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At least 415 records · Page 23Linked to original sources
PubMed2001

Individualized model of human thermoregulation for the simulation of heat stress response.

A population-based dynamic model of human thermoregulation was expanded with control equations incorporating the individual person's characteristics (body surface area, mass, fat%, maximal O(2) uptake, acclimation). These affect both the passive (heat capacity, insulation) and active systems (sweating and skin blood flow function). Model parameters were estimated from literature data. Other data, collected for the study of individual differences (working at relative or absolute workloads in hot-dry [45 degrees C, 20% relative humidity (rh)], warm-humid [35 degrees C, 80% rh], and cool [21 degrees C, 50% rh] environments), were used for validation. The individualized model provides an improved prediction [mean core temperature error, -0.21 --> -0.07 degrees C (P < 0.001); mean squared error, 0.40 --> 0.16 degrees C, (P < 0.001)]. The magnitude of improvement varies substantially with the climate and work type. Relative to an empirical multiple-regression model derived from these specific data sets, the analytical simulation model has between 54 and 89% of its predictive power, except for the cool climate, in which this ratio is zero. In conclusion, individualization of the model allows improved prediction of heat strain, although a substantial error remains.

Acclimatization↗
PubMed2004

Passive movements of the head do not abolish anticipatory firing properties of head direction cells.

Neurons in the anterior dorsal thalamic nucleus (ADN) of the rat selectively discharge in relation to the animal's head direction (HD) in the horizontal plane. Temporal analyses of cell firing properties reveal that their discharge is optimally correlated with the animal's future directional heading by approximately 24 ms. Among the hypotheses proposed to explain this property is that ADN HD cells are informed of future head movement via motor efference copy signals. One prediction of this hypothesis is that when the rat's head is moved passively, the anticipatory time interval (ATI) will be attenuated because the motor efference signal reflects only the active contribution to the movement. The present study tested this hypothesis by loosely restraining the animal and passively rotating it through the cell's preferred direction. Contrary to our prediction, we found that ATI values did not decrease during passive movement but in fact increased significantly. HD cells in the postsubiculum did not show the same effect, suggesting independence between the two sites with respect to anticipatory firing. We conclude that it is unlikely that a motor efference copy signal alone is responsible for generating anticipatory firing in ADN HD cells.

Action Potentials↗
PubMed2002

CCCP algorithms to minimize the Bethe and Kikuchi free energies: convergent alternatives to belief propagation.

This article introduces a class of discrete iterative algorithms that are provably convergent alternatives to belief propagation (BP) and generalized belief propagation (GBP). Our work builds on recent results by Yedidia, Freeman, and Weiss (2000), who showed that the fixed points of BP and GBP algorithms correspond to extrema of the Bethe and Kikuchi free energies, respectively. We obtain two algorithms by applying CCCP to the Bethe and Kikuchi free energies, respectively (CCCP is a procedure, introduced here, for obtaining discrete iterative algorithms by decomposing a cost function into a concave and a convex part). We implement our CCCP algorithms on two- and three-dimensional spin glasses and compare their results to BP and GBP. Our simulations show that the CCCP algorithms are stable and converge very quickly (the speed of CCCP is similar to that of BP and GBP). Unlike CCCP, BP will often not converge for these problems (GBP usually, but not always, converges). The results found by CCCP applied to the Bethe or Kikuchi free energies are equivalent, or slightly better than, those found by BP or GBP, respectively (when BP and GBP converge). Note that for these, and other problems, BP and GBP give very accurate results (see Yedidia et al., 2000), and failure to converge is their major error mode. Finally, we point out that our algorithms have a large range of inference and learning applications.

Algorithms↗
PubMed1985

Mothers of abused children. A comparison study.

A group of 36 mothers whose children had suffered from child abuse at an average of 5 1/2 years previously was compared with a group of mothers of similar social class where there had been no reported instances of abuse of their children. There was no significant difference between the two groups with regard to marital, housing, or financial problems or in physical health. Statistically significant differences were found between the abuse and comparison group mothers in the following areas: the abuse group mothers (1) were less likely to have been brought up by their own parents; (2) had more negative feelings towards their fathers; (3) were more likely to have received help for an emotional disorder; (4) had higher expectations for their children; (5) perceived a greater number of personality problems in their children; and (6) were more likely to have assertive, demanding, and suspicious personality traits. It is possible that these maternal factors will influence the emotional development of their children.

Child↗
PubMed2006

Prediction of IBD based on population history for fine gene mapping.

A novel multiple regression method (RM) is developed to predict identity-by-descent probabilities at a locus L (IBDL), among individuals without pedigree, given information on surrounding markers and population history. These IBDL probabilities are a function of the increase in linkage disequilibrium (LD) generated by drift in a homogeneous population over generations. Three parameters are sufficient to describe population history: effective population size (Ne), number of generations since foundation (T), and marker allele frequencies among founders (p). IBDL are used in a simulation study to map a quantitative trait locus (QTL) via variance component estimation. RM is compared to a coalescent method (CM) in terms of power and robustness of QTL detection. Differences between RM and CM are small but significant. For example, RM is more powerful than CM in dioecious populations, but not in monoecious populations. Moreover, RM is more robust than CM when marker phases are unknown or when there is complete LD among founders or Ne is wrong, and less robust when p is wrong. CM utilises all marker haplotype information, whereas RM utilises information contained in each individual marker and all possible marker pairs but not in higher order interactions. RM consists of a family of models encompassing four different population structures, and two ways of using marker information, which contrasts with the single model that must cater for all possible evolutionary scenarios in CM.

Alleles↗
PubMed2005

The use of random effects models to allow for clustering in individually randomized trials.

BACKGROUND: We describe different forms of clustering that may occur in individually randomized trials, where the observed outcomes for different individuals cannot be regarded as independent. We propose random effects models to allow for such clustering, across a range of contexts and trial designs, and investigate their effect on estimation and interpretation of the treatment effect. METHODS: We apply our proposed models to two individually randomized trials with potential for clustering, a trial of teleconsultation in hospital referral (the main outcome being offer of a further hospital appointment) and a trial of exercise therapy delivered by physiotherapists for low back pain (the outcome being a back pain score). Extensions to the methods include the possibility of explaining heterogeneity between clusters using cluster level characteristics and the potential dilution of cluster effects due to noncompliance. RESULTS: In the teleconsultation trial, the odds ratio was significant (1.52, 95% CI 1.27 to 1.82) when clustering was ignored, but smaller and nonsignificant (1.36, 95% CI 0.85 to 2.13) when clustering by hospital consultant was taken into account. The 95% range of estimated treatment effects across consultants was from 0.21 to 8.76. This variability was only partially explained by the specialty of the consultant. In the back pain trial, although there was an overall benefit of exercise (change of - 0.51 points on the back pain score) and little evidence of clustering, the estimated treatment effects for different physiotherapists ranged from -1.26 to +0.26 points. CONCLUSIONS: Clustering is an important issue in many individually randomized trials. Ignoring it can lead to underestimates of the uncertainty and too extreme P-values. Even when there is little apparent heterogeneity across clusters, it can still have a large impact on the estimation and interpretation of the treatment effect.

Back Pain↗
PubMed2005

Tropospheric CO observed with the NAST-I retrieval methodology, analyses, and first results.

High-resolution infrared spectra from aircraft and space-based observations contain information about tropospheric carbon monoxide (CO) as well as other trace species. A methodology for retrieving tropospheric CO from such remotely sensed spectral data has been developed for the National Polar-Orbiting Operational Environmental Satellite System's Airborne Sounder Testbed-Interferometer (NAST-I). CO profiles of the troposphere, together with its thermodynamic properties, are determined by use of a three-stage retrieval approach that combines the algorithms of physically based statistical eigenvector regression, simultaneous and iterative matrix inversion, and single-variable error-minimization CO profile matrix inverse retrieval. The NAST-I is collecting data while it is aboard high-altitude aircraft throughout many field campaigns. Detailed retrieval analyses based on the NAST-I instrument system along with retrieval results from several recent field campaigns are presented to demonstrate NAST-I CO retrieval capability.

Journal Article↗
PubMed2006

Scene estimation from speckled synthetic aperture radar imagery: Markov-random-field approach.

A novel Markov-random-field model for speckled synthetic aperture radar (SAR) imagery is derived according to the physical, spatial statistical properties of speckle noise in coherent imaging. A convex Gibbs energy function for speckled images is derived and utilized to perform speckle-compensating image estimation. The image estimation is formed by computing the conditional expectation of the noisy image at each pixel given its neighbors, which is further expressed in terms of the derived Gibbs energy function. The efficacy of the proposed technique, in terms of reducing speckle noise while preserving spatial resolution, is studied by using both real and simulated SAR imagery. Using a number of commonly used metrics, the performance of the proposed technique is shown to surpass that of existing speckle-noise-filtering methods such as the Gamma MAP, the modified Lee, and the enhanced Frost.

Journal Article↗
PubMed2002

Proposition of an aging indicator from general health examination in France.

We present an indicator of aging based on eight quantitative variables, measured during the periodical health examination offered by French social security to the general population in France. The used sample derived from the population examined each year. We selected a reference group of 24,510 adults older than 25 years (non-smokers, drinking less than 44 g alcohol per day, with body mass index less than 35, and not using medication). A multiple regression analysis by gender was used to select significant variables to predict age from all quantitative variables measured during the health examination. The resulting biological age could be calculated from the measured variables and the aging indicator was defined as the difference between the calculated age and the chronological age. By definition, this indicator is independent of age in the reference population and gives an indication of the difference between an individual's status in the process of aging and the mean status of people of the same chronological age. Associations between this indicator and life style habits such as tobacco and alcohol use, and occupational status were observed. A geographical analysis also exhibited significant variation over France. Such an indicator can be used at the individual level as a pedagogical tool to explain the observed individual health status. It is also of interest for the epidemiological studies, where it could contribute to a better understanding of the aging process and associated factors.

Adult↗
PubMed2006

Prediction of one-hour running performance using constant duration tests.

Critical velocity (CV) represents, theoretically, the highest velocity that can be sustained without fatigue. The aim of this study was to compare CV computed from 5 mathematical models in order to determine which CV estimate is better correlated with 1-hour performance and which model provides the most accurate prediction of performance. Twelve trained middle- and long-distance male runners (29 +/- 5 years) performed 3 randomly ordered constant duration tests (6, 9, and 12 minutes), a maximal running velocity test for the estimation of CV, and a 1-hour track test (actual performance). Two linear, 2 nonlinear, and 1 exponential mathematical models were used to estimate CV and to predict the highest velocity that could be sustained during 1 hour (predicted performance). Although all CV estimates were correlated with performance (0.80 < r < 0.93, p < 0.01), it appeared that CV estimated from the exponential model was more closely associated with performance than all other models (r = 0.93; p < 0.01). Analysis of the bias +/- 95% interval of confidence between actual and predicted performance revealed that none of the models provided an accurate prediction of the 1-hour performance velocity. In conclusion, the estimation of CV allows us to rank middle- and long-distance runners with regard to their ability to perform well in long-distance running. However, no models provide an accurate prediction of performance that could be used as a reference for coaches or athletes.

Adult↗
PubMed2004

[Prediction of aerobic fitness without stress testing and applicability to epidemiological studies: a systematic review].

Cardiorespiratory fitness is used as an independent factor for evaluating risk of all-cause mortality, but mainly from coronary heart disease. Nevertheless, evaluation of fitness based on stress tests poses numerous epidemiological difficulties. Alternative forms of evaluation have therefore been suggested using non-exercise-based regression models. This study aimed to analyze these models and their applicability to epidemiological studies. A systematic review was conducted of articles published from 1966 to 2002. The models were classified according to: (a) theoretical justification for the explanatory variables included in the model; (b) validation criteria (gold standard); (c) regression models fully reported, including standard error of estimation; and (d) cross-validation. The search process yielded 23 studies, five of which met all established quality criteria. The authors conclude that cardiorespiratory evaluation by non-exercise-based models could be feasible in epidemiological studies. However, few equations appear to meet the minimum external validation requirements to provide data that could be generalized to large populations.

Adolescent↗
PubMedDate not supplied

Knock prediction for dual fuel engines by using a simplified combustion model.

The present work used a methane-air mixture chemical kinetics scheme consisting of 119 elementary reaction steps and 41 chemical species to develop a simplified combustion model for prediction of the knock in dual fuel engines. Calculated values by the model for natural gas operation showed good agreement with corresponding experimental values over a broad range of operating conditions.

Carbon Monoxide↗
PubMed2006

Estimating historical radiation doses to a cohort of U.S. radiologic technologists.

Data have been collected and physical and statistical models have been constructed to estimate unknown occupational radiation doses among 90,000 members of the U.S. Radiologic Technologists cohort who responded to a baseline questionnaire during the mid-1980s. Since the availability of radiation dose data differed by calendar period, different models were developed and applied for years worked before 1960, 1960- 1976 and 1977-1984. The dose estimation used available film-badge measurements (approximately 350,000) for individual cohort members, information provided by the technologists on their work history and protection practices, and measurement and other data derived from the literature. The dosimetry model estimates annual and cumulative occupational badge doses (personal dose equivalent) for each technologist for each year worked from 1916 through 1984 as well as absorbed doses to organs and tissues including bone marrow, female breast, thyroid, ovary, testes, lung and skin. Assumptions have been made about critical variables including average energy of X rays, use of protective aprons, position of film badges, and minimum detectable doses. Uncertainty of badge and organ doses was characterized for each year of each technologist's working career. Monte Carlo methods were used to generate estimates of cumulative organ doses for preliminary cancer risk analyses. The models and predictions presented here, while continuing to be modified and improved, represent one of the most comprehensive dose reconstructions undertaken to date for a large cohort of medical radiation workers.

Adolescent↗
PubMed1990

Course of peripheral occlusive arterial disease in diabetes. Vascular laboratory assessment.

To determine comparative rates of development and progression of peripheral occlusive arterial disease, 110 healthy nondiabetic control subjects, 112 patients with peripheral occlusive arterial disease (POAD), 240 patients with diabetes mellitus (DM), and 100 patients with diabetes mellitus and peripheral occlusive arterial disease (DM + POAD) were studied over 4 yr with noninvasive techniques. The presence of peripheral occlusive arterial disease was determined by postexercise ankle-brachial index (ABI) values; progression of peripheral occlusive arterial disease was determined by the rate of change in postexercise ABI. Patients who underwent peripheral arterial reconstructive surgery or amputation were also classified as having progression of their peripheral occlusive arterial disease. On this basis, follow-up revealed that peripheral occlusive arterial disease developed and therefore progressed in 1 (1%) of the control group and 22 (9%) of the DM. Peripheral occlusive arterial disease progressed in 31 (28%) of the POAD and 26 (26%) of the DM + POAD. The presence of peripheral occlusive arterial disease predisposes to progression of disease, and peripheral occlusive arterial disease is more likely to develop in diabetic patients who do not have peripheral occlusive arterial disease than in nondiabetic control subjects. However, the presence of diabetes mellitus in patients with peripheral occlusive arterial disease does not seem to increase the risk of progression.

Amputation, Surgical↗
PubMed2001

Computed tomographic study of the effect of a tongue-tie on hyoid apparatus position and nasopharyngeal dimensions in anesthetized horses.

OBJECTIVE: To determine the effect of manual tongue protrusion on the dimensions of the hyoid apparatus, nasopharynx, and oropharynx in anesthetized horses. tongue protrusion on the dimensions of the hyoid. ANIMALS: 5 adult horses. PROCEDURE: Horses were anesthetized and positioned in sternal recumbency for 2 sequential computed tomographic (CT) scans. Images were acquired with the tongue in a natural position inside the mouth. Then, the tongue was pulled rostrally and secured, and a second CT scan was performed. Dorsoventral length of the hyoid apparatus and angles of the basisphenoid, basihyoid, and ceratohyoid were measured on 3-dimensional reconstructed CT images. Cross-sectional diameters and areas of the nasopharynx and oropharynx were determined on reformatted images in the transverse and longitudinal planes, using osseous landmarks for consistency. Results were tested between the 2 groups to determine significant differences. RESULTS: We were unable to detect a significant difference between any of the lengths or angles of the hyoid apparatus measured with or without rostral protrusion of the tongue. Similarly, nasopharyngeal and oropharyngeal diameters and cross-sectional areas were not significantly different with or without rostral protrusion of the tongue. CONCLUSIONS AND CLINICAL RELEVANCE: Tying the tongue rostrally out of a horse's mouth did not influence the position of the hyoid apparatus or dimensions of the nasopharynx or oropharynx in anesthetized horses. Currently, no data suggest that application of a tongue-tie is effective for maintaining stability and patency of the nasopharyngeal or orolaryngeal airways in horses during races.

Anesthesia↗
PubMed2003

Evaluation of a stochastic Markov-chain model for the development of forelimb injuries in Thoroughbred racehorses.

OBJECTIVE: To evaluate a Markov-chain model for the development of forelimb injuries in Thoroughbreds and to use the model to determine effects of reducing sprint distance on incidence of metacarpal condylar fracture (CDY) and severe suspensory apparatus injury (SSAI). SAMPLE POPULATION: Weekly exercise and injury data for 122 Thoroughbreds during racing or training. PROCEDURE: Weekly data were used to construct a Markov-chain model with 5 states (uninjured [UNINJ], palpable suspensory apparatus injury [PSAII, SSAI, CDY, and lost to follow-up [LOST]). Transition probabilities between UNINJ and PSAI were estimated as a function of weekly sprint distance by use of linear regression analysis. The model was used to predict distributions of annual CDY and SSAI incidences in southern California racehorses and was validated by using CDY incidence reported by racetrack practitioners. The model was modified by reducing the number of sprint distances that were > 6 furlongs (> 1.20 km) by 20%, and CDY and SSAI incidences were compared with those generated by the baseline model. RESULTS: The model accurately fit development of injuries in the sample population but overestimated development of injuries in the southern California racehorse population. Development of and recovery from PSAI were correlated with distance run at high speeds. Reducing by 20% the number of sprints run at distances > 6 furlongs significantly reduced modeled annual CDY and SSAI incidence by 9%. CONCLUSIONS AND CLINICAL RELEVANCE: Reducing the number of sprints at distances > 6 furlongs, particularly among horses with PSAI, reduces risk of CDY and SSAI.

Animals↗