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Biomedical subjects

K Dunn

Publications and source records attributed to K Dunn.

At least 37 records · Page 2Linked to original sources
PubMed1999

Mechanisms of Surface Precipitation and Dissolution of Barite: A Morphology Approach.

Barite (BaSO4) was synthesized at normal pressure and room temperature by mixing sodium sulfate and barium chloride solutions by gentle flow (0.5 ml/min.). The well-formed rectangular and rhombohedral crystals with smooth faces formed from solutions with low degrees of supersaturation. Most precipitates became single crystals. We employed the scanning electron microscope (SEM) to observe barite dissolution by chemical agent diethylenetrinitrilopentaacetic acid. Molecular modeling was used to assist the interpretation of the surface reaction. A kinetic model for the pit growth (initial dissolution) on the surface was evaluated. With SEM microanalysis of barite and kinetic model of pit growth, important surface phenomena and mechanisms of dissolution can be hypothesized. Surface phenomena and composition are very important in barite dissolution. Experimental results suggest that the initial dissolution starts on the two lowest energy surfaces: (001) and (210), and that the etch pits are elongated in one direction on the (210) surface and formed cavities on the (001) surface. The simulated surface structures by molecular modeling can aid the interpretation the pit formation on those selected surfaces. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Identifying genes predisposing to atopic eczema.

BACKGROUND: Genetic and environmental factors are known to play a role in the development of atopic diseases, such as asthma, eczema, and rhinitis. However, the atopy gene (or genes) has yet to be defined. Studies of familial asthma have identified several regions that may contain genes predisposing to atopy, but the data for candidate regions do not show agreement, which may be due to heterogeneity, ascertainment bias, or stochastic factors. Factors such as an early age of onset, a positive family history, and a clearly defined phenotype favor a genetic origin and improve the chance of identifying genes that predispose to atopy. OBJECTIVE: We sought to define genes that predispose to the development of atopic eczema. METHODS: We have studied nuclear families with multiple cases of early-onset atopic eczema for involvement of the candidate regions on chromosomes 5q31 (IL gene cluster), 11q13 (high-affinity FCepsilon receptor), 14q11.2 (mast cell chymase), and 16p12 (IL-4 receptor alpha-chain, IL4RA gene). RESULTS: Using a recessive model, we find a maximum parametric log of the odds of linkage score of 2. 25 and nonparametric score of 2.54 (P =.006) for a region on chromosome 5q31, which we postulate contains a gene predisposing to atopic eczema, but lack of support for linkage to 11q13. Transmission disequilibrium tests do not support an association with candidate polymorphisms in the mast cell chymase and IL4RA genes. CONCLUSION: We have identified a clinically homogeneous cohort of patients with atopic eczema to identify genetic factors predisposing to the development of atopy. We postulate that there are certain loci that predispose to atopy in general and other loci that determine which of the atopic phenotypes is expressed.

Adolescent↗
PubMed1999

Determinants of HIV-related survival among Texas prison inmates.

Research indicates that being incarcerated adversely affects disease progression and overall health status. Because HIV infection is a growing problem among prison populations in the United States, understanding how incarceration affects HIV-related survival patterns is critical. The present study examined determinants of HIV-related survival in a cohort of 2380 Texas Department of Criminal Justice (TDCJ) inmates who were treated for HIV/AIDS, dating from January 1, 1992 and June 31, 1997. Assessment of the study factors indicated that there were no substantial violations of the assumptions of the Cox's proportional hazards (PH) model in the present study population. Furthermore, to address the potential problem of censoring-related bias, mortality information was collected on all inmates who were paroled on the basis of disease status. The present study's findings indicate that the following factors were associated with significant decreases in HIV-related survival in the TDCJ prison population: male gender, older age, self-report of no known HIV transmission risk factors, and presence of cytomegalovirus (CMV), Mycobacterium avium complex (MAC), and Pneumocystis carinii pneumonia. Moreover, survival decreased in a monotonic fashion with decrease in baseline CD4 count. While the majority of the present study's findings were consistent with those reported for non-incarcerated populations, it will be important for investigators to assess whether these findings persist among future cohorts of prison inmates.

Acquired Immunodeficiency Syndrome↗
PubMed1999

Emergency medicine resident research requirements and director characteristics.

OBJECTIVES: To describe emergency medicine (EM) residency program research requirements, characterize research directors (RDs), and describe their research activities and productivity. METHODS: A survey with questions addressing program research requirements, RDs' background, type of research productivity, time spent, and compensation was mailed to RDs at all Accreditation Council for Graduate Medical Education (ACGME)-approved programs. RESULTS: One hundred of 111 (90%) RDs responded; 54 of the 100 respondents were from university programs. Research is a formal requirement in 80% of EM programs. Writing a manuscript (35%) and major involvement in a project (31%) are the most common minimum requirements. University and community programs had similar research requirements and were equally likely to have delayed/withheld certificates. Eighty-six percent of the RDs were male; 70% held this position for <5 years and 70% plan on being in the position for <5 additional years. More than half were junior faculty and 21 had completed a fellowship. Most (88%) did not serve in an associate RD position, and currently only 20 programs reported having this position. Fifty-four percent had protected time. Median hour/week time allocations are: clinical-22, own research--10, other people's research--6, administration--5, and department administration--5. Factors associated with research productivity were senior rank (OR 6.87), having a research assistant (OR 4.78), protected time for their own research (OR 3.06), and reporting that extramural funding was considered in the RD's performance evaluation (OR 2.69). CONCLUSIONS: Most programs have established research requirements. Most RDs are junior faculty, have limited research training, expect a short tenure in the position, and have variable access to research resources. EM needs to foster an environment that will enable us to thrive in the academic community and create opportunity for residents to participate in meaningful research. This requires that all RDs have protected time, and that a greater proportion be at the associate or full professor level, have qualified research assistants, and receive periodic evaluation reviewing their ability to generate external funds. Appointment of associate RDs may improve research training and help ensure qualified RDs.

Adult↗
PubMed1999

Intestinal permeability and diarrhoeal disease in Aboriginal Australians.

BACKGROUND: Northern Territory Aboriginal children hospitalised with acute gastroenteritis have high rates of acidosis, hypokalaemia, and dehydration. AIMS: To determine whether Aboriginal children with and without diarrhoea have greater impairment in intestinal function than non-Aboriginal children, as assessed by increased permeability ratios. METHODS: A descriptive study of 124 children (96 Aboriginal and 28 non-Aboriginal) hospitalised with and without diarrhoea. Intestinal permeability was assessed by the lactulose to rhamnose (L-R) ratio from a five hour urine collection. RESULTS: In Aboriginal children, mean L-R ratios (95% confidence intervals) were 18.3 (17.1 to 19.6) with diarrhoea and 9.0 (7.3 to 11.0) without diarrhoea, and in non-Aboriginal children they were 5.9 (2.8 to 12. 3) and 4.2 (3.3 to 5.2), respectively. In patients with diarrhoea, L-R ratios were significantly raised when accompanied by acidosis (mean, 22.8; 95% CI, 17.0 to 30.5), hypokalaemia (mean, 20.7; 95% CI, 15.4 to 27.9), and >/= 5% dehydration (mean, 24.3; 95% CI, 19.0 to 29.6) compared with none of these complications (mean, 7.0; 95% CI, 3.5 to 13.8). CONCLUSION: The high incidence of acidosis, hypokalaemia, and dehydration in Aboriginal children admitted with diarrhoeal disease is related to underlying small intestinal mucosal damage.

Acidosis↗
PubMed1999

Determinants of survival in HIV-positive patients.

Variation in the clinical stage at which AIDS is diagnosed has hindered the ability of investigators to generate survival estimates which are stable across study cohorts. As a result, little is known about how clinical and sociodemographic factors are associated with survival, independent of AIDS diagnosis stage. By estimating survival following seroconversion while adjusting for baseline CD4 lymphocyte count, the present study generated survival determinants which were unconfounded by time-related changes in AIDS diagnosis. This study's findings indicate that the following factors were associated with significant decreases in HIV-related survival: older age; self-report of no known HIV transmission risk factors; and presence of cytomegalovirus, Mycobacterium avium complex, and Pneumocystis carinii pneumonia. Furthermore, survival decreased in a monotonic fashion with decreases in baseline CD4 count and with increases in calendar period. While this study's findings are consistent with previous investigators' reports of AIDS survival determinants, it will be important for future investigators to refine and update estimates of HIV-related survival determinants as clinical care for HIV-infected patients continues to improve.

Adult↗
PubMed1999

Evidence-based pressure-ulcer practice: the Ottawa model of research use.

Developing evidence-based nursing practice among diverse health-care settings is a particular challenge in the face of current health-care restructuring. This paper describes application of the Ottawa Model of Research Use (OMRU) to increase evidence-based practice across 3 health-care settings during a time of multiple restructuring changes. The initiative was part of a provincial demonstration project to develop centers of nursing excellence with a view to improving continuity of care across the health continuum. Three Ottawa health-care agencies formed one of 4 participating sites in the Province-Wide Nursing Project (PWNP), a 3-year initiative funded by the Ontario Ministry of Health. The goal of the Ottawa-Carleton site was to increase evidence-based decision-making with a focus on pressure ulcers. The barriers and supports encountered, and the strategies used, in striving to meet this goal in a community-care, tertiary-care, and long-term-care setting are described. Multiple research transfer approaches were used, with an emphasis on education. Implementor consensus and achievements of the project support the OMRU's utility as a guide to implementing research findings in these health-care settings.

Clinical Nursing Research↗
PubMed1998

Decreased dendritic branching in frontal, motor and limbic cortex in Rett syndrome compared with trisomy 21.

The branching of dendrites of pyramidal neurons in premotor frontal, motor and limbic cortex have been identified by us using Golgi technique to be less in Rett Syndrome (RS) brains than in non-Rett control brains. Decreased dendritic branching per se is not pathognomonic of a particular condition and has been reported in numerous disorders associated with mental retardation. This study was designed to test whether the dendritic alterations in Rett Syndrome are the same or different from the alterations present in Down Syndrome (DS), 1 specific form of mental retardation. Sections from Brodmann's areas 6, 4, 20, 43, 28, and 17 of premotor frontal, motor cortex, inferior temporal gyrus, hippocampal formation and the striate cortex from 16 Rett brains, 9 non-Rett brains and 9 Down's brains were prepared for dendrite analysis using the rapid Golgi technique. Drawings of apical and basilar dendrites of pyramidal neurons from 2 cortical layers and Cal were submitted to Sholl analysis. The analyses of Rett brains were compared with the analyses of the Trisomy 21 brains using the repeated measures analysis of covariance, with age as a covariate. The studies demonstrate in our sample that basal dendrites of layer III and V of frontal, layer IV of subiculum, and layer V of motor cortex and apical dendrites of layer III of frontal cortex have a significantly reduced dendritic arborization in RS compared with Trisomy 21. This study suggests that the cortical distribution of the dendritic alterations is specific for Rett Syndrome, and that the premotor frontal, motor and subicular cortex are preferentially involved in the, as yet, undefined process which affects brain growth and function in RS.

Adolescent↗
PubMed1998

Early events in phagosome establishment are required for intracellular survival of Legionella pneumophila.

During infection, the Legionnaires' disease bacterium, Legionella pneumophila, survives and multiplies within a specialized phagosome that is near neutral pH and does not fuse with host lysosomes. In order to understand the molecular basis of this organism's ability to control its intracellular fate, we have isolated and characterized a group of transposon-generated mutants which were unable to kill macrophages and were subsequently found to be defective in intracellular multiplication. These mutations define a set of 20 genes (19 icm [for intracellular multiplication] genes and dotA [for defect in organelle trafficking]). In this report, we describe a quantitative assay for phagosome-lysosome fusion (PLF) and its use to measure the levels of PLF in cells that have been infected with either wild-type L. pneumophila or one of several mutants defective in different icm genes or dotA. By using quantitative confocal fluorescence microscopy, PLF could be scored on a per-bacterium basis by determining the extent to which fluorescein-labeled L. pneumophila colocalized with host lysosomes prelabeled with rhodamine-dextran. Remarkably, mutations in the six genes that were studied resulted in maximal levels of PLF as quickly as 30 min following infection. These results indicate that several, and possibly all, of the icm and dotA gene products act at an early step during phagosome establishment to determine whether L. pneumophila-containing phagosomes will fuse with lysosomes. Although not ruled out, subsequent activity of these gene products may not be necessary for successful intracellular replication.

HL-60 Cells↗
PubMed1998

Ratio imaging instrumentation.

Using ratio imaging to obtain quantitative information from microscope images is a powerful tool that has been used successfully in numerous studies. While ratio imaging reduces the effects of many parameters that can interfere with accurate measurements, it is not a panacea. In designing a ratio-imaging experiment all of the potential problems discussed in this chapter must be considered. Undoubtedly, other problems that were not discussed can also interfere with accurate and meaningful measurements. Many of the problems discussed here were observed in the authors' laboratories. In our experience there are no standard routines or methods that can foresee every problem before it has been encountered. Good experimental design can minimize problems, but the investigator must continue to be alert. Progress in instrumentation continues to overcome some of the difficulties encountered in ratio imaging. CCD cameras with 12- to 14-bit pixel depth are being used more frequently, and several confocal microscope manufacturers are now also using 12-bit digitization. The dramatic increase in the use of confocal microscopes over the past decade is now causing microscope manufacturers to more critically evaluate the effect of axial chromatic aberration in objectives, and recent designs to minimize this problem are being implemented. Other developments such as the use of AOTFs to attenuate laser lines extend the applicability of ratio imaging. Ratio imaging is clearly applicable to a wide range of cell biological problems beyond its widespread use for measuring ion concentrations. Imaginative but careful use of this technique should continue to provide novel insights into the properties of cells.

Animals↗
PubMed1998

Optical methods in renal research.

Light microscopy is a powerful experimental approach that allows the researcher to study the dynamics of cellular responses and subcellular organization. Recent advances in optics, detectors, computerized image processing, and the development of vital dyes promise to extend the utility of light microscopy. Quantitative approaches measuring intracellular pH, sodium or calcium are well known, but future developments may permit quantitative analysis of immunolabeled specimens. This review will describe the basic features of light microscopes and imaging techniques. Specific types of microscopy such as confocal microscopy, wide field microscopes, and epifluorescence microscopy will be considered. In addition, recent advances in cellular labeling techniques will be described. Post production image processing techniques and computerized deconvolution methods will be discussed, and lastly future developments in optics, improved sensitivity in detectors with enhanced signal-to-noise ratios will be explored. Wherever possible, specific applications that have been applied to renal physiology studies will be cited.

Histocytochemistry↗
PubMed1997

Evolutionary diversity of symbiotically induced nodule MADS box genes: characterization of nmhC5, a member of a novel subfamily.

Unique organs called nodules form on legume roots in response to intracellular infection by soil bacteria in the genus Rhizobium. This study describes a new MADS box gene, nmhC5, which along with nmh7 (J. Heard and K. Dunn, Proc. Natl. Acad. Sci. USA 92:5273-5277, 1995), is expressed in alfalfa (Medicago sativa) root nodules. Together, these genes represent the first putative transcription factors identified in nodules. Expression in a root-derived structure supports the growing sentiment that MADS box proteins have diverse roles in plant development. Comparison of the putative translation product of nmhC5 with those of other reported members of the MADS box family suggests that the overall structure of nmhC5 is conserved. Evolutionary analysis among the MADS box family showed that nmhC5 is orthologous to a root-expressed clone in Arabidopsis thaliana, agl17, and that nmh7 is similar to the floral subfamily with AP3 (DefA)/PI (Glo). Consistent with a prediction of homodimer formation, NMHC5 was shown to bind a CArG consensus sequence in vitro. In contrast, NMH7, which shows structural similarity to MADS box proteins that form heterodimers, did not bind the CArG element in an in vitro DNA-binding assay, suggesting the existence of an unknown dimer partner. The root-derived MADS box genes constitute a novel subfamily of vegetatively expressed MADS box genes. The evolutionary diversity between nmh7 and nmhC5 could represent an overall mechanistic conservation between plant developmental processes or could mean that nmh7 and nmhC5 make fundamentally different contributions to the development of the nodule.

Amino Acid Sequence↗
PubMed1997

Extreme sodium derangement in a paediatric inpatient population.

OBJECTIVE: To determine the aetiology, symptoms and outcome of extreme sodium derangement in a paediatric inpatient population. METHODOLOGY: A retrospective study of children with extreme disturbance of their plasma sodium (> or = 165 mmol/L or < or = 115 mmol/L) admitted to a tertiary referral centre during a 72-month period. RESULTS: Twenty-seven cases of hypernatraemia and 21 of hyponatraemia were reviewed. Sodium disturbance developed after hospital admission in 27/57 cases (57%). Gastroenteritis was the most common cause of hypernatraemia (8/27; 30%), four of 27 (15%) had iatrogenic hypernatraemia. Water overload accounted for 8/21 (38%) cases of hyponatraemia. Neurologic symptoms occurred in 19/24 (79%) with hypernatraemia and in 11/19 (58%) with hyponatraemia. Ten (37%) with hypernatraemia and four (19%) with hyponatraemia died. A deterioration in functional status was seen in two patients with hypernatraemia. There was no apparent deterioration in the survivors with hyponatraemia. CONCLUSION: Extreme sodium disturbance often develops after admission to hospital and is caused by a variety of diseases and interventions. Neurologic symptoms are common and the mortality rate is high. The outcome in survivors is survivors is most likely to be dependent on the underlying disease process.

Child↗
PubMed1996

Levels of soluble cell adhesion molecules in patients with dyslipidemia.

BACKGROUND: Increased expression of cell adhesion molecules (CAMs) on the vascular endothelium has been postulated to play an important role in atherogenesis. Both in vitro and in vivo studies have suggested that dyslipidemia may increase expression of CAMs. METHODS AND RESULTS: To determine whether dyslipidemia is associated with increased expression of CAMs, we examined the levels of soluble intercellular adhesion molecule 1 (sICAM-1), soluble vascular cell adhesion molecule 1 (sVCAM-1), and soluble E-selectin (sE-selectin) in individuals with either hypercholesterolemia or hypertriglyceridemia and in control subjects matched for age and sex. Patients with hypertriglyceridemia had significantly higher levels of sVCAM-1 (739 +/- 69 ng/mL) compared with patients with hypercholesterolemia (552 +/- 63 ng/mL) and control subjects (480 +/- 56 ng/mL). Levels of sICAM-1 were significantly increased in both the hypercholesterolemic and hypertriglyceridemic groups (298 +/- 29 and 342 +/- 31 ng/mL, respectively) compared with the control group (198 +/- 14 ng/mL). Levels of sE-selectin were significantly increased in hypercholesterolemic patients (74 +/- 9 ng/mL) compared with control subjects (48 +/- 5 ng/mL). Ten hypercholesterolemic patients were treated aggressively with atorvastatin alone or a combination of colestipol and either atorvastatin or simvastatin for a mean of 42 weeks and had an average LDL cholesterol reduction of 51%. Comparison of soluble CAMs before and after treatment showed a significant reduction only in sE-selectin (77 +/- 11 versus 56 +/- 6 ng/mL, P < or = .03) but not for sVCAM-1 or sICAM-1. CONCLUSIONS: Although severe hyperlipidemia is associated with increased levels of soluble CAMs, aggressive lipid-lowering treatment had only limited effects on the levels. Increased levels of soluble CAMs in patients with hyperlipidemia may be a marker for atherosclerosis.

Anticholesteremic Agents↗
PubMed1996

Vinylpyridine: an unusual cause of a chemical burn.

A case of a chemical burn following cutaneous exposure to vinylpyridine is presented. This unusual injury was distinguished by the delay in onset of pain and erythema, followed by gradual resolution leaving patchy skin discolouration. The properties of vinylpyridine are outlined. This case illustrates the dangers of long-term chemical storage and the importance of proper disposal.

Adult↗