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Results for “Models, Theoretical”

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PubMedDate not supplied

Application of theoretical models to exercise behavior among employed women.

PURPOSE: This study examines the utility of three theoretical models--the stages of change model, self-efficacy theory, and the decisional balance model--in understanding exercise behavior among employed women. DESIGN: Data for this cross-sectional study were collected as part of a routine follow-up of a worksite-based smoking and health risk appraisal study. SETTING: The study was conducted in three Rhode Island worksites, including one manufacturing company, one medical center, and one retail outlet. SUBJECTS: Of a sample of 431 women who completed exercise questionnaires, 293 reported participation in a physical activity over the previous week. The average age of the sample was 41.1 years, and mean years of education was 12.8. MEASURES: Previously validated measures to determine stage of exercise behavior, exercise self-efficacy, exercise decisional balance, and physical activity participation were administered. Additional demographic information was also obtained. RESULTS: Frequency counts revealed that 39% of the population was sedentary, 34% were participating in irregular activity, and 27% were active. MANOVAs followed by one way ANOVAs revealed that women in Precontemplation scored the lowest and those in Maintenance scored the highest on the self-efficacy, pro, and decisional-balance indices, with the trend reversed on the con scale. A chi-square test revealed that women with one or more young children in the home were more likely to be in a lower stage of exercise adoption. CONCLUSIONS: Most of the women in this cross-sectional study did not engage in regular activity. Presence of young children in the home was significantly related to decreased activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Demography↗

PubMedDate not supplied

A theoretical model for intraperitoneal delivery of cisplatin and the effect of hyperthermia on drug penetration distance.

A theoretical model for the intraperitoneal (i.p.) delivery of cisplatin and heat to tumor metastases in tissues adjacent to the peritoneal cavity is presented. The penetration distance (the depth to which drug diffuses directly from the cavity into tissues) is predicted to be on the order of 0.5 mm. The model shows that exchange with the microvasculature has more effect than cellular uptake in limiting the penetration distance. Possible effects of hyperthermia are simulated, including increased cell uptake of drug, increased cell kill at a given level of intracellular drug, and decreased microvascular density. The model suggests that the experimental finding of elevated intracellular platinum levels up to a depth of 3 to 5 mm when drug is delivered i.p. by a heated infusion solution is due to penetration of heat to this distance, causing increased cell uptake of drug. Beyond a depth of about 0.5 mm, the drug is delivered mainly through the circulation. Use of sodium thiosulfate to deactivate systemic cisplatin may therefore be counterproductive when heat is delivered locally. The model suggests that i.p. delivery of heat, combined with systemic delivery of drug, may be as effective as i.p. delivery of heat and drug.

Animals↗

PubMed1992

Mechanism of bradycardia-dependent appearance of manifest extrasystoles in concealed bigeminy. A theoretical model derived from the concepts of longitudinal dissociation and multilevel block in the reentrant pathway of extrasystoles.

A case of bradycardia-dependent appearance of manifest extrasystoles in concealed bigeminy is presented. To explain the mechanism of such bradycardia-dependent appearance, a theoretical model is derived from the concepts of "longitudinal dissociation" and "multilevel block" in the reentrant pathway of extrasystoles. In the theoretical model, functional longitudinal dissociation divides the reentrant pathway into dual pathways F and S. When manifest extrasystoles are not found for a long time, alternate sinus impulses pass through both pathways F and S, but become concealed extrasystoles because of insufficient conduction delay in the pathways. The other alternate sinus impulses are blocked in the pathways; in pathway F, the impulses are blocked at the entrance, while in pathway S, the impulses are blocked at a more distal level. When sinus cycles gradually lengthen, one of such alternate sinus impulses passes through the entrance of pathway F and, traveling very slowly, is blocked at a more distal level. The next sinus impulse is blocked at the entrance of pathway F; namely, 3:2 Wenckebach block occurs at the entrance of pathway F. Thus this sinus impulse enters only pathway S and passes through pathway S with enough conduction delay to become a manifest reentrant extrasystole.

Bradycardia↗

PubMed2001

Theoretical models of catalytic domains of protein phosphatases 1 and 2A with Zn2+ and Mn2+ metal dications and putative bioligands in their catalytic centers.

The oligomeric metalloenzymes protein phosphatases dephosphorylate OH groups of Ser/Thr or Tyr residues of proteins whose actions depend on the phosphorus signal. The catalytic units of Ser/Thr protein phosphatases 1, 2A and 2B (PP1c, PP2Ac and PP2Bc, respectively), which exhibit about 45% sequence similarity, have their active centers practically identical. This feature strongly suggests that the unknown structure of PP2Ac could be successfully homology-modeled from the known structures of PP1c and/or PP2Bc. Initially, a theoretical model of PP1c was built, including a phosphate and a metal dication in its catalytic site. The latter was modeled, together with a structural hydroxyl anion, as a triangular pseudo-molecule (Zno or Mno), composed of two metal cations (double Zn2+ or Mn2+, respectively) and the OH- group. To the free PP1c two inhibitor sequences R29RRRPpTPAMLFR40 of DARPP-32 and R30RRRPpTPATLVLT42 of Inhibitor-1, and two putative substrate sequences LRRApSVA and QRRQRKpRRTI were subsequently docked. In the next step, a free PP2Ac model was built via homology re-modeling of the PP1c template and the same four sequences were docked to it. Thus, together, 20 starting model complexes were built, allowing for combination of the Zno and Mno pseudo-molecules, free enzymes and the peptide ligands docked in the catalytic sites of PP1c and PP2Ac. All models were subsequently subjected to 250-300 ps molecular dynamics using the AMBER 5.0 program. The equilibrated trajectories of the final 50 ps were taken for further analyses. The theoretical models of PP1c complexes, irrespective of the dication type, exhibited increased mobilities in the following residue ranges: 195-200, 273-278, 287-209 for the inhibitor sequences and 21-25, 194-200, 222-227, 261, 299-302 for the substrate sequences. Paradoxically, the analogous PP2Ac models appeared much more stable in similar simulations, since only their "prosegment" residues 6-10 and 14-18 exhibited an increased mobility in the inhibitor complexes while no areas of increased mobility were found in the substrate complexes. Another general observation was that the complexes with Mn dications were more stable than those with Zn dications for both PP1c and PP2Ac units.

Animals↗

PubMedDate not supplied

A theoretical model to address organizational human conflict and disruptive behavior in health care organizations.

This article proposes a theoretical model for leaders to use to address organizational human conflict and disruptive behavior in health care organizations. Leadership is needed to improve interpersonal relationships within the workforce. A workforce with a culture of internal conflict will be unable to achieve its full potential to delivery quality patient care.

Aggression↗

PubMed1989

Comparison of two theoretical models for predicting non-linear propagation in medical ultrasound fields.

Non-linear propagation models are required to predict the fields from medical ultrasonic equipment, particularly diagnostic devices and lithotripters. This need arises because of the requirement to know the safety and effectiveness of these instruments. Several theoretical models have been developed to take account of non-linear propagation as well as diffraction, focusing and attenuation, but little work has been done to validate them. This paper compares two theoretical models with each other and with measurements in the field of a 3.5 MHz focused transducer. One model uses an approximation based on modelling the beam profile with a Gaussian function, whereas the other utilises a full three-dimensional finite difference method, using a uniform transducer excitation function. Comparisons are made in the time and frequency domain at the focus for four different source levels and in general the results agree to within about 10%. However, an important conclusion is that the finite amplitude field of a real transducer may differ significantly from that of an ideal piston source, particularly for the weakly focused beams used in diagnostic ultrasound.

Acoustics↗

PubMed2005

A theoretical model for the myogenic response based on the length-tension characteristics of vascular smooth muscle.

OBJECTIVE: A theoretical model is developed to describe the myogenic response of resistance vessels to changes in intravascular pressure, based on a consideration of the active and passive length-tension characteristics of vascular smooth muscle (VSM). The dependence of model parameters on vessel diameter is examined. METHODS: The vessel wall is represented mechanically as a nonlinear passive component in parallel with an active contractile component. The level of VSM tone is assumed to have a sigmoidal dependence on circumferential wall tension or stress. Model parameters are optimized for each of 18 independent experimental data sets previously obtained using pressure or wire myograph systems. RESULTS: Close fits between model predictions and experimental data are found in each case. An alternative formulation in which VSM tone depends on circumferential wall stress is found also to be consistent with available data. Significant trends in model parameters as a function of diameter are found. CONCLUSIONS: The results support the hypothesis that circumferential tension or stress in the wall provides the signal for myogenic responses. The model provides a basis for simulating steady-state myogenic responses in vascular networks containing a range of vessel diameters.

Animals↗

PubMed1988

Noninvasive diagnosis of renal allograft rejections--application of an information-theoretical model.

This paper describes an information-theoretical model developed for detection of renal allograft rejection on the basis of various laboratory data. In this report the mathematical background of the model is described in detail and the rationale of its use is discussed. An example is given for the practical application of the model in kidney grafted patients. In the 30 patients of the test collective, seven rejection episodes were diagnosed by the clinicians and verified histologically. All seven rejection episodes were detected by the model, in the mean 2.4 days (median; 3 days) before the clinical diagnosis.

Biopsy, Needle↗

PubMed1984

Gas transport during high-frequency ventilation: theoretical model and experimental validation.

We present a theoretical model of gas transport through the dead space during high-frequency ventilation (HFV) with volumes less than dead space volume. The analysis is based on the axial distribution of transit times of gas moving through the dead space. The model predicts that for tidal volumes (V) much less than dead space (VD), gas exchange will be proportional to the product of frequency (f) and V2. If gas transport is analyzed in terms of Fick's law, then the effective diffusion coefficient (Deff) can be shown to be equal to fV2 times a constant, whose value equals the square of the coefficient of dispersion of axial transit times through the dead space (sigma t/t)2. Experimental results in straight tubes fit the predictions of this model quite well. A (sigma t/t) through the entire dead space of about 30% is more than sufficient to account for gas exchange during HFV in physical models or in intact animals. An axial dispersion of this magnitude can be measured directly from a typical Fowler dead space determination in healthy subjects.

Animals↗

PubMed1980

Theoretical models for the covalent assembly of immunoglobulins.

Theoretical models for the formation of interchain disulfide bonds in noncovalently assembled immunoglobulin molecules are presented. The formalism handles independent and cooperative bond formation with equal ease. Analysis of certain experimental results on the covalent assembly of human immunoglobulin G yields information about the pathway of assembly. A model in which the formation of bonds between the light and heavy chains is independent of, but twice as fast as, those between two heavy chains, gives satisfactory agreement with these results. Simple models involving cooperative bond formation are also considered, but the experiments being analyzed are not accurate enough to unambiguously implicate any cooperative pathway.

Animals↗

PubMed1984

Theoretical model of gastrointestinal absorption of lead.

A theoretical model is presented which is used to explain gastrointestinal absorption of ingested lead from use of traditional medicines. Dissolution processes are discussed and the relative contributions of pore and passive diffusion through the intestinal epithelium for the resulting species examined. The determination of the rate of absorption is described in terms of a mathematical three-compartment system and effects of particle size are considered by reference to the Noyes-Whitney dissolution rate law.

Body Fluids↗

PubMed1999

Moving beyond information: evaluation of a nutrition education tool based on a theoretical model.

OBJECTIVE: This study investigated the relative effectiveness of a nutrition education brochure based on a theoretical model versus a more traditional information-based brochure in getting subjects to accurately assess daily calcium intake, make a plan to increase intake if needed, and to implement the plan. DESIGN: A randomized trial involving 216 women between the ages of 19-49y. Subjects were randomly assigned to a group which received educational materials containing an interactive brochure designed using the Motivation Generating model (Calcium CalculatorS), or to a group which received a calcium information brochure (An Appetite for Good Health). Within a two week period the women were contacted by telephone to assess use of materials, calcium intake assessment information, and plans for dietary change. SETTING: Subjects were recruited at five fitness centres in the Vancouver area. The research was conducted by the Institute of Health Promotion Research at the University of British Columbia. RESULTS: Results indicated significantly greater numbers of subjects conducting self- assessment and increased group accuracy for calcium intake assessment in subjects using the interactive brochure. CONCLUSION: Use of a theoretical model designed to create behaviour change such as the Motivation Generating Model can increase specific behaviours which may lead to improvements in dietary consumption.

Adult↗

PubMedDate not supplied

Theoretical models used to guide NIDA's cooperative agreement research and intervention efforts. National Institute on Drug Abuse.

NIDA's Cooperative Agreement program to reach out-of-treatment drug users and provide HIV prevention to reduce HIV drug and sexual risks was initiated in September of 1990. By August, 1994 the program included 23 sites which used various theoretical models to guide prevention strategies, add conceptual coherence to many aspects of behavior change, and allow for clearer interpretation of why behavior change occurs. This article reviews the theoretical models used at each of the NIDA Cooperative Agreement sites, the perceived helpfulness of the models, and recommendations for future initiatives.

Acquired Immunodeficiency Syndrome↗

PubMedDate not supplied

Pattern formation: from theoretical models to molecular biology.

The field of pattern formation in biological systems is viewed, taking into consideration the major theoretical and experimental information. The basic idea which has emerged from the different theoretical models is that short range cell-to-cell interactions could manifest the hierarchy of patterns. These interactions could actually be governed by simple signals in the cell surface. In the second part the experimental evidence is examined, namely, the genes that control pattern formation in Drosophila. The products of these genes display a variety of characteristics ranging from being molecules at the cell surface to regulatory proteins in the nucleus. The hypothesis is presented that molecules in the cytoplasm could connect the two parts. According to this, signals at the cell surface and subsequent cell-to-cell interactions should be of primary importance in the mechanisms that underlie morphogenesis.

Amino Acid Sequence↗

PubMed2005

FEDMA--a simple algorithm for theoretical modeling of linear metabolic pathways: from fuzzy data sets to prediction and experiment.

A theoretical model of a chain of irreversible Michaelis-Menten reactions proceeding inside a living cell, taking cell growth, division and subcellular compartmentation into account, was proposed. It became a basis for the construction of a "fuzzy" enzymatic data-modeling algorithm (FEDMA) - a procedure allowing the estimation of missing parameter values for the modeled system, in accordance both with the derived theoretical rules and the available experimental data. The obtained tool was tested to model the heme biosynthesis pathway in Saccharomyces cerevisiae, where about 40% of parameters remain unknown. The missing parameters estimated by means of FEDMA fall in the range of expected values.

Algorithms↗

PubMed1993

Comparison of three theoretical models of substance use among urban minority high school students.

OBJECTIVE: This study compares the relative explanatory power of three theoretical models of substance use among urban minority high school students. METHOD: A substance use survey was administered in the spring of 1991 to a randomly selected sample of classrooms in the ninth through twelfth grades of three public academic high schools in a New York City borough. Survey participants (N = 919) were 59% black and 34% Hispanic; the mean age was 16.4 years. RESULTS: Substantial proportions of this sample of students reported experimental or occasional alcohol and cigarette use in the past year, and approximately one-tenth reported frequent use of these substances. Only small proportions of students reported past-year marijuana use, and few or no students reported past-year use of cocaine, crack or intravenous heroin. The socialization model of substance use was much more powerful than either the stress/strain or disaffiliation models in explaining past-year use of alcohol, cigarettes, and marijuana. However, certain variables derived from the stress/strain and disaffiliation models were important risk factors for the frequent use of these substances. CONCLUSIONS: These findings suggest that the further elucidation of the social influence process among adolescents, and the development, implementation, and evaluation of especially intensive programs aimed at high-risk youths, should become adolescent substance use prevention research priorities.

Adolescent↗

PubMed1986

A theoretical model of localized heat and water vapor transport in the human respiratory tract.

A steady-state, one-dimensional theoretical model of human respiratory heat and water vapor transport is developed. Local mass transfer coefficients measured in a cast replica of the upper respiratory tract are incorporated into the model along with heat transfer coefficients determined from the Chilton-Colburn analogy and from data in the literature. The model agrees well with reported experimental measurements and predicts that the two most important parameters of the human air-conditioning process are: the blood temperature distribution along the airway walls, and the total cross-sectional area and perimeter of the nasal cavity. The model also shows that the larynx and pharynx can actually gain water over a respiratory cycle and are the regions of the respiratory tract most subject to drying. With slight modification, the model can be used to investigate respiratory heat and water vapor transport in high stress environments, pollutant gas uptake in the respiratory tract, and the connection between respiratory air-conditioning and the function of the mucociliary escalator.

Body Temperature Regulation↗

PubMed2002

A theoretical model of air and steam co-injection to prevent the downward migration of DNAPLs during steam-enhanced extraction.

When steam is injected into soil containing a dense volatile non-aqueous phase liquid contaminant the DNAPL vaporized within the heated soil region condenses and accumulates ahead of the steam condensation front. If enough DNAPL accumulates, gravitational forces can overcome trapping forces allowing the liquid contaminant to flow downward. By injecting air with steam, a portion of the DNAPL vapor remains suspended in equilibrium with the air, decreasing liquid contaminant accumulation ahead of the steam condensation front, and thus reducing the possibility of downward migration. In this work, a one-dimensional theoretical model is developed to predict the injection ratio of air to steam that will prevent the accumulation of volatile DNAPLs. The contaminated region is modeled as a one-dimensional homogeneous porous medium with an initially uniform distribution of a single component contaminant. Mass and energy balances are combined to determine the injection ratio of air to steam that eliminates accumulation of the contaminant ahead of the steam condensation front, and hence reduces the possibility of downward migration. The minimum injection ratio that eliminates accumulation is defined as the optimum injection ratio. Example calculations are presented for three DNAPLs, carbon tetrachloride (CCl4), trichloroethylene (TCE), and perchloroethylene (PCE). The optimum injection ratio of air to steam is shown to depend on the initial saturation and the volatility of the liquid contaminant. Numerical simulation results are presented to validate the model, and to illustrate downward migration for ratios less than optimum. Optimum injection ratios determined from numerical simulations are shown to be in good agreement with the theoretical model.

Air↗