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Results for “Model explainability”

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PubMed1999

Combined effect of cosolvent and cyclodextrin on solubilization of nonpolar drugs.

Solubility enhancement has broad implications in parenteral formulation design. A simple mathematical model has been developed to describe the combined effect of cosolvency and complexation on nonpolar drug solubilization. The total drug solubility is determined by the summation of three drug species present in the solution: free drug [D], drug-ligand binary complex [DL], and drug-ligand-cosolvent ternary complex [DLC]. The proposed model established the dependencies of these three species upon the intrinsic drug solubility, [D(u)], the cosolvent solubilizing power, sigma, the binary and ternary intrinsic complexation constants, K(b)(int) and K(t)(int), and the cosolvent destabilizing powers for the binary and the ternary complexes, rho(b) and rho(t). A nonpolar solute, Fluasterone, is used to evaluate the newly generated equation. The model explains the decline in drug solubility produced by low cosolvent concentrations as well as the increase in the solubility produced by high cosolvent concentrations that are observed at all cyclodextrin concentrations.

2-Hydroxypropyl-beta-cyclodextrin↗

PubMed1991

Predicting the marginal cost of direct nursing care for newborns.

The author describes a study on the cost of nursing care for newborns using cost functions. A sample of 70 institutions in New Jersey were studied during a 2-year period. The models explained 95% of the variation of nursing costs in the study population. This information can be used by nurse executives to more appropriately make decisions about optimal unit size and the profitability of certain services.

Costs and Cost Analysis↗

PubMed2003

Molecular modeling of SCH28080 binding to the gastric H,K-ATPase and MgATP interactions with SERCA- and Na,K-ATPases.

We have used homology molecular modeling based on the srCaATPase E(2) conformation, pdb1kju, to predict side chains involved in docking the K(+) competitive inhibitor, SCH28080, to the H,K-ATPase. A model for SCH28080 binding between residues L809 and A335 in the same space utilized by omeprazole is proposed. We also describe modeling MgATP binding to the E(1) structure of the srATPase, pdb1eul, as a paradigm for the Na,K- and H,K-ATPases. The resulting model, E(1).MgATP, visualizes a conformation not yet available by crystallization and successfully predicts a range of published results, including backbone cleavages near V440 (N domain) and V712 (P domain) mediated by FeATP in the Na,K-ATPase. A separate model for MgATP docked to E(2) (pdb1kju) shows that access of the gamma phosphate to D351 is blocked by the A domain. The E(2). MgATP model explains FeATP-mediated cleavages of the Na,K-ATPase near V440 and E214 (A domain) and homologous results in the H,K-ATPase.

Adenosine Triphosphate↗

PubMed2004

Novel pharmacokinetic-pharmacodynamic model for prediction of outcomes with an extended-release formulation of ciprofloxacin.

The pharmacokinetics of an extended-release (XR) formulation of ciprofloxacin has been compared to that of the immediate-release (IR) product in healthy volunteers. The only significant difference in pharmacokinetic parameters between the two formulations was seen in the rate constant of absorption, which was approximately 50% greater with the IR formulation. The geometric mean plasma ciprofloxacin concentrations were applied to an in vitro pharmacokinetic-pharmacodynamic model exposing three different clinical strains of Escherichia coli (MICs, 0.03, 0.5, and 2.0 mg/liter) to 24 h of simulated concentrations in plasma. A novel mathematical model was derived to describe the time course of bacterial CFU, including capacity-limited replication and first-order rate of bacterial clearance, and to model the effects of ciprofloxacin concentrations on these processes. A "mixture model" was employed which allowed as many as three bacterial subpopulations to describe the total bacterial load at any moment. Comparing the two formulations at equivalent daily doses, the rates and extents of bacterial killing were similar with the IR and XR formulations at MICs of 0.03 and 2.0 mg/liter. At an MIC of 0.5 mg/liter, however, the 1,000-mg/day XR formulation showed a moderate advantage in antibacterial effect: the area under the CFU-time curve was 45% higher for the IR regimen; the nadir log CFU and 24-h log CFU values for the IR regimen were 3.75 and 2.49, respectively; and those for XR were 4.54 and 3.13, respectively. The mathematical model explained the differences in bacterial killing rate for two regimens with identical AUC/MIC ratios.

Adult↗

PubMed1986

A multiple regression analysis of variables influencing birthweight.

Birthweights recorded in a rural maternity centre (1979-1981) in Tanzania are related to parity, gestational age, maternal weight, sex of the child, maternal weight gain in pregnancy, intensity of antenatal care, and systolic blood pressure. The interrelations between these variables were analysed so as to discover their relative importance as determinants of birthweight variations. Only lengths of gestation, parity, sex, and maternal weight were retained in a general model explaining 29 percent of the total variance of birthweight. Short gestation accounted for 70 percent of all cases with low birthweight. For intervention purposes the further study of the causes of short gestation is therefore recommended.

Birth Weight↗

PubMed2005

Plate-wide stress relaxation explains European Palaeocene basin inversions.

During Late Cretaceous and Cenozoic times, many Palaeozoic and Mesozoic rifts and basin structures in the interior of the European continent underwent several phases of inversion (the process of shortening a previously extensional basin). The main phases occurred during the Late Cretaceous and Middle Palaeocene, and have been previously explained by pulses of compression, mainly from the Alpine orogen. Here we show that the main phases differed both in structural style and cause. The Cretaceous phase was characterized by narrow uplift zones, reverse activation of faults, crustal shortening, and the formation of asymmetric marginal troughs. In contrast, the Middle Palaeocene phase was characterized by dome-like uplift of a wider area with only mild fault movements, and formation of more distal and shallow marginal troughs. A simple flexural model explains how domal, secondary inversion follows inevitably from primary, convergence-related inversion on relaxation of the in-plane tectonic stress. The onset of relaxation inversions was plate-wide and simultaneous, and may have been triggered by stress changes caused by elevation of the North Atlantic lithosphere by the Iceland plume or the drop in the north-south convergence rate between Africa and Europe.

Journal Article↗

PubMed2002

Dynamic docking and electron transfer between myoglobin and cytochrome b(5).

The interaction of trypsin-digested bovine cytochrome b(5) (cyt b(5)) with horse heart myoglobin (Mb) and the interprotein electron transfer (ET) between these redox partners have been studied to gain better understanding of ET processes between weakly bound protein partners. The bimolecular rate constant ( k(2)) for photo-induced ET between zinc-substituted Mb (ZnMb) and cyt b(5) decreases with increasing ionic strength, consistent with the predominantly electrostatic character of this complex. The formation of a protein-protein complex has been confirmed and the binding affinities of metMb and ZnMb for cyt b(5) have been measured by two techniques: (1)H NMR titrations at pH 6.0 give binding constants of K(a) approximately (1.0+/-0.1)x10(3) M(-1) for metMb and K(a) approximately (0.75+/-0.1)x10(3) M(-1) for ZnMb; isothermal calorimetry gives K(a) approximately (0.35+/-0.1)x10(3) M(-1) for ZnMb. Brownian dynamic (BD) simulations show that cyt b(5) binds over a broad surface of Mb that includes its heme edge. The experimental results are described in terms of a dynamic docking model which proposes that Mb binds cyt b(5) in a large ensemble of protein binding conformations, not one or a few dominant ones, but that only a small subset are ET reactive. Aided by the BD simulations, this model explains why k(2) decreases with increasing pH: increasing pH not only weakens the binding affinity but also reduces the number of binding conformations with high ET reactivity.

Animals↗

PubMed2005

Oxygen consumption by cultured human cells is impaired by a nucleoside analogue cocktail that inhibits mitochondrial DNA synthesis.

We evaluated oxygen consumption rates in human cells cultured in the presence of a nucleoside analog reverse transcriptase inhibitor (NRTI) cocktail that inhibits mitochondrial DNA synthesis. We treated a proliferating human lymphocyte cell line and a primary culture of human adipose cells with antiretroviral drugs (AZT+ddC+d4T). The effects of these drugs on mitochondrial DNA (mtDNA) levels and oxygen consumption rates were evaluated using semi-quantitative real-time PCR and an on-line monitoring Clark electrode system. We found that the NRTI treatment lowered oxygen consumption rates and inhibited mitochondrial DNA replication in human cell cultures. Inhibition of oxygen consumption was linearly proportional to inhibition of mtDNA replication. These results show for the first time that mitochondrial respiration is impaired in NRTI sensitive cells. The linear relationship between NRTI inhibition of respiration and NRTI inhibition of mtDNA replication indicates that small decreases in mtDNA levels can lead to respiratory deficits in the tissues of patients treated with anti-HIV drugs. We propose a model that takes into account the small differences in metabolic dynamics between peripheral and axial/visceral fat tissues. This model explains how NRTI-related respiratory deficits may lead to the presentation of opposing lipodystrophic syndromes in same patient.

Adipocytes↗

PubMedDate not supplied

Predictors of physical activity in older adults with borderline hypertension.

BACKGROUND: Physical activity (PA) is effective in controlling blood pressure (BP) and is important in the treatment and prevention of hypertension in the elderly. Reasons for engaging in regular PA are complex and are influenced by personal, interpersonal, and environmental factors. OBJECTIVE: To test a predictive model of PA in older adults with borderline hypertension. METHODS: Data were collected from a multiethnic nonprobability sample of 267 men and women 60-75 years of age. The predictor variables were gender, ethnicity, income, previous exercise experience, self-efficacy for PA, perceived health status, awareness of BP, barriers to PA, intrinsic motivation for health, motivation for PA, interpersonal influence, and environmental influence. RESULTS: The hypothesized model was tested and modified using path analysis. The final model explained 44% of the variance in PA. The variables that directly predicted PA were gender, income, previous exercise experience, self-efficacy for PA, and motivation for PA. Variables that indirectly predicted PA were perceived health status, barriers to PA, self-efficacy for PA, intrinsic motivation for health, and environmental influence. CONCLUSIONS: The significant associations between the cognitive appraisal and motivation concepts extend previous research and add to the understanding of the complex factors that influence regular PA. The PA model can be a foundation for further research and practice.

Aged↗

PubMedDate not supplied

[Alexithymia and memory: a more rigorous criterion for acceptance of recognition tasks?].

Alexithymia, the lack of words for affects, is often explained in a neurophysiological way. Many epidemiological studies have shown that this personality characteristic is a common one, frequently observed in the general population and, at least sometimes, context-dependent. Thus, alternatives to the split-brain alike hypothesis are required. In this paper, we focus on promising findings reported by Montreuil and Pedinielli (15): poorer alexithymic performances on memory taks in an incidental learning session. We tried to duplicate these results for a recognition task but failed to do so. Surprisingly, observed data show a trend in the opposite direction and alexithymic subjects perform better on distractors. Response times for the right answers (recognition of targets, elimination of distractors) are longer for this group. Taken together, these results suggest a difference in the managing of uncertainty. Alexithymic criterion for adoption/rejection of candidates to recognition is assumed to need a longer completion because of a greater number of attributes to recover in memory (considering a componential approach of representations in memory). Such a decision model explains why alexithymics perform better on elimination (they need more certainty) and why they show a slight decrease (unsignificant) on target acceptation (for a similar level of uncertainty alexithymics use a more rigorous criterion than the control group). From this decision model an alternative explanation is proposed for the results of Montreuil and Pedinielli in the recognition task. Further, it is suggested that a similar process might be implicated in the alexithymic difficulties about the translation of feelings into words. As it requires a matching between an ambiguous-continuous information (the inner feeling) and a consensual-discrete label (the emotional term), this process probably involves a great degree of uncertainty.

Adolescent↗

PubMed1995

Modelling the increase of contrast sensitivity with grating area and exposure time.

We extended the contrast detection model of human vision to temporal integration by taking into account the effect of exposure duration on contrast sensitivity for stationary gratings. The extended model thus comprised: (i) low-pass filtering due to the optical modulation transfer function of the eye; (ii) high-pass filtering (lateral inhibition) due to the neural modulation transfer function of the visual pathways; (iii) addition of internal neural noise; and (iv) detection by a local matched filter whose efficiency for gratings decreased with increasing area and exposure duration. To test the model we measured binocular contrast sensitivity in foveal photopic vision as a function of exposure duration and area for sinusoidal gratings with equiluminous surround at spatial frequencies of 0.25-16 c/deg. In agreement with the model, contrast sensitivity at all grating areas first increased in proportion to square root of t when exposure duration (t) was shorter than critical duration. Thereafter the increase saturated and contrast sensitivity became independent of exposure time. Critical exposure duration was found to be independent of grating area but increased with spatial frequency. Similarly, at all exposure durations contrast sensitivity first increased in proportion to square root of A when grating area (A) was smaller than critical area. Thereafter the increase saturated and contrast sensitivity became independent of area. Critical area was found to be independent of exposure duration but decreased with increasing spatial frequency. The extended model explained 95-97% of the total variance of our contrast sensitivity data at the spatial frequencies studied. Our results also mean that spatial and temporal integration processes are mutually independent and thus area and time are separable variables in the detection of stationary gratings.

Adult↗

PubMed1995

Symptoms of depression among female nursing students.

This study examines the extent to which depressive symptoms in female nursing students are affected by specific stressors and coping styles. Three hypotheses were examined for differences in symptoms of depression scores and a model was tested for predicting depression in female nursing students. Responses were gathered from three questionnaires (Hassles and Uplifts Scales, Symptoms of Stress Inventory, and Coping Styles) from 408 female baccalaureate, master's and doctoral students from a major Midwest research university. Symptoms of depression were not significantly different among the students and were as high as a comparative group of stress management clients. Path analysis was used to examine the patterns of stressors (hassles, uplifts, personal and student-related stress), coping (coping styles, habits, quitting school, and drug use), and a biological factor (depression around the menstrual cycle) that predicted symptoms of depression. All hypothesized variables had direct paths to symptoms of depression; the path model explained 58% of the variance. Results from this study support the biological and psychological theories of depression in women and raise important questions of particular relevance to women, nursing students and educators.

Adaptation, Psychological↗

PubMed1998

Mechanism of isoniazid uptake in Mycobacterium tuberculosis.

Initial transport kinetics of isoniazid (INH) and its uptake at the plateau were studied in Mycobacterium tuberculosis H37Rv under various experimental conditions. The initial uptake velocity increased linearly with INH concentration from 2 x 10(-6) M to 10(-2) M. It was modified neither by addition of a protonophore that abolished proline transport, nor following ATP depletion by arsenate, which inhibited glycerol uptake, two transport processes taken as controls for secondary active transport and facilitated diffusion, respectively. Microaerobiosis or low temperature (4 degrees C) were without effect on initial uptake. It is thus likely that INH transport in M. tuberculosis proceeds by a passive diffusion mechanism, and that catalase-peroxidase (KatG) is not involved in the actual transport. However, conditions inhibiting KatG activity (high INH concentration, microaerobiosis, low temperature) decrease cell radioactivity at the uptake plateau. It is proposed that INH transport occurs by passive diffusion. KatG is involved only in the intracellular accumulation of oxidized derivatives of INH, especially of isonicotinic acid, which is trapped inside cells in its ionized form. This model explains observed and previously known characteristics of the accumulation of radioactivity in the presence of [14C]INH for various species and strains of mycobacteria.

Antitubercular Agents↗

PubMed1999

Proximal and distal correlates of maternal control style.

Control, as an aspect of maternal interaction, has been found to be an important component to optimal child development. Maternal control style is defined as a mother's tendency to be controlling or supportive of her child's autonomy. The relationship between two types of maternal characteristics, proximal and distal, and maternal control style was investigated in a sample of 184 mothers and their 4-year-old children. Global ratings of videotaped data of two problem-solving tasks were made on a 5-point scale. An optimal maternal control style was associated with higher levels of the distal maternal characteristics of maternal education, age, occupation, and higher levels of the proximal characteristics of maternal responsivity and involvement. A hierarchical regression model explaining 26% of the variance in maternal control style scores supports the importance of both types of maternal characteristics. The results are discussed in relation to the methodology and the theoretical framework of role.

Adult↗

PubMed2004

Numerical modeling of a four-wave-mixing-assisted Raman fiber laser.

We present a new numerical model of cascaded Raman fiber lasers that takes into account the chromatic dispersion of the fiber and includes the full spectrum of the intracavity field. This model explains and describes remarkably well a new operating regime found experimentally and reveals that chromatic dispersion is truly a new degree of freedom in the design of cascaded Raman lasers.

Algorithms↗

PubMed2007

Exploratory factor analysis: strategies used by patients to promote health.

Strategies used by patients to promote health (SUPPH) was used to measure self-care self-efficacy in patients with cancer. The objectives of this study were (1) to determine the extent to which self-efficacy theory explained the factor structure of the SUPPH and (2) to determine the relationship of demographic data with factors of the SUPPH. Subjects were diagnosed with prostate cancer (PCa) and treated with either: (a) radical prostatectomy, (b) intensity modulated radiation therapy (IMRT) + radioactive seed implantation, or (c) IMRT + high dose rate. Subjects completed a demographic questionnaire and the SUPPH. Exploratory factor analysis of the SUPPH was performed using a varimax rotation. Subjects (n = 265) were predominately white and averaged 68 years of age. The model explained 81.3% of the total sum of eigenvalues. Two factors of the SUPPH were identified: physiological efficacy information and performance efficacy information. Younger subjects who were fully employed and earning more money had significantly higher performance self-efficacy than older subjects who were working part time and earning less money. Results are congruent with Bandura's (1997) description of self-efficacy. Use of the SUPPH may facilitate research validating Bandura's (1997) assertion that an individual's self-efficacy is related to quality of life (QOL) during chronic illness. Additional research focusing on self-efficacy and PCa patients' QOL may lead to efficacy enhancing interventions that will improve QOL of patients with PCa.

Adult↗

PubMedDate not supplied

Sources of nitrate exposure in residents of rural areas in Quebec, Canada.

Nitrate exposure was investigated in a group of 187 people using well water and living in four areas of rural Quebec (Canada) with intensive agricultural activities. Nitrate intake was evaluated using a 24-h dietary recall and a food frequency questionnaire, in conjunction with a validated food database and measurements of nitrate concentrations in private wells. The total internal dose was estimated by means of the 24-h urinary nitrate excretion, while taking into account risk factors for endogenous nitrate formation. Mean (geometric) 24-h urinary nitrate excretion was 16.9 mg N for the 100 people with low groundwater contamination (mean nitrate concentration=0.18 mg N/l) and 23.3 mg N in the 87 individuals with moderate groundwater contamination (mean nitrate concentration=7.1 mg N/l). A multivariate analysis revealed that dietary nitrate intake during the last 24 h was the principal source of exposure, followed by water intake during the last 24 h. The Quetelet index was also a significant predictor of urinary excretion. The total predictive model explained only 29% of the variability in urinary nitrate excretion (R2=0.286). Neither the inflammatory status as indicated by elevated C reactive protein, the presence of Helicobacter pylori antibodies nor the occurrence of diarrhea during the last 24 h prior to urine collection were associated with urinary nitrate excretion. In conclusion, food and to a lesser extent water contribute to nitrate exposure in this rural setting with moderate water contamination. Better predictors of endogenous nitrate production are needed to improve our ability to model nitrate body burden and estimate associated health risks.

Adult↗

PubMed2005

Colour matching of isoluminant samples and backgrounds: a model.

A cone-opponent-based vector model is used to derive the activity in the red-green, yellow-blue, and achromatic channels during a sequential asymmetric colour-matching experiment. Forty Munsell samples, simulated under illuminant C, were matched with their appearance under eight test illuminants. The test samples and backgrounds were photometrically isoluminant with each other. According to the model, the orthogonality of the channels is revealed when test illuminants lie along either red-green or yellow blue cardinal axes. The red green and yellow-blue outputs of the channels are described in terms of the hue of the sample. The fact that the three-channel model explains the data in a colour-matching experiment indicates that an early form of colour processing is mediated at a site where the three channels converge, probably the input layer of V1.

Case-Control Studies↗