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At least 469 records · Page 26Linked to original sources
PubMed2002

Asthma and multiple sclerosis: an inverse association in a case-control general practice population.

BACKGROUND: Th1/Th2 imbalance is hypothesized to up-regulate some diseases and down-regulate others. Compared to controls, multiple sclerosis (MS) (Th1-mediated) has been linked to a reduced risk of allergy and asthma (Th2-mediated), based on patient questionnaire studies and a review of asthma medication. AIM: To investigate whether MS is associated with a reduced risk of Th2-associated diseases and an increased risk of Th1-associated diseases. DESIGN: Retrospective matched case-control study. METHODS: Three hundred and twenty MS patients and controls matched for age, gender, location and smoking were selected from the Welsh General Practice Morbidity Database from 1995-99. Case and control records were assessed for Th1-mediated and Th2-mediated diseases. RESULTS: Overall, 346 MS patients were identified, giving a prevalence of 127 per 100 000. There was an inverse relationship between multiple sclerosis (MS) and asthma (OR 0.33; 95%CI 0.15-0.77). No statistically significant relationships emerged between other Th2-associated (eczema, dermatitis) or any Th1-associated (rheumatoid arthritis, thyroid disorders, inflammatory bowel disease [IBD], type 1 diabetes) diseases and MS, although no patient in either group had treated type 1 diabetes. A trend existed for IBD, with 5/320 of cases affected and no controls; OR infinity; 95%CI 1.30-infinity; p=0.063. DISCUSSION: This inverse association between MS and asthma is compatible with a Th1/Th2 imbalance. Although the Th1/Th2 theory is probably an over-simplification in MS, a shift from Th1 cytokine dominance towards Th2 may provide drug-targeting routes for MS.

Adolescent↗
PubMed2000

Rapid tracheal intubation with large-dose rocuronium: a probability-based approach.

UNLABELLED: There are situations in anesthesia in which it may be desirable to achieve rapid tracheal intubation with perfect conditions, i.e., no coughing or straining. To determine the dose of rocuronium that gives a high probability of achieving perfect conditions for rapid (within 60 s) tracheal intubation, we administered a range of doses of rocuronium, some larger than used previously. Sixty adults, anesthetized with thiopental 4 mg/kg IV and alfentanil 10 microg/kg IV, received rocuronium 0.4 to 2.0 mg/kg IV. We used logistic regression to define the relationship of rocuronium dose to probability of achieving perfect intubation conditions. We estimated the doses giving 90% and 95% probability of achieving perfect intubation and used resampling to determine confidence limits for these estimates. Rocuronium 1.85 and 2.33 mg/kg gave, respectively, 90% and 95% probability of perfect intubation conditions. The confidence limits (5th and 95th percentile) for these estimates were 1.15 to 2.31 and 1.23 to 3.22 mg/kg, respectively. In conclusion, it is possible to achieve perfect intubation conditions with large doses of rocuronium, but the long duration of action and expense may limit the usefulness of the technique. IMPLICATIONS: We found that it is possible to have a 90% probability of achieving perfect conditions for rapid tracheal intubation with large (up to 2.0 mg/kg) doses of rocuronium. These large doses of rocuronium may be useful in, for instance, head trauma or open globe injuries if succinylcholine is contraindicated.

Adult↗
PubMed2003

Estimating times of surgeries with two component procedures: comparison of the lognormal and normal models.

BACKGROUND: Variability inherent in the duration of surgical procedures complicates surgical scheduling. Modeling the duration and variability of surgeries might improve time estimates. Accurate time estimates are important operationally to improve utilization, reduce costs, and identify surgeries that might be considered outliers. Surgeries with multiple procedures are difficult to model because they are difficult to segment into homogenous groups and because they are performed less frequently than single-procedure surgeries. METHODS: The authors studied, retrospectively, 10,740 surgeries each with exactly two CPTs and 46,322 surgical cases with only one CPT from a large teaching hospital to determine if the distribution of dual-procedure surgery times fit more closely a lognormal or a normal model. The authors tested model goodness of fit to their data using Shapiro-Wilk tests, studied factors affecting the variability of time estimates, and examined the impact of coding permutations (ordered combinations) on modeling. RESULTS: The Shapiro-Wilk tests indicated that the lognormal model is statistically superior to the normal model for modeling dual-procedure surgeries. Permutations of component codes did not appear to differ significantly with respect to total procedure time and surgical time. To improve individual models for infrequent dual-procedure surgeries, permutations may be reduced and estimates may be based on the longest component procedure and type of anesthesia. CONCLUSIONS: The authors recommend use of the lognormal model for estimating surgical times for surgeries with two component procedures. Their results help legitimize the use of log transforms to normalize surgical procedure times prior to hypothesis testing using linear statistical models. Multiple-procedure surgeries may be modeled using the longest (statistically most important) component procedure and type of anesthesia.

Algorithms↗
PubMed1993

Probability-summation model of multiple laser-exposure effects.

A probability-summation model is introduced to provide quantitative criteria for discriminating independent from interactive effects of multiple laser exposures on biological tissue. Data that differ statistically from predictions of the probability-summation model indicate the action of sensitizing (synergistic/positive) or desensitizing (hardening/negative) biophysical interactions. Interactions are indicated when response probabilities vary with changes in the spatial or temporal separation of exposures. In the absence of interactions, probability-summation parsimoniously accounts for "cumulative" effects. Data analyzed using the probability-summation model show instances of both sensitization and desensitization of retinal tissue by laser exposures. Other results are shown to be consistent with probability-summation. The relevance of the probability-summation model to previous laser-bioeffects studies, models, and safety standards is discussed and an appeal is made for improved empirical estimates of response probabilities for single exposures.

Humans↗
PubMed1998

Modeling the migration of fallout radionuclides in soil using a transfer function model.

A stochastic model for transport of radionuclides in soil is presented. It is based on probability density functions of solute displacements, which are interpreted as impulse response functions of a linear dynamic system. Two transport models are discussed: (1) a convective-stochastic approach which takes into account spatial variability of flow and sorption and leads to a lognormal probability distribution of displacements, and (2) the conventional convective-dispersive model with a constant retardation coefficient. To compare their applicability, both models were applied to depth distributions of 90Sr and 137Cs fallout measured in an Orthic Podsol. The convective-stochastic approach was found to provide a better representation of the observed depth distributions. Using this model, migration rates of the radionuclides were calculated.

Models, Theoretical↗
PubMed2007

Heuristic thinking and inference from observational epidemiology.

Epidemiologic research is an exercise in measurement. Observational epidemiologic results usually include a point estimate, a measure of random error such as a frequentist confidence interval, and a qualitative discussion of study limitations. Without randomization of study subjects to exposure groups, inference from study results requires an educated guess about the strength of the systematic errors compared with the strength of the exposure effects. Although quantitative methods to make these educated guesses exist, the conventional approach is qualitative, which reduces the educated guessing to a problem of reasoning under uncertainty. In circumstances such as these, humans predictably reason poorly. Heuristics and resulting biases that simplify the judgmental tasks tend to underestimate the systematic error, underestimate the uncertainty, and focus the inference on the study's specific evidence while excluding countervailing external information. Common warnings to interpret results with trepidation are an ineffective solution. The methods that quantify systematic error and uncertainty challenge the analyst to specify the alternative explanations for associations that are otherwise too readily judged causal.

Bias↗
PubMedDate not supplied

Statistical correlation between transient pressure drop and cavitation at closure of a mechanical heart valve.

Cavitation on a mechanical heart valve (MHV) is attributable to transient regional pressure drop at the instant of valve closure. As a cavitation bubble collapses, it emits shock waves, which have the characteristics of high frequency oscillations (HFO) on a pressure time trace. The potential for such HFO bursts to cause material damage on an MHV can be measured by the cavitation impulse I, which is defined as the area under the trace of the HFO bursts. In the present study, experiments were conducted on a bileaflet MHV in a durability tester, operated at pulse rates from 300-1,000 bpm. In each case, the transient pressure near an occluder was monitored for 60,000 beats via a transducer. The peak pressure drop Pm and the corresponding cavitation impulse I obtained for the 60,000 beat sequence are found to resemble sample records of two stationary stochastic processes, each of which follows a log normal distribution. Their first order probability density functions are estimated from the records. The correlation is investigated between I and Pm associated with each beat, which is found to be of statistical significance.

Biomedical Engineering↗
PubMed1999

Nonuniversality of compact support probability distributions in random matrix theory.

The two-point resolvent is calculated in the large-n limit for the generalized fixed and bounded trace ensembles. It is shown to disagree with that of the canonical Gaussian ensemble by a nonuniversal part that is given explicitly for all monomial potentials V(M)=M(2p). Moreover, we prove that for the generalized fixed and bounded trace ensemble all k-point resolvents agree in the large-n limit, despite their nonuniversality.

Journal Article↗
PubMed2001

Probability amplitude description of the dynamics of charged particles in a magnetic field in the macrodomain.

The set of Schrödinger-like equations obtained earlier by the author [Phys. Rev. Lett. 26, 417 (1971), Phys. Rev. A 31, 3951 (1985)] for the charged particle dynamics in an inhomogeneous magnetic field in the macrodomain, are derived here starting from the quantum-mechanic Schrödinger equation in its path-integral representation. This derivation enables a generalization of the equations to include a curl-free vector potential in the Schrödinger-like equations. In view of the amplitude character of the latter equations, which now descends directly from that of the quantum-mechanic Schrödinger equation, they now predict the existence in the macrodomain of all such phenomena, which are characteristic of a probability amplitude theory, e.g., the interference, and the observation of a curl-free vector à la Aharonov-Bohm. A discrete energy structure, predicted as interference maxima and minima has already been observed by the author with his co-workers [Mod. Phys. Lett. A 8, 167 (1993)]. A prediction is now made for the observability of a curl-free vector potential in the macrodomain, in the context of the present problem.

Journal Article↗
PubMed2002

Dispersal probability distributions and the wave-front speed problem.

The speed and width of front solutions to reaction-dispersal models are analyzed both analytically and numerically. We perform our analysis for Laplace and Gaussian distribution kernels, both for delayed and nondelayed models. The results are discussed in terms of the characteristic parameters of the models.

Bacteriophages↗
PubMed2005

Rate description of the stick-slip motion in friction force microscopy experiments.

During the stick-slip motion of an atomic force microscope tip contacting with a uniformly moving atomically clean surface, the force developed in the cantilever spring performs random sawtoothlike oscillations resulting from the thermally activated transitions of the tip from one surface site to the next. Using escape rate theory, the probability distribution of forces is calculated numerically to deduce the time-average lateral force as a function of pulling velocity. A transcendental equation for the average force is proposed and its approximate solution is obtained. The accuracy of this analytic approximation is demonstrated via comparison with the numerical results. The analogous force-velocity relations existing in the literature are shown to be the limiting cases of low and high cantilever spring constants of our analytic approximation.

Journal Article↗
PubMed2005

Exact results for the Barabási model of human dynamics.

Human activity patterns display a bursty dynamics with interevent times following a heavy tailed distribution. This behavior has been recently shown to be rooted in the fact that humans assign their active tasks different priorities, a process that can be modeled as a priority queueing system [A.-L. Barabási, Nature (London) 435, 207 (2005)]. In this Letter we obtain exact results for the Barabási model with two tasks, calculating the priority and waiting time distribution of active tasks. We demonstrate that the model has a singular behavior in the extremal dynamics limit, when the highest priority task is selected first. We find that independently of the selection protocol, the average waiting time is smaller or equal to the number of active tasks, and discuss the asymptotic behavior of the waiting time distribution. These results have important implications for understanding complex systems with extremal dynamics.

Activity Cycles↗
PubMed2003

Automated tracing of electron-density maps of proteins.

The tracing of experimental electron maps in the field of protein crystallography is not a rate-limiting step for structure elucidation, but does represent the process that requires the most expertise and user time. This paper presents a method for automatically tracing the electron-density maps of proteins which can reliably generate a C(alpha) trace for protein maps with data in the resolution range 1.5-4 A. The number of C(alpha) atoms placed and the precision of atom placement depends on the quality of the map, but even with poor maps (FOM approximately 0.5) the algorithm can provide a significant saving in time over conventional methods of interpretation. The interpretation of six experimental maps is presented at different resolutions and levels of phase error; these show that data with an FOM of 0.7 or better can be entirely traced with no user intervention.

Algorithms↗
PubMed2003

SAD or MAD phasing: location of the anomalous scatterers.

The method of joint probability distribution functions is applied in order to estimate the structure-factor moduli of the anomalous scatterer substructure both in the SAD (single-wavelength anomalous dispersion) and in the MAD (multi-wavelength anomalous dispersion) cases. The experimental data |F(1)(+)|, |F(1)(-)|, ..., |F(n)(+)|, |F(n)(-)| measured at n wavelengths are used simultaneously to estimate the value of |F(oa)| arising from the normal scattering of the anomalous scatterers. A practical procedure is described that, when applied to the experimental diffraction data of several proteins, shows robustness and efficiency.

Algorithms↗
PubMed2004

Dynamic probability estimator for machine learning.

An efficient algorithm for dynamic estimation of probabilities without division on unlimited number of input data is presented. The method estimates probabilities of the sampled data from the raw sample count, while keeping the total count value constant. Accuracy of the estimate depends on the counter size, rather than on the total number of data points. Estimator follows variations of the incoming data probability within a fixed window size, without explicit implementation of the windowing technique. Total design area is very small and all probabilities are estimated concurrently. Dynamic probability estimator was implemented using a programmable gate array from Xilinx. The performance of this implementation is evaluated in terms of the area efficiency and execution time. This method is suitable for the highly integrated design of artificial neural networks where a large number of dynamic probability estimators can work concurrently.

Artificial Intelligence↗
PubMed2002

A risk analysis for airborne pathogens with low infectious doses: application to respirator selection against Coccidioides immitis spores.

Probability models incorporating a deterministic versus stochastic infectious dose are described for estimating infection risk due to airborne pathogens that infect at low doses. Such pathogens can be occupational hazards or candidate agents for bioterrorism. Inputs include parameters for the infectious dose model, distribution parameters for ambient pathogen concentrations, the breathing rate, the duration of an exposure period, the anticipated number of exposure periods, and, if a respirator device is used, distribution parameters for respirator penetration values. Application of the models is illustrated with a hypothetical scenario involving exposure to Coccidioides immitis, a fungus present in soil in areas of the southwestern United States Inhaling C. immitis spores causes a respiratory tract infection and is a recognized occupational hazard in jobs involving soil dust exposure in endemic areas An uncertainty analysis is applied to risk estimation in the context of selecting respiratory protection with a desired degree of efficacy.

Air Microbiology↗