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Biomedical subjects

W Chan

Publications and source records attributed to W Chan.

At least 91 records · Page 5Linked to original sources
PubMed1996

Assessment of left ventricular function after radiofrequency and direct current atrioventricular node ablation.

BACKGROUND: There is limited information available regarding the effect of catheter ablation of the antioventricular (AV) junction on left ventricular (LV) function. Both deterioration and improvement in LV function have been reported following direct current (DC) ablation of the AV junction. The deterioration of LV function following DC ablation of the AV junction may be due to the accompanying barotrauma, DC arcing and direct coagulation, or even the effects of chronic ventricular pacing. If this deterioration of LV function was a result of the accompanying effects of DC shock, the use of radiofrequency ablation (RF) should not result in deterioration of LV function. AIM: To study LV function before and after different methods of AV junction ablation and in patients with chronic ventricular pacing without AV junction ablation. MATERIAL: This study assessed LV function in patients following RF ablation, low energy DC ablation of the AV junction and compared the results with our previously reported finding in patients who had AV junction ablation using high energy DC shock. A group of patients undergoing permanent single chamber ventricular pacemaker implantation without AV junction ablation were selected as controls. METHODS: All patients were paced in the ventricle at 110 beats/minute during LV function assessment by radionuclide angiography. Global LV function and segmental wall motion abnormalities were assessed before, immediately following and three months after ablation. RESULTS: In the high energy DC ablation group, a fall in global LV function (50 +/- 3.0% to 43 +/- 3.0%, p = 0.02) and impairment of segmental wall motion were detected. Low energy DC ablation resulted in segmental wall motion impairment similar to high energy DC but without affecting global ejection fraction (47.0% +/- 6.7 to 45.5% +/- 3.1, p > 0.05). Neither RF ablation (44.0% +/- 3.3 to 45.3% +/- 3.5, p > 0.05), nor chronic pacing (46.7% +/- 4.9 to 47.0% +/- 2.9 p > 0.05) had any effect on global or segmental LV function. CONCLUSIONS: Low energy DC or RF ablation of the AV junction does not affect global LV ejection fraction. The deterioration of global LV function after high energy DC shock ablation appears to be related to the accompanying effects of DC energy and not to the effects of chronic ventricular pacing.

Adult↗
PubMed1996

Vitamin E ameliorates adverse effects of endothelial injury in brain arterioles.

Endothelium-dependent dilation, produced by applying acetylcholine (ACh) to pial arterioles, was unaffected after 6 mo of a diet with zero vitamin E or 8 mo of a vitamin E-enriched diet. The enriched diet did not affect constriction produced by topically applied NG-monomethyl-L-arginine, an inhibitor of the synthesis of endothelium-derived relaxing factor (EDRF). EDRF mediates the response to ACh and is a basally released dilator and antiplatelet paracrine substance. Endothelial injury produced by a helium-neon laser and Evans blue technique eliminates the response to ACh, but in vitamin E-enriched mice the response to ACh was unaffected by the injury. More prolonged exposure of the laser induces platelet adhesion/aggregation at the injured site. A significantly longer exposure to the laser was required to initiate adhesion/aggregation in vitamin E-enriched mice. Because effects of endothelial damage in this model are mediated at least in part by singlet oxygen produced by injured tissue (W.I. Rosenblum and G.H. Nelson, Am. J. Physiol. 270 (Heart Circ. Physiol. 39): H1258-H1263, 1996.), we conclude that the antioxidant, radical-scavenging actions of vitamin E explain the protective action of the vitamin E-enriched diet. However, raising vitamin E levels did not protect against putative adverse effects of normally occurring oxidants.

Acetylcholine↗
PubMed1996

The effect of recombinant human insulin-like growth factor-I on chronic puromycin aminonucleoside nephropathy in rats.

We recently demonstrated that recombinant hGH exacerbates renal functional and structural injury in chronic puromycin aminonucleoside (PAN) nephropathy, an experimental model of glomerular disease. Therefore, we examined whether recombinant human (rh) IGF-I is a safer alternative for the treatment of growth failure in rats with chronic PAN nephropathy. The glomerulopathy was induced by seven serial injections of PAN over 12 wk. Experimental animals (n = 6) received rhIGF-I, 400 micrograms/d, whereas control rats (n = 6) received the vehicle. rhIGF-I improved weight gain by 14% (p < 0.05), without altering hematocrit or blood pressure in rats with renal disease. Urinary protein excretion was unaltered by rhIGF-I treatment in rats with chronic PAN nephropathy. After 12 wk, the inulin clearance was higher in rhIGF-I-treated rats, 0.48 +/- 0.08 versus 0.24 +/- 0.06 mL/min/100 g of body weight in untreated PAN nephropathy animals, p < 0.05. The improvement in GFR was not associated with enhanced glomerular hypertrophy or increased segmental glomerulosclerosis, tubulointerstitial injury, or renal cortical malondialdehyde content. In rats with PAN nephropathy, administration of rhIGF-I increased IGF-I and GH receptor gene expression, without altering the steady state level of IGF-I receptor mRNA. In normal rats with intact kidneys, rhIGF-I administration (n = 4) did not alter weight gain, blood pressure, proteinuria, GFR, glomerular planar area, renal cortical malondialdehyde content, or glomerular or tubulointerstitial damage, compared with untreated animals (n = 4). rhIGF-I treatment reduced the steady state renal IGF-I mRNA level but did not modify gene expression of the IGF-I or GH receptors. We conclude that: 1) administration of rhIGF-I improves growth and GFR in rats with chronic PAN nephropathy and 2) unlike rhGH, long-term use of rhIGF-I does not worsen renal functional and structural injury in this disease model.

Animals↗
PubMed1996

Vitamin E ameliorates renal injury in an experimental model of immunoglobulin A nephropathy.

IgA nephropathy is one of the most common forms of glomerular disease. Nearly 25% of affected patients progress to end-stage renal disease over a 20-25-y follow-up period. IgA-containing immune complexes stimulate oxygen-free radical production by mesangial cells in vitro. The excessive oxidant stress may mediate glomerular injury in this disorder. Therefore, we studied whether dietary supplementation with the antioxidant agent, vitamin E, attenuates renal disease in an experimental model of incipient IgA nephropathy with mild kidney inflammation. IgA nephropathy was induced in male Lewis rats by oral immunization with 0.1% bovine gamma-globulin (BGG)-containing drinking water for 8 wk. At the completion of this period, animals received BGG, 1 mg/dose i.v., on three successive days. Experimental rats (n = 10) received a specially formulated diet containing 100 IU of vitamin E/kg of chow, whereas control animals (n = 10) were fed chow containing 30 IU of vitamin/kg of chow. The BGG immunization regimen induced mesangial IgA deposition in all rats. Vitamin E supplementation resulted in a nearly 5-fold increase in the serum vitamin E concentration. Vitamin E-treated rats gained more weight and had a lower incidence of hematuria, 20% versus 80% (p < 0.03). Moreover, proteinuria was decreased by 50%, and reduced renal plasma flow was restored to normal, compared with untreated rats with IgA nephropathy. Glomerular hypertrophy occurred in animals with IgA nephropathy, but less so in those receiving vitamin E supplementation. Renal cortical malondialdehyde content was reduced from 1.55 +/- 0.10 to 1.22 +/- 0.09 nmol/mg of protein (p < 0.01) in rats fed the vitamin E-enriched diet. Finally, renal transforming growth factor-beta 1 gene expression was reduced by 34% in rats with IgA nephropathy receiving vitamin E treatment (p < 0.05). We conclude that experimental IgA nephropathy is associated with increased renal oxidant injury. Dietary treatment with the antioxidant agent, vitamin E, attenuated renal functional and structural changes in this experimental glomerulopathy. These studies support the importance of clinical trials for the evaluation of the efficacy of antioxidant therapy in patients with IgA nephropathy.

Animals↗
PubMed1996

Murine red blood cell fragility is not affected by either vitamin E depletion or supplementation.

Male ICR mice were Pair-fed semipurified diets containing 0, 55 (control), and 500 IU/kg of vitamin E. Plasma and hepatic concentrations of vitamin E were determined and found to parallel the vitamin E levels in the diet. Even though plasma vitamin E levels were virtually zero in mice fed the depleted vitamin E diet for up to 304 days, there was no statistical difference in the red blood cell fragility between these animals and controls, as determined by a hypoosmotic fragility test. The diet with enriched vitamin E concentrations also did not affect the fragility of the red blood cell (RBC). Even after 300 days of zero dietary vitamin E, mice appeared healthy, demonstrating neither neurologic dysfunction nor failure to thrive. The data indicates that mice, unlike several other species, are more resistant to vitamin E depletion and may have other mechanisms to compensate for loss of this important antioxidant.

Animals↗
PubMed1996

Non-invasive ambulatory blood pressure monitoring: effect on nocturnal sleep of children and adults.

OBJECTIVE: To investigate whether disturbance of sleep by ambulatory blood pressure monitoring determinations might result in altered blood pressure. METHODS: Ninety-seven subjects (29 children and 68 adults) attending an outpatient chronobiology center wore wrist actigraph motion detectors for 48 h (24 h before ambulatory blood pressure monitoring and 24 h during ambulatory blood pressure monitoring). Sleep variables including sleep efficiency, sleep latency, total time in bed, total sleep time, total minutes awake plus number and average duration of awakenings were derived by a dedicated algorithm. RESULTS: Comparison of the sleep variables for the baseline and ambulatory blood pressure monitoring nights revealed no differences in any of the sleep parameters either in the adults or in the children. Small differences between adults and children during the baseline and monitoring nights for some variables were most likely age- and disease-related. CONCLUSION: Non-invasive ambulatory blood pressure monitoring by the SpaceLabs model 90207 device at hourly intervals during night-time sleep does not significantly affect sleep either in children or adults.

Journal Article↗
PubMed1996

Evaluation of a lead screening program in Houston, Tex.

Universal screening for childhood lead poisoning is widely debated. Our purpose was to compare screening results at three pediatric clinics within Houston and to evaluate the effectiveness of screening according to published criteria. The clinics were chosen for their geographic and socioeconomic diversity. Children between 6 months and 6 years of age were tested, and the results were classified according to current guidelines. We screened 864 children. Results between sites were significantly different, P = 0.002. No children with blood lead levels greater than 0.45 mumol/L (9 micrograms/dL) were identified at Clinic C compared to 76 (8.8%) from Clinics A and B, but no site had children with levels greater than or equal to 2.20 mumol/L (45 micrograms/dL). The prevalence of childhood lead poisoning can vary even within the city. If regional screening is to replace universal screening, statewide as well as citywide data are needed to identify high-risk areas. This could be done by clinic site, zip code, or census track data with a minimum of 3000 children.

Child↗
PubMed1995

Cervical squamous dysplasias and carcinomas with immunodetectable p53 frequently contain HPV.

Studies using cervical carcinoma cell lines usually show mutated p53 in cases without detectable HPV, and wild-type p53 in cases with detectable HPV. These findings suggest that loss of p53 function, either by mutation or by binding to HPV E6, is required for cervical carcinogenesis. Because mutated p53 is usually detectable immunohistochemically, one would predict an inverse relationship between the presence of HPV and detectable p53. In this study we examined 88 formalin-fixed paraffin-embedded clinical specimens of cervix for the presence of HPV and p53 expression. All cases were studied for the presence of p53 using immunohistochemical methods. The antibody used was mouse monoclonal PAb1801 (Biogenex). The presence of HPV was detected by PCR. Twenty-six specimens showed foci of p53 expression (0/7 normal, 1/8 (13%) condylomas, 1/6 (17%) CIN I, 3/7 (43%) CIN II, 6/20 (30%) CIN III, 13/22 (59%) SCC, 2/5 (40%) adenosquamous carcinomas, and 0/13 adenocarcinomas). p53 expression was more frequent in SCC than with CIN (P = 0.026). HPV was present in 15 of 24 cases with detectable p53 and 22 of 48 cases without detectable p53. No correlation was seen between HPV status and detection of p53. With the exception of one case, p53 expression was seen in less than 10% of cells. p53 expression was not detected in any of the 13 adenocarcinomas examined (P = 0.0016 vs SCC). Our results show that alterations of p53 may play a role in the pathogenesis of cervical squamous carcinoma. However, p53 expression was neither sufficient nor required for cervical carcinogenesis, irrespective of HPV status.

Adenocarcinoma↗
PubMed1995

Hiring preferences of diagnostic radiology groups: results of a 1994 survey.

RATIONALE AND OBJECTIVES: We surveyed diagnostic radiology group preferences and considerations in hiring radiologists and compared these findings with those of a survey performed in 1990. We sought to identify changes in hiring practices that might have occurred because of socioeconomic changes. We also sought to identify features of job candidates that make them more attractive to hiring groups. METHODS: One hundred surveys were mailed to a stratified random sample of diagnostic radiology groups identified by the American College of Radiology. We solicited information on the importance of various attributes and the level of experience of a candidate, the fellowship training considered most desirable, and the effect of changes in the health care socioeconomic environment. The responses were weighted by group size and geographic location to estimate what results might have been obtained if we had surveyed all groups in the United States. RESULTS: Seventy-five groups returned the survey. The two most important factors in choosing a candidate were motivation and radiologic knowledge. The fellowships that groups that were hiring considered to be the most desirable were body imaging, neuroradiology, and angiography/interventional radiology. Groups overwhelmingly preferred recent training over long experience. CONCLUSION: Fellowship training increases a candidate's marketability, but the two factors that hiring groups consider the most important are motivation and radiologic knowledge.

Clinical Competence↗
PubMed1995

Evaluation of a patient education program for solid organ transplant patients.

Medication counselling of transplant patients plays a major role in the outcome of the transplant. The medication counselling program at Vancouver Hospital and Health Sciences Centre for Solid Organ Transplant (SOT) patients consists of verbal counselling by a pharmacist, provision of medication teaching sheets, and patient participation in the self-medication program. The objectives of this study were to evaluate the effectiveness of the medication counselling program for SOT patients and to develop a series of tests to serve as a teaching tool. Solid organ transplant patients who were English speaking and tolerated oral medications were enrolled in the study. A prospective evaluation of the medication counselling program was done through a series of identical tests. Percent scores were calculated for each test, and pre-test scores (scores prior to counselling) were compared to post-test scores (scores after counselling). Twenty-eight SOT patients participated in the study. Patients scored an average of 25% on the pre-test prior to the counselling session and 66% on the post-test at the time of discharge. When scores on specific questions were compared, patients did well on drug identification, dosage and indications, but poorly on questions regarding side effects. Patient counselling improves medication knowledge in SOT patients as indicated by an increase in test scores. The combination of repeated counselling sessions and the participation in the self-medication program reinforces medication knowledge and maximizes retention of knowledge.

British Columbia↗
PubMed1994

Altered expression of epidermal growth factor receptor and estrogen receptor in MCF-7 cells after single and repeated radiation exposures.

PURPOSE: Studies on radiation-induced changes in gene expression are likely to be very important in developing a better understanding of cellular responses to ionizing radiation. While there is some information on the activation of cellular signal transduction pathways after radiation, few late reacting target genes have been identified. This study focuses on the characterization of expression modulation of two critical growth regulatory genes, estrogen receptor and epidermal growth factor-receptor in malignant mammary epithelial cells in response to single and repeated ionizing radiation exposures. METHODS AND MATERIALS: MCF-7 cells were used for single radiation exposure (2-50 Gy) experiments and MCF-IR-3 cells, generated by exposure to cumulative doses of 60 Gy in 2 Gy fractions, respectively, were used to study the effects of repeated exposures. Steady-state messenger ribonucleic acid levels for estrogen receptor, epidermal growth factor-receptor, and transforming growth factor-alpha were determined by ribonucleic acid protection experiments. Estrogen receptor and epidermal growth factor-receptor protein expression was quantitated by competitive binding studies with 3H-estradiol and 125I-EGF. RESULTS: MCF-IR-3 cells showed a permanent three-fold down-regulation of the estrogen receptor messenger ribonucleic acid and protein, while epidermal growth factor-receptor was upregulated about nine-fold. Epidermal growth factor-receptor was substantially up-regulated in MCF-7 cells, at both the mRNA and protein levels, within 24 h of a single 2 Gy exposures, while there was a two-fold concomitant increase in transforming growth factor-alpha messenger ribonucleic acid expression. A decrease in estrogen receptor messenger ribonucleic acid and protein was suggested only after higher doses of single radiation exposures. CONCLUSION: Single and repeated radiation exposures modulate the expression of two critical growth promoting genes, estrogen receptor and epidermal growth factor-receptor, in MCF-7 cells. The inverse expression of estrogen receptor and epidermal growth factor-receptor established for estrogen receptor-positive malignant mammary epithelial cells is maintained in MCF-7 cells after single and repeated exposures suggesting that radiation acts through common regulatory circuits and may modulate the cellular phenotype.

Breast Neoplasms↗
PubMed1994

A role for destabilizing amino acid replacements in light-chain amyloidosis.

Light-chain (L-chain) amyloidosis is characterized by deposition of fibrillar aggregates composed of the N-terminal L-chain variable region (VL) domain of an immunoglobulin, generally in individuals overproducing a monoclonal L chain. In addition to proteolytic fragmentation and high protein concentration, particular amino acid substitutions may also contribute to the tendency of an L chain to aggregate in L-chain amyloidosis, although evidence in support of this has been limited and difficult to interpret. In this paper we identify particular amino acid replacements at specific positions in the VL domain that are occupied at frequencies significantly higher in those L chains associated with amyloidosis. Analysis of the structural model for the VL domain of the Bence-Jones protein REI suggests that these positions play important roles in maintaining domain structure and stability. Using an Escherichia coli expression system, we prepared single-point mutants of REI VL incorporating amyloid-associated amino acid replacements that are both rare and located at structurally important positions. These mutants support ordered aggregate formation in an in vitro L-chain fibril formation model in which wild-type REI VL remains soluble. Moreover, the ability of these sequences to aggregate in vitro correlates well with the extent to which domain stability is decreased in denaturant-induced unfolding. The results are consistent with a mechanism for the disease process in which the VL domain, either before or after proteolytic cleavage from the L-chain constant region domain, unfolds by virtue of one or more destabilizing amino acid replacements to generate an aggregation-prone nonnative state.

Amino Acid Sequence↗
PubMed1994

Inhibition of IL-1 release from human monocytes and suppression of streptococcal cell wall and adjuvant-induced arthritis in rats by an extract of Tripterygium wilfordii Hook.

1. It was investigated whether an extract of Tripterygium wilfordii Hook f (TW) inhibits IL-1 production by monocytes and suppresses the development of IL-1-dependent arthritis induced in rats with streptococcal cell wall and adjuvant. 2. TW preferentially inhibited IL-1 alpha and IL-1 beta production by bacterial lipopolysaccharide (LPS)-stimulated human monocytes with IC50 of approximately 1 microgram/ml. 3. Oral administration of TW dose-dependently suppressed joint swelling and structural damage in streptococcal cell wall-induced arthritis (ED50 = 20 mg/kg/day) and in adjuvant-induced arthritis (ED50 = 46 mg/kg/day for developing and 8 mg/kg/day for established arthritis).

Animals↗
PubMed1994

Patterns of professional organization membership among radiologists in the United States.

RATIONALE AND OBJECTIVES: The extent of membership in a professional association is an indicator of the level of cohesiveness or fragmentation of the profession. In this study, membership patterns in the American College of Radiology (ACR) were examined to assess how much different groups within radiology identify with the profession. METHODS: Patterns of membership in the ACR, the principal professional organization (as opposed to scientific society) of American radiologists, were examined by studying different demographic and professional groups within radiology. Data from the 1990 American Medical Association (AMA) Physician Masterfile were matched with ACR membership data for post-training radiologists and nuclear medicine specialists. RESULTS: Seventy-four percent of post-training American Board of Radiology (ABR)--certified diagnostic radiologists and radiation oncologists were ACR members. Membership rates were significantly lower for radiologists who were the following: 1) younger than 45 years of age; 2) women; 3) located in the western United States; 4) not certified by the ABR; or 5) listed their major professional activity as administration, teaching and research, or exclusively hospital-based patient care. Logit analysis showed that each of the above factors had a statistically significant effect on membership independently of the others. There were no statistically significant differences in membership rates between diagnostic radiologists and radiation oncologists, or between diagnostic subspecialists and diagnostic generalists. Among those with ABR certification, there was no significant difference between nuclear medicine specialists and other radiologists. CONCLUSIONS: The data suggest that, to increase the size and representativeness of ACR membership, target areas for recruitment effort might include younger radiologists, female radiologists, and radiologists located in the western United States.

Adult↗
PubMed1994

Catheter ablation of the atrioventricular node using radiofrequency energy.

BACKGROUND: Catheter ablation of the atrioventricular (AV) junction using stored direct current (DC) energy from a standard DC Cardioverter defibrillator was first reported in 1982. Since then many patients have been treated using this procedure for refractory supraventricular arrhythmias, usually atrial fibrillation and flutter. Undesirable thermal effects such as barotrauma and arcing are largely responsible for complications associated with the use of DC energy. This report details our experience of catheter ablation of the AV junction using radiofrequency (RF) energy in a series of 30 consecutive patients. METHODS: RF ablations were performed using steerable Mansfield (Webster Laboratories) 4 mm tipped electrodes and locally assembled RF energy delivery system. RESULTS: The procedure was successful in 27/30 (90%) patients using RF energy, while three patients required DC energy to achieve successful AV junction ablation. General anaesthesia was required in nine patients, six of whom required this for cardioversion to sinus rhythm so that an adequate His Bundle spike could be recorded and three for DC ablation. Dual chamber permanent pacemakers with automatic mode switching were implanted in four patients who had paroxysmal atrial fibrillation or flutter and the remainder had ventricular rate responsive pacemakers. CONCLUSIONS: In patients with drug refractory paroxysmal atrial fibrillation and flutter and in patients with established atrial fibrillation where control of the ventricular rate is difficult, catheter ablation of the AV junction using RF energy is a safe and effective procedure with a high success rate.

Atrial Fibrillation↗
PubMed1994

Insulin-like growth factor and growth hormone receptor in nephrotic rats.

In an attempt to elucidate the mechanism of growth retardation in the nephrotic syndrome, specific serum and hepatic growth factors were measured in Sprague-Dawley rats in which nephrotic syndrome was produced by administration of puromycin (1.5 mg.100 g body wt-1.day-1) for 12 days. On the 13th day, the results of these nephrotic animals were compared with those of an equal number of pair-fed and control animals: the mean dietary intake of the nephrotic group was 71% that of the control group (P < 0.001). Serum insulin-like growth factor (IGF) binding protein-3 was significantly reduced (P < 0.005) in the nephrotic rats, compared with the pair-fed and the control groups. Hepatic IGF-I mRNA in the nephrotic rats averaged 36% that of control (P < 0.001) and 46% that of the pair-fed animals (P < 0.001). Hepatic growth hormone receptor (GHr) mRNA in the nephrotic rats averaged 19% of that of the control (P < 0.001) and 27% of that of the pair-fed rats (P < 0.001). These results indicate that the growth retardation of the nephrotic rats may be associated with the significant decrease in IGF-I mRNA and reduction in GHr mRNA.

Animals↗
PubMed1994

Effects of deflazacort and cortisone on body growth, thymus weight and gene expression of growth-related proteins in the rat.

Deflazacort is an oxazoline derivative of cortisone with presumably less serious side effects, but its effects on growth factors are unknown. The present experiments in Long Evans rats were carried out to investigate how deflazacort administration affected the growing rat, especially in relation to hepatic insulin-like growth factor I (IGF-I) and growth hormone receptor (GHR) messenger ribonucleic acid (mRNA). Four groups of animals were used: those treated with cortisone, with two different doses of deflazacort and with vehicle. Subcutaneous injections were given daily for 8 days. Thymus weight was reduced in all treated groups, with a comparable magnitude of reduction in the groups treated with cortisone and the higher dose of deflazacort (DF1). Daily weight gain was reduced significantly after cortisone treatment, but less so in the DF1 rats. Liver IFG-I and GHR mRNA were lower in the cortisone and deflazacort than in controls. However, GHR mRNA was reduced significantly only by cortisone and not by DF1. We conclude that growth failure is less severe in the DF1 rats compared to cortisone rats, which corresponds to the reduction in hepatic GHR mRNA.

Animals↗