The impact of concussion on cardiac autonomic function: A systematic review

Peculiarities of cardio-respiratory relationships in qualified athletes with different types of heart rhythm regulation according to respiratory maneuver data

INTRODUCTION

Our goal was to determine the differences in changes in cardiovascular and cardiorespiratory interaction indicators during a respiratory maneuver with a change in breathing rate in athletes with different types of heart rate regulation.

METHODS

The results of a study of 183 healthy men aged 21.2 ± 2.3 years, who were systematically involved in various sports, were analyzed. According to the results of the analysis of the HRV study during spontaneous breathing, the athletes were divided into 4 groups taking into account the type of heart rate regulation (HRR). Group 1 (with type I) consisted of 53 people, group 2 (with type II)-29 people, group 3 (with type III)-85 people, group 4 (with type IV)-16 people. The methodology for studying the cardiorespiratory system included combined measurements of the respiratory and cardiovascular system activity indicators in a sitting position using a spiroarteriocardiorhythmograph. The duration of the study was 6 min.

RESULTS

According to changes in cardiorespiratory and cardiovascular interaction indicators during controlled breathing with a frequency of 6 and 15 per minute (CR6 and CR15), it is shown that with a pronounced predominance of parasympathetic influences (type IV) in conditions of excessive cardiorespiratory control and moderate hyperventilation, differences in changes in arterial baroreflex sensitivity (δBRLF and δBRHF) are noted in comparison with other HRR. Athletes with type IV at CR6 in δBRLF significantly differ from athletes with type III (p = 0.026) and do not differ from athletes with type II (p = 0.141). In δBRHF significantly (p = 0.038 and p = 0.043)-from athletes with types I and II. It is shown that with the predominance of sympathetic influences (types I and II), the reactivity of BRS (δBRLF and δBRHF) in response to moderate hyperventilation (CR15) is significantly lower. Changes in the Hildebrandt index and the volume synchronization index additionally differentiate HRR associated with a moderate and pronounced predominance of sympathetic and parasympathetic influences.

CONCLUSION

The use of a respiratory maneuver in a combined study of the cardiorespiratory system in the conditions of current control of athletes showed informativeness in the differentiation of HRR types and states of functional overstrain.

A Systematic Review of the Relationship Between Traumatic Brain Injury and Disruptions in Heart Rate Variability

Autonomic nervous system dysfunction is increasingly recognized as a common sequela of traumatic brain injury (TBI). Heart rate variability (HRV) is a specific measure of autonomic nervous system functioning that can be used to measure beat-to-beat changes in heart rate following TBI. The objective of this systematic review was to determine the state of the literature on HRV dysfunction following TBI, assess the level of support for HRV dysfunction following TBI, and determine if HRV dysfunction predicts mortality and the severity and subsequent recovery of TBI symptoms. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Two raters coded each article and provided quality ratings with discrepancies resolved by consensus. Eighty-nine papers met the inclusion criteria. Findings indicated that TBI of any severity is associated with decreased (i.e., worse) HRV; the severity of TBI appears to moderate the relationship between HRV and recovery; decreased HRV following TBI predicts mortality beyond age; HRV disturbances may persist beyond return-to-play and symptom resolution following mild TBI. Overall, current literature suggests HRV is decreased following TBI and may be a good indicator of physiological change and predictor of important outcomes including mortality and symptom improvement following TBI.

Cardiorespiratory fitness assessment and training in the early sub-acute phase of recovery following traumatic brain injury: a systematic review

OBJECTIVES

To examine the safety of cardiorespiratory fitness (CRF) assessment and training in the early sub-acute phase of recovery (≤3 months) following moderate-to-extremely severe traumatic brain injury (TBI).

METHODS

A systematic review was completed in accordance with the PRISMA guidelines. Studies investigating adults and adolescents ≥15 years with moderate-to-extremely severe TBI were considered for inclusion. The methodological quality of the included studies was evaluated according to the McMaster Guidelines for Critical Review Form - Quantitative Studies.

RESULTS

Eleven studies with a total of 380 participants were included in the review. Adverse events (AEs) and symptom monitoring were poorly reported. Only four studies reported on the occurrence of AEs, with a total of eight AEs reported. Three of the reported AEs were concussion-like symptoms with no further exercise-induced symptom exacerbation reported. No serious AEs were reported.

CONCLUSION

There is no evidence to suggest that CRF assessment and training is unsafe in the early sub-acute phase of recovery following moderate-to-extremely severe TBI. However, despite the low AE and symptom exacerbation rates identified, a timeframe for safe commencement was unable to be established due to poor reporting and/or monitoring of exercise-induced symptoms and AEs in the current literature.

Symptoms Associated With Exercise Intolerance and Resting Heart Rate Following Mild Traumatic Brain Injury

OBJECTIVES

People may experience a myriad of symptoms after mild traumatic brain injury (mTBI), but the relationship between symptoms and objective assessments is poorly characterized. This study sought to investigate the association between symptoms, resting heart rate (HR), and exercise tolerance in individuals following mTBI, with a secondary aim to examine the relationship between symptom-based clinical profiles and recovery.

METHODS

Prospective observational study of adults aged 18 to 65 years who had sustained mTBI within the previous 7 days. Symptoms were assessed using the Post-Concussion Symptom Scale, HR was measured at rest, and exercise tolerance was assessed using the Buffalo Concussion Bike Test. Symptom burden and symptom-based clinical profiles were examined with respect to exercise tolerance and resting HR.

RESULTS

Data from 32 participants were assessed (mean age 36.5 ± 12.6 years, 41% female, 5.7 ± 1.1 days since injury). Symptom burden (number of symptoms and symptom severity) was significantly associated with exercise intolerance ( P = .002 and P = .025, respectively). Physiological and vestibular-ocular clinical profile composite groups were associated with exercise tolerance ( P = .001 and P = .014, respectively), with individuals who were exercise intolerant having a higher mean number of symptoms in each profile than those who were exercise tolerant. Mood-related and autonomic clinical profiles were associated with a higher resting HR (>80 bpm) ( P = .048 and P = .028, respectively), suggesting altered autonomic response for participants with symptoms relating to this profile. After adjusting for age and mechanism of injury (sports- or non-sports-related), having a higher mood-related clinical profile was associated with persisting symptoms at 3 months postinjury (adjusted odds ratio = 2.08; 95% CI, 1.11-3.90; P = .013).

CONCLUSION

Symptom-based clinical profiles, in conjunction with objective measures such as resting HR and exercise tolerance, are important components of clinical care for those having sustained mTBI. These results provide preliminary support for the concept that specific symptoms are indicative of autonomic dysfunction following mTBI.

Complementary and Integrative Medicine in Treating Headaches, Cognitive Dysfunction, Mental Fatigue, Insomnia, and Mood Disorders Following Traumatic Brain Injury: A Comprehensive Review

Traumatic brain injury (TBI) is a complex condition associated with a range of persistent symptoms including headaches, cognitive dysfunction, mental fatigue, insomnia, and mood disorders. Conventional treatments for TBI-related symptoms can be insufficient, leading to interest in complementary and integrative medicine (CIM) approaches. This comprehensive article examines the existing literature on CIM modalities, including mind-body interventions, acupuncture/acupressure, herbal remedies, nutritional supplements, biofeedback, yoga, and tai chi in the context of managing secondary complications following TBI. The article highlights potential benefits and limitations of CIM modalities, while acknowledging the need for further research to better establish efficacy and safety in this specific population.

Assessment of cardiovascular functioning following sport-related concussion: A physiological perspective

There is still much uncertainty surrounding the approach to diagnosing and managing a sport-related concussion (SRC). Neurobiological recovery may extend beyond clinical recovery following SRC, highlighting the need for objective physiological parameters to guide diagnosis and management. With an increased understanding of the connection between the heart and the brain, the utility of assessing cardiovascular functioning following SRC has gained attention. As such, this review focuses on the assessment of cardiovascular parameters in the context of SRC. Although conflicting results have been reported, decreased heart rate variability, blood pressure variability, and systolic (ejection) time, in addition to increased spontaneous baroreflex sensitivity and magnitude of atrial contraction have been shown in acute SRC. We propose that these findings result from the neurometabolic cascade triggered by a concussion and represent alterations in myocardial calcium handling, autonomic dysfunction, and an exaggerated compensatory response that attempts to maintain homeostasis following a SRC. Assessment of the cardiovascular system has the potential to assist in diagnosing and managing SRC, contributing to a more comprehensive and multimodal assessment strategy.

Expanding capabilities to evaluate readiness for return to duty after mTBI: The CAMP study protocol

Physical Therapists affiliated with Intrepid Spirit Centers evaluate and treat Active Duty Service Members (ADSM) who have duty-limiting post-concussion symptoms to improve the ability to perform challenging tasks associated with military service. The Complex Assessment of Military Performance (CAMP) is a test battery that more closely approximates the occupational demands of ADSM without specific adherence to a particular branch of service or military occupational specialty. Subtasks were developed with military collaborators to include high level skills that all service members must be able to perform such as reacting quickly, maintaining visual stability while moving and changing positions, and scanning for, noting, and/or remembering operationally relevant information under conditions of physical exertion.

OBJECTIVE

The purpose of this observational longitudinal study is to: 1- establish typical performance parameters for ADSM on the CAMP test battery 2- determine the element of the CAMP battery that demonstrate the greatest differences from standard performance and serve as predictors for successful return to duty and 3- develop clinician-facing feedback algorithms and displays and 4-develop materials for clinical dissemination. This ongoing multi-site study is currently funded through the CDMRP and has been approved by the Naval Medical Center Portsmouth IRB.

METHODS

ADSM undergoing post-concussion rehabilitation at the Intrepid Spirit Centers will be tested within one week of their initial Physical Therapy evaluation and after completing Physical Therapy. Control participants will include males, females, and ADSM from the Special Operations community. Participants will complete an intake form that includes questions about demographics, military service, deployment and concussion history, and profile and duty status. Other measures include those that explore concussion symptoms, sleep quality, post-traumatic stress, and perceptions of resilience. The CAMP includes three separate 10-15 minute tasks. Movement is recorded by wearable inertial sensors and heart rate variability is recorded with a POLAR10 monitor. The "Run-Roll" task requires rapid position changes, combat rolls and quick running forwards and backwards while carrying a simulated weapon. Visual stability before and after the task is also performed. The "Dual-Task Agility" task includes rapid running with and without a weighted vest and a working memory task. The "Patrol Exertion" task requires repeated stepping onto an exercise step while watching a virtual patrol video. Additional tasks include monitoring direction of travel, observing for signs of enemy presence, and reacting to multiple auditory signals embedded in the video.

DISCUSSION

Measures that evaluate relevant skills are vital to support safe return to duty for ADSM who may be exposed to imminent danger as part of training or mission demands. The CAMP is designed to be an ecologically valid and clinically feasible assessment that may be more sensitive to capturing subtle impairments that impact duty performance as test skills are integrated into dual and multi-tasks that reflect occupational demands. Assessment results may serve as a more robust indicator of readiness for full return to duty after concussion.

History of concussion and lowered heart rate variability at rest beyond symptom recovery: a systematic review and meta-analysis

Introduction

Concussion is a growing concern in worldwide sporting culture. Heart rate variability (HRV) is closely tied with autonomic nervous system (ANS) deficits that arise from a concussion. The objective of this review was to determine if a history of concussion (HOC) can impact HRV values in the time-domain in individuals at rest. This review works to add to the literature surrounding HRV testing and if it can be used to check for brain vulnerabilities beyond the recovery of concussion symptoms.

Materials and methods

The systematic review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) method. A computer based systematic review scanned articles dating from 1996 to June 2023 through PubMed, Cochrane Library, Google Scholar, and EMBASE databases. A risk of bias assessment was conducted using the ROBINS-E tool. The average difference in time between heartbeats (MeanNN), the standard deviation of the differences (SDNN), and the root mean squared of the successive intervals (RMSSD) were measured.

Results

Six total studies were found that fit the inclusion criteria including a total of 242 participants (133 without HOC, 109 with HOC). The average age of the control group was 23.3 ± 8.2, while the average age of the history of TBI group was 25.4 ± 9.7, with no significant difference between the groups (p = 0.202). Four of the studies reported no significant difference in any of the three measures, while two of the studies reported significant difference for all three measures. The meta-analysis was conducted and found that MeanNN (p = 0.03) and RMSSD (p = 0.04) reached statistical significance, while SDNN did not (p = 0.11).

Conclusion

The results of this meta-analysis showed significant difference in two of the three HRV time-domain parameters evaluated. It demonstrates that there can be lowered HRV values that expand beyond the recovery of symptoms, reflecting an extensive period of ANS susceptibility after a concussion. This may be an important variable in determining an athlete's return to play (RTP). Lack of homogenous study populations and testing methods introduces potential for bias and confounding factors, such as gender or age. Future studies should focus on baseline tests to compare individuals to themselves rather than matched controls.

Differences in time-frequency characteristics between healthy controls and TBI patients during hypercapnia assessed via fNIRS

Damage to the cerebrovascular network is a universal feature of traumatic brain injury (TBI). This damage is present during different phases of the injury and can be non-invasively assessed using functional near infrared spectroscopy (fNIRS). fNIRS signals are influenced by partial arterial carbon dioxide (PaCO2), neurogenic, Mayer waves, respiratory and cardiac oscillations, whose characteristics vary in time and frequency and may differ in the presence of TBI. Therefore, this study aims to investigate differences in time-frequency characteristics of these fNIRS signal components between healthy controls and TBI patients and characterize the changes in their characteristics across phases of the injury. Data from 11 healthy controls and 21 TBI patients were collected during the hypercapnic protocol. Results demonstrated significant differences in low-frequency oscillations between healthy controls and TBI patients, with the largest differences observed in Mayer wave band (0.06 to 0.15 Hz), followed by the PaCO2 band (0.012 to 0.02 Hz). The effects within these bands were opposite, with (i) Mayer wave activity being lower in TBI patients during acute phase of the injury (d = 0.37 [0.16, 0.57]) and decreasing further during subacute (d = 0.66 [0.44, 0.87]) and postacute (d = 0.75 [0.50, 0.99]) phases; (ii) PaCO2 activity being lower in TBI patients only during acute phase of the injury (d = 0.36 [0.15, 0.56]) and stabilizing to healthy levels by the subacute phase. These findings demonstrate that TBI patients have impairments in low frequency oscillations related to different mechanisms and that these impairments evolve differently over the course of injury.

Heart rate variability behavior in athletes after a sports concussion: A systematic review

OBJECTIVE

This systematic review aims to investigate the adaptations of the autonomic nervous system (ANS) after a concussion by measuring HRV in athletes over the age of 16 after injury.

METHODS

This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Web of Science, Pubmed, SCOPUS, and Sport Discus were searched using predefined search terms to identify relevant original cross-sectional, longitudinal, and cohort epidemiological studies published before December 2021.

RESULTS

After screening 1737 potential articles, four studies met the inclusion criteria. Studies included participants with concussion (n = 63) and healthy control athletes (n = 140) who practised different sports. Two studies describe a decrease in HRV following a sports concussion, and one proposed that the resolution of symptoms does not necessarily reflect ANS recovery. Lastly, one study concluded that submaximal exercise induces alteration in ANS, not seen in rest after an injury.

CONCLUSIONS

In the frequency domain, a decrease in high frequency power and an increase of low frequency/high frequency ratio is expected, as the activity of the sympathetic nervous system increases, and the parasympathetic nervous system decreases after injury. In the frequency domain, heart rate variability (HRV) may help monitor the activity of ANS evaluating signals of somatic tissue distress and early identification of other types of musculoskeletal injuries. Further research should investigate the relationship between HRV and other musculoskeletal injuries.

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.

Autonomic dysfunction and exercise intolerance in concussion: a scoping review

PURPOSE

Concussion commonly results in exercise intolerance, often limiting return to activities. Improved understanding of the underlying mechanisms of post-concussive exercise intolerance could help guide mechanism-directed rehabilitation approaches. Signs of altered cardiovascular autonomic regulation-a potential contributor to exercise intolerance-have been reported following concussion, although it is not clear how these findings inform underlying mechanisms of post-concussive symptoms. Systematic summarization and synthesis of prior work is needed to best understand current evidence, allowing identification of common themes and gaps requiring further study. The purpose of this review was to (1) summarize published data linking exercise intolerance to autonomic dysfunction, and (2) summarize key findings, highlighting opportunities for future investigation.

METHODS

The protocol was developed a priori, and conducted in five stages; results were collated, summarized, and reported according to PRISMA guidelines. Studies including injuries classified as mild traumatic brain injury (mTBI)/concussion, regardless of mechanism of injury, were included. Studies were required to include both autonomic and exercise intolerance testing. Exclusion criteria included confounding central or peripheral nervous system dysfunction beyond those stemming from the concussion, animal model studies, and case reports.

RESULTS

A total of 3116 publications were screened; 17 were included in the final review.

CONCLUSION

There was wide variability in approach to autonomic/exercise tolerance testing, as well as inclusion criteria/testing timelines, which limited comparisons across studies. The reviewed studies support current clinical suspicion of autonomic dysfunction as an important component of exercise intolerance. However, the specific mechanisms of impairment and relationship to symptoms and recovery require additional investigation.

Changes in the cardiac autonomic control system during rehabilitation in children after severe traumatic brain injury

BACKGROUND

One of the sequalae of severe traumatic brain injury (TBI) in children is impaired function of the cardiac autonomic control system (CACS) at rest. The CACS response to conventional autonomic tests is little known.

OBJECTIVE

To examine the CACS response to conventional autonomic tests in children after severe TBI during the rehabilitation period and to compare with typically developing (TD) children.

METHODS

This study combined a case-control and follow-up design. The severe TBI group (cases) consisted of 33 children aged 9-18 years, 14-142 days after severe TBI who were followed for 8 weeks during rehabilitation. The control group consisted of 19 TD children matched for age and sex. Heart rate (HR) and heart rate variability (HRV) were evaluated with the Polar RS800CX device at rest (sitting), during a handgrip test and during a paced breathing test.

RESULTS

At the first assessment, we found lower HRV values at rest and a lower HRV response during the paced breathing and handgrip tests in the TBI group than the TD group (p<0.01). After 8 weeks, HRV values did not change at rest in the TBI group, but the response to the autonomic tests improved significantly, with increased HRV values in response to the paced breathing test (p<0.01) and the handgrip test (p = 0.01).

CONCLUSIONS

After severe TBI, children exhibited an impaired CACS response to autonomic tests, with parasympathetic suppression and sympathetic arousal. After 8 weeks of rehabilitation, CACS function recovered partially and the response to the autonomic tests improved with no change in CACS function at rest.

Repetitive bout of controlled soccer heading does not alter heart rate variability metrics: A preliminary investigation

Objectives

There is elevated unease regarding how repetitive head impacts, such as those associated with soccer heading, contribute to alterations in brain function. This study examined the extent heart rate variability (HRV) and cardiac baroreceptor sensitivity (BRS) metrics are altered immediately following an acute bout of soccer heading.

Methods

Seven male elite soccer players (24.1 ± 1.5 years) completed 40 successful soccer headers in 20-min. The headers were performed under controlled circumstances using a soccer ball launcher located 25 meters away and using an initial ball velocity of 77.5 ± 3.7 km/h (heading condition). An accelerometer (xPatch) on the right mastoid process quantified linear/rotational head accelerations. Participants also completed sham (body contact) and control (non-contact) sessions. A three-lead ECG and finger photoplethysmography characterized short-term spontaneous HRV/cardiac BRS, before and after each condition. The SCAT3 indexed symptom scores pre-post exposures to all three conditions.

Results

During the heading condition, cumulative linear and rotational accelerations experienced were 1,574 ± 97.9 g and 313,761 ± 23,966 rad/s², respectively. Heart rate trended toward an increase from pre- to post-heading (p = 0.063), however HRV metrics in the time-domain (ps > 0.260) and frequency-domain (ps > 0.327) as well as cardiac BRS (ps > 0.144) were not significantly changed following all three conditions. Following the heading condition, SCAT3 symptom severity increased (p = 0.030) with a trend for symptom score augmentation (p = 0.078) compared to control and sham.

Conclusion

Whereas, symptoms as measured by the SCAT3 were induced following an acute bout of controlled soccer heading, these preliminary findings indicate they were not accompanied by alterations to autonomic function. Ultimately, this demonstrates further research is needed to understand the physiological underpinnings of alterations in brain function occurring immediately after a bout of soccer heading and how these may, over time, contribute to long-term neurological impairments.

Mild simulator sickness can alter heart rate variability, mental workload, and learning outcomes in a 360° virtual reality application for medical education: a post hoc analysis of a randomized controlled trial

Virtual reality (VR) applications could be beneficial for education, training, and treatment. However, VR may induce symptoms of simulator sickness (SS) such as difficulty focusing, difficulty concentrating, or dizziness that could impair autonomic nervous system function, affect mental workload, and worsen interventional outcomes. In the original randomized controlled trial, which explored the effectiveness of using a 360° VR video versus a two-dimensional VR video to learn history taking and physical examination skills, only the former group participants had SS. Therefore, 28 undergraduate medical students who participated in a 360° VR learning module were included in this post hoc study using a repeated measures design. Data of the Simulator Sickness Questionnaire (SSQ), heart rate variability (HRV) analysis, Task Load Index, and Mini-Clinical Evaluation Exercise were retrospectively reviewed and statistically analyzed. Ten (36%) participants had mild SS (total score > 0 and ≤ 20), and 18 (64%) had no SS symptom. Total SSQ score was positively related to the very low frequency (VLF) band power, physical demand subscale, and frustration subscale, and inversely related to physical examination score. Using multilevel modeling, the VLF power mediated the relationship between total SSQ score and physical examination score. Furthermore, frustration subscale moderated the mediating effects of the VLF power. Our results highlight the importance of documenting SS to evaluate a 360° VR training program. Furthermore, the combination of HRV analysis with mental workload measurement and outcome assessments provided the important clinical value in evaluating the effects of SS in VR applications in medical education.

The Cardiac Autonomic Response Recovery to the Modified Tilt Test in Children Post Moderate-Severe Traumatic Brain Injury

OBJECTIVE

To assess the recovery of the cardiac autonomic control system (CACS) response to the modified tilt-test during rehabilitation, in children post moderate-severe TBI at the subacute phase post-injury.

METHOD

Thirty-seven children aged 6-18 years, 14-162 days post moderate-severe TBI, participated in the study. The assessment included CACS values evaluation (heart rate (HR), heart rate variability (HRV) and blood pressure) during the modified tilt-test: five minutes lying supine and five minutes passive standing. Re-assessment was performed after eight weeks of rehabilitation.

RESULTS

In both assessments, only four children reported symptoms associated with orthostatic intolerance during the modified tilt-test. No change was found over time in the HR and HRV values at rest. In response to the modified tilt-test, the systolic blood pressure showed change over time, with a significant interaction effect (p=0.04); while in the first assessment the SBP values showed a hypertension trend in the second assessment the SBP values showed a hypotension trend.

CONCLUSIONS

Children post moderate-severe TBI at the sub-acute phase post-injury, have a better systolic blood pressure response during the modified tilt-test after eight weeks of individually tailored rehabilitation program, despite no change in the CACS values at rest.

CLINICAL TRIAL GOV. NUMBER

NCT03215082.

Concussion History and Heart Rate Variability During Bouts of Acute Stress

CONTEXT

After a sport-related concussion, many athletes experience persisting neurophysiological alterations. These alterations may be absent at rest but emerge during moments of physiological stress. Unnoticed and untreated neurophysiological dysfunction may negatively affect long-term neurologic health in adolescent athletes, as they are at a critical point in development.

OBJECTIVE

To assess cardio-autonomic functioning in athletes with and those without a history of concussion by quantifying measures of heart rate variability (HRV) during times of physical and mental exertion.

DESIGN

Case-control study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Thirty-four male Hockey Quebec Midget-AAA hockey players were separated into those with (n = 16; age = 16.06 ± 0.73 years, body mass index = 23.29 ± 1.79) and those without (n = 18; age = 15.98 ± 0.62 years, body mass index = 23.60 ± 2.49) a history of concussion.

INTERVENTION(S)

All athletes underwent a series of HRV recording sessions (1) at rest, (2) while completing a cognitive task at rest, and (3) while completing a cognitive task after a bout of submaximal aerobic exercise.

MAIN OUTCOME MEASURE(S)

Time-domain measures of HRV, including mean NN intervals, SD of NN intervals, and root mean square of successive NN interval differences, were quantified for each assessment.

RESULTS

No differences in characteristics were evident between groups. No between-groups differences in HRV at rest were observed. However, during the cognitive task at rest and after aerobic exercise, athletes with a history of concussion demonstrated a higher SD of NN intervals (78.1 ± 4.3 versus 63.2 ± 4.1 milliseconds and 71.2 ± 4.3 versus 65.2 ± 3.8 milliseconds, respectively; F1,31 = 4.31, P = .046) and root mean square of successive NN interval differences (75.8 ± 6.0 versus 59.0 ± 5.6 milliseconds and 74.0 ± 5.5 versus 59.0 ± 5.2 milliseconds, respectively; F1,31 = 4.88, P = .04) than athletes without a history of concussion.

CONCLUSIONS

Concussive injuries may result in long-term cardio-autonomic dysfunction. These deficits may not be present at rest but may be triggered by physiological stress.

Heart Rate Variability as a Reliable Biomarker Following Concussion: A Critically Appraised Topic

CLINICAL SCENARIO

Recent systematic reviews show conflicting information regarding the effect of concussion on cardiac autonomic function. Controlled aerobic exercise is the most popular intervention for those recovering from a concussion. There is a gap in the literature supporting the utility of objective metrics during exertional return to play protocols and rehabilitation.

CLINICAL QUESTION

Can heart rate variability (HRV) during physical exertion be a reliable biomarker over time for those who suffered a sport-related concussion?

SUMMARY OF KEY FINDINGS

A literature search produced 3 studies relevant to the clinical question. One, a prospective-matched control group cohort study, reported disturbances in HRV during physical exertion in those with a history of concussion, and identified persistent HRV dysfunction after resolution of subjective complaints, return to play, and with multiple concussive events. Second, a cross-sectional cohort study found an HRV difference in those with and without a history of concussion and in HRV related to age and sex. Finally, the prospective longitudinal case-control cohort study did not find sex or age differences in HRV and concluded that, although postconcussion HRV improved as time passed, resting HRV was not as clinically meaningful as HRV during exertional activities.

CLINICAL BOTTOM LINE

There is emerging evidence to support the use of HRV as an observable biomarker, over time, of autonomic function during physical exertion following a sport-related concussion. However, the meaningfulness of HRV data is not fully understood and the utility seems individualized to the level of athlete, age, and sex and, therefore, cannot be generalizable. In order to be more clinically meaningful and to assist with current clinical decision making regarding RTP, a preinjury baseline assessment would be beneficial as an individualized reference for baseline comparison.

STRENGTH OF RECOMMENDATION

Although HRV is not fully understood, currently, there is grade B evidence to support the use of individualized baseline exertional HRV data as comparative objective metric to assess the autonomic nervous system function, over time, following a concussive event.

Autonomic dysfunction in adults following mild traumatic brain injury: A systematic review

BACKGROUND

Increasing evidence suggests autonomic nervous system (ANS) dysfunction may occur following mild traumatic brain injury (mTBI). Measures of heart rate, heart rate variability, blood pressure and baroreceptor sensitivity can be used to evaluate ANS dysfunction following mTBI.

OBJECTIVE

Summarize the evidence for ANS dysfunction in adults following mTBI.

METHODS

A search of Embase, MEDLINE, Cochrane Central Register, PsycINFO, CINAHL and SPORTDiscus databases was conducted. Search topics included: mTBI and ANS. Identified abstracts were independently reviewed by 2 reviewers followed by full text screening. Risk of bias was assessed using a modified SIGN checklist. A structured synthesis was performed.

RESULTS

Thirty-nine studies (combined 1,467 participants diagnosed with mTBI) evaluating ANS function were included. ANS function was evaluated under various conditions including: rest, during exertion, cold pressor test, Valsalva maneuver, using face cooling and eyeball pressure paradigms. Short-term or ultra-short-term recordings were most common. The majority of studies (28/39) were rated as "unacceptable" for quality of evidence.

CONCLUSIONS

Altered parameters of ANS function have been reported in multiple conditions following mTBI, both acutely and in the post-acute/chronic stages of recovery. However, due to methodological limitations, conclusions regarding the severity and timing of ANS dysfunction following mTBI cannot be drawn.

Autonomic cardiovascular response during and after a graded exercise test in concussed athletes and healthy controls

Objective

Dysfunction of the autonomic cardiovascular system after a concussion is known to cause exercise intolerance due to symptoms exacerbation. The aim of this study was to compare athletes with symptoms of a sport-related concussion and healthy controls with regard to their heart rate during a graded exercise test and their heart rate recovery during the 5 min cool-down after the graded exercise test.

Methods

Sport-related concussion patients ( N = 61; 31% female) and controls ( N = 16; 50% female) participated in a graded exercise test on a cycle ergometer followed by 5 min active cool-down. Based on the results of graded exercise tests they were divided into four groups: (1) patients who reached the symptom threshold and had to stop the graded exercise test (symptom threshold; N = 39; 33.3% female), (2) patients with symptoms who finished the graded exercise test (S; N = 16; 25% female), (3) patients without symptoms (NS; N = 6; 33.3% female), (4) controls ( N = 16; 50% female).

Main outcome measures

Heart rate, severity of headache and dizziness during graded exercise test, heart rate recovery (median (heart rate recoveries/maximal heart rate) ± median absolute deviation (MAD)) 30, 60 and 300 s after the start of cool-down.

Results

Heart rate recovery at 30 s was significantly slower in symptom (0.95 ± 0.01) compared to all other groups ( p < 0.002; symptom threshold: 0.92 ± 0.02, NS: 0.91 ± 0.02, controls: 0.93 ± 0.02). Heart rate recovery at 60 s was significantly slower in symptom (0.90 ± 0.02) compared to the symptom threshold and controls ( p < 0.041; 0.86 ± 0.03, 0.85 ± 0.04). Heart rate recovery at 300 s was significantly slower in symptom threshold (0.72 ± 0.05) compared to controls ( p = 0.003; 0.66 ± 0.02).

Conclusions

Heart rate measurements in athletes with symptoms of sport-related concussion should be continued during cool-down after the graded exercise test, as dysfunction of the autonomic cardiovascular system might manifest also during cool-down.

Use of Mayer wave activity to demonstrate aberrant cardiovascular autonomic control following sports concussion injury

Dysregulation of cardiovascular autonomic control is gaining recognition as a prevailing consequence of concussion injury. Characterizing the presence of autonomic dysfunction in concussed persons is inconsistent and conventional metrics of autonomic function cannot differentiate the presence/absence of injury. Mayer wave (MW) activity originates through baroreflex adjustments to blood pressure (BP) oscillations that appear in the low‐frequency (LF: 0.04–0.15 Hz) band of the BP and heart rate (HR) power spectrum after a fast Fourier transform. We prospectively explored MW activity (∼0.1 Hz) in 19 concussed and 19 noninjured athletes for 5 min while seated at rest within 48 h and 1 week of injury. MW activity was derived from the LF band of continuous digital electrocardiogram and beat‐to‐beat BP signals (LFHR, LF‐SBP, MWHR, and MW‐SBP, respectively); a proportion between MWBP and MWHR was computed (cMW). At 48 h, the concussion group had a significantly lower MWBP and cMW than controls; these differences were gone by 1 week. MWHR, LFHR, and LF‐SBP were not different between groups at either visit. Attenuated sympathetic vasomotor tone was present and the central autonomic mechanisms regulating MW activity to the heart and peripheral vasculature became transiently discordant early after concussion with apparent resolution by 1 week.

Unclear outcomes of heart rate variability following a concussion: a systematic review

PURPOSE

: To systematically regroup articles that were published since the latest systematic search, but with specific inclusion criteria to help comparison that will offer a focused presentation of methods and results. This will offer a full overview of HRV's behavior at rest and during exercise in adults post-concussion.

METHODS

: The systematic review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) method. A computer-based systematic search was conducted in December 2019 through the Pubmed, Scopus and SPORTDiscus databases. A manual search was performed through the reference list of all articles retained. The reliability of the systematic search was assured by having the article selection process entirely repeated by a second author.

RESULTS

: The systematic search yielded a total of 15 articles to be further analyzed. Results show impairment of HRV during exercise for individuals with concussion, heterogenous studies with lack of control over confounding factors and only less than half of the results showing a significant difference between individuals with concussion and controls.

CONCLUSION

: Further research should try standardizing HRV measurement protocols that control confounding factors to allow easier comparison between studies and allows the possibility for an eventual meta-analysis.

The timeframe for safe resumption of high-level mobility following traumatic brain injury is currently unknown: a systematic review

PURPOSE

To examine the safety of high-level mobility (HLM) prescription in the early sub-acute phase of recovery following moderate-to-extremely severe traumatic brain injury (TBI) with specific focus on provocation of concussion-like symptoms.

DESIGN

Systematic review. PROSPERO ID: CRD42017069369.

MAIN MEASURES

Extracted data included study design, brain injury severity, time to commence HLM, type of HLM, physiological and symptom monitoring, and rate of adverse events.

RESULTS

Nineteen studies were included in the review. Fifteen studies included participants who commenced HLM within 6 weeks of injury, with the earliest time to commencement being 3 days. Overall, adverse events and symptom monitoring were poorly reported. A total of six adverse events were reported across three studies. One of the six adverse events was a concussion-like symptom. No falls were reported. No studies monitored concussion-like symptom provocation in direct relation to HLM.

CONCLUSION

A safe timeframe for return to HLM after moderate-to-extremely severe TBI could not be determined due to insufficient reporting of symptom monitoring and adverse events. Further research into the safety of HLM in the early sub-acute rehabilitative stage after moderate-to-extremely severe TBI is required in order to better understand potential sequelae in this population.IMPLICATIONS FOR REHABILITATIONHigh-level mobility assessment and training is commonly reported in the early sub-acute phase of recovery following moderate-to-extremely severe traumatic brain injury.There is no consensus on a safe timeframe to commence high-level mobility assessment or training after moderate-to-extremely severe traumatic brain injury.High-level mobility assessment and training appears to be safe in the early sub-acute phase following moderate-to-extremely severe traumatic brain injury, however, adverse events and symptoms are poorly reported.Clinicians should continue to proceed with caution when assessing and prescribing high-level mobility for patients with moderate-to-extremely severe traumatic brain injury in the early sub-acute phase of recovery and monitor for risks such as falls and exacerbation of concussion-like symptoms.

Does Vestibular-Ocular-Motor (VOM) Impairment Affect Time to Return to Play, Symptom Severity, Neurocognition and Academic Ability in Student-Athletes following acute Concussion?

Introduction: Research indicates Sports-Related Concussion (SRC) impairs Vestibular-Ocular-Motor (VOM) function. The aim was to explore if VOM impairment correlates with longer Return To Play (RTP), symptom burden, neurocognitive performance and academic capability.Participants: 40 (61.4% male) Loughborough University, UK, rugby union student-athletes who sustained 42 SRCs.Methods: Student-athletes completed an assessment battery during pre-season (baseline), 2, 4, 8 and 14 days post-SRC and prior to RTP and were managed according to the rugby Football Union' community pathway.Outcome measures: Vestibular Ocular-Motor Screening (VOMS), Immediate Post-Concussion Assessment and Cognitive Test, Post-Concussion Symptom Scale, Perceived Academic Impairment Tool questionnaire and percentage of academic activities specifically missed due to SRC.Results: VOMS scores were significantly (p < 0.005) greater than baseline at all time points except RTP. Presence of VOM dysfunction at 14 days post-SRC significantly correlated with a longer RTP, greater symptom burden and increased odds ratio at 2, 4 and 8 days and academic time loss at 2, 4 and 8 days post-SRC.Conclusion: VOM impairment is associated with an increased symptom burden and impaired academic capability, and a longer time to RTP when present at 14 days post-SRC.

A pilot study on exertional tasks with physiological measures designed for the assessment of military concussion

Background:

Guidelines for clinicians treating military concussion recommend exertional testing before return-to-duty, yet there is currently no standardized task or inclusion of an objective physiological measure like heart rate variability (HRV).

Methodology & results:

We pilot-tested two clinically feasible exertional tasks that include HRV measures and examined reliability of a commercially available heart rate monitor. Testing healthy participants confirmed that the 6-min step test and 2-min pushup test evoked the targeted physiological response, and the Polar H10 was reliable to the gold-standard electrocardiogram.

Conclusion:

Both tasks are brief assessments that can be implemented into primary care setting including the Polar H10 as an affordable way to access HRV. Additional research utilizing these tasks to evaluate concussion recovery can validate standardized exertional tasks for clinical use.

Predicting Heart Rate Variability Parameters in Healthy Korean Adults: A Preliminary Study

The purpose of the study was to examine the development of a multiple linear regression model to estimate heart rate variability (HRV) parameters using easy-to-measure independent variables in preliminary experiments. HRV parameters (time domain: SDNN, RMSSD, NN50, pNN50; frequency domain: TP, VLF, LF, HF) and the independent variables (e.g., sex, age, body height, body weight, BMI, HR, HR_max, HRR) were measured in 75 healthy adults (male n = 27, female n = 48) for estimating HRV. The HRV estimation multiple linear regression model was developed using the backward elimination technique. The regression model’s coefficient of determination for the time domain variables was significantly high (SDNN = R²: 72.2%, adjusted R²: 69.8%, P < .001; RMSSD = R²: 93.1%, adjusted R²: 92.1%, P < .001; NN50 = R²: 78.0%, adjusted R²: 74.9%, P < .001; pNN50 = R²: 89.1%, adjusted R²: 87.4%, P < .001). The coefficient of determination of the regression model for the frequency domain variable was moderate (TP = R²: 75.6%, adjusted R²: 72.6%, P < .001; VLF = R²: 41.6%, adjusted R²: 40.3%, P < .001; LF = R²: 54.6%, adjusted R²: 49.2%, P < .001; HF = R²: 67.5%, adjusted R²: 63.4%, P < .001). The coefficient of determination of time domain variables in the developed multiple regression models was shown to be very high (adjusted R²: 69.8%–92.1%, P < .001), but the coefficient of determination of frequency domain variables was moderate (adjusted R²: 40.3%–72.6%, P < .001). In addition to the equipment used for measuring HRV in clinical trials, this study confirmed that simple physiological variables could predict HRV.

Change in Heart Rate Variability after Concussion in a Collegiate Soccer Player

Athletes are known to under-report concussion symptoms due to competitive disincentives to report and conflation of concussion symptoms with other conditions associated with rigorous participation in sports. A quantitative biomarker for concussion has the potential to decrease the reliance on inconsistent patient-reported symptoms for the diagnosis of concussion. The objective of this project was to monitor heart rate variability (HRV) patterns of in-season athletes as a potential biomarker for concussion.

Twenty in-season National Collegiate Athletic Association (NCAA) Division 2 collegiate soccer players were given a wristband heart rate sensor with instructions to wear the band full time (24/7) for the entire fall season (approximately 3 months). The athletes were prompted by email to complete a weekly survey on the severity and frequency of any concussion symptoms. The survey and HRV data were de-identified for confidentiality, and to increase the likelihood of accurate reporting the athletes were told their responses would not be used to disqualify them from athletics. Our hypothesis was that HRV would be diminished in those with recent concussion.

One athlete (5% of the cohort) sustained a concussion during the study period. A marked decrease in HRV was identified 7 days following the concussion, which eventually returned to baseline. This normalization of HRV followed the timing of resolution of concussion symptoms. Participants who did not sustain a concussion exhibited minimal variance in HRV over time.

This preliminary study shows that HRV has potential as a biomarker for symptom resolution after clinically apparent concussion. HRV is unlikely to serve as a concussion diagnostic due to the 7-day lag in HRV change after concussion.

Causal Link between Ventricular Ectopy and Concussion

We present a unique case study report of a male individual with a history of mild nonischaemic cardiomyopathy, with no ventricular ectopy, that at the age of 76 years sustained multiple concussions (i.e., mild traumatic brain injury) within a week of each other. Concussion symptoms included cognitive difficulties, "not feeling well," lethargy, fatigue, and signs of depression. He was later medically diagnosed with postconcussion syndrome. The patient, WJT, was referred for cardiac and neurological assessment. Structural neuroimaging of the brain (MRI) was unremarkable, but electrocardiography (ECG) assessments using a 24-hour Holter monitor revealed significant incidence of ventricular ectopy (9.4%; 9,350/99,836 beats) over a period of 5-6 months after injury and then a further increase in ventricular ectopy to 18% (15,968/88,189 beats) during the subsequent 3 months. The patient was then prescribed Amiodarone 200 mg, and his ventricular ectopy and concussion symptoms completely resolved simultaneously within days. To the authors' knowledge, our study is the first to show a direct link between observable and documented cardiac dysregulation and concussion symptomology. Our study has important implications for both cardiac patients and the patients that sustain a concussion, and if medically managed with appropriate pharmacological intervention, it can reverse ventricular ectopy and concussion symptomology. More research is warranted to investigate the mechanisms for this dramatic and remarkable change in cardiac and cerebral functions and to further explore the brain-heart interaction and the intricate autonomic interaction that exists between the extrinsic and intracardiac nervous systems.

Feasibility of Mild Traumatic Brain Injury Assessment Based on Cardiovascular Response to Postural Change

OBJECTIVE

To determine the feasibility of short-term cardiovascular responses to postural change as a screening tool for mild traumatic brain injury (mTBI), using heart rate metrics that can be measured with a wearable electrocardiogram sensor.

SETTING

Military TBI clinic.

DESIGN

Data collected from active-duty service members who had sustained a medically diagnosed mTBI within the prior 72 hours and from age- and sex-matched controls. Cardiac data collected while participants performed a sequence of postural changes.

MAIN MEASURES

Model classification compared with clinical mTBI diagnosis.

RESULTS

Cardiac biomarkers of mTBI were identified and logistic regression classifiers for mTBI were developed from different subsets of biomarkers. The best model achieved 90% sensitivity and 69% specificity using data from 2 different postural changes.

CONCLUSION

Noninvasive measurement of cardiovascular response to postural change is a promising approach for field-deployable post-mTBI screening.

Physical Therapy Evaluation and Treatment After Concussion/Mild Traumatic Brain Injury

Over the last decade, numerous concussion evidence-based clinical practice guidelines (CPGs), consensus statements, and clinical guidance documents have been published. These documents have typically focused on the diagnosis of concussion and medical management of individuals post concussion, but provide little specific guidance for physical therapy management of concussion and its associated impairments. Further, many of these guidance documents have targeted specific populations in specific care contexts. The primary purpose of this CPG is to provide a set of evidence-based recommendations for physical therapist management of the wide spectrum of patients who have experienced a concussive event. J Orthop Sports Phys Ther 2020;50(4):CPG1-CPG73. doi:10.2519/jospt.2020.0301.

Attenuation of Spontaneous Baroreceptor Sensitivity after Concussion

INTRODUCTION

Cardiovascular autonomic nervous system (CV-ANS) function is negatively impacted after concussion. The arterial baroreflex buffers pressor and depressor challenges through efferent modulation of cardiac chronotropism and inotropism, and peripheral vascular tone. Baroreceptor sensitivity (BRS) reflects the capacity of the CV-ANS to accommodate dynamic metabolic demands in the periphery. The impact of concussion on BRS has yet to be defined.

METHODS

Cardiovascular autonomic nervous system assessment (e.g., electrocardiogram and beat-to-beat systolic blood pressure [SBP]) was performed the seated upright position at rest within 48 h (V1) of concussion and 1 wk later (V2) in 10 intercollegiate male athletes with concussion and 10 noninjured male athletes. Changes in HR, SBP, high- and low-frequency HR variabilities (HF-HRV and LF-HRV, respectively), LF-SBP variability and BRS for increasing (BRSn-Up) and decreasing (BRSn-Dn) SBP excursions, and overall BRS (BRSn-Avg) were assessed for differences at V1 and V2.

RESULTS

The concussion (age, 20 ± 1 yr; height, 1.79 ± 0.14 m; weight, 83 ± 10 kg) and control (age, 20 ± 1 yr; height, 1.78 ± 0.10 m; weight, 79 ± 13 kg) groups were matched for demographics. Concussed athletes had a significantly reduced BRSn-Up, BRSn-Dn, and BRSn-Avg compared with controls at V1 or V2; these changes occurred without differences in conventional markers of CV-ANS function (e.g., HF-HRV, LF-HRV, LF-SBP), HR, or SBP at either visit.

CONCLUSIONS

Reduced BRS is a postconcussive consequence of CV-ANS dysfunction during the first postinjury week. Because SBP was similar between groups, it may be speculated that reduced BRS was not afferent in origin, but represents a postinjury consequence of the central nervous system after injury.

Comparison of Rest to Aerobic Exercise and Placebo-like Treatment of Acute Sport-Related Concussion in Male and Female Adolescents

OBJECTIVE

To compare a sample of adolescents with sport-related concussion (SRC) who were prescribed rest with 2 arms of a randomized controlled trial comparing aerobic exercise with placebo-like stretching. We also compared sex differences across the 3 approaches to treatment.

DESIGN

Quasi-experimental trial.

SETTING

University concussion management clinics.

PARTICIPANTS

Adolescent athletes (aged 13-18 years) presenting within 10 days of SRC (mean, 5 days after injury) received a recommendation for rest (rest group [RG], n=48, 15.4±1y, 25% female). Their outcomes were compared with matched samples of adolescents assigned to aerobic exercise (exercise group [EG], n=52, 15.3±2y, 46% female) or placebo-like stretching (placebo group [PG], n=51, 15.4±2y, 47% female) (N=151).

MAIN OUTCOME MEASURES

The primary outcome was median days from injury to recovery. The secondary outcome was proportion classified as normal recovery (<30d) or delayed recovery (≥30d).

RESULTS

The RG recovered in 16 days (interquartile range, 9.25-23.25d), which was significantly delayed (P=.020) compared with EG (13d; interquartile range, 10-18.5d). The PG recovered in 17 days (interquartile range, 13-23d). Four percent of the EG, 14% of the PG, and 13% of the RG had delayed recovery (P=.190). There was no difference in recovery time or delayed recovery between male participants and female participants across groups. Female participants prescribed rest experienced an increase in symptoms vs the other groups (P=.013).

CONCLUSION

Relative rest and a placebo-like stretching program were very similar in days to recovery and symptom improvement pattern after SRC. Both conditions were less effective than subsymptom threshold aerobic exercise. Female adolescents appear to be susceptible to symptom increase when prescribed rest.

Evaluation of Early Submaximal Exercise Tolerance in Adolescents with Symptomatic Sport-related Concussion

PURPOSE

This study aimed to compare cardiorespiratory response to a graded aerobic exercise challenge between adolescents with symptomatic sport-related concussion (SSRC) and healthy control subjects.

METHODS

A quasiexperimental nonrandomized study at a multidisciplinary pediatric concussion program was conducted. Thirty-four adolescents with SSRC (19 males and 15 females) and 40 healthy control subjects (13 males and 27 females) completed the Buffalo Concussion Treadmill Testing (BCTT) until either symptom exacerbation or volitional fatigue. Main outcome measures included heart rate (HR), oxygen consumption (V˙O2), carbon dioxide production (V˙CO2), and minute ventilation (V˙E) at rest and at test termination, and change from rest in variables (ΔHR, ΔV˙O2, ΔV˙CO2, and ΔV˙E) during the first five stages of the BCTT. Main outcomes were analyzed using three-way mixed-model ANOVA, with group status (control vs SSRC) and sex (male vs female) as between-subject factors, and time (BCTT stage) as the within-subject factor.

RESULTS

No group differences in resting HR, systolic and diastolic blood pressure, ΔV˙O2, V˙CO2, and V˙E were observed. During the first five stages of the BCTT, no group differences in ΔV˙O2, V˙CO2, and V˙E were observed; however, SSRC patients demonstrated higher RPE (P < 0.0005) compared with control subjects. No sex-based differences were observed among SSRC patients on measures collected at rest and during early stages of BCTT.

CONCLUSIONS

Although SSRC patients exhibited higher RPE during a graded aerobic exercise challenge, no differences in cardiorespiratory response were observed compared with control subjects exercising at equivalent workloads. Further work is needed to elucidate the physiological mechanisms underlying exercise intolerance after SSRC.

Pediatric Traumatic Brain Injury and Exercise Medicine: A Narrative Review

The multidisciplinary field of pediatric traumatic brain injury (TBI) and exercise medicine is of growing importance. There is active study into the diagnostic and therapeutic potential of exercise in pediatric TBI as well as the effects of TBI on postinjury fitness. With the evidence-based growing, a literature review can help establish the state of the science and inform future research. Therefore, the authors performed a narrative review (based on a search of 6 health sciences databases) to summarize evidence on pediatric TBI and cardiorespiratory fitness, muscular fitness and neuromotor control, and obesity. To date, studies related to cardiorespiratory fitness have centered on exercise tolerance and readiness to return to play, and indicate that protracted rest may not facilitate symptom recovery; this suggests a role for exercise in concussion management. Furthermore, strength and gait may be impaired following pediatric brain injury, and interventions designed to train these impairments may lead to their improvement. Pediatric brain injury can also lead to changes in body composition (which may be related to poorer cognitive recovery), but additional research is required to better understand such associations. This narrative review of pediatric TBI and exercise medicine can serve as a reference for researchers and clinicians alike.

Lifelong consequences of brain injuries during development: From risk to resilience

Traumatic brain injuries in children represent a major public health issue and even relatively mild injuries can have lifelong consequences. However, the outcomes from these injuries are highly heterogeneous, with most individuals recovering fully, but a substantial subset experiencing prolonged or permanent disabilities across a number of domains. Moreover, brain injuries predispose individuals to other kinds of neuropsychiatric and somatic illnesses. Critically, the severity of the injury only partially predicts subsequent outcomes, thus other factors must be involved. In this review, we discuss the psychological, social, neuroendocrine, and autonomic processes that are disrupted following traumatic brain injury during development, and consider the mechanisms the mediate risk or resilience after traumatic brain injury in this vulnerable population.

Activity and Exercise Intolerance After Concussion: Identification and Management of Postural Orthostatic Tachycardia Syndrome

Supplemental Digital Content is Available in the Text.

Background and Purpose:

Postural orthostatic tachycardia syndrome (POTS) is increasingly recognized as a complication affecting recovery from concussion. Individuals with POTS demonstrate refractory dizziness, lightheadedness, cognitive dysfunction, fatigue, headache, chronic pain, nausea and gastrointestinal dysmotility, activity and exercise intolerance, syncope, and tachycardia. Subtypes of POTS may include hypovolemia, hyperadrenergic states, autonomic neuropathy, and underlying autoimmunity, which may variably impact response to rehabilitation in varying ways. The subtle presentation of POTS postconcussion is often mistaken for underlying anxiety, conversion disorder, or lack of motivation for recovery. This article will present clinical features of POTS that may arise after concussion, and propose a role for physical therapists in the diagnosis and management of POTS during concussion recovery.

Summary of Key Points:

Data recorded and entered into a database during clinic visits from a large pediatric institution indicate that 11.4% of individuals diagnosed with POTS report onset of symptoms within 3 months of sustaining a concussion. Activation of the sympathetic nervous system can result in lightheadedness, shortness of breath, chest pain, tachycardia, palpitations on standing or with exertion, and activity and exercise intolerance. Identified comorbidities in people with POTS such as joint hypermobility and autoimmune disorders can further influence recovery.

Recommendations for Clinical Practice:

Physical therapists may identify signs and symptoms of POTS in a subset of individuals who remain refractory to typical interventions and who exhibit symptom exacerbation with orthostatic activity. Incorporation of an individualized POTS exercise program into current established concussion interventions may be useful, with emphasis on initial recumbent exercises and ongoing physical therapy assessment of exercise tolerance for dosing of activity intensity and duration.

Video Abstract available for more insights from the authors (see Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A211).

The Buffalo Concussion Bike Test for Concussion Assessment in Adolescents

BACKGROUND

The Buffalo Concussion Treadmill Test (BCTT) is a graded exertion test for assessing exercise tolerance after concussion, but its utility is limited for certain populations.

HYPOTHESIS

We developed the Buffalo Concussion Bike Test (BCBT) and tested its comparability with the BCTT. We hypothesize that heart rate (HR) at symptom exacerbation on the BCBT will be equivalent to the BCTT.

STUDY DESIGN

Case-control study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Adolescents with acute concussion (AC) (n = 20; mean age, 15.9 ± 1.1 years; 60% male) presenting to a concussion clinic within 10 days of injury and age- and sex-matched healthy controls (n = 20; mean age, 15.9 ± 1.1 years; 60% male) performed the BCTT at first visit and returned within 3 days to perform the BCBT. Test duration, HR, symptom severity (measured using a visual analog scale), and exertion (measured using the Borg Rating of Perceived Exertion) were collected during each test.

RESULTS

Adolescents with AC who were exercise intolerant on the BCTT were also intolerant on the BCBT, with symptom exacerbation occurring at a mean 8.1 ± 2.8 minutes on the BCTT versus 14.6 ± 6.0 minutes on the BCBT (P < 0.01). Two 1-sided t tests showed that the HR at symptom exacerbation in AC patients (137 ± 28 bpm on BCTT vs 135 ± 25 bpm on BCBT; 95% CI, <0.01-0.03) and at voluntary exhaustion for controls (175 ± 13 bpm on BCTT vs 175 ± 13 bpm on BCBT; 95% CI, 0.03-0.03) on each test were statistically equivalent.

CONCLUSION

The HR at symptom exacerbation on BCBT is equivalent to the BCTT for the assessment of exercise tolerance after concussion in adolescents.

CLINICAL RELEVANCE

The BCBT can be used in patients with limited mobility or for research interventions that require limited participant motion.

Quantifying Activity Levels After Sport-Related Concussion Using Actigraph and Mobile (mHealth) Technologies

CONTEXT

Interest in identifying the effects of physical and mental activity on recovery after sport-related concussion is growing. Clinical studies of concussed athletes' activities require well-validated methods for tracking their intensity and timing.

OBJECTIVE

To develop and validate a novel multimodal approach to monitoring activity postconcussion using mobile (mHealth) technologies.

DESIGN

Cohort study.

SETTING

Translational research unit.

PATIENTS OR OTHER PARTICIPANTS

A total of 40 high school and collegiate football players were evaluated at preseason and followed longitudinally after either concussion (n = 25; age = 17.88 ± 1.74 years, height = 182.07 ± 8.08 cm, mass = 98.36 ± 21.70 kg) or selection as a nonconcussed control (n = 15; age = 18.27 ± 1.83 years, height = 180.01 ± 7.19 cm, mass = 93.83 ± 24.56 kg).

MAIN OUTCOME MEASURE(S)

Participants wore a commercial actigraph and completed a daily mobile survey for 2 weeks. Analyses focused on comparisons between groups for actigraph-based physical activity and self-reported physical and mental activity during the follow-up period.

RESULTS

For the first 2 days postinjury, objective measures showed fewer daily steps in concussed (6663 ± 2667 steps) than in control (11 148 ± 3381 steps) athletes (P < .001), and both objective and self-reported measures indicated less moderate to vigorous physical activity in concussed (27.6 ± 32.6 min/d and 25.0 ± 43.6 min/d, respectively) than in control (57.3 ± 38.6 min/d and 67.5 ± 40.1 min/d, respectively) athletes (both P values < .05). Correlations between objective and self-reported measures of moderate to vigorous physical activity were moderate across select 1-week and 2-week averages. We observed no group differences in self-reported mental activities.

CONCLUSIONS

Physical activity after sport-related concussion varied widely across athletes but on average was reduced during the acute and early subacute postinjury periods for both objective and self-reported measures. The lack of differences in mental activities between groups may reflect limited change in mental exertion postconcussion or difficulty accurately measuring mental activities. Assessing concussed athletes' activities using actigraphy and self-reported scales may help monitor their compliance with activity recommendations and be useful in studies aimed at better understanding the effects of physical activity on concussion recovery.

Physical Activity Intolerance and Cardiorespiratory Dysfunction in Patients with Moderate-to-Severe Traumatic Brain Injury

Moderate-to-severe traumatic brain injury (TBI) is a chronic health condition with multi-systemic effects. Survivors face significant long-term functional limitations, including physical activity intolerance and disordered sleep. Persistent cardiorespiratory dysfunction is a potentially modifiable yet often overlooked major contributor to the alarmingly high long-term morbidity and mortality rates in these patients. This narrative review was developed through systematic and non-systematic searches for research relating cardiorespiratory function to moderate-to-severe TBI. The literature reveals patients who have survived moderate-to-severe TBI have ~ 25-35% reduction in maximal aerobic capacity 6-18 months post-injury, resting pulmonary capacity parameters that are reduced 25-40% for weeks to years post-injury, increased sedentary behavior, and elevated risk of cardiorespiratory-related morbidity and mortality. Synthesis of data from other patient populations reveals that cardiorespiratory dysfunction is likely a consequence of ventilator-induced diaphragmatic dysfunction (VIDD), which is not currently addressed in TBI management. Thus, cardiopulmonary exercise testing should be routinely performed in this patient population and those with cardiorespiratory deficits should be further evaluated for diaphragmatic dysfunction. Lack of targeted treatment for underlying cardiorespiratory dysfunction, including VIDD, likely contributes to physical activity intolerance and poor functional outcomes in these patients. Interventional studies have demonstrated that short-term exercise training programs are effective in patients with moderate-to-severe TBI, though improvement is variable. Inspiratory muscle training is beneficial in other patient populations with diaphragmatic dysfunction, and may be valuable for patients with TBI who have been mechanically ventilated. Thus, clinicians with expertise in cardiorespiratory fitness assessment and exercise training interventions should be included in patient management for individuals with moderate-to-severe TBI.

Preliminary Evidence for a Window of Increased Vulnerability to Sustain a Concussion in Females: A Brief Report

A difference exists between sexes for the incidence of concussion injuries and severity of post-injury outcomes with females having a higher incidence rate (in comparable sports) and experience more robust symptoms than males. The basis for this disparity has remained largely unresolved. Recent findings point to a potential biological mechanism that may be related to the menstrual cycle as an arbiter of post-injury outcomes. What has not been addressed, is whether the phase of menstrual cycle (inferred fluctuations of ovarian hormones) contributes to an increased vulnerability to sustain a concussion injury. This prospective, observational study sought to determine if concussions occurred at different frequencies throughout the phase of the menstrual cycle. Female athletes who sustained a concussion injury were queried three times over the 7-day study (e.g., within 48 h of injury, and 4 and 7 days after injury) to recall the number of days that have elapsed since the beginning of their most recent menstruation. Twenty female athletes enrolled after sustaining a concussion; 18 were eumenorrheic and 2 amenorrheic. Among eumenorrheic participants at the time of injury, 2 were in the follicular phase, 4 were in the early luteal phase and 9 were in the late luteal phase. Two athletes were injured on the first and 1 was injured on the second day of menstruation. The greatest number of concussions were sustained during the late luteal phase and during the first 2 days of menstruation. This 9-day window accounted for 2/3rd of the sustained concussions in our study.

Anesthesia for the patient with a recently diagnosed concussion: think about the brain!

Some patients require emergent, urgent, or elective surgery in the time period immediately following diagnosis of concussion. However, changes in brain homeostatic mechanisms following a concussion and concern for secondary brain injury can complicate the decision as to whether or not a surgery should proceed or be postponed. Given the paucity of available evidence, further evaluation of the use of anesthesia in a patient with concussion is warranted. This article summarizes what is currently known about the relevant pathophysiology of concussion, intraoperative anesthesia considerations, and effects of anesthesia on concussion outcomes in an attempt to help providers understand the risks that may accompany surgery and anesthesia in this patient population. While most contraindications to the use of anesthesia in concussed patients are relative, there are nonetheless pathophysiologic changes associated with a concussion that can increase risk of its use. Understanding these changes and anesthetic implications can help providers optimize outcomes in this patient population.

Sensorimotor and Physiological Indicators of Impairment in Mild Traumatic Brain Injury: A Meta-Analysis

OBJECTIVE

To systematically review the literature with meta-analysis to determine whether persistence of sensorimotor or physiological impairment exists between 4 weeks to 6 months post mild traumatic brain injury (mTBI), and assign level of evidence to findings.

METHOD

The databases PubMed, pscyINFO, SPORTdiscus, Medline, CINAHL and Embase were searched from inception to November 2016 using a priori inclusion criteria. Critical appraisal was performed, and an evidence matrix established level of evidence. Meta-analysis of pooled results identified standardized mean difference (SMD) and 95% confidence intervals (95% CI) between mTBI and healthy controls for a variety of physiological and sensorimotor indicators.

RESULTS

Eighteen eligible articles, with a mean quality score of 15.67 (SD = 2.33) were included in the final review. Meta-analysis of center of motion variable; maximal mediolateral center of motion/center of pressure separation distance SMD [95% CI] approached significance at (-0.42 [-0.84, -0.00], I² = 0%) for dual task, level walking indicating a potential reduction in maximal mediolateral excursion during gait in the mTBI group compared to healthy controls. Significantly reduced variability in the standard deviation of heart beat intervals was observed in the mTBI group (-0.51 [-0.74, -0.28], I² = 0%). Overall, significant group differences in 36 sensorimotor and physiological variables (eg, balance, gait velocity and motion analysis outcomes, various oculomotor tasks, as well as heart rate variability frequency domains) were identified.

CONCLUSION

Findings demonstrate that persistence of sensorimotor and physiological changes beyond expected recovery times following subacute mTBI in an adult population is possible. These findings have implications for post-injury assessment and management.

Evidence of a distinct peripheral inflammatory profile in sport-related concussion

Background

Inflammation is considered a hallmark of concussion pathophysiology in experimental models, yet is understudied in human injury. Despite the growing use of blood biomarkers in concussion, inflammatory biomarkers have not been well characterized. Furthermore, it is unclear if the systemic inflammatory response to concussion differs from that of musculoskeletal injury. The purpose of this paper was to characterize systemic inflammation after injury in athletes with sport-related concussion or musculoskeletal injury.

Methods

A prospective, observational cohort study was conducted employing 175 interuniversity athletes (sport-related concussion, n = 43; musculoskeletal injury, n = 30; healthy, n = 102) from 12 sports at a sports medicine clinic at an academic institution.

High-sensitivity immunoassay was used to evaluate 20 inflammatory biomarkers in the peripheral blood of athletes within 7 days of injury (subacute) and at medical clearance. Healthy athletes were sampled prior to the start of their competitive season. Partial least squares regression analyses were used to identify salient biomarker contributions to class separation between injured and healthy athletes, as well as to evaluate the relationship between biomarkers and days to recovery in injured athletes.

Results

In the subacute period after injury, compared to healthy athletes, athletes with sport-related concussion had higher levels of the chemokines’ monocyte chemoattractant protein-4 (p < 0.001) and macrophage inflammatory protein-1β (p = 0.001); athletes with musculoskeletal injury had higher levels of thymus and activation-regulated chemokine (p = 0.001). No significant differences in biomarker profiles were observed at medical clearance. Furthermore, concentrations of monocyte chemoattractant protein-1 (p = 0.007) and monocyte chemoattractant protein-4 (p < 0.001) at the subacute time point were positively correlated with days to recovery in athletes with sport-related concussion, while thymus and activation-regulated chemokine was (p = 0.001) positively correlated with days to recovery in athletes with musculoskeletal injury.

Conclusion

Sport-related concussion is associated with perturbations to systemic inflammatory chemokines that differ from those observed in athletes with a musculoskeletal injury. These results support inflammation as an important facet of secondary injury after sport-related concussion that can be measured systemically in a human model of injury.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1402-y) contains supplementary material, which is available to authorized users.

A Physiological Approach to Assessment and Rehabilitation of Acute Concussion in Collegiate and Professional Athletes

Sport-related concussion is an important condition that can affect collegiate and professional athletes. Expert consensus guidelines currently suggest that all athletes who sustain acute concussion be managed with a conservative approach consisting of relative rest and gradual resumption of school and sport activities with active intervention reserved for those with persistent post-concussion symptoms lasting >10-14 days for adults. Unfortunately, these recommendations place little emphasis on the rapid physical deconditioning that occurs in athletes within days of exercise cessation or the pathophysiological processes responsible for acute concussion symptoms that can be successfully targeted by evidence-based rehabilitation strategies. Based on our evolving approach to patients with persistent post-concussion symptoms, we now present an updated physiological approach to the initial medical assessment, rehabilitation, and multi-disciplinary management of collegiate and professional athletes with acute concussion. Utilizing the results of a careful clinical history, comprehensive physical examination and graded aerobic exercise testing, we outline how team physicians, and athletic training staff can partner with multi-disciplinary experts in traumatic brain injury to develop individually tailored rehabilitation programs that target the main physiological causes of acute concussion symptoms (autonomic nervous system dysfunction/exercise intolerance, vestibulo-ocular dysfunction, and cervical spine dysfunction) while maintaining the athlete's physical fitness during the recovery period. Considerations for multi-disciplinary medical clearance of collegiate and professional athletes as well as the application of this approach to non-elite athletes are also discussed.

Heart rate variability following youth concussion: how do autonomic regulation and concussion symptoms differ over time postinjury?

OBJECTIVES

Following youth concussion, objective physiological indicators are needed to corroborate changes in subjective clinical measures. The objectives of the current study were to: (1) explore the effect of concussion on heart rate variability (HRV) across days postinjury in youth athletes aged 13-18 years old, compared with healthy age-matched and sex-matched controls and (2) examine the relationship between postconcussion symptom domains (physical, cognitive, fatigue and emotional) and HRV.

METHODS

Prospective, longitudinal, case-control study (N=44). This study comprised 29 concussed athletes between the ages of 13 and 18 years old (21 females, 8 males) and 15 age-matched and sex-matched controls). All participants completed baseline testing, which included demographic information (age, sex, concussion history), self-reported concussion symptoms (Post-Concussion Symptom Inventory [PCSI]) and a 24-hour heart rate recording via the Polar RS800CX system. The PCSI and HRV were collected weekly while the participant was symptomatic and then 1, 3 and 6 months following symptom resolution. HRV variables included time and frequency domain measures. Data visualisations and mixed effects modelling were used to derive parsimonious models.

RESULTS

HRV increased across days postinjury. Concussion symptom domains (physical, cognitive, fatigue and emotional) all had a significant main effect on HRV; concussed participants who reported more symptoms had higher HRV compared with those who reported fewer symptoms. Visualisations of HRV depict the recovery trajectory as non-linear across time. No significant differences on HRV measures were found between concussed and control participants.

CONCLUSION

These preliminary findings provide the foundation to understand the varied trajectory and relationship between objective physiological measures and subjective symptom reporting.

High-Intensity Interval Training Is Associated With Alterations in Blood Biomarkers Related to Brain Injury

Purpose: Blood biomarkers are a useful tool to study concussion. However, their interpretation is complicated by a number of potential biological confounds, including exercise. This is particularly relevant in military and athletic settings where injury commonly occurs during physical exertion. The impact of high-intensity interval training (HIIT) on putative brain injury biomarkers remains under-examined. The purpose of this study was to observe the effects of HIIT on a panel of blood biomarkers associated with brain injury.

Methods: Eleven healthy, recreationally active males (median age = 29.0, interquartile range = 26.0–31.5) performed HIIT on a bicycle ergometer (8-12 × 60-s intervals at 100% of peak power output, interspersed by 75-s recovery at 50 W) three times/week for 2 weeks. Peripheral blood samples were collected before and immediately after HIIT during the first and last training sessions. Plasma concentrations of s100 calcium-binding protein beta (S100B), glial fibrillary acidic protein (GFAP), neuron-specific enolase (NSE), brain-derived neurotrophic factor (BDNF), neurogranin (NRGN), peroxiredoxin (PRDX)-6, creatine kinase-BB isoenzyme (CKBB), visinin-like protein (VILIP)-1, von Willebrand factor (vWF), monocyte chemoattractant protein (MCP)-1, matrix metalloproteinase (MMP)-9, and total tau (T-tau) were quantitated by high-sensitivity MULTI-SPOT^® immunoassay, on the MesoScale Diagnostics electrochemiluminescence detection platform. Differences in biomarker concentrations in response to HIIT were evaluated by partial least squares discriminant analysis (PLSDA) within a repeated-measures bootstrapped framework.

Results: Ten of 12 biomarkers were increased pre-to-post HIIT; VILIP-1 remained unchanged, and GFAP was not statistically evaluated due to insufficient detectability. After 2 weeks of HIIT, T-tau was no longer significantly elevated pre-to-post HIIT, and significant attenuation was noted in the acute responses of NRGN, PRDX-6, MMP-9, and vWF. In addition, compared to session 1, session 6 pre-exercise concentrations of NSE and VILIP-1 were significantly lower and higher, respectively.

Conclusion: Blood biomarkers commonly associated with brain injury are significantly elevated in response to a single bout of HIIT. After a 2-week, six-session training protocol, this response was attenuated for some, but not all markers. While biomarkers continue to provide promise to concussion research, future studies are necessary to disentangle the common biological sequelae to both exercise and brain injury.