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PubMed1989

Computer-assisted evaluation of polydisperse two-dimensional gel patterns of polysaccharide-protein conjugate preparations with regard to size and net charge.

Native Hemophilus influenzae polysaccharide-protein conjugate particles were analyzed by a two-dimensional agarose electrophoresis procedure. In view of their preparation by random chemical crosslinking, the conjugates necessarily exhibit a polydisperse two-dimensional gel pattern which varies depending on the conditions of the particular preparation. The polydisperse patterns were interpreted with regard to the size and surface net charge density of the conjugate on the basis of the extended Ogston model. Data processing was performed by a new program, designated ZWEIDI.DO, written in the language of M-LAB (modeling laboratory). The program computes particle and gel fiber specific parameters from the positions of standards and unknown(s) on the two-dimensional gel using a simultaneous linear least-square curve fitting routine. Based on these calculations, the program serves to compute a nomogram of iso-size and iso-free-mobility profiles. Superimposing these profiles on the gel patterns, the size and free mobility range of the polydisperse conjugate mixtures is obtained. Potentially, the procedure could serve as a tool for quality control in the production of conjugates as vaccines and for the physical characterization of polydisperse subcellular particles and vesicles.

Bacterial Proteins↗
PubMed1992

Categorical data analysis in primary care research: log-linear models.

Primary care researchers often wish to perform multiple variable analyses using variables measured at a nominal or ordinal level. This paper provides a step-by-step description of log-linear modeling, an approach uniquely well suited to explore and describe interactions among three or more nominal or ordinal variables. The method of log-linear analysis is illustrated with the use of an example from a primary care research project in which the relationships among hypertension, diet, and sodium were examined. The advantages and disadvantages of log-linear models and logistic regression are compared and available computer software programs discussed.

Humans↗
PubMedDate not supplied

A new algorithm for computing the parameters of linear compartment models in pharmacokinetics.

A new algorithm (FADHA) for computing pharmacokinetic parameter estimates has been developed. This technique is based on the simplex method which is used to minimize a nonlinear cost function. An important property of this program is that the convergence is ensured contrary to the well-known linear or nonlinear least-squares regression analysis which lead to a lack of convergence or to a false one. Two investigations of the comparative performances of FADHA program and other algorithms were undertaken (hexamethylmelamine and Piracetam pharmacokinetics). Least square analysis of data yielded biased estimates whereas FADHA estimates were unbiased and more precise. This new technique, takes into account all the possible observation errors and uses the concept of a weighting function rather than weights as such.

Altretamine↗
PubMed2002

Statistical modelling of the central 10-degree visual field in short-wavelength automated perimetry.

BACKGROUND: Reports of short-wavelength pathway dysfunction in retinal eye disease suggest that short-wavelength automated perimetry may be a useful technique for the investigation of central visual function. The aim of this study was to adapt existing statistical procedures used for the investigation of 30-2 short-wavelength automated perimetry to the 10-2 program of the Humphrey Field Analyser. METHODS: A four- or six-point linear interpolation procedure was used to calculate normal visual field sensitivity for each of the 68 stimulus locations of the 10-2 program using empirical normal data from 51 normal subjects examined using the 30-2 program. Prediction limits for normality were derived at each stimulus location, enabling the calculation of age-corrected global perimetric indices and construction of probability maps for diffuse and focal visual field loss. The normal database was validated by empirical data from five normal subjects, stratified for age. RESULTS: The pointwise distribution of normal sensitivity exhibited a Gaussian distribution at the majority of stimulus locations. The pointwise coefficient of variation did not vary significantly across the visual field. Examples of diabetic pseudophakic patients and a patient with age-related macular degeneration are presented to illustrate the effectiveness of SWAP at detecting visual field abnormality in the central visual field. CONCLUSION: Ten-degree SWAP is able to effectively detect focal visual field loss in central retinal eye disease which may precede those found using conventional perimetry. SWAP may prove to be an invaluable technique for the investigation of central retinal eye disease.

Adult↗
PubMed1994

Effect of chronotropic response pattern on oxygen kinetics.

BACKGROUND: The sinus node is considered to be the model of chronotropic response for pacemakers that use artificial rate modulating sensors. Maximal metabolic exercise testing with measurement of oxygen consumption (VO2) is frequently used to evaluate chronotropic response. Since activities of daily living are generally transient and involve submaximal effort, maximal exercise testing may not provide the most clinically relevant method of assessing rate modulation. The purpose of this study was to determine if an abrupt increase in heart rate (HR) at the onset of submaximal exercise provides improved oxygen kinetics compared with a linear response. METHODS AND RESULTS: Thirteen patients with complete heart block and permanent rate modulating pacemakers implanted following catheter ablation of the atrioventricular junction for refractory atrial fibrillation were chosen for study. The patients first completed a maximal treadmill exercise test using the chronotropic assessment exercise protocol with breath-by-breath analysis of expired gases. The expected HR at 50% of metabolic reserve was calculated for each patient. Three submaximal constant workload exercise tests were then performed at 50% of each patient's metabolic reserve, with the pacemaker randomly programmed to provide three different patterns of chronotropic response: linear (in which HR increased from 70 beats/min to the expected HR at 50% of metabolic reserve), fast (in which HR was abruptly increased to the expected HR at 50% of metabolic reserve), and slow (VVI at 70 beats/min). Oxygen kinetics were compared for the three patterns of chronotropic response. Cumulative oxygen (O2) consumption was significantly greater for the fast pattern (3610 mL) as compared with the linear (3487 mL, P = 0.004) or slow pattern (3277 mL). The O2 deficit was lower for the fast (361 +/- 139 mL) than for the linear (539 +/- 225 mL, P = 0.003) or slow chronotropic pattern (559 +/- 194). Similar improvements in the rate constant of O2 uptake and Borg perceived exertion scores were observed with the fast chronotropic response pattern. CONCLUSION: A rapid increase in pacing rate at the onset of exercise improves oxygen kinetics and results in less perceived exertion as compared to a more gradual rate increase that is more characteristic of sinus node behavior.

Adult↗
PubMed1983

A microcomputer oximeter for whole blood.

A system is described for measuring the percent of oxyhemoglobin in flowing whole blood. The system consists of an Apple II+ computer, a commercially available analog-to-digital converter, a simple electronic circuit to illuminate blood with light at two appropriate wavelengths, and a short program in BASIC. This oximeter is shown to yield a linear measurement of oxyhemoglobin saturation when compared with standard oxygen analyses. Data can be sampled at a sufficiently rapid rate to yield an essentially continuous measurement in typical cardiovascular studies. The system can be implemented by the average investigator from standard electronic components. The oximeter program can be combined into a general-purpose data acquisition program, and 15 analog-to-digital channels remain available for gathering other data.

Animals↗
PubMed1997

The effect of accurate patient screening on the cost-effectiveness of case management programs.

Case management programs are expensive and therefore require careful screening of enrollees to ensure cost-effectiveness. Screening tools, however, are imperfect, with positive predictive values usually below 50%. This article examines the relationship between the accuracy of the screening tools and the cost-effectiveness of case management. Using data from a Medicare health maintenance organization (HMO), we develop an optimized 5-question screening tool. We then simulate the use of this screening tool and its impact on the cost-effectiveness of several hypothetical case management programs. The article demonstrates that even screening tools with only 20-30% positive predictive value could turn a case management program into a cost-effective program.

Activities of Daily Living↗
PubMed2000

Empirical assessments of social networks, fertility and family planning programs: nonlinearities and their implications.

Empirical studies of the diffusion of modern methods of family planning have increasingly incorporated social interaction within nonlinear models such as logits. But they have not considered the full implications of these nonlinear specifications. This paper considers the implications of using nonlinear models in empirical analyses of the impact of family programs, modulated by social interaction, on reproductive behavior. Three implications of nonlinear models, in comparison with linear models, are developed. 1) With nonlinear models, there may be both low and high contraceptive-use equilibria (i.e., the ultimate level of use of modern family planning that a population can be expected to reach after the effects of a sustained change in a family planning program have worked through the population) rather than just one equilibrium as in linear models. If there are multiple equilibria, then one striking and important result is that a transitory large program effort may move a community from sustained low- to high-level contraceptive use. 2) With nonlinear models, the extent to which a social interaction multiplies program efforts depends on whether the community is at a low or high level of contraceptive use rather than being independent of the level of contraceptive use as in linear models. 3) With nonlinear models, intensified social interaction can retard or enhance the diffusion of family planning, in contrast to only enhancing diffusion as within linear models. To clarify these implications, for comparison a simple and more transparent linear model is also discussed. Illustrative estimates are presented of simple linear and nonlinear models for rural Kenya that demonstrate that some of these effects may be considerable.

Contraception↗
PubMed2006

Intraoperative radiation therapy using mobile electron linear accelerators: report of AAPM Radiation Therapy Committee Task Group No. 72.

Intraoperative radiation therapy (IORT) has been customarily performed either in a shielded operating suite located in the operating room (OR) or in a shielded treatment room located within the Department of Radiation Oncology. In both cases, this cancer treatment modality uses stationary linear accelerators. With the development of new technology, mobile linear accelerators have recently become available for IORT. Mobility offers flexibility in treatment location and is leading to a renewed interest in IORT. These mobile accelerator units, which can be transported any day of use to almost any location within a hospital setting, are assembled in a nondedicated environment and used to deliver IORT. Numerous aspects of the design of these new units differ from that of conventional linear accelerators. The scope of this Task Group (TG-72) will focus on items that particularly apply to mobile IORT electron systems. More specifically, the charges to this Task Group are to (i) identify the key differences between stationary and mobile electron linear accelerators used for IORT, (ii) describe and recommend the implementation of an IORT program within the OR environment, (iii) present and discuss radiation protection issues and consequences of working within a nondedicated radiotherapy environment, (iv) describe and recommend the acceptance and machine commissioning of items that are specific to mobile electron linear accelerators, and (v) design and recommend an efficient quality assurance program for mobile systems.

Electrons↗
PubMed2002

High performance liquid chromatographic-mass spectrometric assay for the quantitation of BMS-204352 in dog K(3)EDTA plasma.

A high performance liquid chromatographic-mass spectrometric (LC/MS) assay was developed and validated for the determination of BMS-204352 in dog K(3)EDTA plasma. A 0.5 mL aliquot of control plasma was spiked with BMS-204352 and internal standard (IS) and buffered with 1 mL of 5 mM ammonium acetate. The mixture was then extracted with 3 mL of toluene. After separation and evaporation of the organic phase to dryness using nitrogen at 40 degrees C, the residue was reconstituted in the mobile phase and 25 microL of the sample were injected onto a Hypersil C(18) column (2 x 50 mm; 3 microm) at a flow rate of 0.5 mL/min. The mobile phase was consisted of two solvent mixtures (A and B). Solvent A was composed of 5 mM ammonium acetate and 0.1% triethylamine in 75:25 v/v water:methanol, pH adjusted to 5.5 with glacial acetic acid, and solvent B was 5 mM ammonium acetate in methanol. A linear gradient system was used to elute the analytes. The mass spectrometer was programmed to admit the de-protonated molecules at m/z 352.7 (IS) and m/z 357.9 (BMS-204352). Standard curves of BMS-204352 were linear (r(2) > or = 0.998) over the concentration range of 0.5-1000 ng/mL. The mean predicted quality control (QC) concentrations deviated less than 5.1% from the corresponding nominal values (ie 4, 80, 400 and 2000 ng/mL); the within- and between-assay precision of the assay were within 5.5% relative standard deviation. Stability of BMS-204352 was confirmed after at least three freeze/thaw cycles and BMS-204532 was stable in dog plasma when stored frozen at or below -20 degrees C for at least 16 weeks in spiked QC samples and for at least 4 1/2 weeks for in vivo study samples. BMS-204352 and IS were stable in the injection solvent at room temperature for at least 24 h. The assay was applied to delineate the pharmacokinetic disposition of BMS-204352 in dogs following a single intravenous dose administration. In conclusion, the assay is accurate, precise, specific, sensitive and reproducible for the pharmacokinetic analysis of BMS-204532 in dog plasma.

Animals↗
PubMed1998

Prevention of early childhood caries--results of a fluoride toothpaste demonstration trial on Chinese preschool children after three years.

OBJECTIVES: This field demonstration trial evaluates the long-term effects of introducing daily toothbrushing with fluoride toothpaste in a Chinese kindergarten (test group) compared to caries development in children who had no organized preventive program (control group). METHODS: In the test group teacher-supervised toothbrushing was initiated with 1,000 ppm MFP toothpaste in addition to oral health education activities. Test and control children were examined at baseline (n = 289, aged 3 years) and annually thereafter. RESULTS: After three years, 251 children (87%) were still in the trial. Caries development (dmfs) calculation included only those children who were present at both baseline and subsequent annual examinations. At baseline the mean dmfs was 4.8 in the test group and 6.5 in the control group (NS). After three years the caries increment was 6.2 and 8.4 in the test group and the control group, respectively (P < .05). Adjusting for reversals, the net caries increment was 3.6 and 6.3, respectively (P < .01). Additionally, multiple linear regression analysis indicated that both baseline dmfs, the program and plaque level had a significant effect on the net caries increment. The use of hierarchical caries severity zones was useful for the identification of those children most at risk for further caries development. CONCLUSIONS: We conclude that a daily toothbrushing with limited involvement of professional staff was feasible in a Chinese kindergarten and that caries development was significantly slowed in the test children. Caries severity zones may possibly assist in determining levels of intervention.

Cariostatic Agents↗
PubMed1986

Evaluation of fellowship and residency programs in a comprehensive cancer center.

A Dental Oncology residency and fellowship program was evaluated annually from 1980-1984 by each trainee. Nineteen training program variables were assessed on an Exit from Training Questionnaire using 0-100 mm linear scales. The five annual scores for each variable were subjected to trend analysis. Implication of the results to the training program are discussed. The evaluation method may be used to establish a departmental training program benchmark in relation to which future performance can be measured and as a guide to program modification. The method may be applied to all departmental training programs and, when combined, to the institution as a whole.

Cancer Care Facilities↗
PubMed2005

Influence of electromagnetic interference on implanted cardiac arrhythmia devices in and around a magnetically levitated linear motor car.

This study was designed to determine the susceptibility of implanted cardiac arrhythmia devices to electromagnetic interference in and around a magnetically levitated linear motor car [High-Speed Surface Transport (HSST)]. During the study, cardiac devices were connected to a phantom model that had similar characteristics to the human body. Three pacemakers from three manufacturers and one implantable cardioverter-defibrillator (ICD) were evaluated in and around the magnetically levitated vehicle. The system is based on a normal conductive system levitated by the attractive force of magnets and propelled by a linear induction motor without wheels. The magnetic field strength at 40 cm from the vehicle in the nonlevitating state was 0.12 mT and that during levitation was 0.20 mT. The magnetic and electric field strengths on a seat close to the variable voltage/variable frequency inverter while the vehicle was moving and at rest were 0.13 mT, 2.95 V/m and 0.04 mT, 0.36 V/m, respectively. Data recorded on a seat close to the reactor while the vehicle was moving and at rest were 0.09 mT, 2.45 V/m and 0.05 mT, 1.46 V/m, respectively. Measured magnetic and electric field strengths both inside and outside the linear motor car were too low to result in device inactivation. No sensing, pacing, or arrhythmic interactions were noted with any pacemaker or ICD programmed in either bipolar and unipolar configurations. In conclusion, our data suggest that a permanent programming change or a device failure is unlikely to occur and that the linear motor car system is probably safe for patients with one of the four implanted cardiac arrhythmia devices used in this study under the conditions tested.

Defibrillators, Implantable↗
PubMed1999

PALIREL, a computer program for analyzing particle-to-membrane relations, with emphasis on electron micrographs of immunocytochemical preparations and gold labeled molecules.

Many vital substances, such as receptors, transporters, and ion channels, in cells occur associated with membranes. To an increasing extent their precise localization is demonstrated by immunocytochemical methods including labeling with gold particles followed by electron microscopy. PALIREL has primarily been developed to facilitate such research, enabling rapid analysis of topographic relations of particles (gold or others) to neighboring linear interfaces (membranes). After digitization of membranes and particles, the program particularly allows computation of (1) the particle number and number per unit length of membrane, in individual bins (membrane lengths) interactively defined along the membrane; (2) the distance of each particle from the membrane; (3) the particle number, and the density (number per micron2), in zones defined along (over and under) the membrane; and (4) the particle number and density in "zonebins" resulting from zones and bins being defined simultaneously. If there occurs, somewhere in the membrane, a segment of different nature, such as a synapse, the quantitative data may be had separately for that and the adjoining parts of the membrane. PALIREL allows interactive redefinition of bins, zones, or objects (particle-line files) while other definitions are retained. The results can be presented on the screen as tables and histograms and be printed on request. A dedicated graphic routine permits inspection on screen of lines, particles, zones, and bins. PALIREL is equally applicable to biological investigations of other kinds, in which the topographic relations of points (structures represented as points) to lines (boundaries) are to be examined. PALIREL is available from the authors on a noncommercial basis.

Algorithms↗
PubMed1997

Survival curve fitting using the Gompertz function: a methodology for conducting cost-effectiveness analyses on mortality data.

The analysis of published survival curves can be the basis for incremental cost-effectiveness evaluations in which two treatments are compared with each other in terms of cost per life-year saved. The typical case is when a new treatment becomes available which is more effective and more expensive than the corresponding standard treatment. When effectiveness is expressed using the end-point of mortality, cost-effectiveness analysis can compare the (incremental) cost associated with the new treatment with the (incremental) clinical benefit measured in terms of number of life-years gained. The (incremental) cost-effectiveness ratio is therefore quantified as cost per life-year gained. This pharmacoeconomic methodology requires that the total patients years for the treatment and the control groups are estimated from their respective survival curves. We describe herein a survival-curve fitting method which carries our this estimation and a computer program implementing the entire procedure. Our method is based on a non-linear least-squares analysis in which the experimental points of the survival curve are fitted to the Gompertz function. The availability of a commercial program (PCNONLIN) is needed to carry out matrix handling calculations. Our procedure performs the estimation of the best-fit parameters from the survival curve data and then integrates the Gompertz survival function from zero-time to infinity. This integration yields the value of the area under the survival curve (AUC) which is an estimate of the number of patients years totalled in the population examined. If this AUC estimation is performed separately for the two survival curves of two treatments being compared, the difference between the two AUCs permits to determine the incremental number of patient years gained using the more effective of the two treatments as opposed to the other. The cost-effectiveness analysis can consequently be carried out. An example of application of this methodology is presented in detail.

Antineoplastic Agents↗
PubMed2003

The long-term within- and between-laboratory variability for assay of antithrombin, and proteins C and S: results derived from the external quality assessment program for thrombophilia screening of the ECAT Foundation.

A stable laboratory performance is important for comparability and transferability of laboratory data both within and between laboratories. The lack of a reference system within hemostasis hampers laboratories in establishing their laboratory performance over a prolonged period of time. Therefore, based on data from an external quality assessment program, we evaluated the between laboratory variation (CVBETWEEN) and the long-term within-laboratory variation (LCVa) for antithrombin, and proteins C and S. We evaluated the CVBETWEEN for the period 1996-2001, including the results of 64-240 laboratories from 23 different surveys (protein S activity 15 surveys). We observed a quite high CVBETWEEN and a broad range for each analyte. The CVBETWEEN was significantly higher for antithrombin and protein S for samples with low levels similar to heterozygous deficiencies. We also evaluated the LCVa, including the results of 136 laboratories. The lowest LCVa[median and 95% content interval (CI)] was observed for antithrombin (7.6%; 3.6-35.5%), intermediate values for protein C activity and antigen (8.6%; 3.5-25.3% and 10.8%; 4.8-33.1%, respectively) and highest values for the protein S variables (13.4%; 6.4-50.6% for total protein S antigen, 14.1%; 6.5-79.1% for free protein S antigen and 17.2%; 7.2-84.3% for protein S activity). We concluded that the main reason for the high CVBETWEEN is the long-term within-laboratory variability. Application of linear regression on data of an external quality assessment program is a useful model to demonstrate per analyte per laboratory the long-term variability (LCVa). It is concluded that improvement of the long-term within-laboratory test performance is the first priority in hemostasis to yield important improvements in the comparability and transferability of laboratory data.

Antithrombin III↗
PubMed1998

Overall false positive rates in tests for linear trend in tumor incidence in animal carcinogenicity studies of new drugs.

Based on results of simulation and empirical studies conducted within the Divisions of Biometrics, Center for Drug Evaluation and Research, Food and Drug Administration, and in collaboration with the National Toxicology Program, the Center has recently changed the significance levels for testing positive linear trend in incidence rate for common and rare tumors, respectively, from 0.01 and 0.05 to 0.005 and 0.025. The overall false positive rate resulting from the use of this new rule in the tests for linear trend in a two-species-two-sex study is about 10%, the rate that is judged as the most appropriate in a regulatory setting by the Center. This paper describes two of the studies.

Animals↗
PubMed1995

Evidence that Spitzenkörper behavior determines the shape of a fungal hypha: a test of the hyphoid model.

Hyphae of the fungus Rhizoctonia solani have a characteristic Spitzenkörper in their growing tips and a cell shape described by the mathematical hyphoid equation. A mild disturbance of hyphae growing in a slide culture chamber on a microscope stage caused the Spitzenkörper to move away from its usual position next to the apical pole and wander briefly inside the apical dome. Hyphal elongation rate declined abruptly, and the apex became rounded and increased in diameter. As the Spitzenkörper migrated back to its polar position, rapid cell elongation resumed, and the contour of the growing hyphal tip returned to the typical hyphoid shape. The brief dislocation of the Spitzenkörper left a permanent bulge in the hyphal profile. This morphogenetic sequence was mimicked by computer simulation, based on the hyphoid equation which relates the generation of hyphal shape to the linear displacement of a vesicle supply center (VSC). The VSC was programmed to retrace the observed movements of the Spitzenkörper during the above sequence. The resulting similarity of shape between real and computer-simulated cells reinforces the mathematical prediction that the Spitzenkörper acts as a VSC and that its continuous linear advancement generates a typical hyphal tube with the characteristic hyphoid shape. Accordingly, the hyphoid model and its VSC concept provide a plausible hypothesis to explain the cellular basis of polarized growth of fungal hyphae.

Computer Simulation↗