Search PubMed⌕ Search

Biomedical subjects

W L Ng

Publications and source records attributed to W L Ng.

At least 37 records · Page 2Linked to original sources
PubMed1997

Dobutamine stress echocardiography in the elderly Asian patients.

Dobutamine stress echocardiography (DSE) is an established non-invasive technique for the evaluation of coronary artery disease (CAD). It has been shown to be both safe and accurate. However, its utility and safety in the elderly, in particular, elderly Asian patients has not been studied. Between September 1992 and December 1994, we performed a total of 75 consecutive DSE studies in patients over the age of 65. Of these, 50 (67%) were females. Forty-nine patients had hypertension, 26 had diabetes mellitus, 10 were smokers, 5 had a recent or previous myocardial infarction and another 4 had a history of heart failure. Indications for DSE were, inability to perform the standard treadmill exercise test (40 patients), an abnormal resting electrocardiogram (ECG) (14 patients), a prior false positive or inconclusive treadmill test, risk stratification post myocardial infarction (4 patients) or preoperative cardiac evaluation (23 patients). The test was terminated in the majority of patients following attainment of the target heart rate. Atropine stimulation was required in 61 (81%) patients. Chest pain was provoked in 11 patients. No death or myocardial infarction occurred. Minor non-cardiac symptoms occurred in another 6 patients but this did not necessitate termination of the procedure. Three patients had transient hypotension, none of which was symptomatic. Arrhythmia occurred in 23 patients but the majority were isolated atrial or ventricular premature beats (20); 1 patient had atrial fibrillation and another developed transient junctional rhythm. Only one patient developed ventricular tachycardia but this was not haemodynamically significant and terminated easily with an intravenous dose of lignocaine. A conclusive result could be obtained in 72 (96%) patients. We concluded that DSE could be performed and interpreted in the majority of elderly Asian patients studied. Despite supplemental atropine, an aggressive dosing protocol and the inclusion of patients with a myocardial scar or history of heart failure, adverse effects were rare and often did not require any specific therapy.

Aged↗
PubMed1997

Electrocardiographic abnormalities in right ventricular infarction associated with right bundle branch block.

An 80-year-old woman with pre-existing complete right bundle branch block presented with severe chest pain. The 12-lead electrocardiogram, together with right-sided chest leads, showed complete right bundle branch block and ST segment elevation in leads II, III, aVF, V5, V6 and V4R to V6R. These electrocardiographic abnormalities indicate acute 'Q wave' inferolateral and right ventricular infarction coexisting with right bundle branch block.

Aged↗
PubMed1996

High-throughput plasmid mini preparations facilitated by micro-mixing.

We have developed a reliable high-throughput plasmid isolation system using a 96-well plate format. This system combines a novel glass bead micro-mixing method with modified alkaline lysis and Sephacryl S-500 DNA purification procedures. Mechanical forces generated by vortexing glass beads inside each well of the 96-well plates ensure that the bacterial pellets are homogeneously resuspended, the cells are completely lyzed, and the resulting bacterial lysates are thoroughly mixed with the potassium acetate solution. The vortexing speed and duration for glass bead mixing have been standardized to facilitate plasmid DNA yields without significant adjustments.

Cells, Cultured↗
PubMed1996

Dobutamine stress echocardiography: angiographic correlates.

We started a dobutamine stress echocardiography (DSE) programme in September 1992. Until January 1994, we had performed 300 such procedures. Of these patients, 81 underwent cardiac catheterisation within 6 months of DSE without a cardiac event in the interim. Eleven DSEs were performed to assess myocardial viability and another 6 were inconclusive for myocardial ischaemia. The remaining 64 were correlated with the angiographic data to determine the utility of this technique in our institution. The mean age of the cohort was 57 years. Thirty-six patients were referred for DSE in the workup for chest pain, either anginiform (22) or atypical (14). Fourteen patients had a recent (6) or remote (8) myocardial infarction. Thirteen patients were asymptomatic. Significant obstructive coronary artery disease (CAD) was identified in 36 patients of whom 17 and 19 had single and multivessel disease respectively. The sensitivity of DSE in the entire cohort was 89% and the specificity 82%. Positive and negative predictive values of DSE were 86% and 85% respectively. Although the numbers involved were small, sensitivity figures for single and multivessel disease were 94% and 84% respectively. Of the patients with single vessel CAD, prediction of the artery involved by presumed territorial supply was accurate in 81%. DSE is a highly accurate tool for evaluating CAD, identifying both the patient with CAD and the location of disease.

Adrenergic beta-Agonists↗
PubMed1995

A telemedicine system for high-quality transmission of paper electrocardiographic reports.

To overcome problems associated with the faxing of ECGs, we developed a telemedicine system providing fast transmission of ECGs between physicians and cardiologists at different locations. It digitized ECGs at a resolution of 300 dots/inch (118 dots/cm), processed them, and transmitted them over a standard telephone line in under one minute. The system also paged the cardiologist in order to direct him or her to the location where the ECG would be waiting for interpretation. The system enabled physicians at remote locations to consult using voice, images and simultaneous cursor pointers. A transmitting site was set up at the Medical Centre of the Ministry of Defence and a receiving site at the National University Hospital, about 5 km away. During a six-month trial, 200 ECG reports were transmitted from one site to the other. They were rated excellent in quality by the cardiologists, being virtually indistinguishable from the originals. Our telemedicine system transmits high-quality ECGs rapidly and at low cost.

Algorithms↗
PubMed1994

Cutaneous Rosai-Dorfman disease presenting as a suspicious breast mass.

Cutaneous Rosai-Dorfman disease in a male patient presented as a clinically malignant left breast mass. The intra-operative frozen section indicated a benign inflammatory lesion and a simple excision was performed. The disease was apparently limited to the skin and subcutis of the left breast with no lymph nodes or other organs involvement. While the lesion demonstrated the characteristic morphology of Rosai-Dorfman disease, the diagnosis of granulomatous mastitis, epithelioid sarcoma and other cutaneous xanthohistiocytic proliferations were considered. In the absence of lymphadenopathy, a high index of diagnostic awareness is required to recognize the uncommon, solitary cutaneous Rosai-Dorfman disease.

Adult↗
PubMed1993

Minimal replication origin of the 200-kilobase Halobacterium plasmid pNRC100.

We have identified the replication origin of pNRC100, a 200-kb plasmid of Halobacterium halobium, by assaying for replication ability of miniplasmids containing cloned fragments of pNRC100 and the mevinolin resistance selectable marker of Haloferax volcanii. First, we showed the replication ability of plasmid pNGHCMEV1, which contains the 19-kb HindIII-C fragment of pNRC100, by recovery of plasmid DNA from mevinolin-resistant transformants of H. halobium. The minimal replication origin of approximately 3.9 kb was defined by subcloning successively smaller regions of pNGHCMEV1 and assaying for plasmid replication in either H. halobium or H. volcanii. The same replication origin was also recovered after transformation of H. volcanii with a library of partial Sau3AI fragments of pNRC100. The nucleotide sequence of the minimal replication origin was determined and found to contain a long open reading frame, named repH, transcribed away from a highly A+T-rich region. The transcription start site was identified by primer extension analysis to be 17 to 18 nucleotides 5' to a putative repH start codon. The predicted product of the repH gene, an acidic protein with a molecular weight of 113,442, showed 24 to 27% identity with predicted gene products of H. volcanii plasmid pHV2 and H. halobium plasmid p phi HL, suggesting that each is involved in plasmid replication. One pNRC100 minireplicon, pNG11 delta 12, was analyzed by linker scanning mutagenesis, which showed the requirement of repH for replication. Restoration of the repH reading frame of one replication-defective pNG11 delta 12 derivative by introduction of a second small insertion resulted in reversion to replication proficiency. The replication ability of pNG11delta12 was lost when the entire A+T-rich region, about 550 bp long, was deleted but not when small insertions or deletions were introduced into this region. The presence of only 52 bp of the A+T-rich segment was sufficient to permit replication. The pNG11delta12 minireplicon was lost at high frequency from cells grown without mevinolin selection, suggesting that the plasmid partitioning locus of pNRC100 is absent in the minimal replication origin region. We discuss the possible roles of the repH gene and the A+T-rich region in replication of pNRC100.

Amino Acid Sequence↗
PubMed1992

Genetic transformation of a halophilic archaebacterium with a gas vesicle gene cluster restores its ability to float.

The halophilic archaebacterium, Halobacterium halobium, and many other aquatic bacteria synthesize gas-filled vesicles for flotation. We recently identified a cluster of 13 genes (gvpMLKJIHGFEDACN) on a 200-kb H. halobium plasmid, pNRC100, involved in gas vesicle synthesis. We have cloned and reconstructed the gvp gene cluster on an H. halobium-E. coli shuttle plasmid. Transformation of H. halobium Vac- mutants lacking the entire gas vesicle gene region with the gvp gene cluster results in restoration of their ability to float. These results open the way toward further genetic analysis of gas vesicle gene functions and directed flotation of other microorganisms with potential biotechnological applications.

Archaeal Proteins↗
PubMed1991

Amelioration of gentamicin nephrotoxicity by phospholipids.

The effect of phospholipids on gentamicin-induced nephrotoxicity was studied in Sprague-Dawley rats. Group 1a (5 rats) were given daily intraperitoneal injections of 100 mg/kg of gentamicin and sacrificed on day 7. Group 1b (10 rats) were similarly treated but were sacrificed on day 14. Group 2a (5 rats) were given 30 mg/kg of phospholipids for 6 days and sacrificed on day 7, serving as phospholipid controls. Group 2b (5 rats) were similarly treated, and from day 7 onwards daily intraperitoneal injections of 100 mg/kg of gentamicin were given while oral phospholipids were continued until the rats were sacrificed 7 days after gentamicin treatment. Group 2c (10 rats) were treated in the same manner as group 2b but the animals were sacrificed on day 28 after gentamicin treatment. Group 3 (10 rats) were given 30 mg/kg of phospholipids concurrently with intraperitoneal gentamicin injections and were sacrificed on day 28. Protein concentrations, N-acetyl-beta-glucosaminidase (NAG) activities and creatinine were measured in 24-h urine samples. Serum creatinine concentrations were measured in blood samples and 24-h creatinine clearance calculated. Gentamicin concentrations were determined in kidney tissues from which sections were also taken for light- and electron-microscopy. Results showed that gentamicin induced a marked increase in NAG and protein excretion, and a marked decrease in creatinine clearance with six rats succumbing to uraemia. Phospholipid treatment, whether started before or concurrently with gentamicin injections, reduced gentamicin-induced nephrotoxicity. The rats did not lose weight. Urinary excretion of NAG and protein was significantly reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylglucosaminidase↗
PubMed1991

Structure of the gas vesicle plasmid in Halobacterium halobium: inversion isomers, inverted repeats, and insertion sequences.

Halobacterium-halobium NRC-1 harbors a 200-kb plasmid, pNRC100, which contains a cluster of genes for synthesis of buoyant gas-filled vesicles. Physical mapping of pNRC100 by using pulsed-field gel electrophoresis showed the presence of a large (35 to 38-kb) inverted repeat (IR) sequence. Inversion isomers of pNRC100 were demonstrated by Southern hybridization analysis using two restriction enzymes, AflII and SfiI, that cut asymmetrically within the intervening small single-copy region and the large single-copy region, respectively, but not within the large IRs. No inversion isomers were observed for a deletion derivative of pNRC100 lacking one IR, which suggests that both copies are required for inversion to occur. Additionally, the identities and approximate positions of 17 insertion sequences (IS) in pNRC100 were determined by Southern hybridization and limited nucleotide sequence analysis across the IS element-target site junctions: ISH2, a 0.5-kb element, was found in four copies; ISH3, a 1.4-kb heterogeneous family of elements, was present in seven copies; ISH8, a 1.4-kb element, was found in five copies; and ISH50, a 1.0-kb element, was present in a single copy. The large IRs terminated at an ISH2 element at one end and an ISH3 element at the other end. pNRC100 is similar in structure to chloroplast and mitochondrial genomes, which contain large IRs and other large halobacterial and prokaryotic plasmids that are reservoirs of IS elements but lack the large IRs.

Base Sequence↗
PubMed1989

Analysis of insertion mutants reveals two new genes in the pNRC100 gas vesicle gene cluster of Halobacterium halobium.

The archaebacterium, Halobacterium halobium, achieves buoyancy through synthesis of intracellular gas-filled vesicles. The plasmid-encoded gene (gvpA) specifying the major structural gas vesicle protein has previously been cloned and sequenced allowing the analysis of high-frequency mutations to the vesicle negative phenotype. Among eighteen gas vesicle mutants analyzed, four were observed to contain insertion elements 0.2 to 2 kb upstream of the structural gene. To explain the phenotype of these mutants, the upstream area was analyzed by DNA sequencing and transcriptional mapping. This analysis showed the presence of two open reading frames, gvpD and gvpE, which are of opposite transcriptional orientation to gvpA (gene order gvpA-D-E). gvpD begins 201 nucleotides from the gvpA structural gene and is 1608 nucleotides long while gvpE begins two nucleotides from the 3'-end of gvpD and is 573 nucleotides long. Primer extension analysis showed the occurrence of divergent promoters in the gvpA-gvpD intergenic region with the transcription start sites separated by 109 nucleotides. The sites of three insertion sequences in gas vesicle mutants mapped within gvpE while the fourth insertion site mapped near the N-terminal coding region of gvpD. Homology between the gvpDE gene region and a chromosomal site in a H. halobium NRC-1 derivative and in several other Halobacterium strains was identified by Southern hybridization.

Amino Acid Sequence↗
PubMed1987

Zinc-deficiency and the development of malignant lymphoma in rats given a single intragastric dose of N-methyl-N-nitrosourea.

Zinc-deficient rats that had received a single dose of N-methyl-N-nitrosourea (MNU) intragastrically developed malignant lymphomas involving the liver, spleen, lung and kidney, as well as the usual epithelial tumours at the site of administration. Interestingly, the incidence of squamous-cell carcinoma of the pharynx was significantly higher in zinc-deficient rats than in control animals. Since MNU does not require metabolic activation, the development of the malignant lymphomas might be related to the generally depressed immunological state of zinc-deficient rats.

Animals↗
PubMed1986

Enumerating T-cell subsets on blood smears. An evaluation of an indirect immunoalkaline phosphatase method.

Peripheral blood T-lymphocyte subsets in 179 Chinese subjects were enumerated by an indirect immunoalkaline staining method done on ordinary blood smears. Absolute counts (X 10(9)/L) were 1.32 +/- 0.53 (T11), 0.73 +/- 0.31 (T4), 0.45 +/- 0.22 (T8) for males (n = 135) and 1.22 +/- 0.39 (T11), 0.69 +/- 0.20 (T4), 0.44 +/- 0.19 (T8) for females (n = 44). T4:T8 ratio for males and females were 1.79 and 1.58, respectively (0.05 less than P less than 0.10). Within-film area-to-area difference was 4.2 +/- 2.1% (n = 537 films). Interobserver discrepancy was 54 per 3,000 cells counted, or 1.8%. Film-to-film difference was 5.4 +/- 2.6% (30 pairs). T-lymphocyte subsets enumeration by immunostaining blood smears is a simple and reliable alternative to the immunofluorescence method. It avoids procedures that could artifactually affect lymphocyte subsets. The lower T4:T8 ratios revealed in this study could result because of technical reasons.

Adolescent↗
PubMed1986

Clinical and histopathological predictors of progressive disease in IgA nephropathy.

The clinical course and biopsy findings of twenty-one patients with IgA nephropathy, followed up for a mean period of 37.4 mth (range 24-54 mth) after diagnosis, were reviewed retrospectively to determine whether the clinical presentations, the laboratory findings or histopathologic changes have prognostic implications. An age of 24 yr or above and a serum creatinine of 0.18 mmol/l or above at diagnosis correlated significantly with renal insufficiency at the end of the follow-up (P = 0.023 & 0.03). Proteinuria of 1.5 g/d or more and hypertension (systolic greater than 150 mmHg or diastolic greater than 100 mmHg) when well controlled, were not found to be significant. Asymptomatic proteinuria and gross hematuria, on the other hand, correlated negatively with renal insufficiency at the end of the follow up (P = 0.034). With respect to histopathological changes, greater than 30% global glomerular sclerosis and moderate or marked tubular atrophy correlated significantly with renal insufficiency (P = 0.005 and 0.005). However, less than 10% glomerular crescents, small amounts of mesangial electron dense deposits or absent ultrastructural peripheral glomerular capillary wall abnormalities correlated negatively with renal insufficiency (P = 0.017, 0.03 & 0.03).

Adolescent↗
PubMed1985

A shared antigenic determinant between human B lymphocytes and carcinomas (BLCa).

We have raised a murine IgM monoclonal antibody (MA6) against immunoprecipitate obtained by reacting the serum of an NPC patient with extract of the Burkitt lymphoma cell line, Raji. It reacts against an antigen (BLCa) which is broadly represented on human B lymphoid tissues and cell lines but is different from the functional B-cell markers such as surface immunoglobulins, Ia products, Fc and complement receptors. BLCa was found to occur on lymphoid cell lines representing all stages of B-cell differentiation. These included the pre-B and null-cell lines, Nalm 6 and Reh, the EBV-transformed lymphoid cell lines and the myeloma cell line. MA6 was reactive against all the Burkitt lymphoma cell lines, whether or not these harbored the EBV genomes, with the exception of P3HR-I. The antibody was found to be selectively reactive against a proportion of peripheral blood B lymphocytes and to stain the B-cell-rich primary follicles and mantle zones of secondary follicles in the lymph node. However, MA6 was not reactive against cell lines of T-lymphocyte, myeloid, monocyte fibroblast or epithelial origin. It did, nevertheless selectively stain tumor cells from a variety of carcinoma tissues originating from different anatomical sites, including the nasopharynx.

B-Lymphocytes↗