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Biomedical subjects

D Low

Publications and source records attributed to D Low.

At least 19 recordsLinked to original sources
PubMed1999

Titanium full crown casting: thermal expansion of investments and crown accuracy.

OBJECTIVES: The aim of the present study was to establish a statistical model between thermal expansion values of investments and dimensional accuracy of cast titanium full crowns. METHODS: Thermal expansion (TE) measurements were made on cylindrical specimens (5O x 20 mm) dried to constant mass and full crown wax patterns were prepared from metal dies having the same design. Castings were made using a one-chamber high-pressure casting machine. Dimensional accuracy of the cast crowns was expressed by the discrepancy (micron) between the wax pattern and a casting prepared from the same die. A simple least squares linear regression analysis was made on data accumulated over the last five years. RESULTS: A high correlation coefficient (R = 0.87) was found between dimensional accuracy (Y) and thermal expansion value (X), and the accuracy was predicted by a formula Y = 1040.50X - 1004.45 microns. For zero discrepancy, a thermal expansion of 0.97% was required. SIGNIFICANCE: The dimensional accuracy expressed as the discrepancy between wax pattern and casting is easy to understand and less confusing than the traditional percentage value. The crown accuracy was highly predictable (R = 0.87) from the thermal expansion value of investments determined under controlled laboratory measuring conditions. New investments being released for titanium casting can be under constant modification. For this, regular monitoring of their TE behaviour is essential and use of the same batch is preferable for expansion measurement and crown accuracy assessment.

Analysis of Variance↗
PubMed1998

Role of Streptococcus thermophilus MR-1C capsular exopolysaccharide in cheese moisture retention.

Recent work by our group has shown that an exopolysaccharide (EPS)-producing starter pair, Streptococcus thermophilus MR-1C and Lactobacillus delbrueckii subsp. bulgaricus MR-1R, can significantly increase moisture retention in low-fat mozzarella (D. B. Perry, D. J. McMahon, and C. J. Oberg, J. Dairy Sci. 80:799-805, 1997). The objectives of this study were to determine whether MR-1C, MR-1R, or both of these strains are required for enhanced moisture retention and to establish the role of EPS in this phenomenon. Analysis of low-fat mozzarella made with different combinations of MR-1C, MR-1R, and the non-EPS-producing starter culture strains S. thermophilus TA061 and Lactobacillus helveticus LH100 showed that S. thermophilus MR-1C was responsible for the increased cheese moisture level. To investigate the role of the S. thermophilus MR-1C EPS in cheese moisture retention, the epsE gene in this bacterium was inactivated by gene replacement. Low-fat mozzarella made with L. helveticus LH100 plus the non-EPS-producing mutant S. thermophilus DM10 had a significantly lower moisture content than did cheese made with strains LH100 and MR-1C, which confirmed that the MR-1C capsular EPS was responsible for the water-binding properties of this bacterium in cheese. Chemical analysis of the S. thermophilus MR-1C EPS indicated that the polymer has a novel basic repeating unit composed of D-galactose, L-rhamnose, and L-fucose in a ratio of 5:2:1.

Base Sequence↗
PubMed1998

Use of a two-color genetic screen to identify a domain of the global regulator Lrp that is specifically required for pap phase variation.

The global regulator Lrp plays a central role as both a repressor and an activator in Pap phase variation. Unlike most other members of the Lrp regulon such as ilvIH, activation of papBA transcription requires the coregulator PapI and is methylation dependent. We developed a two-color genetic screen to identify Lrp mutations that inhibit Pap phase variation but still activate ilvIH transcription, reasoning that such mutations might identify PapI binding or methylation-responsive domains. Amino acid substitutions in Lrp at position 126, 133, or 134 greatly reduced the rate of Pap switching from phase off to phase on but had much smaller effects on ilvIH transcription. In vitro analyses indicated that the T134A and E133G Lrp variants maintained affinities for pap and ilvIH DNAs similar to those of wild-type Lrp. In addition, both mutant Lrp's were as responsive to PapI as wild-type Lrp, evidenced by an increase in affinity for pap Lrp binding sites 4, 5, and 6. Thus, in vitro analyses did not reveal the step(s) in Pap phase variation where these Lrp mutants were inhibited. In vivo analyses showed that both the T134A and E133G Lrp mutants activated transcription of a phase-on-locked pap derivative containing a mutation in Lrp binding site 3. Further studies indicated that the T134A Lrp mutant was blocked in a step in Pap phase variation that does not involve PapI. Our data suggest that these mutant Lrp's are defective in a previously unidentified interaction required for the switch from the phase-off to the phase-on pap transcription state.

Amino Acid Sequence↗
PubMed1996

Bowel function survey after segmental colorectal resections.

PURPOSE: Long-term bowel function after right hemicolectomy (RHC), extended right hemicolectomy (ERHC), left hemicolectomy (LHC), sigmoid colectomy (SC), and anterior resection (AR) was evaluated. METHOD: Three hundred fifteen patients (52.3 percent) replied to a questionnaire on stool frequency, fecal continence, and defecation problems. All patients had undergone surgery at least one year before questionnaire was sent to them. Patients with anastomotic leaks and recurrences were excluded. RESULTS: Stool frequency was one to two bowel movements per day in 78 percent of patients after RHC, 75 percent after ERHC, 57.6 percent after LHC, 64.3 percent after SC, and only 44.8 percent after AR (P = 0.01). Continence affected lifestyle in 32 percent of patients after AR, but affected only up to 11.5 percent of patients who had had more proximal resections (P = 0.001). Defecation problems occurred in less than 15.4 percent after RHC, ERHC, and LHC but were encountered more frequently after SC (25 percent) and AR (28.4 percent; P = 0.009). CONCLUSIONS: Problems with postoperative bowel function were appreciably more common after SC and AR.

Colectomy↗
PubMed1996

Epigenetic phase variation of the pap operon in Escherichia coli.

Expression of the pyelonephritis-associated pilus (pap) operon in Escherichia coli is regulated by a complex epigenetic phase-variation mechanism involving the formation of differential DNA-methylation patterns. This review discusses how DNA-methylation patterns are formed by protein-DNA interactions and how methylation patterns, in turn, control pap gene expression.

Bacterial Proteins↗
PubMed1996

Expandable versus conventional esophageal prostheses: easier insertion may not preclude subsequent stent-related problems.

BACKGROUND: Although expandable esophageal endoprostheses may be easier to insert and are associated with fewer procedure-related perforations, data comparing clinical results with these stents to those obtained with conventional prostheses are sparse. METHODS: We reviewed the records of all patients undergoing esophageal stent placement at our institution between October 1983 and July 1995 to define relative risks, clinical results, and need for reintervention prior to death, contrasting conventional to a variety of expandable esophageal endoprostheses. RESULTS: Over the period of review, 47 patients had conventional prostheses (CP) and 38 had expandable prostheses (EP) placed. Fifteen of 44 patients with CP and 14 of 38 with EP for malignancy also had esophago-airway fistulas. Insertion complications, prestent and poststent dysphagia scores, and complete fistula occlusion rates were comparable. Subacute complications were higher in the patients receiving EP (80%) than in those receiving CP (60%), possibly related to the prospective accumulation of data in patients receiving EP. Survival data were virtually identical and approximated 3 months for either group. CONCLUSIONS: Although both CP and EP improve dysphagia and occlude tracheoesophageal fistulae, patients ill enough to require a prosthesis do poorly regardless of prosthesis design. Moreover, although EP may be easier to insert than CP, stent- and patient-related problems persist and may require additional intervention.

Aged↗
PubMed1995

Lobar variation of carbon tetrachloride hepatotoxicity in the rat.

The lobar variation in carbon tetrachloride-induced liver damage in the rat has been assessed by use of a systematic random sampling protocol and quantitative morphometry. A random inter-animal lobar variation in severity of damage was apparent, in contrast with the results obtained previously in which sampling bias, small animal numbers, and lack of fully quantitative measurement were apparent. The route of administration (oral vs. i.p.) did not influence these findings.

Administration, Oral↗
PubMed1994

An experimental model for the assessment of titanium denture casting techniques.

In order to establish the most suitable technique for the construction of cast titanium denture frames, an experimental model was developed for the quantification of casting success. A relatively large wax pattern (36 x 29 x 0.9 mm) was prepared from a grid sheet used for the construction of cast cobalt chromium partial denture frames. The pattern consisted of 100 circles and the number of completely cast circles was counted to obtain a percentage success rate. The castings were complete with pure titanium but incomplete (average 54%) with a titanium alloy. For an inspection of internal defects the radiographic conditions were optimised by adopting a relative density of about 2.0. The procedures described will help in establishing the most suitable casting technique for the construction of titanium denture frames for any casting system employed in a laboratory.

Dental Alloys↗
PubMed1993

An evaluation of two methods of anatomical alignment of radiotherapy portal images.

PURPOSE: Two techniques have been developed at our institution to allow anatomical registration of digitized portal images to a simulation film. Accuracy of the portal image alignment methods is tested and single intrauser and multiple interuser variation is examined using each technique. METHODS AND MATERIALS: Method one requires the identification of anatomical fiducial points on a simulation image and its corresponding portal image. The parameters required to align the corresponding points are calculated by a least squares fit algorithm. Method two uses an anatomical template generated from the simulation image and superimposing it upon a portal image. The template is then adjusted by a computer mouse to obtain the best subjective anatomical fit on the portal image. Megavoltage portal images of a skull phantom with various known shifts and eight clinical image files were aligned by each method. Each data set was aligned several times by both a single user and multiple users. RESULTS: Alignment of the anatomical phantom portal images demonstrates an accuracy of less than 0.8 +/- 0.9 mm and 0.7 +/- 1.0 degrees with either method. As out of plane rotation increased from 0 to 5 degrees, simulating out of plane malpositioning, alignment orthogonal to the plane of rotation worsened to 1.5 +/- 1.1 mm with the point method and 2.4 +/- 1.6 mm with the template method. Alignment parallel to the axis of the gantry rotation was insensitive to this change and remained constant as did the rotational alignment parameters. For the clinical image files the magnitude of variation for a single user is typically less than +/- 1 mm or +/- 1 degree. The magnitude of variation of alignment increased when multiple users aligned the same image files. The variation was dependent upon anatomical site and to a lesser degree the method of alignment used. The root mean square deviation of translational shifts range from +/- 0.68 mm when using the template method in the pelvis to as high as +/- 2.94 mm with the template method to align abdominal portal images. In the thorax and pelvis translational alignments along the horizontal axis were more precise than along the vertical axis. Multiple user variability was in part due to poor image quality, user experience, non rigidity of the anatomical features, and the difficulty in locating an exact point on a continuous anatomical structure. CONCLUSION: In well controlled phantom studies both the fiducial point and template method provide similar and adequate results. The phantom studies show that alignment error and variance increase with distortion in anatomical features secondary to out of plane rotations. In clinical situations intrauser variation is small, however, multiple interuser variation is larger. The magnitude of variation is dependent upon the anatomical site aligned.

Computer Simulation↗
PubMed1993

Regulation of pyelonephritis-associated pili phase-variation in Escherichia coli: binding of the PapI and the Lrp regulatory proteins is controlled by DNA methylation.

Expression of pyelonephritis-associated pili (Pap) in Escherichia coli is under a phase-variation control mechanism in which individual cells alternate between pili+ (ON) and pili- (OFF) states through a process involving DNA methylation by deoxyadenosine methylase (Dam). Methylation of two GATC sites (GATC1028 and GATC1130) within the pap regulatory region is differentially inhibited in phase ON and phase OFF cells. The GATC1028 site of phase ON cells is non-methylated and the GATC1130 site is fully methylated. Conversely, in phase OFF cells the GATC1028 site is fully methylated whereas the GATC1130 site is non-methylated. Two transcriptional activators, PapI and Lrp (leucine-responsive regulatory protein), are required for this specific methylation inhibition. DNA footprint analysis using non-methylated pap DNAs indicates that Lrp binds to a region surrounding the GATC1130 site, whereas PapI does not appear to bind to pap regulatory DNA. However, addition of Lrp and PapI together results in an additional DNaseI footprint around the GATC1028 site. Moreover, Dam methylation inhibits binding of Lrp/PapI near the GATC1028 site and alters binding of Lrp at the GATC1130 site. Our results support a model in which Dam and Lrp/PapI compete for binding near the GATC1028 site, regulating the methylation state of this GATC site and, consequently, the pap transcription state.

Bacterial Proteins↗
PubMed1992

A high incidence of asthma and respiratory symptoms in 4-11 year old children.

A study assessing the prevalence of respiratory symptoms in two primary schools in Birmingham, U.K. was performed. A questionnaire was delivered to pupils in both schools after which three open days were conducted in one of the schools, where probable asthmatics were identified and referred to their General Practitioner, Chest Clinic or a school asthma clinic. In this school 49% of responders and 52.9% in the control school were symptomless on questionnaire: 31% and 20.8%, respectively, had probable asthma, falling to 20% and 15.5% if a positive response to the question on recent recurrent wheeze was disregarded as indicating asthma. Using the total population as a denominator, the overall asthma prevalence was 20% which is significantly higher compared to previous English rates. Forty-two were seen at the Chest Clinic, 14 being followed for more than two visits. None were on regular anti-asthma treatment initially; 12/14 were taking prophylactic treatment on follow-up. In the two schools, 10.0% and 14.2% of responders were 'chesty' with 'colds' having no other typical asthmatic symptoms: these children should be studied further. This high incidence of respiratory symptoms in primary school children could represent a national trend or just a local increase.

Ambulatory Care Facilities↗
PubMed1991

Legionella pneumophila: denizen of defenders.

Legionella pneumophila, the causative agent of legionellosis, is an intracellular parasite of human monocytic cells and neutrophils. The life cycle of Legionella within phagocytic cells is distinct from that of other bacterial pathogens. Adherence of L pneumophila to phagocytes is mediated by attachment of complement proteins to the Legionella cell surface, followed by binding to complement receptors of phagocytes. Opsonized Legionella also may enter phagocytes after engagement of the Fc receptors. Within the host cell, the parasites reside in a membrane-bound vacuole that does not fuse with lysosomes. Activation of mononuclear phagocytes by the cell-mediated immune system serves to limit intracellular bacterial growth. Polymorphonuclear leukocytes are better at killing L pneumophila than are macrophages. However, Legionella also can invade and parasitize granulocytes. Although significant progress has been made in understanding some aspects of the pathogenesis of legionellosis, we know very little about the mechanisms by which these facultative intracellular parasites avoid killing by host defense mechanisms. This is an important area for future research and should lead to a better understanding of host-parasite interactions.

Bacterial Adhesion↗
PubMed1990

Multimodality imaging of a pancreatic transplant. A case report.

A 41-year-old man who had insulin-dependent diabetes mellitus from the age of 14 underwent cadaveric renal transplant in 1984. Two years later, the patient underwent pancreatic allograft transplantation. The patient did well for eight days after the operation and did not require exogenous insulin. After the eighth day, serum glucose levels rose. Multiple radiologic studies were performed to assess the possibility of graft rejection. A Tc-99m DTPA study revealed a gradual decrease in perfusion, and an In-111 oxine WBC study showed nonspecific inflammation. CT scanning and MRI displayed postsurgical anatomical relationships and excluded a peripancreatic fluid collection, but were unable to demonstrate parenchymal abnormality of the pancreas. Tests for infection proved negative. Because the decreased blood flow demonstrated by DTPA study indicated transient ischemia, the patient was treated for graft rejection and stabilized quickly.

Adult↗
PubMed1989

Gal-Gal pili vaccines prevent pyelonephritis by piliated Escherichia coli in a murine model. Single-component Gal-Gal pili vaccines prevent pyelonephritis by homologous and heterologous piliated E. coli strains.

The initial pathogenic step in nonobstructive Escherichia coli pyelonephritis usually involves the binding of a bacterial adhesin with host uroepithelial glycoprotein receptors containing the D-Gal p alpha 1----4 D-Gal p beta 1 (Gal-Gal) moiety. In this study, groups of mice were immunized with Gal-Gal pili and challenged 2 wk later intravesicularly with E. coli strains expressing homologous or heterologous pili. 63 of 129 pili-immunized mice (49%) were protected from subsequent E. coli renal colonization compared with 5 of 85 control mice (6%). Among mice that had E. coli cultured from their right kidney, control mice had greater bacterial colony counts than pili-immunized animals (P less than 0.05). Light microscopic examination of kidneys demonstrated less histopathology among pili immunized mice than among control mice (P less than 0.05). Protection correlated with the presence of specific IgG antibodies in the urine and serum that bind to the major pilin structural polypeptide and not to the Gal-Gal pili tip adhesin per se. These results support the concept that immunization with a bacterial surface-coat constituent can prevent mucosal infection by interfering with colonization. Also Gal-Gal pili of E. coli represent a suitable candidate for immunoprophylaxis against pyelonephritis.

Animals↗