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Biomedical subjects

Y C Chan

Publications and source records attributed to Y C Chan.

At least 55 records · Page 3Linked to original sources
PubMed2000

Characterisation and source identification of PM10 aerosol samples collected with a high volume cascade impactor in Brisbane (Australia).

PM10 (particulate matter with aerodynamic diameter < 10 microm) samples of Brisbane air were collected and fractionated into six size fractions (< 0.5, 0.5-0.61, 0.61-1.3, 1.3-2.7, 2.7-4.9 and 4.9-10 microm) with a high volume cascade impactor. The chemical composition of the samples was analysed by techniques including Ion Beam Analysis. On average, 42% of the aerosol mass is in the > 2.7-microm size fraction, with the < 0.5-microm size fraction also contributes 41% of the aerosol mass. The composition of the < 1.3-microm aerosols is significantly different to that of the > 1.3-microm aerosols. The aerosol mass and concentrations of chemical components related to human activities show a bimodal size-distribution pattern, with most of the mass in the accumulation range (< 0.65 microm). The size geometric mean of aerosol mass is 0.96 microm in the samples collected from an industrial/residential site, and is 1.74 microm in the samples collected from a suburban site. The size geometric mean of concentrations of chemical components related to human activities ranges from 0.16 to 0.57 microm. The concentrations of crustal matter and sea salt show a unimodal size-distribution pattern, and with geometric means of 3.73 and 4.12 microm, respectively. Four source factors were resolved by multivariate analysis techniques for the size-fractionated aerosol samples, namely the soil, sea salt, organics and vehicular exhausts factors. The source fingerprints of the factors vary in the size ranges and have implications on the formation and dispersal processes of the particles. On average, the soil and sea salt factors contribute more than 80% of the aerosol mass in the > 2.7-microm fractions, while the organics and vehicular exhausts factors explain almost all the aerosol mass in the < 0.61-microm fractions.

Aerosols↗
PubMed2000

Photoinduced dehydrogenation of defects in undoped a-si:H using positron annihilation spectroscopy.

We report changes in variable-energy positron annihilation spectroscopy measurements on undoped hydrogenated amorphous silicon films after light soaking. The change, seen predominantly in the high momentum band of the annihilation radiation, is not reversed by thermal annealing. We suggest, following recent models of the Staebler-Wronski effect, that light exposure induces hydrogen trapped in vacancylike defects to become mobile in the Si network. The observations place constraints on models of hydrogen motion fitting macroscopic Staebler-Wronski effect kinetics and may help to achieve a definitive description of metastability in a-Si:H.

Journal Article↗
PubMed2000

Warfarin induced skin necrosis.

BACKGROUND: Warfarin induced skin necrosis is a rare complication with a prevalence of 0.01-0.1 per cent. It was first described in 1943. METHODS: A literature review was undertaken using Medline; all relevant papers on this rare compli-cation of warfarin therapy were used. RESULTS: There are several adverse skin manifestations associated with the use of oral anticoagulants, ranging from ecchymoses and purpura, haemorrhagic necrosis, maculopapular vesicular urticarial eruptions to purple toes. This article concentrates mainly on warfarin induced skin necrosis. The syndrome typically occurs during the first few days of warfarin therapy, often in association with the administration of a large initial loading dose of the drug. Although the precise nature of the disease is still unknown, advances in knowledge about protein C, protein S and antithrombin III anticoagulant pathways have led to a better understanding of the mechanisms involved in pathogenesis. Differential diagnosis between warfarin induced skin necrosis and necrotizing fasciitis, venous gangrene and other causes of skin necrosis may be difficult; the disease may also be confused with other dermatological entities. CONCLUSION: Warfarin induced skin necrosis, while rare, is an important complication. All surgeons should be aware of its existence.

Anticoagulants↗
PubMed2000

Systemic lupus erythematosus presenting initially as hydrogen ATPase pump defects of distal renal tubular acidosis.

Tubulointerstitial involvement is well recognized in systemic lupus erythematosus. The tubular dysfunction is usually latent and usually presents after diagnosis of systemic lupus erythematosus. We report a case presenting that she is well previously and initially diagnosed as periodic paralysis of hypokalemia at emergency room and final diagnosis is systemic lupus erythematosus with H+-ATPase pump defect of distal type renal tubular acidosis. Kidney biopsy showed lupus nephritis classified as mesangial proliferative glomerulonephritis WHO class II B. Her renal tubular acidosis was subsided after steroid therapy was administered.

Acidosis, Renal Tubular↗
PubMed2000

A nucleoside-nucleotide mixture may reduce memory deterioration in old senescence-accelerated mice.

We investigated the effects of a mixture of dietary nucleosides and nucleotides (NS + NT) on memory in 1- and 7-mo-old senescence-accelerated mice (SAM). Memory retention was studied with passive avoidance (step-through) and active avoidance (shuttle) tests. For 14 wk, mice in the control groups were fed a 20 g of casein/100 g diet, whereas the NS + NT groups were fed this diet supplemented with a 0.5 g of NS + NT mixture/100 g. All mice were killed at wk 14, and we studied the brain histopathology. Lipofuscin, monovacuoles and multiple vacuoles of various brain regions were measured. Body weight, food intake and ambulatory activity did not differ between the control and NS + NT groups. In old mice, the time of passive avoidance was significantly higher in the NS + NT group than in the control group at d 1 and 7 (P: < 0.05). However, such an effect of NS + NT was not observed in young mice. In the active avoidance test, the incidence of successful avoidance in old mice was higher in the NS + NT group than in the control group at d 1 and 2 (P: < 0.05). The percentages of specific brain cells containing lipofuscin were lower in NS + NT groups than in the control groups in both young and old mice (P: < 0.05). The number of monovacuoles and multiple vacuoles in specific brain regions tended to be lower (P: = 0.1-0.25) in NS + NT than in control groups, with significant differences in the microvacuoles of the middle cortex of young mice and in the multiple vacuoles in the hind cortex of old mice (P: < 0. 05). These results suggest that increased dietary NS + NT may be associated with decreases in the age-induced deterioration of brain morphology and certain memory tasks.

Age Factors↗
PubMed1999

Contact leukomelanosis induced by the leaves of Piper betle L. (Piperaceae): a clinical and histopathologic survey.

BACKGROUND: In April 1997, an unusual pigmentary disorder was noticed by dermatologists in Taiwan. All patients had a history of using facial dressings with steamed leaves of Piper betle L. (Piperaceae). OBJECTIVE: Our purpose was to clarify the evolution and the origin of this unique leukomelanosis. METHODS: Fifteen patients with an unusual pigmentary disorder, who visited our clinic in September and October 1997, were asked to complete a questionnaire designed to elicit the history related to the disorder. Eight of these 15 patients underwent skin biopsies: 6 on the mottled hyperpigmented area (group A) and 2 on the hypopigmented area (group B). All 8 specimens were prepared with hematoxylin-eosin, Masson-Fontana, and S-100 stains. RESULTS: The results of the questionnaire revealed that these patients had all experienced a temporary erythematous reaction in the first few days of the use of the facial dressing, and 9 of them also complained of an accompanying stinging sensation. A bleaching effect became noticeable approximately 1 week to 1 month later. Eight patients reported that the hyperpigmentation and confetti-like hypopigmentation occurred after overexposure to the sun. In both groups, histopathologic examination revealed some melanophages in the dermis. Masson-Fontana staining of specimens from group A showed local interspersed depigmentation and hyperpigmentation in the basal epidermis and pigmentary incontinence in the dermis. This picture was different from the homogeneous depigmentation within basal epidermis in specimens from group B. In both groups, S-100 staining was negative for melanocytes in the depigmented area. CONCLUSION: The clinical course and histopathologic findings suggest that the evolution of this pigmentary disorder can be divided into 3 stages. The first stage is the immediate bleaching stage, when an irritant reaction is usually conspicuous. The second stage consists of prominent hyperpigmentation visible both grossly and microscopically. The final stage is characterized by confetti-like depigmentation. It may be induced by chemicals in the betel leaves such as phenol, catechol, and benzene derivatives, perhaps through inhibition of melanin synthesis or melanocytotoxicity.

Adult↗
PubMed1999

Anti-heat-shock protein 70 kDa antibodies in vascular patients.

INTRODUCTION AND AIM OF STUDY: there is recent evidence that the immune system plays an essential role in the pathogenesis of atherosclerosis, with both cellular and humoral mechanisms being involved. Heat-shock proteins (HSPs) have been detected in atherosclerotic lesions, and antibodies to HSPs have also been found to be raised in patients with carotid stenoses. The aim of our study was to examine the level of anti-HSP70 antibodies in patients with other vascular diseases. MATERIALS AND METHODS: a questionnaire was designed for the subjects in the study, with documentation of clinical details and ankle-brachial pressure index. Patients with concomitant infection, malignancy, hepatorenal failure, or recent surgery were excluded. Enzyme-linked immunosorbent assay (ELISA) was used to identify anti-HSP70 antibodies in the sera in different dilutions. Graphs of optical density (OD) vs. negative log dilution were plotted, the gradient of which was taken to be the estimated optical density for each subject (proportional to antibody level). Our groups consisted of controls (n =21, mean age 59.0+/-19.2), lower limb claudicants ( n =19, mean age 60.0+/-12.6), patients with lower-limb critical ischaemia ( n =22, mean age 68.5+/-10.07), and patients with abdominal aortic aneurysms ( n =20, mean age 69.9+/-6.2). RESULTS: we found no correlation between age and the estimated OD in our subjects (Spearman's correlation coefficient ( r )=0.123, one-tailed p value was 0.135). Patients with intermittent claudication, critical lower limb ischaemia, and aneurysms had higher estimated OD, and therefore higher anti-HSP70 antibody levels, than controls (Mann-Whitney test p =0.0127, 0.0037, 0.0008, respectively). CONCLUSIONS: our data provide the first evidence of a correlation between anti-HSP70 antibodies and different types of vascular diseases, suggesting that HSP70 might be involved in the pathogenesis and propagation of atherosclerosis. Since the immune response to HSPs can be modulated, this opens up the possibility of new therapeutic approaches.

Adult↗
PubMed1999

Weight satisfaction and dieting practices among college males in Taiwan.

OBJECTIVE: To obtain baseline data regarding body mass index (BMI), weight satisfaction and weight perception in male college students. Approaches used to lose weight and characteristics of dieters were also investigated. METHODS: Written questionnaires and height and weight measurements were used to collect data. Nine-hundred thirty male college students selected by multiple stage sampling among colleges in Taiwan participated in this study. Simple frequency and ANOVA were used to analyze data. Post hoc analyses were performed with the LSD test when the F ratio for the ANOVA was significant at p<0.05. RESULTS: The mean BMI for all subjects was 21.7. Males with a BMI < or =22.5 are considered thin by Taiwanese and world standards. Yet 34% of these males were attempting to lose weight and 14% percent perceived themselves as either overweight or obese. Exercise was the main approach to losing weight for subjects in all weight categories. Subjects in the dissatisfied/dieting group tended to measure body weight more frequently (p<0.05), spent more time exercising and reading nutrition information (p<0.05) and skipped breakfast and lunch more frequently (p<0.05) than non-dieters. Male dieters ate fewer vegetables and less meat than non-dieters. CONCLUSIONS: Male college students had frequent misconceptions and dissatisfaction with their body weight. Behavioral characteristics among those dissatisfied with their weight indicate they are at risk for developing eating disorders.

Adult↗
PubMed1999

A comparison of anthropometry, biochemical variables and plasma amino acids among centenarians, elderly and young subjects.

OBJECTIVE: Aging health is associated with nutritional changes which are not well understood and were therefore evaluated in this study by comparing the nutritional status of centenarians and elderly (in their 70s) relative to young subjects. SUBJECTS: The participants were 27 young subjects (10 males, 17 females), 40 healthy elderly (20 males, 20 females) and 32 centenarians (9 males, 23 females). METHODS: The activities of daily living (ADL), height, weight, body mass index (BMI), biochemical variables (total protein, albumin, triglycerides as well as total, HDL, LDL and VLDL cholesterol) and plasma amino acid profiles were evaluated. RESULTS: Compared with young subjects, lower (p<0.05) height, weight, total protein, albumin and albumin/globulin (A/G) ratio and total cholesterol for centenarians and height, albumin and A/G ratio for elderly were observed in both genders. Total cholesterol of male centenarians was lower than in young and elderly subjects and total and LDL cholesterol concentrations of female elderly were higher than those of young and centenarian subjects. However, the cholesterol concentrations of all the centenarians were within the reference range. The ratios of essential amino acids to nonessential amino acids were significantly lower (p<0.05) in the centenarians than the young subjects. Clear changes in individual amino acids with aging were lower (p<0.05) branched chain amino acids and methionine and higher proline and cystine, which are similar to the amino acid profiles in liver deterioration. CONCLUSION: The results suggest that the centenarians had poor nutritional status, which may be due to their decreased metabolism and the possibility that only short, slender individuals with low lipids, protein and essential amino acids are those that tend to survive to be centenarians.

Activities of Daily Living↗
PubMed1999

Acute bereavement care in the emergency department: does the professional-supported volunteers model work?

The aims of our study were to study the early impact of bereavement and to evaluate the effectiveness of the bereavement care given by our multidisciplinary team to close relatives of a sudden death, measured by the intensity of grief reaction (Texas Revised Inventory of Grief). The study sample consisted of close relatives of patients certified dead at the accident and emergency department (AED) between March 1996 and February 1997. The relatives received immediate care at the AED and were supported continually by the members of the bereavement care team. The control sample (without acute bereavement care) consisted of close relatives contacted by the liaison nursing officer in the previous year. The intensity of grief reactions were assessed by the volunteer grief counsellors at 6 months. The mean score of the intensity of grief reactions were 41.8 and 34.6 in the control (n = 11) and study (n = 18) groups respectively among high risk sample (p = 0.04). However, in the low risk sample, the mean scores were 35.3 and 30.2 in the control (n = 18) and study (n = 25) groups respectively (p = 0.11). Our study suggests that the bereavement care was especially effective in reducing the intensity of the grief at 6 months in the high risk group.

Adolescent↗
PubMed1999

Atypical antipsychotics in older adults.

Psychotic symptoms are common in older adults and reflect a variety of psychiatric and medical conditions. Antipsychotic drugs form the core of the treatment of these symptoms; however, treatment of the elderly is complicated by a high frequency of comorbid medical illnesses, risk of side effects, and age-related changes in pharmacodynamics and pharmacokinetics. The superior safety and efficacy of atypical antipsychotics makes them first-line agents for managing psychotic patients with schizophrenia. Their uses now extend to other conditions such as schizoaffective disorders, delusional disorder, and mood disorders with psychotic features. Although the drugs have been studied extensively in young subjects, well-designed, double-blind, placebo-controlled studies are relatively lacking in the elderly. Our knowledge of their safety, efficacy and dosage in older adults is based on a few studies with small samples or extrapolated from studies of younger patients. Several psychiatric and medical conditions that are associated with psychotic symptoms in older people are reviewed, as well as how these patients may benefit from treatment with these agents.

Aged↗
PubMed1998

Recombinant dengue virus type 1 NS3 protein exhibits specific viral RNA binding and NTPase activity regulated by the NS5 protein.

The full-length dengue virus NS3 protein has been successfully expressed as a 94-kDa GST fusion protein in Escherichia coli. Treatment of the purified fusion protein with thrombin released a 68-kDa protein which is the expected molecular mass for the DEN1 NS3 protein. The identity of this protein was confirmed by Western blotting using dengue virus antisera. Two related activities of the recombinant NS3 protein were characterized, which were the binding of the protein to the 3'-noncoding region of the dengue virus RNA genome and NTPase activity. We demonstrated using a band shift assay that the DEN1 NS3 protein could form a complex with the stem-loop structure in the 3'-noncoding region (3'-NCR), although sites outside the stem-loop may also participate in binding. Using various unlabeled homopolymeric and heteropolymeric RNAs as competitors for binding, it was further shown that the DEN1 NS3 protein exhibits preferential binding to a 94-nt RNA transcript from the 3'-NCR of the dengue virus. The NTPase activity of the recombinant DEN1 NS3 protein was characterized using a thin-layer chromatography assay. We found that the DEN1 NS3 protein possesses some aspects of NTPase activity, which are distinct from those found in other flaviviruses. Although the NS3 protein was able to utilize all four ribonucleoside triphosphates as its substrates, the NS3 protein showed a distinct preference for purine triphosphates (i.e., ATP and GTP). The addition of poly(U) did not stimulate NTPase activity in DEN1 NS3 protein, which contrasts with the reports for other flaviviral NS3 proteins. However, NTPase activity was specifically stimulated by the viral NS5 protein, which was manifested by a more than twofold increase in the rate of ATP hydrolysis and a 25% increase in the yield of ADP at the end of a 120-min reaction. These data suggest that the NTPase activity of the NS3 protein may be regulated by the viral NS5 protein during virus replication.

Adenosine Triphosphatases↗
PubMed1998

Monitoring of dengue viruses in field-caught Aedes aegypti and Aedes albopictus mosquitoes by a type-specific polymerase chain reaction and cycle sequencing.

Virologic surveillance for dengue through the detection of the prevalent serotype(s) circulating in the human population during inter- and intra-epidemic periods constitutes a reliable sentinel system for dengue outbreaks. We have applied a rapid and sensitive, semi-nested, reverse transcription-polymerase chain reaction (RT-PCR) assay using nonstructural protein 3 gene primers for the type-specific-detection of dengue viruses in artificially infected and in field-caught adult Aedes mosquitoes. In laboratory experiments, the assay was sensitive enough to detect one virus-infected mosquito head in pools of up to 59 uninfected heads. In a prospective field study conducted from April 1995 to July 1996, female adult Ae. aegypti and Ae. albopictus mosquitoes were caught from selected dengue-sensitive areas in Singapore and assayed by RT-PCR. Approximately 20% of 309 mosquito pools were positive for dengue viruses. Of the 23 RT-PCR-positive Ae. aegypti pools (containing 1-17 mosquitoes each), 18 pools (78.3%) were positive for dengue 1 virus. There were 40 RT-PCR-positive Ae. albopictus pools (containing 1-33 mosquitoes each) of which 31 (77.5%) were positive for dengue 1 virus. The predominant virus type responsible for the current dengue epidemic since 1995 was also dengue 1. The geographic locations of the virus-infected mosquitoes correlated with the residences or workplaces of patients within dengue outbreak areas. A total of 43.5% of the positive Ae. aegypti pools and 25.0% of the positive Ae. albopictus pools contained only a single mosquito. Both Aedes species showed similar overall minimum infection rates of 57.6 and 50 per 1,000 mosquitoes. Infected Ae. aegypti were detected as early as six weeks before the start of the dengue outbreaks in 1995 and 1996. However, infected Ae. albopictus appeared later, when the number of cases was increasing. Virologic surveillance by RT-PCR for detecting dengue virus-infected Aedes mosquitoes in the field may serve as an early warning monitoring system for dengue outbreaks.

Aedes↗
PubMed1998

Microsurgical management of intracranial epidermoid cysts.

BACKGROUND: Intracranial epidermoid cysts are slow-growing congenital neoplasms that usually spread and adhere to critical neurovascular structures along the basal cistern, particularly the cerebellopontine angle (CPA) and parasellar region. Clinical symptoms include trigeminal neuralgia, headache and dizziness, progressive hemiparesis, unstable gait and hemifacial spasm. With the aid of modern imaging techniques, such as computed tomography (CT) and magnetic resonance imaging (MRI), an effective microsurgical approach can be planned preoperatively to completely remove tumors and avoid complications. METHODS: Twenty-six patients with intracranial epidermoid cysts were microsurgically treated between July 1984 and June 1997. Diagnostic procedures included enhanced CT and/or CT cisternography and MRI. All patients underwent microsurgical treatment for tumor removal. RESULTS: Total tumor removal was achieved in 12 patients (46.2%), near-total removal in seven (26.9%), partial removal in six (23.1%) and stereotactic biopsy in one patient (3.8%). Postoperative deterioration of the neurologic condition was found in three patients who required further surgery, aseptic meningitis in four patients and communicating hydrocephalus requiring shunting in three patients. The functional prognoses were excellent in 23 patients (88.5%), good in two patients (7.7%) and fair in one patient (3.8%). Among the 26 patients, three died of pneumonia three, six and nine months after surgery, respectively. CONCLUSIONS: MRI is particularly useful for defining the anatomic limits of tumor tissue and surgical planning. The surgical results were excellent in patients with near-total tumor removal, as well as in patients with total removal. Aggressive surgical tumor removal may result in transient, but significant, cranial nerve palsy and should be avoided. Perioperative administration of steroids and wound protection may be beneficial for preventing the development of postoperative aseptic meningitis and hydrocephalus.

Adult↗
PubMed1997

Thromboembolism prophylaxis during laparoscopic cholecystectomy.

BACKGROUND: The aim of this study was to determine current UK practice with regard to thromboembolism prophylaxis during laparoscopic cholecystectomy. METHODS: Postal questionnaires were sent to 800 members of the Association of Surgeons; replies were received from 551 surgeons (69 per cent) of whom 417 practised laparoscopic cholecystectomy. RESULTS: Heparin was prescribed to all patients by 74 per cent, and selectively by 20 per cent, of respondents. Surgeons who performed fewer than ten laparoscopic cholecystectomies per annum were significantly less likely to use heparin (P < 0.001) and more likely to believe that heparin produces significant adverse bleeding (P < 0.01). Thirty per cent of respondents used low molecular weight heparin. Stocking to deter thromboembolism were used by 74 per cent, and pneumatic compression by 37 per cent. Indications for heparin varied considerably and were not influenced by Thromboembolic Risk Factors (THRIFT) guidelines. Only 20 per cent of respondents considered that thromboembolism was a problem; 91 per cent reported that they had never experienced a thromboembolic complication following laparoscopic cholecystectomy. CONCLUSION: The rate of thromboembolism after laparoscopic cholecystectomy is unknown but most surgeons believe the risk is very low. Surgeons' attitudes towards thromboembolism prophylaxis are variable, but most experienced surgeons use low-dose heparin.

Adult↗
PubMed1997

The production of recombinant dengue virus E protein using Escherichia coli and Pichia pastoris.

The dengue virus envelope protein was expressed as a GST fusion protein using E. coli and P. pastoris as expression hosts. In E. coli the recombinant E protein is expressed initially as a soluble 81 kDa GST fusion protein. Treatment of the fusion protein with thrombin released a 55 kDa protein, which is the expected size for correctly processed, non-glycosylated recombinant E protein. The antiserum from animals immunised with this recombinant E protein was found to specifically recognise the dengue virus E protein in virus-infected cells, thus demonstrating the immunogenic nature of the recombinant E protein. This expression system allowed production of up to 2 mg of purified recombinant E protein from a 1 1 bacterial culture. In contrast, expression of this GST fusion protein in P. pastoris is associated with extensive proteolytic degradation of the recombinant E protein. However, this proteolytic degradation was not observed in the truncated E protein sequences which were expressed. One of these recombinant fusion proteins, GST E401 was secreted into the culture medium at levels of up to 100 microg/l of growth medium.

Animals↗