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Biomedical subjects

Y C Tam

Publications and source records attributed to Y C Tam.

13 recordsLinked to original sources

Infusion pump performance in an MR environment.

Concerns about life support equipment accompanying the critically ill patient have to date made magnetic resonance imaging (MRI) studies of this patient group the exception. We present here a series of tests performed on an IVAC P3000 infusion pump to investigate its suitability for the magnetic resonance imaging environment. We investigate safety, pump performance and image quality issues. The pump was housed at the end of the patient couch to prevent motion towards the scanner. Gravimetric tests found the pump to work within acceptable parameters at a static field of 10 mT. Image interference issues were addressed.

Artifacts↗

Maintaining the Ineraid cochlear implant.

Managing a patient with acquired profound deafness with a cochlear implant involves a lifetime commitment to rehabilitation and also to maintaining the device in a functioning condition. This paper describes the Cambridge experience of maintaining the Ineraid cochlear implant in a series of 25 patients over a 4 year period. On average, maintenance (repair of replacement) of components was required every 2.3 months of implant use, although some minor variations were noted between patients, and between component type. This rate of failure is sufficient to cause an Implant Centre to consider provision for repairs and holding of spare stock. It should be remembered that each breakdown returns the patient to a deafened state, albeit temporarily, but this can cause significant distress.

Cochlear Implants↗

New mouse somatic cell mutants resistant to cadmium affected in the expression of their metallothionein genes.

Fluctuation tests à la Luria and Delbruck were performed with mouse LMTK cells, and the results indicate that the appearance of variants resistant to cadmium is due to random spontaneous mutations and not to epigenetic events. The rate of spontaneous mutations leading to cadmium resistance was calculated to be 0.92 x 10(-6) per cell per generation. This rate increased 14-fold on treatment with ethyl methane sulfonate. Several stable mutant cell lines resistant to cadmium were selected and characterized with respect to metallothionein (MT) induction. Based on the copy number of mt+ genes and the levels of MT proteins and mRNA, the mutants could be divided into two classes, A and B. Although group A mutants have the same number of mt1+ and mt2+ genes as wild-type cells, upon induction with cadmium, the amount of MT proteins and mRNA in the mutants are greatly increased over wild-type levels. This observation strongly suggests a mutation that regulates MT gene transcription in these cells. In group B mutants, the mt+ genes are amplified about three- to fourfold, and their MT protein and mRNA basal levels are, as expected, much higher than in the wild-type cells, under uninduced and induced conditions.

Animals↗

Automated performance checking of infusion equipment.

A universal method of assessing the performance of infusion devices is described. An electronic balance was interfaced to a personal computer and software was written to provide a graphical display of output rate and to check for inconsistency in performance.

Computer Systems↗

Cloning, nucleotide sequence and molecular evolution of a rabbit processed metallothionein MT-2 pseudogene.

A rabbit metallothionein-2 pseudogene (MT-2 psi) has been isolated from a partial rabbit genomic library. Its unusual sequence shows evidence of complex rearrangements involving recombination and deletion events. There are no intervening sequences, 3' poly A tract or 5' regulatory DNA sequences. The pseudogene is flanked by two sets of direct repeats (CT)3 GT(CT)4 and CTGG(G)CTC. They are most probably the sites of insertion of MT-2 psi in the rabbit genome. In addition, a number of repetitive DNA sequences are observed flanking the MT-2 psi gene. These are features of a processed retrogene.

Amino Acids↗

Cloning, nucleotide sequence and characterization of a New Zealand rabbit metallothionein-I gene.

We have isolated a rabbit metallothionein-I gene from a lambda gt10 library. The coding sequence of this gene is interrupted by two introns occurring at amino acid positions 9 1/3 and 30 1/3. Comparison of the promoter sequence of this gene with the promoters of other metallothionein genes identified a number of oligonucleotide sequences which are recognized by trans-acting proteins involved in the regulation of these genes by heavy metals, glucocorticoids and alpha interferon.

Amino Acid Sequence↗

Effects of extracellular products of a presumed gingival pathogen, the bacterium Peptostreptococcus 84H14S, on cultured human fibroblasts and HeLa cells.

Culture fluids from this microorganism, fibroblasts and HeLa cells contained potent factors which inhibited thymidine uptake in HeLa cells. The outcome of heating the culture fluid and fractionating it by gel filtration suggested that this was not due to bacterial hyaluronidase activity. Purified peptostreptococcal hyaluronidase and several commercially-available mucopolysaccharidases also did not inhibit thymidine uptake.

Cell Adhesion↗

Purification and characterization of hyaluronidase from oral Peptostreptococcus species.

Hyaluronidase was purified to apparent homogeneity from the spent medium of Peptostreptococcus sp. strain 84H14S. The enzyme was purified 310-fold by ethanol precipitation, gel chromatography, and cation-exchange chromatography with a recovery of 42% of the original activity in the culture medium. The molecular weight of the purified enzyme was estimated to be 160,000 by gel filtration with Sephacryl S-300. Like bacterial mucopolysaccharidases of other sources, the enzyme carried out an eliminative reaction with the substrate, producing 4,5-unsaturated disaccharides as the final end products. Its optimum temperature of activity is 46 degrees C. The purified peptostreptococcal hyaluronidase was different from previously reported bacterial hyaluronidases in several respects. It degraded hyaluronic acid rapidly and also exhibited some activity against chondroitin sulfate A and chondroitin sulfate C. The KmS for hyaluronic acid, chondroitin sulfate A, and chondroitin sulfate C were 0.14, 1.4, and 2.6 mg/ml, respectively. The specific activity of hyaluronidase was much higher than that of any previously purified mucopolysaccharidases. The Vmax against hyaluronic acid reached 400 mmol of product per min per mg of protein at 22 degrees C. The peptostreptococcal hyaluronidase was also unique in that its optimum pH of activity was around neutrality, whereas other bacterial hyaluronidases were most active at acidic pHs.

Bacterial Proteins↗

Phase variation of hyaluronidase-producing peptostreptococci associated with periodontal disease.

Peptostreptococci isolated from diseased periodontal pockets produced large amounts of extracellular hyaluronidase throughout their growth cycle. Phase variants, obtained by re-streaking aged colonies of the wild types, had different colonial morphology and shorter generation times. These variants produced less hyaluronidase, and enzyme production occurred only during the early stationary phase.

Humans↗

Use of fluorescence microscopy for monitoring periodontal disease state.

Samples of subgingival plaque from patients with periodontal disease and control subjects were stained with the Fluoretec Fluorescent test kits (Pfizer Inc., New York) developed for the rapid detection of members of the Bacteroides fragilis and B. melaninogenicus groups of anaerobes. The same fluorescent fields were also examined by dark-field microscopy for the total count of bacteria. Bacteroides fragilis and B. melaninogenicus were found in plaque samples of healthy subjects and periodontally diseased patients with no significant difference in percent of total flora. Oral spirochetes also fluoresced with the antisera used. Samples from healthy sites showed virtually no spirochetes; spirochetes were present in diseased sites. Tests with other antisera also showed that fluorescein-labelled antibodies can be adsorbed nonspecifically to the surface of spirochetes. Such a phenomenon can be used to monitor an individual's periodontal disease state.

Bacteroides↗