Biomedical subjects
Publications and source records attributed to C C Chan.
We report a high-efficiency diode-end-pumped polycrystalline Yb:Y2O3 ceramic laser. Pumped by a 976 nm laser diode bar and with an absorbed pump power of 2.8 W, cw output power of 1.74 W at 1078 nm, and 0.73 W at 1040 nm were obtained. The slope efficiency was measured to be 82.4% for the 1078 nm laser emission and 57.1% for the 1040 nm laser emission.
OBJECTIVE: To assess whether lateral semicircular canal (LSCC) ossification is more advanced than that in the cochlear basal turn, in order to judge the value of the former as a predictor. METHODS: Retrospective review of 33 paediatric patients from our cochlear implant programme, with profound sensorineural hearing loss after bacterial meningitis. Magnetic resonance imaging (MRI), computed tomography (CT) scans and operative findings were reviewed. RESULTS: On CT, LSCC ossification scores were more advanced than those for the cochlear basal turn in 69.9 per cent of implanted ears. Forty-five per cent (15/33) of children had ossification at surgery. In predicting this, the sensitivity of CT LSCC ossification was 90 per cent and that of MRI LSCC ossification was 83.3 per cent. CONCLUSIONS: The more advanced ossification found in the LSCC, compared with that in the cochlear basal turn, adds to previous findings of LSCC pathology predicting cochlear ossification. Surprisingly, CT of the LSCC appears to be no less valuable than MRI in pre-operative cochlear implant assessment of post-meningitic children.
By numerically solving the coupled laser Ginzburg-Landau equations and using the pulse tracing technique to incorporate the cavity effect in the simulation, we have explicitly calculated the soliton polarization ellipses throughout the cavity of a fiber-ring laser mode-locked by the nonlinear polarization rotation technique, and investigated the soliton polarization dynamics in laser cavities. It was found that in a conventional stable soliton operation state, although the soliton polarization varies as the pulse propagates, at a fixed position inside the laser cavity the soliton polarization is invariant with time. However, in the presence of laser dynamics, at a fixed location within the cavity the soliton could either have multiple alternating fixed polarization states or no fixed polarization state at all, depending on the soliton dynamics.
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Subchondral insufficiency fracture of the femoral head is a recently recognised entity. There are a few cases reported in Japanese and Caucasian patients but none in the Hong Kong population. The condition typically occurs in elderly females with osteoporosis. Acute hip pain is the usual presentation. The patient may have concomitant insufficiency fractures elsewhere. Magnetic resonance imaging is usually required to make the diagnosis. The prognosis of the condition is unknown. Reported complications include rapid collapse of the femoral head and coxopathy. Joint replacement should be considered if conservative management fails.
A general procedure is proposed for the rapid development of a reversed-phase liquid chromatographic (RP-LC) separation that is "orthogonal" to a pre-existing ("primary") method for the RP-LC separation of a given sample. The procedure involves a change of the mobile-phase organic solvent (B-solvent), the replacement of the primary column by one of very different selectivity, and (only if necessary) a change in mobile phase pH or the use of a third column. Following the selection of the "orthogonal" B-solvent, column and mobile phase pH, further optimization of peak spacing and resolution can be achieved by varying separation temperature and either isocratic %B or gradient time. The relative "orthogonality" of the primary and "orthogonal" RP-LC methods is then evaluated from plots of retention for one method versus the other. The present procedure was used to develop "orthogonal" methods for nine routine RP-LC methods from six pharmaceutical analysis laboratories. The relative success of this approach can be judged from the results reported here.
Osteolytic lesions are frequently encountered in clinical practice. Radionuclide bone scans with technetium-99m-labeled diphosphonates are often performed in the evaluation of both solitary and multiple osteolytic lesions. In this pictorial review, we critically evaluate the current role of bone scan in common osteolytic tumors including aneurysmal bone cyst, simple bone cyst, fibrous dysplasia, nonossifying fibroma, giant cell tumor, eosinophilic granuloma, enchondroma, chondrosarcoma, osteosarcoma, Ewing sarcoma, myeloma, and metastases. The merits and limitations of bone scanning are emphasized.
OBJECTIVES: To assess the usefulness, relative ease of administration, and patient acceptance of the clock drawing test as well as the time and change test for detecting dementia in Chinese elderly adults. DESIGN: Prospective case-controlled study. SETTING: Memory clinic and geriatric clinic of a district hospital, Hong Kong. PARTICIPANTS: A convenient sample of 85 subjects aged 65 years or older attending the two clinics during the period from September 2002 to June 2003. MAIN OUTCOME MEASURES: The clock drawing test scored according to Lam's method; the time and change test with modification to the making change task; and the Chinese version of the Mini-Mental State Examination. RESULTS: Demented subjects were matched with non-demented ones with respect to age, sex, educational level, and co-morbidity status. The clock drawing test had a comparable sensitivity (89.4%) but a lower specificity (47.1%) when compared with that of the Chinese version of the Mini-Mental State Examination (96.0 and 76.5%, respectively). In contrast, the time and change test had a lower sensitivity (62.7%) but higher specificity (94.1%). Both tests took significantly less time to complete than the Chinese version of the Mini-Mental State Examination. All except four subjects completed the clock drawing test while all subjects accepted the time and change test well. CONCLUSIONS: The Chinese version of the Mini-Mental State Examination is still the best among the three tests despite the longer time to completion. The clock drawing test may be a good alternative to the Mini-Mental State Examination as an effective screening test for dementia when time does not permit. The time and change test, although time-saving, is not suitable to be used alone because of its low sensitivity.
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Previous work has shown that the selectivity of reversed-phase columns for HPLC can be described by means of five column parameters: H (hydrophobicity), S* (steric resistance), A (hydrogen-bond acidity), B (hydrogen-bond basicity) and C (cation-exchange capacity). Values of H, S*, etc. can be determined by carrying out retention measurements for 18 test solutes under standardized conditions. The reproducibility of the latter procedure has been evaluated by comparison testing in four different laboratories and found acceptable. An alternative 10-solute test procedure which is more reproducible and convenient (but somewhat less accurate), requires only 2-3 h per column.
The column selectivity parameters (H, S*, A, B and C) described in the preceding paper [L.R. Snyder, A. Maule, A. Heebsch, R. Cuellar, S. Paulson, J. Carrano, L. Wrisley C.C. Chan, N. Pearson, J.W. Dolan, J.J. Gilroy, J. Chromatogr. A 1057 (2004) 49-57] can be used to compare columns in terms of selectivity. A detailed procedure for such column comparisons is presented here, and evaluated by its use in finding suitable replacement columns for 12 different routine separations performed in five different pharmaceutical analysis laboratories.
BACKGROUND: An in vitro multidrug resistance (MDR) system from a human colonic cancer cell line (SW620-MDR) has been established. To further study the mechanisms at molecular level and prevention of multidrug resistance in clinical practice, it was demonstrated that the expressions of several apoptosis-related and cell cycle regulator genes were changed in the cells. METHODS: A multidrug-resistant colonic cell line (SW620-MDR) was established, and the Atlas human cDNA expression array was used for studying the pattern of gene expression in this cell line. Furthermore, Northern hybridization or real-time PCR analysis confirmed the pattern of gene expression. RESULTS: In the SW620-MDR cell line the pro-apoptosis genes, CASP4, BIK, PDCD2, and TACE were expressed with decreased levels, and the antiapoptosis genes CD27-L and IGFBP2 were over-expressed. Furthermore, the cell cycle regulator genes such as CDK6, CCND1, CDC27HS, CDC16HS, Wee1Hu, MAPKK1, and IGFBP6 were expressed with decreased levels in the drug-resistant cell line. CONCLUSIONS: It is worthwhile investigating whether the differentially expressed pattern of the aforementioned genes exists in the drug-resistant cancer specimens, and to further understand their functions in the cancer drug-resistance mechanism.
OBJECTIVES: To provide an overall pattern of morbidity in unintentional residential childhood injuries (URCI) in Hong Kong. METHODOLOGY: A cross-sectional telephone survey of caregivers of children aged under 16-years and adolescents suffering from URCI and admitted to three selected local Accident and Emergency Departments. RESULTS: Falls, cuts and scalds were the most common external causes of URCI observed, while boys predominated in the sample population. Most of the observed URCI were of moderate to mild severity. Children of new immigrant mothers were more likely to receive first aid immediately after the incidents. Parents were aware of potentially injurious behaviour and intervened on occasion, but most resorted to verbal warnings only. CONCLUSIONS: Prevalence of falls among observed URCI offers evidence in support of the hypothesis that the high population density in Hong Kong plays an integral role in understanding mechanisms of morbidity. Parents show concern about URCI but often lack substantial action that modifies injury risk. Considering the local injury differentials, an active prevention effort such as behavioural intervention and education for parents may be useful.
BACKGROUND: Helicobacter pylori is a bacterial pathogen strongly associated with ulcer diseases and gastric cancer. The bacterial-induced alteration of cell-cycle control in host cells may play a role in the pathogenetic mechanisms. The aims of this study were to define the effect of H. pylori on the G2/M to G1 transition in a gastric cell line. METHODS: Cultured gastric cells, AGS, were synchronized in the S/early G2 phase and treated with intact H. pylori. The cell-cycle distribution of AGS cells was determined by flow cytometry. The activity of cdc2 kinase, as well as of some parameters that affect the kinase activity, was also examined. RESULTS: H. pylori delays cell-cycle progression at the G2/M phase in AGS cells. The G2/M delay was associated with reduced activity of cdc2 kinase. Both down-regulation of cell-cycle regulators (p34cdc2, cyclin B1 and cdc25C) and decreased association between p34cdc2 and cyclin B1 were found to be associated with the activity of cdc2 kinase abated after the H. pylori infection. In addition, the H. pylori-induced G2/M delay required direct contact between the bacteria and host cells. CONCLUSIONS: H. pylori inhibits G2/M to G1 progression and causes a reduction of cell division in gastric epithelial cells.
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1. Type 4 phosphodiesterase (PDE4) inhibitors mimic the pharmacological actions of alpha(2)-adrenoceptor antagonists. This has been postulated as the mechanism by which PDE4 inhibitors induce emesis and was also demonstrated by their ability to reverse xylazine/ketamine-induced anaesthesia. We further characterized this latter effect since it appears to reflect the emetic potential of PDE4 inhibitors. 2. Selective inhibitors of PDE 1, 2, 3, 4 and 5 were studied in rats, on the duration of anaesthesia induced by the combination of xylazine (10 mg kg(-1), i.m.) and ketamine (10 mg kg(-1), i.m.). PMNPQ (i.e. 6-(4-pyridylmethyl)-8-(3-nitrophenyl)quinoline) - PDE4 inhibitor: 0.01 - 3 mg kg(-1)), like MK-912 (alpha(2)-adrenoceptor antagonist: 0.01 - 3 mg kg(-1)), dose-dependently reduced the duration of anaesthesia. In contrast, vinpocetine (PDE1 inhibitor), EHNA (PDE2 inhibitor), milrinone (PDE3 inhibitor) and zaprinast (PDE5 inhibitor) had no significant effect at the doses tested (1 - 10 mg kg(-1)). Analysis of plasma and cerebrospinal fluid (CSF) of treated animals confirmed the absorption and distribution to the brain of the inactive inhibitors. 3. Neither MK-912 (3 mg kg(-1)) nor PMNPQ (0.1 - 1 mg kg(-1)) altered the duration of anaesthesia induced via a non-alpha(2)-adrenoceptor pathway (sodium pentobarbitone 50 mg kg(-1), i.p.). 4. Central NK(1) receptors are involved in PDE4 inhibitor-induced emesis. Consistently, [sar(9), Met(O(2))(11)]-substance P (NK(1) receptor agonist, 6 microg i.c.v.) reduced the duration of anaesthesia induced by xylazine/ketamine. 5. In summary, this model is functionally coupled to PDE4, specific to alpha(2)-adrenoceptors and relevant to PDE4 inhibitor-induced emesis. It therefore provides a novel way of evaluating the emetic potential of PDE4 inhibitors in rats.
PURPOSE: Patients infected with HIV-1 develop ocular manifestations, some due to opportunistic infections and others attributed to the virus itself. Among the latter are retinal microvasculopathy and uveitis. We have analysed the ocular phenotype in HIV-transgenic mice. METHODS: We have studied T26 transgenic mice which bear a gag-pol deleted HIV-1 genome. Transgene RNA was detected by Northern analysis. Ocular pathology was assessed by conventional histology, immunostaining for gp120 envelope protein, and in situ apoptosis detection with end-labelling. RESULTS: Abnormalities of lens epithelial cell development were detected as early as embryonic day 14.5. Histological changes included the malformation of an embryonal lens nucleus and poor closure of the lens suture lines. This resulted in congenital nuclear cataracts, as occur in congenital viral infections in human patients. In the adult animals, lenses were notable for extensive vacuolation, liquefaction, and degeneration of the cortex. Mild iridocyclitis and vitritis were also noted in adult transgenic mice. Immunostaining demonstrated the expression of gp 120 envelope protein within the lens epithelial and fibre cells. End-labelling with terminal deoxyribonucleotidyl transferase showed increased numbers of apoptotic cells in the adult lens. CONCLUSIONS: These findings suggest that one or more HIV-1 proteins are associated with congenital nuclear cataract formation and uveitis in HIV-transgenic mice.