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Biomedical subjects

D G Nelson

Publications and source records attributed to D G Nelson.

At least 19 recordsLinked to original sources
PubMed1998

Evaluation of febrile children with petechial rashes: is there consensus among pediatricians?

BACKGROUND: The evaluation of febrile children with petechial rashes evokes controversy. Although many of these children have viral infections, on occasion such patients may be infected with Neisseria meningitidis. OBJECTIVE: To investigate differences in practice trends for the evaluation and management of non-toxic-appearing febrile children with petechial rashes among pediatric specialty groups. METHODS: We surveyed 833 pediatricians in 4 specialties [community (CGP) and academic (AGP) general pediatrics, emergency medicine (EM) and infectious diseases] regarding 4 hypothetical non-toxic-appearing febrile children ages 1, 2, 5 and 7 years. The patients differed with regard to clinical appearance, distribution of petechiae and complete blood count results. We compared specialty group responses, adjusting for practice setting, population size and years in practice using multiple logistic regression analysis. RESULTS: The survey was completed and returned by 416 (50%) pediatricians. There was substantial variation in the evaluation of the 2 younger febrile children without clear sources for their petechiae. For the 1-year-old the overall blood culture (BCx) rate was 82%, with the EM group (91%) more often requesting BCx than either the CGP (76%) or AGP (73%, P=0.001) groups. The overall hospital admission rate was 31%, with CGP less often requesting admission than infectious disease pediatricians (22% vs. 40%, P=0.007). In the regression analysis the only significant difference between groups was in BCx rate between the EM and AGP groups. For the 2-year-old the overall rate of BCx was 95%, lumbar puncture was 41% and admission was 44%, with no significant differences among groups. For the scenarios involving the 2 older febrile children with sources for their petechiae, the majority of respondents chose neither lumbar puncture nor admission. There was disagreement regarding BCx, both within and between groups, although most of the between group differences did not persist in the regression analysis. CONCLUSIONS: There are substantial differences among pediatricians in the evaluation of young non-toxic-appearing febrile children with petechial rashes. Although there are some differences between pediatric subspecialties, most of these differences do not persist after adjusting for practice setting, population size and physician experience.

Adult↗
PubMed1997

Effects of triclosan and triclosan monophosphate on maximum specific growth rates, biomass and hydrolytic enzyme production of Streptococcus sanguis and Capnocytophaga gingivalis in continuous culture.

Dental plaque species, Streptococcus sanguis and Capnocytophaga gingivalis, were grown in continuous culture with progressively increasing concentrations of triclosan or its phosphorylated derivative, triclosan monophosphate (TMP). For both organisms, the maximum specific growth rates decreased with increasing concentrations of triclosan or TMP until complete inhibition of growth occurred, which for S. sanguis was at 20 mg/L and 50 mg/L, and for C. gingivalis was at 10 mg/L and 5 mg/L for triclosan and TMP respectively. For both species, biomass levels remained approximately constant or, in some cases, increased slightly at low levels of triclosan or TMP. However, biomass levels then decreased significantly as the triclosan or TMP concentrations approached lethal levels. For S. sanguis, levels of hydrolytic enzymes (acid phosphatase, leucine aminopeptidase and esterase) generally remained approximately constant or increased with increasing concentrations of triclosan or TMP until close to inhibitory levels where enzyme levels were reduced. The ratio of extracellular soluble enzymes to cell-bound enzymes remained constant or increased slightly with increasing levels of triclosan or TMP. For C. gingivalis, production of hydrolytic enzymes (neutral phosphatase, leucine aminopeptidase and trypsin-like protease) remained constant or were reduced when grown with low levels of triclosan and TMP but in some cases increased with higher levels of agents. The proportion of extracellular soluble activity increased significantly when concentrations of agent neared inhibitory levels. The results taken together show that the physiology of cells is significantly altered and that hydrolytic enzymes are released from the cells when these are grown in the presence of increasing concentrations of triclosan or TMP. Enzyme release is more pronounced in the Gram-negative C. gingivalis and indicates that triclosan or TMP can cause membrane perturbation with subsequent release of membrane-located (S. sanguis) or periplasmic (C. gingivalis) hydrolytic enzymes. S. sanguis was more sensitive to triclosan than TMP while C. gingivalis was more sensitive to TMP. This suggests that, in C. gingivalis, TMP may diffuse into the cell wall more easily than triclosan and then be converted to triclosan by phosphatase activity within the cell wall complex, where it may give rise to high localized concentrations and subsequent cell damage.

Acid Phosphatase↗
PubMed1997

Lymphoma of the extrahepatic biliary ducts in acquired immunodeficiency syndrome.

Gastrointestinal neoplasia in acquired immunodeficiency syndrome (AIDS) frequently presents as a non-Hodgkin's lymphoma or Kaposi's sarcoma, at sites including the oral cavity, esophagus, small bowel, and mesenteries. Primary lymphoma of the biliary ducts, even in the setting of AIDS, is rare. This patient, an older male with no preoperatively known AIDS risk factors, presented with painless jaundice and radiographic findings of focal hepatic duct stenosis, suggesting either a Klatskin tumor or sclerosing cholangitis. Only after the pathologic diagnosis of a malignant large cell lymphoma from the en bloc tumor specimen was his human immunodeficiency virus status ascertained and noted to be positive.

Aged↗
PubMed1996

Fluoride analysis of apatite crystals with a central planar OCP inclusion: concerning the role of F- ions on apatite/OCP/apatite structure formation.

To study the roles of F- ions in the formation of apatite crystals embedding octacalcium phosphate (OCP) lamella in the center of apatite (Ap), a range of the Ap/OCP/Ap lamellar-mixed crystals were synthesized under various concentrations of fluoride ion (F-) from 0. 1-1.0 ppm at pH 6.5 and 37 degrees C. The products were analyzed for the F- incorporation, F- distribution, and the amount of OCP and Ap by chemical analysis, X-ray diffraction (XRD), electron probe microanalysis (EPMA), and nuclear magnetic resonance (NMR) techniques. The F- content and the amount of apatite in the crystalline product increased with an increase in the F- concentration in solution, whereas the amount of OCP and the yield of total product decreased. EPMA indicated that F- ions are distributed in the crystals almost homogeneously. The combined analysis suggested that a low-substituted fluoridated hydroxyapatite (FHAp) grew on a small amount of F--containing OCP or on a surface-reaction layer of OCP, which has accumulated a small amount of F-. The roles of F- ions were hypothesized as the reduction of the growth rate and/or the critical thickness in the a*-axis direction of OCP, the enhancement of hydrolysis of OCP, and the activation of the growth of FHAp, resulting in thinner OCP lamella and thicker apatite lamella in the a*-axis direction with an increase in F- concentration.

Apatites↗
PubMed1996

Hydrolysis of triclosan monophosphate by dental plaque and selected species of oral micro-organisms.

Triclosan monophosphate is a phosphorylated derivative of the antimicrobial agent, triclosan. In comparison with triclosan, it is highly soluble in aqueous solutions. It is hypothesized that, within the oral environment, triclosan monophosphate (which may be devoid of antimicrobial activity) will be hydrolyzed into triclosan by the action of microbial phosphatases. The liberated triclosan may then exert antimicrobial activity. To test this hypothesis, we designed experiments to measure the phosphatase activity of plaque and selected species of oral micro-organisms and to demonstrate hydrolysis of triclosan monophosphate. Tests comparing the minimal inhibitory concentration and minimal bactericidal concentration of triclosan and triclosan monophosphate were also undertaken. Dental plaque and the majority of the bacterial strains tested showed phosphatase activity against p-nitrophenyl phosphate which peaked below neutral pH (acid phosphatases) or above neutral pH (alkaline phosphatases). Dental plaque showed the highest levels of alkaline phosphatase (optimum at pH 9.0) and relatively high levels of acid phosphatase (optimum at pH 6.0 to 6.5). Dental plaque and selected species of micro-organisms were all capable of hydrolyzing triclosan monophosphate, albeit at different rates. The minimal inhibitory concentration and minimal bactericidal concentration values for triclosan monophosphate against eight bacterial strains were always considerably higher than the corresponding values for triclosan. Addition of triclosan monophosphate to an established culture (ca. 10(9) cfu/mL) of Capnocytophaga gingivalis growing continuously showed that triclosan monophosphate was rapidly hydrolyzed into triclosan with concomitant loss of total bacterial viability. It is therefore likely that triclosan monophosphate will be broken down into triclosan within the oral environment with concomitant antimicrobial activity.

Anti-Infective Agents, Local↗
PubMed1994

What child is this? What interval was that? Familiar tunes and music perception in novice listeners.

In the laboratory, musical novices often seem insensitive even to basic structural elements of music (octaves, intervals, etc.), undermining long-held theories of music perception, and threatening to leave current theories applicable only to experts. Consequently it is important to demonstrate novices' basic listening competence where possible. Two experiments examined the perception of musical intervals (minor thirds, major thirds and perfect fourths) by musical novices. Subjects received either standard instructions or familiar folk-tune labels to aid performance. The folk-tune labels greatly improved identification performance, producing expert-caliber performance by some musically inexperienced subjects. The effectiveness of the folk-tune manipulation was much more limited in a difficult discrimination task. The results suggest that novices do have some basic competence when assayed appropriately, and that familiar musical tokens may be a critical element in such assays. Larger implications of the role of familiarity in novices' competence are discussed, including those that relate to music cognition and aesthetics.

Adolescent↗
PubMed1994

Does sentential prosody help infants organize and remember speech information?

Theories that propose a mapping between prosodic and syntactic structures require that prosodic units in fluent speech be perceptually salient for infants. Although previous studies have demonstrated that infants are sensitive to prosodic markers of syntactic units, they do not show that prosodic information really has an impact on how infants encode the speech they hear. Two experiments were conducted to examine whether infants as young as 2 months old might actually use the prosody afforded by sentences to organize and remember spoken information. The results suggest that infants better remember the phonetic properties of (1) words that are prosodically linked together within a single clause as opposed to individual items in a list (Experiment 1); and (2) words that are prosodically linked within a single clausal unit as opposed to spanning two contiguous fragments (Experiment 2). Taken together, the evidence from both experiments suggests that the prosodic organization of speech into clausal units enhances infants' memory for spoken information. These findings are discussed with regard to their implications for theories of language acquisition.

Female↗
PubMed1994

Mode of action of fluoride: application of new techniques and test methods to the examination of the mechanism of action of topical fluoride.

Modern techniques in dental research continue to assist in the study of the mode of (anticaries) action of topical fluorides. The Plaque Glycolysis and Regrowth Model (PGRM) facilitates the standardized assessments of antimicrobial effects on plaque following use of test formulations in vivo without complications arising from coincident mineral reactivity. In vivo plaque glycolysis testing demonstrates that topically applied fluoride, at conventional levels found in dentifrices, has only modest effects on the metabolic (acid-producing) activity of dental plaque. Any 'plaque' contribution to fluoride efficacy must come from more subtle effects on plaque acidogenicity than those measured in PGRM. The 19-FMAS NMR (Magic Angle Spinning Nuclear Magnetic Resonance) technique provides unambiguous measures of the reaction products of F-enamel interactions. Studies have revealed a new 'reaction product' of fluoride-enamel interactions--designated as Non-Specifically-Adsorbed Fluoride, NSAF. This species, along with FAP (fluoroapatite), FHAP (fluorohydroxyapatite), and CaF2 (calcium fluoride), contributes to the remineralization/demineralization benefits of fluoride. pH cycling and in situ denture chip studies permit quantitative assessments to be made of the relative benefits of fluoride in promoting remineralization and in inhibiting demineralization. Results from pH cycling/in situ experiments are strongly supportive of Koulourides' 'Acquired Acid Resistance' concept, describing fluoride's decay-preventive effects. The continued application of new analytical/physical techniques and testing regimens to the study of fluoride anticaries mechanisms may lead to the development of improved fluoride agents/treatment modalities for the prevention of dental caries.

Analysis of Variance↗
PubMed1993

Processing integral dimensions: the whole view.

In the traditional view, integral dimensions are said to be processed as unitary whole and only occasionally analyzed. Converging operations establish that (a) pitch and loudness and (b) hue, saturation, and brightness are true psychological dimensions and yet constitute integral dimensions in just this sense. Recent challenges provided by R. D. Melara, L. E. Marks, and their colleagues are shown to be based on narrow and faulty interpretations of evidence for privileged axes. They are also undermined by strong evidence of the holistic processing of pitch and loudness and of the dimensions of color that emerge within both their own data and the larger literature. The traditional view--including the strong claim that integrality entails mandatory holistic processing--continues to fare very well as an account of a substantial and varied set of findings.

Attention↗
PubMed1992

Perception of acoustic correlates of major phrasal units by young infants.

How might young learners parse speech into linguistically relevant units? Sensitivity to prosodic markers of these segments is one possibility. Seven experiments examined infants' sensitivity to acoustic correlates of phrasal units in English. The results suggest that: (a) 9 month olds, but not 6 month olds, are attuned to cues that differentially mark speech that is artificially segmented at linguistically COINCIDENT as opposed to NONCOINCIDENT boundaries (Experiments 1 and 2); (b) the pattern holds across both subject phrases and predicate phrases and across samples of both Child- and Adult-directed speech (Experiments 3, 4, and 7); and (c) both 9 month olds and adults show the sensitivity even when most phonetic information is removed by low-pass filtering (Experiments 5 and (6). Acoustic analyses suggest that pitch changes and in some cases durational changes are potential cues that infants might be using to make their discriminations. These findings are discussed with respect to their implications for theories of language acquisition.

Attention↗
PubMed1992

Crystallographic changes in calcium phosphates during plasma-spraying.

Coating hydroxyapatite (HA) onto metal implant surfaces using the plasma-spraying technique has been investigated in several laboratories as a means of improving the mechanical properties of the bulk ceramic. This study describes crystallographic changes which can occur during the plasma-spraying of calcium phosphate powders. A precipitated calcium-deficient apatite and a high temperature near-stoichiometric HA were each sprayed onto metal substrate in an argon plasma using several hydrogen gas flow conditions at various temperatures. The surfaces were examined by X-ray diffraction and scanning electron microscopy. The plasma-sprayed products were identified as a mixture of calcium phosphates including HA, beta-tricalcium phosphate (beta-TCP) and calcium oxide. Stoichiometric HA when plasma-sprayed showed the least (5%) degradation. Since beta-TCP is more resorbable than HA in vivo, varying the HA/beta-TCP ratio on the plasma-sprayed surface may provide a method to control surface dissolution of the coating.

Biocompatible Materials↗
PubMed1992

High resolution fluoride profiles of artificial in vitro lesions treated with fluoride dentifrices and mouthrinses during pH cycling conditions.

A pH cycling model which incorporated a severe demineralization component was used to evaluate fluoride uptake and lesion progression for each of a NaF-based dentifrice, NaF-based mouthrinse and a monofluorophosphate (MFP)-based dentifrice. Simultaneous transverse fluoride and calcium profiles across the resulting artificial lesions were obtained using a proton microprobe technique with a resolution of approximately 10 microns. Longitudinal microhardness testing and proton microprobe calcium profiles were used to determine the extent of lesion progression (delta Z) with respect to untreated controls. Under the pH cycling conditions of the present study, the NaF dentifrice and mouthwash were observed to have a considerably higher uptake of fluoride in the lesion than the MFP dentifrice. Although the mineral content profiles of the lesions differed for treatments with each of the fluoride products, the differences were not significantly different in this model.

Calcium↗
PubMed1990

Backscattered electron imaging of partially-demineralized enamel.

Backscattered electron (BE) microscopy is being used increasingly as a technique to study the dissolution of dental enamel because of its high resolution and relatively easy sample preparation. Subsurface details such as striae of Retzius, cross-striations and prism microstructure have been observed with a resolution better than 0.1 micrometers using this technique. Since BE images of demineralized enamel appear very similar to microradiography images, it is tempting to interpret them in a similar fashion. We attempt to show that the interpretation of BE images is not straightforward because enamel is not a homogeneous one-phase material, but a two-component composite material consisting of variable amounts of apatite mineral and organic matter. During re- and demineralization, other calcium phosphate phases may precipitate to further complicate the interpretation of the images. BE images of partially demineralized enamel are affected by local variations in the protein/mineral ratio and also by the reprecipitation of other calcium phosphate phases. BE images are not mineral density maps, but are mean atomic number maps.

Dental Enamel↗
PubMed1989

High resolution electron microscopy of nonstoichiometric apatite crystals.

The application of high resolution electron microscopy, computer image processing, and image simulation techniques to the investigation of synthetic nonstoichiometric apatites has provided new details of apatite crystal growth mechanisms. Under certain precipitation conditions, calcium-deficient apatites with distinct octacalcium phosphate (OCP)-apatite intergrowths have been observed. Apatite crystals with unit-cell thick overgrowths of OCP on their surfaces confirmed the stepwise hydrolysis crystal growth mechanism initially proposed by Brown (Nature 196:1048-1050). However, many crystals also contained a central two-dimensional OCP inclusion one to two unit cells thick, embedded in an apatite matrix. Similar planar defects have been observed in dental enamel, dentin, and bone crystals. We have developed a modified version of Brown's stepwise OCP hydrolysis apatite crystal growth mechanism to explain the formation of crystals with OCP central planar defects. The mechanism involves the nucleation of an OCP seed that grows until it reaches a critical size, rh, before OCP hydrolysis occurs. Apatite subsequently grows epitaxially on the OCP seed, thereby embedding it in the center of an apatite crystal. Apatite growth is facilitated by partial screw dislocations emanating from the planar defect.

Animals↗
PubMed1989

Proton microprobe determination of fluorine profiles in the enamel and dentine of erupting incisors from sheep given low and high daily doses of fluoride.

Developmental defects in incisors were induced by daily oral ingestion of sodium fluoride solutions. Teeth extracted at eruption from sheep that had been subjected to four different fluoride regimens--0.2 or 0.5 mg F/kg body weight daily for 6 months, 2 or 6 mg F/kg body weight daily for 21 days--were analysed for fluorine by gamma emission using a proton microprobe. Calcium and zinc profiles were also measured using proton-induced X-ray emission. Diffuse opacities, similar in appearance to mild human fluorosis, were produced by the first two regimens, whereas the last two produced hypoplastic lesions. Different distributions of fluoride were found in the unerupted enamel and dentine, and these patterns reflected variations in both the duration and concentration of the fluoride dose used to induce the fluorotic lesions.

Animals↗
PubMed1989

Microstructural features of carious human enamel imaged with back-scattered electrons.

We have used back-scattered electrons (BE) in the scanning electron microscope to produce mineral density images of enamel. Flat surfaces of artificially-carious enamel, softened in an intra-oral experiment, and naturally-carious (white spot) enamel were polished to a high gloss with diamond lapping compound, rendering them almost featureless by secondary electron scanning electron microscopy. They were then examined at 10 to 30 kV in a Philips 505 instrument fitted with a 4-quadrant BE detector. Study of surfaces prepared approximately parallel to the natural surface showed that mineral was lost from both prism core and the interprismatic region, leaving a thin mineral-rich rim at the prism periphery. The same lesions viewed longitudinally on a surface prepared perpendicular to the natural surface showed mineral-rich bands at the prism margins in the outer enamel. Near the advancing front of the lesion, the prism junctions were widened and the prism cores sometimes hypermineralized. Natural lesions sectioned in the prism long axis showed features previously seen with other techniques, e.g., cross-striations and striae of Retzius, but in much greater detail. Mineral enrichment at the prism periphery in the lesion body and a widening of the prism junction at the advancing fronts of lesions in permanent teeth were most obvious. Calculations showed that with an accelerating voltage of 30 kV, the images reflected mineral density up to 4 microns beneath the surface. BE microscopy produces a high-resolution image of mineral loss or gain in carious enamel, with relatively easy sample preparation.

Dental Caries↗
PubMed1989

Macroscopic and scanning electron microscopic appearance and hardness values of developmental defects in human permanent tooth enamel.

Defects present in 12 human permanent teeth were classified on the basis of their macroscopic appearance as hypoplasia (three teeth), diffuse opacities (three teeth), white demarcated opacities (one tooth but two defects), or yellow demarcated opacities (five teeth but six defects). The hardness values and SEM appearance of the defective enamel were determined after the teeth were sectioned through the lesion(s) and were distinctive for each type of defect. The thin enamel of the hypoplastic lesions was either opaque (with reduced hardness values) or translucent (with near-normal hardness values and sometimes a change in prism orientation external to an incremental line). The enamel of the diffuse and demarcated opacities was of normal thickness. The changes in the macroscopic and SEM appearance, and the reduced hardness values of the diffuse patchy opacities, were restricted to the outer 150 microns of the enamel. The demarcated opacities varied in position and depth, and in places had a clearly marked boundary with the adjacent normal enamel. Hardness values were related to color change, with yellow lesions being softer than white. Although prism direction was normal within demarcated opacities, prism outlines were less distinct. The findings suggest that temporary and permanent dysfunction of ameloblasts can occur in both secretory and maturation phases, influencing the final appearance of the lesion.

Dental Enamel↗