Search PubMed⌕ Search

Biomedical subjects

R Dickman

Publications and source records attributed to R Dickman.

At least 19 recordsLinked to original sources
PubMed2006

Non-cardiac chest pain: an update.

Non-cardiac chest pain (NCCP) is very common, affecting up to a quarter of the USA adult population. Recent studies have shown that the disorder has a profound impact on patient's quality of life and is associated with marked increase in utilization of healthcare resources. Non-cardiac chest pain is a heterogeneous disorder with gastrointestinal and non-gastrointestinal causes. After excluding a cardiac cause, most NCCP patients are treated by cardiologists or primary care physicians and only the minority are referred to a gastroenterologist for further work-up. Gastro-oesophageal reflux disease (GORD) is the most common cause for NCCP. The role of oesophageal dysmotility in NCCP has been discounted in recent years. However, visceral hyperalgesia has been shown to play an important role in symptom generation of non-GORD-related NCCP. The main therapeutic interventions in GORD-related NCCP patients are potent antireflux modalities and pain modulators in those with non-GORD-related NCCP.

Chest Pain↗
PubMed2006

Correlation of gastroesophageal reflux disease symptoms characteristics with long-segment Barrett's esophagus.

Thus far, there has been a paucity of studies that have assessed the value of the different gastroesophageal reflux disease (GERD) symptom characteristics in identifying patients with long-segment Barrett's esophagus versus those with short-segment Barrett's esophagus. To determine if any of the symptom characteristics of GERD correlates with long-segment Barrett's esophagus versus short-segment Barrett's esophagus. Patients seen in our Barrett's clinic were prospectively approached and recruited into the study. All patients underwent an endoscopy, validated GERD symptoms questionnaire and a personal interview. Of the 88 Barrett's esophagus patients enrolled into the study, 47 had short-segment Barrett's esophagus and 41 long-segment Barrett's esophagus. Patients with short-segment Barrett's esophagus reported significantly more daily heartburn symptoms (84.1%) than patients with long-segment Barrett's esophagus (63.2%, P = 0.02). There was a significant difference in reports of severe to very severe dysphagia in patients with long-segment Barrett's esophagus versus those with short-segment Barrett's esophagus (76.9%vs. 38.1%, P = 0.02). Longer duration in years of chest pain was the only symptom characteristic of gastroesophageal reflux disease associated with longer lengths of Barrett's mucosa. Reports of severe or very severe dysphagia were more common in long-segment Barrett's esophagus patients. Only longer duration of chest pain was correlated with longer lengths of Barrett's esophagus.

Adult↗
PubMed2005

The effect of a therapeutic trial of high-dose rabeprazole on symptom response of patients with non-cardiac chest pain: a randomized, double-blind, placebo-controlled, crossover trial.

BACKGROUND: Therapeutic trials with high-dose lansoprazole and omeprazole have been shown to be sensitive clinical tools for diagnosing patients with gastro-oesophageal reflux disease-related non-cardiac chest pain. AIM: To determine the clinical value of a therapeutic trial of high-dose rabeprazole over 7 days in detecting patients with gastro-oesophageal reflux disease-related non-cardiac chest pain. METHODS: Double-blind, randomized, placebo-controlled, crossover study. Patients referred by a cardiologist after a comprehensive cardiac work-up were enrolled into the study. Oesophageal mucosal disease was determined by upper endoscopy and 24-h oesophageal pH monitoring assessed acid exposure. Patients were then randomized to either placebo or rabeprazole 20 mg am and 20 mg pm for 7 days. After a washout period of 1 week, patients crossed over to the other arm of the study for an additional 7 days. Patients completed a daily diary assessing severity and frequency of chest pain throughout the baseline, treatment and wash-out periods. The rabeprazole therapeutic trial was considered as a diagnostic tool, if chest pain scores improved > or =50% from baseline. RESULTS: Of the 35 patients enrolled, 16 (46%) were diagnosed as gastro-oesophageal reflux disease-positive and 19 (54%) as gastro-oesophageal reflux disease-negative. Of the gastro-oesophageal reflux disease-positive patients, 12 of 16 (75%) had a significant symptom improvement on rabeprazole when compared with 3 of 16 (19%) on placebo (P = 0.029). Of the gastro-oesophageal reflux disease-negative group, only two of 19 (11%) improved significantly on the medication and four of 19 (21%) on placebo (P = 0.6599). The calculated sensitivity and specificity of the rabeprazole therapeutic trial was 75% and 90%, respectively. CONCLUSIONS: A rabeprazole therapeutic trial is highly sensitive and specific for diagnosing gastro-oesophageal reflux disease-related non-cardiac chest pain patients.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed2005

Feasibility and tolerability of transnasal/per-oral placement of the wireless pH capsule vs. traditional 24-h oesophageal pH monitoring--a randomized trial.

BACKGROUND: The wireless pH is a new technique to monitor oesophageal acid exposure. AIM: To compare the feasibility and tolerability of the wireless pH capsule vs. the traditional pH probe. METHODS: Consecutive patients referred for a pH test were enrolled into the study. Patients were randomized to traditional pH probe, or wireless pH capsule. Patients recorded their activities, food consumption, symptoms, satisfaction with the test and completed a quality of life questionnaire. RESULTS: Of the 50 patients recruited, 25 patients underwent placement of the traditional pH probe, and 25 the wireless pH capsule. Patients with the wireless pH capsule had less nose pain, runny nose, throat pain, throat discomfort and headache as compared with those with the traditional pH probe (P = 0.047, P = 0.001, P = 0.032, P = 0.001, P = 0.009, respectively). Patients in the wireless pH capsule group had more chest discomfort during the pH test (P = 0.037). Patients in the wireless pH capsule group perceived the test as interfering less with their overall daily activities, eating and sleep (P =0.001, P = 0.003, P = 0.025, respectively), and had overall satisfaction with the test (P = 0.023). CONCLUSIONS: Transnasal/per-oral placement of the wireless pH capsule is significantly better tolerated then the traditional pH probe.

Capsules↗
PubMed2003

Avalanche exponents and corrections to scaling for a stochastic sandpile.

We study distributions of dissipative and nondissipative avalanches in Manna's stochastic sandpile, in one and two dimensions. Our results lead to the following conclusions: (1) avalanche distributions, in general, do not follow simple power laws, but rather have the form P(s) approximately s(-tau(s))(ln s)(gamma)f(s/s(c)), with f a cutoff function; (2) the exponents for sizes of dissipative avalanches in two dimensions differ markedly from the corresponding values for the Bak-Tang-Wiesenfeld (BTW) model, implying that the BTW and Manna models belong to distinct universality classes; (3) dissipative avalanche distributions obey finite-size scaling, unlike in the BTW model.

Journal Article↗
PubMed2001

Critical behavior of a one-dimensional fixed-energy stochastic sandpile.

We study a one-dimensional fixed-energy version (that is, with no input or loss of particles) of Manna's stochastic sandpile model. The system has a continuous transition to an absorbing state at a critical value of the particle density, and exhibits the hallmarks of an absorbing-state phase transition, including finite-size scaling. Critical exponents are obtained from extensive simulations, which treat stationary and transient properties, and an associated interface representation. These exponents characterize the universality class of an absorbing-state phase transition with a static conserved density in one dimension; they differ from those expected at a linear-interface depinning transition in a medium with point disorder, and from those of directed percolation.

Journal Article↗
PubMed2001

Continuously variable survival exponent for random walks with movable partial reflectors.

We study a one-dimensional lattice random walk with an absorbing boundary at the origin and a movable partial reflector. On encountering the reflector at site x, the walker is reflected (with probability r) to x-1 and the reflector is simultaneously pushed to x+1. Iteration of the transition matrix, and asymptotic analysis of the probability generating function show that the critical exponent delta governing the survival probability varies continuously between 1/2 and 1 as r varies between 0 and 1. Our study suggests a mechanism for nonuniversal kinetic critical behavior, observed in models with an infinite number of absorbing configurations.

Journal Article↗
PubMed2001

First- and second-order phase transitions in a driven lattice gas with nearest-neighbor exclusion.

A lattice gas with infinite repulsion between particles separated by < or = 1 lattice spacing, and nearest-neighbor hopping dynamics, is subject to a drive favoring movement along one axis of the square lattice. The equilibrium (zero drive) transition to a phase with sublattice ordering, known to be continuous, shifts to lower density, and becomes discontinuous for large bias. In the ordered nonequilibrium steady state, both the particle and order-parameter densities are nonuniform, with a large fraction of the particles occupying a jammed strip oriented along the drive. The drive thus induces separation into high- and low-density regions in a system with purely repulsive interactions. Increasing the drive can provoke a transition to the ordered phase, and thereby, a sharp reduction in current.

Journal Article↗
PubMed2000

Pernicious anemia, gastric carcinoid, and autoimmune thrombocytopenia in a young woman.

The association between gastric carcinoid tumors and pernicious anemia is well recognized. Such tumors occur in the presence of achlorhydria, chronic atrophic gastritis, hypergastrinemia, and enterochromaffin-like cell hyperplasia. In this case report, a 29-year-old woman with pernicious anemia and autoimmune thrombocytopenia who developed gastric carcinoid tumors of the gastric body is described. This is the second description of pernicious anemia associated with autoimmune thrombocytopenia. This association in a young woman together with the therapeutic options and decisions that were taken in the treatment of the patient are discussed.

Adult↗
PubMed2000

Absorbing-state phase transitions in fixed-energy sandpiles

We study sandpile models as closed systems, with the conserved energy density zeta playing the role of an external parameter. The critical energy density zeta(c) marks a nonequilibrium phase transition between active and absorbing states. Several fixed-energy sandpiles are studied in extensive simulations of stationary and transient properties, as well as the dynamics of roughening in an interface-height representation. Our primary goal is to identify the universality classes of such models, in hopes of assessing the validity of two recently proposed approaches to sandpiles: a phenomenological continuum Langevin description with absorbing states, and a mapping to driven interface dynamics in random media.

Journal Article↗
PubMed2000

Interface scaling in the contact process

A correspondence between lattice models with absorbing states and models of pinned interfaces in random media can be established by defining local height variables h(x,t) as integrals of the activity at point x up to time t. Within this context we study the interface representation of a prototypical model with absorbing states, the contact process, in dimensions 1-3. Simulations confirm the scaling relation beta(W)=1-straight theta between the interface-width growth exponent beta(W) and the exponent straight theta governing the decay of the order parameter. A scaling property of the height distribution, which serves as the basis for this relation, is also verified. The height-height correlation function shows clear signs of anomalous scaling, in accord with Lopez' analysis [Phys. Rev. Lett. 83, 4594 (1999)], but no evidence of multiscaling.

Journal Article↗
PubMed1999

Avalanche and spreading exponents in systems with absorbing states.

We present generic scaling laws relating spreading critical exponents and avalanche exponents (in the sense of self-organized criticality) in general systems with absorbing states. Using these scaling laws we present a collection of the state-of-the-art exponents for directed percolation, dynamical percolation, and other universality classes. This collection of results should help to elucidate the connections of self-organized criticality and systems with absorbing states. In particular, some nonuniversality in avalanche exponents is predicted for systems with many absorbing states.

Journal Article↗
PubMed1999

Theory of the NO+CO surface-reaction model.

We derive a pair approximation (PA) for the NO+CO model with instantaneous reactions. For both the triangular and square lattices, the PA, derived here using a simpler approach, yields a phase diagram with an active state for CO-fractions y in the interval y(1)<y<y(2), with a continuous (discontinuous) phase transition to a poisoned state at y(1) (y(2)). This is in qualitative agreement with simulation for the triangular lattice, where our theory gives a rather accurate prediction for y(2). To obtain the correct phase diagram for the square lattice, i.e., no active stationary state, we reformulate the PA using sublattices. The (formerly) active regime is then replaced by a poisoned state with broken symmetry (unequal sublattice coverages), as observed recently by Kortlüke et al. [Chem. Phys. Lett. 275, 85 (1997)]. In contrast with their approach, in which the active state persists, although reduced in extent, we report here the qualitatively correct theory of the NO+CO model on the square lattice. Surface diffusion of nitrogen can lead to an active state in this case. In one dimension, the PA predicts that diffusion is required for the existence of an active state.

Journal Article↗
PubMed1999

Pair contact process in two dimensions.

We study the stationary properties of the two-dimensional pair contact process, a nonequilibrium lattice model exhibiting a phase transition to an absorbing state with an infinite number of configurations. The critical probability and static critical exponents are determined via Monte Carlo simulations, as well as order-parameter moment ratios and the scaling of the initial density decay. The static critical properties fall in the directed percolation universality class.

Journal Article↗
PubMed1999

Reweighting in nonequilibrium simulations.

A simple reweighting scheme is proposed for Monte Carlo simulations of interacting particle systems, permitting one to study various parameter values in a single study, and improving efficiency by an order of magnitude. Unlike earlier reweighting schemes, the present approach does not require knowledge of the stationary probability distribution, and so is applicable out of equilibrium. The method is applied to the contact process in two and three dimensions, yielding the critical parameter and spreading exponents to unprecedented precision.

Journal Article↗
PubMed1998

Viremia, genetic heterogeneity, and immunity to hepatitis G/GB-C virus in multiply transfused patients with thalassemia.

BACKGROUND: Thalassemia patients are at high risk for posttransfusion hepatitis. Hepatitis G virus (HGV) has been suspected of being responsible for acute and chronic hepatitis. STUDY DESIGN AND METHODS: The prevalence of HGV infection, its possible association to liver disease, the genetic heterogeneity among the various HGV isolates, and immunity to HGV were studied in 36 thalassemia patients with reverse transcriptase-polymerase chain reaction assay and sequence analysis. RESULTS: HGV RNA was detected in seven patients (19.4%), only two of whom had evidence of hepatitis C virus infection as well. Sequence analysis of the NS3 gene from isolates of the five patients infected with HGV alone revealed 84.7 to 90.9 percent homology at the nucleotide level. Prolonged HGV viremia was not associated with significant liver enzyme elevation. All five patients were chronically infected with the same viral strain. E2 antibodies were detected in 57 percent of the HGV-nonviremic patients and in only 1 of 7 viremic patients. CONCLUSION: HGV is associated with persistent viremia but not with significant biochemical evidence of liver damage. There is some genetic heterogeneity among HGV isolates from thalassemia patients in Israel.

Amino Acid Sequence↗