627). The search strategy was applied to PubMed, as this database indexes all biomedical journals. Original articles on TCD for athletes with medically diagnosed SRC were included. Title/abstract and full-text screening were completed by three authors. Two authors completed data extraction and risk of bias using the Methodological Index for Non-Randomized Studies and Scottish Intercollegiate Guideline Network checklists. Of the 141 articles identified, 14 met the eligibility criteria. One article used an NVC challenge, eight assessed CVR, and six investigated dCA. Methodologies varied widely among studies, and results were heterogeneous. There was evidence of cerebrovascular impairment in all three domains roughly 2 days post-SRC, but the magnitude and recovery of these impairments were not clear. There was evidence that clinical symptom resolution occurred before cerebrovascular function, indicating that physiological deficits may persist despite clinical recovery and return to play. Collectively, this emphasizes an opportunity for the use of TCD to illuminate the cerebrovascular deficits caused by SRC. It also highlights that there is need for consistent methodological rigor when employing TCD in a SRC population.

Effects of Low-Level Blast on Neurovascular Health and Cerebral Blood Flow: Current Findings and Future Opportunities in Neuroimaging

Low-level blast (LLB) exposure can lead to alterations in neurological health, cerebral vasculature, and cerebral blood flow (CBF). The development of cognitive issues and behavioral abnormalities after LLB, or subconcussive blast exposure, is insidious due to the lack of acute symptoms. One major hallmark of LLB exposure is the initiation of neurovascular damage followed by the development of neurovascular dysfunction. Preclinical studies of LLB exposure demonstrate impairment to cerebral vasculature and the blood-brain barrier (BBB) at both early and long-term stages following LLB. Neuroimaging techniques, such as arterial spin labeling (ASL) using magnetic resonance imaging (MRI), have been utilized in clinical investigations to understand brain perfusion and CBF changes in response to cumulative LLB exposure. In this review, we summarize neuroimaging techniques that can further our understanding of the underlying mechanisms of blast-related neurotrauma, specifically after LLB. Neuroimaging related to cerebrovascular function can contribute to improved diagnostic and therapeutic strategies for LLB. As these same imaging modalities can capture the effects of LLB exposure in animal models, neuroimaging can serve as a gap-bridging diagnostic tool that permits a more extensive exploration of potential relationships between blast-induced changes in CBF and neurovascular health. Future research directions are suggested, including investigating chronic LLB effects on cerebral perfusion, exploring mechanisms of dysautoregulation after LLB, and measuring cerebrovascular reactivity (CVR) in preclinical LLB models.

Neuroimaging to enhance understanding of cardiovascular autonomic changes associated with mild traumatic brain injury: a scoping review

BACKGROUND

Cardiovascular changes, such as altered heart rate and blood pressure, have been identified in some individuals following mild traumatic brain injury (mTBI) and may be related to disturbances of the autonomic nervous system and cerebral blood flow.

METHODS

We conducted a scoping review according to PRISMA-ScR guidelines across six databases (Medline, CINAHL, Web of Science, PsychInfo, SportDiscus and Google Scholar) to explore literature examining both cardiovascular parameters and neuroimaging modalities following mTBI, with the aim of better understanding the pathophysiological basis of cardiovascular autonomic changes associated with mTBI.

RESULTS

Twenty-nine studies were included and two main research approaches emerged from data synthesis. Firstly, more than half the studies used transcranial Doppler ultrasound and found evidence of cerebral blood flow impairments that persisted beyond symptom resolution. Secondly, studies utilizing advanced MRI identified microstructural injury within brain regions responsible for cardiac autonomic function, providing preliminary evidence that cardiovascular autonomic changes are a consequence of injury to these areas.

CONCLUSION

Neuroimaging modalities hold considerable potential to aid understanding of the complex relationship between cardiovascular changes and brain pathophysiology associated with mTBI. However, it is difficult to draw definitive conclusions from the available data due to variability in study methodology and terminology.

Role of biomarkers and emerging technologies in defining and assessing neurobiological recovery after sport-related concussion: a systematic review

OBJECTIVE

Determine the role of fluid-based biomarkers, advanced neuroimaging, genetic testing and emerging technologies in defining and assessing neurobiological recovery after sport-related concussion (SRC).

DESIGN

Systematic review.

DATA SOURCES

Searches of seven databases from 1 January 2001 through 24 March 2022 using keywords and index terms relevant to concussion, sports and neurobiological recovery. Separate reviews were conducted for studies involving neuroimaging, fluid biomarkers, genetic testing and emerging technologies. A standardised method and data extraction tool was used to document the study design, population, methodology and results. Reviewers also rated the risk of bias and quality of each study.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies were included if they: (1) were published in English; (2) represented original research; (3) involved human research; (4) pertained only to SRC; (5) included data involving neuroimaging (including electrophysiological testing), fluid biomarkers or genetic testing or other advanced technologies used to assess neurobiological recovery after SRC; (6) had a minimum of one data collection point within 6 months post-SRC; and (7) contained a minimum sample size of 10 participants.

RESULTS

A total of 205 studies met inclusion criteria, including 81 neuroimaging, 50 fluid biomarkers, 5 genetic testing, 73 advanced technologies studies (4 studies overlapped two separate domains). Numerous studies have demonstrated the ability of neuroimaging and fluid-based biomarkers to detect the acute effects of concussion and to track neurobiological recovery after injury. Recent studies have also reported on the diagnostic and prognostic performance of emerging technologies in the assessment of SRC. In sum, the available evidence reinforces the theory that physiological recovery may persist beyond clinical recovery after SRC. The potential role of genetic testing remains unclear based on limited research.

CONCLUSIONS

Advanced neuroimaging, fluid-based biomarkers, genetic testing and emerging technologies are valuable research tools for the study of SRC, but there is not sufficient evidence to recommend their use in clinical practice.

PROSPERO REGISTRATION NUMBER

CRD42020164558.

Co-administration of Nanowired Oxiracetam and Neprilysin with Monoclonal Antibodies to Amyloid Beta Peptide and p-Tau Thwarted Exacerbation of Brain Pathology in Concussive Head Injury at Hot Environment

Environmental temperature adversely affects the outcome of concussive head injury (CHI)-induced brain pathology. Studies from our laboratory showed that animals reared at either cold environment or at hot environment exacerbate brain pathology following CHI. Our previous experiments showed that nanowired delivery of oxiracetam significantly attenuated CHI-induced brain pathology and associated neurovascular changes. Military personnel are the most susceptible to CHI caused by explosion, blasts, missile or blunt head trauma leading to lifetime functional and cognitive impairments affecting the quality of life. Severe CHI leads to instant death and/or lifetime paralysis. Military personnel engaged in combat operations are often subjected to extreme high or low environmental temperature zones across the globe. Thus, further exploration of novel therapeutic agents at cold or hot ambient temperatures following CHI are the need of the hour. CHI is also a major risk factor for developing Alzheimer's disease by enhancing amyloid beta peptide deposits in the brain. In this review, effect of hot environment on CHI-induced brain pathology is discussed. In addition, whether nanodelivery of oxiracetam together with neprilysin and monoclonal antibodies (mAb) to amyloid beta peptide and p-tau could lead to superior neuroprotection in CHI is explored. Our results show that co-administration of oxiracetam with neprilysin and mAb to AβP and p-tau significantly induced superior neuroprotection following CHI in hot environment, not reported earlier.

Pediatric Sports-Related Concussion: An Approach to Care

Sports-related concussion (SRC) is a common sports injury in children and adolescents. With the vast amount of youth sports participation, an increase in awareness of concussion and evidence that the injury can lead to consequences for school, sports and overall quality of life, it has become increasingly important to properly diagnose and manage concussion. SRC in the student athlete is a unique and complex injury, and it is important to highlight the differences in the management of child and adolescent concussion compared with adults. This review focuses on the importance of developing a multimodal systematic approach to diagnosing and managing pediatric sports-related concussion, from the sidelines through recovery.

Longitudinal assessment of hemodynamic alterations after mild traumatic brain injury in adolescents: Selected case study review

Alterations in the neurovasculature after traumatic brain injury (TBI) represents a significant sequelae. However, despite theoretical and empirical evidence supporting the near-ubiquity of vascular injury, its pathophysiology remains elusive. Although this has been shown for all grades of TBI, the vascular changes after injuries with the broad mild traumatic brain injuries (mTBI) classification, remain particularly difficult to describe. Our group has previously demonstrated hemodynamic alterations in mTBI by utilizing transcranial Doppler ultrasound and cerebrovascular reactivity in a cross-sectional study. That work identified a phasic progression of deviations over varying days post-injury. These phases were then characterized by a set of inverse models that provided a hypothetical process of hemodynamic dysfunction after mTBI. This model set provides a framework with the potential for guiding clinical treatment over the course of recovery. However, it is still unclear if individual patients will progress through the phases of dysfunction similar to that found at the population level. The work presented here explores six individual patients with high-density data collected during their post-injury recovery. Breath-hold index (BHI) was found to be the most robust feature related to mTBI longitudinally. All six subjects exhibited BHI recovery curves that followed the population model's progression. The changes in pulsatile features lacked the universality of BHI, but were present in subjects with higher self-reported symptom scores and longer periods of recovery. This work suggests neurovascular dysfunction after an mTBI may be a robust phenomenon. Additionally, the capabilities of TCD in capturing these changes highlights its potential for aiding clinicians in monitoring patient's recovery post mTBI.

Cerebral Blood Flow Predicts Recovery in Children with Persistent Post-Concussion Symptoms after Mild Traumatic Brain Injury

Persistent post-concussion symptoms (PPCS) following pediatric mild traumatic brain injury (mTBI) are associated with differential changes in cerebral blood flow (CBF). Given its potential as a therapeutic target, we examined CBF changes during recovery in children with PPCS. We hypothesized that CBF would decrease and that such decreases would mirror clinical recovery. In a prospective cohort study, 61 children and adolescents (mean age 14 [standard deviation = 2.6] years; 41% male) with PPCS were imaged with three-dimensional (3D) pseudo-continuous arterial spin-labelled (pCASL) magnetic resonance imaging (MRI) at 4-6 and 8-10 weeks post-injury. Exclusion criteria included any significant past medical history and/or previous concussion within the past 3 months. Twenty-three participants had clinically recovered at the time of the second scan. We found that relative and mean absolute CBF were higher in participants with poor recovery, 44.0 (95% confidence interval [CI]: 43.32, 44.67) than in those with good recovery, 42.19 (95% CI: 41.77, 42.60) mL/min/100 g gray tissue and decreased over time (β = -1.75; p < 0.001). The decrease was greater in those with good recovery (β = 2.29; p < 0.001) and predicted outcome in 77% of children with PPCS (odds ratio [OR] 0.54, 95% CI: 0.36, 0.80; p = 0.002). Future studies are warranted to validate the utility of CBF as a useful predictive biomarker of outcome in PPCS.

Preseason Cerebrovascular Function in Adolescent Athletes

The purpose of this study was to investigate the effects of sport participation, concussion history, and age of first exposure to football on preseason cerebrovascular function in adolescent athletes. Athletes (n = 53, age = 15.8 ± 1.2 years) were examined based on three exposure groupings: (1) sport participation (football vs. non-collision), (2) concussion history (none vs. ≥ 1), and (3) age of first exposure (football participants only). Transcranial Doppler assessed cerebrovascular reactivity (CVR) and neurovascular coupling (NVC), and separate independent samples t-tests evaluated group differences in CVR and NVC outcomes. Separate univariate linear regressions determined how age of first exposure related to CVR and NVC outcomes. Linear mixed effects models assessed group differences in CVR and NVC relative response curves. Differential response to NVC visual task response was significantly greater in non-collision sport athletes (F_1,2946 = 38.69, p < 0.0001) and athletes without a concussion history (F_1,2946 = 25.23, p < 0.0001). Older age of first exposure significantly predicted reduced breath-holding CVR response (F_1,1560 = 2.92, p = 0.03). Healthy adolescent athletes have similar pre-season cerebrovascular function despite different sport participation and concussion history. However, age of first exposure may predict CVR in adolescent football athletes. Developmental literature identifies cerebrovascular function as dynamically changing throughout adolescence. Our study provides fundamental data informing the clinical meaningfulness of short- and long-term physiological function changes.

A Promising Subject-Level Classification Model for Acute Concussion Based on Cerebrovascular Reactivity Metrics

Concussion imaging research has primarily focused on neuronal disruption with lesser emphasis directed toward vascular dysfunction. However, blood flow metrics may be more sensitive than measures of neuronal integrity. Vascular dysfunction can be assessed by measuring cerebrovascular reactivity (CVR)-the change in cerebral blood flow per unit change in vasodilatory stimulus. CVR metrics, including speed and magnitude of flow responses to a standardized well-controlled vasoactive stimulus, are potentially useful for assessing individual subjects following concussion given that blood flow dysregulation is known to occur with traumatic brain injury. We assessed changes in CVR metrics to a standardized vasodilatory stimulus during the acute phase of concussion. Using a case control design, 20 concussed participants and 20 healthy controls (HCs) underwent CVR assessment measuring blood oxygen-level dependent (BOLD) magnetic resonance imaging using precise changes in end-tidal partial pressure of CO₂ (PETCO₂). Metrics were calculated for the whole brain, gray matter (GM), and white matter (WM) using sex-stratification. A leave-one-out receiver operating characteristic (ROC) analysis classified concussed from HCs based on CVR metrics. CVR magnitude was greater and speed of response faster in concussed participants relative to HCs, with WM showing higher classification accuracy compared with GM. ROC analysis for WM-CVR metrics revealed an area under the curve of 0.94 in males and 0.90 in females for speed and magnitude of response respectively. These greater than normal responses to a vasodilatory stimulus warrant further investigation to compare the predictive ability of CVR metrics against structural injury metrics for diagnosis and prognosis in acute concussion.

Repetitive Head Impact Exposure and Cerebrovascular Function in Adolescent Athletes

The purpose of this study was to determine how subconcussive head impact exposure in high school collision sport student-athletes influenced cerebrovascular function. Transcranial Doppler was used to assess pre- to post-season changes in: (1) resting middle (MCA) and posterior cerebral arteries (PCA), (2) cerebrovascular reactivity (CVR) via breath-holding index (BHI), vasomotor reactivity response (VMRr) and overall MCA response curve, and (3) neurovascular coupling (NVC) via NVC response magnitude and overall PCA response curve. Fifty-three high school-aged athletes (age = 15.8 ± 1.2years, height = 175.8 ± 8.1cm, mass = 69.4 ± 13.5kg) were recruited into two groups (collision vs. non-collision sport). All participants completed a pre-season cerebrovascular function assessment. Following a 4- to 5-month window (118.6 ± 12.2 days), 48 athletes from the original sample (age = 16.0 ± 1.2 years, height = 175.5 ± 8.1 cm, mass = 68.6 ± 4.0 kg) repeated the cerebrovascular assessment. There were no group differences in any cerebrovascular measures at pre-season testing (p > 0.05). At post-season testing, collision sport athletes demonstrated greater positive change in BHI (t₄₄ = -2.21, p = 0.03) while non-collision sport athletes demonstrated greater negative change in the NVC response magnitude to the reading task (t₄₄ = 1.98, p = 0.048), and lower overall PCA response curve to the reading task (F_1,2710 = 101.54, p < 0.001). All other pre- to post-season change values were non-significant (p > 0.05). Our data indicate that single-season changes in cerebrovascular outcomes may differ between collision and non-collision sport athletes. Although the clinical interpretation is still unclear, our study demonstrates that CVR and NVC assessments may be sensitive to the dynamic cerebrovascular changes occurring in adolescent athletes. Future research should continue to assess these outcomes following both subconcussive head impact exposure and throughout the recovery trajectory following concussion.

Neurovascular Coupling by Functional Near Infra-Red Spectroscopy and Sport-Related Concussion in Retired Rugby Players: The UK Rugby Health Project

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.