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Biomedical subjects

D Low

Publications and source records attributed to D Low.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1987

The frequency of expression of pyelonephritis-associated pili is under regulatory control.

The Escherichia coli urinary tract isolate C1212 contains two pyelonephritis-associated pili (pap) DNA sequences designated here as pap-17 and pap-21. Each of these pap sequences encodes antigenically-distinct pilin monomers, pilin-17 and pilin-21, respectively. Most individual strain C1212 cells isolated from a single bacterial colony expressed pilin-21. Only a small fraction (5%) of strain C1212 cells expressed pilin-17. Most of the latter population simultaneously expressed pilin-21, but a low percentage of cells expressed pili composed of pilin-17 alone. In contrast, almost every E. coli K-12 cell containing multicopy pap-17 expressed pilin-17 at the cell surface. These results indicated that the regulation of pilin-17 expression observed for strain C1212 was lost when pap-17 was in the multicopy state. Transfer of pap-17 to a single copy vector resulted in a pilin-17 expression frequency lower than strain C1212 (1%). Using E. coli K-12 containing single copy pap-17, we found that the frequency of pilin-17 expression increased about 15-fold when pap-21 was present in multiple copies in trans. Subcloning of pap-21 showed that a 2.2 kilobase-pair DNA sequence adjacent to, but not including, the pilin-21 structural gene was sufficient for activation of pilin-17 expression.

Bacterial Outer Membrane Proteins↗
PubMed1985

Gal-Gal binding and hemolysin phenotypes and genotypes associated with uropathogenic Escherichia coli.

To determine whether uropathogenic strains of Escherichia coli exhibit a distinctive constellation of phenotypes, we examined 44 urinary isolates from women with radiologically normal urinary tracts and pyelonephritis, cystitis, or asymptomatic bacteriuria and 73 fecal isolates from healthy control subjects. The strains were characterized by their O serogroup, by their binding specificity (as determined by adhesins), and by their production of hemolysin and colicin V. In addition, the strains were assessed for homologous gene sequences by means of DNA-hybridization probes prepared from cistrons that encode hemolysin and the Gal-Gal binding adhesin--two determinants of virulence, which cause tissue injury and promote bacterial colonization of uroepithelia, respectively. In contrast to most isolates from normal feces and from the urine of patients with asymptomatic bacteriuria, pyelonephritis strains belong to a small number of O serogroups; all express the Gal--Gal binding adhesin and 75 per cent are hemolytic. A gene probe for the Gal--Gal binding adhesin, derived from the chromosome of one strain from a patient with pyelonephritis, hybridized with the DNA of all other pyelonephritis strains. The probe for the hemolysin gene hybridized with DNA from all other hemolytic strains. These data indicate that most cases of pyelonephritis are due to a small number of pathogenic clones that express critical determinants of virulence, and that the nucleotide sequences for hemolysin and the Gal--Gal binding adhesin in heterologous strains share homology. We are tempted to speculate that the gene products of these shared regions of the genome might form the basis for a vaccine against pyelonephritis.

Adhesiveness↗
PubMed1985

The use of omental grafts in operations performed upon the colon and rectum.

The greater omentum is an organ with numerous potential uses. A simple procedure to create a vascularized pedicle based on solid anatomic principles coupled with adequate nutrition, careful operative technique and good preparation of the intestine will help ensure a postoperative course that is free of complications.

Colectomy↗
PubMed1984

Complications of chronic glue (toluene) abuse in adolescents.

Recently there has been an alarming increase in the number of schoolchildren sniffing glue (toluene). The medical complications seen in 18 boys, aged 14 to 18 years, include physical and mental dependence, pulmonary hypertension with cor pulmonale, restrictive lung defect, encephalopathy, peripheral neuropathy and high frequency, continuous discharges ( neuromyotonia ) on electromyogram. Glue sniffing took place in small groups and abusers sniffed directly from cans containing glue. Lower socio-economic status, overcrowding, lack of attention by working parents, school failure and easy availability of the glue were commonly cited associated factors.

Adolescent↗
PubMed1984

Gene clusters governing the production of hemolysin and mannose-resistant hemagglutination are closely linked in Escherichia coli serotype O4 and O6 isolates from urinary tract infections.

The genes encoding alpha-hemolysin and mannose-resistant hemagglutination were shown to be closely linked in cloned DNA from two Escherichia coli urinary tract isolates of serotypes O4 (J96) and O6 (C1212). DNA hybridization experiments demonstrated that the hly and mrh gene clusters of other E. coli O6 serotypes were also linked. Colony hybridizations showed that most normal fecal E. coli do not contain hly and mrh DNA but much of the intervening DNA between these two gene clusters is common among all E. coli. We have further demonstrated that there is a small (about 1 kilobase) region of homology located on both sides of the hly sequence and present elsewhere in the C1212 strain. We suggest that linkage of hly and mrh occurred through a transposition event, and we discuss the potential significance of this linkage in the acquisition of virulence determinants by these bacteria.

Base Sequence↗