Regional blood volume and peripheral blood flow in postural tachycardia syndrome

Persistent Autonomic and Immunologic Abnormalities in Neurologic Post-Acute Sequelae of SARS-CoV2 Infection

OBJECTIVES

After acute coronavirus disease-2019 (COVID-19), people often experience fatigue, "brain fog," or other central neurologic symptoms (neuro-post-acute SARS-CoV2, or "Neuro-PASC"). In this observational study we evaluated whether abnormalities noted on initial evaluation persist after at least another year.

METHODS

Neuro-PASC research participants who had undergone comprehensive inpatient testing at the NIH Clinical Center returned after at least 1 year for follow-up assessments including symptoms rating scales, MRI, lumbar puncture for tests of the CSF, physiologic recordings during the Valsalva maneuver and head-up tilting (with serial plasma catechols and cardiac Doppler ultrasound during the tilting), blood volume measurement, skin biopsies to examine sympathetic innervation, and blood sampling for neuroendocrine and immunologic measures.

RESULTS

7 patients with Neuro-PASC (6 women, age range 42-63 years) underwent follow-up testing. 71% of initially abnormal test results remained abnormal at follow-up, including the pattern of CSF and serum oligoclonal bands, CSF indices of central catecholamine deficiency, baroreflex-cardiovagal dysfunction, the occurrence of tilt-evoked sudden hypotension, white matter hyperintensities on MRI, and adaptive responses in CSF.

DISCUSSION

In Neuro-PASC most of the autonomic and immunologic abnormalities found initially are still present after more than a year.

Postural Orthostatic Tachycardia Syndrome Associated with COVID-19: A Narrative Review

Postural orthostatic tachycardia syndrome (POTS) is a complex condition marked by an atypical autonomic response to standing, leading to orthostatic intolerance and significant tachycardia without accompanying hypotension. In recent studies, a considerable number of individuals recovering from COVID-19 have been reported to experience POTS within 6 to 8 months post-infection. Key symptoms of POTS include fatigue, difficulty with orthostatic tolerance, tachycardia, and cognitive challenges. The underlying causes of POTS following COVID-19 remain unknown, with various theories proposed such as renin-angiotensin-aldosterone system (RAAS) dysregulation, hyperadrenergic reaction, and direct viral infection. Healthcare professionals should be vigilant for POTS in patients who have recovered from COVID-19 and are experiencing signs of autonomic dysfunction and use diagnostic procedures such as the tilt-up table test for confirmation. COVID-19-related POTS should be approached with a holistic strategy. Although many patients show improvement with initial non-drug treatments, for subjects who do not respond and exhibit more severe symptoms, medication-based therapies may be necessary. The current understanding of COVID-19-related POTS is limited, underscoring the need for more research to increase knowledge and enhance treatment approaches.

Nonpelvic comorbid symptoms of 45 patients with pain of pelvic venous origin, before and after treatment

OBJECTIVE

To report the prevalence and severity of nonpelvic symptoms for patients with venous-origin chronic pelvic pain (VO-CPP) and to describe outcomes after pelvic vein stenting and embolization.

METHODS

We retrospectively reviewed outcomes of 45 women with VO-CPP who underwent treatment with iliac vein stenting and/or embolization. Patients completed symptom-severity questionnaires before and after treatment that assessed for pelvic pain, and multiple other symptoms, including brain fog, anxiety, depression, musculoskeletal pain, fatigue, migraines and more.

RESULTS

Patient age ranged from 18 to 65 years. The prevalence of common symptoms was as follows: migraines, 69%; brain fog, 76%; anxiety attacks, 58%; excess sweating, 64%; hip pain, 73%; diarrhea, 62%; constipation, 76%; and abdominal bloating, 82%. After treatment, most symptom scores improved by more than 50%; exceptions were excessive sweating (41% improvement) and bloating (47% improvement). Prevalence of individual symptoms that bundle into POTS ranged from 29% to 76%, where symptom improvement ranged from 23% to 59% after treatment. Overlapping individual symptoms characteristic of fibromyalgia and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) were present in 64% to 82% of patients and all improved by 49% to 63% after treatment.

CONCLUSIONS

Pelvic venous flow abnormality is linked causally to a spectrum of interrelated symptoms, of which many can be bundled into named syndromes of unknown cause. With catheter- based treatment of pelvic venous pooling, nonpelvic symptom and syndrome scores improved.

Deep abdominal breathing reduces heart rate and symptoms during orthostatic challenge in patients with postural orthostatic tachycardia syndrome

BACKGROUND AND PURPOSE

This study investigated the effects of deep abdominal breathing on cardiovascular parameters and symptoms in patients with postural orthostatic tachycardia syndrome (POTS) during head-up tilt-table (HUT) challenge.

METHODS

Thirty POTS patients completed two consecutive rounds of 10-min HUT in a crossover design. One round was HUT without intervention, and one round combined the HUT with deep breathing at a rate of 6 breaths/min. Cardiovascular parameters, including mean blood pressure and maximum and mean heart rate (HR), were measured supine and standing. Symptoms were assessed using the Vanderbilt Orthostatic Symptom Score (VOSS).

RESULTS

During the breathing technique, the mean HR increase was -7.35 bpm (95% confidence interval [CI] = -11.71 to -2.98), and the maximum HR increase was -6.27 bpm (95% CI = -11.85 to -0.68, p = 0.041), significantly lower compared to normal breathing. Additionally, improvements were observed in all absolute cardiovascular parameters during standing, with VOSS symptoms simultaneously and significantly decreasing by -5.38 (95% CI = -10.43 to -0.36).

CONCLUSIONS

Slow deep abdominal breathing can act as a simple technique to reduce the standing HR increase upon HUT in patients with POTS. This suggests that modulation of the cardiopulmonary neurocircuits and the respiratory pump may reduce HR increase and symptoms in patients with POTS. The findings of this study highlight the use of a safe, zero-cost, and simple behavioral tool to suggest to POTS patients for symptom relief apart from standard treatment. The observed improvements in cardiovascular parameters and symptoms offer a promising therapeutic approach for patients in times of inadequate treatment options.

Improvement in chronic pelvic pain, orthostatic intolerance and interstitial cystitis symptoms after treatment of pelvic vein insufficiency

OBJECTIVES

Comorbidities associated with venous origin chronic pelvic pain (VO-CPP) were evaluated pre and post venous treatment to assess change.

MATERIALS AND METHODS

45 women with VO-CPP were treated with venous stenting and/or embolization. Four surveys assessed symptoms pre- and post-treatment: IPPS (chronic pelvic pain), PUF (interstitial cystitis), OHQ (dysautonomia), and modified ROME III (IBS). Prevalence of joint hypermobility was investigated.

RESULTS

Ages were 18-65. Pretreatment, 64% and 49% of women were in the severe range for PUF and OHQ, respectively. 40% and 56% met criteria for IBS and Ehlers-Danlos syndrome/Hypermobility Spectrum Disorder (EDS/HSD), respectively. 17eceived an iliac stent, 5 pelvic embolization, and 23 both. Post-treatment, average scores improved: IPPS (by 55%), PUF (34%), and OHQ (49%). Rome III improved only slightly.

CONCLUSION

Pelvic pain, interstitial cystitis, and dysautonomia were frequently found with VO-CPP and improved after venous treatment. EDS/HSD and IBS were common in these women.

Head-down tilt reduces the heart rate in postural tachycardia syndrome in acute setting: a pilot study

BACKGROUND

Reduced preload and thoracic blood volume accompany postural tachycardia syndrome (POTS). Head-down tilt (HDT) increases both preload and intrathoracic blood volume. The objective of this study was to assess the safety and efficacy of HDT in POTS in acute settings.

METHODS

This retrospective study evaluated POTS patients. Analyzed data included heart rate, blood pressure, cerebral blood flow velocity (CBFv) in the middle cerebral artery, and capnography. The baseline supine hemodynamic data were compared with the data obtained at the second minute of the -10° HDT. A linear mixed-effects model was used to assess the effect of HDT on hemodynamic variables.

RESULTS

The HDT was explored in seven POTS patients and an additional seven POTS patients without HDT served as controls. In the HDT arm, four POTS patients had overlapping diagnoses of myalgic encephalopathy/chronic fatigue syndrome (ME/CFS) and one patient had comorbidity of post-acute sequelae of SARS-CoV-2 infection (PASC). HDT lowered heart rate by 10% and increased end-tidal CO2 by 8%. There was no change in other cardiovascular variables.

CONCLUSIONS

In the acute setting, HDT is safe. HDT reduces the heart rate presumably by modulating baroreflex by enhancing preload and stroke volume, which in turn increases thoracic blood volume with a net effect of parasympathetic cardiovagal activation and/or sympathetic withdrawal. This pilot study provides a foundation to proceed with longitudinal studies exploring the long-term effect of repetitive HDT in conditions associated with preload failure such as POTS, ME/CSF, and PASC.

Post-COVID dysautonomias: what we know and (mainly) what we don't know

Following on from the COVID-19 pandemic is another worldwide public health challenge that is referred to variously as long COVID, post-COVID syndrome or post-acute sequelae of SARS-CoV-2 infection (PASC). PASC comes in many forms and affects all body organs. This heterogeneous presentation suggests involvement of the autonomic nervous system (ANS), which has numerous roles in the maintenance of homeostasis and coordination of responses to various stressors. Thus far, studies of ANS dysregulation in people with PASC have been largely observational and descriptive, based on symptom inventories or objective but indirect measures of cardiovascular function, and have paid little attention to the adrenomedullary, hormonal and enteric nervous components of the ANS. Such investigations do not consider the syndromic nature of autonomic dysfunction. This Review provides an update on the literature relating to ANS abnormalities in people with post-COVID syndrome and presents a theoretical perspective on how the ANS might participate in common features of PASC.

Association of adolescent postural tachycardia syndrome classifications with anxiety: a cross sectional study

BACKGROUND

Postural tachycardia syndrome (POTS), a subset of orthostatic dysregulation, has been reported to be associated with anxiety. POTS can be classified into two forms based on the degree of tachycardia during orthostasis. Reportedly, POTS with decreased orthostatic heart rate increase is associated with suppressed cardiac parasympathetic activity and increased sympathetic activity in the supine position. In this study, the relationship between the two types of POTS and anxiety was evaluated in terms of autonomic function.

METHODS

Fifty-two patients (23 male, age 10-15 years) who were diagnosed with POTS at the Department of Pediatrics, Osaka Medical and Pharmaceutical University from 2019 to 2021, completed a standing test and were accordingly classified into a Su group, with tachycardia from the supine position and a low heart rate increase on standing, a SI group, with a high heart rate increase during standing. They then completed the State-Trait Anxiety Scale for Children (STAIC) questionnaire. Autonomic function was assessed by frequency analysis (MemCalc method) based on heart rate, blood pressure changes, heart rate and blood pressure variability during the orthostatic test.

RESULTS

Patients in the Su group had higher trait anxiety and state anxiety, lower cardiac parasympathetic activity (RR-HF) in the supine position, and greater variability in cardiac parasympathetic activity during orthostasis than were found for patients in the SI group. The Su group had a greater decrease in cardiac index on standing than that of the SI group.

CONCLUSIONS

The Su group results may be partly attributed to chronically low venous return. We also found that patients in the Su group had low parasympathetic activity in the supine position, which may interact with the anxiety-prone characteristics of these patients. Therefore, it seems necessary to consider both physical and psychosomatic treatment approaches for patients with POTS.

Episodic Migraine and POTS

PURPOSE OF REVIEW

Migraine is prevalent in patients with postural orthostatic tachycardia syndrome (POTS). The purpose of this review is to summarize and interpret studies that examine stress response systems in patients with migraine, focusing on their relevance to the pathologies associated with POTS. Important structural and functional components of the stress response network are also reviewed.

RECENT FINDINGS

In patients with migraine, studies examining the autonomic nervous system have demonstrated interictal sympathetic hypofunction and ictal sympathetic hyperfunction, while those focusing on the hypothalamic-pituitary-adrenal axis have demonstrated elevated responsivity. There is evidence that activation of these stress response systems during a migraine episode may exacerbate vascular dysfunction and play a role in the development of central sensitization. Activation of the stress response systems during an episode of migraine has the potential to exacerbate the pathology of POTS. Treatment approaches for the patient with comorbid episodic migraine and POTS should consider the etiology of POTS.

Long COVID: pathophysiological factors and abnormalities of coagulation

Acute COVID-19 infection is followed by prolonged symptoms in approximately one in ten cases: known as Long COVID. The disease affects ~65 million individuals worldwide. Many pathophysiological processes appear to underlie Long COVID, including viral factors (persistence, reactivation, and bacteriophagic action of SARS CoV-2); host factors (chronic inflammation, metabolic and endocrine dysregulation, immune dysregulation, and autoimmunity); and downstream impacts (tissue damage from the initial infection, tissue hypoxia, host dysbiosis, and autonomic nervous system dysfunction). These mechanisms culminate in the long-term persistence of the disorder characterized by a thrombotic endothelialitis, endothelial inflammation, hyperactivated platelets, and fibrinaloid microclots. These abnormalities of blood vessels and coagulation affect every organ system and represent a unifying pathway for the various symptoms of Long COVID.

Fear conditioning as a pathogenic mechanism in the postural tachycardia syndrome

Despite its increasing recognition and extensive research, there is no unifying hypothesis on the pathophysiology of the postural tachycardia syndrome. In this cross-sectional study, we examined the role of fear conditioning and its association with tachycardia and cerebral hypoperfusion upon standing in 28 patients with postural tachycardia syndrome (31 ± 12 years old, 25 women) and 21 matched controls. We found that patients had higher somatic vigilance (p = 0.0167) and more anxiety (p < 0.0001). They also had a more pronounced anticipatory tachycardia right before assuming the upright position in a tilt-table test (p = 0.015), a physiologic indicator of fear conditioning to orthostasis. While standing, patients had faster heart rate (p < 0.001), higher plasma catecholamine levels (p = 0.020), lower end-tidal CO2 (p = 0.005), and reduced middle cerebral artery blood flow velocity (p = 0.002). Multi-linear logistic regression modeling showed that both epinephrine secretion and excessive somatic vigilance predicted the magnitude of the tachycardia and the hyperventilation. These findings suggest that the postural tachycardia syndrome is a functional psychogenic disorder in which standing may acquire a frightful quality, so that even when experienced alone, it elicits a fearful conditioned response. Heightened somatic anxiety is associated with and may predispose to a fear-conditioned hyperadrenergic state when standing. Our results have therapeutic implications.

Biomarkers and Hemodynamic Parameters in the Diagnosis and Treatment of Children with Postural Tachycardia Syndrome and Vasovagal Syncope

In children, vasovagal syncope and postural tachycardia syndrome constitute the major types of orthostatic intolerance. The clinical characteristics of postural tachycardia syndrome and vasovagal syncope are similar but their treatments differ. Therefore, their differential diagnosis is important to guide the correct treatment. Therapeutic methods vary in patients with the same diagnosis because of different pathomechanisms. Hence, in patients with vasovagal syncope or postural tachycardia syndrome, routine treatments have an unsatisfactory efficacy. However, biomarkers could increase the therapeutic efficacy significantly, allowing for an accurate and detailed assessment of patients and leading to improved therapeutic effects. In the present review, we aimed to summarize the current state of research into biomarkers for distinguishing the diagnosis of pediatric vasovagal syncope from that of postural tachycardia syndrome. We also discuss the biomarkers that predict treatment outcomes during personalized therapy for each subtype.

Neurovascular Dysregulation and Acute Exercise Intolerance in ME/CFS: A Randomized, Placebo-Controlled Trial of Pyridostigmine

BACKGROUND

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is characterized by intractable fatigue, postexertional malaise, and orthostatic intolerance, but its pathophysiology is poorly understood. Pharmacologic cholinergic stimulation was used to test the hypothesis that neurovascular dysregulation underlies exercise intolerance in ME/CFS.

RESEARCH QUESTION

Does neurovascular dysregulation contribute to exercise intolerance in ME/CFS, and can its treatment improve exercise capacity?

STUDY DESIGN AND METHODS

Forty-five subjects with ME/CFS were enrolled in a single-center, randomized, double-blind, placebo-controlled trial. Subjects were assigned in a 1:1 ratio to receive a 60-mg dose of oral pyridostigmine or placebo after an invasive cardiopulmonary exercise test (iCPET). A second iCPET was performed 50 min later. The primary end point was the difference in peak exercise oxygen uptake (Vo₂). Secondary end points included exercise pulmonary and systemic hemodynamics and gas exchange.

RESULTS

Twenty-three subjects were assigned to receive pyridostigmine and 22 to receive placebo. The peak Vo₂ increased after pyridostigmine but decreased after placebo (13.3 ± 13.4 mL/min vs -40.2 ± 21.3 mL/min; P < .05). The treatment effect of pyridostigmine was 53.6 mL/min (95% CI, -105.2 to -2.0). Peak vs rest Vo₂ (25.9 ± 15.3 mL/min vs -60.8 ± 25.6 mL/min; P < .01), cardiac output (-0.2 ± 0.6 L/min vs -1.9 ± 0.6 L/min; P < .05), and right atrial pressure (1.0 ± 0.5 mm Hg vs -0.6 ± 0.5 mm Hg; P < .05) were greater in the pyridostigmine group compared with placebo.

INTERPRETATION

Pyridostigmine improves peak Vo₂ in ME/CFS by increasing cardiac output and right ventricular filling pressures. Worsening peak exercise Vo₂, cardiac output, and right atrial pressure following placebo may signal the onset of postexertional malaise. We suggest that treatable neurovascular dysregulation underlies acute exercise intolerance in ME/CFS.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov; No.: NCT03674541; URL: www.

CLINICALTRIALS

gov.

Postural orthostatic tachycardia syndrome: A respiratory disorder?

Postural orthostatic tachycardia syndrome (POTS) is a disorder epitomized by the story of the blind men and the elephant. Patients may see primary care internists or pediatricians due to fatigue, be referred to neurologists for “spells”, to cardiologists for evaluation of pre-syncope or chest pain, to gastroenterologists for nausea or dyspepsia, and even pulmonologists for dyspnea. Adoption of a more systematic approach to their evaluation and better characterization of patients has led to greater understanding of comorbidities, hypotheses prompting mechanistic investigations, and pharmacologic trials. Recent work has implicated disordered sympathetic nervous system activation in response to central (thoracic) hypovolemia. It is this pathway that leads one zero in on a putative focal point from which many of the clinical manifestations can be explained – specifically the carotid body. Despite heterogeneity in etiopathogenesis of a POTS phenotype, we propose that aberrant activation and response of the carotid body represents one potential common pathway in evolution. To understand this postulate, one must jettison isolationist or reductionist ideas of chemoreceptor and baroreceptor functions of the carotid body or sinus, respectively, and consider their interaction and interdependence both locally and centrally where some of its efferents merge. Doing so enables one to connect the dots and appreciate origins of diverse manifestations of POTS, including dyspnea for which the concept of neuro-mechanical uncoupling is wanting, thereby expanding our construct of this symptom. This perspective expounds our premise that POTS has a prominent respiratory component.

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Dyspnea affects ~⅓ patients with postural orthostatic tachycardia syndrome (POTS).

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POTS is characterized by thoracic hypovolemia and compromised cephalad perfusion when upright.

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Carotid body and adjacent carotid sinus mediate chemo- and baro- reflexes, respectively.

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These are not independent and stimulation of either activates sympathetic discharge.

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We speculate that carotid body mediates hyperventilation and dyspnea in POTS.

Compression Garment Reduces Orthostatic Tachycardia and Symptoms in Patients With Postural Orthostatic Tachycardia Syndrome

BACKGROUND

Postural orthostatic tachycardia syndrome (POTS) is a chronic form of orthostatic intolerance associated with a significant symptom burden. Compression garments are a frequently prescribed treatment, but the effectiveness of waist-high compression has not been evaluated in adults with POTS.

OBJECTIVES

This study evaluated compression garments as a treatment for POTS using a head-up tilt test (HUT), and a noninflatable core and lower body compression garment.

METHODS

Thirty participants completed 10-min HUT with each of 4 compression conditions in a randomized crossover design. The conditions were no compression (NONE), lower leg compression (LEG), abdominal/thigh compression (ABDO), and full abdominal/leg compression (FULL). Heart rate, beat-to-beat blood pressure, and Vanderbilt Orthostatic Symptom Score ratings were measured during each HUT.

RESULTS

The compression garment reduced heart rate (NONE: 109 ± 19 beats/min; LEG: 103 ± 16 beats/min; ABDO: 97 ± 15 beats/min; FULL: 92 ± 14 beats/min; p < 0.001) and improved symptoms (p < 0.001) during HUT in a dose-dependent manner. During HUT, stroke volume and systolic blood pressure were better maintained with FULL and ABDO compression compared with LEG and NONE compression.

CONCLUSIONS

Abdominal and lower body compression reduced heart rate and improved symptoms during HUT in adult patients with POTS. These effects were driven by improved stroke volume with compression. Abdominal compression alone might also provide a clinical benefit if full lower body compression is not well tolerated. (Hemodynamic Effects of Compression in POTS; NCT03484273).

Postural orthostatic tachycardia syndrome (POTS): State of the science and clinical care from a 2019 National Institutes of Health Expert Consensus Meeting - Part 1

Postural orthostatic tachycardia syndrome (POTS) is a chronic and often disabling disorder characterized by orthostatic intolerance with excessive heart rate increase without hypotension during upright posture. Patients often experience a constellation of other typical symptoms including fatigue, exercise intolerance and gastrointestinal distress. A typical patient with POTS is a female of child-bearing age, who often first displays symptoms in adolescence. The onset of POTS may be precipitated by immunological stressors such as a viral infection. A variety of pathophysiologies are involved in the abnormal postural tachycardia response; however, the pathophysiology of the syndrome is incompletely understood and undoubtedly multifaceted. Clinicians and researchers focused on POTS convened at the National Institutes of Health in July 2019 to discuss the current state of understanding of the pathophysiology of POTS and to identify priorities for POTS research. This article, the first of two articles summarizing the information discussed at this meeting, summarizes the current understanding of this disorder and best practices for clinical care. The evaluation of a patient with suspected POTS should seek to establish the diagnosis, identify co-morbid conditions, and exclude conditions that could cause or mimic the syndrome. Once diagnosed, management typically begins with patient education and non-pharmacologic treatment options. Various medications are often used to address specific symptoms, but there are currently no FDA-approved medications for the treatment of POTS, and evidence for many of the medications used to treat POTS is not robust.

Circulating levels of growth hormone in postural orthostatic tachycardia syndrome

Postural orthostatic tachycardia syndrome (POTS) is a cardiovascular autonomic disorder with poorly understood etiology and underlying pathophysiology. Since cardiovascular morbidity has been linked to growth hormone (GH), we studied GH levels in patients with POTS. We conducted an age-sex-matched case-control study in patients with POTS (age 31 ± 9 years; n = 42) and healthy controls (32 ± 9 years; n = 46). Plasma GH levels were measured using high-sensitivity chemiluminescence sandwich immunoassay. The burden of orthostatic intolerance symptoms was assessed by the Orthostatic Hypotension Questionnaire (OHQ), consisting of a symptom assessment scale (OHSA) and a daily activity scale (OHDAS). POTS patients had significantly higher composite OHQ score than controls, more symptoms and less activity. Supine heart rate and diastolic blood pressure (BP), but not systolic BP, were significantly higher in POTS. Median plasma GH levels were significantly lower in POTS (0.53 ng/mL) than controls (2.33 ng/mL, p = 0.04). GH levels were inversely related to OHDAS in POTS and supine systolic BP in POTS and controls, but not heart rate neither group. POTS is associated with lower GH levels. Impairment of daily life activities is inversely related with GH in POTS. A higher supine diastolic BP is inversely associated with GH levels in POTS and healthy individuals.

Decreased Stroke Volume and Venous Return in School Children with Postural Tachycardia Syndrome

In postural tachycardia syndrome (POTS), a subtype of orthostatic intolerance, the changes in hemodynamics due to postural changes are poorly understood. We speculated that inappropriate venous return, which may occur in the upright position in patients with school-aged POTS, could be detected by echocardiography. Our prospective study was conducted with 100 POTS patients (45 boys and 55 girls), aged 13.1 ± 1.5 years and 52 age- and sex-matched healthy subjects (control). Echocardiography was performed in the supine and sitting positions. Cardiac parameters [stroke volume index, cardiac index, heart rate, and the maximum inferior vena cava diameter (max IVC)] were evaluated in addition to pulse pressure. Unlike the control subjects, POTS patients demonstrated decreased stroke volume index (P = 0.02) and max IVC (P < 0.01) irrespective of posture. The rates of max IVC change did not differ between control and POTS groups. The enrolled POTS patients were divided into two subgroups [dilatation (n = 57) and contraction (n = 43)] based on whether the change rate of max IVC was less than zero or not. The contraction group showed a significantly higher heart rate than the dilatation group with respect to posture (P = 0.03), indicating the poor response of peripheral vessels in the lower limbs only in the contraction group. In conclusion, echocardiographic assessment detected decreased stroke volume and venous return in POTS. The changes in max IVC in response to postural changes may indicate an underlying pathophysiology in POTS.

Insights From Invasive Cardiopulmonary Exercise Testing of Patients With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

BACKGROUND

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) affects tens of millions worldwide; the causes of exertional intolerance are poorly understood. The ME/CFS label overlaps with postural orthostatic tachycardia (POTS) and fibromyalgia, and objective evidence of small fiber neuropathy (SFN) is reported in approximately 50% of POTS and fibromyalgia patients.

RESEARCH QUESTION

Can invasive cardiopulmonary exercise testing (iCPET) and PGP9.5-immunolabeled lower-leg skin biopsies inform the pathophysiology of ME/CFS exertional intolerance and potential relationships with SFN?

STUDY DESIGN AND METHODS

We analyzed 1,516 upright invasive iCPETs performed to investigate exertional intolerance. After excluding patients with intrinsic heart or lung disease and selecting those with right atrial pressures (RAP) <6.5 mm Hg, results from 160 patients meeting ME/CFS criteria who had skin biopsy test results were compared with 36 control subjects. Rest-to-peak changes in cardiac output (Qc) were compared with oxygen uptake (Qc/VO₂ slope) to identify participants with low, normal, or high pulmonary blood flow by Qc/VO₂ tertiles.

RESULTS

During exercise, the 160 ME/CFS patients averaged lower RAP (1.9 ± 2 vs 8.3 ± 1.5; P < .0001) and peak VO₂ (80% ± 21% vs 101.4% ± 17%; P < .0001) than control subjects. The low-flow tertile had lower peak Qc than the normal and high-flow tertiles (88.4% ± 19% vs 99.5% ± 23.8% vs 99.9% ± 19.5% predicted; P < .01). In contrast, systemic oxygen extraction was impaired in high-flow vs low- and normal-flow participants (0.74% ± 0.1% vs 0.88 ± 0.11 vs 0.86 ± 0.1; P < .0001) in association with peripheral left-to-right shunting. Among the 160 ME/CFS patient biopsies, 31% were consistent with SFN (epidermal innervation ≤5.0% of predicted; P < .0001). Denervation severity did not correlate with exertional measures.

INTERPRETATION

These results identify two types of peripheral neurovascular dysregulation that are biologically plausible contributors to ME/CFS exertional intolerance-depressed Qc from impaired venous return, and impaired peripheral oxygen extraction. In patients with small-fiber pathology, neuropathic dysregulation causing microvascular dilation may limit exertion by shunting oxygenated blood from capillary beds and reducing cardiac return.

Impaired Endothelial Function in Patients With Postural Tachycardia Syndrome

The purpose of this study is to evaluate endothelial function in postural tachycardia syndrome (PoTS), a poorly understood chronic condition characterized by a state of consistent orthostatic tachycardia (delta heart rate ≥30 beats per minute) upon standing without orthostatic hypotension. Nineteen patients with PoTS and 9 healthy controls were studied after 3 days of a fixed, caffeine-free, normal sodium (150 milliequivalents/day) diet. All participants underwent autonomic function testing, including sinus arrhythmia, valsalva maneuver, hyperventilation, cold pressor, handgrip, and a standing test with catecholamine measurements, followed by endothelial function testing. We analyzed 3 measures of endothelial function: percent brachial flow-mediated dilation, digital pulsatile arterial tonometry, and postischemic percent leg blood flow. Flow-mediated dilation was significantly lower in patients with PoTS (6.23±3.54% for PoTS) than in healthy controls (10.6±4.37% for controls versus, P=0.014). PoTS and controls had similar digital pulsatile arterial tonometry (1.93±0.40 arbitrary units for controls versus 2.13±0.63 arbitrary units for PoTS). PoTS had similar but suggestive percent leg blood flow to controls (313±158% for PoTS versus 468±236% for controls, P=0.098). Patients with PoTS have significantly reduced flow-mediated dilation compared with healthy controls, suggesting that PoTS is characterized by endothelial dysfunction in conduit arteries. Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT01308099.

Supine Parasympathetic Withdrawal and Upright Sympathetic Activation Underly Abnormalities of the Baroreflex in Postural Tachycardia Syndrome: Effects of Pyridostigmine and Digoxin

[Figure: see text].

Postural Tachycardia Syndrome in Children and Adolescents: Pathophysiology and Clinical Management

Postural tachycardia syndrome (POTS), characterized by chronic (≥6 months) orthostatic intolerance symptoms with a sustained and excessive heart rate increase while standing without postural hypotension, is common in children and adolescents. Despite the unclear pathogenesis of POTS, the present opinion is that POTS is a heterogeneous and multifactorial disorder that includes altered central blood volume, abnormal autonomic reflexes, "hyperadrenergic" status, damaged skeletal muscle pump activity, abnormal local vascular tension and vasoactive factor release, mast cell activation, iron insufficiency, and autoimmune dysfunction. A number of pediatric POTS patients are affected by more than one of these pathophysiological mechanisms. Therefore, individualized treatment strategies are initiated in the management of POTS, including basal non-pharmacological approaches (e.g., health education, the avoidance of triggers, exercise, or supplementation with water and salt) and special pharmacological therapies (e.g., oral rehydration salts, midodrine hydrochloride, and metoprolol). As such, the recent progress in the pathogenesis, management strategies, and therapeutic response predictors of pediatric POTS are reviewed here.

Pathophysiology and Individualized Management of Vasovagal Syncope and Postural Tachycardia Syndrome in Children and Adolescents: An Update

Vasovagal syncope (VVS) and postural tachycardia syndrome (POTS) are the main forms of orthostatic intolerance in pediatrics and both are underlying causes of neurally-mediated syncope. In recent years, increasing attention has been paid to the management of VVS and POTS in children and adolescents. A number of potential mechanisms are involved in their pathophysiology, but the leading cause of symptoms varies among patients. A few studies thus have focused on the individualized treatment of VVS or POTS based on selected hemodynamic parameters or biomarkers that can predict the therapeutic effect of certain therapies and improve their effectiveness. This review summarizes the latest developments in individualized treatment of VVS and POTS in children and indicates directions for further research in this field.

Postural Orthostatic Tachycardia Syndrome: Mechanisms and New Therapies

Postural orthostatic tachycardia syndrome (POTS) is a clinically heterogeneous disorder with multiple contributing pathophysiologic mechanisms manifesting as symptoms of orthostatic intolerance in the setting of orthostatic tachycardia (increase in heart rate by at least 30 beats per minute upon assuming an upright position) without orthostatic hypotension. The three major pathophysiologic mechanisms include partial autonomic neuropathy, hypovolemia, and hyperadrenergic state. Patients often will exhibit overlapping characteristics from more than one of these mechanisms. The approach to the treatment of POTS centers on treating the underlying pathophysiologic mechanism. Stockings, abdominal binders, and vasoconstrictors are used to enhance venous return in partial neuropathic POTS. Exercise and volume expansion are the main treatment strategies for hypo-volemic POTS. For hyperadrenergic POTS, beta-blockers and avoidance of norepinephrine reuptake inhibitors is important. Attempts should be made to discern which pathophysiologic mechanism(s) may be afflicting patients so that treatment regimens can be individualized.

Mechanisms of tilt-induced vasovagal syncope in healthy volunteers and postural tachycardia syndrome patients without past history of syncope

Upright tilt table testing has been used to test for vasovagal syncope (VVS) but can result in "false positives" in which tilt-induced fainting (tilt+) occurs in the absence of real-world fainting. Tilt+ occurs in healthy volunteers and in patients with postural tachycardia syndrome (POTS) and show enhanced susceptibility to orthostatic hypotension. We hypothesized that the mechanisms for hypotensive susceptibility differs between tilt+ healthy volunteers (Control-Faint (N = 12)), tilt+ POTS patients (POTS-Faint (N = 12)) and a non-fainter control group of (Control-noFaint) (N = 10). Subjects were studied supine and during 70° upright tilt while blood pressure (BP), cardiac output (CO), and systemic vascular resistance (SVR), were measured continuously. Impedance plethysmography estimated regional blood volumes, flows, and vascular resistance. Heart rate was increased while central blood volume was decreased in both Faint groups. CO increased in Control-Faint because of reduced splanchnic vascular resistance; splanchnic pooling was similar to Control-noFaint. Splanchnic blood flow in POTS-Faint decreased and resistance increased similar to Control-noFaint but splanchnic blood volume was markedly increased. Decreased SVR and splanchnic arterial vasoconstriction is the mechanism for faint in Control-Faint. Decreased CO caused by enhanced splanchnic pooling is the mechanism for faint in POTS-Faint. We propose that intrahepatic resistance is increased in POTS-Faint resulting in pooling and that both intrahepatic resistance and splanchnic arterial vasoconstriction are reduced in Control-Faint resulting in increased splanchnic blood flow and reduced splanchnic resistance.

Clinical neurophysiology of postural tachycardia syndrome

Postural tachycardia syndrome (POTS) is one of several disorders of orthostatic intolerance (OI). It is defined by the development of symptoms of cerebral hypoperfusion or sympathetic activation and a sustained heart rate increment of 30 beats/min or more (40 beats/min for teenagers) within 10min of standing or head-up tilt in the absence of orthostatic hypotension; the standing heart rate is often 120 beats/min or higher. POTS is approximately five times more common in women than men. This heterogeneous syndrome is caused by several pathophysiologic mechanisms (limited autonomic neuropathy, hyperadrenergic state, hypovolemia, venous pooling, deconditioning), which are not mutually exclusive. Anxiety and somatic hypervigilance play significant roles in POTS. Common comorbidities include visceral pain and dysmotility, chronic fatigue and fibromyalgia, migraine, joint hypermobility, mitral valve prolapse, and inappropriate sinus tachycardia. Patients with suspected POTS should undergo comprehensive cardiac and neurologic examinations and autonomic and laboratory tests to determine the most likely pathophysiologic basis of OI. The objectives of POTS management are to (1) increase the time that patients can stand, perform daily activities, and exercise and (2) avoid syncope. Management involves nonpharmacologic (fluid and salt loading, physical countermaneuvers, compression garments, exercise training) and pharmacologic (β-blockers, pyridostigmine, fludrocortisone, midodrine) approaches.

Postural Tachycardia Syndrome (POTS) and the GI Tract: A Primer for the Gastroenterologist

Postural tachycardia syndrome (POTS) is one of the most common causes of orthostatic intolerance and is being increasingly recognized in clinical practice. Gastrointestinal (GI) symptoms are reported commonly in patients with POTS and pose a considerable management challenge, making it imperative that gastroenterologists be aware of this condition and its GI comorbidities. Although the evidence presented herein does not prove causation, it does support an association between GI symptoms, GI dysmotility, and POTS. At present, the evaluation and treatment of GI symptoms in patients with POTS remains largely empirical. General measures to treat POTS may lead to improvement in both GI and non-GI symptoms. GI symptoms refractory to these measures should prompt further diagnostic evaluation of gastrointestinal dysmotility and appropriate dietary and pharmacologic management. This review focuses its attention on the involvement of the GI tract in POTS including a discussion of GI symptoms and conditions associated with POTS, followed by an analysis of abnormalities in gut physiology described in POTS, and concluding with an overview of management and suggestions for research directions.

Pediatric Disorders of Orthostatic Intolerance

Orthostatic intolerance (OI), having difficulty tolerating an upright posture because of symptoms or signs that abate when returned to supine, is common in pediatrics. For example, ∼40% of people faint during their lives, half of whom faint during adolescence, and the peak age for first faint is 15 years. Because of this, we describe the most common forms of OI in pediatrics and distinguish between chronic and acute OI. These common forms of OI include initial orthostatic hypotension (which is a frequently seen benign condition in youngsters), true orthostatic hypotension (both neurogenic and nonneurogenic), vasovagal syncope, and postural tachycardia syndrome. We also describe the influences of chronic bed rest and rapid weight loss as aggravating factors and causes of OI. Presenting signs and symptoms are discussed as well as patient evaluation and testing modalities. Putative causes of OI, such as gravitational and exercise deconditioning, immune-mediated disease, mast cell activation, and central hypovolemia, are described as well as frequent comorbidities, such as joint hypermobility, anxiety, and gastrointestinal issues. The medical management of OI is considered, which includes both nonpharmacologic and pharmacologic approaches. Finally, we discuss the prognosis and long-term implications of OI and indicate future directions for research and patient management.

Postural tachycardia syndrome: current perspectives

Postural tachycardia syndrome (POTS) is the combination of an exaggerated heart rate response to standing, in association with symptoms of lightheadedness or pre-syncope that improve when recumbent. The condition is often associated with fatigue and brain fog, resulting in significant disruptions at a critical time of diagnosis in adolescence and young adulthood. The heterogeneity of the underlying pathophysiology and the variable response to therapeutic interventions make management of this condition challenging for both patients and physicians alike. Here, we aim to review the factors and mechanisms that may contribute to the symptoms and signs of POTS and to present our perspectives on the clinical approach toward the diagnosis and management of this complex syndrome.

Reduced Systolic Volume: Main Pathophysiological Mechanism in Patients with Orthostatic Intolerance?

Background

Orthostatic intolerance patients' pathophysiological mechanism is still obscure, contributing to the difficulty in their clinical management.

Objective

To investigate hemodynamic changes during tilt test in individuals with orthostatic intolerance symptoms, including syncope or near syncope.

Methods

Sixty-one patients who underwent tilt test at - 70° in the phase without vasodilators were divided into two groups. For data analysis, only the first 20 minutes of tilting were considered. Group I was made up of 33 patients who had an increase of total peripheral vascular resistance (TPVR) during orthostatic position; and Group II was made up of 28 patients with a decrease in TPVR (characterizing insufficient peripheral vascular resistance). The control group consisted of 24 healthy asymptomatic individuals. Hemodynamic parameters were obtained by a non-invasive hemodynamic monitor in three different moments (supine position, tilt 10' and tilt 20') adjusted for age.

Results

In the supine position, systolic volume (SV) was significantly reduced in both Group II and I in comparison to the control group, respectively (66.4 ±14.9 ml vs. 81.8±14.8 ml vs. 101.5±24.2 ml; p<0.05). TPVR, however, was higher in Group II in comparison to Group I and controls, respectively (1750.5± 442 dyne.s/cm⁵ vs.1424±404 dyne.s/cm⁵ vs. 974.4±230 dyne.s/cm⁵; p<0.05). In the orthostatic position, at 10', there was repetition of findings, with lower absolute values of SV compared to controls (64.1±14.0 ml vs 65.5±11.3 ml vs 82.8±15.6 ml; p<0.05). TPVR, on the other hand, showed a relative drop in Group II, in comparison to Group I.

Conclusion

Reduced SV was consistently observed in the groups of patients with orthostatic intolerance in comparison to the control group. Two different responses to tilt test were observed: one group with elevated TPVR and another with a relative drop in TPVR, possibly suggesting a more severe failure of compensation mechanisms.

Postural Tachycardia Syndrome: Diagnosis and Management in Adolescents and Young Adults

Postural tachycardia syndrome (POTS) represents a common form of orthostatic intolerance that disproportionately affects young women from puberty through adulthood. Patients with POTS have day-to-day orthostatic symptoms with the hallmark feature of an excessive, sustained, and symptomatic rise in heart rate during orthostatic testing. Although considerable overlap exists, three subtypes of POTS have been described: neuropathic, hyperadrenergic, and hypovolemic forms. The wide spectrum of symptoms and comorbidities can make treatment particularly challenging. Volume expansion with fluid and salt, exercise, and education constitute a reasonable initial therapy for most patients. Several medicines are also available to treat orthostatic intolerance and the associated comorbidities. Defining the POTS subtypes clinically in each patient may help to guide medicine choices. A multidisciplinary approach to overall management of the patient with POTS is advised. This review highlights several aspects of POTS with a specific focus on adolescent and young adult patients. [Pediatr Ann. 2017;46(4):e145-e154.].

Cardiac responses to exercise distinguish postural orthostatic tachycardia syndrome variants

We previously showed that one‐third of adolescents with postural orthostatic tachycardia syndrome (POTS) have hyperkinetic circulation. In a subsequent cohort, we compare participants with POTS grouped according to cardiac output (Q˙) versus oxygen uptake (V˙O2) function, whose circulatory response to exercise lay at the lower end of this distribution. We hypothesized that such grouping determines the circulatory response to incremental‐protocol, upright, cycle ergometry by whatever blend of flow and resistance adjustments best maintains normal blood pressure. We reviewed data on 209 POTS participants aged 10–19 years (73% female) grouped as follows: Q˙−V˙O2 < 3.20 L·min⁻¹ per L·min⁻¹ were designated low Q˙ or hypokinetic variant (N = 31); normal‐Q˙ had slopes between 3.21 and 7.97; hyperkinetic participants had Q˙−V˙O2 slope >8 L·min⁻¹ per L·min⁻¹ (N = 32). Heart rate response to exercise was virtually identical in each group. Mean stroke volume (SV) rose normally in the hyperkinetic group (51 ± 38%); less in the normal Q˙ group (22 ± 27%); but was flat in the low Q˙ group (−7 ± 16%). Mean arterial pressure was similar at rest while systemic vascular conductance was flat from rest to exercise in the hypokinetic group, and by comparison rose more steeply in the normal Q˙ (P < 0.001) and in the hyperkinetic (P = 0.02) groups. In conclusion, we identified a variant of POTS with a hypokinetic circulation maintained by a vasoconstricted state. We speculate that they cannot muster preload to augment exercise SV due to profound thoracic hypovolemia, and must resort to vasoconstriction in order to maintain perfusion pressure within working muscle.

Serial Measurements of Splanchnic Vein Diameters in Rats Using High-Frequency Ultrasound

The purpose of this study was to investigate serial ultrasound imaging in rats as a fully non-invasive method to (1) quantify the diameters of splanchnic veins in real time as an indirect surrogate for the capacitance function of those veins, and (2) assess the effects of drugs on venous dimensions. A 21 MHz probe was used on anesthetized male Sprague–Dawley rats to collect images containing the portal vein (PV), superior mesenteric vein (SMV), abdominal inferior vena cava (IVC), and splenic vein (SpV; used as a landmark in timed studies) and the abdominal aorta (AA). Stable landmarks were established that allowed reproducible quantification of cross-sectional diameters within an animal. The average diameters of vessels measured every 5 min over 45 min remained within 0.75 ± 0.15% (PV), 0.2 ± 0.09% (SMV), 0.5 ± 0.12% (IVC), and 0.38 ± 0.06% (AA) of baseline (PV: 2.0 ± 0.12 mm; SMV: 1.7 ± 0.04 mm; IVC: 3.2 ± 0.1 mm; AA: 2.3 ± 0.14 mm). The maximal effects of the vasodilator sodium nitroprusside (SNP; 2 mg/kg, i.v. bolus) on venous diameters were determined 5 min post SNP bolus; the diameters of all noted veins were significantly increased by SNP, while mean arterial pressure (MAP) decreased 29 ± 4 mmHg. By contrast, administration of the venoconstrictor sarafotoxin (S6c; 5 ng/kg, i.v. bolus) significantly decreased PV and SpV, but not IVC, SMV, or AA, diameters 5 min post S6c bolus; MAP increased by 6 ± 2 mmHg. In order to determine if resting splanchnic vein diameters were stable over much longer periods of time, vessel diameters were measured every 2 weeks for 8 weeks. Measurements were found to be highly reproducible within animals over this time period. Finally, to evaluate the utility of vein imaging in a chronic condition, images were acquired from 4-week deoxycorticosterone acetate salt (DOCA-salt) hypertensive and normotensive (SHAM) control rats. All vessel diameters increased from baseline while MAP increased (67 ± 4 mmHg) in DOCA-salt rats compared to SHAM at 4 weeks after pellet implantation. Vessel diameters remained unchanged in SHAM animals. Together, these results support serial ultrasound imaging as a non-invasive, reliable technique able to measure acute and chronic changes in the diameter of splanchnic veins in intact rats.

Arterial flow waveforms, vascular tone, and chronic fatigue: a case report

We present the case of a patient with chronic fatigue secondary to Postural Orthostatic Tachycardia Syndrome (POTS) who had distinctive abnormalities in his arterial waveform morphology as assessed by pulse oximetry. Moreover, the patient's arterial waveform changed markedly from being supine to upright, suggesting that arterial flow patterns may be abnormal in our patient. Analysis of the waveform suggested a positional hypovolemia as the cause of his orthostatic intolerance. We review general aspects of arterial flow waveform analysis pertinent to health care providers and discuss the pathophysiology of POTS.

High flow variant postural orthostatic tachycardia syndrome amplifies the cardiac output response to exercise in adolescents

Postural orthostatic tachycardia syndrome (POTS) is characterized by chronic fatigue and dizziness and affected individuals by definition have orthostatic intolerance and tachycardia. There is considerable overlap of symptoms in patients with POTS and chronic fatigue syndrome (CFS), prompting speculation that POTS is akin to a deconditioned state. We previously showed that adolescents with postural orthostatic tachycardia syndrome (POTS) have excessive heart rate (HR) during, and slower HR recovery after, exercise – hallmarks of deconditioning. We also noted exaggerated cardiac output during exercise which led us to hypothesize that tachycardia could be a manifestation of a high output state rather than a consequence of deconditioning. We audited records of adolescents presenting with long‐standing history of any mix of fatigue, dizziness, nausea, who underwent both head‐up tilt table test and maximal exercise testing with measurement of cardiac output at rest plus 2–3 levels of exercise, and determined the cardiac output () versus oxygen uptake () relationship. Subjects with chronic fatigue were diagnosed with POTS if their HR rose ≥40 beat·min⁻¹ with head‐up tilt. Among 107 POTS patients the distribution of slopes for the , relationship was skewed toward higher slopes but showed two peaks with a split at ~7.0 L·min⁻¹ per L·min⁻¹, designated as normal (5.08 ± 1.17, N = 66) and hyperkinetic (8.99 ± 1.31, N = 41) subgroups. In contrast, cardiac output rose appropriately with in 141 patients with chronic fatigue but without POTS, exhibiting a normal distribution and an average slope of 6.10 ± 2.09 L·min⁻¹ per L·min⁻¹. Mean arterial blood pressure and pulse pressure from rest to exercise rose similarly in both groups. We conclude that 40% of POTS adolescents demonstrate a hyperkinetic circulation during exercise. We attribute this to failure of normal regional vasoconstriction during exercise, such that patients must increase flow through an inappropriately vasodilated systemic circulation to maintain perfusion pressure.

e12122

Forty percent of postural orthostatic tachycardia syndrome (POTS) adolescents who, by definition have abnormal sympathetic control of HR and BP, demonstrate a hyperkinetic circulation during exercise. We attribute this to failure of normal regional vasoconstriction during exercise, such that patients must increase flow through an inappropriately vasodilated systemic circulation to maintain perfusion pressure.

Neuronal and hormonal perturbations in postural tachycardia syndrome

The Postural Tachycardia Syndrome (POTS) is the most common disorder seen in autonomic clinics. Cardinal hemodynamic feature of this chronic and debilitating disorder of orthostatic tolerance is an exaggerated orthostatic tachycardia (≥30 bpm increase in HR with standing) in the absence of orthostatic hypotension. There are multiple pathophysiological mechanisms that underlie POTS. Some patients with POTS have evidence of elevated sympathoneural tone. This hyperadrenergic state is likely a driver of the excessive orthostatic tachycardia. Another common pathophysiological mechanism in POTS is a hypovolemic state. Many POTS patients with a hypovolemic state have been found to have a perturbed renin-angiotensin-aldosterone profile. These include inappropriately low plasma renin activity and aldosterone levels with resultant inadequate renal sodium retention. Some POTS patients have also been found to have elevated plasma angiotensin II (Ang-II) levels, with some studies suggesting problems with decreased angiotensin converting enzyme 2 activity and decreased Ang-II degradation. An understanding of these pathophysiological mechanisms in POTS may lead to more rational treatment approaches that derive from these pathophysiological mechanisms.

Variant cardiovascular regulation in children with postural tachycardia syndrome

BACKGROUND

Postural tachycardia syndrome (POTS) manifests as marked tachycardia while standing. We noticed two forms of circulatory response to orthostatic stress in POTS. We investigated cardiovascular and autonomic nervous response to orthostatic stress in the two forms.

METHODS

We studied 79 patients with POTS and 38 healthy control subjects (Ct). Beat-to-beat blood pressure (BP) and heart rate (HR) were non-invasively and continuously measured in the supine and standing positions. Autonomic nervous function was evaluated on power spectral analysis of HR variability and diastolic BP variability. We divided the subjects into two groups: standing-induced tachycardia (SI group; increase in HR ≥35 beats/min) and supine tachycardia (Su group; standing HR ≥115 beats/min with standing-induced HR increase <35 beats/min).

RESULTS

The Su group had higher supine BP and HR compared with the other groups, indicating dominant sympathetic control of the heart in the supine position. While rising, the SI group had a higher increase in HR than the Ct group, indicating excessive withdrawal of vagal tone. The Su group had a smaller increase in HR and a greater decrease of systolic BP and cardiac index by standing compared with the SI group. These results suggest that compensatory mechanisms of sympathetic function during standing failed in the Su group, probably because of exhaustion by the nearly maximum effort to generate sympathetic drive even in the supine position with low central blood volume.

CONCLUSION

There is a difference between the two types of POTS, in the balance of resting autonomic function and hemodynamic response to standing.

The Neuropsychological Profile of Postural Orthostatic Tachycardia Syndrome: Sibling Case Study

Postural orthostatic tachycardia syndrome (POTS), estimated to affect 500,000 people in the United States alone, is a growing source of impairment and disability. Symptoms often consist of physical, cognitive, and psychological impairment. The symptoms are driven by fluctuations in cerebral blood flow. Cerebral perfusion is tightly controlled and linked to brain function as changes in posture can result in quick hemovascular regulation by the autonomic nervous system. Any delay in hemoregulation and cerebral blood flow can result in neurological symptoms. POTS is associated with chronic autonomic dysregulation, and people with POTS suffer differing degrees of cerebral hypoperfusion causing variability in symptoms. This article reviews the cases of two siblings (22 years old and 19 years old) who both suffer from POTS. They suffered physical symptoms along with difficulty organizing thoughts, sustaining attention, thinking quickly, multitasking, and recalling recent information, as well as depression and anxiety. These sisters have Full-Scale IQs (FSIQ) above average, yet they received academic accommodations and have ongoing cognitive dysfunction that prevents them from furthering their true potential. These cases illustrate the need for neuropsychologists and other treating providers to understand POTS, the related pathophysiology, and how cognitively debilitating POTS can be, even in the context of intact and high FSIQ scores.

Caught in the thickness of brain fog: exploring the cognitive symptoms of Chronic Fatigue Syndrome

Chronic Fatigue Syndrome (CFS) is defined as greater than 6 months of persistent fatigue that is experienced physically and cognitively. The cognitive symptoms are generally thought to be a mild cognitive impairment, but individuals with CFS subjectively describe them as "brain fog." The impairment is not fully understood and often is described as slow thinking, difficulty focusing, confusion, lack of concentration, forgetfulness, or a haziness in thought processes. Causes of "brain fog" and mild cognitive impairment have been investigated. Possible physiological correlates may be due to the effects of chronic orthostatic intolerance (OI) in the form of the Postural Tachycardia Syndrome (POTS) and decreases in cerebral blood flow (CBF). In addition, fMRI studies suggest that individuals with CFS may require increased cortical and subcortical brain activation to complete difficult mental tasks. Furthermore, neurocognitive testing in CFS has demonstrated deficits in speed and efficiency of information processing, attention, concentration, and working memory. The cognitive impairments are then perceived as an exaggerated mental fatigue. As a whole, this is experienced by those with CFS as "brain fog" and may be viewed as the interaction of physiological, cognitive, and perceptual factors. Thus, the cognitive symptoms of CFS may be due to altered CBF activation and regulation that are exacerbated by a stressor, such as orthostasis or a difficult mental task, resulting in the decreased ability to readily process information, which is then perceived as fatiguing and experienced as "brain fog." Future research looks to further explore these interactions, how they produce cognitive impairments, and explain the perception of "brain fog" from a mechanistic standpoint.

Diabetic cardiovascular autonomic neuropathy: clinical implications

Diabetic cardiovascular autonomic neuropathy (DCAN), the impairment of the autonomic balance of the cardiovascular system in the setting of diabetes mellitus (DM), is frequently observed in both Type 1 and 2 DM, has detrimental effects on the quality of life and portends increased mortality. Clinical manifestations include: resting heart rate disorders, exercise intolerance, intraoperative cardiovascular lability, orthostatic alterations in heart rate and blood pressure, QT-interval prolongation, abnormal diurnal and nocturnal blood pressure variation, silent myocardial ischemia and diabetic cardiomyopathy. Clinical tests for autonomic nervous system evaluation, heart rate variability analysis, autonomic innervation imaging techniques, microneurography and baroreflex analysis are the main diagnostic tools for DCAN detection. Aldose reductase inhibitors and antioxidants may be helpful in DCAN therapy, but a regular, more generalized and multifactorial approach should be adopted with inclusion of lifestyle modifications, strict glycemic control and treatment of concomitant traditional cardiovascular risk factors, in order to achieve the best therapeutic results. In the present review, the authors provide aspects of DCAN pathophysiology, clinical presentation, diagnosis and an algorithm regarding the evaluation and management of DCAN in DM patients.

Diabetic autonomic neuropathy

Autonomic neuropathy, once considered to be the Cinderella of diabetes complications, has come of age. The autonomic nervous system innervates the entire human body, and is involved in the regulation of every single organ in the body. Thus, perturbations in autonomic function account for everything from abnormalities in pupillary function to gastroparesis, intestinal dysmotility, diabetic diarrhea, genitourinary dysfunction, amongst others. "Know autonomic function and one knows the whole of medicine!" It is now becoming apparent that before the advent of severe pathological damage to the autonomic nervous system there may be an imbalance between the two major arms, namely the sympathetic and parasympathetic nerve fibers that innervate the heart and blood vessels, resulting in abnormalities in heart rate control and vascular dynamics. Cardiac autonomic neuropathy (CAN) has been linked to resting tachycardia, postural hypotension, orthostatic bradycardia and orthostatic tachycardia (POTTS), exercise intolerance, decreased hypoxia-induced respiratory drive, loss of baroreceptor sensitivity, enhanced intraoperative or perioperative cardiovascular lability, increased incidence of asymptomatic ischemia, myocardial infarction, and decreased rate of survival after myocardial infarction and congestive heart failure. Autonomic dysfunction can affect daily activities of individuals with diabetes and may invoke potentially life-threatening outcomes. Intensification of glycemic control in the presence of autonomic dysfunction (more so if combined with peripheral neuropathy) increases the likelihood of sudden death and is a caveat for aggressive glycemic control. Advances in technology, built on decades of research and clinical testing, now make it possible to objectively identify early stages of CAN with the use of careful measurement of time and frequency domain analyses of autonomic function. Fifteen studies using different end points report prevalence rates of 1% to 90%. CAN may be present at diagnosis, and prevalence increases with age, duration of diabetes, obesity, smoking, and poor glycemic control. CAN also cosegregates with distal symmetric polyneuropathy, microangiopathy, and macroangiopathy. It now appears that autonomic imbalance may precede the development of the inflammatory cascade in type 2 diabetes and there is a role for central loss of dopaminergic restraint on sympathetic overactivity. Restoration of dopaminergic tone suppresses the sympathetic dominance and reduces cardiovascular events and mortality by close to 50%. Cinderella's slipper can now be worn!

Postural tachycardia syndrome: a heterogeneous and multifactorial disorder

Postural tachycardia syndrome (POTS) is defined by a heart rate increment of 30 beats/min or more within 10 minutes of standing or head-up tilt in the absence of orthostatic hypotension; the standing heart rate is often 120 beats/min or higher. POTS manifests with symptoms of cerebral hypoperfusion and excessive sympathoexcitation. The pathophysiology of POTS is heterogeneous and includes impaired sympathetically mediated vasoconstriction, excessive sympathetic drive, volume dysregulation, and deconditioning. POTS is frequently included in the differential diagnosis of chronic unexplained symptoms, such as inappropriate sinus tachycardia, chronic fatigue, chronic dizziness, or unexplained spells in otherwise healthy young individuals. Many patients with POTS also report symptoms not attributable to orthostatic intolerance, including those of functional gastrointestinal or bladder disorders, chronic headache, fibromyalgia, and sleep disturbances. In many of these cases, cognitive and behavioral factors, somatic hypervigilance associated with anxiety, depression, and behavioral amplification contribute to symptom chronicity. The aims of evaluation in patients with POTS are to exclude cardiac causes of inappropriate tachycardia; elucidate, if possible, the most likely pathophysiologic basis of postural intolerance; assess for the presence of treatable autonomic neuropathies; exclude endocrine causes of a hyperadrenergic state; evaluate for cardiovascular deconditioning; and determine the contribution of emotional and behavioral factors to the patient's symptoms. Management of POTS includes avoidance of precipitating factors, volume expansion, physical countermaneuvers, exercise training, pharmacotherapy (fludrocortisone, midodrine, β-blockers, and/or pyridostigmine), and behavioral-cognitive therapy. A literature search of PubMed for articles published from January 1, 1990, to June 15, 2012, was performed using the following terms (or combination of terms): POTS; postural tachycardia syndrome, orthostatic; orthostatic; syncope; sympathetic; baroreceptors; vestibulosympathetic; hypovolemia; visceral pain; chronic fatigue; deconditioning; headache; Chiari malformation; Ehlers-Danlos; emotion; amygdala; insula; anterior cingulate; periaqueductal gray; fludrocortisone; midodrine; propranolol; β-adrenergic; and pyridostigmine. Studies were limited to those published in English. Other articles were identified from bibliographies of the retrieved articles.

Cardiovascular responses to lower body negative pressure before and after 4 h of head-down bed rest and seated control in men and women

Cardiovascular deconditioning after a 4-h head-down bed rest (HDBR) might be a consequence of the time of day relative to pre-HDBR testing, or simply 4 h of confinement and inactivity rather than the posture change. Ten men and 11 women were studied during lower body negative pressure (LBNP) before and after 4-h HDBR and 4-h seated posture (SEAT) as a control for time of day and physical inactivity effects to test the hypotheses that cardiovascular deconditioning was a consequence of the HDBR posture, and that women would have a greater deconditioning response. Following HDBR, men and women had lower blood volume, higher heart rate with a greater increase during LBNP, a greater decrease of stroke volume during LBNP, lower central venous pressure, smaller inferior vena cava diameter, higher portal vein resistance index with a greater increase during LBNP, but lower forearm vascular resistance, lower norepinephrine, and lower renin. Women had lower vasopressin and men had higher vasopressin after HDBR, and women had lower pelvic impedance and men higher pelvic impedance. Following SEAT, brachial vascular resistance was reduced, thoracic impedance was elevated, the reduction of central venous pressure during LBNP was changed, women had higher angiotensin II whereas men had lower levels, and pelvic impedance increased in women and decreased in men. Cardiovascular deconditioning was greater after 4-h HDBR than after SEAT. Women and men had similar responses for most cardiovascular variables in the present study that tested the responses to LBNP after short-duration HDBR compared with a control condition.

Twenty-four-hour urinary sodium excretion and postural orthostatic tachycardia syndrome

OBJECTIVE

To investigate whether 24-hour urinary sodium excretion could be an indicator of the effectiveness of salt supplementation in children with postural orthostatic tachycardia syndrome (POTS).

STUDY DESIGN

The patient group comprised 30 children with POTS, and the control group comprised 10 healthy children. Serum sodium and 24-hour urinary sodium excretion were measured in all children, and the relationship between 24-hour urinary sodium and symptom severity was analyzed in the 30 patients. At 1 month after initiation of salt supplementation, the receiver operating characteristic curve was used to explore the probability of correctly discriminating responders to salt supplementation from nonresponders using 24-hour urinary sodium excretion as an indicator.

RESULTS

Patients with POTS had lower 24-hour urinary sodium excretion than controls (P = .022). Symptom severity was negatively correlated with 24-hour urinary sodium excretion (OR, -0.754; P = .000). The receiver operating characteristic curve demonstrated a sensitivity of 76.9% and specificity of 93% for correct prediction of responders and nonresponders to salt supplementation when a 24-hour urinary sodium excretion of 124 mmol/24 hours was used as the cutoff value.

CONCLUSION

Our results indicate that 24-hour sodium excretion of <124 mmol/24 hours is an indicator of the effectiveness of salt supplementation in children and adolescents with POTS.

Cutaneous constitutive nitric oxide synthase activation in postural tachycardia syndrome with splanchnic hyperemia

Models of microgravity are linked to excessive constitutive nitric oxide (NO) synthase (NOS), splanchnic vasodilation, and orthostatic intolerance. Normal-flow postural tachycardia syndrome (POTS) is a form of chronic orthostatic intolerance associated with splanchnic hyperemia. To test the hypothesis that there is excessive constitutive NOS in POTS, we determined whether cutaneous microvascular neuronal NO and endothelial NO are increased. We performed two sets of experiments in POTS and control subjects aged 21.4 ± 2 yr. We used laser-Doppler flowmetry to measure the cutaneous response to local heating as an indicator of bioavailable neuronal NO. To test for bioavailable endothelial NO, we infused intradermal acetylcholine through intradermal microdialysis catheters and used the selective neuronal NOS inhibitor l-N(ω)-nitroarginine-2,4-L-diamino-butyric amide (N(ω), 10 mM), the selective inducible NOS inhibitor aminoguanidine (10 mM), the nonspecific NOS inhibitor nitro-l-arginine (NLA, 10 mM), or Ringer solution. The acetylcholine dose response and the NO-dependent plateau of the local heating response were increased in POTS compared with those in control subjects. The local heating plateau was significantly higher, 98 ± 1%maximum cutaneous vascular conductance (%CVC(max)) in POTS compared with 88 ± 2%CVC(max) in control subjects but decreased to the same level with N(ω) (46 ± 5%CVC(max) in POTS compared with 49 ± 4%CVC(max) in control) or with NLA (45 ± 3%CVC(max) in POTS compared with 47 ± 4%CVC(max) in control). Only NLA blunted the acetylcholine dose response, indicating that NO produced by endothelial NOS was released by acetylcholine. Aminoguanidine was without effect. This is consistent with increased endothelial and neuronal NOS activity in normal-flow POTS.

Ascorbate improves circulation in postural tachycardia syndrome

Low flow postural tachycardia syndrome (LFP) is associated with vasoconstriction, reduced cardiac output, increased plasma angiotensin II, reduced bioavailable nitric oxide (NO), and oxidative stress. We tested whether ascorbate would improve cutaneous NO and reduce vasoconstriction when delivered systemically. We used local cutaneous heating to 42°C and laser Doppler flowmetry to assess NO-dependent conductance (%CVC(max)) to sodium ascorbate and the systemic hemodynamic response to ascorbic acid in 11 LFP patients and in 8 control subjects (aged 23 ± 2 yr). We perfused intradermal microdialysis catheters with sodium ascorbate (10 mM) or Ringer solution. Predrug heat response was reduced in LFP, particularly the NO-dependent plateau phase (56 ± 6 vs. 88 ± 7%CVC(max)). Ascorbate increased baseline skin flow in LFP and control subjects and increased the LFP plateau response (82 ± 6 vs. 92 ± 6 control). Systemic infusion experiments used Finometer and ModelFlow to estimate relative cardiac index (CI) and forearm and calf venous occlusion plethysmography to estimate blood flows, peripheral arterial and venous resistances, and capacitance before and after infusing ascorbic acid. CI increased 40% after ascorbate as did peripheral flows. Peripheral resistances were increased (nearly double control) and decreased by nearly 50% after ascorbate. Calf capacitance and venous resistance were decreased compared with control but normalized with ascorbate. These data provide experimental support for the concept that oxidative stress and reduced NO possibly contribute to vasoconstriction and venoconstriction of LFP.

Two types of orthostatic dysregulation assessed by diameter of inferior vena cava

AIMS

Orthostatic dysregulation (OD) is common in adolescents. This study was conducted to evaluate the usefulness of the measurement of the diameter of the inferior vena cava (IVC) for objective assessment of patients with OD.

METHODS

Twenty children with OD (median 14 years, range 9-15 years) and 23 age-matched healthy children (median 12 years, range 10-15 years) were enrolled. A diameter of IVC was measured by an abdominal echogram before and after a head-up tilt table testing (HUT). Changes in IVC was assessed by an arbitrary parameter, collapse index (CI) as the following equation: [(maximal IVC diameter in the supine position - maximal IVC diameter in the standing position)/(maximal IVC diameter in the supine position)]× 100. CI was evaluated 4 weeks after treatment with an adrenergic agent.

RESULTS

Children with OD demonstrated either higher CI or lower CI compared to that in control children: CI was more than 50 (range 50-71) in 12 patients with OD while that was equal to or less than 0 (range -225 to 0) in eight out of 20 patients. In contrast, CI was between 0 and 50 (range 1-26) in 23 healthy children. Pharmacological treatment induced the normalization in the CI in both higher and lower CI group.

CONCLUSION

OD can be classified into two subtypes: by HUT, one is characterized by an increase of IVC diameter while another is characterized by its decrease. Measurement of IVC diameter by HUT is useful to understand the pathophysiology and to assess the efficacy of treatment.