Autonomic dysfunction syndromes after acute brain injury

Modification of heart rate variability induced by focal muscle vibration in patients with severe acquired brain injury

BACKGROUND/PURPOSE

Heart rate variability (HRV) is a biomarker of autonomic nervous system (ANS) reaction in persons with severe acquired brain injury (sABI) who undergo a rehabilitation treatment, such as focal muscle vibration (FMV).This study aims to evaluate if and how FMV can modulate HRV and to compare potential differences in FMV modulation in HRV between patients with sABI and healthy controls.

METHODS

Ten patients with sABI and seven healthy controls have been recruited. Each individual underwent the same stimulation protocol (four consecutive trains of vibration of 5 minutes each with a 1-minute pause). HRV was analyzed through the ratio of frequency domain heart-rate variability (LF/HF).

RESULTS

In the control group, after performing FMV, a significant LF/HF difference was observed in the in the second vibration session compared to the POST phase. Patients with SABI treated on the affected side showed a statistically significant LF/HF difference in the PRE compared to the first vibration session.

CONCLUSION

These preliminary results suggest that FMV may modify the cardiac ANS activity in patients with sABI.

Nervous System Response to Neurotrauma: A Narrative Review of Cerebrovascular and Cellular Changes After Neurotrauma

Neurotrauma is a significant cause of morbidity and mortality worldwide. For instance, traumatic brain injury (TBI) causes more than 30% of all injury-related deaths in the USA annually. The underlying cause and clinical sequela vary among cases. Patients are liable to both acute and chronic changes in the nervous system after such a type of injury. Cerebrovascular disruption has the most common and serious effect in such cases because cerebrovascular autoregulation, which is one of the main determinants of cerebral perfusion pressure, can be effaced in brain injuries even in the absence of evident vascular injury. Disruption of the blood-brain barrier regulatory function may also ensue whether due to direct injury to its structure or metabolic changes. Furthermore, the autonomic nervous system (ANS) can be affected leading to sympathetic hyperactivity in many patients. On a cellular scale, the neuroinflammatory cascade medicated by the glial cells gets triggered in response to TBI. Nevertheless, cellular and molecular reactions involved in cerebrovascular repair are not fully understood yet. Most studies were done on animals with many drawbacks in interpreting results. Therefore, future studies including human subjects are necessarily needed. This review will be of relevance to clinicians and researchers interested in understanding the underlying mechanisms in neurotrauma cases and the development of proper therapies as well as those with a general interest in the neurotrauma field.

Fecal Incontinence after Severe Brain Injury: A Barrier to Discharge after Inpatient Rehabilitation?

BACKGROUND

In this study, we aimed to investigate the incidence of fecal incontinence (FI) after severe acquired brain injuries (sABIs) and to determine whether this symptom can lead to an inability to return home after rehabilitation.

METHODS

This was a retrospective observational cohort study. In total, 521 acute sABI inpatients were enrolled from the Department of Neurorehabilitation at an academic tertiary care hospital. Patients were divided into two groups, with and without FI, at the end of the rehabilitation phase. The primary and secondary endpoints were the incidence of persistent FI and any difference in the discharge destination.

RESULTS

Upon admission, new-onset FI was found in 443 (85%) patients, of which 38% had traumatic sABI. Moreover, 62.7% of all patients had FI upon admission. At discharge, 53.3% (264/495) of patients still had FI. Of these, 75.4% (199/264) had a Rancho Level of Cognitive Functioning Scale (LCFS) ≥3. A statistically significant correlation between FI at discharge and the presence of frontal lesions, autonomic crises, and increased LCFS scores was noted. Among the patients discharged to their homes, the proportion with persistent FI was lower (34% vs. 53.3).

CONCLUSIONS

FI was significantly persistent after sABI, even after recovery from unconsciousness, and must be considered as a consequence of, rather than an independent risk factor for, unfavorable outcomes.

Clinical Potential of Immunotherapies in Subarachnoid Hemorrhage Treatment: Mechanistic Dissection of Innate and Adaptive Immune Responses

Subarachnoid hemorrhage (SAH), classified as a medical emergency, is a devastating and severe subtype of stroke. SAH induces an immune response, which further triggers brain injury; however, the underlying mechanisms need to be further elucidated. The current research is predominantly focused on the production of specific subtypes of immune cells, especially innate immune cells, post-SAH onset. Increasing evidence suggests the critical role of immune responses in SAH pathophysiology; however, studies on the role and clinical significance of adaptive immunity post-SAH are limited. In this present study, we briefly review the mechanistic dissection of innate and adaptive immune responses post-SAH. Additionally, we summarized the experimental studies and clinical trials of immunotherapies for SAH treatment, which may form the basis for the development of improved therapeutic approaches for the clinical management of SAH in the future.

Paroxysmal Sympathetic Hyperactivity in Stroke

OBJECTIVE

Paroxysmal sympathetic hyperactivity (PSH) is a life-threatening neurological emergency associated with severe brain injury. Stroke-related PSH, particularly post-aneurysmal subarachnoid hemorrhage (aSAH) PSH, has been relatively understudied and is often misdiagnosed as an aSAH-related hyperadrenergic crisis. This study aims to clarify the feature of stroke-related PSH.

METHODS

This study discusses the case of a patient with post-aSAH PSH and identifies 19 articles (25 cases) on stroke-related PSH by searching the PubMed database from 1980 to 2021.

RESULTS

In the total cohort, 15 (60.0%) patients were male and the average age was 40.1 ± 16.6 years. The primary diagnoses included intracranial hemorrhage (13 cases, 52.0%), cerebral infarction (7 cases, 28.0%), subarachnoid hemorrhage (4 cases, 16.0%), and intraventricular hemorrhage (1 case, 4.0%). The sites of stroke damage were predominantly the cerebral lobe (10 cases, 40.0%), basal ganglia (8 cases, 32.0%), and the pons (4 cases, 16.0%). The median time of PSH onset after admission was 5 (1-180) days. Most cases employed combination therapy with sedation drugs, beta-blockers, gabapentin, and clonidine. On the Glasgow Outcome Scale, outcomes included death (4 cases, 21.1%), vegetative state (2 cases, 10.5%), severe disability (7 cases, 36.8%), and in only one case (5.3%) was a good recovery noted.

CONCLUSIONS

The clinical features and treatment of post-aSAH PSH differed from those of aSAH-related hyperadrenergic crises. Early diagnosis and treatment can prevent severe complications. PSH should be acknowledged as a potential complication of aSAH. Differential diagnosis can aid in developing individualized treatment plans and improving patient prognosis.

Pathophysiology, Management, and Therapeutics in Subarachnoid Hemorrhage and Delayed Cerebral Ischemia: An Overview

Subarachnoid hemorrhage (SAH) is a type of hemorrhagic stroke resulting from the rupture of an arterial vessel within the brain. Unlike other stroke types, SAH affects both young adults (mid-40s) and the geriatric population. Patients with SAH often experience significant neurological deficits, leading to a substantial societal burden in terms of lost potential years of life. This review provides a comprehensive overview of SAH, examining its development across different stages (early, intermediate, and late) and highlighting the pathophysiological and pathohistological processes specific to each phase. The clinical management of SAH is also explored, focusing on tailored treatments and interventions to address the unique pathological changes that occur during each stage. Additionally, the paper reviews current treatment modalities and pharmacological interventions based on the evolving guidelines provided by the American Heart Association (AHA). Recent advances in our understanding of SAH will facilitate clinicians' improved management of SAH to reduce the incidence of delayed cerebral ischemia in patients.

Plants and their Bioactive Compounds as a Possible Treatment for Traumatic Brain Injury-Induced Multi-Organ Dysfunction Syndrome

BACKGROUND & OBJECTIVE

Traumatic brain injury is an outcome of the physical or mechanical impact of external forces on the brain. Thus, the silent epidemic has complex pathophysiology affecting the brain along with extracranial or systemic complications in more than one organ system, including the heart, lungs, liver, kidney, gastrointestinal and endocrine system. which is referred to as Multi-Organ Dysfunction Syndrome. It is driven by three interconnected mechanisms such as systemic hyperinflammation, paroxysmal sympathetic hyperactivity, and immunosuppression-induced sepsis. These multifaceted pathologies accelerate the risk of mortality in clinical settings by interfering with the functions of distant organs through hypertension, cardiac arrhythmias, acute lung injury, neurogenic pulmonary edema, reduced gastrointestinal motility, Cushing ulcers, acute liver failure, acute kidney injury, coagulopathy, endocrine dysfunction, and many other impairments. The pharmaceutical treatment approach for this is highly specific in its mode of action and linked to a variety of side effects, including hallucinations, seizures, anaphylaxis, teeth, bone staining, etc. Therefore, alternative natural medicine treatments are widely accepted due to their broad complementary or synergistic effects on the physiological system with minor side effects.

CONCLUSION

This review is a compilation of the possible mechanisms behind the occurrence of multiorgan dysfunction and reported medicinal plants with organoprotective activity that have not been yet explored against traumatic brain injury and thereby, highlighting the marked possibilities of their effectiveness in the management of multiorgan dysfunction. As a result, we attempted to respond to the hypothesis against the usage of medicinal plants to treat neurodegenerative diseases.

Dysautonomia and functional impairment in rare developmental and epileptic encephalopathies: the other nervous system

AIM

To determine whether functional impairments and autonomic symptoms are correlated in young people with developmental and epileptic encephalopathies (DEEs).

METHOD

Cross-sectional, online surveys (2018-2020) of parents recruited from family groups obtained information on several aspects of children's conditions including functional abilities (mobility, hand use, eating, and communication), 18 autonomic symptoms in six groups (cardiac, respiratory, sweating, temperature, gastrointestinal, and other), and parental stress. Bivariate and multivariable logistic regression analyses examined associations of dysautonomias with functional impairment, adjusted for type of DEE and age.

RESULTS

Of 313 participants with full information on function and dysautonomias, 156 (50%) were females. The median age was 8 years (interquartile range 4-12y); 255 (81%) participants had symptoms in at least one autonomic symptom group; 283 (90%) had impairment in at least one functional domain. The number of functional impairment domains and of autonomic symptom groups varied significantly across DEE groups (both p<0.001). The number of functional impairment domains and of autonomic symptom groups were correlated (Spearman's r=0.35, p<0.001) on bivariate and multivariable analysis adjusted for DEE group and age. Parental stress was also independently correlated with dysautonomias (p<0.001).

INTERPRETATION

Parent-reported dysautonomias are common in children with DEEs. They correlate with extent of functional impairment and may contribute to caregiver stress. What this paper adds Dysautonomic symptoms are common in young people with developmental and epileptic encephalopathies (DEEs). Burden of dysautonomias is strongly correlated with burden of functional impairments. Aspects of dysautonomic function may provide biomarkers of DEE disease severity.

Brain Injury and Mental Health Among the Victims of Intimate Partner Violence: A Case-Series Exploratory Study

Intimate partner violence (IPV) survivors frequently report face, head, and neck as their injury site. Many mild traumatic brain injuries (TBIs) are undiagnosed or underreported among IPV survivors while these injuries may be linked to changes in brain function or pathology. TBI sustained due to IPV often occurs over time and ranges in severity. The aim of this case-series study was to explore risk factors, symptoms, and brain changes unique to survivors of intimate partner violence with suspicion of TBI. This case-series exploratory study examines the potential relationships among IPV, mental health issues, and TBI. Participants of this study included six women: 3 women with a history of IPV without any experience of concussive blunt force to the head, and 3 women with a history of IPV with concussive head trauma. Participants completed 7T MRI of the brain, self-report psychological questionnaires regarding their mental health, relationships, and IPV, and the Structured Clinical Interview. MRI scans were analyzed for cerebral hemorrhage, white matter disturbance, and cortical thinning. Results indicated significant differences in resting-state connectivity among survivors of partner violence as well as differences in relationship dynamics and mental health symptoms. White matter hyperintensities are also observed among the survivors. Developing guidelines and recommendations for TBI-risk screening, referrals, and appropriate service provision is crucial for the effective treatment of TBI-associated IPV. Early and accurate characterization of TBI in survivors of IPV may relieve certain neuropsychological consequences.

Restoring neuro-immune circuitry after brain and spinal cord injuries

Neuro-immune interactions are essential for our body's defense and homeostasis. Anatomical and physiological analyses have shown that the nervous system comprises multiple pathways that regulate the dynamics and functions of immune cells, which are mainly mediated by the autonomic nervous system and adrenal signals. These are disturbed when the neurons and circuits are damaged by diseases of the central nervous system (CNS). Injuries caused by stroke or trauma often cause immune dysfunction by abrogation of the immune-regulating neural pathways, which leads to an increased risk of infections. Here, I review the structures and functions of the neural pathways connecting the brain and the immune system, and the neurogenic mechanisms of immune dysfunction that emerge after CNS injuries. Recent technological advances in manipulating specific neural circuits have added mechanistic aspects of neuro-immune interactions and their dysfunctions. Understanding the neural bases of immune control and their pathological processes will deepen our knowledge of homeostasis and lead to the development of strategies to cure immune deficiencies observed in various CNS disorders.

Autonomic Hyperactivity

PURPOSE OF REVIEW

Autonomic hyperactivity is a relatively common consequence of severe acute brain injury and can also be seen with spinal cord and peripheral nerve disorders. This article reviews basic pathophysiologic concepts regarding autonomic hyperactivity, its various forms of clinical presentation, and practical management considerations.

RECENT FINDINGS

Paroxysmal sympathetic hyperactivity is most common after traumatic brain injury but can also occur after other forms of severe acute diffuse or multifocal brain injury. Formal criteria for the diagnosis and severity grading of paroxysmal sympathetic hyperactivity have now been proposed. A growing body of literature is beginning to elucidate the mechanisms underlying this disorder, but treatment remains based on observational data. Our mechanistic understanding of other distinct forms of autonomic hyperactivity, such as autonomic dysreflexia after traumatic spinal cord injury and dysautonomia after Guillain-Barré syndrome, remains rudimentary, yet clinical experience shows that their appropriate management can minimize the risk of serious complications.

SUMMARY

Syndromes of autonomic hyperactivity can result from injury at all levels of the neuraxis. Much more research is needed to refine our understanding of these disorders and guide optimal management decisions.

Traumatic brain injury and the misuse of alcohol, opioids, and cannabis

Traumatic brain injury (TBI), most often classified as concussion, is caused by biomechanical forces to the brain resulting in short- or long-term impairment in brain function. TBI resulting from military combat, sports, violence, falls, and vehicular accidents is a major cause of long-term physical, cognitive, and psychiatric dysfunction. Psychiatric disorders associated with TBI include depression, anxiety, and substance use disorder, all having significant implications for post-TBI recovery and rehabilitation. This chapter reviews the current preclinical and clinical literature describing the bidirectional relationship between TBI and misuse of three commonly abused drugs: alcohol, opioids, and cannabis. We highlight the influence of each of these drugs on the incidence of TBI, as well as trends in their use after TBI. Furthermore, we discuss factors that may underlie post-injury substance use. Understanding the complex relationship between TBI and substance misuse will enhance the clinical treatment of individuals suffering from these two highly comorbid conditions.

Role of Acupuncture in the Management of Severe Acquired Brain Injuries (sABIs)

Acupuncture therapy has been used to treat several disorders in Asian countries and its use is increasing in Western countries as well. Current literature assessed the safety and efficacy of acupuncture in the acute management and rehabilitation of patients with neurologic disorders. In this paper, the role of acupuncture in the treatment of acute severe acquired brain injuries is described, acting on neuroinflammation, intracranial oedema, oxidative stress, and neuronal regeneration. Moreover, beneficial effects of acupuncture on subacute phase and chronic outcomes have been reported in controlling the imbalance of IGF-1 hormone and in decreasing spasticity, pain, and the incidence of neurovegetative crisis. Moreover, acupuncture may have a positive action on the arousal recovery. Further work is needed to understand the effects of specific acupoints on the brain. Allegedly concurrent neurophysiological measurements (e.g., EEG) may help in studying acupuncture-related changes in central nervous system activity and determining its potential as an add-on rehabilitative treatment for patients with consciousness disorders.

Baroreflex sensitivity and heart rate variability are predictors of mortality in patients with aneurysmal subarachnoid haemorrhage

OBJECT

We aimed to investigate the link between the autonomic nervous system (ANS) impairment, assessed using baroreflex sensitivity (BRS) and heart rate variability (HRV) indices, and mortality after aneurysmal subarachnoid haemorrhage (aSAH).

METHODS

A total of 57 patients (56 ± 18 years) diagnosed with aSAH were retrospectively enrolled in the study, where 25% of patients died in the hospital. BRS was calculated using a modified cross-correlation method. Time- and frequency-domain HRV indices were calculated from a time-series of systolic peak intervals of arterial blood pressure signals. Additionally, cerebral autoregulation (CA) was assessed using the mean velocity index (Mxa), where Mxa > 0 indicates impaired CA.

RESULTS

Both BRS and HRV indices were lower in non-survivors than in survivors. The patients with disturbed BRS and HRV had more extensive haemorrhage in the H-H scale (p = .040) and were more likely to die (p = .013) when compared to patients with the intact ANS. The logistic regression model for mortality included: the APACHE II score (p = .002; OR 0.794) and the normalised high frequency power of the HRV (p < <.001; OR 0.636). A positive relationship was found between the Mxa and BRS (R = 0.48, p = .003), which suggests that increasing BRS is moderately strongly associated with worsening CA.

CONCLUSION

Our results indicated that lower values of HRV indices and BRS correlate with mortality and that there is a link between cerebral dysautoregulation and the analysed estimates of the ANS in aSAH patients.

Placebo Effects in Traumatic Brain Injury

In recent years, several randomized controlled trials evaluating pharmaceutical treatments for traumatic brain injury (TBI) have failed to demonstrate efficacy over placebo, with both active and placebo arms improving at comparable rates. These findings could be viewed in opposing ways, suggesting on the one hand failure of the tested outcome, but on the other, representing evidence of robust placebo effects in TBI. In this article, we examine several of the primary psychological processes driving placebo effects (verbal suggestion, cognitive re-framing, interpersonal interactions, conditioning, therapeutic alliance, anxiety reduction) as well as placebo neurobiology (top-down cortical regulation, reward system activation, dopaminergic and serotonergic neurotransmission). We then extrapolate from the literature to explore whether something inherent in TBI makes it particularly responsive to placebos. Viewed as such here, placebos may indeed represent a powerful and effective treatment for a variety of post-TBI complaints.

Traumatic brain injury, dry eye and comorbid pain diagnoses in US veterans

AIMS

The purpose of the study is to evaluate the relationship between dry eye (DE) and pain diagnoses in US veterans with and without traumatic brain injury (TBI).

METHODS

Retrospective cohort study of veterans who were seen in the Veterans Administration Hospital (VA) between 1 January 2010 and 31 December 2014. Veterans were separated into two groups by the presence or absence of an International Classification of Diseases, Ninth Revision diagnosis of TBI and assessed for DE and other comorbidities. A dendrogram was used to investigate the linkage between TBI, DE, chronic pain and other comorbid conditions.

RESULTS

Of the 3 265 894 veterans seen during the 5-year period, 3.97% carried a diagnosis of TBI. Veterans with TBI were more likely to have a diagnosis of DE compared with their counterparts without TBI (37.2% vs 29.1%, p<0.0005). The association was stronger between TBI and ocular pain (OR 3.08; 95% CI 3.03 to 3.13) compared with tear film dysfunction (OR 1.09; 95% CI 1.07 to 1.10). Those with TBI were also about twice as likely to have a diagnosis of chronic pain, headache, depression or post-traumatic stress disorder compared with their counterparts without TBI. Cluster analysis of TBI, DE and pain diagnoses of interest revealed that central pain syndrome, cluster headache, sicca syndrome, keratoconjunctivitis sicca and late effect of injury to the nervous system (as can be seen after TBI) were all closely clustered together.

CONCLUSIONS

DE and pain disorders occur at higher frequencies in patients with a diagnosis of TBI, suggesting a common underlying pathophysiology.

Autonomic Nervous System Dysfunctions as a Basis for a Predictive Model of Risk of Neurological Disorders in Subjects with Prior History of Traumatic Brain Injury: Implications in Alzheimer's Disease

Autonomic dysfunction is very common in patients with dementia, and its presence might also help in differential diagnosis among dementia subtypes. Various central nervous system structures affected in Alzheimer's disease (AD) are also implicated in the central autonomic nervous system (ANS) regulation. For example, deficits in central cholinergic function in AD could likely lead to autonomic dysfunction. We recently developed a simple, readily applicable evaluation for monitoring ANS disturbances in response to traumatic brain injury (TBI). This ability to monitor TBI allows for the possible detection and targeted prevention of long-term, detrimental brain responses caused by TBI that lead to neurodegenerative diseases such as AD. We randomly selected and extracted de-identified medical record information from subjects who have been assessed using the ANS evaluation protocol. Using machine learning strategies in the analysis of information from individual as well as a combination of ANS evaluation protocol components, we identified a novel prediction model that is effective in correctly segregating between cases with or without a documented history of TBI exposure. Results from our study support the hypothesis that trauma-induced ANS dysfunctions may contribute to clinical TBI features. Because autonomic dysfunction is very common in AD patients it is possible that TBI may also contribute to AD and/or other forms of dementia through these novel mechanisms. This study provides a novel prediction model to physiologically assess the likelihood of subjects with prior history of TBI to develop clinical TBI complications, such as AD.

Age-related changes in baroreflex sensitivity and cardiac autonomic tone in children mirrored by regional brain gray matter volume trajectories

BackgroundThe baroreflex and central autonomic brain regions together control the cardiovascular system. Baroreflex sensitivity (BRS) decreases with age in adults. Age-related changes in brain regions for cardiovascular control in children are unknown. We studied age-related changes in BRS, cardiac autonomic tone, and gray matter volume (GMV) of brain regions associated with cardiovascular control.MethodsBeat-to-beat blood pressure and heart rate (HR) were recorded in 49 children (6-14 years old). Spontaneous BRS was calculated by the sequence method. Cardiac autonomic tone was measured by spectral analysis of HR variability. GMV was measured using voxel-based morphometryin 112 healthy children (5-18 years old).ResultsAge-related changes in BRS were significantly different in children <10 years and ≥10 years. Age-related changes in GMV in regions of interest (ROI) were also significantly different between children <10 and ≥10 years and between children <11 and ≥11 years. However, age-related changes in cardiac autonomic tone were progressive.ConclusionsSignificant changes in BRS trajectories between <10 and ≥10 years may be associated with similar age-related changes of GMV in brain ROI. This new knowledge will guide future studies examining whether childhood cardiovascular disruption manifests as deviated maturation trajectories of specific brain regions.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Heart-Brain Axis: Effects of Neurologic Injury on Cardiovascular Function

A complex interaction exists between the nervous and cardiovascular systems. A large network of cortical and subcortical brain regions control cardiovascular function via the sympathetic and parasympathetic outflow. A dysfunction in one system may lead to changes in the function of the other. The effects of cardiovascular disease on the nervous system have been widely studied; however, our understanding of the effects of neurological disorders on the cardiovascular system has only expanded in the past 2 decades. Various pathologies of the nervous system can lead to a wide range of alterations in function and structure of the cardiovascular system ranging from transient and benign electrographic changes to myocardial injury, cardiomyopathy, and even cardiac death. In this article, we first review the anatomy and physiology of the central and autonomic nervous systems in regard to control of the cardiovascular function. The effects of neurological injury on cardiac function and structure will be summarized, and finally, we review neurological disorders commonly associated with cardiovascular manifestations.

Detection of Impaired Sympathetic Cerebrovascular Control Using Functional Biomarkers Based on Principal Dynamic Mode Analysis

This study sought to determine whether models of cerebrovascular function based on Laguerre-Volterra kernels that account for nonlinear cerebral blood flow (CBF) dynamics can detect the effects of functional cerebral sympathetic blockade. We retrospectively analyzed continuous beat-to-beat blood pressure, middle cerebral blood velocity, and partial-pressure of end-tidal CO₂ (P_ETCO₂) recordings from eighteen healthy individuals who were treated with either an oral dose of the α₁-adrenergic receptor blocker Prazosin or a placebo treatment. The global principal dynamic modes (PDMs) were analyzed using Laguerre-Volterra kernels to examine the nonlinear system dynamics. Our principal findings were: (1) very low frequency (<0.03 Hz) linear components of first-order kernels for BP and P_ETCO₂ are mutually coupled to CBF dynamics with the ability to separate individuals between control and blockade conditions, and (2) the gains of the nonlinear functions associated with low-pass and ≈0.03 Hz global PDMs for the BP are sensitive to sympathetic blockade. Collectively these results suggest that very low frequency global PDMs for BP may have potential utility as functional biomarkers of sympathetic neurovascular dysfunction which can occur in conditions like autonomic failure, stroke and traumatic brain injury.

Noradrenergic dysregulation in the pathophysiology of PTSD

A central role for noradrenergic dysregulation in the pathophysiology of post-traumatic stress disorder (PTSD) is increasingly suggested by both clinical and basic neuroscience research. Here, we integrate recent findings from clinical and animal research with the earlier literature. We first review the evidence for net upregulation of the noradrenergic system and its responsivity to stress in individuals with PTSD. Next, we trace the evidence that the α₁ noradrenergic receptor antagonist prazosin decreases many of the symptoms of PTSD from initial clinical observations, to case series, to randomized controlled trials. Finally, we review the basic science work that has begun to explain the mechanism for this efficacy, as well as to explore its possible limitations and areas for further advancement. We suggest a view of the noradrenergic system as a central, modifiable link in a network of interconnected stress-response systems, which also includes the amygdala and its modulation by medial prefrontal cortex. Particular attention is paid to the evidence for bidirectional signaling between noradrenaline and corticotropin-releasing factor (CRF) in coordinating these interconnected systems. The multiple different ways in which the sensitivity and reactivity of the noradrenergic system may be altered in PTSD are highlighted, as is the evidence for possible heterogeneity in the pathophysiology of PTSD between different individuals who appear clinically similar. We conclude by noting the importance moving forward of improved measures of noradrenergic functioning in clinical populations, which will allow better recognition of clinical heterogeneity and further assessment of the functional implications of different aspects of noradrenergic dysregulation.