The 2014 epidemic of Ebola virus disease (EVD) has had a devastating impact in West Africa. Sequencing of ebolavirus (EBOV) from infected individuals has revealed extensive genetic variation, leading to speculation that the virus may be adapting to humans, accounting for the scale of the 2014 outbreak. We computationally analyze the variation associated with all EVD outbreaks, and find none of the amino acid replacements lead to identifiable functional changes. These changes have minimal effect on protein structure, being neither stabilizing nor destabilizing, are not found in regions of the proteins associated with known functions and tend to cluster in poorly constrained regions of proteins, specifically intrinsically disordered regions. We find no evidence that the difference between the current and previous outbreaks is due to evolutionary changes associated with transmission to humans. Instead, epidemiological factors are likely to be responsible for the unprecedented spread of EVD.
•We study the current and previous outbreaks of Ebola virus disease.•There are many non-synonymous (amino-acid altering) changes in the viral sequences.•We can identify no changes that alter any molecular functions in the virus.•The large number of infections is probably due to epidemiological factors.
Ebola; Evolution; Adaptation; Protein structure; Protein function
There are numerous options available to achieve various tasks in bioinformatics, but until recently, there were no tools that could systematically identify mentions of databases and tools within the literature. In this paper we explore the variability and ambiguity of database and software name mentions and compare dictionary and machine learning approaches to their identification.
Through the development and analysis of a corpus of 60 full-text documents manually annotated at the mention level, we report high variability and ambiguity in database and software mentions. On a test set of 25 full-text documents, a baseline dictionary look-up achieved an F-score of 46 %, highlighting not only variability and ambiguity but also the extensive number of new resources introduced. A machine learning approach achieved an F-score of 63 % (with precision of 74 %) and 70 % (with precision of 83 %) for strict and lenient matching respectively. We characterise the issues with various mention types and propose potential ways of capturing additional database and software mentions in the literature.
Our analyses show that identification of mentions of databases and tools is a challenging task that cannot be achieved by relying on current manually-curated resource repositories. Although machine learning shows improvement and promise (primarily in precision), more contextual information needs to be taken into account to achieve a good degree of accuracy.
Bioinformatics; Computational biology; CRF; Dictionary; Resource extraction; Text-mining
Postural Tachycardia Syndrome (POTS) induces disabling chronic orthostatic intolerance with an excessive increase in heart rate (HR) upon standing, and many POTS patients have a hyperadrenergic state. Medications that restrain HR are a promising approach to this problem.
We tested the hypothesis that melatonin will attenuate the tachycardia and improve symptom burden in patients with POTS.
Patients with POTS (n=78) underwent acute drug trials with melatonin 3 mg orally and placebo, on separate mornings, in a randomized crossover design. Blood pressure, HR and symptoms were assessed while seated and after standing for up to 10 minutes prior to, and hourly for 4 hours following, study drug administration.
The reduction in standing HR was significantly greater two hours after melatonin compared to placebo (P=0.017). There was no significant difference in the reduction of systolic blood pressure between melatonin and placebo, either with standing or while seated. The symptom burden was not improved with melatonin compared with placebo.
Oral melatonin produced a modest decrease in standing tachycardia in POTS. Further research is needed to determine the effects of regular night-time use of this medication in POTS.
tachycardia; melatonin; autonomic nervous system; sympathetic nervous system; drugs; orthostatic intolerance
Postural tachycardia syndrome (POTS) is characterized by excessive increases in heart rate (HR) upon standing. Previous studies have shown that standing HR decreases over time in POTS patients given placebo. We hypothesized that this reduction is due to cardiovascular physiological alteration, as opposed to psychological benefit from perceived therapy. To prospectively test this hypothesis, we examined the effects of an open-label "No Treatment" intervention (NoRx) compared to a patient-blinded placebo on standing HR in POTS patients. Twenty-one POTS patients participated in a randomized, crossover trial with oral placebo versus NoRx administered at 9 AM. Seated blood pressure (BP) and HR were measured at baseline and every hour for 4 hours (h). Similarly, BP and HR were measured while patients stood for 10 minutes at these time points. Standing HR significantly decreased over time with both NoRx (baseline: 112 ± 13 bpm, 4h: 103 ± 16 bpm) and placebo (baseline: 112 ± 14 bpm, 4h: 102 ± 16 bpm; Ptime<0.001), but this effect was not different between interventions (Pdrug=0.771). POTS patients have exaggerated orthostatic tachycardia in the morning that decreases over time with either placebo or NoRx interventions, suggesting this phenomenon is due to cardiovascular physiologic variation. These data highlight the need for a placebo arm in hemodynamic clinical trials in POTS, and may have important implications for diagnosis of these patients.
placebo; postural tachycardia syndrome; diurnal variability
CGRP is reported to play important roles in cardiovascular regulation in human and animal models. In spite of this, its role remains controversial. We aim to clarify this by studying the autonomic cardiovascular function and vascular structure in CGRP knockout (CGRP−/−) mice.
Blood pressure (BP) and heart rate (HR) were assessed by telemeters. Urine (24-hr) and blood were collected for catecholamines measurements. Baroreflex sensitivity was assessed using phenylephrine and sodium nitroprusside administered in an acute study.
Daytime mean arterial blood pressure (MAP, 12-hr period) was significantly higher in the CGRP−/− mice than in the WT mice (114.5 vs.104.5 mmHg; p=0.04). Norepinephrine was elevated in plasma and 24-hr urine in the knockouts (Urine: 956 vs. 618 pg/ml, p=0.004; Plasma: 2505 vs. 1168 pg/ml, p = 0.04). Paradoxically, cardiovagal baroreflex sensitivity was higher in CGRP−/− mice (3.2 vs.1.4 ms/mmHg, p=0.03). To increase insight, we studied aortic stiffness in CGRP−/− mice and found it increased compared to age-matched WT mice, as evidenced by the depression of the compliance curve (p<0.05).
CGRP−/− mice have higher BP due to elevated sympathetic signals and abnormalities in blood vessel structure and CGRP plays an important role in the regulation of the cardio-vagal tone.
Baroreflex sensitivity; Catecholamines; sympathetic activities; vagal tone
When developing a new diagnostic test for a disease, there are often multiple candidate classifiers to choose from, and it is unclear if any will offer an improvement in performance compared with current technology. A two-stage design can be used to select a promising classifier (if one exists) in stage one for definitive validation in stage two. However, estimating the true properties of the chosen classifier is complicated by the first stage selection rules. In particular, the usual maximum likelihood estimator (MLE) that combines data from both stages will be biased high. Consequently, confidence intervals and p-values flowing from the MLE will also be incorrect. Building on the results of Pepe et al. (SIM 28:762–779), we derive the most efficient conditionally unbiased estimator and exact confidence intervals for a classifier's sensitivity in a two-stage design with arbitrary selection rules; the condition being that the trial proceeds to the validation stage. We apply our estimation strategy to data from a recent family history screening tool validation study by Walter et al. (BJGP 63:393–400) and are able to identify and successfully adjust for bias in the tool's estimated sensitivity to detect those at higher risk of breast cancer. © 2015 The Authors. Statistics in Medicine published by John Wiley & Sons Ltd.
diagnostic tests; group sequential design; family history; uniformly minimum variance unbiased estimator
Our recognition of familiar faces is excellent, and generalises across viewing conditions. However, unfamiliar face recognition is much poorer. For this reason, automatic face recognition systems might benefit from incorporating the advantages of familiarity. Here we put this to the test using the face verification system available on a popular smartphone (the Samsung Galaxy). In two experiments we tested the recognition performance of the smartphone when it was encoded with an individual’s ‘face-average’ – a representation derived from theories of human face perception. This technique significantly improved performance for both unconstrained celebrity images (Experiment 1) and for real faces (Experiment 2): users could unlock their phones more reliably when the device stored an average of the user’s face than when they stored a single image. This advantage was consistent across a wide variety of everyday viewing conditions. Furthermore, the benefit did not reduce the rejection of imposter faces. This benefit is brought about solely by consideration of suitable representations for automatic face recognition, and we argue that this is just as important as development of matching algorithms themselves. We propose that this representation could significantly improve recognition rates in everyday settings.
Objective: Caring for someone diagnosed with an eating disorder (ED) is associated with a high level of burden and psychological distress which can inadvertently contribute to the maintenance of the illness. The Eating Disorders Symptom Impact Scale (EDSIS) and Accommodation and Enabling Scale for Eating Disorders (AESED) are self-report scales to assess elements of caregiving theorised to contribute to the maintenance of an ED. Further validation and confirmation of the factor structures for these scales are necessary for rigorous evaluation of complex interventions which target these modifiable elements of caregiving. Method: EDSIS and AESED data from 268 carers of people with anorexia nervosa (AN), recruited from consecutive admissions to 15 UK inpatient or day patient hospital units, were subjected to confirmatory factor analysis to test model fit by applying the existing factor structures: (a) four-factor structure for the EDSIS and (b) five-factor structure for the AESED. Results: Confirmatory factor analytic results support the existing four-factor and five-factor structures for the EDSIS and the AESED, respectively. Discussion: The present findings provide further validation of the EDSIS and the AESED as tools to assess modifiable elements of caregiving for someone with an ED.
caregiving; eating disorders; confirmatory factor analysis; burden; accommodation and enabling
We used functional magnetic resonance imaging (fMRI) to identify brain regions involved in the process of mapping coherent discourse onto a developing mental representation. We manipulated discourse coherence by presenting sentences with definite articles (which lead to more coherent discourse) or indefinite articles (which lead to less coherent discourse). Comprehending connected discourse, compared with reading unrelated sentences, produced more neural activity in the right than left hemisphere of the frontal lobe. Thus, the right hemisphere of the frontal lobe is involved in some of the processes underlying mapping. In contrast, left-hemisphere structures were associated with lower-level processes in reading (such as word recognition and syntactic processing). Our results demonstrate the utility of using fMRI to investigate the neural substrates of higher-level cognitive processes such as discourse comprehension.
Mutations in genes potentially lead to a number of genetic diseases with differing severity. These disease genes have been the focus of research in recent years showing that the disease gene population as a whole is not homogeneous, and can be categorized according to their interactions. Locus heterogeneity describes a single disorder caused by mutations in different genes each acting individually to cause the same disease. Using datasets of experimentally derived human disease genes and protein interactions, we created a protein interaction network to investigate the relationships between the products of genes associated with a disease displaying locus heterogeneity, and use network parameters to suggest properties that distinguish these disease genes from the overall disease gene population. Through the manual curation of known causative genes of 100 diseases displaying locus heterogeneity and 397 single-gene Mendelian disorders, we use network parameters to show that our locus heterogeneity network displays distinct properties from the global disease network and a Mendelian network. Using the global human proteome, through random simulation of the network we show that heterogeneous genes display significant interconnectivity. Further topological analysis of this network revealed clustering of locus heterogeneity genes that cause identical disorders, indicating that these disease genes are involved in similar biological processes. We then use this information to suggest additional genes that may contribute to diseases with locus heterogeneity.
locus heterogeneity; protein interaction network; systems biology; Bardet–Biedl syndrome; Leigh syndrome; Kabuki syndrome
African green monkeys (AGMs) are naturally infected with simian immunodeficiency virus (SIV) at high prevalence levels and do not progress to AIDS. Sexual transmission is the main transmission route in AGM, while mother-to-infant transmission (MTIT) is negligible. We investigated SIV transmission in wild AGMs to assess whether or not high SIV prevalence is due to differences in mucosal permissivity to SIV (i.e., whether the genetic bottleneck of viral transmission reported in humans and macaques is also observed in AGMs in the wild). We tested 121 sabaeus AGMs (Chlorocebus sabaeus) from the Gambia and found that 53 were SIV infected (44%). By combining serology and viral load quantitation, we identified 4 acutely infected AGMs, in which we assessed the diversity of the quasispecies by single-genome amplification (SGA) and documented that a single virus variant established the infections. We thus show that natural SIV transmission in the wild is associated with a genetic bottleneck similar to that described for mucosal human immunodeficiency virus (HIV) transmission in humans. Flow cytometry assessment of the immune cell populations did not identify major differences between infected and uninfected AGM. The expression of the SIV coreceptor CCR5 on CD4+ T cells dramatically increased in adults, being higher in infected than in uninfected infant and juvenile AGMs. Thus, the limited SIV MTIT in natural hosts appears to be due to low target cell availability in newborns and infants, which supports HIV MTIT prevention strategies aimed at limiting the target cells at mucosal sites. Combined, (i) the extremely high prevalence in sexually active AGMs, (ii) the very efficient SIV transmission in the wild, and (iii) the existence of a fraction of multiparous females that remain uninfected in spite of massive exposure to SIV identify wild AGMs as an acceptable model of exposed, uninfected individuals.
IMPORTANCE We report an extensive analysis of the natural history of SIVagm infection in its sabaeus monkey host, the African green monkey species endemic to West Africa. Virtually no study has investigated the natural history of SIV infection in the wild. The novelty of our approach is that we report for the first time that SIV infection has no discernible impact on the major immune cell populations in natural hosts, thus confirming the nonpathogenic nature of SIV infection in the wild. We also focused on the correlates of SIV transmission, and we report, also for the first time, that SIV transmission in the wild is characterized by a major genetic bottleneck, similar to that described for HIV-1 transmission in humans. Finally, we report here that the restriction of target cell availability is a major correlate of the lack of SIV transmission to the offspring in natural hosts of SIVs.
Protein interactions from painful states form a coherent network that can be used to inform further study. We identify proteins key to painful subnetworks.
Understanding the molecular mechanisms associated with disease is a central goal of modern medical research. As such, many thousands of experiments have been published that detail individual molecular events that contribute to a disease. Here we use a semi-automated text mining approach to accurately and exhaustively curate the primary literature for chronic pain states. In so doing, we create a comprehensive network of 1,002 contextualized protein–protein interactions (PPIs) specifically associated with pain. The PPIs form a highly interconnected and coherent structure, and the resulting network provides an alternative to those derived from connecting genes associated with pain using interactions that have not been shown to occur in a painful state. We exploit the contextual data associated with our interactions to analyse subnetworks specific to inflammatory and neuropathic pain, and to various anatomical regions. Here, we identify potential targets for further study and several drug-repurposing opportunities. Finally, the network provides a framework for the interpretation of new data within the field of pain.
Networks; Protein–protein interactions; Gene expression; Neuropathic pain; Inflammatory pain; Text mining
With 29 individual antiretroviral drugs available from six classes that are approved for the treatment of HIV-1 infection, a combination of different phenotypic and genotypic tests is currently needed to monitor HIV-infected individuals. In this study, we developed a novel HIV-1 genotypic assay based on deep sequencing (DeepGen HIV) to simultaneously assess HIV-1 susceptibilities to all drugs targeting the three viral enzymes and to predict HIV-1 coreceptor tropism. Patient-derived gag-p2/NCp7/p1/p6/pol-PR/RT/IN- and env-C2V3 PCR products were sequenced using the Ion Torrent Personal Genome Machine. Reads spanning the 3′ end of the Gag, protease (PR), reverse transcriptase (RT), integrase (IN), and V3 regions were extracted, truncated, translated, and assembled for genotype and HIV-1 coreceptor tropism determination. DeepGen HIV consistently detected both minority drug-resistant viruses and non-R5 HIV-1 variants from clinical specimens with viral loads of ≥1,000 copies/ml and from B and non-B subtypes. Additional mutations associated with resistance to PR, RT, and IN inhibitors, previously undetected by standard (Sanger) population sequencing, were reliably identified at frequencies as low as 1%. DeepGen HIV results correlated with phenotypic (original Trofile, 92%; enhanced-sensitivity Trofile assay [ESTA], 80%; TROCAI, 81%; and VeriTrop, 80%) and genotypic (population sequencing/Geno2Pheno with a 10% false-positive rate [FPR], 84%) HIV-1 tropism test results. DeepGen HIV (83%) and Trofile (85%) showed similar concordances with the clinical response following an 8-day course of maraviroc monotherapy (MCT). In summary, this novel all-inclusive HIV-1 genotypic and coreceptor tropism assay, based on deep sequencing of the PR, RT, IN, and V3 regions, permits simultaneous multiplex detection of low-level drug-resistant and/or non-R5 viruses in up to 96 clinical samples. This comprehensive test, the first of its class, will be instrumental in the development of new antiretroviral drugs and, more importantly, will aid in the treatment and management of HIV-infected individuals.
Our previous gene expression microarray studies identified a number of genes differentially expressed in patients with type 1 diabetes (T1D) and islet autoantibody-positive subjects. This study was designed to validate these gene expression changes in T1D patients and to identify gene expression changes in diabetes complications.
RESEARCH DESIGH AND METHODS
We performed high-throughput real-time RT-PCR to validate gene expression changes in peripheral blood mononuclear cells (PBMCs) from a large sample set of 928 T1D patients and 922 control subjects.
Of the 18 genes analyzed here, eight genes (S100A8, S100A9, MNDA, SELL, TGFB1, PSMB3, CD74, and IL12A) had higher expression and three genes (GNLY, PSMA4, and SMAD7) had lower expression in T1D patients compared with control subjects, indicating that genes involved in inflammation, immune regulation, and antigen processing and presentation are significantly altered in PBMCs from T1D patients. Furthermore, one adhesion molecule (SELL) and three inflammatory genes mainly expressed by myeloid cells (S100A8, S100A9, and MNDA) were significantly higher in T1D patients with complications (odds ratio [OR] 1.3–2.6, adjusted P value = 0.005–10−8), especially those patients with neuropathy (OR 4.8–7.9, adjusted P value <0.005).
These findings suggest that inflammatory mediators secreted mainly by myeloid cells are implicated in T1D and its complications.
Motivation: As a natural consequence of being a computer-based discipline, bioinformatics has a strong focus on database and software development, but the volume and variety of resources are growing at unprecedented rates. An audit of database and software usage patterns could help provide an overview of developments in bioinformatics and community common practice, and comparing the links between resources through time could demonstrate both the persistence of existing software and the emergence of new tools.
Results: We study the connections between bioinformatics resources and construct networks of database and software usage patterns, based on resource co-occurrence, that correspond to snapshots of common practice in the bioinformatics community. We apply our approach to pairings of phylogenetics software reported in the literature and argue that these could provide a stepping stone into the identification of scientific best practice.
Availability and implementation: The extracted resource data, the scripts used for network generation and the resulting networks are available at http://bionerds.sourceforge.net/networks/
A cardinal manifestation of chronic autonomic failure is neurogenic orthostatic hypotension (OH), which often is associated with supine hypertension, posing a therapeutic dilemma. We report here success in a first step toward development of a “prosthetic baroreceptor system” to maintain blood pressure during orthostasis without worsening supine hypertension. In all of four patients with neurogenic OH, titrated i.v. NE infusion kept directly recorded intra-arterial pressure at or above baseline during progressive head-up tilt. We conclude that titrated i.v. NE infusion temporarily eliminates OH.
Norepinephrine; Orthostatic hypotension; Sympathetic nervous system; Baroreflex
Recently we reported that gold nanoparticles (AuNPs) inhibit ovarian tumor growth and metastasis in mice by reversing epithelial-mesenchymal transition (EMT). Since EMT is known to confer drug resistance to cancer cells, we wanted to investigate whether anti-EMT property of AuNP could be utilized to sensitize ovarian cancer cells to cisplatin. Herein, we report that AuNPs prevent cisplatin-induced acquired chemoresistance and stemness in ovarian cancer cells and sensitize them to cisplatin. AuNPs inhibit cisplatin induced EMT, decrease the side population cells and key stem cell markers such as ALDH1, CD44, CD133, Sox2, MDR1 and ABCG2 in ovarian cancer cells. Mechanistically, AuNPs prevent cisplatin-induced activation of Akt and NF-κB signaling axis in ovarian cancer cells that are critical for EMT, stem cell maintenance and drug resistance. In vivo, AuNPs sensitize orthotopically implanted ovarian tumor to a low dose of cisplatin and significantly inhibit tumor growth via facilitated delivery of both AuNP and cisplatin. These findings suggest that by depleting stem cell pools and inhibiting key molecular pathways gold nanoparticles sensitize ovarian cancer cells to cisplatin and may be used in combination to inhibit tumor growth and metastasis in ovarian cancer.
gold nanoparticle; chemoresistance; cancer stem cell; EMT; NF-κB
Severely affected patients with autonomic failure require pressor agents to counteract the blood pressure fall and improve presyncopal symptoms upon standing. Previous studies suggest that combination ergotamine and caffeine may be effective in the treatment of autonomic failure, but the efficacy of this drug has not been evaluated in controlled trials. Therefore, we compared the effects of ergotamine/caffeine on seated blood pressure and orthostatic tolerance and symptoms in 12 primary autonomic failure patients without history of coronary artery disease. Patients were randomized to receive a single oral dose of placebo, midodrine (5–10 mg), or ergotamine and caffeine (1 and 100 mg, respectively) in a single-blind, crossover study. Blood pressure was measured while patients were seated and after standing for up to 10 min, at baseline and at 1 h post-drug. Ergotamine/caffeine increased seated systolic blood pressure (SBP), the primary outcome, compared with placebo (131 ± 19 and 95 ± 12 mmHg, respectively, at 1 h post-drug; p = 0.003 for time effect). Midodrine also significantly increased seated SBP (121 ± 19 mmHg at 1 h post-drug; p = 0.015 for time effect vs. placebo), but this effect was not different from ergotamine/caffeine (p = 0.621). There was no significant effect of either medication on orthostatic tolerance; however, ergotamine/caffeine improved presyncopal symptoms (p = 0.034). These findings suggest that combination ergotamine and caffeine elicits a seated pressor response that is similar in magnitude to midodrine, and improves symptoms in autonomic failure. Thus, ergotamine/caffeine could be used as an alternate treatment for autonomic failure, in carefully selected patients without comorbid coronary artery disease.
autonomic failure; orthostatic hypotension; ergotamine; caffeine; pressor agent
No available treatments slow or halt progression of multiple system atrophy, which is a rare, progressive, fatal neurological disorder. In a mouse model of multiple system atrophy, rifampicin inhibited formation of α-synuclein fibrils, the neuropathological hallmark of the disease. We aimed to assess the safety and efficacy of rifampicin in patients with multiple system atrophy.
In this randomised, double-blind, placebo-controlled trial we recruited participants aged 30–80 years with possible or probable multiple system atrophy from ten US medical centres. Eligible participants were randomly assigned (1:1) via computer-generated permuted block randomisation to rifampicin 300 mg twice daily or matching placebo (50 mg riboflavin capsules), stratified by subtype (parkinsonian vs cerebellar), with a block size of four. The primary outcome was rate of change (slope analysis) from baseline to 12 months in Unified Multiple System Atrophy Rating Scale (UMSARS) I score, analysed in all participants with at least one post-baseline measurement. This study is registered with ClinicalTrials.gov, number NCT01287221.
Between April 22, 2011, and April 19, 2012, we randomly assigned 100 participants (50 to rifampicin and 50 to placebo). Four participants in the rifampicin group and five in the placebo group withdrew from study prematurely. Results of the preplanned interim analysis (n=15 in each group) of the primary endpoint showed that futility criteria had been met, and the trial was stopped (the mean rate of change [slope analysis] of UMSARS I score was 0·62 points [SD 0·85] per month in the rifampicin group vs 0·47 points [0·48] per month in the placebo group; futility p=0·032; efficacy p=0·76). At the time of study termination, 49 participants in the rifampicin group and 50 in the placebo group had follow-up data and were included in the final analysis. The primary endpoint was 0·5 points (SD 0·7) per month for rifampicin and 0·5 points (0·5) per month for placebo (difference 0·0, 95% CI –0·24 to 0·24; p=0·82). Three (6%) of 50 participants in the rifampicin group and 12 (24%) of 50 in the placebo group had one or more serious adverse events; none was thought to be related to treatment.
Our results show that rifampicin does not slow or halt progression of multiple system atrophy. Despite the negative result, the trial does provide information that could be useful in the design of future studies assessing potential disease modifying therapies in patients with multiple system atrophy.
National Institutes of Health, Mayo Clinic Center for Translational Science Activities, and Mayo Funds.
Inappropriate sinus tachycardia (IST) and postural tachycardia syndrome (POTS) are 2 disorders characterized by sinus tachycardia. It is debated whether the pathophysiology of IST and POTS results from abnormal autonomic regulation or abnormal sinus node function. We hypothesized that intrinsic heart rate (IHR) after autonomic blockade would be increased in patients with IST but not POTS.
Methods and Results
We enrolled 48 POTS patients, 8 IST patients, and 17 healthy control (HC) subjects. Intravenous propranolol and atropine were given to block the sympathetic and parasympathetic limbs of the autonomic nervous system in order to determine the IHR. Patients with IST have a higher sympathetic contribution to heart rate when compared with POTS patients (31±13 bpm versus 12±7 bpm, P<0.001) and HC (8±4 bpm; P<0.001) and a trend to less parasympathetic contribution than POTS and HC (IST: 31±11 bpm versus POTS: 46±11 bpm versus HC: 48±11 bpm, ANOVA P=0.108). IHR was not significantly different between IST and either POTS or HC (IST: 111±11 bpm versus POTS: 108±11 bpm versus HC: 106±12 bpm, ANOVA P=0.237).
IST patients have more sympathetic tone when compared with either POTS or HC, but IST patients do not have abnormal sinus node automaticity. These data suggest that the treatment of IST and POTS should focus on sympatholysis, reserving sinus node modification for patients with continued debilitating symptoms after beta‐blockade and possibly ivabradine.
Clinical Trial Registration
URL: http://clinicaltrials.gov/. Unique identifier: NCT00262470.
autonomic nervous system; inappropriate sinus tachycardia; postural tachycardia syndrome; sinus node; sympathetic nervous system
At least half of primary autonomic failure patients exhibit supine hypertension, despite profound impairments in sympathetic activity. While the mechanisms underlying this hypertension are unknown, plasma renin activity is often undetectable suggesting renin-angiotensin pathways are not involved. However, because aldosterone levels are preserved, we tested the hypothesis that angiotensin II is intact and contributes to the hypertension of autonomic failure. Indeed, circulating angiotensin II was paradoxically increased in hypertensive autonomic failure patients (52±5 pg/ml, n=11) compared to matched healthy controls (27±4 pg/ml, n=10; p=0.002), despite similarly low renin activity (0.19±0.06 versus 0.34±0.13 ng/ml/hr, respectively; p=0.449). To determine the contribution of angiotensin II to supine hypertension in these patients, we administered the AT1 receptor blocker losartan (50 mg) at bedtime in a randomized, double-blind, placebo-controlled study (n=11). Losartan maximally reduced systolic blood pressure by 32±11 mmHg at 6 hours after administration (p<0.05), decreased nocturnal urinary sodium excretion (p=0.0461), and did not worsen morning orthostatic tolerance. In contrast, there was no effect of the captopril on supine blood pressure in a subset of these patients. These findings suggest that angiotensin II formation in autonomic failure is independent of plasma renin activity, and perhaps angiotensin converting enzyme. Furthermore, these studies suggest that elevations in angiotensin II contribute to the hypertension of autonomic failure, and provide rationale for the use of AT1 receptor blockers for treatment of these patients.
autonomic nervous system; hypertension; angiotensin; drugs; natriuresis
We report a case of a 55 year old man with non-small cell lung cancer who underwent radiation, chemotherapy with carbotaxol and paclitaxel, and left upper lobe removal two years prior to evaluation. He was referred for disabling orthostatic hypotension (113/69 supine, 66/47 mmHg standing after 10 minutes without a compensatory heart rate increase (57 to 59 bpm), fatigue, and constipation with episodes of ileus. Clinical examination showed mild ptosis bilaterally, fatiguable neck flexor weakness and hip flexor weakness. Blood pressure response to Valsalva maneuver was abnormal with absence of phase 4 overshoot and a Valsalva heart rate ratio of 1.04, The plasma norepinephrine level was low (79 pg/ml supine to 330 pg/ml standing). Single fiber EMG of the right extensor digitorum communis revealed normal mean MCD (jitter) but several pairs exceeded a jitter of 100 µs. Antibodies against muscle acetylcholine receptor [(AChR) 0.66 nmol/L, normal <0.02] and ganglionic AChR (0.34 nmol/L, normal <0.02) were present. Treatment with plasma exchange normalized responses to standing posture (105/68 supine to 118/82 mmHg standing, 66 to 79 bpm), to Valsalva (normal blood pressure overshoot, HR ratio 1.47), norepinephrine (194 pg/ml supine, 763 standing), and jitter measurements. We conclude that autoimmune autonomic ganglionopathy and myasthenia gravis can coexist and suggest that the latter should be excluded in patients with autoimmune autonomic ganglionopathy who complain of fatigue that is improved with non-supine rest.
autoimmune autonomic ganglionopathy; myasthenia gravis; paraneoplastic syndrome
Obstructive sleep apnea (OSA) has been hypothesized to cause a hypersympathetic state, which may be the mechanism for the increased incidence of cardiovascular disease in OSA. However, there is a high prevalence of hyperglycemia in OSA patients which may also contribute to autonomic dysfunction.
Thirty-five patients with OSA and eleven controls with average body-mass index (BMI) of 32.0 ± 4.6 underwent polysomnography, glucose tolerance testing, autonomic function tests, lying and standing catecholamines, overnight urine collection, and baseline ECG and continuous blood pressure measurements for spectral analysis. A linear regression model adjusting for age and BMI was used to analyze spectral data, other outcome measures were analyzed with Kruskal-Wallis test.
Twenty-three OSA patients and two control patients had hyperglycemia (based on 2001 American Diabetes Association criteria). AHI correlated with total power and low frequency (LF) power (r=0.138, 0.177, p=0.031; and r= 0.013) but not with the LF/high frequency (HF) ratio (p=0.589). Glucose negatively correlated with LF systolic power (r=-0.171, p=0.038) but not AHI (p=0.586) and was marginally associated with pnn50, total power, LF, and HF power (p ranged from 0.07 to 0.08).
These data suggest that patients with OSA and mild hyperglycemia have a trend towards lower heart rate variability and sympathetic tone. Hyperglycemia is an important confounder and should be evaluated in studies of OSA and autonomic function.
To study the role of nitric oxide (NO) on cardiovascular regulation
in healthy subjects and postural tachycardia syndrome (POTS) patients.
Both reduced neuronal NO function, which could contribute to a
hyperadrenergic state, and increased NO-induced vasodilation, which could
contribute to orthostatic intolerance, have been reported in POTS.
In protocol 1, 13 healthy volunteers (33±3 years) underwent
autonomic blockade with trimethaphan and were administered equipressor doses
of L-NMMA (NO synthase inhibitor) and phenylephrine to determine the direct
chronotropic effects of NO (independent of baroreflex modulation). In
protocol 2, we compared the effects of L-NMMA in 9 POTS patients
(31±3 years) and 14 healthy (32±2 years) volunteers during
During autonomic blockade, L-NMMA and phenylephrine produced similar
increases in systolic blood pressure (SBP; 27±2 vs. 27±3
mmHg). Phenylephrine produced only minimal heart rate (HR) changes, whereas
L-NMMA produced a modest but significant bradycardia (−0.8±0.4
vs. −4.8±1.2 bpm, p=0.011). There were no differences between
POTS and healthy volunteers in the SBP increase (22±2 and 28±5
mmHg) or HR decrease (−6±2 and −4±1 bpm for POTS
and controls, respectively) produced by L-NMMA.
In the absence of baroreflex buffering, inhibition of endogenous NO
synthesis results in a significant bradycardia, reflecting direct tonic
modulation of heart rate by NO in healthy individuals. We found no evidence
of a primary alteration in NO function in POTS. If NO dysfunction plays a
role in POTS it is through its interaction with the autonomic nervous
Nitric Oxide; Postural Tachycardia Syndrome; Autonomic Nervous System; Autonomic Blockade; Heart Rate; blood pressure