Cerebral autoregulation and symptoms of orthostatic hypotension in familial dysautonomia

Familial dysautonomia

Familial dysautonomia (FD) is an autosomal recessive hereditary sensory and autonomic neuropathy (HSAN, type 3) expressed at birth with profound sensory loss and early death. The FD founder mutation in the ELP1 gene arose within the Ashkenazi Jews in the sixteenth century and is present in 1:30 Jews of European ancestry. The mutation yield a tissue-specific skipping of exon 20 and a loss of function of the elongator-1 protein (ELP1), which is essential for the development and survival of neurons. Patients with FD produce variable amounts of ELP1 in different tissues, with the brain producing mostly mutant transcripts. Patients have excessive blood pressure variability due to the failure of the IXth and Xth cranial nerves to carry baroreceptor signals. Neurogenic dysphagia causes frequent aspiration leading to chronic pulmonary disease. Characteristic hyperadrenergic "autonomic crises" consisting of brisk episodes of severe hypertension, tachycardia, skin blotching, retching, and vomiting occur in all patients. Progressive features of the disease include retinal nerve fiber loss and blindness, and proprioceptive ataxia with severe gait impairment. Chemoreflex failure may explain the high frequency of sudden death in sleep. Although 99.5% of patients are homozygous for the founder mutation, phenotypic severity varies, suggesting that modifier genes impact expression. Medical management is currently symptomatic and preventive. Disease-modifying therapies are close to clinical testing. Endpoints to measure efficacy have been developed, and the ELP1 levels are a good surrogate endpoint for target engagement. Early intervention may be critical for treatment to be successful.

Cerebrovascular regulation in patients with vasovagal syncope and autonomic failure due to familial amyloidotic polyneuropathy

INTRODUCTION

While there is strong evidence for autonomic involvement in cerebrovascular function acutely, long-term role of autonomic nervous system in cerebrovascular function has been controversial. We assessed autoregulation in 10 healthy individuals, nine patients with vasovagal syncope (VVS), and nine with Familial Amyloidotic Polyneuropathy (FAP), in response to head-up tilt test (HUTT).

METHODS

Arterial blood pressure heart rate, cardiac output, and bilateral cerebral blood flow velocity (CBFV) at the M1 segment of middle cerebral artery (transcranial Doppler ultrasound) were recorded during supine rest and 70° HUTT. Autoregulation was quantified using a validated nonlinear and nonparametric approach based on projection pursuit regression. Plasma adrenaline and noradrenaline were also measured at rest and during HUTT.

RESULTS

During supine rest and HUTT, plasma noradrenaline content was lower in FAP patients. During HUTT, VVS patients had a hyperadrenergic status; CBFV decreased in all groups, which was greater in FAP patients (p < 0.01). Healthy controls responded to HUTT with a reduction in CBFV responses to increases (p = 0.01) and decreases (p < 0.01) in arterial pressure without any change in the range or effectiveness of autoregulation. VVS patients responded to HUTT with a reduction in falling (p = 0.02), but not rising slope (p = 0.40). Autoregulatory range (p < 0.01) and effectiveness increased (p = 0.09), consistent with the rapid increase in levels of catecholamines. In FAP patients, the level of increase in range of autoregulation was significantly related to the magnitude of increase in plasma noradrenaline in response to HUTT (R² = 0.26, p = 0.05).

CONCLUSION

Autonomic dysfunction affects the cerebral autoregulatory response orthostatic to challenge.

Spreading Diffusion-Restriction Events in the Gyrencephalic Brain After Subarachnoid Hemorrhage Revealed by Continuous Magnetic Resonance Imaging

BACKGROUND

How widely spreading depolarizations (SDs) propagate through the gyrencephalic brain, including sulci and deeper cortical areas, remains an important clinical question. Here, we investigated SDs that occur spontaneously after subarachnoid placement of autologous blood clots in sulci of the juvenile swine brain.

METHODS

To investigate the three-dimensional spread of waves, animals underwent continuous diffusion-weighted magnetic resonance imaging (DW-MRI) for up to 6 h following clot placement. SD is the mechanism of the cytotoxic edema of developing infarction that is diagnosed by DW-MRI, and DW-MRI also captures transient diffusion restriction caused by SD in less injured or healthy brains. Here, images (b = 0, 375, and 750) were acquired across five coronal slices with 1.25 × 1.25-mm in-plane resolution and 5-mm slice thickness, and the protocol was repeated every 6.83-9.15 s. Spatial drift correction, temporal smoothing, and signal intensity normalization were applied to generate videos of diffusion signal intensity changes for each coronal slice.

RESULTS

Review of video data from five animals revealed ten discrete events consisting of focal diffusion restriction that propagated through cerebral cortex. All events originated in the cortex surrounding the sulcal clot, either in the gyrus (n = 4) or in the sulcal depth (n = 6). In six cases, two to three independent waves spread simultaneously in medial, lateral, and antero-posterior directions. Waves traveled within sulcal walls, traversed the depths of sulci to re-emerge on the adjacent gyrus, and, in three cases, spread fully around the dorsolateral convexity. One event spread deep to olfactory regions along midline cortex, and no events were observed contralateral to the subarachnoid clot.

CONCLUSIONS

Together, these results suggest that SDs in the injured gyrencephalic brain originate near the injury focus and can spread extensively through the cortex to wide and deep uninjured regions. These findings have implications for transient neurologic deficits in the neurocritically ill patient and relevance to patient monitoring and therapeutics.

Symptom Score: A New Instrument to Assess Orthostatic Intolerance in Children and Adolescents

OBJECTIVE

To develop an orthostatic intolerance symptom scoring system to assess orthostatic intolerance and then to compare the symptom score among different head-up tilt test responses.

METHODS

272 subjects (5-18 years) presenting with orthostatic intolerance symptoms finished questionnaire and head-up tilt test. According to head-up tilt test hemodynamic responses, the subjects were divided into head-up tilt test negative, vasovagal syncope, and postural tachycardia syndrome groups.

RESULTS

We built up a symptom score according to the frequency of dizziness, headache, blurred vision, palpitations, chest discomfort, gastrointestinal symptoms, profuse perspiration, and syncope. The median score in postural tachycardia syndrome subjects was highest. A score of 2.5 for predicting vasovagal syncope yielded a sensitivity of 75.0% and specificity of 50.3%, a score of 5.5 for predicting postural tachycardia syndrome yielded a sensitivity of 69.7% and specificity of 72.0%. Furthermore, the median score in postural tachycardia syndrome subjects was significantly higher than that in head-up tilt test negative subjects with heart rate increment of 30-39 beats/min (P < .01).

CONCLUSIONS

This suggests that the symptom score has some predictive value in head-up tilt test results, which can be served as a preliminary assessment instrument.

Afferent Baroreflex Dysfunction: Decreased or Excessive Signaling Results in Distinct Phenotypes

Head and neck tumors can affect afferent baroreceptor neurons and either interrupt or intermittently increase their signaling, causing blood pressure to become erratic. When the afferent fibers of the baroreflex are injured by surgery or radiotherapy or fail to develop as in familial dysautonomia, their sensory information is no longer present to regulate arterial blood pressure, resulting in afferent baroreflex failure. When the baroreflex afferents are abnormally activated, such as by paragangliomas in the neck, presumably by direct compression, they trigger acute hypotension and bradycardia and frequently syncope, by a mechanism similar to the carotid sinus syndrome. We describe our observations in a large series of 23 patients with afferent baroreflex dysfunction and the cardiovascular autonomic features that arise when the sensory baroreceptor neurons are injured or compressed. The management of afferent baroreceptor dysfunction is limited, but pharmacological strategies can mitigate blood pressure swings, improve symptoms, and may reduce hypertensive organ damage. Although rare, the prevalence of afferent baroreflex dysfunction appears to be increasing in middle-aged men due to human papillomavirus related oropharyngeal cancer.

Clinical Trials for Neurogenic Orthostatic Hypotension: A Comprehensive Review of Endpoints, Pitfalls, and Challenges

Neurogenic orthostatic hypotension (nOH) is among the most debilitating nonmotor features of patients with Parkinson's disease (PD) and other synucleinopathies. Patients with PD and nOH generate more hospitalizations, make more emergency room visits, create more telephone calls/mails to doctors, and have earlier mortality than those with PD but without nOH. Overall, the health-related cost in patients with PD and OH is 2.5-fold higher compared with patients with PD without OH. Hence, developing effective therapies for nOH should be a research priority. In the last few decades, improved understanding of the pathophysiology of nOH has led to the identification of therapeutic targets and the development and approval of two drugs, midodrine and droxidopa. More effective and safer therapies, however, are still needed, particularly agents that could selectively increase blood pressure only in the standing position because supine hypertension is the main limitation of available drugs. Here we review the design and conduct of nOH clinical trials in patients with PD and other synucleinopathies, summarize the results of the most recently completed and ongoing trials, and discuss challenges, bottlenecks, and potential remedies.

Cerebral Blood Flow Is Reduced in Severe Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Patients During Mild Orthostatic Stress Testing: An Exploratory Study at 20 Degrees of Head-Up Tilt Testing

Introduction: In a study of 429 adults with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), we demonstrated that 86% had symptoms of orthostatic intolerance in daily life. Using extracranial Doppler measurements of the internal carotid and vertebral arteries during a 30-min head-up tilt to 70 degrees, 90% had an abnormal reduction in cerebral blood flow (CBF). A standard head-up tilt test of this duration might not be tolerated by the most severely affected bed-ridden ME/CFS patients. This study examined whether a shorter 15-min test at a lower 20 degree tilt angle would be sufficient to provoke reductions in cerebral blood flow in severe ME/CFS patients. Methods and results: Nineteen severe ME/CFS patients with orthostatic intolerance complaints in daily life were studied: 18 females. The mean (SD) age was 35(14) years, body surface area (BSA) was 1.8(0.2) m² and BMI was 24.0(5.4) kg/m². The median disease duration was 14 (IQR 5–18) years. Heart rate increased, and stroke volume index and end-tidal CO₂ decreased significantly during the test (p ranging from <0.001 to <0.0001). The cardiac index decreased by 26(7)%: p < 0.0001. CBF decreased from 617(72) to 452(63) mL/min, a 27(5)% decline. All 19 severely affected ME/CFS patients met the criteria for an abnormal CBF reduction. Conclusions: Using a less demanding 20 degree tilt test for 15 min in severe ME/CFS patients resulted in a mean CBF decline of 27%. This is comparable to the mean 26% decline previously noted in less severely affected patients studied during a 30-min 70 degree head-up tilt. These observations have implications for the evaluation and treatment of severely affected individuals with ME/CFS.

Symptom Recognition Is Impaired in Patients With Orthostatic Hypotension

Failure to recognize symptoms of orthostatic hypotension (OH) may result in falls, syncope, and injuries. The relationship between orthostatic changes in blood pressure and symptom occurrence and severity is not known. The goal of the present study was to define the relationship between the occurrence and severity of the symptoms of orthostatic hypotension (OH) and (1) the upright systolic blood pressure (SBP) and (2) the fall in SBP after tilting in patients with OH. We prospectively studied 89 patients with OH. Reported BP values include the lowest BP in the first 3 minutes of tilt and the change in blood pressure during tilt. Subjects were queried about symptoms of orthostatic intolerance while supine and during the first 3 minutes of tilt testing using Question 1 of the Orthostatic Hypotension Questionnaire. Mean tilted SBP was 101.6±26.1 mm Hg and mean SBP fall 47.9±18.1 mm Hg. Mean symptom scores when upright were: light-headedness (2.3/10±2.7), dizziness (1.6/10±2.5), and impending blackout (0.8/10±1.9). The majority of patients were asymptomatic or mildly symptomatic and no discrete cutoff for symptoms was observed. The magnitude of the SBP fall (r=-0.07, P=NS) and the lowest upright SBP (r=0.08, P=NS) did not correlate with any reported symptom. These results suggest a poor relationship between the magnitude of the orthostatic BP fall, the upright orthostatic BP, and symptoms. Many patients are asymptomatic despite substantial SBP falls and low orthostatic blood pressures. These findings have implications for clinical care of patients with OH and clinical trials to treat patients with OH.

Cerebral blood flow is reduced in ME/CFS during head-up tilt testing even in the absence of hypotension or tachycardia: A quantitative, controlled study using Doppler echography

OBJECTIVE

The underlying hypothesis in orthostatic intolerance (OI) syndromes is that symptoms are associated with cerebral blood flow (CBF) reduction. Indirect CBF measurements (transcranial Doppler flow velocities), provide inconsistent support of this hypothesis. The aim of the study was to measure CBF during a 30 min head-up tilt test (HUT), using Doppler flow imaging of carotid and vertebral arteries, in individuals with chronic fatigue syndrome/myalgic encephalomyelitis (ME/CFS), a condition with a high prevalence of OI.

METHODS

429 ME/CFS patients were studied: 247 had a normal heart rate (HR) and blood pressure (BP) response to HUT, 62 had delayed orthostatic hypotension (dOH), and 120 had postural orthostatic tachycardia syndrome (POTS). We also studied 44 healthy controls (HC). CBF measurements were made at mid-tilt and end-tilt. Before mid-tilt, we administered a verbal questionnaire to ascertain for 15 OI symptoms.

RESULTS

End-tilt CBF reduction was 7% in HC versus 26% in the overall ME/CFS group, 24% in patients with a normal HR/BP response, 28% in those with dOH, and 29% in POTS patients (all P < .0005). Using a lower limit of normal of 2SD of CBF reduction in HC (13% reduction), 82% of patients with normal HR/BP response, 98% with dOH and 100% with POTS showed an abnormal CBF reduction. There was a linear correlation of summed OI symptoms with the degree of CBF reduction at mid-tilt (P < .0005).

CONCLUSIONS

During HUT, extracranial Doppler measurements demonstrate that CBF is reduced in ME/CFS patients with POTS, dOH, and even in those without HR/BP abnormalities.

SIGNIFICANCE

This study shows that orthostatic intolerance symptoms are related to CBF reduction, and that the majority of ME/CFS patients (90%) show an abnormal cerebral flow reduction during orthostatic stress testing. This may have implications for the diagnosis and treatment of ME/CFS patients.

Orthostatic Hypotension in Parkinson Disease

Orthostatic hypotension (OH) is a sustained fall in blood pressure on standing that can cause symptoms of organ hypoperfusion. OH is associated with increased morbidity and mortality and leads to a significant number of hospital admissions. OH can be caused by volume depletion, blood loss, cardiac pump failure, large varicose veins, medications, or defective activation of sympathetic nerves and reduced norepinephrine release upon standing. Neurogenic OH is a frequent and disabling problem in patients with synucleinopathies such as Parkinson disease, multiple system atrophy, and pure autonomic failure, and it is commonly associated with supine hypertension. Several therapeutic options are available.

A Controlled Trial of Inhaled Bronchodilators in Familial Dysautonomia

BACKGROUND

Chronic lung disease is a leading cause of premature death in patients with familial dysautonomia (FD). A significant number of patients have obstructive airway disease, yet it is not known whether this is pharmacologically reversible.

METHODS

We conducted a double-blind, placebo-controlled, randomized clinical trial comparing the beta 2 agonist albuterol with the muscarinic blocker ipratropium bromide in patients homozygous for the IKBKAP founder mutation. Albuterol, ipratropium bromide, and placebo were administered on 3 separate days via nebulizer in the seated position. Airway responsiveness was evaluated using spirometry and impulse oscillometry 30 min post dose. Cardiovascular effects were evaluated by continuous monitoring of blood pressure, RR intervals, cardiac output, and systemic vascular resistance.

RESULTS

A total of 14 patients completed the trial. Neither active agent had significant detrimental effects on heart rate or rhythm or blood pressure. Albuterol and ipratropium were similar in their bronchodilator effectiveness causing significant improvement in forced expiratory volume in 1-s (FEV1, p = 0.002 and p = 0.030). Impulse oscillometry measures were consistent with a reduction in total airway resistance post nebulization (resistance at 5 Hz p < 0.006).

CONCLUSION

Airway obstruction is pharmacologically reversible in a number of patients with FD. In the short term, both albuterol and ipratropium were well tolerated and not associated with major cardiovascular adverse events.

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

Transcranial Doppler in autonomic testing: standards and clinical applications

When cerebral blood flow falls below a critical limit, syncope occurs and, if prolonged, ischemia leads to neuronal death. The cerebral circulation has its own complex finely tuned autoregulatory mechanisms to ensure blood supply to the brain can meet the high metabolic demands of the underlying neuronal tissue. This involves the interplay between myogenic and metabolic mechanisms, input from noradrenergic and cholinergic neurons, and the release of vasoactive substrates, including adenosine from astrocytes and nitric oxide from the endothelium. Transcranial Doppler (TCD) is a non-invasive technique that provides real-time measurements of cerebral blood flow velocity. TCD can be very useful in the work-up of a patient with recurrent syncope. Cerebral autoregulatory mechanisms help defend the brain against hypoperfusion when perfusion pressure falls on standing. Syncope occurs when hypotension is severe, and susceptibility increases with hyperventilation, hypocapnia, and cerebral vasoconstriction. Here we review clinical standards for the acquisition and analysis of TCD signals in the autonomic laboratory and the multiple methods available to assess cerebral autoregulation. We also describe the control of cerebral blood flow in autonomic disorders and functional syndromes.

Epidemiology, Diagnosis, and Management of Neurogenic Orthostatic Hypotension

BACKGROUND

Orthostatic hypotension (OH) is a sustained fall in blood pressure on standing which can cause symptoms of organ hypoperfusion. OH is associated with increased morbidity and mortality and leads to a significant number of hospital admissions particularly in the elderly (233 per 100,000 patients over 75 years of age in the US). OH can be due to volume depletion, blood loss, large varicose veins, medications, or due to defective activation of sympathetic nerves and reduced norepinephrine release upon standing (i.e., neurogenic OH).

METHODS AND FINDINGS

Literature review. Neurogenic OH is a frequent and disabling problem in patients with synucleinopathies such as Parkinson disease, multiple system atrophy, and pure autonomic failure, and is commonly associated with supine hypertension. Several pharmacological and non-pharmacological therapeutic options are available.

CONCLUSIONS

Here we review the epidemiology, diagnosis, and management of neurogenic OH, and provide an algorithm for its treatment emphasizing the importance of removing aggravating factors, implementing non-pharmacologic measures, and selecting appropriate pharmacological treatments.

Dexmedetomidine for refractory adrenergic crisis in familial dysautonomia

OBJECTIVE

Adrenergic crises are a cardinal feature of familial dysautonomia (FD). Traditionally, adrenergic crises have been treated with the sympatholytic agent clonidine or with benzodiazepines, which can cause excessive sedation and respiratory depression. Dexmedetomidine is a centrally-acting α ₂-adrenergic agonist with greater selectivity and shorter half-life than clonidine. We evaluated the preliminary effectiveness and safety of intravenous dexmedetomidine in the treatment of refractory adrenergic crisis in patients with FD.

METHODS

Retrospective chart review of patients with genetically confirmed FD who received intravenous dexmedetomidine for refractory adrenergic crises. The primary outcome was preliminary effectiveness of dexmedetomidine defined as change in blood pressure (BP) and heart rate (HR) 1 h after the initiation of dexmedetomidine. Secondary outcomes included incidence of adverse events related to dexmedetomidine, hospital and intensive care unit (ICU) length of stay, and hemodynamic parameters 12 h after dexmedetomidine cessation.

RESULTS

Nine patients over 14 admissions were included in the final analysis. At 1 h after the initiation of dexmedetomidine, systolic BP decreased from 160 ± 7 to 122 ± 7 mmHg (p = 0.0005), diastolic BP decreased from 103 ± 6 to 65 ± 8 (p = 0.0003), and HR decreased from 112 ± 4 to 100 ± 5 bpm (p = 0.0047). The median total adverse events during dexmedetomidine infusion was 1 per admission. Median hospital length of stay was 9 days [interquartile range (IQR) 3-11 days] and median ICU length of stay was 7 days (IQR 3-11 days).

CONCLUSIONS

Intravenous dexmedetomidine is safe in patients with FD and appears to be effective to treat refractory adrenergic crisis. Dexmedetomidine may be considered in FD patients who do not respond to conventional clonidine and benzodiazepine pharmacotherapy.