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Biomedical subjects

C Chan

Publications and source records attributed to C Chan.

At least 37 records · Page 2Linked to original sources
PubMed1995

Pseudospecific docking surfaces on electron transfer proteins as illustrated by pseudoazurin, cytochrome c550 and cytochrome cd1 nitrite reductase.

The structure of pseudoazurin from Thiosphaera pantotropha has been determined and compared to structures of both soluble and membrane-bound periplasmic redox proteins. The results show a matching set of unipolar, but promiscuous, docking motifs based on a positive hydrophobic surface patch on the electron shuttle proteins pseudoazurin and cytochrome c550 and a negative hydrophobic patch on the surface of their known redox partners. The observed electrostatic handedness is argued to be associated with the charge-asymmetry of the membrane-bound components of the redox chain due to von Heijne's 'positives-inside' principle. We propose a 'positives-in-between' rule for electron shuttle proteins, and expect a negative hydrophobic patch to be present on both the highest and lowest redox potential species in a series of electron carriers.

Azurin↗
PubMed1995

Comparison of outcomes and complications for open and laparoscopic cholecystectomy in Mexico.

A retrospective analysis of the outcome and surgical complications of two groups of patients undergoing cholecystectomy was performed. Group I consisted of 253 patients who underwent laparoscopic cholecystectomy between 1991 and 1994, and group II was formed by 292 patients who met the same preoperative criteria than patients of group I and underwent open cholecystectomy between 1986 and 1990, prior to the introduction of laparoscopic cholecystectomy in our hospital. General characteristics and associated clinical conditions were similar for both groups. Intraoperative cholangiography was used more frequently in group II whereas preoperative ERCP was performed more frequently in group I patients. There was no operative mortality in any of the groups. There were no statistically significant differences between both groups in terms of type and number of complications.

Cholangiopancreatography, Endoscopic Retrograde↗
PubMed1995

Angioscopic evaluation of prolonged vs standard balloon inflations during coronary angioplasty. A randomized study.

UNLABELLED: To study the immediate effects of prolonged total balloon inflation during PTCA, 41 patients (44 lesions) with chronic stable angina were randomized for prolonged sequential inflations (three to five inflations of 3 to 5 min each, for a total duration of > or = 12 min, group 1, n = 20 lesions) or 'standard' sequential inflations (three to five inflations of < or = 1 min each, for a total duration of < or = 3 min, group 2, n = 24 lesions). The mean duration of total balloon inflation time was 958 +/- 129 s in group 1 vs 205 +/- 46 s in group 2. Results of angioplasty were assessed on both angiography and percutaneous transluminal coronary angioscopy performed immediately after the procedure. High quality imaging of the coronary lumen and lesion morphology was possible on angioscopy in all patients without any complications. Post-PTCA angiographic percent diameter stenosis was significantly less in group 1 compared to group 2: 26 +/- 10% vs 36 +/- 8% (P < 0.05). On angioscopy, flaps were seen in 16 patients in group 2, but in only six in group 1 (P < 0.02). There was no difference in the incidence of thrombi on angioscopy between the two groups (group 1: nine cases, group 2: 10 cases). Sensitivity of angiographic detection of flaps and thrombi was poor: 10% and 12% respectively. One patient in each group developed a longitudinal dissection, detected on both angiography and angioscopy. CONCLUSIONS: (1) prolonged sequential balloon inflations lead to less residual luminal stenosis after PTCA, with a decreased incidence of intimal flaps in comparison with standard inflations. (2) Post-PTCA transluminal coronary angioscopy is safe and offers better assessment of luminal effects of PTCA than angiography.

Adult↗
PubMed1995

Clinical behavior and prognostic factors of periampullary adenocarcinoma.

OBJECTIVE: The authors evaluated the outcome and potential prognostic factors of 60 patients with surgically resected periampullary tumors. SUMMARY BACKGROUND DATA: Periampullary carcinomas exhibit different clinical behaviors according to their site of origin. There are no prognostic factors for deciding the type of surgery to be used or for choosing patients with tumors that have a poor prognosis for adjuvant treatment. METHODS: A retrospective review was performed of 15 clinical and pathologic variables encountered among 60 patients with periampullary tumors. Tumors were divided into four groups according to their site of origin. Kaplan-Meier survival curves of the four groups were plotted and differences were evaluated with the log-rank test. Cox's proportional hazards model was used to test for separate and combined independent predictors of disease-free survival. RESULTS: Twenty-nine ampullary carcinomas, 20 ductal pancreatic carcinomas, 7 distal common bile duct carcinomas, and 4 carcinomas of the periampullary duodenum were found. Five-year disease-free survival was 43%, 0%, 0%, and 75%, respectively. According to the Cox analysis, absence of neural invasion and use of adjuvant chemotherapy were significant factors for longer survival of patients with ampullary tumors. Lymphatic invasion was related to a shorter survival in patients with pancreatic carcinoma. CONCLUSIONS: Five-year disease-free survival of patients with periampullary tumors is related to tumor type. Prognosis was better for ampullary tumors if neural invasion was absent and if adjuvant chemotherapy was used. Lymphatic invasion was associated with a shorter recurrence-free survival among patients with pancreatic carcinoma.

Adenocarcinoma↗
PubMed1995

Angiographic evaluation after portal blood flow preserving operations.

We carried out a prospective study comparing postoperative portal angiographic characteristics in patients with hemorrhagic portal hypertension treated electively by two different portal blood flow preserving procedures. Between 1986 and 1991, a total of 81 patients underwent operation: 38 selective shunts and 43 Sugiura-Futagawa procedures. Cirrhosis was shown by biopsy in 50 cases, 26 of them secondary to alcoholism. We found rebleeding in 5% of the patients, incapacitating postoperative encephalopathy in 8%, and an operative mortality of 7%. Fifty-two cases were evaluated in the postoperative period with angiography; 21 patients treated with a Sugiura-Futagawa operation were excluded due to portal vein thrombosis shown in the preoperative studies. Postoperative portal vein thrombosis was found in 11 cases (21%) [seven cases in the Warren group (21%) and four cases in the Sugiura-Futagawa group (20%)]. Decreased portal vein diameter was seen in eight cases (15%). The two procedures maintained hepatopedal portal blood flow, and no change was seen in relation to the preoperative state in 66% of the operated patients. We found no significant differences between the two procedures. Selection of procedure depends on the individual characteristics of each patient.

Adult↗
PubMed1995

Hospital reorganization after merger.

Major organizational changes among hospitals, like system affiliation, merger, and closure, would seem to offer substantial opportunities for hospitals and health systems to be strategic in the local reconfiguration of health services. This report presents the results of a unique survey on what happened to hospitals after mergers occurring between 1983 and 1988, inclusive. Building on an ongoing verification process of the American Hospital Association, surviving institutions from all 74 mergers that occurred during the study frame were surveyed in the fall of 1991. Responses were received from 60 of the 74 mergers (81%), regarding the primary, postmerger use of the hospitals involved. Topics surveyed included the premerger competition between the hospitals and in their environment, and what happened to the hospitals after their mergers. Mergers frequently served to convert acute, inpatient capacity to other functions, with less than half of acquired hospitals continuing acute services after merger. In the context of health care reform, mergers may offer an expeditious way locally to restructure health services. Evidence on the postmerger uses of hospitals and about the reasons given for merger suggests that mergers may reflect two general strategies: elimination of direct acute competitors or expansion of acute care networks.

Data Collection↗
PubMed1995

Expression of the genes encoding the rat renal insulin-like growth factor-I system.

Insulin-like growth factor-I (IGF-I) modulates renal function, growth, and repair. IGF-I produced in the kidney is one component of the intrarenal IGF-I system comprising the IGF-I receptor (IGF-IR) and six IGF-binding proteins (IGFBP). Because of the physiologic importance of IGF-I and its potential therapeutic properties, the renal sites of mRNA synthesis for IGF-I, IGF-IR, and IGFBP-I through IGFBP-5 were characterized in rat kidney by in situ hybridization. Anatomical heterogeneity was prominent. IGF-I mRNA was present in the thick ascending limb of Henle in the outer medulla, whereas IGF-IR mRNA was diffusely present at low levels throughout the kidney. IGFBP-I mRNA was localized to cells within the distal convoluted tubules as well as the thick ascending limb of Henle. IGFBP-2 mRNA was expressed in glomeruli, medullary ray collecting ducts, pelvic smooth muscle and uroepithelium, and the papilla tip; IGFBP-3 mRNA was localized to the cortical interstitium, whereas IGFBP-4 mRNA was expressed in proximal tubules, medullary ray collecting ducts, and glomeruli. IGFBP-5 was strongly positive throughout the medulla with lesser expression in the distal convoluted tubules and glomeruli. This study highlights the complexity of the intrarenal IGF-I system. The striking heterogeneity of IGFBP gene expression suggests that the various IGFBP may have diverse modulatory effects on the action of IGF-I or discrete effects of their own.

Animals↗
PubMed1995

Effectiveness and safety of paediatric interventional cardiac catheterisation in a subregional cardiothoracic unit.

OBJECTIVE: To assess the effectiveness and safety of paediatric interventional cardiac catheterization during the development of the service. SETTING: Sub-regional Paediatric Cardiothoracic Centre. PATIENTS AND METHODS: All paediatric admissions for cardiac catheterisation between January, 1985 and December, 1992. Data were collected on all patients in whom interventional cardiac catheterisation was performed excluding babies undergoing balloon atrial septostomy. Results were compared with those reported previously by the larger centres. RESULTS: One hundred and seventy eight interventional procedures were performed in 158 patients, progressing from pulmonary valvuloplasty (1985) and aortic valvuloplasty (1986) to arterial duct occlusion and coil embolisation of shunts (1991). During the study period there was a rise in the number and variety of conditions for which interventional cardiac catheterisation was performed. In terms of morbidity, mortality and technical success, results compared favourably with those published from larger centres. CONCLUSIONS: Interventional cardiac catheterisation in children can be established effectively and safely in a relatively smaller set up.

Adolescent↗
PubMed1995

Sustained vasoconstriction associated with daily cyclosporine dose in heart and lung transplant recipients: potential pathophysiologic role of endothelin.

Transient decreases in glomerular filtration rate (GFR) and renal plasma flow (RPF) have been associated with each daily dose of cyclosporine (CYA) in patients with renal allografts. We examined the differential dose effects of CYA on native renal function in 24 recipients of heart or lung transplants (treated with 7.3 +/- 0.5 mg/kg/day [mean +/- SEM]) and in seven patients with psoriasis (treated with 4.2 +/- 0.7 mg/kg/day). GFR and RPF were measured by urinary inulin and para-aminohippuric acid clearances 2 hours before the morning CYA dose and for 6 hours after. The age of heart and lung transplant recipients at renal study (2 months after transplantation) was 47 +/- 2.0 years. Their serum creatinine levels rose from 80 +/- 4.0 mumol/L during the first week after transplantation to 120 +/- 4.0 mumol/L at renal study (p < 0.0001). Their GFR and RPF were decreased before the CYA dose at 64 +/- 2.4 and 340 +/- 16 ml/min per 1.73 m2 and did not vary during the study. In comparison, the age of patients with psoriasis was 51 +/- 4.6 years at renal study (24 +/- 4.0 months after CYA treatment). Their serum creatinine levels rose from 80 +/- 4.0 mumol/L before treatment to 100 +/- 10 mumol/L at renal study (p = 0.07). Transient decreases of their baseline GFR and RPF (85 +/- 7.4 and 380 ml/min per 1.73 m2) with a nadir occurring during the first 2 hours of CYA ingestion were observed together with the recovery of these parameters toward baseline by the end of the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporine↗
PubMed1995

Correlation between steady-state plasma concentration of antituberculous drugs and age, inclusion of rifampicin in the treatment regimen, adverse drug reactions and other clinical parameters.

A regional hospital in Hong Kong examined the correlation between plasma concentrations of rifampicin, pyrazinamide, isoniazid and its metabolite hydrazine and age, inclusion of rifampicin in the treatment regimen, adverse drug reactions and other clinical parameters. One hundred eighty subjects with tuberculosis were admitted consecutively to the medical wards of the Prince of Wales Hospital over a one and a half year period. Elderly patients > 65 years were randomized into one of two treatments with and without rifampicin in addition to isoniazid, pyrazinamide and ethambutol; younger patients received all four drugs. Plasma antituberculous drug concentrations were determined using high performance liquid chromatography. Elderly patients taking rifampicin had a higher mean steady-state concentration of isoniazid, together with a higher incidence of adverse effects compared with those not taking rifampicin. No age related differences were observed for the other drugs. For the whole group, higher mean concentrations of hydrazine, rifampicin and pyrazinamide were associated with a higher incidence of adverse effects and the presence of coexisting diseases. It is concluded that in sick elderly patients with coexisting diseases, use of rifampicin in the antituberculous regimen should be accompanied by close monitoring for side effects, and that there may be an indication for use of lower dosages of antituberculous drugs in such patients.

Adult↗
PubMed1995

Percutaneous balloon valvuloplasty in mitral restenosis after previous surgical commissurotomy.

OBJECTIVES: The aim of this study was to determine the safety profile, mitral valve outcome and follow-up functional status after percutaneous balloon mitral valvuloplasty (PBMV) in patients with mitral restenosis post-surgical commissurotomy. METHODS: Sixteen patients with symptomatic mitral restenosis after previous surgical commissurotomy underwent valvuloplasty using the Inoue balloon stepwise dilatation method. Echocardiography was performed before and after the procedure to evaluate the mitral valve area. RESULTS: All procedures were successfully completed without cardiac perforation, thromboembolism, resultant severe mitral regurgitation or death. The mitral valve area improved from 0.9 +/- 0.2 to 1.6 +/- 0.3 (p = 0.0001), accompanied by a significant immediate reduction in the left atrial pressure and transmitral gradient. Compared with PBMV in patients without past mitral surgery, patients with mitral restenosis undergoing PBMV experienced less valve area improvement but the difference was not significant (p = 0.137). Optimal valve enlargement resulting in mild mitral stenosis was achieved in 12 of the 16 patients. Midterm symptomatic benefit was observed in almost all patients. CONCLUSIONS: In view of the excellent success rate, low complication risk, the optimal haemodynamic results and favourable functional outcome afforded by mitral balloon valvuloplasty in patients with mitral restenosis after prior surgical commissurotomy, it is logical that balloon mitral valvuloplasty, where available, should be the initial treatment modality in this group of patients with suitable valve morphology before considering repeat mitral surgery.

Adult↗
PubMed1994

Determinants of serum 1,25-dihydroxyvitamin D concentration in healthy premenopausal subjects.

Concentrations of serum phosphate and parathyroid hormone (PTH) are well known regulators of the production of 1,25-dihydroxyvitamin D (1,25-(OH)2D) and acidosis is known to affect the serum concentration of 1,25-(OH)2D. However, the factors that play a role in the regulation of serum 1,25-(OH)2D concentration in healthy subjects have not been fully evaluated. The associations of ionised calcium, pH, serum concentration of phosphate, PTH, 25-hydroxyvitamin D (25-OHD) and serum 1,25-(OH)2D were examined in 296 healthy premenopausal women (age range 17-40 years). Calculation of partial correlation coefficients showed that serum 1,25-(OH)2D was significantly correlated with phosphate (r = -0.148, P < 0.01), pH (r = 0.221, P < 0.001) and PTH (r = 0.136. P < 0.01). Ionised calcium was not related to serum 1,25-(OH)2D. When the results were stratified according to quartiles based on serum 1,25-(OH)2D concentration, significant trends (by analysis of variance) were seen in phosphate, pH, age, albumin and 25-OHD. Stepwise multiple regression analysis showed that phosphate and pH were the major contributors of serum 1,25-(OH)2D levels. There was a small contribution from PTH and 25-OHD. The results suggest that in young healthy premenopausal women plasma phosphate and pH may be important determinants of serum 1,25-(OH)2D concentration.

Adolescent↗
PubMed1994

Thiopyrano[2,3,4-cd]indoles as 5-lipoxygenase inhibitors: synthesis, biological profile, and resolution of 2-[2-[1-(4-chlorobenzyl)-4-methyl-6-[(5-phenylpyridin-2-yl)methoxy]-4,5 -dihydro-1H-thiopyrano[2,3,4-cd]indol-2-yl]ethoxy]butanoic acid.

Leukotriene biosynthesis inhibitors have potential as new therapies for asthma and inflammatory diseases. The recently disclosed thiopyrano[2,3,4-cd]indole class of 5-lipoxygenase (5-LO) inhibitors has been investigated with particular emphasis on the side chain bearing the acidic functionality. The SAR studies have shown that the inclusion of a heteroatom (O or S) in conjunction with an alpha-ethyl substituted acid leads to inhibitors of improved potency. The most potent inhibitor prepared contains a 2-ethoxybutanoic acid side chain. This compound, 14d (2-[2-[1-(4-chlorobenzyl)-4-methyl-6-[(5-phenylpyridin-2-yl)methox y]- 4,5-dihydro-1H-thiopyrano[2,3,4-cd]indol-2-yl]ethoxy]-butanoic acid, L-699,333), inhibits 5-HPETE production by human 5-LO and LTB4 biosynthesis by human PMN leukocytes and human whole blood (IC50s of 22 nM, 7 nM and 3.8 microM, respectively). The racemic acid 14d has been shown to be functionally active in a rat pleurisy model (inhibition of LTB4, ED50 = 0.65 mg/kg, 6 h pretreatment) and in the hyperreactive rat model of antigen-induced dyspnea (50% inhibition at 2 and 4 h pretreatment; 0.5 mg/kg po). In addition, 14d shows excellent functional activity against antigen-induced bronchoconstriction in the conscious squirrel monkey [89% inhibition of the increase in RL and 68% inhibition in the decrease in Cdyn (0.1 mg/kg, n = 3)] and in the conscious sheep models of asthma (iv infusion at 2.5 micrograms/kg/min). Acid 14d is highly selective as an inhibitor of 5-LO activity when compared to the inhibition of human 15-LO, porcine 12-LO and ram seminal vesicle cyclooxygenase (IC50 > 5 microM) or competition in a FLAP binding assay (IC50 > 10 microM). Resolution of 14d affords 14g, the most potent diastereomer, which inhibits the 5-HPETE production of human 5-LO and LTB4 biosynthesis of human PMN leukocytes and human whole blood with IC50s of 8 nM, 4 nM, and 1 microM respectively. The in vitro and in vivo profile of 14d is comparable to that of MK-0591, which has showed biochemical efficacy in inhibiting ex vivo LTB4 biosynthesis and urinary LTE4 excretion in clinical trials.

Animals↗
PubMed1994

Determinants of bone mass in Chinese women aged 21-40 years. II. Pattern of dietary calcium intake and association with bone mineral density.

A study on the determinants of bone mass in young women is being carried out among 287 young Chinese women aged 21-40 years. The baseline cross-sectional data show that the mean dietary calcium intake, estimated from the quantitative food frequency method, was 448 mg/day (standard deviation = 219). About 50% of the calcium source was from vegetables and 22% from dairy products. Among women aged 21-30 years, those with a dietary calcium intake of at least 600 mg/day had a 4%-7% higher mean bone mineral density at the spine and femur when compared with those with a mean intake below 300 mg/day. In women aged 31-40 years, subjects belonging to the highest quartile of calcium density (> or = 35 mg/420 kJ) had a 3%-8% higher mean bone mineral density at the spine and femur when compared with those in the lowest quartile (< 20.8 mg/420 kJ). Favorable calcium intake is beneficial in this population of young women with habitual low dietary calcium intake.

Adult↗
PubMed1994

Expression of I mu-C gamma hybrid germline transcripts subsequent to immunoglobulin heavy chain class switching.

Germline CH transcripts initiate from a non-coding I exon and terminate downstream of the associated CH exons. Ig heavy chain class switch recombination from the VDJ-C mu gene to particular downstream CH genes appears to be regulated by a process that involves mitogen and/or cytokine induction of germline CH transcripts from the downstream genes. We have examined the expression of germline C mu transcripts (I mu-C mu transcripts) in splenic B cells and pre-B cell lines after cytokine and mitogen stimulation. In contrast to the expression of the germline transcripts from downstream CH genes, expression of germline C mu transcripts was constitutive and unaffected by mitogen and cytokine treatment. After a primary switch recombination event, the germline I mu promoter, which is now associated with a downstream CH gene, continues to be active--leading to the generation of a novel germline transcript consisting of the I mu exon spliced to the CH exons of the switched CH gene. We discuss the potential role of the expression of hybrid I mu-containing transcripts in the class switch process. We also describe a novel and sensitive assay, based on the detection of the hybrid I mu-containing transcripts, that allows detection of class switch recombination events even in heterogeneous populations of cells.

Animals↗
PubMed1994

Congenital cutis laxa with a dominant inheritance and early onset emphysema.

Two cases (mother and daughter) are reported of autosomal dominant cutis laxa which are unusual in being associated with early onset emphysema. Both mother and daughter have been smokers and are heterozygotes for the alpha 1 antitrypsin genotype. The combination of cigarette smoking and subnormal alpha 1 antitrypsin levels may explain the pulmonary spread in these two women who have what is usually a benign form of cutis laxa limited to the skin.

Adult↗
PubMed1994

Acute outcome of percutaneous Inoue-balloon mitral commissurotomy.

This study examines the acute results and the potential impact, if any, of 16 clinical, echocardiographic, hemodynamic and balloon-related variables on the acute outcomes of Inoue-balloon percutaneous transvenous mitral commissurotomy (PTMC). Of 107 patients, PTMC was successfully completed in 105 (98%) without cardioembolism or death, and resulted in an increase in mitral valve area from 0.8 +/- 0.2 cm2 to 1.7 +/- 0.4 cm2 (p = 0.0001) as assessed echocardiographically. Optimal results defined as a valve area improvement of > or = 50% and/or a final valve area of > or = 1.5 cm2 without significant mitral regurgitation (> or = 2 grade increase in mitral regurgitation or a final regurgitation > or = 3+) was obtained in 96 patients (91%). Significant mitral regurgitation was observed in six patients. On univariate analysis, patients with suboptimal results were older (52 +/- 7 vs. 44 +/- 10 years, p = 0.037) and were likely to have the procedure performed during the learning phase (first 33 vs.. subsequent 72 patients, p = 0.007) than those with optimal results, and patients with resultant significant mitral regurgitation had more severe pre-existing mitral regurgitation compared with those without (1.4 +/- 0.5 vs. 0.7 +/- 0.7, p = 0.0098). However, there were no independent predictors of either acute outcome identified in multivariate analysis. We therefore conclude that although Inoue-balloon PTMC is a safe and highly effective procedure with a low risk of creating severe mitral regurgitation, the acute outcomes cannot be accurately predicted.

Adult↗