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At least 685 records · Page 38Linked to original sources
PubMed2000

The risks of transfusion-transmitted infection: direct estimation and mathematical modelling.

Direct measurement of the risk of transfusion-transmitted infection (TTI) is practical and accurate only if the level of risk is high. Historically, studies that established frozen repositories of transfusion recipient and/or blood donor samples were important in establishing the risk of many TTI agents, including the human immunodeficiency virus (HIV), hepatitis B virus (HBV) and hepatitis C virus (HCV). However, given the current very low risk of TTI, mathematical modelling is necessary to estimate the magnitude of such a risk. For agents for which routine blood donor screening is performed, most of this risk comes from transfusion of units collected in the window period between donor infection and a positive blood screening assay. The incidence/window period model has been used to estimate the magnitude of such risks (of the order of 1:100 000 to 1:1 000 000) and for predicting the extent of risk reduction that can be expected with implementation of new tests. Direct estimation and mathematical modelling approaches are both important tools for future assessment of potential, new or emerging TTI agents.

Blood Donors↗
PubMed1999

Mathematical models for predicting indoor air quality from smoking activity.

Much progress has been made over four decades in developing, testing, and evaluating the performance of mathematical models for predicting pollutant concentrations from smoking in indoor settings. Although largely overlooked by the regulatory community, these models provide regulators and risk assessors with practical tools for quantitatively estimating the exposure level that people receive indoors for a given level of smoking activity. This article reviews the development of the mass balance model and its application to predicting indoor pollutant concentrations from cigarette smoke and derives the time-averaged version of the model from the basic laws of conservation of mass. A simple table is provided of computed respirable particulate concentrations for any indoor location for which the active smoking count, volume, and concentration decay rate (deposition rate combined with air exchange rate) are known. Using the indoor ventilatory air exchange rate causes slightly higher indoor concentrations and therefore errs on the side of protecting health, since it excludes particle deposition effects, whereas using the observed particle decay rate gives a more accurate prediction of indoor concentrations. This table permits easy comparisons of indoor concentrations with air quality guidelines and indoor standards for different combinations of active smoking counts and air exchange rates. The published literature on mathematical models of environmental tobacco smoke also is reviewed and indicates that these models generally give good agreement between predicted concentrations and actual indoor measurements.

Air Pollution, Indoor↗
PubMedDate not supplied

[An experimental study and a mathematical model of interactions in mixed culture of invertebrates and algae in the "producer-consumer" aquatic biotic cycle].

An experimental investigation was carried out, and a mathematical model of interaction between invertebrates (infusoria Paramecium caudatum and rotifera Brachionus plicatilis) and algae (Chlorella vulgaris and Scenedesmus quadricauda) in the "producer-consumer" aquatic biotic cycle with spatially divided links was constructed. The model describes the dynamics of a mixed culture of infusoria and rotifera in the "consumer" link, when they consume a mixed culture of algae coming from the "producer" link. A negative influence of products of algae Scenedesmus metabolism upon the reproduction of infusoria P. caudatum was revealed. Taking this into account, a qualitative coincidence of the results of mathematical modeling with experimental data was obtained. It was shown that the co-existence of mixed algae culture in the "producer" link with invertebrates in the "consumer" link in the "producer-consumer" aquatic biotic cycle is impossible because of the displacement of infusoria P. caudatum by rotifera Brachionus plicatilis.

Animals↗
PubMed2005

A mathematical model for evaluation of maternal cell contamination in cultured cells from spontaneous abortions: significance for cytogenetic analysis of prenatal selection factors.

OBJECTIVE: To develop a mathematical model for more precise estimation of the incidence of chromosomal abnormalities and the sex ratio among spontaneous abortions masked by maternal cell contamination. DESIGN: Retrospective analysis. SETTING: Academic medical center. PATIENT(S): One hundred twelve samples of spontaneous abortion with a "46,XX" karyotype and 97 parents with aborted embryos. INTERVENTION(S): The presence of Y chromosome DNA in native tissues of "46,XX" spontaneous abortions was detected by amelogenin locus analysis. Detection of aneuploidies in noncultured tissues of "46,XX" abortions was performed by microsatellite DNA analysis and confirmed by fluorescence in situ hybridization. MAIN OUTCOME MEASURE(S): Accuracy of cytogenetic evaluation of spontaneous abortions. RESULT(S): Y chromosome DNA was revealed in 16% of the embryos with a "46,XX" karyotype. According to the mathematical model proposed, the frequency of chromosomal abnormalities in a sample of 478 abortions increased from 54.6% to 60.3%, and the sex ratio in embryos with normal karyotype changed from 0.66 to 1.02. The experimental validation of the model has shown that the observed and expected incidences of chromosomal abnormalities in "46,XX" abortions were in good agreement. CONCLUSION(S): Maternal cell contamination clearly affects the incidence of registered chromosomal abnormalities and the sex ratio in spontaneous abortions. Correction for maternal cell contamination should be taken into account before invoking biological explanations of sex ratio bias and might be useful to include in diagnostic reporting.

Abortion, Spontaneous↗
PubMed1989

Circulatory assistance by intrathoracic pressure variations: optimization and mechanisms studied by a mathematical model in relation to experimental data.

The hemodynamic effects of phasic variations in intrathoracic pressure (ITP) timed to the cardiac cycle were predicted by a mathematical model and were compared with data from canine experimental studies. The model was used to predict the hemodynamic effects of changing the onset of the ITP rise relative to the start of cardiac systole, as well as the hemodynamic effects of changes in the duration and amplitude of the ITP rise. The predictions of the model were compared with hemodynamic data from seven anesthetized dogs. Cardiac function was depressed with large doses of verapamil and propranolol, and the hearts were atrioventricular sequentially paced at a rate of 72 beats/min. Phasic ITP variations were generated by a perithoracic vest and were electronically timed to the cardiac cycle. The model predicted, and the experimental data confirmed, that phasic intrathoracic pressure variations generated by vest inflation, timed to the cardiac cycle, can augment both peak and mean aortic flow. The following predictions of the model were also confirmed by the experimental data: 1) Maximum flow augmentation occurs when the onset of the ITP rise is simultaneous with the onset of left ventricular isovolumic contraction, and the ITP rise has a duration of 400 msec. 2) The magnitude of the flow augmentation is a function of the amplitude of the ITP rise. The experimental data showed that there was little further flow augmentation when the ITP rise was greater than 30-40 mm Hg. 3) The magnitude of flow augmentation was inversely proportional to the peak left ventricular elastance (Emax). The best fit between the measured and predicted flow augmentations was obtained for an assumed Emax of 0.5 mm Hg/ml, while Emax measurements in three dogs, using a volume conductance catheter and transient vena caval occlusion, yielded values of 0.4-1.6 mm Hg/ml. Thus, both the mathematical model and canine experiments showed that relatively low-amplitude ITP variations, rising synchronously with the onset of cardiac systole and having an optimal duration, assist the failing heart by augmentation of aortic flow. The degree of cardiac assistance decreases if the ITP variations do not rise synchronously with the onset of systole, or if their duration is not optimal. Thus, properly applied ITP variations may be used as an efficient, noninvasive method to temporarily assist the failing heart.

Animals↗
PubMed2005

[Mathematical model in prediction and evaluation of the effects on control measures for schistosomiasis].

OBJECTIVE: To carry out a theoretical research on the rule that a mathematical model may play on predicting and evaluating the control effect of schistosomiasis japonica. METHODS: Earbour's two-host model was used to predict and evaluate the effect of different control measures by computer simulation. Pilot samples in two villages of Shanghai suburb in 1950s were applied for the analysis. RESULTS: When the prevalence was high, synchronous chemotherapy for human and cattle populations quickly reduced the indices of the infection. Mollusciciding provided positive impact on the effect of chemotherapy. Added with the environmental measures for snail control, the basic reproductive rate (BRR) and equilibrium prevalence in human and bovines were sustainably reduced and even reached an interruption of transmission. The effect of chemotherapy could be consolidated by the anti-fecundity vaccine for bovines. Satisfied control effect could also be obtained by chemotherapy in human and bovines combined with behaviour intervention for human and vaccination for bovines without snail control. In areas with lower levels of transmission velocity, BRR and prevalence, the effect of various interventions was better than that obtained in areas with higher levels of the above three infection indices, and the disease control could be easier. Conclusion The Barbour's mathematical model can be used to roughly predict and evaluate the effects of schistosomiasis control measures.

Animals↗
PubMed1984

T helper cell inclusion into the mathematical model of immunological tolerance.

The experimentally observed recovery from tolerance to HSA in chickens is much slower than the values calculated by means of the simple mathematical model of B cell tolerance. The model assumes that tolerance is due to elimination or irreversible inactivation of immunocompetent cells reactive to the tolerated antigen, and that the recovery from tolerance is caused by the differentiation of new immunocompetent cells. Even when two collaborating B cell populations reactive to HSA were considered, the calculated recovery from tolerance was much slower than the observed one. Therefore, T helper cell tolerance was suspected and included into the mathematical model. The experimental data agreed best with the calculated values of the recovery from tolerance to HSA obtained with a T cell lifespan of 200 days. On the other hand, when two T helper cell populations cooperated with B cells in anti-HSA antibody production, the curve best fitting the experimental data corresponded to the T cell lifespan of 60 days.

Animals↗
PubMed1997

Hemodynamic consequences of replacing the aorta by vascular grafts simulated in a mathematical model.

OBJECTIVE: Replacing parts of the aorta by a noncompliant vascular prosthesis results in marked alterations of the aortic input impedance and influences arterial hemodynamics. We propose a mathematical model of circulation able to predict hemodynamic changes after simulation of vascular grafting. METHODS: Using a mathematical 128-branch model of the human arterial system a digitized aortic flow wave was chosen as the input signal to this system. After determination of the modules of elasticity of native vascular tissue and customary prostheses in technical experiments, replacement of any part of the aorta with a prosthesis was simulated by increasing the elasticity in the parts desired. RESULTS: During control conditions, the model displayed a physiologic distribution of flow and pressure waves throughout the arterial system. Simulated replacement of the aorta resulted in an increase of pressure amplitude and a partial loss of the aortic "Windkessel" function. Calculation of the aortic input impedance showed an increase of the characteristic impedance, while the peripheral resistance remained unaltered. CONCLUSION: This mathematical model of the arterial circulation proves to be useful to simulate hemodynamic changes after implantation of vascular grafts. The results of the model analysis are consistent with previous work done in experimental setups.

Aorta↗
PubMedDate not supplied

Mathematical modeling and analysis in biochemical engineering: past accomplishments and future opportunities.

This is a personal commentary on the history and future prospects of mathematical modeling and analysis in biochemical engineering. Major transitions in these fields were driven by the appearance of the Aiba, Humphrey, and Millis text, Fredrickson's guidance on conceptualizing mathematical representations of cell populations, and Ramkrishna's development of the cybernetic modeling approach. The value of mathematical models to organize data, to consider interactions in complex systems in a rational way, to correct the conventional wisdom, and to understand essential qualitative features of biological systems has been clearly documented in prior research. The impact of this research in biotechnology discovery has so far been limited, but this will change in the future if we are adept in recognizing emerging opportunities and in integrating new concepts and tools into our research. Mathematical structures and methods, allied with extraordinary contemporary computing power, are essential to the emerging field of functional genomics. Important in this quest is a hierarchy of powerful modeling, analysis, and computational tools which can capture essential quantitative features of available experimental data and use these effectively for analysis and design of metabolism.

Animals↗
PubMed2000

[Prediction of physiological response from mathematical models].

The ability to predict the physiological responses of workers exposed to extreme environmental conditions, has been a challenge to environmental physiologists for more than 3 decades. Therefore, mathematical models have been developed to predict metabolic rate under various levels of work intensity and dynamic changes in body temperature and heart rate. Based on the effect of exercise on the cardiovascular system, a model was developed to predict mean arterial blood pressure as a function of heart rate. Physiological strain could also be estimated on the basis of thermoregulatory and cardiovascular strains. This paper summarizes knowledge accumulated during 25 years of studies in the field of mathematical modeling of physiological parameters. Besides analyzing the logic underlying each model, it explains the scientific approach in developing a model from its early concept to the model's application in the field.

Blood Pressure↗
PubMed2006

A mathematical model for constituent ratios of energy expenditure in human.

In order to assess the constituent ratios of energy expenditure in human, the deductive process of establishing a mathematical model for assessing the constituent ratios of the three major nutrients in energy expenditure in human was described in this paper. Total oxygen consumption, total carbon dioxide output and total nitrogen (urine nitrogen + skin nitrogen) excretion are related to the oxidation of the three major nutrients and the physiological combustion values of the three nutrients are already known. Based on these measurable and known parameters, the mathematical model established by the authors will help understand the characteristics of the tested individual's energy expenditure.

Carbon Dioxide↗
PubMed1982

An application of mathematical models in posturography.

The measurement of the horizontal displacements (HD) of the centre of mass of the human body when standing still, is often performed by means of a platform. The resulting measured HD as a function of time, both in the left-right or sinister-dexter and the posterior-anterior direction, are known as stabilograms. Such stabilograms are being more widely used to obtain the so called measured statokinesigram, similar to a Lissajous-figure, by eliminating time from the sinister-dexter stabilogram and the posterior-anterior stabilogram. It is shown that in using mathematical models of the standing person to obtained the stabilograms, the resulting statokinesigram is very different from the measured statokinesigram. It is also shown that the quantity line-integral calculated from a statokinesigram is much smaller when determined from a statokinesigram corrected by means of the mathematical models.

Humans↗
PubMedDate not supplied

[The use of mathematical modelling in improving the orthodontic treatment of end defects of the dental arches].

Mathematical modelling allowed to use specially designed software package for calculation of the necessary number of variants of dimensions of denture carcass while planning the orthodontic treatment. This could be done for each patient individually, thus ensuring the correct choice of orthodontic technique to replace the end defects of the dentition.

Computer Simulation↗
PubMed1987

A mathematical model of the population biology of Ostertagia ostertagi in calves and yearlings.

A mathematical model of the population biology of Ostertagia ostertagi is described. The model assumes that the natural control and regulation of parasite numbers is mediated by four processes: the effect of climate on the development and survival of the free-living stages; changes in the rate of establishment of the infective larvae, and density-dependent variations in parasite survival and fecundity. The model is used to compare the course of the infection in two groups of calves. One group is assumed to have been reared under conditions typical of S.E. England and the other under conditions typical of Louisiana, USA. The more general behaviour of the model is discussed in the context of sensitivity analysis. The model is an excellent mimic of the epidemiology of bovine ostertagiasis. It can be used as a simple screening procedure to help determine which of many possible anthelmintic control strategies should be selected for more detailed examination in the field, and it provides a theoretical framework within which ideas concerning the epidemiology of parasitic gastroenteritis can be assessed and refined.

Animals↗
PubMedDate not supplied

[A mathematical model of the incompatibility of plasmids using a mechanism of master replication].

A mathematical model of incompatibility for plasmids that use master-replication was worked out. Formulas for calculating the segregation velocity of two incompatible plasmids and for determining the number of cell generations (l gamma), necessary to achieve a gamma-share of polyplasmid cells are given. It is shown that l gamma strives to -8 lg gamma with the increase of the copy number N, i.e. it does not depend on N. This is the main distinction of model presented from those by Novick at al. and Ishii et al., who consider the mechanisms of regular and random replication. For these mechanisms l gamma increases proportional to N. So, at N greater than 30, the difference between l gamma, calculated for the master-replication and the random replication exceeds 10. This allows to determine the mechanism of replication used by the plasmid by measuring the velosity of incompatible plasmids segregation.

DNA Replication↗
PubMed2004

TNF-alpha neutralization in cytokine-driven diseases: a mathematical model to account for therapeutic success in rheumatoid arthritis but therapeutic failure in systemic inflammatory response syndrome.

OBJECTIVES: Neutralization of TNF-alpha with either monoclonal antibodies or soluble receptors, although not curative, has significant clinical benefit in patients with rheumatoid arthritis (RA). In contrast, blockade of TNF-alpha has little clinical benefit in the majority of patients with systemic inflammatory response syndrome (SIRS) in spite of the identification of TNF-alpha as a key factor in its pathology. It is not clear why there is such a significant difference in the responses to TNF-alpha neutralization in these two conditions. Here we use mathematical modelling to investigate this discrepancy. METHODS: Using the known pharmacokinetic and pharmacodynamic properties of TNF-alpha-blocking biological agents, we constructed a mathematical model of the biological actions of soluble(s) TNFR2, Etanercept and Infliximab. RESULTS: Our model predicts that all three inhibitors, but especially Etanercept, are effective at controlling TNF-alpha levels in RA, which we propose is a condition in which TNF-alpha production and inhibition are in equilibrium. However, when free TNF-alpha drops to a low level, as can occur in SIRS, which we propose is a non-equilibrium condition, the sequestered TNF-alpha can act as a slow-release reservoir, thereby sabotaging its effectiveness. CONCLUSIONS: These results may explain the effectiveness of TNF-alpha blockade in the equilibrium condition RA and the ineffectiveness in the non-equilibrium condition SIRS.

Antibodies, Monoclonal↗
PubMed1986

A mathematical model applying the random-walk method to the environment of a neuron.

A mathematical model describing the supply and demand relationships existing in the environment of a brain cell (neuron of the cerebral cortex) was developed. The stochastic random-walk technique was applied to the representation and solution of the system which consisted of a neuron being supplied with nutrients by an adjoining capillary. The random-walk method incorporated a uniformly generated random number which was weighted by the normal distribution curve to determine the random walk of a molecule. The resultant weighted value was designated as defining the motion of any particular species in space. The distribution curve was a function of diffusivity and time. The method allowed the tracking of individual molecules as they proceeded through the metabolic reactions in the cell. Oxygen, glucose, carbon dioxide and lactate were selected as the primary components of study, since they represent the major input and output parameters of metabolism inside the cell. The consumption and/or production of these components were dependent on probability values assigned to each metabolic reaction into which they entered. The solution of the model was based on the number of molecules existing in the tissue as a function of PO2, (partial pressure of oxygen), glucose level, etc. The model was very sensitive to perturbations of metabolic scheme parameters and to PO2 levels in the capillary. The model predicted an excess of O2, (oxygen) in the tissue. The effects of edema on intercapillary distances as well as changes in the size and number of mitochondria within the neuron were examined using the model.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗