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Biomedical subjects

S C Chan

Publications and source records attributed to S C Chan.

At least 37 records · Page 2Linked to original sources
PubMed2001

Prevention of recurrent central venous stenosis using endovascular irradiation following stent placement in hemodialysis patients.

This study was done to evaluate the outcome after brachytherapy (BT) given to prevent restenosis after stent insertion for central venous stenosis in patients with ipsilateral hemodialysis arteriovenous fistulas (AVF). Angioplasty and stenting were performed on 9 primary central venous stenoses in 8 patients with AVF followed by BT, delivering Iridium-192 radiation using an afterloading technique. BT was also administered to three patients with five recurrent stenoses at the stent margins. There was no residual stenosis after angioplasty and stenting. Venographic follow-up (77-644 days, mean 272 days) showed no restenosis in seven primary stenoses. New strictures (45%-100%) developed at the stent margin in six veins (five patients). Angioplasty or stenting was performed for five margin stenoses in three patients, followed by a second BT. Residual stenosis before BT was 0-30%. In our venographic follow-up (140-329 days, mean 215 days), three restenoses occurred (35%-100%). All progressed to complete occlusion on later venographic follow-up irrespective of whether BT was given to the stent margin or not. The mean primary and assisted primary patency of the central veins were 359 days and 639 days, respectively. Endovascular irradiation with a noncentering source does not prolong the patency after angioplasty and stenting of central venous stenosis in hemodialysis patients.

Adult↗
PubMed2001

Significance of local electrostatic interactions in staphylococcal nuclease studied by site-directed mutagenesis.

In this paper, we show that amino acids Glu(73) and Asp(77) of staphylococcal nuclease cooperate unequally with Glu(75) to stabilize its structure located between the C-terminal helix and beta-barrel of the protein. Amino acid substitutions E73G and D77G cause losses of the catalytic efficiency of 24 and 16% and cause thermal stability losses of 22 and 26%, respectively, in comparison with the wild type (WT) protein. However, these changes do not significantly change global and local secondary structures, based on measurements of fluorescence and CD(222 nm). Furthermore, x-ray diffraction analysis of the E75G protein shows that the overall structure of mutant and WT proteins is similar. However, this mutation does cause a loss of essential hydrogen bonding and charge interactions between Glu(75) and Lys(9), Tyr(93), and His(121). In experiments using double point mutations, E73G/D77G, E73G/E75G, and E75G/D77G, significant changes are seen in all mutants in comparison with WT protein as measured by fluorescence and CD spectroscopy. The losses of thermal stability are 47, 59, and 58%, for E73G/D77G, E73G/E75G, and E75G/D77G, respectively. The triple mutant, E73G/E75G/D77G, results in fluorescence intensity and CD(222 nm) close to those of the denatured state and in a thermal stability loss of 65% relative to the WT protein. Based on these results, we propose a model in which significant electrostatic interactions result in the formation of a locally stable structure in staphylococcal nuclease.

Calorimetry, Differential Scanning↗
PubMed2001

Organic light-emitting materials based on bis(arylacetylide)platinum(II) complexes bearing substituted bipyridine and phenanthroline ligands: photo- and electroluminescence from 3MLCT excited states.

We present the synthesis and photophysical and electroluminescent properties for a series of platinum(II) alpha-diimine bis(arylacetylide) complexes. The molecular structures of five derivatives have been elucidated by X-ray crystallography. Intermolecular pi-pi interactions (between aromatic diimine and phenylacetylide moieties) are apparent in the crystal lattices of two of these. All bis(phenylacetylide) derivatives exhibit intense triplet metal-to-ligand charge transfer (MLCT) photoluminescence in the solid state and in fluid solutions at room temperature. The impact of different solvents, substituents on the diimine ligands, and complex concentrations upon their emissive behavior have been examined and demonstrates that their emission energies can be systematically modified. Application of the 3MLCT excited state of the [Pt(alpha-diimine) (C(triple bond)CPh)2] materials in single- and double-layer organic light-emitting devices are described. The bis(butadiynyl) complex [Pt(4,4'-dtbpy)(C(triple bond)C-C(triple bond)CPh)2] (dtbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) displays strong solid-state and solution phosphorescence at 77 and 298 K; the associated excited state is proposed to arise from both acetylenic 3pi pi*(C(triple bond)C-C(triple bond)CPh) and 3MLCT [Pt --> pi*(diimine)] transitions.

Journal Article↗
PubMed2001

Secretin facilitates GABA transmission in the cerebellum.

Secretin was the first hormone discovered in human history, and yet, its function as a neuropeptide has been overlooked in the past. The recent discovery of the potential use of secretin in treating autistic patients, together with the conflicting reports on its effectiveness, urges an in-depth investigation of this issue. We show here that in the rat cerebellar cortex, mRNAs encoding secretin are localized in the Purkinje cells, whereas those of its receptor are found in both Purkinje cells and GABAergic interneurons. Immunoreactivity for secretin is localized in the soma and dendrites of Purkinje cells. In addition, secretin facilitates evoked, spontaneous, and miniature IPSCs recorded from Purkinje cells. We propose that secretin is released from the somatodendritic region of Purkinje cells and serves as a retrograde messenger modulating GABAergic afferent activity.

Adenylyl Cyclases↗
PubMed2001

Neurologic injury after endovascular stent-graft and bilateral internal iliac artery embolization for infrarenal abdominal aortic aneurysm.

The authors report a rare neurologic complication after the implantation of a bifurcated stent-graft for abdominal aortic aneurysm. The stent-graft was extended to both external iliac arteries after embolization of both internal iliac arteries. The patient subsequently had weakness and numbness of both lower limbs with bowel and bladder incontinence. He probably had ischemic injury to the nerve roots or the lumbosacral plexus, which was related to extensive occlusion of their supplying arteries. The mechanism of spinal cord and neurologic ischemia after aortic stent-graft implantation is discussed.

Aged↗
PubMed2001

The management of severe infectious mononucleosis tonsillitis and upper airway obstruction.

Acute tonsillectomy has been advocated for severe infectious mononucleosis (IM) pharyngotonsillitis with upper airway obstruction (UAO) and not responding to corticosteroids. This paper reviews and rationalizes our management. A five-year chart review was carried out with a follow-up telephone survey. There were 36 admissions. Nine had UAO of whom 89 per cent (eight of nine patients) had a tonsillectomy. The diagnosis of UAO was not standardized. Twenty-seven patients did not have UAO and only a small proportion of these patients, 16 per cent (four of 25) went on to have an elective tonsillectomy. Corticosteroids made no significant difference to the tonsillectomy rate. UAO appears to identify patients with more severe disease who are likely to suffer recurrent tonsillitis. Acute tonsillectomy is an appropriate treatment option for this subgroup. The diagnosis of significant IM UAO is not defined and a schema is proposed. Recurrent tonsillitis is an uncommon sequela of severe IM pharyngotonsillitis without UAO.

Adolescent↗
PubMed2001

Efficacy of zafirlukast in the treatment of patients with bronchial asthma.

Zafirlukast is a drug newly used for the treatment of asthma. In this study, we examined the efficacy of zafirlukast on asthmatic patients and compared this efficacy between patients in different age groups and with different severities of pulmonary function. Patients concurrently inhaled long-acting beta2-agonist, corticosteroid or taken an oral aminophylline regimen, were treated with 20 mg oral zafirlukast twice daily for 6 weeks. In total, 32 asthmatic patients were included in the study. The primary efficacy measures included morning and evening peak expiratory flows (PEFs); secondary efficacy measures were the scoring of asthma symptoms including sleeping, coughing, and wheezing scores. Pulmonary functions including forced expiratory flow in 1 sec (FEV1), forced vital capacity (FVC), and PEF rate (PEFR) were examined during each clinical visit. Results showed that oral zafirlukast administration resulted in improvements in morning and evening PEFs and asthma symptom scores with the following statistical p values: morning PEF (285.8 vs 308.4 L/min), p = 0.003; evening PEF (293.3 vs 312.1 L/min), p = 0.007; coughing score (1.03 vs 0.72), p = 0.011; and wheezing score (0.71 vs 0.51), p = 0.009. As to the pulmonary function during the clinical visit, only the improvement of PEFR reached a statistically significant level (74.3 vs 82, p = 0.017). We compared the efficacy between asthmatic patients of different ages and those with different severities of pulmonary function. In patients aged below 50 years, those with FEV1 above 80% of the predicted value and FVC above 85% of the predicted value were more responsive to zafirlukast. In conclusion, we demonstrate the efficacy of zafirlukast in asthma therapy particularly for those patients who are younger and have better pulmonary function. When asthmatic patients do not respond to inhaled corticosteroid, long-acting beta2-agonist, or oral aminophylline, zafirlukast may provide an adjunct effect for asthma therapy.

Administration, Oral↗
PubMed2001

Enhanced prostaglandin E2 secretion in sputum from asthmatic patients after zafirlukast therapy.

BACKGROUND AND PURPOSE: Leukotrienes are important inflammatory mediators of bronchial asthma that cause bronchoconstriction, mucous secretion, and increased vascular permeability. Current guidelines recommend anti-leukotriene agents as alternative treatments for asthma; however, data on their anti-inflammatory effect is lacking. METHODS: The purpose of this study was to determine the anti-inflammatory effect of zafirlukast, a leukotriene antagonist, in patients with bronchial asthma. A total of 30 adult patients with mild persistent asthma received 6 weeks of zafirlukast treatment. Peak expiratory flow rate (PEFR) was determined before and after therapy to assess clinical efficacy. Both serum and sputum samples were collected before and after therapy and concentrations of eosinophil cationic protein (ECP), prostaglandin E2 (PGE2), and leukotriene E4 (LTE4) were measured. RESULTS: A significant improvement in PEFR was found after zafirlukast therapy (p = 0.017). There was also a significant reduction in serum ECP concentration (13.6 +/- 2.4 micrograms/L vs 10.3 +/- 2.1 micrograms/L, p < 0.025) and a significant increase in sputum PGE2 concentration (112.7 +/- 14.0 pg/mL vs 176.8 +/- 32.1 pg/mL, p < 0.01). The percentage eosinophil count and the concentrations of ECP and LTE4 in the sputum were not significantly different after therapy. CONCLUSION: This study found a significant reduction in serum ECP and a significant increase in sputum PGE2 concentrations in asthmatic patients after zafirlukast treatment, both of which were significantly associated with improvement in PEFR. The modulation of PGE2 and ECP production might occur through the anti-inflammatory effect of zafirlukast.

Adult↗
PubMed2000

Sonographic diagnosis of a small fistulous communication between a subphrenic abscess and a perforated duodenal ulcer.

We report a case of a fistula between a subphrenic abscess and a perforated duodenal ulcer diagnosed by sonography and confirmed by CT. The sonographic findings included a subphrenic fluid collection connected to the anterior aspect of the superior duodenum by a nonpulsatile, anechoic tubular lesion. Manual compression of the upper epigastrium resulted in movement of echogenic debris from the antrum and superior duodenum through the fistulous tract into the abscess.

Aged↗
PubMed2000

A randomized clinical trial comparing autologous blood clot and gelfoam in transarterial chemoembolization for inoperable hepatocellular carcinoma.

BACKGROUND/AIM: Inoperable hepatocellular carcinoma is common in Asia and is usually treated with repeated transarterial chemoembolization. Gunji et al. showed better survival and fewer complications with autologous blood clot as compared with gelfoam used for embolization. Our aim was to compare the effect of blood clot versus gelfoam. METHODS: We conducted a prospective randomized trial in 100 patients with inoperable hepatocellular carcinoma, and compared the side effects and cumulative survival in the two groups. Cox's proportional hazard model was used to study the prognostic factors. RESULTS: The diameter of the main tumor was 7.9+/-4.6 cm. Our study did not show additional beneficial effects of blood clot. The proportion of side effects was similar and the common ones included fever, pain and vomiting. Though the hepatic artery remained patent for a longer period with blood clot (p=0.061), there was no difference in survival (p=0.129 for Okuda I disease and p=0.388 for Okuda II disease). Subgroup analysis showed longer survival in patients with vascular occlusion (p=0.034 for Okuda I and p=0.029 for Okuda II disease). The independent factors of survival were sex, Child's class, Okuda stage, tumor type and presence of metastases. CONCLUSION: This study showed no additional benefits of blood clot in patients with inoperable hepatocellular carcinoma, in Okuda I and II disease. The longer survival in patients with vascular occlusion suggested that the damage to normal liver tissue by planned periodic transarterial chemoembolization may outweigh its benefit in later sessions of repeated TACE in certain patients.

Aged↗
PubMed2000

Neutrophil-mediated degradation of lung proteoglycans: stimulation by tumor necrosis factor-alpha in sputum of patients with bronchiectasis.

Neutrophil-mediated degradation of bronchial matrix has been proposed as a pathogenetic factor in bronchiectasis. We hypothesize that neutrophils, found in abundance in the bronchial lumens of patients with bronchiectasis, are capable of degrading lung matrix proteoglycans and that proinflammatory mediators in bronchial secretions of these patients can enhance the degradative action of neutrophils. We used rat bronchoalveolar proteoglycans entrapped in polyacrylamide gel beads as a substrate for test incubations with neutrophils from healthy volunteers and sputum sol from patients with idiopathic bronchiectasis. Coincubations with specimens of sputum sol and neutrophils showed proteoglycan degradation indices (PDIs) in excess of the sum of indices due to incubation with either heat-inactivated sputum sol or heat-inactivated neutrophils, suggesting sputum stimulation of the neutrophil response. Mediation of this stimulation by tumor necrosis factor (TNF)-alpha was suggested because (1) indices for the coincubations correlated with sputum levels of TNF-alpha and (2) an anti-TNF-alpha antibody completely attenuated the sputum-stimulated effect. Furthermore, recombinant human TNF-alpha required accompanying sputum sol to exert an enhancing effect on neutrophil-mediated proteoglycan degradation. Because neutrophil-mediated proteoglycan degradation in the coincubations was inhibited largely (90%) by Eglin C and much less so (8% to 20%) by ethylenediamine tetraacetic acid, we conclude that serine proteases secreted by neutrophils were mainly responsible for degradation of proteoglycans in the model matrix and that the secretion was stimulated by TNF-alpha in the presence of cofactors in the bronchial secretions of patients with bronchiectasis.

Animals↗
PubMed2000

Effects of an extended-interval dosing regimen of triptorelin depot on the hormonal profile of patients with endometriosis: prospective observational study.

OBJECTIVE: To evaluate the suppression of pituitary gonadotrophins and ovarian steroid hormone with the administration of triptorelin depot at 6-weekly intervals. DESIGN: Prospective observational study. SETTING: Obstetrics and gynaecology department of a public hospital, Hong Kong. PATIENTS: Consecutive patients with endometriosis, as diagnosed by laparoscopy or laparotomy from June 1998 through February 1999. INTERVENTION: Administration of four doses of triptorelin depot 3.75 mg either subcutaneously or intramuscularly every 6 weeks (21 patients), or conventional 4-weekly six-dose regimen (five patients). MAIN OUTCOME MEASURES: Serum levels of 17-beta-oestradiol, luteinizing hormone, and follicle-stimulating hormone; and pelvic pain symptoms. RESULTS: For the patients receiving the extended-interval dosing regimen of triptorelin, the levels of oestradiol and luteinizing hormone, and the pain score were significantly reduced throughout the treatment period and up to 10 weeks after the injection of the last dose. The level of follicle-stimulating hormone increased slowly but was still significantly lower than pretreatment levels. The hormonal profile was similar to that of patients receiving the conventional regimen. CONCLUSION: The use of the extended-interval dosing regimen of triptorelin depot results in a consistent hypo-oestrogenised state, which is similar to that achieved by the conventional regimen and which would be considered satisfactory for the medical treatment of pelvic endometriosis. The new regimen thus reduces the cost of treatment without compromising the effect on hormonal suppression.

Adult↗
PubMed1999

'Equivalent geometry' of the knee and the prediction of tensions along the cruciates: an experimental study.

In this paper we introduce the concept of the functional (or equivalent) geometry of the knee, which is an attempt to reduce the natural knee with its complex geometry, frictional resistance and deformable cartilage into a two-dimensional joint comprising rigid femur and tibia in frictionless contact. An apparatus and method are described to measure the slope of the tangent to the surfaces of the 'equivalent' bones at their 'point' of contact. An antero posterior force of +/-300-500 N and axial compressive load of twice body weight were applied on cadaveric knee joints. The corresponding displacement of the tibia in the saggital plane was measured firstly with both cruciates intact and then when each was severed in turn. From the data obtained both the slope of the tangent mentioned above and the tensions developed along the cruciates under the influence of the forces applied were calculated. The results showed that the functional geometry of the knee in the saggital plane can be represented by a convex femur and a concave tibia. The tensions along the cruciates calculated on the basis of the experimental measurements were nearly always lower than the antero posterior force applied, and although this corroborated the trend demonstrated in a previous theoretical analysis, they were lower still. The reason for this may be the deformation of the cartilage under load, thus modifying the geometry of contact resulting in a more concave tibia of the 'equivalent' knee joint, than that of the rigid model used in the theoretical analysis.

Anterior Cruciate Ligament↗
PubMed1999

Hepatic abscess due to gastric perforation by ingested fish bone demonstrated by computed tomography.

Perforation of the gastrointestinal tract by ingested foreign bodies is rare. Preoperative diagnosis of complications due to foreign bodies in the gastrointestinal tract can rarely be achieved because the conventional radiographic appearance is nonspecific. This report describes a 69-year-old woman who presented with vague clinical manifestations, intermittent abdominal pain, and low-grade fever. Hepatic abscess, secondary to a foreign body penetrating the gastric wall, was diagnosed preoperatively using computed tomography findings. On exploration, the foreign body turned out to be a fish bone. The abscess was confirmed and drained during surgery and a partial gastrectomy was performed. This case illustrates the value of CT in the evaluation of this condition.

Aged↗
PubMed1999

Appropriateness of medical admissions from a Malaysian public primary care clinic.

Appropriateness of medical admissions from a Malaysian public primary care clinic (Outpatient Department, Hospital Ipoh) was assessed by two physicians using a modified appropriateness evaluation protocol. Of 122 admissions between 16/6/96 and 15/7/96, 107 records (88%) could be traced from the records office. Eighty percent (86/107) were found to be appropriate and 20% (21/107) inappropriate admissions. Inappropriate admissions included admissions to the wrong discipline and patients who could be investigated and stabilised as outpatients or could be referred to specialist clinics. Protocols, provisions for urgent referrals and medical updates for doctors are recommended.

Ambulatory Care Facilities↗
PubMed1999

Practice of breast self-examination amongst women attending a Malaysian Well Person's Clinic.

The practice of breast self-examination (BSE) amongst 1,303 women registered with the Well Person's Clinic, Outpatient Department, Hospital Ipoh between April 1995 and March 1997 were assessed through a questionnaire. Majority (98.2%) were never taught and did not practise BSE, 17(1.3%) practised BSE while 6 (0.5%) were taught BSE but failed to put it into practice. Only 5.8% of 52 women with past/family history of breast cancer/lump and 2.9% of 207 women with past/family history of other cancers were practising BSE regularly. Three out of 64 women with breast lumps found on clinical breast examination discovered the lumps themselves. Five of the 64 women were subsequently confirmed to have breast carcinoma.

Ambulatory Care Facilities↗