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E Ackerman

Publications and source records attributed to E Ackerman.

At least 37 records · Page 2Linked to original sources
PubMed1993

Parameter sensitivity of a model of viral epidemics simulated with Monte Carlo techniques. IV. Parametric ranges and optimization.

A model is presented of the spread of influenza into and within a nursing home. To use this model for studies involving surveillance and vaccine efficacy, it is necessary to estimate optimal ranges of a group of parameters. Attempts to do so by manual methods proved unsatisfactory. Initial use of the methods presented in the previous three papers of this series led to points that were also unsatisfactory. However, by noting which parameters were placed at the outer surface of the chosen hypervolume, it was possible to choose new ranges and to select an optimal point in hyperspace that satisfied the epidemiologically preselected characteristics.

Community-Acquired Infections↗
PubMed1992

Iontophoretic delivery of morphine for postoperative analgesia.

Iontophoresis is a method of transdermal administration of ionized drugs in which electrically charged molecules are propelled through the skin by an external electrical field. This was a prospective, randomized, single-blind study to determine the effectiveness of iontophoretically delivered morphine HCl for the control of postoperative pain. Thirty-eight patients who underwent total knee or hip replacement completed this clinical trial. Informed consent was obtained before surgery and patients were instructed on the use of a patient-controlled analgesia (PCA) device. Postoperatively, pain in the recovery room was initially controlled with IV meperidine, and thereafter with PCA therapy using meperidine, 2 mg/cc, with a dose of 10 mg IV and a lock-out period of 15 min. The dose was adjusted as necessary and the lock-out period remained the same. The number of patient requests and the dose (mg) administered was recorded hourly. On the morning following surgery, iontophoresis devices were attached for 6 hr to patients who received either morphine HCl or lactated ringers solution. During this period and for 12 hr following completion of iontophoresis, PCA analgesia remained available to patients. Venous blood samples for determination of morphine levels were obtained every 30 min during iontophoresis, then every 60 min for 2 hr following iontophoresis. Of the 38 patients, 17 received iontophoresed morphine, and 21 received iontophoresed lactated ringers. The morphine group utilized the PCA device more than the control group during the baseline period. However, following the institution of iontophoresis and continuing up to 12 hr following completion of iontophoresis, the morphine group used significantly less PCA meperidine to maintain analgesia than the control group (p = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Pancreatitis induced by mesalamine.

Sulphasalazine is an active agent in the treatment of chronic inflammatory bowel disease, but there are a number of well-known side effects, including pancreatitis. The newer 5-ASA agents are thought to be equally effective but less toxic. Here we describe a patient who developed a pancreatitis due to mesalamine; this was confirmed at rechallenge.

Acute Disease↗
PubMed1991

Polychotomous multivariate models for coronary heart disease simulation. I. Tests of a logistic model.

Stochastic compartmental modeling techniques have been employed to simulate coronary heart disease morbidity and mortality. In the current paper, polychotomous logistic models are used to describe the relationship between risk of disease and multiple risk factors, effect modification and confounding variables. The process of estimating the parameters for two risk factors and three types of outcomes is described for a population followed for five years. A Statistical Analysis System (SAS) procedure was used to estimate risk factor coefficients based on two partial periods and on the entire five year epoch. Most of the estimated coefficients were found to be statistically significant. The model performance was evaluated by comparing the observational data with simulated outcomes using a micropopulation and Monte Carlo techniques. Two different tests of goodness of fit were used. Satisfactory fits were obtained both for the risk coefficients based on two partial periods and those based on the entire epoch. This indicates that the model is suitable for simulation of the effects of intervention strategies. The use of the entire epoch involved estimates of one half as many parameters as did the use of two partial periods. Accordingly, it is concluded that only the entire epoch need be considered for future studies of this population.

Adult↗
PubMed1991

An expert system for simulation of coronary heart disease risk factor interventions.

The feasibility of using an expert system to support intervention studies within CRISPERS was investigated. A prototype expert system named CRISPERT was designed to accept user inputs, adjust the values to CRISPERS requirements, start a sequence of simulations, and analyze and interpret the results. The rule-based system was implemented using the expert system development language OPS5 combined with FORTRAN, as well as SAS procedures and DEC VMS system service routines. Results of initial tests suggest that using an expert system as an interface between users and CRISPERS is a viable approach. The development of CRISPERT facilitates the usability of CRISPERS for intervention studies of coronary heart disease.

Computer Simulation↗
PubMed1990

LINKERS: a simulation programming system for generating populations with genetic structure.

Significant features are described of a Monte Carlo simulation system, LINKERS, that generates nuclear family data conforming to one locus and two loci genetic models. Software engineering techniques help to produce a user friendly environment for studies of genetic ascertainment. LINKERS' 39 code modules are maintained and optimized using VAXset. Within a VAX/VMS workstation environment LINKERS generates a useful population of 10,000 families in 1 min. An example is presented to illustrate the use of LINKERS. Generated data were analysed using the segregation program POINTER. Likelihood ratio tests showed the effects of multiple alleles, gene frequency and incorrect specification of disease prevalence.

Computer Simulation↗
PubMed1990

Cardiovascular effects of large doses of pentamorphone in the dog.

The cardiovascular effects of large doses of pentamorphone were evaluated in nine mongrel dogs basally anesthetized with sodium thiopental, 25 to 30 mg/kg, intravenously. All dogs were mechanically ventilated with 100% oxygen, and the PaCO2 was maintained between 35 and 40 mm Hg. Mean arterial pressure (MAP), central venous pressure, heart rate (HR), cardiac output (CO), pulmonary artery pressure, and pulmonary artery occluded pressure were measured, and stroke volume and systemic and pulmonary vascular resistances were calculated. Baseline measurements were obtained, then pentamorphone, 10 micrograms/mL, was given as an intravenous infusion at 2.5 micrograms/kg/min. Additional data were obtained after infusion of 25, 50, 75, 100, 125, 150, 200, 250, 300, and 350 micrograms/kg of pentamorphone. The inspired gases were then changed to 50% nitrous oxide in oxygen, and after a 20-minute equilibration period, an additional set of data was collected. Pentamorphone, 25 micrograms/kg, decreased HR 50%, MAP 65%, and CO 54%. No further changes in any measured or calculated variables were observed with additional doses of pentamorphone. The addition of 50% nitrous oxide to the inspired gas mixture had no effect on any measured or calculated hemodynamic variable. The minimal hemodynamic effects of pentamorphone in the dog suggest that further investigation into its use as an anesthetic is warranted.

Analysis of Variance↗
PubMed1990

Simulation of mechanisms of viral interference in influenza.

Biological interference among viral agents might have significant implications for disease prevention and therapy. Field data for influenza yield conflicting evidence concerning the independence of infection rates, or disease severity, for two co-circulating viruses. To examine the effects of several assumed modes of interference for influenza, simulations of a Monte Carlo micropopulation model of influenza epidemics have been performed. Model parameters were selected so that the simulated attack rates for each of two different viral strains matched actual field data. Rates of infection were compared for single agents and for two viruses with only behavioural interference. Other simulations included temporary immunity to the other virus for the duration of the infection, and/or reduced shedding of viral particles for dual infections. Simulated viral competition had little impact on epidemic severity, duration, or size distribution. Under the conditions studied, viral interference in natural populations would be difficult to infer from field observations of attack rates. Other simulations extended a partial immunity and/or reduced viral shedding during an infection with a second virus. These indicated that interference might be suggested by field data, but it could not be demonstrated conclusively. Still other simulations showed that for epidemics with much higher attack rates for both viruses, it would be relatively easy to demonstrate interference. However, in order to observe interference between influenza strains, it would be necessary to monitor on an almost daily basis, using a method of viral detection which would have to be both highly specific and also very sensitive.

Adolescent↗
PubMed1988

Latin hypercube sampling and the sensitivity analysis of a Monte Carlo epidemic model.

Discrete, algorithmic simulation and Monte Carlo methodologies are currently used in population biology, connectionist cognitive modeling, and physics. However, little is typically known about the sensitivity of such models to changes in the values of the model features. Traditional methods of sensitivity analysis for systems of differential equations do not apply. Sometimes, one or two parameters are modified at a time in an ad hoc fashion in an attempt to assess sensitivity. To include more model features and their interactions in a sensitivity study, while limiting computer utilization, various sampling methods have been suggested. In this article, a sensitivity study based on a Latin hypercube (LH) sampling design is compared with a similar study using a full factorial (FF), fixed-point sample. A discrete, Monte Carlo model of epidemics of influenzavirus infections in a human community is used for illustrative purposes. Although the FF scheme used over 14 times as many samples as the LH sampling one, both provided comparable predictive ability and comparable information about simulation sensitivity to model features.

Adolescent↗
PubMed1988

Order of response surfaces for representation of a Monte Carlo epidemic model.

Response hypersurfaces for two selected outcomes and for 6 model features were generated for Latin Hypercube (LH) samples of the parameter space of a discrete, micro-population, Monte Carlo model of an epidemic of an infectious disease agent. SAS stepwise, multivariate regression routines were used to generate response hypersurfaces of first, second and third order in the model features for each outcome. These are used as illustrative examples to examine the appropriateness of the order of the polynomial describing the response hypersurface. The response hypersurfaces are very dependent on the model outcomes and also on the selected ranges of the model features. Results indicate that there is little reason to prefer any particular order for the response hypersurfaces. Further, it is suggested that apparent interaction terms found when using quadratic and cubic response hypersurfaces may represent artifacts of the choice of a particular order for the response hypersurface. Nonetheless, the comparison of the 3 orders of response hypersurfaces can, under some circumstances, reveal basic characteristics of the sensitivity of the outcome to the model features.

Computer Simulation↗
PubMed1988

Measles: clinical and laboratory observations in young adults during an epidemic.

We describe the spectrum of clinical and laboratory findings in 130 young nonvaccinated adults who had measles during an epidemic, and give special emphasis to liver involvement. The data from these cases are compared to those of other selected groups of hospitalized young adults. Since measles seems to cause severe morbidity in adults, active measures should be taken to identify and vaccinate vulnerable nonimmunized individuals.

Acute Disease↗
PubMed1986

Contributions to the impedance cardiogram waveform.

We have developed a cylindrically symmetric model with which to study what physiologic variables might contribute to the impedance cardiogram signal. We find the major contributions in this model to be due to dilation of the aorta and carotid arteries, changes in conductivity of blood in these same vessels due to red cell reorientation during flow, changes in the conductivity of the lungs, and changes in heart volume. The calculations suggest that the popular equation used to determine stroke volume from thoracic impedance data is not accurate under all conditions of the circulatory system.

Adult↗
PubMed1986

Effects of sampling location on data sensitivity in a three compartment model.

A computer simulation of a three compartment model was developed to examine the effect of sampling location on the accuracy of estimates of system parameters. Results indicate that the best estimates are obtained when all three compartments are sampled. Sampling from only one compartment tends to result in the poorest estimates.

Biometry↗
PubMed1984

Simulation studies of influenza epidemics: assessment of parameter estimation and sensitivity.

The influenza simulation model of Elveback et al is used to evaluate the accuracy of the maximum likelihood procedure of Longini et al for estimating the secondary attack rate in households. The sample population from the Tecumseh Respiratory Illness Study is mapped into the simulation model and simulations are carried out over a range of parameter values and conditions, some of which were derived from influenza seasons in Tecumseh and from the Seattle Flu Study for the years 1975-1980. The estimation procedure is found to be quite robust for parameter values preset within appropriate limits for influenza. However, a significant difference is found between the preset and estimated household contact parameter for epidemics of medium and high intensity when the preset value is zero. Incremental increases in the household contact parameter are shown to produce marked increases in the overall infection attack rate demonstrating that household spread is an important link in maintaining infection in other mixing groups such as schools, preschool groups and neighbourhood clusters of households.

Adolescent↗
PubMed1983

The activation of RNA synthesis by somatic nuclei injected into amphibian oocytes.

Previous work has shown that nuclei of cultured cells or erythrocytes are transcriptionally activated when injected into the germinal vesicle of Xenopus oocytes. We now find that the total amount of stable RNA synthesized by an oocyte with injected nuclei is about twice that of an uninjected oocyte (approximately 15 ng/day). At least half of the RNA transcribed by the injected nuclei is low-molecular-weight RNA of discrete sizes, and is transcribed by RNA polymerase III. Part of this is attributable to a new class of gene (referred to as OAX) which makes a transcript about 180 nucleotides long, and which is activated by at least 50-fold in somatic nuclei injected into oocytes. OAX RNA is not a degradation or processing variant of ribosomal or 5 S RNA, and is not coded by mitochondrial DNA. It enters oocyte cytoplasm, but turns over with a half-life of less than 3 hr, as judged by the culture of enucleate oocyte cytoplasms for several days during which 4 and 5 S RNAs are stable. OAX RNA synthesis is not detected by labelling cultured cells or their nuclei. The results emphasize the selectivity with which components of an oocyte germinal vesicle activate genes in injected somatic nuclei.

Animals↗
PubMed1982

Cornea plana: a case report.

A case of cornea plana with its typical clinical findings has been presented along with ultrasonographic documentation confirming the axial length of the globe to be normal in this condition. It is presented to draw attention to the clinician that although cornea plana is rare, it should be considered in the differential diagnosis of a patient with small eyes or suspected microcornea.

Aged↗