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Biomedical subjects

K H Chan

Publications and source records attributed to K H Chan.

At least 73 records · Page 4Linked to original sources
PubMed2003

Modeling the reaction kinetics of Fenton's process on the removal of atrazine.

The degradation of pesticide, atrazine (ATZ), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine, by Fenton's reagent (FR) was investigated as a function of reagents' concentrations and ratios in a batch reactor. The degradation of ATZ was effectively achieved by hydroxyl radicals, which were generated in the FR process. The decay rates of ATZ and the oxidation capacities of FR were found to depend on the concentrations of hydrogen peroxide and ferrous ion. The removal kinetics of ATZ are initiated by a rapid decay and then followed by a much slower one. After an extended reaction time (5-10 min), the reactions ceased because the Fe(II) and H(2)O(2) were consumed and would be deactivated in the process. A mathematical model was successfully developed to describe the two-stage reaction kinetics by using two simple but critical parameters: the initial ATZ decay rate and the final oxidation capacity of Fenton's process. In general, higher [Fe(II)] or H(2)O(2) concentrations result in faster initial decay rate and higher oxidation capacity. However, the oxidation capacity is more sensitive to the initial [Fe(II)] due to the presence of side reactions as discussed in the paper.

Atrazine↗
PubMed2003

The dose and ratio effects of Fe(II) and H2O2 in Fenton's process on the removal of atrazine.

The degradation of pesticide, atrazine (ATZ), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine, by Fenton's reagent (FR) was investigated as a function of reagents' concentrations and ratios in a batch reactor. The degradation of ATZ was effectively achieved by hydroxyl radicals, which were generated in the FR process. The decay rates of ATZ and the oxidation capacities of FR were found to depend on the concentrations of hydrogen peroxide and ferrous ion. The removal kinetics of ATZ are initiated by a rapid decay and then followed by a much slower one. After an extended reaction time (5 to 10 minutes), the reactions ceased because the Fe2+ and H2O2 were consumable and would be deactivated in the process. The oxidation capacity of FR was found to have a nonlinear correlation to the doses of [Fe2+] and [H2O2] due to the involvement of some unwanted side reactions at both high and low FR ratios. In addition, it was also found that the FR ratio has little effect on the oxidation capacity at high [Fe2+] concentration, but it becomes more critical at lower [Fe2+], which is justified by the involvement of two parallel pathways for the oxidation of ATZ, i.e. the catalyzed oxidation of ATZ induced by FR and the direct oxidation of ATZ by H2O2.

Atrazine↗
PubMed2003

Welded tracheal stent removal in a child under cardiopulmonary bypass.

Metallic tracheal stents have been used in the treatment of paediatric tracheomalacia for more than a decade. We describe a case in which critical airway obstruction occurred during removal of a welded tracheal stent using a rigid bronchoscope under general anaesthesia. Life-saving cardiopulmonary bypass was instituted urgently, and the welded stent was then removed successfully by directly opening the trachea.

Airway Obstruction↗
PubMed2003

Clinical relevance of hydrocephalus as a presenting feature of tuberculous meningitis.

BACKGROUND: Hydrocephalus is a common complication of tuberculous meningitis (TBM). AIM: To study the incidence, associated clinical features, and impact on outcome of hydrocephalus at presentation in TBM. DESIGN: Observational study. SETTING: Regional hospital serving 500,000 people. METHODS: Adult patients with TBM were studied over 57 months. Those with hydrocephalus on initial CT scan were assessed by neurosurgeons. Clinical, neuroradiological, and biochemical features of patients with hydrocephalus upon presentation were compared to those without initial hydrocephalus. RESULTS: Of 31 TBM patients during the study period, nine (29.0%) had hydrocephalus at presentation, and eight of them (25.8% of all) underwent urgent neurosurgical intervention. Of the 22 patients without initial hydrocephalus, hydrocephalus developed after commencement of chemotherapy in one patient only. Hydrocephalus at presentation was associated with a longer duration of presenting symptoms (p = 0.01), ataxia (p = 0.001), later stages of TBM (p = 0.045), a longer delay before commencement of anti-tuberculous chemotherapy (p = 0.001), stroke (p = 0.012), and a poor outcome at 1 year (p = 0.001). DISCUSSION: Hydrocephalus upon presentation is common in our TBM patients. This may be a poor prognostic marker associated with severe TBM and a higher risk of stroke.

Adult↗
PubMed2003

Evaluation of reverse transcription-PCR assays for rapid diagnosis of severe acute respiratory syndrome associated with a novel coronavirus.

The reverse transcription (RT)-PCR protocols of two World Health Organization (WHO) severe acute respiratory syndrome (SARS) network laboratories (WHO SARS network laboratories at The University of Hong Kong [WHO-HKU] and at the Bernhard-Nocht Institute in Hamburg, Germany [WHO-Hamburg]) were evaluated for rapid diagnosis of a novel coronavirus (CoV) associated with SARS in Hong Kong. A total of 303 clinical specimens were collected from 163 patients suspected to have SARS. The end point of both WHO-HKU and WHO-Hamburg RT-PCR assays was determined to be 0.1 50% tissue culture infective dose. Using seroconversion to CoV as the "gold standard" for SARS CoV diagnosis, WHO-HKU and WHO-Hamburg RT-PCR assays exhibited diagnostic sensitivities of 61 and 68% (nasopharyngeal aspirate specimens), 65 and 72% (throat swab specimens), 50 and 54% (urine specimens), and 58 and 63% (stool specimens), respectively, with an overall specificity of 100%. For patients confirmed to have SARS CoV and from whom two or more respiratory specimens were collected, testing the second specimen increased the sensitivity from 64 and 71% to 75 and 79% for the WHO-HKU and WHO-Hamburg RT-PCR assays, respectively. Testing more than one respiratory specimen will maximize the sensitivity of PCR assays for SARS CoV.

Humans↗
PubMed2003

The complete genome sequence of severe acute respiratory syndrome coronavirus strain HKU-39849 (HK-39).

The complete genomic nucleotide sequence (29.7kb) of a Hong Kong severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) strain HK-39 is determined. Phylogenetic analysis of the genomic sequence reveals it to be a distinct member of the Coronaviridae family. 5' RACE assay confirms the presence of at least six subgenomic transcripts all containing the predicted intergenic sequences. Five open reading frames (ORFs), namely ORF1a, 1b, S, M, and N, are found to be homologues to other CoV members, and three more unknown ORFs (X1, X2, and X3) are unparalleled in all other known CoV species. Optimal alignment and computer analysis of the homologous ORFs has predicted the characteristic structural and functional domains on the putative genes. The overall nucleotides conservation of the homologous ORFs is low (<5%) compared with other known CoVs, implying that HK-39 is a newly emergent SARS-CoV phylogenetically distant from other known members. SimPlot analysis supports this finding, and also suggests that this novel virus is not a product of a recent recombinant from any of the known characterized CoVs. Together, these results confirm that HK-39 is a novel and distinct member of the Coronaviridae family, with unknown origin. The completion of the genomic sequence of the virus will assist in tracing its origin.

3' Untranslated Regions↗
PubMed2003

The effects of selective ibotenate lesions of the hippocampus on conditioned inhibition and extinction.

Previously, Solomon (1977) reported that aspiration lesions of the dorsal hippocampus in rabbits had no effect either on the acquisition of Pavlovian conditioned inhibition or on performance during a subsequent retardation test. The present experiment confirmed and extended these findings by showing that rats with ibotenate lesions of the complete hippocampus (the dorsal and ventral hippocampus and the dentate gyrus) were also unimpaired on the same types of tasks. Additional tests with the same rats showed that removing the hippocampus significantly impaired extinction of responding to a stimulus that had been previously trained with an appetitive unconditioned stimulus. The performance of the lesioned rats on a summation test was also marginally, but not significantly, different from that of controls. The data are discussed with reference to the idea that the hippocampus is involved with the formation of some, but not all, types of inhibitory associations.

Animals↗
PubMed2003

A prevalence study of epilepsy in Hong Kong.

OBJECTIVES: To examine epidemiological data on epilepsy for the Hong Kong west region. DESIGN. Descriptive study. SETTING: Epilepsy clinic, university teaching hospital, Hong Kong. PATIENTS AND METHODS: The epilepsy clinic of Queen Mary Hospital manages the majority of adult patients (aged 15 years or older) with chronic seizure disorders resident in the Hong Kong west area with an adult population of 475,900. All patients underwent electroencephalography examination and each subject was independently assessed by two epileptologists for diagnosis and classified according to the International League Against Epilepsy recommendations. RESULTS: Seven hundred and thirty-six patients (female, 42.9%; male, 57.1%; mean age, 40.8 years; standard deviation, 13.6 years) with epilepsy were enrolled in the study. The prevalence rate of active epilepsy in the population 15 years or older was estimated at 1.54 per 1000 on 1 January 2002. Two hundred and eighty-five (38.7%) patients had idiopathic epilepsy syndromes, 100 (13.6%) had cryptogenic epilepsy, and 285 (38.7%) had a remote symptomatic aetiology. Seizure type was partial in 408 (55.4%) patients and generalised in 285 (38.7%). Thirty-one (4.2%) patients had a positive family history. Idiopathic generalised epilepsy syndromes described as common in the literature, such as juvenile myoclonic epilepsy and childhood absence epilepsy, were infrequently seen at 0.68% and 0.95% of cases, respectively. CONCLUSIONS: This study provides baseline data for epilepsy service development and research in Hong Kong. The prevalence rate of active epilepsy in this Chinese, adult population was low compared with that reported in other developed countries. Further population-based epidemiological research is indicated to confirm the prevalence of seizure disorders in this locality.

Adolescent↗
PubMed2002

Evaluation of the Directigen FluA+B test for rapid diagnosis of influenza virus type A and B infections.

Directigen FluA+B (BD Diagnostic Systems, Sparks, Md.), a new rapid test for the detection of influenza virus types A and B, was evaluated with nasopharyngeal aspirate specimens collected from 250 patients in comparison with culture and direct fluorescent antigen (DFA) detection tests. The patients studied were predominantly children, 80% being </=6 years old. Specimens negative by culture but positive by the Directigen FluA+B or DFA tests were analyzed by reverse transcription-PCR to resolve the discrepant results. The resolved sensitivity, specificity, and positive and negative predictive values of the Directigen FluA+B test for influenza virus type A were 96%, 99.6%, 96%, and 99.6%, respectively, and for influenza virus type B they were 87.5%, 96.8%, 80%, and 98%, respectively. Storage of nasopharyngeal aspirates in virus transport medium at 2 to 8 degrees C for 48 h had little adverse effect on the detection of influenza virus type A, but diagnosis of influenza virus type B is best carried out with fresh specimens. The test detected a range of human and animal influenza virus A subtypes, including the H5N1 and H9N2 viruses that recently caused human disease in Hong Kong.

Diagnosis, Differential↗
PubMed2002

Coronary artery stretch versus deep injury in the development of in-stent neointima.

OBJECTIVE: To investigate the relative importance of stent induced arterial stretch and deep injury to the development of in-stent neointima. SETTING: Normal porcine coronary arteries METHODS: 30 BiodivYsio stents (Biocompatibles) were deployed at a stent to artery ratio of 1.25:1 (a moderate injury) and harvested at 28 days. Multiple serial cross sections were analysed morphometrically and the neointimal areas were correlated with the type and degree of injury. RESULTS: Arterial stretch occurred in 78% of struts (77% of sections) and produced moderate neointimal growth (neointimal area 1.93 (0.13) mm2). Deep injury (rupture of the internal elastic lamina) occurred in 20% of struts (23% of sections) and produced a 1.7-fold increase in neointimal area (3.33 (0.41) mm2) compared with stretch only (p = 0.0002). With even deeper injury (rupture of the external elastic lamina), there was a 2.6-fold increase in neointimal area (5.01 (0.48) mm2) compared with stretch only (p = 0.02). A new injury score, incorporating both stretch and deep injury, correlated with neointimal area (r = 0.60, p < 0.001). CONCLUSIONS: Stretch of the coronary artery in a stent is common, and a major contributor to neointima formation, even in the absence of deep injury. Deep injury is, however, a more potent stimulus to neointima formation than stretch. Greater degrees of stretch are associated with thicker neointima. Where neither deep injury nor stretch are seen, the stent has no effect upon the development of neointima.

Animals↗
PubMed2002

Angiopeptin-eluting stents: observations in human vessels and pig coronary arteries.

Local drug delivery from polymer-coated coronary stents may reduce the incidence of in-stent restenosis. Angiopeptin, an inhibitor of smooth muscle cell proliferation, may reduce the clinical impact of restenosis. The objectives of this study were to characterize the release kinetics and distribution of angiopeptin-loaded phosphorylcholine (PC)-coated drug delivery (DD) BiodivYsio stents and assess their safety and efficacy at reducing neointima formation. I125-angiopeptin-loaded DD-PC-coated stents were implanted into human saphenous vein segments ex vivo, and I125 angiopeptin was detected in the medial layer at 1 hour. When implanted in pig coronary arteries, I125 angiopeptin was found adjacent to the stent at intervals up to 28 days. No significant amounts were found elsewhere. To assess efficacy, twelve angiopeptin-loaded DD-PC-coated stents, twelve non-loaded DD-PC stents, ten standard PC-coated stents and 8 uncoated stents were implanted into normal porcine coronary arteries. Stents were harvested at 28 days and neointima formation was assessed by computerized morphometry. No adverse tissue reactions were seen with any of the PC-coated stents. No significant differences were seen in neointimal or luminal cross-sectional areas between study groups. Local delivery of I125 angiopeptin into the vascular wall can be achieved using a PC-coated stent. Delivery of angiopeptin from drug delivery PC-coated stents is safe, but does not lead to a significant reduction in neointimal growth at 28 days within the parameters of this study.

Animals↗
PubMed2002

Respiratory conditions in Malaysian asbestos cement workers.

A cross-sectional study was conducted to determine the prevalence and type of respiratory conditions including asbestos-related diseases among Malaysian asbestos cement workers. The study population consisted of 1164 workers who had undergone medical surveillance from 1995 to 1997, including full history, physical examination, chest radiography and spirometry. More than half the male workers were smokers or ex-smokers, with smokers having more respiratory symptoms and signs, and reduced FEV1 compared with non smokers. The five most common respiratory conditions diagnosed were bronchial asthma, chronic bronchitis, pulmonary tuberculosis, upper respiratory tract infections and allergic rhinitis. On follow-up, there were also two cases of asbestosis and one case of bronchial carcinoma. The asbestosis cases were probably related to heavy occupational exposure to asbestos fibres in the past, before governmental regulations were gazetted in 1986. Further follow-up is essential for continued monitoring of the health status of asbestos workers.

Adolescent↗
PubMed2001

Reconsideration of the role of the hippocampus in learned inhibition.

The purpose of this article is to reconsider the role of the hippocampus in learning tasks that require suppression or prevention of memories or responses. This type of learning has generally been referred to as inhibitory learning. Although early theories proposed that the hippocampus was important for inhibitory learning, these ideas have generally fallen out of favor. However, new developments in the conceptual understanding of inhibition along with recent experimental evidence require that we review these conceptual changes with regard to hippocampal function. We review three general categories of 'inhibition' that have been used with reference to hippocampal function: neural inhibition, inhibition of attention and associative or learned inhibition. We then consider recent developments in the field of animal learning that call for changes in the early conceptualizations of learned inhibition. Specifically, current findings suggest that different types of learning paradigms can yield conditioned inhibitors that are embedded in different associative structures, at least some of which can co-exist with conditioned excitation. Next we proceed to review a number of recent experiments from our laboratory as well as others that encouraged renewed interest in the role for the hippocampus in inhibitory learning. We then conclude by considering some of the implications of the idea that the hippocampus is involved with performance of conditioned responses based on cues that are concurrently embedded in inhibitory and excitatory associations.

Animals↗