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Biomedical subjects

K C Chan

Publications and source records attributed to K C Chan.

At least 19 recordsLinked to original sources
PubMed2006

Initial transcatheter palliation of hypoplastic left heart syndrome.

Initial percutaneous transcatheter palliation of hypoplastic left heart syndrome is now feasible. The primary procedures for palliation include stenting of the ductus arteriosus with a self expanding nitinol stent to secure an adequate systemic blood flow, placement of an internal pulmonary arterial band to protect the pulmonary vascular bed and to prevent pulmonary overcirculation, and widening of the interatrial communication by blade and balloon septostomy or static balloon dilation to decompress the left atrium. Anatomic variations of the ductus arteriosus have important implications for technical success with ductal stenting. Patients who have undergone complete transcatheter palliation with the internal pulmonary band appear to have less immediate morbidity at the time of transplant, with preserved integrity and growth of the branch pulmonary arteries at one year follow-up.

Blood Flow Velocity↗
PubMed2005

Nitrite-induced methaemoglobinaemia - aetiology, diagnosis and treatment.

A 41-year-old woman presented with the clinical features of methaemoglobinaemia after drinking Chinese herbal medicine. A life threatening methaemoglobin level of 68% was measured. Both clinical and laboratory diagnostic difficulties were encountered. The pitfalls of pulse oximeter, blood gas analysis and co-oximeter interpretation during diagnosis and after methylene blue administration are discussed.

Adult↗
PubMed2004

Short-term and long-term results of endoscopic balloon dilation for achalasia: 12 years' experience.

BACKGROUND AND STUDY AIMS: This retrospective study reports 12 years' experience with pneumatic dilation treatment in patients with achalasia and attempts to define factors capable of predicting failure of endoscopic dilation. PATIENTS AND METHODS: Consecutive patients with achalasia who received endoscopic balloon dilation were studied retrospectively. Repeat dilation was carried out if dysphagia persisted or recurred. A structured symptom score questionnaire (the Eckardt score) was conducted by phone with patients who had received dilation and had been followed up for more than 2 years. Failure was defined as the presence of significant dysphagic symptoms after more than two repeat dilations. Data for the first 2 years (short-term) and for the subsequent follow-up (long-term) were analyzed. RESULTS: From 1989 to 2001, 66 patients underwent endoscopic balloon dilation for achalasia; three perforations (4.5 %) occurred, with no mortalities. Dysphagic symptoms significantly improved 12 weeks after the procedure ( P < 0.05). Fourteen patients (20 %) required a second dilation procedure within a median of 7 months (range 1 - 52 months), and 13 of them underwent repeat dilations within the first 2 years. Five patients (7.5 %) required further surgical or endoscopic therapy. Fifty-eight patients received pneumatic dilation for more than 2 years; 32 (55 %) responded to the questionnaire. The mean dysphagia score was 1.7 (SD 1.2), with only five patients (16 %) having significant dysphagic symptoms during a median follow-up period of 55 months (range 26 - 130 months). The cumulative success rates for pneumatic dilation after 5 and 19 years were 74 % and 62 %, respectively. Cox regression analysis identified small balloon size (30 mm) as the only significant factor capable of predicting failure of endoscopic dilation ( P = 0.009; relative risk 5.3; 95 % confidence interval, 1.7 to 40.9). CONCLUSIONS: Endoscopic balloon dilation is an effective treatment for achalasia, with minimal morbidity (60 % experience long-term benefit).

Adolescent↗
PubMed2004

Performance of large-size superconducting coil in 0.21T MRI system.

A high-temperature superconductor (HTS) was used on magnetic resonance imaging (MRI) receiver coils to improve image quality because of its intrinsic low electrical resistivity. Typical HTS coils are surface coils made of HTS thin-film wafers. Their applications are severely limited by the field of view (FOV) of the surface coil configuration, and the improvement in image quality by HTS coil is also reduced as the ratio of sample noise to coil noise increases. Therefore, previous HTS coils are usually used to image small in vitro samples, small animals, or peripheral human anatomies. We used large-size HTS coils (2.5-, 3.5-, and 5.5-in mean diameter) to enhance the FOV and we evaluated their performance through phantom and human MR images. Comparisons were made among HTS surface coils, copper surface coils, and cool copper surface coils in terms of the signal-to-noise ratio (SNR) and sensitivity profile of the images. A theoretical model prediction was also used to compare against the experimental result. We then selected several human body parts, including the wrist, feet, and head, to illustrate the advantage of HTS coil over copper coil when used in human imaging. The results show an SNR gain of 200% for 5.5-in HTS coil versus same size copper coils, while for 2.5- and 3.5-in coils it is 250%. We also address the various factors that affect the performance of large size HTS coils, including the coil-to-sample spacing due to cryogenic probe and the coil-loading effect.

Electric Conductivity↗
PubMed2003

Two-port versus four-port laparoscopic cholecystectomy.

BACKGROUND: Two-port laparoscopic cholecystectomy has been reported to be safe and feasible. However, whether it offers any additional advantages remains controversial. This study reports a randomized trial that compared the clinical outcomes of two-port laparoscopic cholecystectomy versus conventional four-port laparoscopic cholecystectomy. METHODS: One hundred and twenty consecutive patients who underwent elective laparoscopic cholecystectomy were randomized to receive either the two-port or the four-port technique. All patients were blinded to the type of operation they underwent. Four surgical tapes were applied to standard four-port sites in both groups at the end of the operation. All dressings were kept intact until the first follow-up 1 week after surgery. Postoperative pain at the four sites was assessed on the first day after surgery using a 10-cm unscaled visual analog scale (VAS). Other outcome measures included analgesia requirements, length and difficulty of the operation, postoperative stay, and patient satisfaction score on surgery and scars. RESULTS: Demographic data were comparable for both groups. Patients in the two-port group had shorter mean operative time (54.6 +/- 24.7 min vs 66.9 +/- 33.1 min for the four-post group; p = 0.03) and less pain at individual subcostal port sites [mean score using 10-cm unscaled VAS: 1.5 vs 2.8 ( p = 0.01) at the midsubcostal port site and 1.3 vs 2.3 ( p = 0.02) at the lateral subcostal port site]. Overall pain score, analgesia requirements, hospital stay, and patient satisfaction score on surgery and scars were similar between the two groups. CONCLUSION: Two-port laparoscopic cholecystectomy resulted in less individual port-site pain and similar clinical outcomes but fewer surgical scars compared to four-port laparoscopic cholecystectomy. Thus, it can be recommended as a routine procedure in elective laparoscopic cholecystectomy.

Adult↗
PubMed2003

Biological response to hormonal manipulation in oestrogen receptor positive ductal carcinoma in situ of the breast.

Adjuvant antioestrogen therapy with tamoxifen is recommended for all women following breast-conserving surgery for ductal carcinoma in situ (DCIS) to reduce local recurrence, despite 50% of lesions being oestrogen receptor (OR) negative. We have investigated the response to hormone manipulation in DCIS by studying changes in epithelial proliferation and progesterone receptor (PR) expression as surrogate molecular markers of treatment effects in DCIS of known OR status. Women were identified who had undergone diagnostic core biopsy followed by surgery for DCIS 14-41 days later. Ki67 (a measure of epithelial cell proliferation) and PR expression were determined by immunohistochemistry on paired paraffin sections of the core biopsy and operative specimens for each patient, with OR and HER-2 measured on the operative specimen. Women were divided into three groups according to whether they had changed hormone therapy (stopped hormone replacement therapy (HRT), group 1), continued taking HRT (group 2) or were not taking HRT (group 3) between core biopsy and surgery. In OR-positive (but not in OR-negative) DCIS after oestrogen withdrawal (group 1), a fall in the mean cell proliferation (P&<0.01) was observed. A fall in PR expression between core biopsy and surgery was also seen in this group (P=0.02). No change in either mean cell proliferation or PR expression was seen in the other two groups in OR-positive or -negative DCIS. The fall in proliferation and PR expression occurred regardless of HER-2 status. In conclusion, a biological response to hormone manipulation is only seen in OR-positive DCIS tumours. Any clinical value of antioestrogen therapy is likely to be restricted to this group.

Adult↗
PubMed2003

Value of the Van Nuys Prognostic Index in prediction of recurrence of ductal carcinoma in situ after breast-conserving surgery.

BACKGROUND: The Van Nuys Prognostic Index (VNPI), an algorithm based on tumour size, tumour grade, presence of necrosis and excision margin width, is claimed to predict local recurrence after breast-conserving surgery for ductal carcinoma in situ (DCIS). The aim of this study was to examine the validity of the VNPI in a UK population. METHODS: Clinicopathological data, including VNPI subgroups, for 237 patients who had breast-conserving operations for DCIS were examined. Multivariate data analysis was performed using a Cox regression model to examine the independence and relative importance of different variables in predicting recurrence, and to compare the data with those used in derivation of the VNPI. RESULTS: The median follow-up was 47 months. There were 37 ipsilateral local recurrences. Excision margin width (P < 0.001) and tumour grade (by Van Nuys grading (P = 0.014) or simple nuclear grading (P = 0.004)) were the only independent risk factors for local recurrence. Excision margin width had three times more power than grade in predicting local recurrence. Subgrouping data by VNPI score predicted recurrence-free survival (P < 0.001), but stratified 78 per cent of patients into a group with a moderate risk of local recurrence. CONCLUSION: Excision margin width is the most important predictor of local recurrence after breast-conserving surgery for DCIS. The VNPI lacked discriminatory power for guiding further patient management.

Adult↗
PubMed2003

Superconducting RF coils for clinical MR imaging at low field.

RATIONALE AND OBJECTIVES: A number of recent reports in the MRI literature have established that substantial signal-to-noise ratio (SNR) gains can be achieved with small samples or low resonance frequencies, through the use of high-quality factor high-temperature superconducting (HTS) RF receive coils. We show the application of HTS coils to the imaging of human subjects with improved SNR compared with copper coils. MATERIALS AND METHODS: HTS coils were constructed from 7.62-cm YBa2Cur3O7-delta thin films on LaAlO3 substrate and cooled in a liquid nitrogen cryostat. Human and phantom images were acquired on a 0.2-T scanner. The SNR improvements compared with equivalent-sized copper coils are reported. RESULTS: SNR gains of 2.8-fold and 1.4-fold were observed in images of a phantom acquired with an HTS coil versus a room temperature copper coil and a liquid nitrogen-cooled copper coil, respectively. Preliminary results suggest higher image quality can be obtained in vivo with an HTS coil compared with copper coil imaging. Images of human orbit, brain, temporomandibular joint, and wrist are presented. CONCLUSION: The experimental results show that benefits can be expected from application of HTS surface coils in human MR imaging with low-field scanners. These potential benefits justify the continued development of practical HTS coil imaging systems despite the considerable technical difficulties involved in cryostat and coil design.

Brain↗
PubMed2002

Two liters of polyethylene glycol-electrolyte lavage solution versus sodium phosphate as bowel cleansing regimen for colonoscopy: a prospective randomized controlled trial.

BACKGROUND AND STUDY AIMS: As a bowel cleansing agent for colonoscopy, sodium phosphate (NaP) has been reported to have equal effectiveness and better patient tolerance in comparison with 4 l polyethylene glycol-electrolyte lavage (PEG-EL) solution. Poor patient tolerance is frequently associated with a large amount of fluid consumed, and better patient tolerance might therefore be expected if the volume of PEG-EL solution could be reduced. This study aimed to compare 2 l PEG-EL solution with NaP in relation to patients' tolerance and its effectiveness as a bowel cleansing agent. PATIENTS AND METHODS: Two hundred consecutive patients admitted to the day-procedure ward for elective colonoscopy were prospectively randomized to receive either a 2-l PEG-EL solution or a 90-ml oral NaP regimen. Patients with a history of congestive heart failure, impaired renal function (creatinine > 1.5 mg/dl), or previous colectomy were excluded from the study. The patients completed a questionnaire to assess their tolerance of bowel preparation before the colonoscopy. Endoscopists, who were blinded to the type of regimen that had been used, scored the adequacy of bowel preparation from the rectum to cecum using a defined endoscopic score. RESULTS: Two hundred patients were included in this randomized trial. Nine patients were excluded, due to either an incomplete questionnaire (two in the PEG-EL group, one in the NaP group) or inability to complete the bowel preparation regimen (four in the PEG-EL group and two in the NaP group). The demographic data were comparable in the two groups. There were no differences between the two groups with regard to willingness to repeat the regimen, ease of consumption, acceptability of the bowel preparation regimen, or the endoscopists' satisfaction with the quality of bowel preparation. The NaP group had a better mean endoscopic score at the cecum compared with the PEG-EL group (1.47 +/- 1.15 vs. 1.05 +/- 0.76; P = 0.007). CONCLUSIONS: The effectiveness and patient tolerance of the 2-l PEG-EL solution is comparable with that of oral NaP. The 2-l PEG-EL solution is therefore an effective alternative as a bowel-cleansing agent for colonoscopy.

Adult↗
PubMed2002

Transoesophageal echocardiographic monitoring of pulmonary venous obstruction induced by sternotomy closure during infant heart transplantation.

A case of an infant receiving orthotopic heart transplantation with over-sized donor heart was reported. Left lower pulmonary venous obstruction after sternotomy closure was detected by transoesophageal echocardiography (TOE) and the decision to delay sternal closure was made and the clinical outcome was very satisfactory. The usefulness of intraoperative TOE monitoring and postoperative TOE follow-up for infant heart transplantation, especially in those cases of size mismatch, was well demonstrated.

Echocardiography, Transesophageal↗
PubMed2001

Substrate-Binding reactions of the 3[dsigma*psigma] excited state of binuclear gold(I) complexes with bridging bis(dicyclohexylphosphino)methane ligands: emission and time-resolved absorption spectroscopic studies.

The complexes [Au2(dcpm)2]-Y2 (dcpm = bis(dicyclohexylphosphino)methane; Y=ClO4 (1), PF6- (2), CF3SO3- (3), Au(CN)2- (4), Cl- (5), SCN (6) and I- (7)) were prepared, and the structures of 1 and 4-7 were determined by X-ray crystallography. Complexes 1-4 display intense phosphorescence with lambdamax at 360-368 nm in the solid state at room temperature as well as in glassy solutions at 77 K. The solid-state emission quantum yields of the powdered samples are 0.37 (1), 0.74 (2), 0.53 (3) and 0.12 (4). Crystalline solid 5 displays both high-energy UV (lambdamax = 366 nm) and low-energy visible emissions (lambdamax = 505 nm) at room temperature, whereas either 6 or 7 shows only an intense emission with lambdamax at 465 or 473 nm, respectively. All the complexes in degassed acetonitrile solutions exhibit an intense phosphorescence with lambdamax ranging from 490 to 530 nm. The high-energy UV emission is assigned to the intrinsic emission of the 3[dsigma*psigma] excited state of [Au2(dcpm)2]2+, whereas the visible emission is attributed to the adduct formation of the triplet excited state with the solvent/counterion. The quenching rate constants of the visible emission of [Au2(dcpm)2]2+ in acetonitrile by various anions are 6.08 x 10(5) (ClO4-), 9.18 x l0(5) (PF6 ), 1.55 x 10(7) (Cl-) and 4.06 x 10(9) (I-) mol(-1) dm3s(-1). The triplet-state difference absorption spectra of 1-4 in acetonitrile show an absorption band with lambdamax at 350 nm and a shoulder/absorption maxima at 395-420 nm; their relative intensities are dependent upon the halide ion present in solution. Substrate binding reactions of the 3[dsigma*psigma] excited state with halide (X-) to give [Au2(dcpm)2X]+* would account for the lower energy absorption maxima in the triplet-state difference absorption spectra. With iodide as the counterion, complex 7 undergoes a photoinduced electron-transfer reaction with I- to give the radical anion I2-.

Journal Article↗
PubMed2001

Extent of excision margin width required in breast conserving surgery for ductal carcinoma in situ.

BACKGROUND: Breast conserving surgery (BCS) is common practice for unifocal ductal carcinoma in situ (DCIS) less than 4 cm in size, but the extent of tumor free margin width around DCIS necessary to minimize recurrence is unclear. METHODS: Clinical and pathologic details were recorded from all patients with pure DCIS < 4 cm in size, treated with BCS between 1978 and 1997. Histologic margins were measured by using an ocular micrometer. Patients with clear margins (> 1 mm) were divided up into 3 groups for analysis based on margin of normal tissue excised: 1.1-5 mm, 5.1-10 mm, and 10.1-40 mm. RESULTS: There were 66 patients with close margins (< or = 1 mm), of which 25 cases (37.9%) recurred. The recurrence rates for the 3 clear margin groups ranged from 4.5-7.1%. Median followup was 47 months (range 12-197 mos). Risk of recurrence in the group with close margins was greater than the subgroups with clear margins (P < 0.001); no differences in recurrence was seen between the individual subgroups with clear margins. Nuclear Grade 3 was predictive of recurrence (P = 0.03). Following excision alone, the recurrence rate was 18.6%, compared with 11.1% when radiotherapy was given as adjuvant therapy. Women with clear margins following excision had a recurrence rate of only 8.1%. CONCLUSION: After BCS for DCIS, close margins were associated with a high risk of local recurrence. Radiotherapy did not compensate for inadequate surgical clearance.

Adult↗
PubMed2001

Multidimensional high performance liquid chromatography--capillary electrophoresis separation of a protein digest: an update.

The trypsin digest of a mixture of two proteins, namely cytochrome c and myoglobin, was first separated in the first dimension by high-performance liquid chromatography (HPLC). Fractions from the HPLC were collected every 30s with the aid of a fraction collector into a 96-well microtiter plate. After concentration, all the collected fractions were analyzed simultaneaosly in the second dimension by a 96-array capillary electrophoresis system. The labeled peptides were detected by laser-induced fluorescence. An internal standard, allura red, was added to all the fractions, prior to capillary electrophoretic analysis. The internal standard serves two functions, migration time correction and signal intensity correction. The data are presented in two different formats, as an electropherogram of all the fractions and in a two-dimensional (2-D) format. The 2-D plot of the data shows the density of each spot, which corresponds to the concentration of the migrating peptides. The total experimental time for the HPLC and capillary electrophoretic analyses ist less than 1 h, which ist much faster than using 2-D slab-gel electrophoresis or single-capillary capillary electrophoresis.

Chromatography, High Pressure Liquid↗
PubMed2001

Blockade of growth factor receptors in ductal carcinoma in situ inhibits epithelial proliferation.

BACKGROUND: Ductal carcinoma in situ (DCIS) expresses c-erbB-2 receptor and epidermal growth factor receptor (EGFR). The aim of this study was to determine whether blocking of c-erbB-2 receptor with a humanized monoclonal antibody, 4D5 (HerceptinTM), or of EGFR with an epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI), ZD1839 (IressaTM), would decrease epithelial proliferation in DCIS. METHODS: DCIS tissue from 18 women undergoing surgery was implanted into 16 to 20 athymic nude mice per experiment (eight xenografts per mouse). Treatment commenced 2 weeks after implantation and consisted either of twice-weekly intraperitoneal injections of 4D5 10 mg/kg or of daily gavage with ZD1839 at 100-200 mg/kg for 14 days; appropriate controls were included. Xenografts were removed on days 14, 21 and 28. Proliferation was assessed by counting 1000 epithelial cells after Ki67 immuno- staining. RESULTS: ZD1839 inhibited proliferation compared with that in controls after 14 days (P < 0.01), whereas 4D5 did not. CONCLUSION: Proliferation in DCIS was decreased by EGFR tyrosine kinase inhibition but not by c-erbB-2 receptor blockade. ZD1839, an orally active and selective EGFR-TKI, has potential as adjuvant therapy in DCIS.

Adult↗
PubMed2001

Optimization of stacked half-hitch knots for arthroscopic surgery.

PURPOSE: This study was conducted to determine the optimal configuration of stacked half-hitch knots that would give the maximum knot-holding capacity (KHC). TYPE OF STUDY: Mechanical testing study. METHODS: The 2 types of suture materials tested were No. 1 PDS II monofilament and No. 2 Ethibond braided (Ethicon, Somerville, NJ) because these are the 2 most commonly used sutures in arthroscopic surgery. Twelve configurations of stacked half-hitch knots including 2 versions of the Revo knot were tested. Knots were tied between 2 steel hooks 7 mm apart on a manual knot-testing machine. The steel hooks were spread apart to break the knot and the KHC was determined by the peak load recorded on the digital force transducer. Maximum KHC was achieved for No. 1 PDS II sutures by locking the knot with 2 RHAPs (reversing half-hitch on alternate post) and, for No. 2 Ethibond sutures, by locking the knot with 3 RHAPs. Because of the possibility of PDS II sutures unraveling, it is recommended for both No. 1 PDS II and No. 2 Ethibond sutures, that all stacked half-hitches be locked with 3 RHAPs. By adding 1 RHAP to the Revo knot, failure by slippage can be eliminated. RESULTS: The recommended knots tied with braided No. 2 Ethibond sutures were 1.5 times stronger than knots tied with No. 1 PDS II sutures. Although there was variability in the KHC of the recommended knots tied by different surgeons using different knot tiers, the greatest difference in the mean KHC was less than 10%. CONCLUSIONS: Stacked half-hitch knots locked with 3 RHAPs are unlikely to fail by slippage.

Arthroscopy↗