Search PubMed⌕ Search

Biomedical subjects

S G Tan

Publications and source records attributed to S G Tan.

At least 37 records · Page 2Linked to original sources
PubMed2000

Identification and characterization of Malaysian river catfish, Mystus nemurus (C&V): RAPD and AFLP analysis.

This work represents the first application of the amplified fragment length polymorphism (AFLP) technique and the random amplified polymorphic DNA (RAPD) technique in the study of genetic variation within and among five geographical populations of M. nemurus. Four AFLP primer combinations and nine RAPD primers detected a total of 158 and 42 polymorphic markers, respectively. The results of AFLP and RAPD analysis provide similar conclusions as far as the population clustering analysis is concerned. The Sarawak population, which is located on Borneo Island, clustered by itself and was thus isolated from the rest of the populations located in Peninsular Malaysia. Both marker systems revealed high genetic variability within the Universiti Putra Malaysia (UPM) and Sarawak populations. Three subgroups each from the Kedah, Perak, and Sarawak populations were detected by AFLP but not by RAPD. Unique AFLP fingerprints were also observed in some unusual genotypes sampled in Sarawak. This indicates that AFLP may be a more efficient marker system than RAPD for identifying genotypes within populations.

Animals↗
PubMed2000

Biochemical polymorphism in yellow catfish, Mystus nemurus (C&V), from Thailand.

Yellow catfish, Mystus nemurus (Cuv. & Val.), is becoming one of the major freshwater species farmed by aquaculturists in Southeast Asia. It was of interest to examine levels of genetic subpopulation differentiation among samples of this species obtained from parts of its range, as well as to compare the genetics of wild and hatchery-bred fish. Horizontal starch gel electrophoresis and histochemical staining techniques were used to examine genetic variation within and among eight wild and one hatchery populations of M. nemurus from northern, northeastern, central and southern Thailand. Four tissues (heart, liver, kidney, and muscle) from individual specimens were used to analyze variations at 23 protein-coding loci. Fifteen of the 23 loci examined (65.22%), namely, ACP*, AAT-1*, EST-1*, EST-2*, GPI*, IDH-1*, IDH-2*, MDH-1*, MDH-2*, MDH-3*, ME*, PGM*, 6PGD*, SOD*, and HB*, were polymorphic at the 0.95 level. Observed heterozygosities ranged from 0.041 to 0.111, with an average of 0.068 +/- 0.028. Genetic distances ranged from 0.005 to 0.164. The greatest genetic distance was found between the Chainat and the Suratthani populations (0.164), a level indicative of subspecific differentiation in M. nemurus from within Thailand.

Alleles↗
PubMed2000

Perioperative and rehabilitative outcomes after amputation for ischaemic leg gangrene.

INTRODUCTION: Amputation of the severely ischaemic leg is often done when limb salvage is not possible or the patient is not fit enough for it. It is therefore important to determine the natural history of these amputees as our understanding of this will have significant impact on decision making. The aim of this study was to determine the early and late morbidity and mortality rates and rehabilitative outcome of these patients with lower limb amputation for end-stage arterial occlusive disease. MATERIALS AND METHODS: A retrospective study was done on 72 patients with 77 lower limb amputations for critical limb ischaemia (rest pain, gangrene, ischaemic ulcers) from 1993 to 1998 at the Singapore General Hospital. RESULTS: The mean age of the amputees was 69.7 years. Fifty-one per cent of the patients were male. Forty-five (58%) of the amputations were performed because the limb vasculature was not reconstructable, 12 (16%) because the limbs were too late for salvage and the remaining 20 (26%) because vascular reconstruction failed. Below knee amputations account for 63.6% of all amputations, above knee amputations account for 35.1% and through knee amputations account for 1.3%. Fifteen (19%) of the amputations had wound infection and 8% of amputations required re-amputation at a higher level for wound infection or failure of wound healing. The contralateral amputation rate was 21%. The 30-day mortality for all amputations was 11.1% and the commonest cause was acute myocardial infarction which accounted for 37.5%. Vascular reconstruction did not alter the overall or perioperative mortality rate. Cumulative survival figures showed that at the end of four years, only 38% of all amputees were still alive. 52.5% of amputees were wheelchair-bound, only 15% were household ambulators and 27.5% were community ambulators. Of all the patients with unilateral below knee amputations, 40% could walk out of home while only 20% of unilateral above amputations and 12.5% of bilateral below knee amputations could walk out of home. CONCLUSION: Early and late rehabilitation after amputation for critical limb ischaemia remain poor and efforts should be made to salvage critically ischaemic limbs wherever possible in patients who are fit enough.

Adult↗
PubMed1999

Chronic haemodialysis with PTFE arterio-venous grafts.

BACKGROUND/AIM OF STUDY: End-stage renal failure (ESRF) patients requiring long-term haemodialysis need a durable vascular access. The arterio-venous fistula (AVF) with its long patency rate and low complication profile is usually the first choice procedure for vascular access creation. However when superficial veins are not suitable for AVF creation or have all been exhausted as a result of repeated AVF procedures, arterio-venous grafts (AVG) using polytetraflouroethylene (PTFE) to bridge arteries and veins is an alternative for provision of continued vascular access for haemodialysis. This study is a review of our experience in using PTFE AVGs for vascular access in patients requiring chronic haemodialysis. METHODS AND MATERIALS: A retrospective review was done on 92 grafts in 77 patients placed by 3 vascular access surgeons at the Singapore General Hospital from January 1989 to December 1994. RESULTS: There were 58 female and 19 male patients with a median age of 43 years (range 15-76 years). Twelve patients (16%) were diabetic and 6 patients (8%) had systemic lupus erythematosis requiring long-term steroids. Seventy-three percent of patients had up to 2 previous AVF creations before placement of AVG over the forearm (64%), upper arm (23%) or thigh (6.5%). Complications include graft infection (19), pseudoaneurysm formation (10), graft thrombosis (24), steal syndrome (1), venous congestion (1) and venous end stenosis (1). Diabetic status and long-term steroid therapy did not significantly increase the incidence of graft infection. The patency rates at 24 months and 36 months were 77% and 58% respectively. However serviceability rates were 61% at 2 years and 38% at 3 years mainly due to infective complications. CONCLUSION: PTFE AVGs offer reasonable patency and serviceability rates as a vascular access modality but in view of their complication profile, the native vein arteriovenous fistula should continue to be the first choice procedure for vascular access in patients requiring chronic haemodialysis.

Adolescent↗
PubMed1998

Artifacts induced by concomitant magnetic field in fast spin-echo imaging.

It has been observed that fast spin-echo (FSE) images with a large field of view (>40 cm) in certain directions exhibit unusual ghosting artifacts that cannot be eliminated with existing ghost removal methods. These artifacts have been related to a higher-order magnetic field perturbation (known as the concomitant field, or Maxwell field) concomitant to the linear imaging gradient, in accordance with the Maxwell equations V z B = 0 and V x B approximately 0. Several methods have been developed to eliminate or minimize the effects of the concomitant magnetic field by redesigning the FSE pulse sequences. In the slice-selection direction, the gradient waveforms are made symmetrical about the refocusing RF pulses wherever possible. Surrounding the first refocusing pulse, such symmetry cannot be achieved due to the slice-refocusing gradient, which is often combined with the left crusher. In this case, it is shown how crusher gradients can be reshaped to nullify the phase due to the concomitant field. In the phase-encoding direction, the gradient amplitude is reduced and its duration is prolonged. Artifacts due to the readout gradient are eliminated by reshaping the prephasing lobe, while keeping its area fixed. In all the three directions, the gradient waveforms are adjusted so that they have minimal overlap. Selected methods have been implemented on a clinical scanner, and typically reduce the ghost intensities in phantom and human images by a factor of 3.

Artifacts↗
PubMed1998

Genetic diversity of Asian water buffalo (Bubalus bubalis): mitochondrial DNA D-loop and cytochrome b sequence variation.

Swamp and river buffalo mitochondrial DNA (mtDNA) was sequenced for 303 bp of the cytochrome b gene for 54 animals from 14 populations, and for 158 bp of the D-loop region for 80 animals from 11 populations. Only one cytochrome b haplotype was found in river buffalo. Of the four haplotypes identified in swamp buffalo, one found in all populations is apparently ancestral both to the other swamp haplotypes and to the river haplotype. The phylogenetic relationships among the 33 D-loop haplotypes, with a cluster of 11 found in swamp buffalo only, also support the evolution of domesticated swamp and river buffalo from an ancestral swamp-like animal, most likely represented today by the wild Asian buffalo (Bubalus arnee). The time of divergence of the swamp and river types, estimated from the D-loop data, is 28,000 to 87,000 years ago. We hypothesise that the species originated in mainland south-east Asia, and that it spread north to China and west to the Indian subcontinent, where the rive type evolved and was domesticated. Following domestication in China, the domesticated swamp buffalo spread through two separate routes, through Taiwan and the Philippines to the eastern islands of Borneo and Sulawesi, and south through mainland south-east Asia and then to the western islands of Indonesia.

Animals↗
PubMed1998

Surgical reconstruction for mesenteric angina in a patient with infra-renal aortic occlusive disease--a case report and review.

Mesenteric angina is an uncommon condition which is underdiagnosed, or diagnosed too late when the patient has a mesenteric infarct. The preferred treatment is by surgical reconstruction. A case presented here illustrates the condition and the modifications necessary to reconstruct a completely occluded lower abdominal aorta in treating both mesenteric angina and claudication.

Aorta, Abdominal↗
PubMed1998

Early experience of limb salvage in critical leg ischaemia.

BACKGROUND: We report the retrospective review of 82 leg bypass grafts done in 79 patients who had critical leg ischaemia between May 1993 and November 1996. The mean age of the patients was 68 years (range 50 to 82). PATIENTS: There were 49 male and 35 female patients. Fifty-nine percent of the study population presented with gangrene, 33% had ischaemic ulceration and 58% had rest pain. Seventy-five percent of them were diabetics. Thirty-eight femoro-popliteal, 28 femoro-distal, 6 popliteal-distal, 5 pedal, 1 aorto-bifemoral, 3 axillo-bifemoral and 1 cross-over bypass grafts were done. RESULTS: The peri-operative mortality rate was 11.3% and 71% of patients were discharged with salvaged feet. Ninety percent of these legs were still viable 12 months after the operation.

Aged↗
PubMed1997

Genetic variation within and relationships among populations of Asian water buffalo (Bubalus bubalis).

Genetic variation at 53 protein-coding loci (25 polymorphic) was analysed for 17 water buffalo populations-12 swamp, three Lankan and two of the Murrah breed (river type), to determine the magnitude of genetic differentiation and the genetic relationships among the populations. In accord with previous cytological studies, the Lankan buffalo clearly are river type. Significant deviations from Hardy-Weinberg equilibrium were shown for a number of locus-population combinations, with all populations but one showing significant heterogeneity in these deviations among loci. By contrast, heterogeneity among populations for each locus was much less, indicating locus-specific deviations, which suggest selection affecting allele frequencies at some loci. There was significant genetic differentiation among populations of both the swamp and river types. The differentiation among the swamp populations may reflect the geography of south-east Asia and the presumed spread of the swamp buffalo through this region. Phylogenies derived from pairwise genetic distance estimates show the clear separation of swamp and river types, but the topology of the swamp populations shows rather poor consistency with their geographic locations. For at least one population (Australia), it is clear that bottleneck effects have distorted the phylogenetic topology. Average genetic distances for both the swamp and river types, as compared with previous studies of livestock breeds, show that the genetic differentiation of each of these sets of populations is of the same order of magnitude as that among well-recognized and established breeds of other species.

Animals↗
PubMed1997

Genetic diversity of Asian water buffalo (Bubalus bubalis): microsatellite variation and a comparison with protein-coding loci.

Twenty-one microsatellite loci in 11 populations of Asian water buffalo (eight swamp, three river type) were analysed and, within and among populations, genetic variability was compared with results from 25 polymorphic protein-coding loci. Within-population mean heterozygosity ranged from 0.380-0.615, approximately twice that estimated from the protein-coding loci (0.184-0.346). Only eight significant departures from Hardy-Weinberg equilibrium (involving four loci) were detected; global tests showed significant heterozygote deficiencies for these four loci. Non-amplifying alleles are likely to be segregating in some or all populations for one of these loci, and probably for the other three. There was significant differentiation between the swamp and river types of water buffalo, and among populations within each buffalo type. Estimates of theta (measure of population differentiation) for each locus for the eight swamp populations were all highly significant (mean theta = 0.168 +/- 0.018). Mean theta for protein-coding loci was not significantly different (0.182 +/- 0.041). The variance among protein-coding loci was significantly higher than among microsatellite loci, suggesting balancing selection affecting allele frequencies at some protein-coding loci. Genetic distances show clear separation of the swamp and river types, which were estimated to have diverged at least 10,000-15,000 years ago. The topology of the swamp populations' microsatellite tree is consistent with their geographical distribution and their presumed spread through south-east Asia. By contrast, the tree based on the protein-coding loci distances is quite different, being clearly distorted by a bottleneck effect in one population, and possibly in at least two others. As many domestic livestock breeds are possibly descended from small numbers of founders, microsatellite-based trees are to be preferred in assessing breed genetic relationships.

Alleles↗
PubMed1996

Diffusion weighted fMRI at 1.5 T.

Functional magnetic resonance imaging (fMRI) is capable of detecting task-induced blood oxygenation changes using susceptibility sensitive pulse sequences such as gradient-recalled echo-planar imaging (EPI). The local signal increases seen in the time course are believed to be due to an increase in oxygen delivery that is incommensurate with oxygen demands. To help isolate the sources of functional signal changes, the authors have incorporated various forms of diffusion weighting into EPI pulse sequences to characterize the apparent mobility of the functionally modulated protons. Results suggest that the majority of the functional signal at 1.5 T arises from protons that have apparent diffusion coefficients that are approximately four or five times higher than that of brain tissue. This implies that significant functional signal sources are either protons within the vascular space or protons from the perivascular space that is occupied by cerebrospinal fluid.

Adult↗
PubMed1995

Isozyme and morphological characteristics of the anaerobic fungus Piromyces mae isolated from the duodenum, rumen and faeces of sheep.

Isolates of anaerobic fungi obtained from the rumen, duodenum and faeces of sheep were identified as Piromyces mae based on their morphological characteristics observed using light microscopy. There was no significant morphological variation among the isolates of P. mae from the rumen, duodenum and faeces. Isozymes of 12 isolates of P. mae (one each from the rumen, duodenum and faeces from 4 different sheep) were analysed by PAGE. A total of 12 isozymes were studied and 5 isozyme loci were successfully typed. They were malic enzyme, malate dehydrogenase, shikimate dehydrogenase, alpha-esterase and beta-esterase. All the isolates of P. mae regardless of whether they were from the rumen, duodenum or faeces or from different animals produced very similar isozyme banding patterns for each of the enzyme systems. The similar isozyme profiles of the isolates indicate that they are of the same species although they exist in different regions of the alimentary tract.

Anaerobiosis↗
PubMed1995

A set of polymorphic DNA microsatellites useful in swamp and river buffalo (Bubalus bubalis).

DNA microsatellites have found widespread application in gene mapping, pedigree determination and population genetics. In closely related species such as bovids, heterologous polymerase chain reaction (PCR) primers may in some cases be used, bypassing the need to isolate and characterize microsatellite-containing sequences and design PCR primers. We report on the ability of a set of eighty bovine derived DNA microsatellite primers to amplify sequences in the two types (swamp and river) of water buffalo (Bubalus bubalis). Number of alleles and per cent heterozygosities in a large number of animals were determined on a subset of microsatellite loci selected on the robustness of the primers. These loci will form the basis of a set of polymorphic DNA markers for use in water buffalo.

Alleles↗
PubMed1995

Does routine gowning reduce nosocomial infection and mortality rates in a neonatal nursery? A Singapore experience.

A 1 year prospective study on routine gowning before entering a neonatal unit was conducted in a maternity hospital in Singapore. This study was done based on previous work by Donowitz, Haque and Chagla and Agbayani et al., as there have been no known studies done in Singapore. The aim of the study was to test the hypothesis that routine gowning before entering a neonatal nursery does not reduce nosocomial infection and mortality rate. A total of 212 neonates from the neonatal intensive care unit (NICU) and 1694 neonates from the neonatal special care unit (NSCU) were studied. Neonates admitted during the 1 year study were assigned to the gowning (control) and no routine gowning (trial) group on every alternate 2 months. The hospital infection control nurse provided data on nosocomial infection. The overall nosocomial infection rate in the NICU was 24% (25 of 104 admissions) during gowning periods compared to 16.6% (18 of 108 admissions) when plastic aprons were not worn before entry. In the NSCU, the overall infection rate was 1.5% (12 of 800 admissions) during gowning periods compared to 2.1% (19 of 894 admissions) when no gown was worn before entry. Results of the study found no significant differences in the incidences of nosocomial infection and mortality in the neonates. The cost of gowns used during the no routine gowning periods was S$2012.8 compared to S$3708 used during the routine gowning procedure. The investigators recommend that routine gowning before entering a neonatal unit is not essential and cost effective for the purpose of reducing infection. Rather the focus should be on adequate handwashing by all hospital personnel and visitors before handling neonates.

Cross Infection↗
PubMed1995

Resection and anastomosis of obstructed left colonic cancer: primary or staged?

A retrospective analysis of the treatment of 70 patients with obstructed left colonic cancer was undertaken in order to assess whether staged or primary resection was more appropriate. Thirty-four patients had initial colostomy and staged resection (group 1) while 36 patients were treated by primary resection and immediate anastomosis following intra-operative bowel washout (group 2). There were seven deaths (10%), five in group 1 and two in group 2. The wound infection rate and average hospital stay were 44% and 36 days in group 1 and 19.4% and 16.5 days in group 2, respectively. Twenty per cent of patients in group 1 did not complete their staged procedures and had to live with their colostomies. The smoother postoperative recovery and shorter hospital stay was particularly significant in group 2 patients. As primary resection and anastomosis can now be performed with relative safety and reduced morbidity, we conclude that staged procedures can no longer be accepted as standard treatment for left colonic obstruction.

Anastomosis, Surgical↗
PubMed1995

PCR cycle sequencing protocol for population mitochondrial cytochrome b analysis.

Laboratories intending to adopt cycle sequencing of PCR products in their routine analysis often face a confusing range of methods and kits. Through the study of mitochondrial cytochrome b, we have shown that clean and highly reproducible sequences could be obtained by using a combination of existing simple and economical methods in the preparation of DNA templates, PCR, purification of PCR products and sequencing. Our protocol is useful in itself or as a standard in typing other PCR-amplified DNA at the population level.

Animals↗