Distinct Serum Glial Fibrillary Acidic Protein and Neurofilament Light Time-Courses After Rapid Head Rotations.

Traumatic brain injury (TBI) causes significant neurophysiological deficits and is typically associated with rapid head accelerations common in sports-related incidents and automobile accidents. There are over 1.5 million TBIs in the United States each year, with children aged 0-4 being particularly vulnerable. TBI diagnosis is currently achieved through interpretation of clinical signs and symptoms and neuroimaging; however, there is increasing interest in minimally invasive fluid biomarkers to detect TBI objectively across all ages. Pre-clinical porcine models offer controlled conditions to evaluate TBI with known biomechanical conditions and without comorbidities. The objective of the current study was to establish pediatric porcine healthy reference ranges (RRs) of common human serum TBI biomarkers and to report their acute time-course after nonimpact rotational head injury. A retrospective analysis was completed to quantify biomarker concentrations in porcine serum samples collected from 4-week-old female (n = 215) and uncastrated male (n = 6) Yorkshire piglets. Subjects were assigned to one of three experimental groups (sham, sagittal-single, sagittal-multiple) or to a baseline only group. A rapid nonimpact rotational head injury model was used to produce mild-to-moderate TBI in piglets following a single rotation and moderate-to-severe TBI following multiple rotations. The Quanterix Simoa Human Neurology 4-Plex A assay was used to quantify glial fibrillary acidic protein (GFAP), neurofilament light (Nf-L), tau, and ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1). The 95% healthy RRs for females were calculated and validated for GFAP (6.3-69.4 pg/mL), Nf-L (9.5-67.2 pg/mL), and UCH-L1 (3.8-533.7 pg/mL). Rising early, GFAP increased significantly above the healthy RRs for sagittal-single (to 164 and 243 pg/mL) and increased significantly higher in sagittal-multiple (to 494 and 413 pg/mL) groups at 30 min and 1 h postinjury, respectively, returning to healthy RRs by 1-week postinjury. Rising later, Nf-L increased significantly above the healthy RRs by 1 day in sagittal-single (to 69 pg/mL) and sagittal-multiple groups (to 140 pg/mL) and rising further at 1 week (single = 231 pg/mL, multiple = 481 pg/mL). Sagittal-single and sagittal-multiple UCH-L1 serum samples did not differ from shams or the healthy RRs. Sex differences were observed but inconsistent. Serum GFAP and Nf-L levels had distinct time-courses following head rotations in piglets, and both corresponded to load exposure. We conclude that serum GFAP and Nf-L offer promise for early TBI diagnosis and intervention decisions for TBI and other neurological trauma.

Regional variations distinguish auditory from visual evoked potentials in healthy 4 week old piglets.

Objective.Evoked potentials (EP), measured using electroencephalographic (EEG) recordings provide an opportunity to monitor cognitive dysfunctions after neurological diseases or traumatic brain injury (TBI). The 4 week old piglet is an established model of paediatric TBI; therefore, healthy piglets were studied to establish feasibility of obtaining responses to auditory and visual stimuli. A secondary aim was to input the EEG data into a piglet computational model to localize the brain sources related to processing. We tested the hypotheses: (1) visual, auditory-standard, and auditory-target stimuli elicit responses, (2) there is an effect of stimulus type, day tested, and electrode region on EPs from EEG, (3) there is an effect of stimulus type, day tested, and brain region on localized sources from a computational model.Approach.Eleven 4 week old female piglets were fitted with a 32-electrode net and presented with a simple white light stimulus and an auditory oddball click train (70 standard; 30 target tones).Main results.N1 andP2 amplitudes were consistently observed for all stimulus types. Significant interaction effects between brain region and stimulus for EP and current density demonstrate that cognitive responses are specific to each modality with auditory localizing to the temporal region and visual to the occipital regions. There was a day effect where larger responses were found on the first day than day 2 and 3 and may be due to the novelty of the stimulus on the first day. Visual stimuli had largerP1 amplitudes and earlier latencies (P1,N1) than auditory which coincides with current density results at 50 ms where larger activations were observed for visual. At 85 ms, auditory had significantly larger current densities coincident with larger and longerN1 amplitudes and latencies than visual.Significance.Auditory and visual processing were successfully and consistently obtained in a porcine model and can be evaluated as a diagnostic assessment for TBI.

Multiple Head Rotations Result in Persistent Gait Alterations in Piglets.

Multiple/repeated mild traumatic brain injury (mTBI) in young children can cause long-term gait impairments and affect the developmental course of motor control. Using our swine model for mTBI in young children, our aim was to (i) establish a reference range (RR) for each parameter to validate injury and track recovery, and (ii) evaluate changes in gait patterns following a single and multiple (5×) sagittal rapid non-impact head rotation (RNR). Gait patterns were studied in four groups of 4-week-old Yorkshire swine: healthy (n = 18), anesthesia-only sham (n = 8), single RNR injury (n = 12) and multiple RNR injury (n = 11). Results were evaluated pre-injury and at 1, 4, and 7 days post-injury. RR reliability was validated using additional healthy animals (n = 6). Repeated mTBI produced significant increases in gait time, cycle time, and stance time, as well as decreases in gait velocity and cadence, on Day One post-injury compared to pre-injury, and these remained significantly altered at Day Four and Day Seven post-injury. The gait metrics of the repeated TBI group also significantly fell outside the healthy RR on Day One, with some recovery by Day Four, while many remained altered at Day Seven. Only a bilateral decrease in hind stride length was observed at Day Four in our single RNR group compared to pre-injury. In sum, repeated and single sagittal TBI can significantly impair motor performance, and gait metrics can serve as reliable, objective, quantitative functional assessments in a juvenile porcine RNR TBI model.

Target detection in healthy 4-week old piglets from a passive two-tone auditory oddball paradigm.

BACKGROUND: Passive auditory oddball tests are effort independent assessments that evaluate auditory processing and are suitable for paediatric patient groups. Our goal was to develop a two-tone auditory oddball test protocol and use this clinical assessment in an immature large animal model. Event-related potentials captured middle latency P1, N1, and P2 responses in 4-week old (N = 16, female) piglets using a custom piglet 32- electrode array on 3 non-consecutive days. The effect of target tone frequency (250 Hz and 4000 Hz) on middle latency responses were tested in a subset of animals. RESULTS: Results show that infrequent target tone pulses elicit greater N1 amplitudes than frequent standard tone pulses. There was no effect of day. Electrodes covering the front of the head tend to elicit greater waveform responses. P2 amplitudes increased for higher frequency target tones (4000 Hz) than the regular 1000 Hz target tones (p < 0.05). CONCLUSIONS: Two-tone auditory oddball tests produced consistent responses day-to-day. This clinical assessment was successful in the immature large animal model.

Toward development of clinically translatable diagnostic and prognostic metrics of traumatic brain injury using animal models: A review and a look forward.

Traumatic brain injury is a leading cause of cognitive and behavioral deficits in children in the US each year. There is an increasing interest in both clinical and pre-clinical studies to discover biomarkers to accurately diagnose traumatic brain injury (TBI), predict its outcomes, and monitor its progression especially in the developing brain. In humans, the heterogeneity of TBI in terms of clinical presentation, injury causation, and mechanism has contributed to the many challenges associated with finding unifying diagnosis, treatment, and management practices. In addition, findings from adult human research may have little application to pediatric TBI, as age and maturation levels affect the injury biomechanics and neurophysiological consequences of injury. Animal models of TBI are vital to address the variability and heterogeneity of TBI seen in human by isolating the causation and mechanism of injury in reproducible manner. However, a gap between the pre-clinical findings and clinical applications remains in TBI research today. To take a step toward bridging this gap, we reviewed several potential TBI tools such as biofluid biomarkers, electroencephalography (EEG), actigraphy, eye responses, and balance that have been explored in both clinical and pre-clinical studies and have shown potential diagnostic, prognostic, or monitoring utility for TBI. Each of these tools measures specific deficits following TBI, is easily accessible, non/minimally invasive, and is potentially highly translatable between animals and human outcomes because they involve effort-independent and non-verbal tasks. Especially conspicuous is the fact that these biomarkers and techniques can be tailored for infants and toddlers. However, translation of preclinical outcomes to clinical applications of these tools necessitates addressing several challenges. Among the challenges are the heterogeneity of clinical TBI, age dependency of some of the biomarkers, different brain structure, life span, and possible variation between temporal profiles of biomarkers in human and animals. Conducting parallel clinical and pre-clinical research, in addition to the integration of findings across species from several pre-clinical models to generate a spectrum of TBI mechanisms and severities is a path toward overcoming some of these challenges. This effort is possible through large scale collaborative research and data sharing across multiple centers. In addition, TBI causes dynamic deficits in multiple domains, and thus, a panel of biomarkers combining these measures to consider different deficits is more promising than a single biomarker for TBI. In this review, each of these tools are presented along with the clinical and pre-clinical findings, advantages, challenges and prospects of translating the pre-clinical knowledge into the human clinical setting.

The biomechanics of concussion for ice hockey head impact events.

The purpose of this research was to conduct reconstructions of concussive and non-concussive impacts in ice hockey to determine the biomechanics and thresholds of concussive injury in ice hockey. Videos of concussive and non-concussive impacts in an elite professional ice hockey league in North America were reconstructed using physical and finite element model methods. Eighty concussive and 45 non-concussive events were studied. Logistic regressions indicate significant thresholds for concussion for linear/rotational acceleration and CSDM10%. Impacts in ice hockey were mostly long duration events, longer than 15 ms. These results have significant implications for helmet standards and development to prevent concussion.

Brain tissue analysis of impacts to American football helmets.

Concussion in American football is a prevalent concern. Research has been conducted examining frequencies, location, and thresholds for concussion from impacts. Little work has been done examining how impact location may affect risk of concussive injury. The purpose of this research was to examine how impact site on the helmet and type of impact, affects the risk of concussive injury as quantified using finite element modelling of the human head and brain. A linear impactor was used to impact a helmeted Hybrid III headform in several locations and using centric and non-centric impact vectors. The resulting dynamic response was used as input for the Wayne State Brain Injury Model to determine the risk of concussive injury by utilizing maximum principal strain as the predictive variable. The results demonstrated that impacts that occur primarily to the side of the head resulted in higher magnitudes of strain in the grey and white matter, as well as the brain stem. Finally, commonly worn American football helmets were used in this research and significant risk of injury was incurred for all impacts. These results suggest that improvements in American football helmets are warranted, in particular for impacts to the side of the helmet.

A comparison of head dynamic response and brain tissue stress and strain using accident reconstructions for concussion, concussion with persistent postconcussive symptoms, and subdural hematoma.

OBJECT: Concussions typically resolve within several days, but in a few cases the symptoms last for a month or longer and are termed persistent postconcussive symptoms (PPCS). These persisting symptoms may also be associated with more serious brain trauma similar to subdural hematoma (SDH). The objective of this study was to investigate the head dynamic and brain tissue responses of injury reconstructions resulting in concussion, PPCS, and SDH. METHODS: Reconstruction cases were obtained from sports medicine clinics and hospitals. All subjects received a direct blow to the head resulting in symptoms. Those symptoms that resolved in 9 days or fewer were defined as concussions (n = 3). Those with symptoms lasting longer than 18 months were defined as PPCS (n = 3), and 3 patients presented with SDHs (n = 3). A Hybrid III headform was used in reconstruction to obtain linear and rotational accelerations of the head. These dynamic response data were then input into the University College Dublin Brain Trauma Model to calculate maximum principal strain and von Mises stress. A Kruskal-Wallis test followed by Tukey post hoc tests were used to compare head dynamic and brain tissue responses between injury groups. Statistical significance was set at p < 0.05. RESULTS: A significant difference was identified for peak resultant linear and rotational acceleration between injury groups. Post hoc analyses revealed the SDH group had higher linear and rotational acceleration responses (316 g and 23,181 rad/sec(2), respectively) than the concussion group (149 g and 8111 rad/sec(2), respectively; p < 0.05). No significant differences were found between groups for either brain tissue measures of maximum principal strain or von Mises stress. CONCLUSIONS: The reconstruction of accidents resulting in a concussion with transient symptoms (low severity) and SDHs revealed a positive relationship between an increase in head dynamic response and the risk for more serious brain injury. This type of relationship was not found for brain tissue stress and strain results derived by finite element analysis. Future research should be undertaken using a larger sample size to confirm these initial findings. Understanding the relationship between the head dynamic and brain tissue response and the nature of the injury provides important information for developing strategies for injury prevention.

Current and future concepts in helmet and sports injury prevention.

Since the introduction of head protection, a decrease in sports-related traumatic brain injuries has been reported. The incidence of concussive injury, however, has remained the same or on the rise. These trends suggest that current helmets and helmet standards are not effective in protecting against concussive injuries. This article presents a literature review that describes the discrepancy between how helmets are designed and tested and how concussions occur. Most helmet standards typically use a linear drop system and measure criterion such as head Injury criteria, Gadd Severity Index, and peak linear acceleration based on research involving severe traumatic brain injuries. Concussions in sports occur in a number of different ways that can be categorized into collision, falls, punches, and projectiles. Concussive injuries are linked to strains induced by rotational acceleration. Because helmet standards use a linear drop system simulating fall-type injury events, the majority of injury mechanisms are neglected. In response to the need for protection against concussion, helmet manufacturers have begun to innovate and design helmets using other injury criteria such as rotational acceleration and brain tissue distortion measures via finite-element analysis. In addition to these initiatives, research has been conducted to develop impact protocols that more closely reflect how concussions occur in sports. Future research involves a better understanding of how sports-related concussions occur and identifying variables that best describe them. These variables can be used to guide helmet innovation and helmet standards to improve the quality of helmet protection for concussive injury.