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Biomedical subjects

A W Miller

Publications and source records attributed to A W Miller.

At least 37 records · Page 2Linked to original sources
PubMed1998

Marginal fit and surface roughness of crowns made with an accelerated casting technique.

STATEMENT OF PROBLEM: Conventional investing and casting techniques following the manufactures' recommendations are time-consuming. Accelerated casting techniques have been reported, but their accuracy has not been adequately studied for complete crown castings. PURPOSE: This study evaluated the marginal fit and surface roughness of complete crowns made with a conventional and an accelerated casting technique. MATERIALS AND METHODS: Part I of the study determined the mean time interval required for each investment to reach its maximum exothermic setting reaction temperature. Part II determined the marginal discrepancy of standardized complete crowns cast in a high noble metal ceramic alloy, with the use of four phosphate-bonded investments. A conventional technique (as recommended by the manufacturer) was compared with an accelerated technique that used 13- to 17-minute bench set time (as determined in part 1 for each investment)_ and 15-minute wax elimination cycle in a 815 degrees C (1500 degrees F) preheated furnace. Part III evaluated the surface roughness of castings made with the same techniques as in part II. RESULTS: For the marginal discrepancy and surface roughness, crowns fabricated with the accelerated casting technique were not significantly (P > 0.05) different from those fabricated with the conventional technique. CONCLUSION: The accelerated casting technique described in this study could be a vital alternative to the time-consuming conventional techniques.

Crowns↗
PubMed1998

High-dose lidocaine does not affect defibrillation efficacy: implications for defibrillation mechanisms.

This study assessed the effect of low (10 mg.kg-1.h-1) and very high (18 mg.kg-1.h-1) doses of lidocaine on defibrillation energy requirements (DER) to relate changes in indexes of sodium-channel blockade with changes in DER values using a dose-response study design. In group 1 (control; n = 6 pigs), DER values were determined at baseline and during treatment with 5% dextrose in water (D5W) and with D5W added to D5W. In group 2 (n = 7), DER values were determined at baseline and during treatment with low-dose lidocaine followed by high-dose lidocaine. In group 3 (n = 3), DER values were determined at baseline and high-dose lidocaine. Group 3 controlled for the order of lidocaine treatment with the addition of high-dose lidocaine after baseline. DER values in group 1 did not change during D5W. In group 2, low-dose lidocaine increased DER values by 51% (P = 0.01), whereas high-dose lidocaine added to low-dose lidocaine reduced DER values back to within 6% of baseline values (P = 0.02, low dose vs. high dose). DER values during high-dose lidocaine in group 3 also remained near baseline values (16.2 +/- 2.7 to 12.9 +/- 2.7 J), demonstrating that treatment order had no impact on group 2. Progressive sodium-channel blockade was evident as incremental reduction in ventricular conduction velocity as the lidocaine dose increased. Lidocaine also significantly increased ventricular fibrillation cycle length as the lidocaine dose increased. However, the greatest increase in DER occurred when ventricular fibrillation cycle length was minimally affected, demonstrating a negative correlation (P = 0.04). In summary, lidocaine has an inverted U-shaped DER dose-response curve. At very high lidocaine doses, DER values are similar to baseline and tend to decrease rather than increase. Increased refractoriness during ventricular fibrillation may be the electrophysiological mechanism by which high-dose lidocaine limits the adverse effects that low-dose lidocaine has on DER values. However, there is a possibility that an unidentified action of lidocaine is responsible for these effects.

Animals↗
PubMed1998

Disparate effects of biphasic and monophasic shocks on postshock refractory period dispersion.

The magnitude by which a defibrillation shock extends the refractory period immediately postshock (refractory period extension, RPE) does not explain why biphasic shocks defibrillate with greater efficacy than monophasic shocks. It may be that spatial heterogeneity of RPE is a more important regulator of defibrillation efficacy. We measured RPE in 15 pentobarbital-anesthetized swine using 400-V biphasic and monophasic shocks of equal pulse duration at three discrete myocardial sites. Spatial heterogeneity of RPE was calculated as the difference between the maximum and minimum values of the three recording sites. Monophasic shocks produced greater magnitude of RPE than biphasic shocks at all sites tested (82 +/- 6 to 99 +/- 13 and 64 +/- 6 to 68 +/- 5 ms, respectively; P < 0.05). However, RPE dispersion was significantly less with biphasic shocks versus monophasic shocks (29 +/- 4 and 48 +/- 7 ms, respectively; P < 0.05). This suggests that one potential mechanism by which biphasic shocks defibrillate with greater efficacy is limiting postshock spatial heterogeneity of refractoriness. Thus these data support our hypothesis that RPE heterogeneity is a more likely predictor of defibrillation efficacy than magnitude of RPE.

Action Potentials↗
PubMed1998

Endothelial dysfunction precedes hypertension in diet-induced insulin resistance.

The insulin-resistant (IR) syndrome may be an impetus for the development of hypertension (HTN). Unfortunately, the mechanism by which this could occur is unclear. Our laboratory and others have described impaired endothelium-mediated relaxation in IR, mildly hypertensive rats. The purpose of the current study is to determine if HTN is most likely a cause or result of impaired endothelial function. Sprague-Dawley rats were randomized to receive a fructose-rich diet for 3, 7, 10, 14, 18, or 28 days or were placed in a control group. The control group received rat chow. After diet treatment, animals were instrumented with arterial cannulas, and while awake and unrestrained, their blood pressure (BP) was measured. Subsequently, endothelium-mediated relaxation to acetylcholine was determined (in vitro) by measuring intraluminal diameter of phenylephrine-preconstricted mesenteric arteries ( approximately 250 microM). Serum insulin levels were significantly elevated in all groups receiving fructose feeding compared with control, whereas there were no differences in serum glucose levels between groups. Impairment of endothelium-mediated relaxation starts by day 14 [mean percent maximal relaxation (Emax): 69 +/- 10% of baseline] and becomes significant by day 18 (Emax: 52 +/- 11% of baseline; P < 0.01). However, the mean BP (mmHg) does not become significantly elevated until day 28 [BP: 132 +/- 1 (day 28) vs. 116 +/- 3 (control); P < 0.05]. These findings demonstrate that both IR and endothelial dysfunction occur before HTN in this model and suggest that endothelial dysfunction may be a mechanism linking insulin resistance and essential HTN.

Animals↗
PubMed1996

Rapid DNA sequencing of more than 1000 bases per run by capillary electrophoresis using replaceable linear polyacrylamide solutions.

The read length for DNA sequencing using capillary electrophoresis and replaceable linear polyacrylamide (LPA) solutions has been extended to more than 1000 bases with a run time of 80 min. This result was successfully achieved through the combined use of cycle sequencing with dye-labeled primers, improved matrix and separation conditions, and enhanced base-calling software. The influences of LPA molecular weight and concentration on separation were investigated. Additionally, the separation buffer, column temperature, and electric field were adjusted to increase the number of resolvable DNA fragments per run while maintaining an enhanced separation speed. Using low concentrations [2% (w/v)] of high molecular weight LPA polymers (> 5.5 x 10(6) Da), elevated column temperature (50 degrees C) and moderately high field (150 V/cm), rapid sequencing analysis for more than 1000 bases on a model ssM13mp18 template was obtained with 96.8% accuracy.

Acrylic Resins↗
PubMed1996

The use of elevated column temperature to extend DNA sequencing read lengths in capillary electrophoresis with replaceable polymer matrices.

Capillary electrophoresis with a replaceable linear polyacrylamide matrix operated at elevated column temperatures of 55 degrees and 60 degrees C was used to extend the separation of DNA sequencing fragments to lengths greater than 800 bases. A solid-state heater was employed to provide stable, uniform temperature control over a significant portion of the capillary. The polymer matrix, 3% w/v linear polyacrylamide in a denaturing buffer, was replaced in the capillary after each run. Using dye-labeled primers and Sequenase chemistry on an M13mp18 single-stranded template, four-color separations for the sequencing products were obtained, with read lengths in excess of 800 bases. This paper also briefly discusses the effects of buffer denaturants and capillary temperature on separation speed, resolution, and gel compression.

Acrylic Resins↗
PubMed1996

DNA sequencing by capillary electrophoresis using short oligonucleotide primer libraries.

Two strategies for DNA sequencing by primer walking using short oligonucleotide primer libraries have been successfully employed along with capillary electrophoresis using replaceable polymer solutions of linear polyacrylamide and fluorescence detection. A 3.5-kb stretch of the single-stranded M13mp18 template was sequenced with T7 PRISM dye-terminator/Sequenase chemistry. An in-house base-calling program offered read lengths of roughly 450 bases with an average of 97.8% accuracy.

Base Sequence↗
PubMed1995

Structural and serological studies of lipopolysaccharides from proposed new serotypes (O25 and O26) of Serratia marcescens.

The surface polysaccharides of the two most recently proposed O-serotype strains of Serratia marcescens, O25 and O26, were characterised in terms of their chemical structure and immunological reactions. No polymer was isolated from O25, which was shown to lack both capsular K-antigen and smooth, O-antigenic lipopolysaccharide. A neutral polysaccharide was isolated from O26 and shown to be a polymer of rhamnose and N-acetylgalactosamine of the type previously found in the O9 and O15 reference strains. Serological cross-reactions among all three strains were demonstrated by using both whole-cell enzyme-linked immunosorbent assay and immunoblotting of lipopolysaccharide resolved by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. No acidic polysaccharide was found in O26 and this was consistent with the absence of an immunogenic capsule. Thus, neither strain qualifies for inclusion as a new serotype in either an O-typing or a K-typing scheme.

Lipopolysaccharides↗
PubMed1995

Structure of the O10 antigen of Stenotrophomonas (Xanthomonas) maltophilia.

A polysaccharide containing L-rhamnose and L-xylose was isolated from the lipopolysaccharide extracted from the cell walls of the reference strain for Stenotrophomonas (Xanthomonas) maltophilia serogroup O10. By means of NMR studies and methylation analysis, the repeating unit of the polymer was identified as a branched tetrasaccharide of the structure shown. [formula: see text]

Carbohydrate Sequence↗
PubMed1994

Paget's disease in an adolescent arising in a supernumerary nipple.

Paget's disease of the breast generally affects middle-aged and older females. In the majority of cases, it is considered to be the result of epidermal spread from a contiguous mammary duct carcinoma. We report the first case in an adolescent female with an accessory nipple. The histomorphology and immunophenotypic findings support the hypothesis of in situ transformation and suggest a histologic spectrum exists in terms of cytologic atypia.

Adolescent↗
PubMed1993

DNA sequencing by capillary electrophoresis with replaceable linear polyacrylamide and laser-induced fluorescence detection.

Replaceable linear polyacrylamide (LPA) has been utilized as a sieving matrix for DNA sequencing by capillary electrophoresis (CE). Difficulties associated with cross-linked polyacrylamide gel stability have been overcome for the routine application of CE to DNA sequencing. A simple laser-induced fluorescence (LIF) detection system based on a single laser and two photomultipliers (PMT) has been adopted for this work. Sequencing information for four bases has been obtained from two fluorescent dyes and two peak height ratios, detected in two optical channels. FAM- and JOE-labeled M13 (-21) primers have been chosen because both dyes are efficiently excited with a low-power argon ion laser, can be optically separated, and exhibit minimal dye-based shifts in DNA fragment mobilities. Addition of denaturants to the electrophoresis running buffer (1 x TBE, 3.5 M urea, 30% formamide) and column operation at 32 degrees C permitted the resolution of difficult compressed sites in the sequence of phage M13mp18. Careful examination of the polymerization reaction of LPA has led to methodology that has proven to be reproducible for obtaining DNA sequencing information of M13mp18 phage for 350 nucleotides in close to 30 min.

Acrylic Resins↗
PubMed1992

Separation of noncutaneous epithelia in a fetus diagnosed in utero with junctional epidermolysis bullosa.

This study was undertaken to identify the extent of involvement of cutaneous and noncutaneous epithelia during expression in utero of junctional epidermolysis bullosa. Skin and other organs from a 19-wk estimated gestational age fetus affected with junctional epidermolysis bullosa and from age-matched controls were examined by light and transmission electron microscopy. In the affected fetus, skin samples from different body regions including trunk, leg, arm, and finger all showed some separation at the dermal-epidermal junction in the plane of the lamina lucida. Hemidesmosomes were absent or hypoplastic, whereas anchoring fibrils appeared normal in structure and number. Interfollicular epidermis appeared to have separated easily, whereas some follicles remained anchored in the dermis. Areas of epithelium in the trachea and bronchi had separated, but within the lung parenchyma the epithelium of smaller bronchioles and alveoli remained attached to supporting connective tissue. The transitional epithelium of the urinary bladder showed small areas of separation compared with the gall bladder epithelium, which showed extensive separation. Gall bladder epithelium in several control fetuses also was consistently separated. In the affected fetus as well as in controls, gall bladder had multiple layers of basal lamina, a previously unrecognized structural feature of human fetal gall bladder. Epithelia that remained intact included the linings of the stomach and small and large intestines and endothelium of large and small vessels in all organs. Kidney, spleen, liver, and lymph nodes appeared normal in all aspects. In control samples, neither skin nor most of the noncutaneous epithelia had separated from the underlying connective tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Ligand-induced isomerizations of Escherichia coli ornithine transcarbamoylase. An ultraviolet difference analysis.

Ligand-induced ultraviolet difference spectra have been determined for Escherichia coli ornithine transcarbamoylase. The most prominent feature of the spectra is an absorbance difference which resembles a single period of a sine wave spanning the 245-320 nm region with a maximum at approximately 270 nm and a minimum at around 295-300 nm. This broad absorbance difference is typical of a blue-shift 1La band of tryptophan. Superimposed on the broad band in the 275-310 nm region is a series of smaller, narrow peaks resulted from red-shifted 1Lb bands of tryptophan and tyrosine residues. At pH 8.5, only carbamoyl phosphate and its analog phosphonacetamide yield a large ultraviolet difference absorbance (approximately 1800 M-1 cm-1) when bound to the enzyme. The spectra obtained are essentially the same in lineshape to and 80% in intensity of that produced by the bisubstrate analogy, N-(phosphonacetyl)-L-ornithine. In contrast, inorganic phosphate, a product of the reaction, induces small protein absorbance changes (approximately 300 M-1 cm-1) mainly in the 275-310 nm range. When complexed to the free enzyme, L-ornithine yields a marginally discernible ultraviolet difference spectrum in the 275-310 nm region, and its analogs L-norvaline and L-citrulline provide no absorbance change. However, inorganic phosphate in combination with any of the L-amino acids produces a difference spectrum similar to that given by carbamoyl phosphate alone. Collectively, these spectra suggest that carbamoyl phosphate elicits an isomerization required for the formation of the ternary complex and are consistent with the compulsory ordered mechanism of the enzyme at pH 8.5 with carbamoyl phosphate being the first substrate bound. Below pH 8, there is a kinetically discernible amount of random binding, but ordered addition is still the preferred pathway (Wargnies B., Legrain, C., and Stalon, V. (1978) Eur J. Biochem. 89, 203-212). Reflecting this change, the difference absorbance of the enzyme bound with carbamoyl phosphate is also pH dependent. The 1La band in the carbamoyl phosphate difference spectrum diminishes by approximately 20% at low pH. The PALO-induced changes, however, are pH invariant suggesting that full extent of the induced-fit isomerization is always reached in the ternary complex.

Carbamyl Phosphate↗
PubMed1990

Zn2+ regulation of ornithine transcarbamoylase. I. Mechanism of action.

Ornithine transcarbamoylase catalyzes the formation of L-citrulline from carbamoyl phosphate and L-ornithine. The anabolic enzyme from Escherichia coli is composed of three identical subunits and resembles, in both primary and quaternary structures, the catalytic unit of aspartate transcarbamoylase. However, ornithine transcarbamoylase has no regulatory subunits. Although this enzyme does not bind its substrates co-operatively, fluorescence spectroscopic experiments show that zinc adds allosterically to the free enzyme. The metal binding process is dictated by deprotonation of an enzymic group with a pKa less than 7. The saturation binding curve of the metal ion is sigmoidal and yields a Hill coefficient of 1.6 at pH 8.5 and 25 degrees C. In the absence of substrates, zinc further promotes a slow enzyme isomerization, which occurs with a first-order rate constant of 7 min-1; thus, the metal is a slow, tight-binding inhibitor. The isomerized enzyme is inactive and contains three zinc ions. When the enzyme is first bound with carbamoyl phosphate, steady-state kinetic assays reveal that zinc again binds co-operatively to the binary enzyme complex, with a Hill coefficient of 1.5, but the metal ion now behaves simply as a classical, reversible inhibitor; it is competitive against L-ornithine, non-competitive against carbamoyl phosphate, and induces no enzyme isomerization. However, as a result of the competition between zinc and L-ornithine for the same site on the enzyme, the L-ornithine saturation curve becomes sigmoidal. Displacement of the allosteric zinc from the enzyme by L-ornithine is the cause of co-operative addition of this substrate. The combined results suggest that zinc regulates ornithine transcarbamoylase via two routes: (1) as an allosteric cofactor of the substrate-bound enzyme in mediating site-site interactions; and (2) as a slow, tight-binding inhibitor of the free enzyme in inducing inactivation. The concentration of zinc that is effective for action is in the micromolar range. The finding that E. coli ornithine transcarbamoylase can be induced to express co-operativity in binding its substrates has recently been confirmed by site-directed mutagenesis experiments. When the active site residue Arg106 is altered to a glycine, the resultant mutant enzyme exhibits both homotropic and heterotropic interactions towards its substrates. In view of the quaternary structure of holoenzyme aspartate transcarbamoylase, the "silent" co-operativity of ornithine transcarbamoylase is of particular interest in the study of evolution of complex, regulatory proteins.

Edetic Acid↗
PubMed1989

Intravascular lipoleiomyomatosis: a report of two cases.

Two cases of intravascular leiomyomatosis (IVL) with histologic features of a lipoleiomyoma (LPL) are reported. Both tumors arose from preexisting uterine leiomyomata. One tumor was found incidentally in a uterus removed for leiomyomata. The other tumor extended up the inferior vena cava into the right side of the heart and presented as a cardiac mass. Although LPL is considered to be a benign lesion, IVL recurs in approximately 10% of reported cases, and must be distinguished from low-grade endometrial stromal sarcoma and leiomyosarcoma with vascular invasion. The combination of features in these cases lends support to the theory that IVL may arise by intravascular extension of a preexisting leiomyoma.

Adult↗
PubMed1988

Site-directed mutagenesis of Escherichia coli ornithine transcarbamoylase: role of arginine-57 in substrate binding and catalysis.

In the carbamoyl-transfer reaction catalyzed by ornithine transcarbamoylase, an arginine residue in the active site of the Escherichia coli enzyme has been suggested to bind the phosphate moiety of the substrate carbamoyl phosphate. With the application of site-specific mutagenesis, the most likely arginine residue among three candidates at the binding site of carbamoyl phosphate, Arg-57, has been replaced with a glycine. The resultant Gly-57 mutant enzyme is drastically inefficient in catalysis. In the synthesis of L-citrulline from carbamoyl phosphate and L-ornithine with the release of inorganic phosphate, the turnover rate of the mutant is 21,000-fold lower than that of the wild type. However, the mutation of Arg-57 affects only moderately the binding of carbamoyl phosphate; the dissociation constant of this substrate, measured under steady-state turnover condition, is increased from 0.046 to 3.2 mM by the mutation. On the other hand, ornithine binding is substantially affected as estimated by the change in the dissociation constant of its analogue L-norvaline. The dissociation constant of L-norvaline increases about 500-fold from 54 microM for the wild type to 25 mM for the mutant. Since Arg-57 is expected to be distal from the ornithine site and the amino acid (both ornithine and norvaline) binds only after carbamoyl phosphate in the wild-type reaction, the poor norvaline affinity to the mutant suggests that Arg-57 is involved in interactions essential for productive addition of the amino acid. This interpretation is supported by difference ultraviolet absorption spectra which show that the conformational changes induced in the wild type by carbamoyl phosphate upon binding are absent in the mutant. Furthermore, steady-state kinetic data reveal that the ordered binding mechanism of the wild-type enzyme is transformed into a random binding mechanism in the mutant. Thus, the presence of carbamoyl phosphate in the mutant active site is no longer a requisite for ornithine binding. In the 5-50 degrees C temperature range, transcarbamoylation catalyzed by either the wild type or the mutant observes the Arrhenius rate law with almost identical enthalpies of activation, 11 and 10 kcal/mol, respectively. The entropy of activation is -5.5 eu for the wild-type reaction and -29 eu for the mutant reaction, accounting for a loss of 6-7 kcal/mol in the rate-determining step of the enzymic reaction.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1988

Miliary tuberculosis in an in-vitro fertilization pregnancy: a case report.

A 33-yr-old woman with primary infertility of no known cause of 10 years duration underwent in-vitro fertilization. Mild flu-like symptoms and intermittent vaginal bleeding developed, and miliary mottling was seen throughout both lung fields. At 14 weeks she aborted a normal male fetus; urine culture was positive for M. bovis. Six months later, after a course of antituberculous drugs, the patient was symptom-free.

Adult↗