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PubMed1987

Stereoelectronic model to explain the resolution of enantiomeric ibuprofen amides on the Pirkle chiral stationary phase.

A chiral recognition model is proposed which incorporates the electronic and steric interactions between amide derivatives of ibuprofen and the (R)-N-(3,5-dinitrobenzoyl)phenylglycine-derived Pirkle chiral stationary phase during high-performance liquid chromatography. Based on this rationale, amide derivatives of ibuprofen were prepared using 4-chloroaniline, 4-bromoaniline, aniline, 4-methoxyaniline and 1-aminonaphthylene to improve the enantiomer separation over previously reported results with this column. The amides prepared gave separation values of 1.16, 1.16, 1.19, 1.21 and 1.23, respectively. These high separation values are consistent with the proposed model.

Amides↗
PubMed1988

An embryogenic model to explain cytogenetic inconsistencies observed in chorionic villus versus fetal tissue.

While the fetus and placenta have a common ancestry, chorionic villus tissue does not always reflect fetal genotype. Data are presented from 15 CVS subjects in whom cytogenetic inconsistencies were observed when comparing (1) cultured chorionic villi, (2) direct chromosome preparations of intact villi, and (3) cultured fetal tissue. Embryogenic models are presented to explain these discrepancies. Mosaicism confined to direct chromosome preparations was the most commonly observed inconsistency. This can be explained by postzygotic non-disjunction limited to cytotrophoblast. In all but one instance, the abnormal cell line was limited to the placenta, with the normal cell line reflecting fetal genotype. Analysis of direct chromosome preparations from multiple individually processed villus fragments may be helpful in recognizing mosaicism confined to the placenta. While both direct chromosome preparations and villus cultures can be misleading, the latter are more likely to reflect fetal genetic status since they are derived from the extraembryonic mesoderm.

Chorionic Villi↗
PubMed1990

Determinants of health-promoting lifestyle in ambulatory cancer patients.

The Health Promotion Model was tested as an explanatory framework for health-promoting lifestyle in a sample of 385 ambulatory cancer patients undergoing treatment in 13 clinical sites in the midwestern United States. The aim of this study was to determine the extent to which cognitive/perceptual and modifying variables identified in the Health Promotion Model explain the occurrence of health-promoting behaviors in adults with cancer. A secondary aim was to determine the potential of illness-specific cognitive/perceptual and modifying variables for further explaining the occurrence of health-promoting behaviors in adults with cancer. Multiple regression analyses revealed that 23.5% of the variance in health-promoting lifestyle was explained by the model cognitive/perceptual variables definition of health, perceived health status and perceived control of health and the modifying variables education, income, age and employment. When illness-specific variables were included in the analysis, initial reaction to the diagnosis of cancer was found to be a significant contributor to the regression. Study results support the importance of both general health-related and cancer-specific cognitive/perceptual factors in explaining the occurrence of health-enhancing behaviors among ambulatory cancer patients; these factors may therefore be suitable targets for interventions to encourage adoption of healthy lifestyles.

Adult↗
PubMed1978

A tunnelling model to explain the reduction of ferricytochrome c by H and OH radicals.

The kinetics of the reaction of OH radicals with ferricytochrome c was studied in the time range 1 microsecond to 1 s by means of pulse radiolysis. The OH radicals reduce ferricytochrome c by 40% +/- 10%. The time course of the reduction is explained by a mechanism whereby a radical formed after hydrogen has been abstracted from the outer surface of the protein reduces the iron by electron tunnelling. We have calculated that the reducing electron in the radical is bound with an energy of at least 1.75 eV and that the frequency factor of the tunnelling process is v=10(11.5)s-1. This model accounts for the observed absorbance change in time range 5 . 10(-6)--10(-1)s. The time course of the reduction of ferricytochrome c by H radicals (Lichtin, N.N., Shafferman A. and Stein, G. (1974) Biochim. Biophys. Acta 357, 386--398) is explained by the same model.

Calorimetry↗
PubMed1990

A bivariate negative binomial model to explain traffic accident migration.

The phenomenon of "regression to the mean" is now widely known in the study of the effectiveness of remedial treatment of traffic accident blackspots. What happens is that the criterion used for selection of sites at which treatment is to be applied gives rise to bias in the estimate of the effectiveness: the conditional expectation of the after frequency is less than the true mean, even if the treatment is totally ineffective. It has been reported in some previous studies that accident "migration" has been observed. This is the phenomenon whereby the accident rate apparently rises at sites that are untreated but that are neighbours to treated sites. If this were a genuine effect, it would have serious implications for the assessment of remedial treatments. This paper aims to explain this migration effect in purely probabilistic terms, without recourse to the concept of physical migration. The model used is a new bivariate negative binomial distribution, incorporating spatial correlation between the true mean site accident rates. As with the regression to mean effect, the migration effect can then be explained in terms of the conditioning implicit in the selection process.

Accidents, Traffic↗
PubMedDate not supplied

An educational model for explaining hospice services.

Explaining the concept and philosophy of hospice can be difficult. There is a reluctance in our society to openly address dying/death issues; there is a reluctance on the part of many health-care professionals to look beyond physical issues. The following model has been used successfully to explain hospice to both the general public and health care professionals. It is not intended to introduce hospice to a patient/family during the initial referral/assessment visit.

Health Education↗
PubMed1995

Development of factor-score-based models to explain and predict maximal box-lifting performance.

The objectives of the study were threefold: (1) to develop factor-score-based models to predict maximum mass on a box-lifting task using multiple regressions; (2) to compare predictive and explanatory powers of factor-score-based models to models derived from data-level variables; and (3) to apply these findings to ergonomic research and practical problem-solving situations. Forty-eight volunteers (25 women and 23 men) completed a maximal box-lifting task and a maximal isoinertial lifting test on an Incremental Lifting Machine (ILM). Dynamic data collected during isoinertial testing were summarized into 32 lift parameters, and then subjected to principal components analyses using the 'FACTOR PROCEDURE' from the Statistical Analysis System (SAS). Factor scores were calculated for each participant on each of the four factors comprising the final solution, and multiple regression equations for men, women and combined data were generated using the 'GENERAL LINEAR MODELS' procedure from SAS. Results revealed that prediction of box-lifting performance was optimized when regression equations were developed using numerous data-level variables as predictors, i.e., all 32 lift parameters and ILM mass. In comparison, explanation was enhanced but predictive capabilities were reduced when linear models were formed using ILM mass and the factor scores derived from analyses of isoinertial lifting. The use of variables loading on the factors gave slightly increased predictive power than did the factor-score-based models. Similar trends in predictive and explanatory powers appeared when the data were analysed according to gender. Ergonomic applications of factor-score-based models were discussed with regard to ongoing research as well as to practical problem-solving situations. It was concluded that the advantages and usefulness of factor-score-based models warranted their inclusion in future investigations of lifting performance.

Adult↗
PubMed1976

Simple model to explain effects of plasma protein binding and tissue binding on calculated volumes of distribution, apparent elimination rate constants and clearances.

A simple pharmacokinetic model, incorporating linear plasma protein binding, linear tissue binding, and first order elimination of free (unbound) drug, was studied. If Clp is the plasma clearance, Vf is the "true" volume of distribution of free drug, beta is the apparent elimination rate constant, sigma is the fraction of the drug which is free in plasma, f is the fraction of the drug which is free in the entire body, kf is the intrinsic elimination rate constant for free drug, and AoTB is the initial amount of drug which is bound to tissues, then the model indicates that the following relationships hold: (1) Clp = Vfsigma kf; (2) beta = f kf; and Vdext = (sigma/f) Vf. Only sigma, and not f, can be measured experimentally. Dividing Clp by sigma provides an estimate of the intrinsic clearance of free drug, Vfkf. A plot of Vdext versus sigma has an intercept equal to Vf, and the ratio of the slope/intercept is an estimate of AoTB/Aof, where Aof is the initial amount of free drug (equal to Vf times initial concentration of free drug in plasma). Thus, an estimate of AoTB may be obtained. Dividing the intrinsic clearance by Vf provides an estimate of kf. Thus, theoretically, estimates of Vf, kf, AoTB and f may be obtained. The variables are not separated when beta is plotted versus sigma, and curvature of such plots is expected; no useful information is obtained from such plots.

Blood Proteins↗
PubMed1993

New urodynamic model to explain micturition disorders in benign prostatic hyperplasia patients. Pressure-flow relationships in collapsable tubes, hydraulic analysis of the urethra and evaluation of urethral resistance.

How can the hydrodynamic disorders caused by benign prostatic hyperplasia (BPH) be explained? And how can they be measured in order to assess the efficiency of treatment? To answer these questions, a model based on the results of experiments performed in collapsable tubes and on a hydraulic analysis of the urethra is elaborated. A BPH combining hypertonia and/or hypertrophy, essentially leads to a rise in the opening pressure which increases bladder work before micturition, as well as a reduction in the functional caliber of the prostatic urethra. Whatever its origin, this reduction in caliber is the only explanation for the importance of the urethral resistance increase noticed in cases of BPH. Instantaneous resistance calculation, based on the pressure/maximum flow rate relationship, measured when the flow is steady (for a few seconds), would be a good experimental physical parameter. However, on a clinical basis, an exact calculation is impossible, which makes its precision and reliability not as good as they should be. In order to calculate the resistance to micturition as a whole, particularly taking into account the difficulty in urethral opening, it was suggested to include the opening pressure in the pressure/flow study. But this fits neither with fluid mechanics data nor with the results of experiments carried out in collapsable tubes. Eventually, considering that no evaluation method of the resistance to urinary flow is acknowledged to be accurate on a hydraulic basis or urodynamically applicable, one wonders whether placing more confidence in simple data obtained in a noninvasive way, and used without mathematical tricks, is not preferable.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1991

A kinetic-dynamic model to explain the relationship between high potency and slow onset time for neuromuscular blocking drugs.

To account for experimental data showing increased onset time with increased potency of neuromuscular blocking drugs, a pharmacokinetic-pharmacodynamic model is presented. It is characterized by a finite concentration of receptors (R) in the effect compartment. Transfer from central to effect compartment is linearly related to concentration gradient. A sigmoid Emax model is used to describe the relationship between receptor occupancy and effect. Plasma concentrations found in the literature are used. Differential equations are solved numerically for equipotent doses of drugs of different potencies. Because the density of receptors constitutes a significant drain of drug molecules for potent drugs, the model predicts an inverse relationship between speed of onset and potency. The concentration of receptors in the effect compartment R which best fits experimental data obtained in humans is 0.28 mumol/L. With this value of R, onset times are prolonged when the ED95 (dose for 95% blockade) is less than 0.1 mumol/kg. It is concluded that, in the development of a short-acting nondepolarizing neuromuscular blocking drug, agents having an ED95 of 0.1 mumol/kg or greater appear more promising.

Dose-Response Relationship, Drug↗
PubMed1995

LTP--a structural model to explain the inconsistencies.

One of the major controversies in neuroscience concerns whether the expression of long-term potentiation (LTP) is a pre- or postsynaptic phenomenon, with apparently contradictory data being the norm. The model that is outlined in this article combines anatomical and electrophysiological evidence to allow apparently contradictory data to be compatible. Development of LTP involves both influx of Ca2+ through NMDA receptors, and activation of another factor, perhaps the metabotropic glutamate receptor. These two processes might result, respectively, in the insertion of activation of additional postsynaptic receptors, and the growth of microfilaments that could split simple synapses into perforated synapses, consisting of multiple active zones. Whether the latter occurred, and at what rate, would be likely to depend on multiple factors, such as temperature, the metabolic state of the cell, buffering of Ca2+, and the concentration of factors such as nitric oxide. These subtle experimental variables would thus determine whether the dominant effect observed was pre- or postsynaptic.

Long-Term Potentiation↗