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W L Baker

Publications and source records attributed to W L Baker.

At least 19 recordsLinked to original sources
PubMed2001

An evaluation of analysis options for the one-group-per-condition design. Can any of the alternatives overcome the problems inherent in this design?

This article addresses the analytic problems associated with a design in which one identifiable group is allocated to each treatment condition and members of those groups are measured to assess the intervention. Such designs are often called quasi-experiments if the groups are not randomized to conditions and group-randomized trials if the groups are randomized. They present special problems, and previous reports have argued against their use in efficacy or effectiveness trials. Even so, this design still appears with surprising frequency. This article presents the results from a new simulation study that underscores the analytic problems associated with this design.

Group Processes↗
PubMed1999

Fluorimetric determination of ampicillin by use of non-toxic catalysts. Estimation of beta-lactamase activity and parameters.

A fluorescence assay based on the use of biological reducing agents as catalysts rather than heavy metal ions has been developed for estimation of ampicillin concentrations. The assay is based on the conversion of ampicillin to its penicilloate, by treatment with sodium hydroxide, then neutralization, dilution with 0.5 M acetate buffer at pH4 and heating for 30 min at 100 degrees C in the presence of ascorbic acid (0.5 mg) and EDTA (50 microM). Reduced glutathione, cysteine and N-acetylcysteine also catalysed the development of fluorescence. A practical sensitivity range of 0.5-50 microM ampicillin was used. The assay was used to estimate ampicillin in some biological solutions to which the antibiotic has been added. Milk, blood serum, trypticase soy broth and nutrient broth containing 25 microM antibiotic assayed at 18.5, 21.7, 16.5 and 14.7 microM, respectively, with standard deviations between 1.2 and 0.7%. The low results were attributed to binding of some ampicillin by proteins or peptides which were removed by pretreatment. Urine containing 5 mM ampicillin assayed at 4.97 mM with a standard deviation of 3%. A modification of the procedure was used to measure beta-lactamase activity against ampicillin in several organisms in a fixed time assay. Kinetic parameters of a commercial beta-lactamase preparation from Bacillus cereus could also be determined by an additional modification. In both instances a correction was required for the intrinsic fluorescence of ampicillin remaining in the solution. The preparation examined had a Michaelis constant (Km) of 0.32 mM, a maximum velocity (Vmax) of 5398 micromol ampicillin hydrolysed mg(-1) min(-1), an apparent catalytic constant (Kcat, turnover number) of 20,220 s(-1) and a Kcat/Km ratio of 0.63 x 10(7) M(-1) s(-1). The major advantage of using this assay technique is that toxic metals are not used in the development of fluorescence so it is more environmentally acceptable. The technique is useful for examining beta-lactamase activity against ampicillin and might be useful for pharmaceutical products-for determining available therapeutic levels and for monitoring the activity of penicillin acylase against the penicilloate of ampicillin.

Ampicillin↗
PubMed1998

Analysis of data from group-randomized trials with repeat observations on the same groups.

This study used Monte Carlo simulations to evaluate the performance of alternative models for the analysis of group-randomized trials having more than two time intervals for data collection. The major distinction among the models tested was the sampling variance of the intervention effect. In the mixed-model ANOVA, the sampling variance of the intervention effect is based on the variance among group x time-interval means. In the random coefficients model, the sampling variance of the intervention effect is based on the variance among the group-specific slopes. These models are equivalent when the design includes only two time intervals, but not when there are more than two time intervals. The results indicate that the mixed-model ANOVA yields unbiased estimates of sampling variation and nominal type I error rates when the group-specific time trends are homogenous. However, when the group-specific time trends are heterogeneous, the mixed-model ANOVA yields downwardly biased estimates of sampling variance and inflated type I error rates. In contrast, the random coefficients model yields unbiased estimates of sampling variance and the nominal type I error rate regardless of the pattern among the groups. We discuss implications for the analysis of group-randomized trials with more than two time intervals.

Analysis of Variance↗
PubMed1998

Chromatographic separation of fluorescent thiol adducts of 4-chloro-7-sulphobenzofurazan. Use as substrates for enzymes of the mercapturic acid xenobiotic pathway.

Fluorescent adducts of 4-chloro-7-sulphobenzofurazan with cysteine, cysteinylglycine, reduced glutathione and N-acetylcysteine were prepared. Adducts were separated by HPLC on a 3-mm Nova-Pak C18 reversed-phase column using isocratic elution with a solvent of acetonitrile-0.15 M phosphoric acid (5:95) buffered at pH 2.5. The adducts were detected using a fluorescence detector set at an excitation wavelength of 365 nm and an emission wavelength of 510 nm and an ultraviolet detector at 254 nm. The adduct of reduced glutathione was also formed by the action of the enzyme glutathione-S-transferase. This adduct acted as a substrate for the enzyme gamma-glutamyltranspeptidase and the product of this reaction, the 4-chloro-7-sulphobenzofurazanyl derivative of cysteinylglycine, acted as a substrate for either dipeptidase or aminopeptidase M. The sequential enzymic effects could be detected by changes in the relative fluorescence intensity of the solutions to which the respective enzymes had been added but were more appropriately followed by changes in the HPLC elution profiles after enzymic treatment of solutions.

Acetylcysteine↗
PubMed1997

Phenolic substrates for fluorometric detection of laccase activity.

A fluorometric procedure has been developed for detection and estimation of laccase activity in fungal broth cultures. Laccase solution was pretreated with catalase for 1 h at 37 degrees C and pH 5. Homovanillic acid was then added and the reaction mixture incubated for a further hour at 37 degrees C. The fluorescence was then developed by addition of 0.1 M glycine buffer at pH 10. Laccase preparations from Pyricularia oryzae, Coriolus hirsutus and Pycnoporus cinnabarinus catalysed formation of a fluorescent product of HVA but the optimum pH values of enzyme activities varied. The culture fluids of several other fungi also catalysed development of fluorescence in solutions containing HVA. p-Hydroxyphenylacetic acid was a poor substrate for all laccases in vivo except that produced by Perennipora tephropora.

Benzothiazoles↗
PubMed1997

Modified fluorimetric assay for estimating ampicilloate concentrations and its use for detecting beta-lactamase and penicillin acylase activity in bacteria.

Sodium ampicilloate concentrations were estimated fluorimetrically by heating solutions with ascorbic acid, EDTA and a modified Lowry A reagent which was prepared by including copper sulfate and potassium sodium tartrate in 0.5 mol dm-3 acetate buffer at pH 4. A concentration range of 0.5-50 mumol dm-3 was used for the estimations. The reaction was used to estimate beta-lactamase activity on ampicillin but the substrate also showed some fluorescence and a calculation was required to determine the amount of ampicilloate formed when both substances were present in the one reaction mixture. The beta-lactamase was inhibited by treatment with trichloroacetic acid so the procedure could be used to assay the enzyme activity after a fixed time. 6-Aminopenicillanic acid did not fluoresce on treatment with the modified reagent and organisms which contained penicillin acylase lowered the amount of ampicillin which could be converted to ampicilloate. When penicillin acylase and beta-lactamase co-existed in the one organism, the respective activities were determined by use of the copper-ascorbate-EDTA fluorescence assay for ampicilloate coupled with a fluorescamine assay for 6-aminopenicillanic acid determinations. On prolonged incubation, some organisms containing penicillin acylases lowered the amount of ampicilloate which formed a fluorescent product. This effect was attributed to deacylation of ampicilloate by the penicillin acylases.

Ampicillin↗
PubMed1996

Community education for cardiovascular disease prevention. Morbidity and mortality results from the Minnesota Heart Health Program.

The Minnesota Heart Health Program was a community trial of cardiovascular disease prevention methods that was conducted from 1980 to 1990 in three Upper Midwestern communities with three matched comparison communities. A 5- to 6-year intervention program used community-wide and individual health education in an attempt to decrease population risk. A major hypothesis was that the incidence of validated fatal and nonfatal coronary heart disease and stroke in 30- to 74-year-old men and women would decline differentially in the education communities after the health promotion program was introduced. This hypothesis was investigated using mixed-model regression. The intervention effect was modeled as a series of annual departures from a linear secular trend after a 2-year lag from the start of the intervention program. In the education communities, 2,394 cases of coronary heart disease and 818 cases of stroke occurred, with 2,526 and 739 cases, respectively, being seen in the comparison communities. The overall decline in coronary heart disease incidence was 1.8 percent per year in men (p = 0.03) and 3.6 percent per year in women (p = 0.007). For stroke, there were no significant secular trends. The authors recently published findings showing minimal effects of sustained intervention on risk factor levels. In the current report, there was no evidence of a significant intervention effect on morbidity or mortality, either for coronary heart disease or for stroke.

Adult↗
PubMed1996

A Monte Carlo study of alternative responses to intraclass correlation in community trials. Is it ever possible to avoid Cornfield's penalties?

Strategies to avoid the penalties of extra variation and reduced degrees of freedom in community trials were compared in Monte Carlo simulations. Three conditions were found necessary to ensure nominal Type I and II error rates: (a) Condition variation must be assessed against assignment unit variation, (b) the critical value for the test statistic must be based on the assignment unit degrees of freedom, and (c) estimation of negative intraclass correlations must be allowed in the analysis. Using other test statistics and other degrees of freedom, and fixing negative intraclass correlations at zero often gave Type I and II error rates far from their nominal levels.

Analysis of Variance↗
PubMed1994

Assessing intervention effects in the Minnesota Heart Health Program.

The Minnesota Heart Health Program is a 13-year research and demonstration project to reduce morbidity and mortality from coronary heart disease in whole communities in the upper Midwest. Six communities were selected for the study: three intervention and three comparison sites, matched to increase baseline comparability. After 2-4 years of baseline observations, a 5- to 6-year program of intensive intervention was introduced in the three intervention communities. Periodic cross-sectional and cohort surveys provided data on risk factors and related behaviors. Regression adjustments within and between communities reduced the confounding influences of important covariates and the variance inflation associated with the nesting of individuals within communities and surveys. Post hoc stratification allowed exploration of the main and strata-specific effects of the intervention program. Finally, the intervention effect was modeled as a departure from the trend line fit to the nonintervention city-year means. Together, these procedures explicitly acknowledged the component of variance associated with communities, and so avoided a major source of bias created in the usual analysis when that variation is ignored. They also increased the interpretability of the analyses and reduced the mean square errors used to assess the treatment effects.

Cohort Studies↗
PubMed1993

A planning process for a fast track to IAIMS.

The strategic planning process that is part of Vanderbilt University's fast track to IAIMS is evolving based on feedback from the process itself. Led by a committee of VUMC's top management, broad-based sub-committees for administration, education, patient care, and research worked initially on the following strategic issues: identifying key external pressures that constrain and provide opportunities, visioning how VUMC might operate in the future, and establishing a mission and high-level goals for information management. Next steps include identifying the critical mass of function that will prompt daily use of the IAIMS by everyone at VUMC and adding groups to focus on information and technology architectures and developing academic informatics. This manuscript gives detailed, practical information about the evolution of the planning process, committees' responsibilities, working relationships, and lessons learned.

Academic Medical Centers↗
PubMed1992

Co-existence of beta-lactamase and penicillin acylase in bacteria; detection and quantitative determination of enzyme activities.

Twenty-six bacteria were examined for the presence of penicillin acylase and beta-lactamase. A copper reducing assay, which was sensitive in the analytical range 2-20 micrograms/ml, was used for determination of penicilloates and a fluorescamine assay was used to determine 6-aminopenicillanic acid concentrations when both substances were produced by the action of the enzymes on a single substrate. Seventeen bacteria contained beta-lactamases, six contained penicillin acylases and four contained both enzymes. Two bacteria contained a Type 1 penicillin acylase and four bacteria contained a Type II enzyme. No ampicillin acylases were detected. All beta-lactamases were constitutive enzymes in those organisms where both enzymes co-existed. Bacillus subtilis and B. cereus produced inducible and extracellular beta-lactamases. Acinetobacter calcoaceticus ATCC 21288 produced a constitutive beta-lactamase which was detected extracellularly.

Anti-Bacterial Agents↗
PubMed1991

Potential interference of hydrogen peroxide in the 2,2'-bicinchoninic acid protein assay.

At a concentration of 20-800 nmol/0.1 ml hydrogen peroxide instantly reacts with a 2,2'-bicinchoninic acid copper color reagent. It also reacts with a reformulated reagent at pH 7 but the color develops less rapidly. While the effect may interfere with protein estimations at alkaline pH, the effect of pH 7 may be used to determine the possible extent of hydrogen peroxide interference after treatment with catalase.

Catalase↗
PubMed1991

Estimation of cellulase activity using a glucose-oxidase-Cu(II) reducing assay for glucose.

In the presence of the Cu(I)-chelating agent neocuproine (2,10-dimethyl-1,9-phenanthroline) hydrogen peroxide acts as a reductant of Cu(II). The reaction does not proceed in the absence of neocuproine and the addition of EDTA to the reaction mixture prior to addition of Cu(II) also inhibits the reduction. Colour development can be arrested and stabilized by addition of EDTA. The reaction can be used to estimate hydrogen peroxide concentrations in the range 0.68-6.8 micrograms/ml and glucose concentrations in the range 3.6-36 micrograms/ml (20-200 microM). Horseradish peroxidase is not required for the peroxide assay but glucose oxidase must be used for glucose estimations. Thermostable cellulase activity has been estimated at 60 degrees C against cellobiose, carboxymethylcellulose and cellulose substrates by estimation of the glucose released from the substrates.

Cellulase↗
PubMed1990

Breath-stacking increases the depth and duration of chest expansion by incentive spirometry.

Although the objective of incentive spirometry is to achieve and hold high lung volumes, many patients with pain or weakness are unable to sustain the effort needed to perform effective exercises. We questioned whether using a one-way valve to prevent exhalation would allow rest between inspiratory efforts and cause volume to cumulate during successive tidal efforts, improving both the depth and duration of the inspiratory maneuver. We studied 26 cooperative but naive patients recovering from surgery, trauma, or critical illness whose pain or weakness impaired ability to achieve and sustain deep inspiration. All subjects breathed via mouthpiece from a spirometer prefilled with 100% oxygen. Three different maneuvers were performed in random order by all subjects: (1) standard inspiratory capacity without valve or inspiratory hold, (2) inspiratory capacity (IC) with breathholding aided by a one-way valve, and (3) uncoached breath-stacking, during which successive tidal breaths were cumulated by one-way valving. A fourth maneuver was added in the last 13 subjects studied: an initial coached IC effort with subsequent valved stacking of tidal efforts. When compared with IC, "breath stacking" (valved) maneuvers increased inspired volume by an average of 15 to 20% (p less than 0.05). More importantly, there was a severalfold increase in the time over which high lung volume was sustained (p less than 0.001). Our results indicate that one-way valving helps to achieve and sustain deep inspiration, even in uncoached patients.

Humans↗
PubMed1989

Spectrophotometric determination of penicilloates in penicillins.

A procedure has been developed for the determination of penicilloates based on the reduction of CuII and detection of CuI using neocuproine. The sensitivity range is 5.6-56 microns penicilloate and the standard deviation was found to be between 1 and 2%. All the penicilloates tested reduced CuII under the conditions of the assay and a slight modification allowed a reasonably accurate determination of the level of this biologically inactive ingredient in a mixture with the parent penicillin. The deterioration of solutions of benzylpenicillin was also studied.

Copper↗
PubMed1987

Disulfide inhibition of copper-catalyzed oxidation of ascorbic acid: spectrophotometric evidence for accumulation of a stable complex.

Copper-catalyzed oxidation of ascorbic acid was retarded in the presence of the biological disulfide compounds cystine and oxidized glutathione. The evidence suggested that this effect was due to the formation of a stable complex involving the copper ion, the disulfide compound, and ascorbic acid or a derivative formed during the oxidative process. This indicated that less copper was available for the formation of oxygen complexes which are not as stable as the disulfide complexes. Ellman's reagent (Nbs2) was reduced when it was substituted for the biological disulfides or when added, with EDTA, to solutions in which ascorbic acid, copper ion, and the biological disulfides had been allowed to interact. The complex formed with cystine was detected at 360 nm but the glutathione complex was not detected at this wavelength. It is proposed that disruption of cystine or glutathione complexes by EDTA results in formation of 2,3-diketogulonic acid which acts as a reductant of Ellman's reagent.

Ascorbic Acid↗