Exact mathematical equivalence of the venous equilibration ("well-stirred") model, the sinusoidal perfusion ("parallel-tube") model, and a specific two-compartment open model.
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Humans↗
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Results for “Model”
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[Modeling of bromsulphthalein distribution curves in plasma, hepatocytes, and bile. I. Storage gradient and transport maximum as starting variables of the model. Method of modeling].
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Bile↗
[Human and nursing models. 4. Johnson's behavior system model--selection and introduction of a nursing model].
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Behavioral Sciences↗
[Cognitive modeling in psychiatry: from symbolic models to parallel and distributed models].
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Artificial Intelligence↗
The five-factor model of the Positive and Negative Syndrome Scale II: a ten-fold cross-validation of a revised model.
OBJECTIVE: The lack of fit of 25 previously published five-factor models for the PANSS items, can be due to the statistics used. The purpose of this study was to use a 'new' statistical method to develop and confirm an improved five-factor model. The improved model is both complex and stable. Complex means that symptoms can have multiple factor loadings, because they have multiple causes, not because they are ill defined. Stable means that the complex structure is found repeatedly in validations. METHODS: A ten-fold cross-validation (10 CV) was applied on a large data set (N = 5769) to achieve an improved factor model for the PANSS items. The advantages of 10 CV are minimal effect of sample characteristics and the ability to investigate the stability of items loading on multiple factors. RESULTS: The results show that twenty-five items contributed to the same factor all ten validations with one item showing a consistent loading on two factors. Three items were contributing to the same factor nine out of ten validations, and two items were contributing to the same factor six to eight times. The resulting five-factor model covers all thirty items of the PANSS, subdivided in the factors: positive symptoms, negative symptoms, disorganization, excitement, and emotional distress. The five-factor model has a satisfactory goodness-of-fit (Comparative Fit Index = .905; Root Mean Square Error of Approximation = .052). CONCLUSIONS: The five-factor model developed in this study is an improvement above previously published models as it represents a complex factor model and is more stable.
Affect↗
The German cervical cancer screening model: development and validation of a decision-analytic model for cervical cancer screening in Germany.
BACKGROUND: We sought to develop and validate a decision-analytic model for the natural history of cervical cancer for the German health care context and to apply it to cervical cancer screening. METHODS: We developed a Markov model for the natural history of cervical cancer and cervical cancer screening in the German health care context. The model reflects current German practice standards for screening, diagnostic follow-up and treatment regarding cervical cancer and its precursors. Data for disease progression and cervical cancer survival were obtained from the literature and German cancer registries. Accuracy of Papanicolaou (Pap) testing was based on meta-analyses. We performed internal and external model validation using observed epidemiological data for unscreened women from different German cancer registries. The model predicts life expectancy, incidence of detected cervical cancer cases, lifetime cervical cancer risks and mortality. RESULTS: The model predicted a lifetime cervical cancer risk of 3.0% and a lifetime cervical cancer mortality of 1.0%, with a peak cancer incidence of 84/100,000 at age 51 years. These results were similar to observed data from German cancer registries, German literature data and results from other international models. Based on our model, annual Pap screening could prevent 98.7% of diagnosed cancer cases and 99.6% of deaths due to cervical cancer in women completely adherent to screening and compliant to treatment. Extending the screening interval from 1 year to 2, 3 or 5 years resulted in reduced screening effectiveness. CONCLUSIONS: This model provides a tool for evaluating the long-term effectiveness of different cervical cancer screening tests and strategies.
Adolescent↗
The cost effectiveness of anesthesia workforce models: a simulation approach using decision-analysis modeling.
UNLABELLED: The objective of this study was to evaluate the incremental cost effectiveness of anesthesia workforce staffing scenarios, as a function of skill mix, by using the technique of decision analysis. A decision tree model was constructed to compare the incremental cost effectiveness of alternative delivery systems for anesthesia care from the perspective of the payer. Five different staffing scenarios, ranging from physician-intensive to nurse-intensive, were modeled. In the nurse-intensive model, low- and intermediate-risk patients were cared for by solo certified registered nurse anesthetists (CRNAs) and high-risk patients were cared for by physicians. In the physician-intensive model, physicians anesthetized all patients. In the first-, second-, and third-team models, all high-risk patients were cared for by physicians working alone, and all intermediate-risk patients were cared for using an anesthesia care team approach with a ratio of one physician to two CRNAs. The low-risk patients were managed by using an anesthesia care team approach with physician to CRNA ratios of 1:2, 1:4, and 1:8 in the first-, second-, and third-team models, respectively. The findings of this decision-analysis model suggest that physician-only anesthesia is not cost effective. However, the third-team model is cost effective when compared with the nurse-intensive model. IMPLICATIONS: An anesthesia care-team approach with a physician to certified registered nurse anesthetist (CRNA) ratio of 1:2 is the preferred staffing scenario for intermediate-risk patients. Although medical direction of CRNAs caring for low-risk patients is cost-effective, the small improvement in outcome resulting from increasing the physician to CRNA ratio from 1:8 to 1:4 may not be justified by the added cost.
Adult↗
Glial phosphorylated p38 MAP kinase mediates pain in a rat model of lumbar disc herniation and induces motor dysfunction in a rat model of lumbar spinal canal stenosis.
STUDY DESIGN: Immunohistochemical and behavioral study using rat models of lumbar disc herniation and cauda equina syndrome. OBJECTIVE: To investigate the expression of activated p38 mitogen-activated protein kinases (p38 MAP kinase; p38) in the spinal cord and to determine the effect of intrathecal administration of a specific p38 inhibitor on pain in a lumbar disc herniation model and on motor function and hypoalgesia in a spinal canal stenosis (SCS) model. SUMMARY OF BACKGROUND DATA: In pathologic lumbar disc herniation-induced neuropathic pain and compression of cauda equina-induced motor dysfunction and hypoalgesia caused by SCS, glia are activated and produce certain cytokines, including tumor necrosis factor-alpha (TNF-alpha) and interleukins, which play a crucial role in the pathogenesis of nerve degeneration. p38 is phosphorylated by these cytokines, suggesting that it may play an important role in pain transmission and nerve degeneration. Here we have examined the role of p38 in rat models of lumbar disc herniation and SCS. METHODS: Six-week-old male Sprague-Dawley rats were used. For the disc herniation model, autologous nucleus pulposus was applied to L5 nerve roots, which were then crushed. For the SCS model, a piece of silicon was placed under the lamina of the fourth lumbar vertebra. We assessed mechanical allodynia, hypoalgesia, and motor function using von Frey hairs, treadmill tests, and immunohistochemical localization of phosphorylated p38 (P-p38) in the cauda equina, dorsal root ganglion (DRG), and spinal cord, which were also double-stained with NeuN (neuronal marker), GFAP (astrocyte/Schwann cell marker), or isolectin B4 (IB4; microglia marker). We also examined the effects of intrathecal administration of a specific p38 inhibitor, FR167653, on nucleus pulposus-induced pain, hypoalgesia, and motor dysfunction following SCS. RESULTS: We demonstrated that activated P-p38-immunoreactive cells in the spinal cord and cauda equina were not observed before nerve injury but appeared in the cauda equina, DRG, and spinal dorsal horn in the disc herniation and SCS models. Double-labeling revealed that most P-p38-immunoreactive cells were isolectin B4-labeled microglia and GFAP-immunoreactive Schwann cells. Intrathecal administration of the p38 inhibitor FR167653 decreased mechanical allodynia in the disc herniation model and improved hypoalgesia and intermittent motor dysfunction in the SCS model. CONCLUSIONS: Our findings suggest that activated p38 may play an important role in the involvement of microglia in the pathophysiology of pain following lumbar disc herniation and mechanical hypoalgesia, and motor nerve dysfunction of cauda equina following SCS.
Animals↗
Evaluating the impact of modeling choices on the performance of integrated genetic and clinical models.
The value of genetic information for improving the performance of clinical risk prediction models has yielded variable conclusions. Many methodological decisions have the potential to contribute to differential results across studies. Here, we performed multiple modeling experiments integrating clinical and demographic data from electronic health records (EHR) and genetic data to understand which decision points may affect performance. Clinical data in the form of structured diagnostic codes, medications, procedural codes, and demographics were extracted from two large independent health systems and polygenic risk scores (PRS) were generated across all patients with genetic data in the corresponding biobanks. Crohn's disease was used as the model phenotype based on its substantial genetic component, established EHR-based definition, and sufficient prevalence for model training and testing. We investigated the impact of PRS integration method, as well as choices regarding training sample, model complexity, and performance metrics. Overall, our results show that including PRS resulted in higher performance by some metrics but the gain in performance was only robust when combined with demographic data alone. Improvements were inconsistent or negligible after including additional clinical information. The impact of genetic information on performance also varied by PRS integration method, with a small improvement in some cases from combining PRS with the output of a clinical model (late-fusion) compared to its inclusion an additional feature (early-fusion). The effects of other modeling decisions varied between institutions though performance increased with more compute-intensive models such as random forest. This work highlights the importance of considering methodological decision points in interpreting the impact on prediction performance when including PRS information in clinical models.
Preprint↗
Interacting damage models mapped onto Ising and percolation models.
We introduce a class of damage models on regular lattices with isotropic interactions between the broken cells of the lattice. Quasi-static fiber bundles are an example. The interactions are assumed to be weak, in the sense that the stress perturbation from a broken cell is much smaller than the mean stress in the system. The system starts intact with a surface-energy threshold required to break any cell sampled from an uncorrelated quenched-disorder distribution. The evolution of this heterogeneous system is ruled by Griffith's principle which states that a cell breaks when the release in potential (elastic) energy in the system exceeds the surface-energy barrier necessary to break the cell. By direct integration over all possible realizations of the quenched disorder, we obtain the probability distribution of each damage configuration at any level of the imposed external deformation. We demonstrate an isomorphism between the distributions so obtained and standard generalized Ising models, in which the coupling constants and effective temperature in the Ising model are functions of the nature of the quenched-disorder distribution and the extent of accumulated damage. In particular, we show that damage models with global load sharing are isomorphic to standard percolation theory and that damage models with a local load sharing rule are isomorphic to the standard Ising model, and draw consequences thereof for the universality class and behavior of the autocorrelation length of the breakdown transitions corresponding to these models. We also treat damage models having more general power-law interactions, and classify the breakdown process as a function of the power-law interaction exponent. Last, we also show that the probability distribution over configurations is a maximum of Shannon's entropy under some specific constraints related to the energetic balance of the fracture process, which firmly relates this type of quenched-disorder based damage model to standard statistical mechanics.
Journal Article↗
Mathematical modeling of tumor therapy with oncolytic viruses: regimes with complete tumor elimination within the framework of deterministic models.
BACKGROUND: Oncolytic viruses that specifically target tumor cells are promising anti-cancer therapeutic agents. The interaction between an oncolytic virus and tumor cells is amenable to mathematical modeling using adaptations of techniques employed previously for modeling other types of virus-cell interaction. RESULTS: A complete parametric analysis of dynamic regimes of a conceptual model of anti-tumor virus therapy is presented. The role and limitations of mass-action kinetics are discussed. A functional response, which is a function of the ratio of uninfected to infected tumor cells, is proposed to describe the spread of the virus infection in the tumor. One of the main mathematical features of ratio-dependent models is that the origin is a complicated equilibrium point whose characteristics determine the main properties of the model. It is shown that, in a certain area of parameter values, the trajectories of the model form a family of homoclinics to the origin (so-called elliptic sector). Biologically, this means that both infected and uninfected tumor cells can be eliminated with time, and complete recovery is possible as a result of the virus therapy within the framework of deterministic models. CONCLUSION: Our model, in contrast to the previously published models of oncolytic virus-tumor interaction, exhibits all possible outcomes of oncolytic virus infection, i.e., no effect on the tumor, stabilization or reduction of the tumor load, and complete elimination of the tumor. The parameter values that result in tumor elimination, which is, obviously, the desired outcome, are compatible with some of the available experimental data. REVIEWERS: This article was reviewed by Mikhail Blagosklonny, David Krakauer, Erik Van Nimwegen, and Ned Wingreen. OPEN PEER REVIEW: Reviewed by Mikhail Blagosklonny, David Krakauer, Erik Van Nimwegen, and Ned Wingreen. For the full reviews, please go to the Reviewers' comments section.
Journal Article↗
A comparison of the gamma knife model C and the automatic positioning system with Leksell model B.
OBJECT: The authors sought to compare the quality of treatment planning, radiation protection, and the time taken for treatment in the Leksell gamma knife model B with that using the model C Automatic Positioning System (APS). METHODS: Data were obtained in 463 patients treated with the B model and 518 patients treated with the C model. Data were analyzed in patients in whom the following diagnoses had been made: vestibular schwannoma, pituitary adenoma, meningioma, solitary metastasis, and other benign and malignant solitary tumors. Patients with arteriovenous malformations, ocular lesions, and functional diagnoses were excluded from this study. CONCLUSIONS: With the C model there was a better conformity for most treated targets, such as vestibular schwannomas (p = 0.005) and meningiomas (p = 0.015). The level of radiation exposures to personnel was significantly decreased when using the model C (p < 0.001). There was no significant difference in radiation exposure of extracranial structures for the same number of shots in patients treated by both models. The mean time saved using the C model with the APS was 41 minutes per treatment. It would seem that the gamma knife model C permits better dose conformity, shorter treatment times, and less radiation exposure to personnel.
Adenoma↗
Modeling and modification of medical 3D objects. The benefit of using a haptic modeling tool.
The Computer Laboratory of the medical faculty in Goteborg (Mednet) has since the end of 1998 been one of a limited numbers of participants in the development of a new modeling tool together with SensAble Technologies Inc [http:¿www.sensable.com/]. The software called SensAble FreeForm was officially released at Siggraph September 1999. Briefly, the software mimics the modeling techniques traditionally used by clay artists. An imported model or a user defined block of "clay" can be modified using different tools such as a ball, square block, scrape etc via the use of a SensAble Technologies PHANToM haptic arm. The model will deform in 3D as a result of touching the "clay" with any selected tool and the amount of deformation is linear to the force applied. By getting instantaneous haptic as well as visual feedback, precise and intuitive changes are easily made. While SensAble FreeForm lacks several of the features normally associated with a 3D modeling program (such as text handling, application of surface and bumpmaps, high-end rendering engines, etc) it's strength lies in the ability to rapidly create non-geometric 3D models. For medical use, very few anatomically correct models are created from scratch. However, FreeForm features tools enable advanced modification of reconstructed or 3D scanned models. One of the main problems with 3D laserscanning of medical specimens is that the technique usually leaves holes or gaps in the dataset corresponding to areas in shadows such as orifices, deep grooves etc. By using FreeForms different tools, these defects are easily corrected and gaps are filled out. Similarly, traditional 3D reconstruction (based on serial sections etc) often shows artifacts as a result of the triangulation and/or tessellation processes. These artifacts usually manifest as unnatural ridges or uneven areas ("the accordion effect"). FreeForm contains a smoothing algorithm that enables the user to select an area to be modified and subsequently apply any given amount of smoothing to the object. While the final objects need to be exported for further 3D graphic manipulation, FreeForm addresses one of the most time consuming problems of 3D modeling: modification and creation of non-geometric 3D objects.
Computer Simulation↗
A model for diagnostics in neurological rehabilitation: an answer to 'the biopsychosocial disease consequence model in rehabilitation' of Talo et al.
In 1996, Talo et al. published their comprehensive version of a bio-psycho-social disease consequence model in rehabilitation, which deals with 'model development in the Finnish "Work hardening" programme for chronic pain'. The explanations given here serve to check the theoretical background of this model for certain basic assumptions as well as for the possibility to transfer it to other fields of rehabilitation. This is done from the viewpoint of neurological rehabilitation. The starting point is the consideration that the conceptions underlying the ICIDH are not suitable to serve as a mainstay of a model for diagnostics in rehabilitation because they do not reflect essential characteristics of the diagnostic process which is the basis for intervention. A model for diagnostics in neurological rehabilitation is contrasted to that of Talo et al. Regarding the theoretical background this model has different characteristics compared to that developed by the Finnish authors. It is guided by the process of gaining cognition in two different ways: (1) On the assumption that the diagnostic process reflects the same principles basically valid for theory-development in science, the basis of the model are conceptions for description and explanation of a patient's current condition. (2) Due to a holistic idea of disablement these conceptions are related to the individual's bio-psychosocial existence. As it relates to the model developed by Talo et al. this one represents a type of 'meta-level'. With regard to the long-term objective the main interest associated with the alternative model refers to its implications concerning the conception of the rehabilitation process as a prerequisite for internal quality management.
Chronic Disease↗
A large class of models derived from generalized linear models.
Generalized linear models may be extended in several ways. This paper describes five such extensions: (i) generalized additive models; (ii) the use of quasi-likelihood; (iii) joint modelling of mean and dispersion; (iv) introduction of extra random components to give hierarchical generalized linear models; (v) modelling of correlated responses within subjects in longitudinal models. These extensions are largely independent, and so can be combined in many ways to produce a large class of models. Finally, a further extension to dynamic forms of the models is sketched.
Linear Models↗
Comparison of Bayesian model averaging and stepwise methods for model selection in logistic regression.
Logistic regression is the standard method for assessing predictors of diseases. In logistic regression analyses, a stepwise strategy is often adopted to choose a subset of variables. Inference about the predictors is then made based on the chosen model constructed of only those variables retained in that model. This method subsequently ignores both the variables not selected by the procedure, and the uncertainty due to the variable selection procedure. This limitation may be addressed by adopting a Bayesian model averaging approach, which selects a number of all possible such models, and uses the posterior probabilities of these models to perform all inferences and predictions. This study compares the Bayesian model averaging approach with the stepwise procedures for selection of predictor variables in logistic regression using simulated data sets and the Framingham Heart Study data. The results show that in most cases Bayesian model averaging selects the correct model and out-performs stepwise approaches at predicting an event of interest.
Age Factors↗
Locally regularized spatiotemporal modeling and model comparison for functional MRI.
In this work we treat fMRI data analysis as a spatiotemporal system identification problem and address issues of model formulation, estimation, and model comparison. We present a new model that includes a physiologically based hemodynamic response and an empirically derived low-frequency noise model. We introduce an estimation method employing spatial regularization that improves the precision of spatially varying noise estimates. We call the algorithm locally regularized spatiotemporal (LRST) modeling. We develop a new model selection criterion and compare our model to the SPM-GLM method. Our findings suggest that our method offers a better approach to identifying appropriate statistical models for fMRI studies.
Arousal↗
Suitability of a batch in vitro fermentation model using human faecal microbiota for prediction of conversion of flaxseed lignans to enterolactone with reference to an in vivo rat model.
BACKGROUND: In vitro fermentation models have been used widely for studies of shortchain fatty acid (SCFA) formation from carbohydrates, whereas the suitability of these methods for enterolactone (ENL) formation has received less attention. AIM: The aim was to study the suitability of an in vitro fermentation model for prediction of bioconversion of lignans to ENL, to compare the approach with that of an in vivo rat model and to study the SCFA formation in both models. METHODS: Predigested samples of rye bran (R), flaxseed meal (F) alone, or in combination with rye bran (R&F) and a faecal control were incubated in an in vitro fermentation model using human faecal microbiota. In the in vivo experiment rats consumed a non-fibre control diet (C) or diets supplemented either with rye bran (R), flaxseed meal (F) alone, or with their combination (R&F) for four weeks. Enterodiol (END), ENL and SCFA concentrations were measured from in vitro faecal fermentation samples and from the intestinal contents of rats. Plasma ENL concentrations from rats were also measured. RESULTS: The highest ENL production was found in vitro with the F supplement (areas under curve: 740 +/- 4, 7,500 +/- 400, 2,600 +/- 500 and 1,520 +/- 70 nmol x h for the R, F, R&F supplements and faecal control, respectively). In vivo, the concentration of ENL in caecal digesta from flaxseed meal was significantly (P < 0.05) enhanced by the presence of rye bran (medians 261, 407 and 24 nmol/g in the F, R&F and C groups, respectively). No correlation was found between the models regarding ENL production, possibly due to different responses to the presence of rye bran matrix, differences in microbiota or application of a batch in the in vitro fermentation model. Rye bran supplementation enhanced butyrate production both in vitro and in vivo. CONCLUSION: In vitro fermentation and the in vivo rat models responded differently to the presence of rye bran and no correlation with regard to the ENL formation from flaxseed lignans was observed.
4-Butyrolactone↗