PubMed Health⌕ Search

Biomedical subjects

A M Chen

Publications and source records attributed to A M Chen.

At least 19 recordsLinked to original sources
PubMed2006

Variations in consenting practice for laparoscopic cholecystectomy.

INTRODUCTION: To compare the variations in consenting practice amongst trainees and consultant surgeons for laparoscopic cholecystectomy with specific reference to the documentation of significant risks of surgery. PATIENTS AND METHODS: A proforma was devised which included significant and/or commonly recognised complications of laparoscopic cholecystectomy. This was then cross-referenced with the consent forms for the 80 patients included in the study and the documented risks explained in each case were noted. RESULTS: The results showed that there is considerable variation between the three grades of clinicians involved in obtaining a patient's consent for laparoscopic cholecystectomy. There was a clear difference in emphasis of the significant complications depending on the seniority of the consenter. Over 80% of the consents in this study were still being obtained by junior staff. CONCLUSIONS: More often than not, patients are not provided with consistent information to make an informed choice. We suggest that a preprinted consent form will provide a more uniform approach to consenting practice for laparoscopic cholecystectomy.

Cholecystectomy, Laparoscopic↗
PubMed2005

Aggregation between xanthan and nonyphenyloxypropyl beta-hydroxyltrimethylammonium bromide in aqueous solution: MesoDyn simulation and binding isotherm measurement.

The aggregation behavior of nonyphenyloxypropyl beta-hydroxyltrimethylammonium bromide (C9phNBr) and xanthan (XC) in aqueous solution was investigated by MesoDyn density functional simulation and binding isotherm measurement. The process of aggregate formation and the aggregate morphology are reported. The formation of aggregates includes three stages and the morphology of XC-C9phNBr aggregates is rodlike or ellipsoidal. The effects of temperature and XC concentration on the aggregation are analyzed. Results indicate that the formation of aggregates is an exothermic process, and their formation becomes more difficult and the formation rate decreases with increasing temperature. The formation of aggregates is also related to XC concentration, and it becomes much more difficult when the concentration of XC is higher than 20 vol %. The simulation results agree with binding isotherms of C9phNBr to XC obtained via the potentiometric titration method, which shows a typical cooperative binding between C9phNBr and XC.

Journal Article↗
PubMed2001

Interim assessment of a community intervention to improve breast and cervical cancer screening among Korean American women.

Breast and cervical cancer screening practices are suboptimal among Korean American women. A community intervention program was launched in 1996 to improve breast and cervical cancer screening among Korean American women in Alameda County, California. After 18 months, interim program assessment revealed that mammograms improved, but Pap smears, breast self-examinations, and clinical breast examinations did not change significantly. However, results were similar for the control county probably because the program was not implemented fully. Several strategies for improving program implementation are discussed including recommendations for researchers planning community intervention projects.

Adult↗
PubMed2001

Current and future applications of immunological attenuation via pegylation of cells and tissue.

Prevention of immunological rejection of transplanted tissues is of crucial importance in transplantation medicine. Current procedures primarily use pharmacological agents such as cyclosporin, which, while effective, must be typically administered for the life of the individual. Furthermore, the drug-induced global immunosuppression of the patient predisposes the individual to infection and enhances their risk of developing certain forms of cancer. Hence, additional methods are needed to both enhance tissue engraftment and diminish the adverse effects of current immunosuppressive therapy. Studies from blood transfusion (i.e. a specialised form of cellular transplantation) suggest that covalent modification of cells and tissues with methoxypoly(ethylene glycol) [mPEG] can significantly diminish rejection episodes and may further enhance the induction of tolerance to donor tissues. The mechanisms underlying mPEG-mediated immunocamouflage are the loss of antigen recognition, impaired cell-cell interaction, and an inability of endogenous antibodies (e.g. immunoglobulin G) to effectively recognise and bind foreign epitopes. As a consequence of the global camouflage imparted by mPEG, the weak co-stimulation of alloreactive T cells may subsequently induce apoptosis, thus leading to tolerance. Initial studies on the transplantation of pegylated isogeneic rat pancreatic islets demonstrates that mPEG-derivatisation does not impair in vivo cellular signalling and function. Thus, in contrast to the pharmacological inhibition of the recipient's immune response, the mPEG-mediated immunocamouflage directly addresses the inherent antigenicity and immunogenicity of the donor tissue itself while leaving the recipient a fully competent immune system.

Animals↗
PubMed2001

[Experimental study on the hemostatic properties of collagen sponge].

OBJECTIVE: To validate the hemostatic properties of collagen sponge made in China. METHODS: The experimental model of superficial cut of liver was established in 20 Sprague-Dawley adult rats, which were divided into two groups randomly. Collagen sponge or gelatin sponge was used to cover the cut respectively. Hemostatic result was observed. Afterwards, standard liver trauma model by resection left front liver lobe was made, wound was treated with collagen sponge or gelatin sponge respectively. Hemostatic result was observed. Concurrent hemostatic time and bleeding amount were noted. At 7, 14 and 20 days after operation, intra-abdominal adhension, infection and healing state of liver were observed by exploratory laparotomy. The histological changes of regenerate liver tissue were observed by microscopy. RESULTS: Collagen sponge adhered to wound well. Concurrent hemostatic time and bleeding amount in collagen sponge group were superior to those of gelatin sponge (P < 0.05). The histological examination showed that collagen sponge was absorbed and degraded rapidly, regenerative hepatocytes could be induced. CONCLUSION: Collagen sponge has fine hemostatic properties and can induce regeneration of hepatocytes effectively. It is worth popularizing for its convenience in clinical application and its properties of rapid degradation and absorption.

Animals↗
PubMed2001

[Study on adriamycin-porous tricalcium phosphate ceramic drug delivery system and its drug release test in vivo].

OBJECTIVE: To manufacture adriamycin-porous tricalcium phosphate (A-PTCP) ceramic drug delivery system (DDS) as a possible method for bone defect treatment after bone tumor operation. METHODS: A-PTCP DDS was made from putting adriamycin into PTCP. Thirty rabbits were divided randomly into group A(24 rabbits) and group B(6 rabbits). A-PTCP was implanted in the greater trochanter of the right femur in group A. Adriamycin were injected into veins in group B. Muscle around A-PTCP and plasma were taken out at different period. Adriamycin concentrations in muscle and plasma were measured by high performance liquid chromatography (HPLC). RESULTS: A-PTCP could gradually release adriamycin over 10 weeks. Adriamycin concentrations in the muscle were higher than that in plasma. CONCLUSION: A-PTCP may be a new method for repairing bone defects after bone tumor operation.

Animals↗
PubMed2000

Porcine stem cell engraftment and seeding of murine thymus with class II+ cells in mice expressing porcine cytokines: toward tolerance induction across discordant xenogeneic barriers.

BACKGROUND: Mixed hematopoietic chimerism is a reliable means of tolerance induction, but its utility has not been demonstrated in discordant xenogeneic combinations because of the difficulty in achieving lasting hematopoietic engraftment. Miniature swine are likely to be suitable organ donors for humans. To evaluate the ability of mixed chimerism to induce swine-specific tolerance in widely disparate xenogeneic recipients, this study aimed to achieve long-lasting chimerism in a pig to mouse combination. METHODS: Immunodeficient transgenic mice were developed by crossing transgenic founders carrying porcine interleukin-3, granulocyte macrophage-colony stimulating factor, and stem cell factor genes with severe combined immunodeficient mice or non-obese diabetic/severe combined immunodeficient mice. Swine bone marrow transplantation was performed in these mice, and porcine chimerism was followed for 20 weeks. RESULTS: Whereas swine cells became undetectable in all non-Tg littermates by 7 weeks, high levels of porcine hematopoietic chimerism, including the presence of porcine class II+ cells in the host thymus were maintained in Tg mice for >20 weeks. Colony-forming assays revealed the presence of large numbers of swine hematopoietic progenitor cells in the marrow of these mice at 20 weeks after bone marrow transplantation. CONCLUSIONS: These transgenic mice demonstrate for the first time that spontaneous migration of marrow donor antigen-presenting cells to an intact recipient thymus can occur and that porcine stem cells can persist in this highly disparate species combination. These data therefore support the feasibility of the eventual goal of tolerance induction by mixed chimerism in discordant xenogeneic combinations.

Animals↗
PubMed2000

Role of antibody-independent complement activation in rejection of porcine bone marrow cells in mice.

BACKGROUND: Although complement activation has been shown to be important in the rejection of solid organs in some xenogeneic species combinations, its role in the rejection of xenogeneic marrow engraftment is unknown. METHODS: The effect of complement depletion with cobra venom factor on porcine bone marrow cell (BMC) engraftment was examined in 3 Gy-irradiated C.B-17 severe combined immunodeficiency mice receiving 10(8) pig BMC. RESULTS: At 26 days after transplantation, the percentages of swine class I+, myeloid, and CD2+ cells in marrow, spleen, and peripheral blood, and the numbers of porcine myeloid progenitor cells in marrow, were increased in cobra venom factor-treated recipients compared with simultaneous control recipients. Consistent with the in vivo results, preheating serum (56 degrees C for 30 min) reduced the inhibitory effect of severe combined immunodeficiency mouse serum on the proliferation of pig BMC in vitro. CONCLUSION: Murine complement is capable of resisting xenogeneic hematopoietic engraftment through an antibody-independent mechanism.

Animals↗
PubMed2000

Development and analysis of transgenic mice expressing porcine hematopoietic cytokines: a model for achieving durable porcine hematopoietic chimerism across an extensive xenogeneic barrier.

The capacity of mixed hematopoietic chimerism to induce tolerance has not been demonstrated in discordant xenogeneic species combinations because of the difficulty in achieving lasting hematopoietic engraftment. In an effort to create a model of long-lasting disparate xenogeneic hematopoietic chimerism, we have developed transgenic (Tg) mice carrying porcine cytokines. Three lines of Tg mice were generated: one carrying porcine IL-3 and GM-CSF genes only (termed IL/GM) and the remaining two lines carrying in addition, the soluble SCF gene (termed IL/GM/sS) or membrane-bound SCF gene (termed IL/GM/mS). Sera from mice with IL/GM and IL/GM/sS transgenes markedly stimulated the proliferation of swine marrow cells in vitro. However, proliferation of swine marrow cells was not induced in cultures containing IL/GM/mS sera. Consistent with these observations, ELISA assays revealed detectable levels of porcine cytokines in the sera of IL/ GM and IL/GM/sS, but not in sera of IL/GM/mS Tg mice. Marrow stromal cells prepared from all three kinds of Tg mice, but not those from non-Tg littermates, were capable of supporting the growth of porcine hematopoietic cells in vitro. Immunodeficient Tg mice were generated by crossing Tg founders with C.B-17 SCID mice for five generations. All Tg immunodeficient mice showed improved porcine hematopoietic engraftment compared with non-Tg controls. These Tg mice provide a useful model system for studying porcine hematopoietic stem cells, and for evaluating the feasibility of donor-specific tolerance induction by mixed chimerism across highly disparate xenogeneic barriers.

Animals↗
PubMed2000

Underprediction of visibly complex chromosome aberrations by a recombinational-repair ('one-hit') model.

PURPOSE: Published low-LET FISH data were used to test two models of chromosome aberration production based on breakage-and-reunion or recombinational repair. MATERIALS AND METHODS: Randomness of DNA double strand break induction and misrejoining is analyzed comprehensively and adopted as a working hypothesis. Proximity effects are approximated by using interaction sites. Model results are calculated using CAS (chromosome aberration simulator) Monte Carlo computer software with two adjustable parameters. CAS can emulate the specifics of any experimental painting protocol, allowing very detailed tests of the models. RESULTS: To reasonable approximation, breakage-and-reunion model predictions are consistent with low-LET FISH results, including two large, elaborate, one-paint data sets. An explicitly specified version of the recombinational-repair model severely underpredicts the frequency of the visibly complex aberration patterns most commonly observed with one-paint FISH, and is inconsistent with some observed multi-paint patterns. When high-dose effects (distortion and saturation) are taken into account quantitatively, a dose-response relation for apparently simple interchanges slightly favours the breakage-and-reunion model over the recombinational-repair model, despite being approximately linear over the dose range 2-6 Gy. CONCLUSIONS: The random breakage-and-reunion model gives comprehensive baseline predictions that are sufficiently accurate for the organization of experimental results. The data speak against complex aberrations being formed by the random recombinational repair pathway discussed here.

Chromosome Aberrations↗
PubMed2000

Random breakage and reunion chromosome aberration formation model; an interaction-distance version based on chromatin geometry.

PURPOSE: Using published FISH data for chromosome aberration production in human fibroblasts by hard X-rays to test a breakage-and-reunion model. METHODS: The model assumed pairwise misrejoining, random apart from proximity effects, of DNA double-strand break (DSB) free ends. CAS (chromosome aberration simulator) Monte Carlo computer software implementing the model was modified to use a distance algorithm for misrejoining instead of using DSB interaction sites. The modification (called CAS2) allowed a somewhat more realistic approach to large-scale chromatin geometry, chromosome territories and proximity effects. It required adding a third adjustable parameter, the chromosome territory intersection factor, quantifying the amount of intertwining among different chromosomes. RESULTS: CAS2 gave somewhat better results than CAS. A reasonable fit with a few discrepancies was obtained for the frequencies at three different radiation doses of many different aberration types and of aberrations involving various specific chromosomes in a large data set using one-paint FISH scoring. The optimal average chromosome territory intersection factor was approximately 1.1, indicating that, for an arbitrarily chosen location in the nucleus, on average slightly more than two chromosomes have very nearby loci. Without changing the three parameter values, a fit was also obtained for a corresponding, smaller, two-paint data set. CONCLUSIONS: A random breakage-and-reunion model incorporating proximity effects by using a distance algorithm gave acceptable approximations for many details of hard X-ray aberration patterns. However, enough discrepancies were found that the possibility of an additional or alternate formation mechanism remains.

Algorithms↗
PubMed2000

[The effect of cefazolin loaded bone matrix gelatin on repairing large segmental bone defects and preventing infection after operation].

OBJECTIVE: To explore the possibility of repair long segmental bone defects and preventing infection with cefazolin loaded bone matrix gelatin (C-BMG). METHODS: C-BMG was made from putting cefazolin into BMG by vacuum adsorption and freeze-drying techniques. The sustaining period of effective drug concentration in vitro and in vivo was detected by inhabition bacteria, and the drug concentration in local tissues (bone and muscle) and plasma after implantation of C-BMG was examined by high performance liquid chromatography(HPLC). RESULTS: The effective inhibition time to staphylococcus aureus of C-BMG was 22 days in vitro, while 14 days in vivo. The drug concentration in local tissues(bone and muscle) were higher than that of plasma, and the drug concentration in local tissues was higher in early stage, later it kept stable low drug release. It suggested that C-BMG had excellent ability to repair segmental long bone defects. CONCLUSION: C-BMG can gradually release cefazolin with effective drug concentration and has excellent ability to repair segmental long bone defects. It may be a novel method to repair segmental long bone defects and prevent infection after the operation.

Animals↗
PubMed1999

Clustering of radiation-produced breaks along chromosomes: modelling the effects on chromosome aberrations.

PURPOSE: For high-LET radiations, and perhaps even for hard X-rays, DNA double-strand breaks (dsb) are clustered nonrandomly along chromosomes; disproportionately, many inter-dsb segments are less than a few Mbp (10(6) base pairs). The implications of such dsb clustering for chromosome aberrations are analysed. METHODS: Chromosome segments between different dsb within one dsb cluster are assumed too small to detect in the aberration assay. Enumeration or Monte-Carlo computer simulations are used to compute the relative frequencies of many observable aberration patterns: apparently simple or visibly complex. The theoretical predictions are compared with X-ray data for human fibroblasts, involving painted chromosomes 1, 2, 4, 5, 7 or 13. RESULTS AND CONCLUSIONS: Surprisingly, cryptic dsb multiplicity does not affect the frequency ratios predicted for aberration patterns by a random breakage-and-rejoining model. The model is generally consistent with current data on many different types of aberrations, whether or not dsb usually occur in cryptic clusters. For a Revell-type exchange model, however, the predictions do depend on clustering configurations; they gradually approach the predictions of the breakage-and-rejoining model as average cluster multiplicity increases. The model is consistent with the data, for example with the ratio of visibly complex to apparently simple aberrations, only if there is considerable dsb clustering even at low-LET, with approximately 1.5 or more reactive dsb per cluster on average.

Chromosome Aberrations↗
PubMed1999

Measurement of vertebral rotation: a comparison of two methods based on CT scans.

This study compared Ho's and Aaro's method to measure vertebral axial rotation in order to find the more accurate one. Two hundred fifty-nine CT scans were taken from 11 cadaver vertebrae. The scans were performed with vertebrae in neutral position and angulated up to 20 degrees in the sagittal and frontal plane to simulate kyphosis/lordosis and side bending. Axial rotation was measured according to both methods. The mean difference between true and measured values was 3.7 +/- 6.7 (95% confidence limit) (Ho's method) and 2.3 +/- 3.7 (Aaro's method), respectively. Correlation with true axial rotation was r2 = 0.66 (Ho's method) and r2 = 0.77 (Aaro's method). We recommend using Aaro's method as the more accurate measure of axial rotation in scoliotic vertebrae.

Cadaver↗
PubMed1998

Rates and independent correlates of Pap smear testing among Korean-American women.

OBJECTIVES: This study reports population estimates of Pap smear testing among Korean-American women and evaluates correlates of testing. METHODS: Korean Americans in 2 California counties were surveyed by telephone. Frequencies were age-adjusted to the 1990 census to produce population estimates of testing. Logistic regression models were used to evaluate independent correlates of testing RESULTS: Only 50% of the Korean-American women surveyed had a Pap test in the previous 2 years. The strongest independent correlate was having had a regular check-up in the previous 2 years (odds ratio 7.2, 95% confidence interval 4.2, 12.1). CONCLUSIONS: Rates of Pap testing among Korean-American women are well below national objectives. Collaboration and community-sensitive research are essential to collect data and design programs to improve the health of ethnic minority communities.

Asian↗
PubMed1998

Misrejoining of double-strand breaks after X irradiation: relating moderate to very high doses by a Markov model.

Misrejoining of double-strand breaks (DSBs) detected with pulsed-field gel electrophoresis (PFGE) after X irradiation of human cells at very high doses (80-160 Gy) is related to dose-response relationships for chromosome aberrations at moderate doses (1-5 Gy) by the Sax-Markov binary eurejoining/misrejoining (SMBE) model. The SMBE model applies Sax's breakage-and-reunion hypothesis to a subset of DSBs active in binary misrejoining and in binary eurejoining (accidental restitution). The model is numerically consistent with both data on chromosome aberrations and the data obtained by PFGE if proximity effects (restrictions on the range of interactions of DSB free ends) are present. Proximity effects are modeled by partitioning the cell's nucleus into approximately 400 interaction sites, with two active DSB free ends capable of rejoining only if they were produced within the same site. Neglecting one-track action, the SMBE model predicts a quadratic-linear dose-response relationship for DSB misrejoining after exposure to low-LET radiation; i.e., there is a quadratic response at moderate doses which becomes linear as the dose becomes large, rather than vice versa. The linear region results because at very high doses almost all of the active DSB free ends misrejoin rather than eurejoin.

DNA↗
PubMed1997

Diversification of T cell responses to carboxy-terminal determinants within the 65-kD heat-shock protein is involved in regulation of autoimmune arthritis.

The T cell response to the 65-kD mycobacterial heat-shock protein (Bhsp65) has been implicated in the pathogenesis of autoimmune arthritis. Adjuvant arthritis (AA) induced in the Lewis rat (RT-1(l)) by injection of Mycobacterium tuberculosis serves as an experimental model for human rheumatoid arthritis (RA). However, the immunological basis of regulation of acute AA, or of susceptibility/resistance to AA is not known. We have defined the specificity of the proliferative T cell responses to Bhsp65 during the course of AA in the Lewis rat. During the early phase of the disease (6-9 d after onset of AA), Lewis rats raised T cell responses to many determinants within Bhsp65, spread throughout the molecule. Importantly, in the late phase of the disease (8-10 wk after onset of AA), there was evidence for diversification of the T cell responses toward Bhsp65 carboxy-terminal determinants (BCTD) (namely, 417-431, 441-455, 465-479, 513-527, and 521-535). Moreover, arthritic rats in the late phase of AA also raised vigorous T cell responses to those carboxy-terminal determinants within self(rat) hsp65 (Rhsp65) that correspond in position to the above BCTD. These results suggest that the observed diversification is possibly triggered in vivo by induction of self(Rhsp65)-reactive T cells. Interestingly, another strain of rat, the Wistar Kyoto (WKY/NHsd) rat (RT-1(l)), with the same major histocompatibility complex class II molecules as the Lewis rat, was found to be resistant to AA. In WKY rats, vigorous responses to the BCTD, to which the Lewis rat responded only in the late phase of AA, were observed very early, 10 d after injection of M. tuberculosis, Strikingly, pretreatment with the peptides comprising the set of BCTD, but not its amino-terminal determinants, provided significant protection to naive Lewis rats from subsequent induction of AA. Thus, T cell responses to the BCTD are involved in regulating inflammatory arthritis in the Lewis rat and in conferring resistance to AA in the WKY rat. These results have important implications in understanding the pathogenesis of RA and in devising new immunotherapeutic strategies for this disease.

Amino Acid Sequence↗