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PubMed2002

Predictive modeling of the mechanical properties of particulate hydroxyapatite reinforced polymer composites.

The influence of particle geometry and volume fraction on the mechanical properties of a hydroxyapatite (HAp) particulate reinforced polymer (poly-L-lactide and collagen) matrix composite was investigated through finite-element (FE) analysis. For cube-shaped (near sharp and curved corners and edges) embedded particles, it was found that the maximum stress concentration factor (SCF) in the matrix decreases with an increase of the HAp particle volume fraction (PVF). The maximum stress concentration in the matrix material containing a spherical inclusion has low sensitivity to the PVF. The compressive Young's modulus was found to be slightly dependent on particle shape, but very sensitive to PVF. Calculated stiffness values from FE analysis were compared to the experimental results available in the literature and with predictions from the Halpin-Tsai model.

Biomechanical Phenomena↗
PubMed1992

Macro model prediction of elderly people's injury and death in road traffic accidents in Croatia.

The case of elderly people injured and killed in traffic accidents in Croatia is used to illustrate a prediction method. This method consists of several steps. First, the most important variables are selected. Second, to overcome intercorrelation, new variables are constructed that include the old ones. Third, the new variables and its first derivatives are used in a rank correlation method. The results show good predictive capabilities.

Accidents, Traffic↗
PubMed1979

A prediction model for bovine ostertagiasis.

A mathematical model based on development and mortality rates, and incorporating data on the infectivity, fecundity and migratory behaviour of Ostertagia ostertagi, was used to predict the level of pasture contamination and the occurrence of clinical ostertagiasis in grazing calves during 1975 and 1976. A comparison of the predicted and observed events showed a good correlation.

Animals↗
PubMed2002

Nomograms as predictive models.

Nomograms are valuable tools for estimating the likelihood of cancer being diagnosed, the pathologic features of a localized cancer, and the prognosis of a patient after treatment. Although the available nomograms are reasonably accurate, better predictive factors including additional clinical factors and new molecular analyses are needed to improve the accuracy or predictions. Nomogram performance will also be enhanced with larger datasets of patients and longer follow-up. We review the concepts of risk stratification and the development and use of nomograms as predictive tools.

Expert Systems↗
PubMed2000

A prediction model for prehospital triage of patients with suspected cardiac ischemia.

The American College of Cardiology recommends that patients with high risk acute myocardial infarction (AMI) be triaged to hospitals with percutaneous transluminal coronary angioplasty capability. However, there are no prehospital triage criteria to select candidates for bypassing community hospitals and being taken directly to "cardiac centers." This article assesses which independent variables predict death within 7 days in patients with suspected AMI transported by EMS. This is a retrospective study of 291 AMI patients transported by ambulance to 3 hospitals during 1996-1997. Included were patients who were (n = 244) > or =18 years of age, had a ED chief complaint of chest pain or dyspnea for whom we had mortality data. Mortality at 7 days, our primary outcome measure, was obtained by using a metropolitan Detroit tricounty death index records. Differences between the survivors and nonsurvivors were assessed using the Student's t-test and chi-square tests. Multiple triage criteria were assessed for optimal identification of high risk patients by constructing a logistic multivariate model. Among the study population, 15% died within 7 days (95% confidence interval (CI) 10.3-19.2), and this group represented 63.2% of all deaths over a 2 year surveillance period. Survivors, compared to nonsurvivors, were 14.1 years younger (P < or = .001) and more often men (P < or = 0.001). The dispatch time to ED arrival was less among survivors than nonsurvivors (42.8 vs. 50.6 min, P < or = .01). EMS vital signs differed by survivor status. Among survivors, HR was lower (-11.9 bpm; P < or = 0.01), RR was lower (-6.7 rpm; P < or = .001), SBP was higher (+14.5 mmHg; P < or = 0.05) and DBP was higher (+13.2 mm Hg; P < or = .01). A multivariate model identified the following as independent predictors of early mortality: female gender (OR = 2.3; P < or = .05), age > or =65 (OR = 5.9; P < or = .01), RR > or = 20 (OR = 4.6; P < or = .001), SBP < 120 (OR = 2.4; P < or = .05). The overall model was 86% sensitive and 53% specific with an area under the receiving operating characteristic curve of 0.8 (P < or = .001). A triage rule based on a multivariate model can identify the group at high risk of early cardiac death. This decision rule needs to be prospectively validated.

Aged↗
PubMed2005

Down syndrome screening in the first and/or second trimester: model predicted performance using meta-analysis parameters.

OBJECTIVE: To predict the screening performance for 17 policies currently in use or being considered for the near future. METHODS: Multivariate Gaussian modeling using parameters derived from published meta-analyses and new meta-analyses for gestation-specific nuchal translucency and between trimester correlations. RESULTS: For a 1% to 5% false-positive rate, first trimester screening achieved detection rates up to 16% to 25% higher than the best second trimester combination. Screening in both trimesters sequentially could yield an even greater increase in detection of 24% to 35%. The most efficient sequential policy was contingent screening, which has a high detection rate with only 15% of women needing second trimester tests. CONCLUSION: Modeling with meta-analysis derived parameters provides a reliable guide for policy and favors a contingent screening policy. The widespread practice of calculating first and second trimester risks separately should be abandoned.

Chorionic Gonadotropin↗
PubMed1993

Estimation of the magnitude of the HIV epidemic among homosexual men: utilization of survey data in predictive models.

A group of 709 randomly selected males aged 18-55 years living in the city of Amsterdam, the Netherlands, were questioned about sexual lifestyle and related behavior. A substantial proportion (10%) of these men appeared to be homo- or bisexual. Of these homo- and bisexual men, 16.5% were predicted to be HIV seropositive, using their behavioral information in logistic regression models derived from a second study among 506 homo- or bisexual volunteers who were questioned and tested for HIV antibodies as well. Generalizing the results of the sample, the magnitude of the homo- and bisexual population in Amsterdam is estimated to be 21,500 (95% confidence interval: 17,000-26,000) of whom 3500 are HIV seropositive. This is in agreement with estimations on the basis of AIDS surveillance data. The study shows that in the absence of serological data it is possible to estimate HIV prevalence, given that the relation between the presence of HIV antibodies and sexual activity or indicators for sexual activity is known. Since serological data are lacking in many occasions, this method may be of help to estimate HIV prevalence in other geographic locations and risk groups.

Adolescent↗
PubMed2003

Daily cost prediction model in neonatal intensive care.

OBJECTIVES: One barrier to economic evaluation alongside neonatal randomized controlled trials is the expense of collecting detailed patient resource information. To reduce this data collection burden, we identified the key resource items that predict daily ancillary costs for extremely low birth weight infants. METHODS: Participants were 385 infants enrolled in the Trial of Indomethacin Prophylaxis for Preterms in nine tertiary level neonatal intensive care units in Canada. Information on eighty-nine nonpersonnel resource items was abstracted from the hospital chart from admission to tertiary hospital discharge. Unit costs were derived from a provincially standardized cost accounting system. Using stepwise linear regression, models correlating total daily ancillary costs with key resource items were constructed for each of five periods of admission. Models were derived in a randomly split half of the total sample of patient days and validated against the remainder. RESULTS: The 385 infants contributed resource information from 23,354 admission days. The regression model for weeks one to twelve included the covariates surfactant, chest radiograph, red blood cell transfusion, cranial ultrasound, abdominal radiograph, parenteral amino acid infusion, surgery, platelet transfusion, and echocardiogram and explained 91% of the variability in daily nonpersonnel costs (P<.0001). Models for other admission periods similarly included between four and eight covariates, were highly significant (P<.0001) and explained between 76% and 94% of daily ancillary cost variability. The regression equations showed excellent predictive power when applied to the second half of the patient data set. CONCLUSIONS: Daily nonpersonnel costs for extremely low birth weight infants are driven by a limited number of key resource variables. The ability to predict total ancillary costs with minimal data collection will facilitate inclusion of economic evaluations in neonatal trials.

Ancillary Services, Hospital↗
PubMed2002

Use of predictive modeling for Propionibacterium strain classification.

Computed data analysis of biochemical or molecular profiles is currently used in studies of microbial taxonomy, epidemiology, and microbial diversity. We assessed the use of Partial Least Squares (PLS) regression for multivariate data analysis in bacteriology. We identified clear relationships between RAPD profiles of propionibacteria strains and their species classification, autolytic capacities, and their origins. The PLS regression also predicted species identity of some strains with RAPD profiles partially related to those of reference strains. The PLS analysis also allowed us to identify key characteristics to use to classify strains. PLS regression is particularly well adapted to i) describing a collection of bacterial isolates, ii) justifying bacterial groupings using several sets of data, and iii) predicting phenotypic characters of strains that have been classified by routine typing methods.

Autolysis↗
PubMed2000

Gemifloxacin and ciprofloxacin pharmacodynamics in an in-vitro dynamic model: prediction of the equivalent AUC/MIC breakpoints and doses.

To compare the antimicrobial effects (AMEs) of gemifloxacin (GEM) and ciprofloxacin (CIP) on Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, a series of pharmacokinetic profiles of GEM (a single dose with the half-life (T(1/2)) of 7.4 h and CIP (two 12 h doses with T(1/2) of 4 h) were simulated in vitro over eight-fold ranges of the AUC/MIC ratio. Species- and strain-independent linear relationships observed between the intensity of AME (I(E)) and log AUC/MIC were not superimposed for GEM and CIP (r(2)=0.99 and 0.98, respectively). The predicted ratio for GEM that might be equivalent to a clinically established breakpoint value of AUC/MIC=125 (mg h/l)/(mg/l) for CIP was estimated at 110 (mg h/l)/(mg/l). It was calculated, that a daily dose of CIP that might provide the same AME as a clinical dose of GEM (320 mg) on a hypothetical strain of S. aureus with MICs=MIC(50)s would be as high as 2 x 3200 mg.

Anti-Infective Agents↗
PubMed2003

A DFT-derived model predicts solvation-dependent configurational stability of organolithium compounds: a case study of a chiral alpha-thioallyllithium compound.

Density functional theory calculations (B3LYP/6-31+G*) were performed to evaluate a model previously published by us which suggests that aggregation and solvation of organolithium compounds can be of large importance for their configurational stability. In this study, we demonstrate how THF solvation of the monomer of a chiral alpha-thioallyllithium compound impedes the racemization, while upon dimerization the inversion process accelerates. These findings agree with experiments performed by Hoppe and co-workers. These findings may be used to further develop organolithium compounds which should be designed to resist aggregation and efficient transition-state solvation.

Lithium↗
PubMed2006

Evaluation of BRCA1 and BRCA2 mutation prevalence, risk prediction models and a multistep testing approach in French-Canadian families with high risk of breast and ovarian cancer.

BACKGROUND AND OBJECTIVE: In clinical settings with fixed resources allocated to predictive genetic testing for high-risk cancer predisposition genes, optimal strategies for mutation screening programmes are critically important. These depend on the mutation spectrum found in the population under consideration and the frequency of mutations detected as a function of the personal and family history of cancer, which are both affected by the presence of founder mutations and demographic characteristics of the underlying population. The results of multistep genetic testing for mutations in BRCA1 or BRCA2 in a large series of families with breast cancer in the French-Canadian population of Quebec, Canada are reported. METHODS: A total of 256 high-risk families were ascertained from regional familial cancer clinics throughout the province of Quebec. Initially, families were tested for a panel of specific mutations known to occur in this population. Families in which no mutation was identified were then comprehensively tested. Three algorithms to predict the presence of mutations were evaluated, including the prevalence tables provided by Myriad Genetics Laboratories, the Manchester Scoring System and a logistic regression approach based on the data from this study. RESULTS: 8 of the 15 distinct mutations found in 62 BRCA1/BRCA2-positive families had never been previously reported in this population, whereas 82% carried 1 of the 4 mutations currently observed in > or =2 families. In the subset of 191 families in which at least 1 affected individual was tested, 29% carried a mutation. Of these 27 BRCA1-positive and 29 BRCA2-positive families, 48 (86%) were found to harbour a mutation detected by the initial test. Among the remaining 143 inconclusive families, all 8 families found to have a mutation after complete sequencing had Manchester Scores > or =18. The logistic regression and Manchester Scores provided equal predictive power, and both were significantly better than the Myriad Genetics Laboratories prevalence tables (p<0.001). A threshold of Manchester Score > or =18 provided an overall sensitivity of 86% and a specificity of 82%, with a positive predictive value of 66% in this population. CONCLUSION: In this population, a testing strategy with an initial test using a panel of reported recurrent mutations, followed by full sequencing in families with Manchester Scores > or =18, represents an efficient test in terms of overall cost and sensitivity.

Adolescent↗
PubMed2005

Sensitivity of kinematics-based model predictions to optimization criteria in static lifting tasks.

The effect of eight different cost functions on trunk muscle forces, spinal loads and stability was investigated. Kinematics-based approach combined with nonlinear finite element modeling and optimization were used to model in vivo measurements on isometric forward flexions at approximately 40 degrees and approximately 65 degrees in sagittal plane with or without a load of 180N in hands. Four nonlinear (summation stress(3), summation stress(2), summation force(2) and muscle fatigue) and four linear (summation stress, summation force, axial compression and double-linear) criteria were considered. Predicted muscle activities were compared with measured EMG data. All predictions, irrespective of the cost function used, satisfied required kinetic, kinematics and stability conditions all along the spine. Four criteria (summation stress(3), summation stress(2), fatigue and double-linear) predicted muscle activities that qualitatively matched measured EMG data. The fatigue and double-linear criteria were inadequate in predicting greater forces in larger muscles with no consideration for their moment arms. Nearly the same stability margin was computed under these four cost functions. At the lower lumbar levels, the compression forces differed by <20% and the shear forces by <14% as various cost functions were considered. Smaller axial compression and anterior shear forces (by less than or approximately equal 6%) were computed when only the active components rather than the total muscle forces were taken as unknown in the summation stress(3) cost function. Overall, one single cost function of summation stress(2) or summation stress(3) rather than a multi-criteria one was found sufficient and adequate in yielding plausible results comparable with measured EMG activities and disc pressure.

Algorithms↗
PubMed2006

Predictive modelling of topology and loop variations in dimeric DNA quadruplex structures.

We have used a combination of simulated annealing (SA), molecular dynamics (MD) and locally enhanced sampling (LES) methods in order to predict the favourable topologies and loop conformations of dimeric DNA quadruplexes with T2 or T3 loops. This follows on from our previous MD simulation studies on the influence of loop lengths on the topology of intramolecular quadruplex structures [P. Hazel et al. (2004) J. Am. Chem. Soc., 126, 16 405-16 415], which provided results consistent with biophysical data. The recent crystal structures of d(G4T3G4)2 and d(G4BrUT2G4) (P. Hazel et al. (2006) J. Am. Chem. Soc., in press) and the NMR-determined topology of d(TG4T2G4T)2 [A.T. Phan et al. (2004) J. Mol. Biol., 338, 93-102] have been used in the present study for comparison with simulation results. These together with MM-PBSA free-energy calculations indicate that lateral T3 loops are favoured over diagonal loops, in accordance with the experimental structures; however, distinct loop conformations have been predicted to be favoured compared to those found experimentally. Several lateral and diagonal loop conformations have been found to be similar in energy. The simulations suggest an explanation for the distinct patterns of observed dimer topology for sequences with T3 and T2 loops, which depend on the loop lengths, rather than only on G-quartet stability.

Computer Simulation↗