Vikram K. Yeragani's research while affiliated with University of Alberta and other places

Publications (206)

Article
Posttraumatic stress disorder is a chronic, debilitating condition that has become a growing concern among combat veterans. Previous research suggests that posttraumatic stress disorder disrupts normal autonomic responding and may increase the risk of cardiovascular disease and mortality. Measures of heart rate variability and QT interval variabili...
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Depressive disorders are known to be associated with higher risks of cardiovascular diseases. Several studies have reported an imbalance within the autonomic nervous system (ANS) as one putative cause. Previous investigations showed decreased cardio-respiratory coupling in depressive patients that were treated with nortriptyline. We aimed to compar...
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We investigated to what degree tonic skin conductance levels (SCL) and cardiac autonomic dysfunction are interrelated in schizophrenia. Heart rate variability (HRV) and SCL were simultaneously assessed in 18 unmedicated patients and 18 controls matched for age, sex, weight, and smoking habits. For comparison to prior studies, phasic sympathetic ski...
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African Americans bear a disproportionate burden of hypertension with racism postulated as a unique stressor contributing to the noted disparities. Epidemiological studies have found differences in the prevalence of hypertension among African Americans based on the amount of perceived racism reported, and experimental studies have shown increased c...
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Increased mortality in anorexia nervosa is associated with autonomic dysfunction and prolongation of the QT interval. In this study, we examined the relative importance of repolarization abnormalities and vagal modulation of heart rate. In particular, we hypothesized that patients with anorexia nervosa show increased QT interval variability, partic...
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Major depressive disorder is associated with increased cardiac mortality. A decrease in vagal modulation related to reduced heart rate variability might contribute to increased mortality among many other factors. We sought to examine the hypothesis that nortriptyline treatment will be associated with a decrease in heart rate variability and couplin...
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Various measures of autonomic function have been developed, and their applicability and significance during exercise are controversial. Physiological data were therefore obtained from 23 sport students before, during, and after exercise. Measures of R-R interval variability, QT variability index (QTvi), and electrodermal activity (EDA) were calcula...
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Age has been identified as an independent risk factor for cardiovascular diseases. In addition, autonomic imbalance toward sympathetic preponderance has been shown to facilitate the occurrence of heart disease. Here, we aimed to assess autonomic modulation of cardiovascular parameters during normal ageing applying well-established linear and novel...
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Previous studies have observed reduced vagal modulation in patients with acute schizophrenia and their first-degree relatives, thus suggesting a genetic predisposition. To investigate vagal modulation, we analyzed the coupling between heart rate and breathing as a putative measure of central autonomic function in 19 patients, 19 of their relatives...
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Introduction Bipolar disorder (BD) type I is characterised by the occurrence of one or more manic or mixed episodes, and although a depressive episode is not always required for a diagnosis, virtually all patients experience depressive episodes, often more commonly than manic episodes. Bipolar disorder type II is characterised by the occurrence of...
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Recent studies applying functional magnetic resonance imaging have focused on the description of cerebral substrates of changes in cardiac function during diverse autonomic maneuvers or stressful cognitive tasks. These studies might be limited by the indistinguishable neuronal activity due to cognitive processes, which are known to influence autono...
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Somatic symptoms of the gastrointestinal tract occur frequently in major depressive disorder (MDD) and might be associated with the known autonomic imbalance in the disease. Hence, we have investigated gastric electrical activity in patients suffering from major depression before and after treatment by means of electrogastrography (EGG) to investig...
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To investigate cardiac autonomic dysfunction in patients with major depressive disorder (MDD). Research in this area has faced several limitations because of the heterogeneity of the disease, the influence of medication, and methodological shortcomings. Participants were 75 patients suffering from an acute recurrent episode of MDD and 75 matched co...
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Cardiac autonomic dysfunction has been reported in patients suffering from schizophrenia. The aim of the present study was to evaluate gastric electrical activity in unmedicated patients suffering from acute schizophrenia in relation to their symptoms. Electrogastrography was performed before and after test meal ingestion in 26 patients suffering f...
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To understand the significance of cardiac autonomic function in patients with schizophrenia, we extended these studies to relatives of patients. In this study, we assessed cardiac and gastric autonomic modulation in healthy first-degree relatives, patients and controls. First-degree relatives showed decreased vagal modulation of heart rate, decrea...
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Though increased risk of sudden death in patients with schizophrenia is well-documented, the mechanisms remain unclear. Recent studies report two known risk factors for sudden cardiac death and other arrhythmias in schizophrenia, i.e., decreased RR interval variability (RRV) and increased QT interval variability (QTV). However, these studies did no...
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Full-text available
Recent studies revealed cardiac autonomic dysfunction in patients with acute schizophrenia, which appears to be mainly related to reduced vagal and increased sympathetic modulation. To understand the significance of cardiac autonomic function in patients with schizophrenia, we extended these studies to relatives of patients. In this study, we asses...
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Altered amygdala activity in patients with schizophrenia can influence respiratory patterns and consequently cardiovascular parameters. Hence, we examined respiration and heart rate time series complexity as well as coupling of both signals. Electrocardiograms and respiratory signals were obtained from 25 unmedicated patients with schizophrenia and...
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Information on autonomic modulation can be derived from different organs that are innervated by the sympathetic and the parasympathetic nervous system, when assessing e.g. heart rate or blood pressure fluctuations or the pupil's reaction to light. Correlations between parameters from different target organs might reveal information on hierarchicall...
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Full-text available
Frontotemporal dementia (FTD) is a progressive neurodegenerative syndrome occurring between 45 and 65 years. The syndrome is also called frontotemporal lobar degeneration (FTLD). However, FTLD refers to a larger group of disorders FTD being one of its subgroups. The other subgroups of FTLD are progressive nonfluent aphasia (PFNA), and semantic deme...
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Previous studies have shown that untreated patients with acute schizophrenia present with reduced heart rate variability and complexity as well as increased QT variability. This autonomic dysregulation might contribute to increased cardiac morbidity and mortality in these patients. However, the additional effects of newer antipsychotics on autonomi...
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In patients with panic disorder, an anxiety disorder, isoproterenol increases beat-to-beat QRS amplitude variability much more than in normal controls. In this pilot study, we found that patients with panic disorder had significantly higher beat-to-beat QRS amplitude variability compared to controls in resting supine and standing postures. This may...
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We have previously shown that nonlinear measures of regularity and complexity are very useful as complimentary measures to the linear measures of time and frequency domain of beat-to-beat heart rate and QT intervals. In this study, we have applied Cross-ApEn, a nonlinear measure that can give an index of dissociation between two time series. We hav...
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Background: Chronic alcoholism represents a risk factor for cardiac arrhythmias. One underlying mechanism is a sympathetically dominated autonomic imbalance. This is especially apparent during acute withdrawal from alcohol. Since linear analysis of heart rate variability may not be entirely adequate to detect such autonomic dysfunction in acute al...
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Cardiac autonomic dysregulation has been reported in patients with schizophrenia. However, there are no definite data examining whether other branches of the autonomic nervous system are compromised as well and how they interrelate with cardiac function. In this study, we tested the hypothesis that the autonomic dysregulation at the heart is reflec...
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Cardiac mortality is known to be increased in depressive patients. However, the underlying mechanisms remain elusive to date. Decreased heart rate variability (HRV) has been discussed as contributing to increased cardiac mortality, but studies examining patients suffering from major depressive disorder (MDD) have revealed inconsistent results. This...
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Depressed patients frequently complain about vegetative symptoms. The aim of the present study was to evaluate gastric electrical activity in patients suffering from major depression in relation to their symptoms. Electrogastrography (EGG) was performed before and after a test meal ingestion in 21 patients suffering from major depression and contro...
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This article examines some of the findings from recent studies on cardiac autonomic function and the effects of exercise in women. Exercise, in general, induces a state of cardiovascular vagal predominance, which is beneficial to health. This area of research is especially important in relation to the neurohormonal influences on cardiovascular func...
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In patients with ischemic heart disease, dobutamine provoked-stress increases beat-to-beat QRS amplitude variability, which may be due to an electrical instability of the myocardium. Our results in this pilot study showed that patients with congestive heart failure had significantly higher beat-to-beat QRS amplitude variability compared to controls...
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Cardiovascular mortality is significantly increased in patients suffering from schizophrenia. The mechanisms currently discussed contain unhealthy lifestyle with obesity and smoking, increased incidence of diabetes, adverse pro-arrhythmic effects of antipsychotic medication and altered autonomic function. It is therefore likely that the adaptation...
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Patients with schizophrenia have been reported to experience sudden cardiac death 3 times more likely than individuals from the general population. One important factor related to an increased risk of cardiac arrhythmias and sudden death is the prolongation of the QTc interval. This study examined whether acute psychosis might influence the beat-to...
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Acute alcohol withdrawal is associated with increased cardiovascular mortality, most likely due to cardiac arrhythmias. As the QT interval reflects the most critical phase for the generation of reentry and thus for arrhythmia, we examined QT variability in patients suffering from acute alcohol withdrawal. High resolution electrocardiographic record...
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Full-text available
Decreased vagal activity has been described in acute schizophrenia and might be associated with altered cardiovascular regulation and increased cardiac mortality. The aim of this study was to assess baroreflex sensitivity in the context of psychopathology. Twenty-one acute, psychotic, unmedicated patients with a diagnosis of paranoid schizophrenia...
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Anxiety symptoms are associated with a marked increase in sudden cardiac death, suggesting an abnormality in cardiac autonomic function. Our previous studies show a relationship between R amplitude variability and sympathetic function. We examined the effects of beta-adrenergic stimulation on R and T amplitude variability in panic disorder patients...
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This study aimed to further investigate autonomic function in schizophrenic patients using long-term electrocardiographic (ECG) recordings. Twenty unmedicated patients suffering from an acute episode of paranoid schizophrenia and 20 matched control subjects were recruited and 24-h ambulatory electrocardiograms were recorded. In order to investigate...
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Several psychiatric conditions are associated with frequent fluctuations of affect. In this study, we propose a new technique to uniformly score depression and mania objectively and use a new mathematical technique to model the frequent fluctuations in mood using simulated data. Our main aim is to examine the usefulness of this measure for evaluati...
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QT interval on the surface electrocardiogram reflects the time for repolarization of myocardium. Prolongation of rate-corrected QT interval, QTc is strongly associated with sudden cardiac death. Recent studies using novel techniques on beat-to-beat QT interval variability have shown that an increase in QT interval variability is associated with inc...
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QT interval on the surface electrocardiogram (ECG) reflects the time for repolarization of myocardium and prolongation of QTc is strongly associated with sudden cardiac death. Studies using novel techniques on beat-to-beat QT interval variability (QTV) have shown that it is influenced by the autonomic nervous system and is a predictor of sudden car...
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Administration of caffeine in the evening produces poor sleep. Patients with insomnia have characteristic electrocardiogram (ECG) changes, including increased heart rate (HR), increased sympathetic activity, and decreased parasympathetic activity. Fifteen young adult normal subjects slept in the laboratory for several nights prior to randomization...
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Caffeine intake is associated with an increase in heart rate (HR) variability. This study sought to examine the effects of caffeine on HR variability measures before and during progressive exercise in 11 healthy volunteers in a double-blind randomized and counterbalanced placebo-controlled paradigm. As expected, there were significant increases in...
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In this study, we investigated spectral measures and measures of nonlinear dynamics and chaos of heart rate (HR) time series in 10 normal controls and 10 patients with panic disorder (a condition associated with anxiety) during awake and sleep periods and 28 normal control subjects and 42 age-matched patients with panic disorder, in supine and stan...
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In this study, we analyzed heart rate variability during sexual activity using complex demodulation, which is a useful technique to study continuous changes in different frequency bands over short periods of time. Complex demodulation has the advantage of having higher time resolution compared to spectral analysis. We quantified the low frequency (...
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We investigated the effects of treatment with the tricyclic antidepressant (TCA) imipramine in eight children in supine and standing postures. We used 256 seconds of real-time data for the analyses. Spectral analysis showed a significant decrease of high-frequency (HF) power (0.15-0.5 Hz), especially in the standing posture. Low frequency (LF) HF r...
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Full-text available
Panic disorder is associated with an elevated risk of cardiovascular disease and sudden death. Individuals with panic disorder have been shown to have reduced variability in heart rate and increased variability in the QT interval on electrocardiogram (ECG), patterns predictive of sudden cardiac death in certain forms of cardiomyopathy. Given that p...
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Arterial blood pressure (BP) variability increases progressively with the development of hypertension and an increase in BP variability is associated with end organ damage and cardiovascular morbidity. On the other hand, a decrease in heart rate (HR) variability is associated with significant cardiovascular mortality. There is a strong association...
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Several psychiatric conditions are associated with lability of affect. In this study, we investigated regularity of mood using APEN (Approximate Entropy) on daily subjective ratings using a Visual Analog Scale with 11 items pertaining to mood. APEN was applied to the data in a double-blind placebo controlled investigation on the effects of fluoxeti...
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1. Background: The post-exercise period is associated with a profound decrease in sympathetic activity and arterial pressure. We have recently shown that endurance exercise training in rats is associated with highly significant decreases of low frequency (LF: 0.19–) power of blood pressure (BP). In this study, we measured cardiac output (CO) and sy...
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Background: Endurance exercise is associated with a decrease in post-exercise sympathetic nerve activity (SNA) and arterial pressure (AP) in humans and experimental animals. In this study, we measured pulsatile arterial pressure continuously for at least 5min in rats before (n=22) and after 8 weeks of daily exercise (n=10) exercise. The purpose of...
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Full-text available
Clinical depression is a risk factor for cardiac mortality in patients with coronary heart disease. High QT interval variability is a risk factor for arrhythmic events, including sudden cardiac death. The purpose of this study was to determine whether depression is associated with increased QT variability in patients recovering from myocardial infa...
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Studies have linked depression to sudden death and serious cardiovascular events in patients with preexisting cardiac illness. Recent studies have shown decreased vagal function in cardiac patients with depression and depressed patients without cardiac illness. We compared 20-hour, sleeping, and awake heart period variability measures using spectra...
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Stationarity is an important methodological issue while computing any linear or nonlinear measures. While one generally assumes that nonstationarity is not desirable for the computation of several measures including spectral analysis, little is known about the physiological basis of stationarity, while analyzing biological signals such as heart rat...
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This study was designed to test the hypothesis that daily spontaneous running (DSR) reduces measures of heart rate and blood pressure variability in spontaneously hypertensive rats (SHR). After 8 weeks of DSR or sedentary control, rats were chronically instrumented with arterial catheters. Daily exercise reduced most measures of heart rate (HR) and...
Article
Depression is associated with increased cardiovascular mortality in patients with preexisting cardiac illness. A decrease in cardiac vagal function as suggested by a decrease in heart rate variability (HRV) or heart period variability has been linked to sudden death in patients with cardiac disease as well as in normal controls. Recent studies have...
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There is increasing evidence supporting the additional utility of nonlinear techniques such as chaos analysis of heart rate (HR) time series as indictors of prognosis in cardiac patients. Prolongation of rate-corrected QT interval, QTc, is strongly associated with sudden cardiac death. Recent studies of beat-to-beat QT interval variability (QTV) ha...
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This study examined the differences of heart rate variability measures between children of parents with panic disorder and children of healthy controls using linear as well as nonlinear techniques. Supine and standing heart rate variability indices were measured in all children using power spectral analysis and a measure of chaos, the largest Lyapu...
Article
Anxiety symptoms are associated with a marked increase in sudden cardiac death, suggesting an abnormality in the autonomic control of the heart. We examined the effects of sympathetic stimulation on QT interval variability in panic disorder patients by infusing the ss-adrenergic agonist isoproterenol in 6 panic disorder patients and 11 normal subje...
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R. Cohen. A time domain approach for the fluctuation analysis of heart rate related to instantaneous lung volume. IEEE Trans. Biomed. Eng., 40(1):74--81, 1993. [164] G. Yang and T. Chen. On statistical methods in neuronal spike-train analysis. Mathematical Biosciences, 38:1--34, 1978. [165] V. Yeragani, R. Balon, C. Ramesh, D. Glitz, P. Weinberg, a...
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Excess cardiovascular morbidity has been reported in association with phobic anxiety as well as in association with hostility and type-A behavior. The aim of this study was to investigate the relationship between the measures of hostility and type-A behavior, and heart period (HP) and QT variability in normal controls and patients with panic disord...
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This study compared beat-to-beat heart rate and QT variability in children with anxiety disorders (n = 7) and normal controls (n = 15) by using an automated algorithm to compute QT intervals. An increase in QT variability appears to be associated with a higher risk for sudden cardiac death. A decrease in heart rate variability is also linked to sig...
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Heart rate variability is influenced significantly by age. Recent studies have shown the utility of QT variability to study temporal repolarization lability, and increased QT variability is reportedly associated with sudden death. Because beat-to-beat QT interval variability appears to closely follow heart rate variability, this study investigated...
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This study investigated beat-to-beat QT variability in patients with panic disorder and depression, and normal control subjects using an automated algorithm to compute QT intervals. An increase in QT variability appears to be associated with symptomatic patients with dilated cardiomyopathy and also with an increased risk for sudden death. QT(vm) (Q...
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This study investigated measures of nonlinearity (NL) and a measure of predictability and chaoticity of heart rate time series by quantifying the Largest Lyapunov Exponent (LLE) in 23 normal control subjects (31.3 6 7.6 years) and 32 patients with a diagnosis of panic disorder (31.6 6 5.1 years). The mean supine and standing heart rates were signif...
Article
This study investigated beat-to-beat QT variability in patients with panic disorder before and after treatment with nortriptyline (n = 13) and paroxetine (n = 16), using an automated algorithm to compute QT intervals. An increase in QT variability appears to be associated with symptomatic patients with dilated cardiomyopathy and also with an increa...
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Recent literature emphasizes the utility of QT variability to study ventricular electrophysiologic function. In this investigation, we sought to test the hypothesis that beat-to-beat fluctuations in QT intervals are mediated by sympathetic activity in normal subjects using postural challenge and isoproterenol infusions. We obtained ECG in the supin...
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Time series of heart period are not linear and recent studies illustrated the importance of using nonlinear methods to quantify the complexity of these time series. We compared different techniques to quantify the nonlinear complexity of these time series in patients with panic disorder and normal controls and correlated these measures with spectra...
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We investigated cardiac autonomic function in 16 patients with panic disorder before and after treatment with paroxetine using Holter ECG records. Our previous data suggest a relative increase in sympathetic activity in patients with panic disorder, especially during sleep. Data for 20 h and awake and sleep periods were analyzed using spectral anal...