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S C Yu

Publications and source records attributed to S C Yu.

At least 19 recordsLinked to original sources
PubMed2006

On the kinetics of apatite growth on substrates under physiological conditions.

Derived from reaction kinetics, a simple but useful method, based on "apatite forming capacity" or AFC of solutions mimicking blood plasma, is proposed to decipher the rate of calcium phosphate mineralization. Apatite growth rate constants were calculated using this method for a model composite surface varying the volume fraction of synthetic hydroxyapatite (HA) in a polymer matrix. Previously reported data for mineralized surfaces on Ta, Ti, and its alloys are also analyzed similarly and compared. Utilizing the growth rate constant, the bioactivity of the materials was indexed in vitro. Complementarily, semiempirical quantum mechanical calculation (ZINDO method) showed that the interaction of cations with TRIS-hydroxymethyl aminomethane molecules in the solution is stronger than that with the polymer substrate considered, but weaker than hydrated Ti and TiO(2) surfaces. This analysis then quantifies for example the extent of polymer inertness and the "bioactivity" of alkali treated Ti. The growth rate constants for the model materials prepared in this work are explained on the basis of localized dissolution of HA, the amount of which simply increases with increasing volume fraction of HA in the composite.

Apatites↗
PubMed2003

Tensile properties, tension-tension fatigue and biological response of polyetheretherketone-hydroxyapatite composites for load-bearing orthopedic implants.

Polyetheretherketone-hydroxyapatite composites were developed as alternative materials for load-bearing orthopedic applications. The amount of hydroxyapatite (HA) incorporated into the polyetheretherketone (PEEK) polymer matrix ranges from 5 to 40 vol% and these materials were successfully fabricated by injection molding. This study presents the mechanical and biological behavior of the composite materials developed. It was found that the amount of HA in the composite influenced the tensile properties. Dynamic behavior under tension-tension fatigue revealed that the fatigue-life of PEEK-HA composites were dependent on the HA content as well as the applied load. The biological responses of PEEK-HA composites carried out in vivo verified the biocompatibility and bioactive nature of the composite materials.

Animals↗
PubMed2002

Addition of meperidine to bupivacaine for spinal anaesthesia for Caesarean section.

BACKGROUND: In a prospective, randomized, double-blind, placebo-controlled trial, we investigated the effect of adding meperidine 10 mg to intrathecal bupivacaine on the duration of early postoperative analgesia in 40 patients having elective Caesarean section under spinal anaesthesia. METHODS: Patients received intrathecal injection of 0.5% hyperbaric bupivacaine 2.0 ml plus either normal saline 0.2 ml (saline group) or 5% meperidine 0.2 ml (meperidine group). After operation, all patients were given i.v. patient-controlled analgesia using morphine. RESULTS: The duration of effective analgesia, defined as the time from intrathecal injection to first patient-controlled analgesia demand, was greater in the meperidine group (mean 234 min, 95% confidence interval 200-269 min) compared with the saline group (mean 125 min, 95% confidence interval 111-138 min; P<0.001). The 24 h morphine requirement was similar in the two groups. The meperidine group had a greater incidence of intraoperative nausea or vomiting compared with the saline group (11 vs 3; P=0.02). CONCLUSION: Addition of meperidine 10 mg to intrathecal bupivacaine for Caesarean section is associated with prolonged postoperative analgesia but with greater intraoperative nausea and vomiting.

Adjuvants, Anesthesia↗
PubMed2001

Use of Japanese medaka (Oryzias latipes) and Tilapia (Oreochromis mossambicus) in toxicity tests on different industrial effluents in Taiwan.

In Taiwan, aquatic toxicity tests for industrial effluents are not required for discharge permits. However, relying on traditional chemical and physical characteristics of an effluent to monitor and regulate such discharges to manage water quality of a receiving water is insufficient. In this study, we used two fish species, Japanese medaka (Oryzias latipes) and tilapia (Oreochromis mossambicus), and three toxic endpoints, including acute and subacute toxicity, to determine toxicity of seven different types of industrial effluents. Prior to the study, two reference toxicants were tested on two fish species. The LC50s of CdCl2 for tilapia and medaka juveniles were 29.6 +/- 15.3 mg/L and 2.2 +/- 1.2 mg/L, respectively. The sensitivity of medaka embryo mortality and hatching inhibition to CdCl2 were about the same, with the LC50 and EC50 of 0.3 +/- 0.1 mg/L and 0.1 +/- 0.1 mg/L, respectively. The LC50s for tilapia and medaka juveniles to sodium dodecyl sulfate (SDS) were 19.7 +/- 10.6 mg/L and 12.5 +/- 5.9 mg/L. The medaka embryo was less sensitive to SDS than to CdCl2. The embryo's LC50 for SDS was 5.8 +/- 2.8 mg/L and the hatching inhibition EC50 was 1.3 +/- 1.1 mg/L. Results of toxicity tests on different effluents showed that the electroplating effluent was the most toxic, followed by acrylonitrile manufacturing and pulp/paper mill discharges. The LC50s of the electroplating effluent to different assays were in the range of several percents of the whole effluent. The pulp/paper effluent was toxic only to the medaka embryo. The rest of the industrial effluents tested showed either moderate or no toxicity to the animals.

Animals↗
PubMed2001

The management of residual and recurrent intracranial aneurysms after previous endovascular or surgical treatment--a report of eighteen cases.

OBJECT: We wish to report our experience in the management of residual or recurrent intracranial aneurysm after previous endovascular or surgical treatment. METHODS: We performed a retrospective review of the clinical notes, operation records and cerebral angiograms of eighteen patients who were known to have undergone treatment for residual or recurrent aneurysms. RESULTS: During the period of April 1994 to May 1999, 210 patients were treated for an intracranial aneurysm either surgically or by endovascular methods. Eighteen of these patients (8.6%) were subsequently treated for residual or recurrent aneurysm. Thirteen achieved a complete occlusion. Complete occlusion was achieved in five of the eight patients who underwent endovascular treatment as a second procedure. Seven out of ten surgical cases achieved complete occlusion. Fifteen patients made a good recovery according to the Glasgow Outcome Score. Two patients who presented in a poor grade subarachnoid haemorrhage (SAH) were left severely disabled. One patient died after retreatment. CONCLUSIONS: The treatment of cerebral aneurysm remnants can be performed effectively using a variety of modalities. The original purpose of the treatment, which is total occlusion of the lesion, can thus be achieved.

Adult↗
PubMed2001

Microsomal monooxygenase activity in Tilapia (Oreochromis mossambicus) exposed to a bleached kraft mill effluent using different exposure systems.

Bleached kraft pulp and paper mill effluents (BKMEs) are known to have adverse effects on aquatic organisms. One of the effects of BKMEs is its ability to induce cytochrome P4501A activity in exposed fish. 7-Ethoxyresorufin O-deethylase (EROD) activity is the most common biomarker used to measure the mixed-function monooxygenase activity. In this study, Tilapia were exposed to BKMEs using different exposure systems and their hepatic EROD activity, as well as liver/somatic index (LSI), were determined. In the Phase I study, Tilapia treated with betaNF and a whole (100%) BKME using a static, non-renewal system exhibited statistically significant EROD induction, but LSI values were not altered. In the Phase II study, fish were either caged in the mill's fishpond with the whole effluent passing through or cultured in tanks receiving 100% of the BKME continuously using a flow-through system in the laboratory. Their EROD activities were then compared with the non-exposed fish (control). The EROD activities in both groups of fish were elevated significantly with the greatest induction being observed in the field-exposed group. The LSI values in all of the field-exposed fish were significantly greater than the control Tilapia. The EROD assay was sensitive in detecting biological changes in fish exposed to the BKME. Further studies are warranted to better understand the impacts of BKMEs on aquatic organisms in Taiwan.

Animals↗
PubMed2001

Comparison of non-breath-hold high resolution gadolinium-enhanced MRA with digital subtraction angiography in the evaluation on allograft renal artery stenosis.

AIM: The study objective was to compare the diagnostic accuracy of non-breath-hold high resolution gadolinium-enhanced magnetic resonance angiography (Gd-MRA) with intra-arterial digital subtraction angiography (DSA) in the evaluation of allograft renal artery stenosis (ARAS). MATERIALS AND METHODS: We studied 17 renal transplant recipients (six men, 11 women, age 34-64 years) with a systolic bruit in the transplant region beyond the early post-operative period. Gadolinium-enhanced magnetic resonance angiography was performed by non-breath-hold high resolution 3D acquisition in the oblique coronal plane using a 256 x 512 matrix.Digital subtraction angiography was performed with AP and oblique views and ARAS was graded as < or =50% or >50% diameter stenosis on the view that displayed the maximal narrowing. RESULTS: Digital subtraction angiography showed >50% stenosis in seven patients, all of whom were diagnosed correctly on Gd-MRA. Gadolinium-enhanced magnetic resonance angiography diagnosed two patients with >50% stenosis which were not confirmed on DSA. Eight patients had no or < or =50% stenosis on both Gd-MRA and DSA. The sensitivity and specificity of Gd-MRA in revealing >50% stenosis were 100% and 75%, respectively, using DSA as the gold standard. CONCLUSION: High resolution Gd-MRA employing a non-breath-hold technique is highly sensitive in the diagnosis of ARAS greater than 50%. It is preferred as a non-invasive screening technique to DSA in suspected ARAS.

Adult↗
PubMed2001

Liver iron estimation in beta-thalassaemia: comparison of MRI biochemical assay and histological grading.

AIMS: The aims of the study were to compare the efficacy of magnetic resonance imaging (MRI), biochemical assay and histological grading in estimating liver iron content, and to evaluate the value of liver to muscle signal intensity ratio (L/M ratio) on spin-echo T1-weighted images in this role. MATERIALS AND METHODS: Thirty-nine homozygous beta-thalassaemics had their L/M ratio measured on MRI, followed by ultrasound-guided liver biopsies with histological grading of iron storage and biochemical quantification of liver iron concentration (LIC-b) using atomic absorption spectrophotometry. RESULTS: A significant difference in L/M ratios between the four grades of iron storage on histology was observed (P < 0.001). The coefficient of correlation was -0.67 between L/M ratio and LIC-b ranging from 2 to 21.6 mg/g dry weight. Specific values of L/M ratio reliably reflected liver iron content at clinically important levels. A L/M ratio of < 0.6 has 86% sensitivity and 100% specificity in the prediction of grade 3 or 4 iron storage histologically and 81% sensitivity and 81% specificity in predicting LIC-b > 15 mg/g. A L/M ratio of > 0.8 predicts a histological iron storage grading of 0 or 1 with a 100% sensitivity and 74% specificity. CONCLUSION: L/M ratio on MRI is of value as a non-invasive alternative to repeated liver biopsies for estimating liver iron content at clinically important thresholds.

Adolescent↗
PubMed2001

Preoperative systemic chemoimmunotherapy and sequential resection for unresectable hepatocellular carcinoma.

OBJECTIVE: To examine the surgical and pathologic findings of 15 patients who had initially unresectable hepatocellular carcinoma (HCC) and received preoperative systemic chemoimmunotherapy and sequential resection. SUMMARY BACKGROUND DATA: More than 80% of patients with HCC present for treatment at an unresectable stage. Conventional treatment has produced a low tumor response rate in this group of patients. Recently, new systemic chemoimmunotherapy has been found to be effective and able to make previously unresectable HCC resectable. Sequential resection after response to chemoimmunotherapy could therefore induce complete clinical remission. METHODS: From July 1996 to February 1999, 150 patients with unresectable HCC were treated with systemic chemoimmunotherapy consisting of cisplatin, alpha-interferon, doxorubicin, and 5-fluorouracil for a maximum of six cycles. The residual tumors were reassessed for resectability after treatment aiming at complete remission in the patients after combined modality treatment. Twenty-seven patients had a more than 50% regression in tumor size (2 complete remissions, 25 partial remissions). Fifteen patients had resectable disease after treatment, and all underwent sequential resection with curative intent. Treatment outcome and the surgical and pathologic features of these 15 patients were studied. RESULTS: Fifteen of 150 patients responded to chemoimmunotherapy and underwent sequential resection. They were considered to have unresectable disease as a result of extensive local disease (with and without major vascular involvement) in 10 patients and the presence of extrahepatic or metastatic disease in 5 patients. All patients except two were hepatitis B carriers. Surgical resection of the residual lesion after chemoimmunotherapy was successful for all patients. Eight of the patients had complete pathologic remission. The rest had minimal residual disease (<5%) only. All 15 patients entered complete clinical remission after surgery. Thirteen patients were still alive as of this writing and two had died of recurrent disease. The 1-, 2-, and 3-year survival rates were 100%, 100%, and 53%, respectively. The mean follow-up period was 27 months (range 15-37). Neither the median disease-free nor overall survival had been reached. Ten patients remained in complete remission as of this writing. CONCLUSION: Combined modalities with systemic chemoimmunotherapy and surgical resection can achieve complete clinical remission and long-term control of disease in patients with unresectable HCC.

Adolescent↗
PubMed2001

US-guided percutaneous biopsy of small (< or = 1-cm) hepatic lesions.

PURPOSE: To determine the accuracy of ultrasonography (US)-guided percutaneous biopsy in diagnosing malignant neoplasms for hepatic lesions 1 cm or smaller. MATERIALS AND METHODS: In this prospective study, 64 consecutive patients with 74 discrete focal hepatic lesions depicted at US were referred for liver biopsy to confirm the exact nature of the lesions. Mean lesion size was 0.84 cm +/- 0.13 (range, 0.5-1.0 cm). Biopsy was performed with an 18-gauge automated biopsy gun in 46 lesions (once [n = 37], twice [n = 7], three times [n = 2]) or a 22-gauge needle in 28 lesions (once [n = 23], twice [n = 4], three times [n = 1]). Measures were taken to ensure accurate and effective lesion sampling. The histologic diagnosis of malignant tumor and findings on follow-up US images of "benign" nodules for 15-39 months were the criterion standard. RESULTS: No complications occurred. All specimens obtained were sufficient for diagnosis. Histologic examination revealed various types of primary and secondary malignant tumors (n = 44), hemangioma (n = 5), cirrhosis (n = 13), focal fatty change (n = 8), focal fatty sparing (n = 2), and abscess (n = 2). The diagnostic discrimination of US-guided biopsy in diagnosing malignant tumors in these small lesions was sensitivity, 98%; specificity, 100%; positive predictive value, 100%; negative predictive value, 97%; and accuracy, 99%. CONCLUSION: Percutaneous biopsy under US control is highly accurate in providing a definitive histologic diagnosis of malignant neoplasms for small hepatic lesions if measures for ensuring precise and effective lesion sampling are taken.

Adolescent↗
PubMed2001

A comparative study of three different methods of administering metaraminol during spinal anaesthesia in the elderly.

We compared three methods of administering metaraminol during spinal (subarachnoid) anaesthesia. Fifty-two elderly patients with fractured hips were studied. Blood pressure was maintained by either intramuscular (i.m.) metaraminol (0.1 mg x kg(-1)), intravenous (i.v.) boluses (0.01 mg x kg(-1)) or an infusion (0.05 mg x kg(-1) x h(-1)). Non-invasive blood pressure was recorded every one-minute. Spinal anaesthesia initially decreased the systolic arterial pressure by 15 (14) % compared to 35 (15) % for diastolic pressure (P<0.001). I.m. metaraminol restored the systolic arterial pressure back to baseline values (-3%), but there was significant between-subject variability resulting in a very unpredictable effect. I.v. boluses and infusion had a more predictable effect and maintained systolic arterial pressure at about 20% below baseline. Range of effect, measured by inter-quartile range and variance, was greatest in the i.m. group and least in the infusion group (P<0.003). I.m. metaraminol during spinal anaesthesia has a very unpredictable effect. Infusions of metaraminol provided the best blood pressure control. Diastolic blood pressure fell significantly after spinal anaesthesia and this merits further investigation.

Aged↗
PubMed2001

Scaling laws for wall shear stress through stenoses under steady and pulsatile flow conditions.

Most patients with atherosclerosis exhibit isolated stenoses of one or more epicardial coronary arteries. The wall shear stresses produced in high-grade stenosis are important in the understanding of atheromatous plaque rupture and thrombosis. This study is designed to establish a method which can be used to scale the different wall shear stresses obtained under different flow conditions to be normalized and subsequently collapsed on to a single general curve. The simulations include both steady and pulsatile flow. The reduced area percentages of the stenoses studied are 50, 75 and 90 per cent. Scaling laws for steady and pulsatile flow conditions are proposed and presented. It can be found from the results that the scaling analysis for pulsatile flow conditions is more complicated than for steady flow conditions and is restricted to, and only valid at, certain time intervals.

Arteriosclerosis↗
PubMed2000

The flow patterns within the impeller passages of a centrifugal blood pump model.

The effects of impeller geometry on the performance of a centrifugal blood pump model [the MSCBP design of Akamatsu and Tsukiya (The Seventh Asian Congress of Fluid Mechanics (1997), 7-10) at a 1:1 scale] have been investigated both experimentally and computationally. Four impeller designs were tested for pump hydraulic performance at the operating point (i.e. 2000 rpm), using blood analog as the working fluid. Each impeller has seven blades with different configurations including the radial straight blade and backward swept blade designs. The results show that both designs can achieve a stable head of about 100 mm Hg at the operating point. Subsequent investigations involved the visualization of the relative flow field within the impeller passages via the image de-rotation system coupled with a 2.5 W argon ion laser. Flow structures in all sectors of each impeller were examined and discussed. To further quantify the possible effects of blade geometry to thrombus formation and hemolysis, computational fluid dynamics (CFD) was used to simulate a simplified two-dimensional blade-to-blade flow analysis so as to estimate the shear stress levels. The results indicate that the stress levels found within the blade passages are generally below the threshold level of 150 N/m(2) for extensive erythrocyte damage to occur. There are some localized regions near the leading edge of the blades where the stress levels are 60% above the threshold level. However, given such a short residence time for the fluid particles to go through these high shear stress regions, their effects appear to be insignificant.

Blood Flow Velocity↗
PubMed2000

Variations of the bilirubin uridine-diphosphoglucuronosyl transferase 1A1 gene in healthy Taiwanese.

The activity of uridine-diphosphoglucuronosyl transferase 1 (UGT1) may influence the concentration of serum bilirubin. Because UGT1 is too labile to be measured with classical biochemical methods, we analysed the whole UGT1A1 gene in 290 healthy Taiwanese adults by using the polymerase chain reaction method, and investigated the relationship between UGT1A1 genotypes and serum bilirubin levels. The results showed that slightly more than 50% of the subjects had one or more variant sites in UGT1A1 gene. The most common variant was A(TA)6TAA/A(TA)7TAA (6/7) in the promoter area, followed by heterozygous variation within the coding region, compound heterozygous and homozygous variations. Among the four variant sites within the coding region, 211 G to A was the predominate one, 1091 C to T was a novel variation, and 686 C to A was associated with 6/7. Subjects with 6/7 or heterozygous variation within the coding region or compound heterozygous (plus one homozygous) variation had significantly higher bilirubin levels than those with wild UGT1A1 gene. When the 290 subjects were stratified into six groups according to their serum bilirubin concentrations, the bilirubin levels were correlated well to the frequencies of variant UGT1A1 gene. Our results show that there is a strong association between UGT1A1 gene and bilirubin levels in healthy Taiwanese adults. The occurrence of A(TA)7TAA allele was relatively rare and the variation rate within the coding region was much higher in Taiwanese compared to that in Caucasians.

Adult↗
PubMed2000

Cholangiographic features in the diagnosis and management of obstructive icteric type hepatocellular carcinoma.

In 11 years and 3 months, 2,037 patients with HCC were seen and 48 patients (2.4%) were diagnosed to have obstructive icteric type HCC. Five patients were terminally ill and were not investigated further. Forty three patients were initially investigated by endoscopic retrograde cholangiography (ERC) or percutaneous transhepatic cholangiogram (PTC) and classified as having obstructive icteric type 1, 2, or 3 HCC based on the cholangiographic findings. The obstruction in type 1 HCC was due to intraluminal tumour casts and/or tumour fragments obstructing the hepatic ductal confluence or common bile duct, while intraluminal blood clots, from haemobilia, filling the biliary tree was the cause in type 2 HCC. The pathology in type 3 HCC was extraluminal obstruction by extensive tumour encasement of the intra-hepatic biliary ductal system and/or extrinsic compression of the hepatic and common bile ducts by tumour(s) and/or malignant lymph nodes. At the initial ERC/PTC, 10 patients (5 resected, 50%) had obstructive icteric type 1 and 23 patients (0 resected) had obstructive icteric type 3 HCC. Of the 10 patients initially classified according to cholangiography to have obstructive icteric type 2 HCC, subsequent investigations revealed that 6 patients had type 1 HCC (4 resectable,67%) and 4 patients had type 3 HCC (0 resectable). The classification of the obstructive icteric type HCC into types 1, 2, and 3, based on the initial cholangiographic appearances has simplified and rationalized our management strategy for this condition.

Algorithms↗
PubMed2000

Experimental and computational studies of the relative flow field in a centrifugal blood pump.

The relative flow field within the impeller passage of a centrifugal blood pump had been examined using flow visualization technique and computational fluid dynamics. It was found that for a seven-blade radial impeller design, the required flow rate and static pressure rise across the pump could be achieved but the flow field within the blades was highly undesirable. Two vortices were observed near the suction side and these could lead to thrombus formation. Preliminary results presented in this article are part of our overall effort to minimize undesirable flow patterns such flow separation and high shear stress regions within the centrifugal blood pump. This will facilitate the future progress in developing a long-term clinically effective blood pump.

Computer Simulation↗