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PubMed2004

Woodpecker cavity aeration: a predictive model.

We studied characteristics of the Syrian woodpecker (Dendrocopos syriacus) cavities in the field and a laboratory model, and rates of gas exchange in the laboratory. Night temperature of occupied cavities is 4.3 degrees C higher than empty ones, representing energy savings of approximately 24%. Oxygen conductance (GNO2) of an empty cavity is 7.1 ml[STPD] (Torr h)(-1), and is affected by winds at velocities up to 0.8 m/s. Day and night body temperatures were 42.0 and 40.1 degrees C, respectively. Steady-state O2 consumption rates (MO2) were 3.49 +/- 0.49 and 2.53 +/- 0.26 ml[STPD] (g h)(-1) during day and night respectively -- higher than predicted by allometry. A mathematical model describing PO2 in a cavity, taking into consideration MO2, GNO2, heat convection and wind speed, from the moment birds inhabit it, was developed. It shows that on the average, one woodpecker staying in its cavity at night does not encounter hypoxic conditions. However, in nest cavities with below the average GNO2, with more inhabitants (e.g. during the breeding season), hypoxia may become a problem.

Animals↗
PubMed2006

Dental attrition models predicting temporomandibular joint disease or masticatory muscle pain versus asymptomatic controls.

AIMS: To determine whether patients with temporomandibular joint disease or masticatory muscle pain can be usefully differentiated from asymptomatic controls using multifactorial classification tree models of attrition severity and/or rates. METHODS: Measures of attrition severity and rates in patients diagnosed with disc displacement (n = 52), osteoarthrosis (n = 74), or masticatory muscle pain only (n = 43) were compared against those in asymptomatic controls (n = 132). Cross-validated classification tree models were tested for fit with sensitivity, specificity, accuracy and log likelihood accountability. RESULTS: The model for identifying asymptomatic controls only required the three measures of attrition severity (anterior, mediotrusive and laterotrusive posterior) to be differentiated from the patients with a 74.2 +/- 3.8% cross-validation accuracy. This compared with cross-validation accuracies of 69.7 +/- 3.7% for differentiating disc displacement using anterior and laterotrusive attrition severity, 68.7 +/- 3.9% for differentiating disc displacement using anterior and laterotrusive attrition rates, 70.9 +/- 3.3% for differentiating osteoarthrosis using anterior attrition severity and rates, 94.6 +/- 2.1% for differentiating myofascial pain using mediotrusive and laterotrusive attrition severity, and 92.0 +/- 2.1% for differentiating myofascial pain using mediotrusive and anterior attrition rates. The myofascial pain models exceeded the > or =75% sensitivity and > or =90% specificity thresholds recommended for diagnostic tests, and the asymptomatic control model approached these thresholds. CONCLUSION: Multifactorial models using attrition severity and rates may differentiate masticatory muscle pain patients from asymptomatic controls, and have some predictive value for differentiating intracapsular temporomandibular disorder patients as well.

Adolescent↗
PubMed2003

Risk model predictive of severe anemia requiring RBC transfusion after chemotherapy in pediatric solid tumor patients.

PURPOSE: Severe anemias requiring RBC transfusions is a frequent complication of chemotherapy. A model elaborated by Ray-Coquard et al in adults pointed to three independent risk factors for RBC transfusion: performance status (PS) more than 1, hemoglobin less than 12 g/dL, and prechemotherapy absolute lymphocyte count (ALC) < or = 700/microL. This model is tested on a pediatric population. PATIENTS AND METHODS: One hundred nineteen children with solid tumors consecutively admitted for conventional chemotherapy throughout 1 year were included. The study end point was the RBC-transfusion risk in the month following chemotherapy. Only one course was considered for each patient. Age, sex, number of courses, platinum-containing regimens, PS, and hemoglobin and lymphocyte count at day 1 were tested in univariate and multivariate analyses. RESULTS: Thirty-one (26%) of 119 children required RBC transfusion within 31 days of chemotherapy. Three factors correlated to transfusion risk in the univariate analysis: PS more than 1 (P <.001), hemoglobin less than 12 g/dL (P =.007), and pretreatment ALC < or = 700/microL (P <.001). In the multivariate analysis, hemoglobin less than 12 g/dL, PS more than 1, and ALC < or = 700/microL were identified as independent factors predicting RBC transfusion. The calculated probability of receiving RBC transfusion within 31 days of chemotherapy was high with three risk factors (96%), intermediate with two risk factors (53% to 77%), low with one risk factor (10% to 26%), and very low when no risk factor was present (2%). The difference of transfusion needs was significant (P <.001). CONCLUSION: The risk model elaborated for adults may also segregate children at high risk of postchemotherapy RBC transfusion, thus facilitating assessment of risk of transfusion and/or prophylactic erythropoietin support.

Adolescent↗
PubMed1992

Dynamic model prediction of the value of reduced solubility of alfalfa silage protein for lactating dairy cows.

A net carbohydrate and protein system was used to develop model diets for lactating dairy cattle with various protein solubilities in the alfalfa silage component of the diet. The objective was to determine the level to which alfalfa silage could be used to replace supplemental protein sources as the silage protein solubility decreased and to estimate the value of silage treatments needed to reduce protein solubility. Four cow groups were considered: early lactation multiparous cows, primiparous cows, midlactation cows, and late lactation cows. Diets were balanced for metabolizable protein, metabolizable energy, and ammonia and peptides for rumen bacteria; limits on DMI and effective NDF were enforced. Lower protein solubility was predicted to increase the yield of bacteria per unit of alfalfa silage DM and the yield of metabolizable protein per unit of alfalfa silage CP. Because of reduced protein supplements, diet costs were decreased. The savings per unit of silage in these rations increased as alfalfa silage protein solubility decreased. For example, with a reduction in solubility from 61 to 51% of CP, the savings ranged from $2.96 to $3.26/tonne of silage across the four cow groups. The value of acid treatment of silage needed to effect these reductions exhibited diminishing returns as application rate increased and appeared to be most cost effective when used on high quality alfalfa fed to high producing cows with application rates less than 2 kg/tonne. Management practices that reduce silage temperatures were predicted to save $.50 to $1.50/tonne of silage when the diets were balanced to account for protein degradability.

Animals↗
PubMed2002

Pancreatic islet transplantation using the nonhuman primate (rhesus) model predicts that the portal vein is superior to the celiac artery as the islet infusion site.

We've established a nonhuman primate islet allotransplant model to address questions such as whether transplanting islets into the gut's arterial system would more safely and as effectively support long-term islet allograft survival compared with the traditional portal vein approach. We reasoned that islets make up <2% of pancreatic cell mass but consume an estimated 20% of arterial blood flow, suggesting an advantage for the arterial site. Access to the arterial system is also easier and safer than the portal system. Pancreatectomized rhesus macaques were transplanted with allogeneic islets infused into either the portal vein (n = 6) or the celiac artery (n = 4). To prevent rejection, primates were given daclizumab, tacrolimus, and rapamycin. In five of six portal vein experiments, animals achieved normoglycemia without exogenous insulin. In contrast, none of the animals given intra-arterial islets showed even transient insulin independence (P = 0.048). Two of the latter animals received a second islet transplant, this time to the portal system, and both achieved insulin independence. Thus, intraportal islet transplantation under conventional immunosuppression is feasible in primates and can result in long-term insulin independence when adequate immunosuppression is maintained. Arterial islet injection, however, does not appear to be a viable islet transplantation technique.

Animals↗
PubMed2005

Prediction model of coronary heart disease in patients with chronic kidney disease: role of plasma fibrinogen as a new prognostic variable.

BACKGROUND: The Framingham-Anderson (FA) risk equation can predict coronary heart disease (CHD) risk in the general population. However, this formula's validity in predicting CHD risk in chronic kidney disease (CKD) patients is not extensively evaluated. METHODS: In a group of 96 patients with CKD stage 2 to 4, free of CHD at the time of the start of follow-up, and prospectively followed for 4 to 12 years (7.4 +/- 2.2 years, mean +/- SD), we calculated the FA index. RESULTS: During the follow-up period, twenty-one patients experienced fatal and non-fatal myocardial infarction (CHDobs+), and 75 remain free of CHD (CHDobs-). The median FA index was 7.1% for CHDobs - patients and 10.3% for CHDobs+ patients. The specificity of the model was acceptable (89%), but the sensitivity was low (24%). Sensitivity analysis by adding fibrinogen led to an improvement in the CHD risk index and the sensitivity of the model (48%) as well. However, despite the addition of fibrinogen to the FA risk factors, full CHD risk in CKD patients remains underestimated. CONCLUSIONS: Our results show that the FA index is a weak predictor of CHD in CKD stage 2 to 4 patients, and emphasized the role of inflammation in predicting the CHD risk.

Aged↗
PubMedDate not supplied

Single-dose model for predicting steady-state valproic acid serum concentrations in seizure patients.

Valproic acid serum concentrations predicted by a single-dose prediction model were compared with steady-state serum concentrations measured after the start of therapy in seizure patients. Ten patients receiving valproic acid for the first time or who had not been taking the drug for two or more weeks were entered into the study. The patients' therapies were initiated with the prescribed doses of valproic acid and then maintained on fixed doses and dosing intervals until steady-state trough serum samples were obtained. Initial 5-ml blood samples were collected six to 14 hours after the ingestion of the first dose; a 5-ml steady-state trough sample was drawn in the same manner three to seven days later. Both free and total drug concentrations were determined within 48 hours of sample collection using gas-liquid chromatography. The elimination rate constant was estimated from age-specific population half-life values found in the literature. Six patients (five children, aged four to 16 years) and one adult (aged 87 years) completed the study. There was a statistically significant correlation between predicted and measured steady-state valproic acid serum concentrations for both free and total concentrations. The single-dose prediction model accurately predicted steady-state valproic acid serum concentrations in these seizure patients.

Adolescent↗
PubMed1995

Survival of Campylobacter jejuni in foods and comparison with a predictive model.

Campylobacter jejuni was inoculated into a range of raw and cooked foods and survival determined during storage at 2 degrees, 10 degrees and 20 degrees C for up to 56 d. To facilitate easy enumeration, two antibiotic-resistant strains of Camp. jejuni, which had similar survival characteristics to the parent strain, were used. Campylobacter jejuni survived for longer at lower temperatures in all foods and inactivation was most rapid in pâté. There was generally good agreement between the survival data and predictions from a Camp. jejuni survival model (Food MicroModel).

Anti-Bacterial Agents↗
PubMed2004

Predictive modelling of post-onset xenoma growth during microsporidial gill disease (Loma salmonae) of salmonids.

Loma salmonae, an obligate intracellular microsporidian parasite, is the causal agent of microsporidial gill disease of salmon (MGDS), characterized by the production, growth and eventual rupture of spore-filled xenomas. MGDS in farmed chinook salmon remains occult until xenoma rupture, at which time the infected fish respond with intense branchitis and high rates of mortality. The present study showed that in experimentally infected fish the rate of change of xenoma diameter could be modelled through regression analysis, particularly through the period of 4-9 weeks post-infection, yielding the predictive equation: xenoma diameter=-42.9 microns +15.3 microns x (number of weeks post-infection). This provides a tool for diagnosticians to predict the time to xenoma rupture and hence to the initiation of the clinical phase of MGDS.

Animals↗
PubMed2004

A clinicobiological model predicting survival in medulloblastoma.

PURPOSE: The purpose of this study was to determine the relative contributions of biological and clinical predictors of survival in patients with medulloblastoma (MB). EXPERIMENTAL DESIGN: Clinical presentation and survival information were obtained for 119 patients who had undergone surgery for MB at the Hospital for Sick Children (Toronto, Ontario, Canada) between 1985 and 2001. A tissue microarray was constructed from the tumor samples. The arrays were assayed for immunohistochemical expression of MYC, p53, platelet-derived growth factor receptor-alpha, ErbB2, MIB-1, and TrkC and for apoptosis (terminal deoxynucleotidyl transferase-mediated nick end labeling). Both univariable and multivariable analyses were conducted to characterize the association between survival and both clinical and biological markers. For the strongest predictors of survival, a weighted predictive score was calculated based on their hazard ratios (HRs). The sum of these scores was then used to give an overall prediction of survival using a nomogram. RESULTS: The four strongest predictors of survival in the final multivariable model were the presence of metastatic disease at presentation (HR, 2.02; P=0.01) and p53 (HR, 2.29; P=0.02), TrkC (HR, 0.65; P=0.14), and ErbB2 (HR, 1.51; P=0.21) immunopositivity. A linear prognostic index was derived, with coefficients equal to the logarithm of these HRs. The 5-year survival rate for patients at the 10th, 50th, and 90th percentiles of the score distribution was 80.0%, 71.0%, and 35.7%, respectively, with radiation therapy and 70.5%, 58.5%, and 20.0%, respectively, without radiation therapy. CONCLUSIONS: In this study, we demonstrate an approach to combining both clinical and biological markers to quantify risk in MB patients. This provides further prognostic information than can be obtained when either clinical factors or biological markers are studied separately and establishes a framework for comparing prognostic markers in future clinical studies.

Adolescent↗
PubMed2026

Massively parallel characterization and predictive modelling of neuronal regulatory variation.

Disease-associated variants reside frequently in noncoding cis-regulatory elements (CREs), yet their functional consequences remain poorly understood. We performed a large-scale lentiMPRA in human excitatory neurons, quantifying the impact of >46,000 naturally occurring variants across >27,000 candidate CREs near 524 disease-associated genes. These data improved regulatory variant effect predictions beyond state-of-the-art models. Significant allelic effects occurred at comparable rates across common, rare, and singleton variants, demonstrating that, within MPRA-measurable effects, population frequency carries limited information about per-variant regulatory impact. Variant effect detectability and magnitude were governed primarily by baseline activity of the enclosing regulatory element and local sequence context. Regulatory effects were distributed across numerous transcription factors rather than concentrated in master regulators, consistent with a combinatorial enhancer architecture. We establish a large-scale functional variant catalog and provide a complementary benchmark and resource for developing and evaluating models of noncoding regulatory variation.

Journal Article↗
PubMed1997

Red-green and achromatic temporal filters: a ratio model predicts contrast-dependent speed perception.

We simultaneously measured detection and identification performance by using isoluminant red-green (RG) and achromatic flickering stimuli and fitted these data with a modified line-element model that does not make high-threshold assumptions. The modeling shows that detection and identification data are adequately described by postulating only two underlying temporal filters each for RG and achromatic vision, even when more than two threshold classifications are evident. We use a spatial frequency of 1.5 cycles per degree (c/deg) and compare the derived temporal impulse response functions with those obtained previously with the use of 0.25 c/deg stimuli under otherwise identical conditions [J. Opt. Soc. Am. A 13, 1969 (1996)]. We find that at 1.5 c/deg the luminance impulse response functions peak later and integrate out to longer times compared with those measured at 0.25 c/deg. For RG stimuli, although their relative overall sensitivities change, the impulse response functions are similar across spatial frequency, indicating a constancy of chromatic temporal properties across spatial scales. In a second experiment, we measured RG and achromatic flicker discrimination over a wide range of suprathreshold contrasts. These data suggest a common nonlinear contrast response function operating after initial temporal filtering. Using a ratio model of speed perception in which both RG and achromatic filters are combined at a common motion site, we can predict (1) the perceived slowing of RG stimuli compared with the perceived drift of achromatic drifting stimuli, (2) the contrast dependency of speed perception for RG and achromatic drifting stimuli, and (3) how this dependency changes with base speed. Thus we conclude that there is no need to postulate separate mechanisms for fast and slow motion [Nature (London) 367, 268 (1994)], since a unified ratio model can explain both RG and achromatic contrast-speed dependency.

Color Perception↗
PubMed2003

Finite element models predict in vitro vertebral body compressive strength better than quantitative computed tomography.

The correlation between bone mineral density and vertebral strength is not based on mechanical principles and thus the method cannot reflect the effects of subtle geometric features and densitometric inhomogeneities that may substantially affect vertebral strength. Finite element models derived from quantitative computed tomography (QCT) scans overcome such limitations. The overall goal of this study was to establish that QCT-based "voxel" finite element models are better predictors of vertebral compressive strength than QCT measures of bone mineral density with or without measures of cross-sectional area. QCT scans were taken of 13 vertebral bodies excised from 13 cadavers (L1-L4; age: 37-87 years; M = 6, F = 7) and used to calculate bone mineral density (BMD(QCT)). The QCT voxel data were converted into linearly elastic finite element models of each vertebra, from which measures of vertebral stiffness and strength were computed. The vertebrae were biomechanically tested in compression to measure strength. Vertebral strength was positively correlated with the finite element measures of strength (r(2) = 0.86, P < 0.0001) and stiffness (r(2) = 0.82, P < 0.0001), the product of BMD(QCT) and vertebral minimum cross-sectional area (r(2) = 0.65, P = 0.0008), and BMD(QCT) alone (r(2) = 0.53, P = 0.005). These results demonstrate that highly automated "voxel" finite element models are superior to correlation-based QCT methods in predicting vertebral compressive strength and therefore offer great promise for improvement of clinical fracture risk assessment.

Adult↗
PubMed2006

Finite element modeling predictions of region-specific cell-matrix mechanics in the meniscus.

The knee meniscus exhibits significant spatial variations in biochemical composition and cell morphology that reflect distinct phenotypes of cells located in the radial inner and outer regions. Associated with these cell phenotypes is a spatially heterogeneous microstructure and mechanical environment with the innermost regions experiencing higher fluid pressures and lower tensile strains than the outer regions. It is presently unknown, however, how meniscus tissue mechanics correlate with the local micromechanical environment of cells. In this study, theoretical models were developed to study mechanics of inner and outer meniscus cells with varying geometries. The results for an applied biaxial strain predict significant regional differences in the cellular mechanical environment with evidence of tensile strains along the collagen fiber direction of approximately 0.07 for the rounded inner cells, as compared to levels of 0.02-0.04 for the elongated outer meniscus cells. The results demonstrate an important mechanical role of extracellular matrix anisotropy and cell morphology in regulating the region-specific micromechanics of meniscus cells, that may further play a role in modulating cellular responses to mechanical stimuli.

Animals↗
PubMed2001

Testing a predictive model of what makes a critical thinker.

The goal of nursing education is to help individuals become self-determining, independent thinkers. Cognitive development may be the outcome that best characterizes such a thinker. The purpose of this study was to test a model of cognitive development in which four independent variables--knowledge base, critical thinking skills, critical thinking dispositions, and experience--were used to predict cognitive development. Data were analyzed from 232 practicing registered nurses. Three hierarchical levels of cognitive development were examined: dualism, relativism, and commitment. Critical thinking skill was a significant contributor only to the dualistic level of cognitive development. Critical thinking dispositions contributed to all three levels of cognitive development. Experience contributed only to the commitment level. The results of this study suggest that the development of a critical thinker may require time and experience. These findings can be used to examine current policy regarding the criteria used to evaluate nursing education.

Clinical Competence↗