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C K Chan

Publications and source records attributed to C K Chan.

At least 73 records · Page 4Linked to original sources
PubMed2001

Spiral wave dynamics under feedback derived from a confined circular domain.

Spiral waves are induced in a thin layer of the light-sensitive Belousov-Zhabotinsky reaction and controlled by a time-dependent uniform illumination. The intensity of the illumination is taken to be proportional to the average wave activity observed within a circular domain of the reaction layer. Stabilization and destabilization of spiral waves, as well as the existence of additional types of attractors, are demonstrated. A simple mathematical description is proposed in order to explain the existence of the attractors and the dependence of their size on the time delay in the feedback loop.

Journal Article↗
PubMed2001

Systemically expressed soluble Tie2 inhibits intraocular neovascularization.

Retinal and choroidal neovascularization are the most frequent causes of severe and progressive vision loss. Studies have demonstrated that Tie2, an endothelial-specific receptor tyrosine kinase, plays a key role in angiogenesis. In this study, we determined whether adenovirus-mediated gene delivery of extracellular domain of the Tie2 receptor (ExTek) could inhibit experimental retinal and choroidal neovascularization. Immunofluorescence histochemistry with a monoclonal antibody to human Tie2 showed that Tie2 expression is prominent around and within the base of newly formed blood vessels of retinal and choroidal neovascular lesions. A single intramuscular injection of adenovirus expressing ExTek genes achieved plasma levels of ExTek exceeding 500 microg/ml in mice for 10 days (in neonates) and 7 days (in adults). This treatment inhibited retinal neovascularization by 47% (p < 0.05) in a murine model of ischemia-induced retinopathy. The same treatment reduced the incidence and extent of sodium fluorescein leakage from choroidal neovascular lesions by 52% (p < 0.05) and 36% (p < 0.01), respectively, in a laser-induced murine choroidal neovascularization model. The same mice showed a 45% (p < 0.001) reduction of integrated area of the choroidal neovascularization. These findings indicate that Tie2 signaling is a common component of the angiogenic pathway in both retinal and choroidal neovascularization, providing a potentially useful target in the treatment of intraocular neovascular diseases.

Adenoviridae↗
PubMed2001

Combined diffusion model for the sorption of cadmium, copper, and zinc ions onto bone char.

The ability of bone char to remove three single-component metals (namely, cadmium, copper and zinc) from aqueous solutions has been studied. Equilibrium isotherms have been measured and analyzed using a Langmuir isotherm model. A series of batch contact time experiments were performed to study the effect of sorbent mass and initial metal ion concentration for the three systems. A new film-pore diffusion model has been applied to the batch contact time results, and good correlation is obtained between theoretical predictions and experimental data. A further extension to the new model was made to include a surface diffusion term. The agreement between theoretical results and experimental data improved as the sum of the squares of the errors (SSE) improved by around 20% for cadmium and zinc but by 50% for copper. Therefore, the sorptions of cadmium and zinc ions onto bone char are primarily film-pore diffusion controlled, but for the copper system film-pore-surface diffusion must be considered.

Adsorption↗
PubMed2001

Experimental study of the sampling artifact of chloride depletion from collected sea salt aerosols.

Sampling artifact of chloride depletion from collected sea salt particles was studied, based on simultaneous measurements of size distribution measurements by a 10-stage Micro-Orifice Uniform Deposit Impactor (MOUDI) and of PM2.5 measurements by a Compact Porous Metal Denuder Sampler (PMDS) at a coastal site in Hong Kong on May 7, 8, 9, 11, and 29, 1998. The ambient concentrations of SO2, HNO3, HNO2, and NH3 were also measured by the PMDS. PM2.5 measurements by the PMDS, which is equipped with denuders and nylon back filters, are compared with the PM1.8 and PM3.1 measurements by the MOUDI. The percentages of chloride depletion from sea salt aerosols in PM1.8 and PM3.1 were 4-45% higher than that in PM2.5. This suggests that chloride evaporation in PM1.8 and PM3.1 collected on Teflon filters of the MOUDI during sampling was present. From the sum of the contributions of particles on the Teflon and nylon filters of the PMDS, nitrate formation almost completely accounts for chloride depletion in PM2.5 prior to collection since the equivalent ratio of [Na+] to ([NO3-] + [Cl-]) is close to the seawater ratio of 0.85. However, it was found that 22-74% of nitrate and 45-86% of chloride in the collected particles on the Teflon filter of the PMDS evaporated during sampling. Excess chloride depletion unexplained by NO3- and nss-SO4(2-) was found in the collected particles on the Teflon filter of the PMDS. Similarly, an amount of 3.7-27.2 nequiv m-3 of excess depleted chloride (equivalent to 8-55% of total chloride depletion) was found in supermicron particles collected by the MOUDI. In the 1.8-3.1 microns particles, the excess depleted chloride is positively correlated to the chloride evaporated from the deposited particles. Particle--particle interactions are proposed to explain the evaporation of nitrates and chlorides in the PMDS and MOUDI measurements. The observed chloride depletion from seasalt aerosols was partially attributed to sampling artifact due to particle--particle interactions.

Aerosols↗
PubMed2001

Atovaquone suspension for treatment of Pneumocystis carinii pneumonia in HIV-infected patients.

OBJECTIVE: To describe clinical experience with atovaquone suspension for the treatment of Pneumocystis carinii pneumonia (PCP) in HIV-infected patients. DESIGN: A retrospective chart review. METHODS: The medical records of 54 HIV-infected patients with PCP treated with atovaquone were examined. The outcomes of 34 patients treated with atovaquone suspension (750 mg twice a day) were compared with those of 20 patients treated with atovaquone tablets (750 mg three times a day). RESULTS: The proportion of patients successfully treated was similar with the suspension (74%) and tablet (70%) formulations of atovaquone. The proportion of patients with an inadequate response to therapy was lower for patients treated with atovaquone suspension (15%) than tablets (30%). Both formulations were well tolerated. CONCLUSION: Atovaquone suspension is effective and well tolerated for the treatment of PCP.

AIDS-Related Opportunistic Infections↗
PubMed2001

Phonological processing in reading Chinese among normally achieving and poor readers.

Ninety-four children in grades one to six (7 to 12 years old) in Hong Kong were individually administered a Chinese reading test consisting of 80 characters that varied in frequency (high or low) and orthographic structure (simple or complex). Phonological processing tasks, including short-term memory, pseudo-character recognition, and tone discrimination, were also administered. During reading, younger normal and poor readers made more semantic and visual errors, whereas older and normally achieving children made more phonologically related errors. Normally achieving readers also performed at a higher level than poor readers on short-term memory, pseudo-character recognition, and tone discrimination tasks. Phonological processing apparently plays a significant part in the development of reading skills in Chinese.

Child↗
PubMed2001

Mutation of proline 409 to arginine in the meander region of cytochrome p450c17 causes severe 17 alpha-hydroxylase deficiency.

We elucidated the molecular basis of 17 alpha-hydroxylase deficiency in a Chinese patient with male pseudohermaphroditism. The patient is a compound heterozygote, carrying two different mutant alleles in the CYP17 gene. The first mutation, g.6333--6341delGACTCTTTCA, located in exon 8, was reported in a Thai patient living in a rural village in Thailand. We suggest that g.6333--6341delGACTCTTTCA may be a prevalent mutation causing P450c17 deficiency in Southeast Asia. The second mutation is a missense mutation, g.5582C>G, located in exon 7, changing the codon 409 from CCG to CGG, and changing the coded amino acid from proline to arginine, i.e., P409R. This proline residue is conserved in P450c17 of other species and other human P450 proteins. Site-directed mutagenesis, in vitro expression, and functional analysis of the P409R mutant in COS-1 cells show that it has a complete lack of 17 alpha-hydroxylase activity. The proline residue probably causes a turn in the meander region of P450c17, and we hypothesize, by comparison to homologous proteins, that the change in the protein conformation may abolish heme incorporation or may prevent P450c17 from interacting with electron donors.

Adolescent↗
PubMed2001

Macular hole after laser in situ keratomileusis and photorefractive keratectomy.

PURPOSE: To describe three myopic patients who developed unilateral macular hole after undergoing bilateral laser in situ keratomileusis or photorefractive keratectomy. METHODS: Case reports. RESULTS: Three eyes of three myopic patients developed a macular hole in one eye after bilateral laser in situ keratomileusis or photorefractive keratectomy. The macular hole formed between 4 to 7 weeks after laser in situ keratomileusis in case 1 (a 48-year-old woman), and within 2 months after laser in situ keratomileusis in case 2 (a 36-year-old woman). In case 3 (a 45-year-old man), the macular hole was found 9 months after photorefractive keratectomy. A vitrectomy closed the macular hole of case 1 with final best-corrected visual acuity of 20/25 and case 2 with 20/30, whereas case 3 declined further surgery. CONCLUSION: A macular hole may develop in myopic eyes after laser in situ keratomileusis or photorefractive keratectomy. Vitreoretinal interface changes may play a role.

Adult↗
PubMed2001

Management of dislocated intraocular implants.

Implant dislocation may occur in the absence of appropriate capsular or zonular support (PCIOL) (11,35,53) or following traumatic injury to anterior ocular tissues (ACIOL). (11,19,20) Other factors (e.g., advanced patient age, high myopia, previous vitrectomy, pseudoexfoliation syndrome, and certain connective tissue disorders) also may predispose implant dislocation. (9,52) Although reported for all types of IOLs, implant dislocation is becoming more manageable because of the advancement of surgical techniques. A dislocated ACIOL or PCIOL may be explanted, exchanged, or repositioned. (11,48,71) Repositioning the dislocated PCIOL in the ciliary sulcus with modern vitreoretinal techniques provides an optimal environment for visual recovery. (11,71) Implant repositioning techniques generally may be categorized into the external or the internal approaches. (8,11) The former involves external suturing methods for a primary or secondary implant in the absence of adequate capsular or zonular support (15,16,31,42,56,60,61,64,66,73,76) and the latter is achieved through modern pars plana techniques. 8,11,62,69) Recently, several implant repositioning methods gaining increasing acceptance include the scleral loop fixation, (45) the snare approach, (43) the use of the 25-gauge implant forceps, (13) temporary haptic externalization, (8,11,36,71) and the use of perfluorocarbon liquids. (1,28,40,41,44) The temporary haptic externalization method combines the best features of the external and the internal approaches, avoids complex intraocular maneuvers, and allows precise scleral fixation of the dislocated IOL on a consistent basis. (8,11,71) Endoscopy provides the surgeon with optimal viewing of the anterior retropupillary anatomy that is often difficult to appreciate (e.g., capsular-zonular complex, ciliary sulcus, anterior retina, and vitreous base). (6,11) As a result, precise haptic placement is possible during the repositioning process. (6,11) However, a three-dimensional birds-eye view is lacking, and there may be a steep learning curve with endoscopy. (11) Certain characteristics of a silicone plate implant may enhance implant dislocation. (11,33,34,46,49,58) Capsular contraction following an Nd:YAG posterior capsulotomv may result in a posterior dislocation of the silicone plate implant. (11,33,34,46,49,50,58) Special techniques are available for the retrieval of the slippery dislocated silicone plate implant from the retinal surface without causing injury. (33,58) Repositioning the plate implant anterior to capsular remnants or in the ciliary sulcus may lead to recurrent dislocation, and its removal is frequently the best option. (11) Placing a second implant in the presence of a disLocated implant is ill advised because subsequent surgical management becomes more complex. (11) Surgical options include removing the dislocated implant through a Limbal or pars plana incision with special techniques, (74,75) repositioning the dislocated implant after removing the second implant," and explanting both implants. (11) Considering the increased morbidities and complications associated with the management of double implants, the surgeon should avoid the placement of a second implant in the setting of a dislocated implant. (11)

Cataract Extraction↗
PubMed2001

Enhancement of MSH receptor- and GAL4-mediated gene transfer by switching the nuclear import pathway.

Efficient nuclear delivery of plasmid DNA represents a major barrier in nonviral gene transfer. One approach has been to use DNA-binding proteins such as GAL4 from yeast as DNA carriers with nuclear targeting properties. We recently showed, however, that GAL4 is inefficient in targeting DNA to the nucleus because its DNA-binding and nuclear targeting activities are mutually exclusive, which relates to the fact that GAL4 nuclear import occurs via a novel pathway. Here, we 'switch' this pathway to a more conventional one by adding a modified poly-lysine to which an optimized nuclear targeting signal, based on that of the SV40 large T-antigen, is linked. We also use a chimeric GAL4-alpha-melanocyte stimulating hormone (MSH) fusion protein to enable gene transfer to cells expressing the MSH receptor. Switching the nuclear import pathway of the transfecting complex significantly enhances receptor-mediated gene transfer through enabling interaction with desired components of the cellular nuclear import machinery. The present study represents the first demonstration that nuclear targeting signals can enhance receptor-mediated gene delivery, the approaches having important relevance to research and clinical applications, such as in generating transgenic or knock-out animals, or in gene therapy.

Active Transport, Cell Nucleus↗
PubMed2001

One-week ranitidine bismuth citrate-based triple therapy for the eradication of Helicobacter pylori in Hong Kong with high prevalence of metronidazole resistance.

AIM: To compare 1-week ranitidine bismuth citrate-based (RBC) triple therapy vs. omeprazole-based (O) triple therapy for the eradication of Helicobacter pylori infection in Hong Kong with high prevalence of metronidazole resistance. METHODS: Patients with non-ulcer dyspepsia and H. pylori infection were randomized to receive either: (i) RBCCM: ranitidine bismuth citrate (pylorid) 400 mg, clarithromycin 250 mg and metronidazole 400 mg; or (ii) OCM: omeprazole 20 mg, clarithromycin 250 mg and metronidazole 400 mg, each given twice daily for 1 week. Endoscopy (CLO test, histology and culture) and 13C-urea breath test were performed before randomization and 6 weeks after drug treatment. RESULTS: A total of 180 patients were randomized. H. pylori eradication rates (intention-to-treat, n=180/per protocol, n=166) were 83%/92% for RBCCM and 66%/70% for OCM (P=0.01, intention-to-treat and P=0.001, per protocol, respectively). RBCCM treatment was unaffected by metronidazole susceptibility and achieved a significantly higher eradication rate in metronidazole-resistant cases (89%) than the OCM group (45%, P=0.0064). CONCLUSION: One-week ranitidine bismuth citrate-based triple therapy is significantly better than omeprazole-based triple therapy for the eradication of H. pylori infection, especially in metronidazole-resistant cases. It is an effective regimen for the eradication of H. pylori infection in regions with a high prevalence of metronidazole resistance.

Adult↗
PubMed2001

An evaluation of invasive and non-invasive tests for the diagnosis of Helicobacter pylori infection in Chinese.

BACKGROUND: Different tests are available for diagnosing Helicobacter pylori infection. AIM: To compare the most commonly used tests either alone or in combination in Chinese patients with respect to routine clinical use or research purpose. METHODS: A total of 294 consecutive dyspeptic patients without previous H. pylori treatment were recruited. During upper endoscopy, biopsies were taken from the antrum and corpus, for a commercially available CLO-test, an in-house rapid urease test, culture, polymerase chain reaction and histological examination. Patients then received a 13C-urea breath test. The H. pylori status of each patient was determined by a concordance of test results. RESULTS: For routine clinical use, histology (antral plus corpus biopsies) had an accuracy of 100%, whilst the rapid urease test had an accuracy of 99.7%. The 13C-urea breath test was equally reliable, with an accuracy of 94.5%. Combinations of two tests did not confer additional advantage over the most accurate single test. For research purposes, the accuracy of using the criteria of two positives out of three diagnostic tests was 100% and equivocal results were not found. CONCLUSION: Histology with or without a rapid urease test was highly accurate for routine clinical use. Alternatively, the 13C-urea breath test was an equally reliable non-invasive test. The two positives out of three tests approach was highly reliable in predicting H. pylori status of untreated Chinese patients in a research setting.

Biopsy↗
PubMed2001

Three-day lansoprazole quadruple therapy for Helicobacter pylori-positive duodenal ulcers: a randomized controlled study.

AIM: To compare the efficacy and tolerability of a 3-day quadruple therapy with a standard 7-day triple therapy in eradicating Helicobacter pylori infection and healing duodenal ulcers. METHODS: Patients with H. pylori-positive duodenal ulcers were randomized to receive either lansoprazole 30 mg, clarithromycin 500 mg, and metronidazole 400 mg twice daily for 7 days (LCM-7) or lansoprazole 30 mg, clarithromycin 500 mg, metronidazole 400 mg, and bismuth subcitrate 240 mg twice daily for 3 days (LCMB-3). No pre- or post-treatment acid suppression was used. Follow-up endoscopy was performed at week 6. RESULTS: A total of 118 patients were recruited. Sixty patients in the LCM-7 group and 53 patients in the LCMB-3 group returned for endoscopy. Intention-to-treat eradication rates were 87% and 86% (P=0.94) and per protocol eradication rates were 87% and 94% (P=0.29) in the LCM-7 and LCMB-3 groups, respectively. Per protocol and intention-to-treat ulcer healing rates were 98% and 98% in LCM-7 and 100% and 91% in LCMB-3, respectively. There were no significant differences in efficacy in relation to the initial metronidazole and clarithromycin susceptibility. Significant reduction in the duration of side-effects was found in the LCMB-3 group. CONCLUSION: The 3-day quadruple therapy is highly effective, better tolerated and can be considered as a first-line therapy in duodenal ulcer management.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed2001

Clinical and endoscopic characteristics of non-Helicobacter pylori, non-NSAID duodenal ulcers: a long-term prospective study.

BACKGROUND: The proportion of duodenal ulcers not associated with Helicobacter pylori infection or the use of non-steroidal anti-inflammatory drugs (NSAIDs) is increasing. AIM: To identify the clinical and endoscopic characteristics of non-H. pylori, non-NSAID duodenal ulcers. METHODS: Clinical and endoscopic data and H. pylori status were prospectively collected from consecutive patients who underwent upper endoscopy from 1997 to 1999. Patients with duodenal ulcers were identified, and those with non-H. pylori, non-NSAID duodenal ulcers were analysed further. RESULTS: A total of 11 717 upper endoscopies were performed in 8344 patients. Of these, 1153 (14%) had duodenal ulcers. Of 599 patients with active ulcers and known H. pylori status, 104 (17%) had ulcers not associated with H. pylori or the use of NSAIDs, 393 (66%) had ulcers associated with H. pylori alone, 51 (8.5%) had ulcers associated with the use of NSAIDs alone and 51 (8.5%) had ulcers associated with both. Multivariate logistic regression analysis revealed that the presence of concomitant diseases (odds ratio=15.0; 95% confidence interval, 8.64-25.9; P < 0.001) and the absence of epigastric pain/discomfort (odds ratio=0.52; 95% confidence interval, 0.29-0.91; P=0.022) were independent predictors for non-H. pylori, non-NSAID duodenal ulcers. CONCLUSIONS: Non-H. pylori, non-NSAID duodenal ulcers exhibit certain distinct clinical and endoscopic characteristics. The presence of concomitant diseases is an important predictive factor.

Adult↗
PubMed2001

Transmission of hepatitis B infection from hepatitis B core antibody--positive liver allografts is prevented by lamivudine therapy.

Donor shortage has led to the use of hepatitis B core antibody (anti-HBc)--positive (anti-HBc(+)) liver allografts for patients in need of relatively urgent orthotopic liver transplantation (OLT). Because anti-HBc(+) allografts transmit hepatitis B virus (HBV) infection at a high rate, effective prophylaxis is required. We assessed the effectiveness of lamivudine in preventing HBV transmission by anti-HBc(+) allografts. Between March 1996 and March 2000 at Cedars-Sinai Medical Center (Los Angeles, CA), 15 of 169 patients (8.9%) received liver allografts from anti-HBc(+) donors. Six patients were hepatitis B surface antigen (HBsAg)(+) (group 1), and 9 patients were HBsAg negative (HBsAg(-); group 2) before OLT. All patients were administered lamivudine, 100 or 150 mg/d, orally after OLT. Patients who were HBsAg(+) before OLT also were administered hepatitis B immunoglobulin (HBIG) prophylaxis. Hepatitis B serological tests were performed on all patients, and HBV DNA was determined in liver tissues in 10 patients. All 15 patients remained HBsAg(-) at their last follow-up 2 to 40 months (mean, 17 months) post-OLT. All patients in group 1 had antibody to HBsAg (anti-HBs) titers greater than 250 mIU/mL post-OLT (mean follow-up, 20 months; range, 7 to 40 months). Of the 2 patients in group 1 who underwent liver biopsy after OLT, 1 patient had detectable hepatic HBV DNA despite being anti-HBs(+) and HBsAg(-). Among the patients in group 2, none acquired anti-HBc or HBsAg. Hepatic HBV DNA was undetectable in the 7 patients in group 2 who underwent liver biopsy after OLT. Anti-HBc(+) allografts can be safely used in patients who undergo OLT for chronic hepatitis B and susceptible transplant recipients if prophylaxis with combination HBIG and lamivudine or lamividine alone is administered after OLT, respectively. However, more data are needed to determine the efficacy of lamivudine monotherapy in preventing transmission of HBV infection from anti-HBc(+) liver allografts to susceptible recipients.

Adult↗
PubMed2001

Community acquired pneumonia (CAP): an update.

Community-acquired pneumonia (CAP) remains a common and serious infectious disease worldwide. Recent investigations highlight the difficulties in making etiological diagnosis while emphasizing the importance of atypical pathogens in CAP. Prognostic tools such as the pneumonia severity index have been validated and widely endorsed as an aid in making site of care decisions in managing CAP patients. Empiric treatment guidelines for CAP have been developed and their use has been shown to simplify treatment regimens and improve outcome.

Administration, Oral↗
PubMed2001

Risk factors for prophylaxis failure in patients receiving aerosol pentamidine for Pneumocystis carinii pneumonia prophylaxis.

OBJECTIVE: The purposes of this study were (1) to determine the incidence of prophylaxis failure in HIV-infected patients receiving aerosol pentamidine (AP) for Pneumocystis carinii pneumonia (PCP) prophylaxis, and (2) to identify risk factors for PCP prophylaxis failure. SETTING AND DESIGN: In Ontario, Canada, AP has been made available for outpatient PCP prophylaxis through a centralized government program, the Ontario Drug Distribution and Monitoring Program. Data from this administrative observational database were extracted for 2,227 patients who received AP between May 1989 and December 1998. OUTCOME MEASUREMENTS: The incidence of breakthrough PCP (BPCP) was calculated from the database. A Cox regression model with time-varying covariates was created to examine factors associated with BPCP. The follow-up time was divided into three eras: 1989 to 1991, 1992 to 1994, and 1995 to 1998. These eras were meant to reflect major changes in antiretroviral medication regimens. RESULTS: The overall risk of BPCP was 16.2% over a mean follow-up of 1.67 years. The overall BPCP rate was 9.7/100 patient-years, with rates of 8.8/100, 13.1/100, and 6.3/100 patient-years in each of the three treatment eras. In the multivariate analysis, significant risk factors for prophylaxis failure were low CD4 count, previous diagnosis of PCP, history of AIDS-defining conditions other than PCP, and antiretroviral treatment era defined above. CONCLUSION: The overall rate of PCP prophylaxis failure has decreased significantly after 1995, coincident with the era of highly active antiretroviral therapies. Initiation of PCP prophylaxis remains necessary in patients with risk factors.

Adult↗