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Biomedical subjects

M Chan

Publications and source records attributed to M Chan.

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

Detection and assessment of intracranial aneurysms: value of CT angiography with shaded-surface display.

OBJECTIVE: The purpose of this study was to evaluate the efficacy of circle of Willis CT angiography with shaded-surface display in the detection and assessment of suspected intracranial aneurysms. MATERIALS AND METHODS: Twenty-three patients who had clinical or radiologic suspicion of intracranial aneurysms were studied prospectively with CT angiography and conventional angiography. The images were obtained and interpreted in a double-blind fashion by different radiologists. Conventional angiography, which was the reference standard in this study, diagnosed 17 aneurysms in 15 patients. The usefulness of the two types of images for surgical planning was evaluated by two neurosurgeons. RESULTS: No aneurysms were detected with either technique in eight patients. Both techniques showed 15 aneurysms in 14 patients. The maximum dimensions were less than 3.0 mm in three cases, 3.0-5.0 mm in four cases, and greater than 5.0 mm in eight cases. With conventional angiography used as the reference standard, CT angiography has one false-positive and two false-negative findings, resulting in a sensitivity of 88% (15/17) and a specificity of 89% (8/9). For 12 of 15 aneurysms, CT angiography was rated equal or superior to conventional angiography in depicting all aspects (shape, orientation, neck, and parent vessel) of the aneurysms. CONCLUSION: We were able to detect aneurysms of the circle of Willis as small as 2 mm in size. Using conventional angiography as the reference standard, CT angiography has a sensitivity of 88% and a specificity of 89% for the detection of aneurysms in the circle of Willis. In almost all cases, CT angiography was equal or superior to conventional angiography in characterizing the aneurysms for surgical planning.

Adolescent↗
PubMed1995

[Diagnostic score for acute appendicitis].

Scoring systems seem to be ideal for supporting diagnosis of acute appendicitis because they are non invasive, require no special equipment and can be used in clinical routine. Several scores for appendicitis have been developed with good results in the original publications. Unfortunately these good results could not be reproduced on a German data base. Therefore we developed a new score using multivariate statistics and a quality controlled prospective data base. The score covers 8 variables: tenderness, rebound tenderness, micturition, type of pain, leucocytes, age, relocation of pain, rigidity. Independent evaluation of the score on a Dutch database resulted in a negative appendicectomy rate of 21% and a missing appendicitis rate of 2%. The results are encouraging, so that further testing and clinical application can be recommended.

Acute Disease↗
PubMed1994

Mutations affecting the activity of toxic shock syndrome toxin-1.

Toxic shock syndrome toxin-1 (TSST-1), the potent staphylococcal exoprotein linked to most cases of the toxic shock syndrome, is a V beta-restricted T-cell mitogen (a so-called "superantigen"). TSST-ovine (TSST-O) is a natural variant of TSST-1, and is produced by certain ovine mastitis-associated strains of Staphylococcus aureus. Compared to TSST-1, TSST-O is only weakly mitogenic for leporine or murine splenocytes. It differs from TSST-1 at 7 amino acid residues over its 194 amino acid length. Terminus shuffling between the two proteins has suggested that their C-terminal differences (T69, Y80, E132, and I140 in TSST-1; 169, W80, K132, and T140 in TSST-O) are in part responsible for their discrepant mitogenic properties. In order to explore further the functional consequences of altering TSST-1 at residues 132 and 140, we engineered point mutants of TSST-1 at those positions. The mutant proteins were purified to homogeneity from culture supernants of a nontoxigenic strain of S. aureus using a combination of ultrafiltration, liquid-phase isoelectric focusing, and ion-exchange chromatography. The mutants retained global structural integrity as evidenced by circular dichroism spectroscopy, their preserved resistance to trypsin digestion, and their preserved binding to a neutralizing murine monoclonal antibody. The mutants were then tested for mitogenicity for human T-cells: The mutant I140T was approximately as active as wild-type TSST-1, while the mutant E132D was about 10-fold attenuated. On the other hand, the mutants E132A or E132K were each at least 1000-fold attenuated.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Toxins↗
PubMed1994

Decay-accelerating factor (CD55), a glycosylphosphatidylinositol-anchored complement regulatory protein, is a receptor for several echoviruses.

Echoviruses are human pathogens belonging to the picornavirus family. Decay-accelerating factor (DAF) is a glycosylphosphatidylinositol (GPI)-anchored surface protein that protects cells from lysis by autologous complement. Anti-DAF monoclonal antibodies prevented echovirus 7 attachment to susceptible cells and protected cells from infection. HeLa cells specifically lost the capacity to bind echovirus 7 when treated with phosphatidylinositol-specific phospholipase C, an enzyme that releases GPI-anchored proteins from the cell surface, indicating that the virus receptor, like DAF, is a GPI-anchored protein. Although Chinese hamster ovary cells do not bind echovirus 7, transfectants expressing human DAF bound virus efficiently, and binding was prevented by pretreatment with an anti-DAF monoclonal antibody. Anti-DAF antibodies prevented infection by at least six echovirus serotypes. These results indicate that DAF is the receptor mediating attachment and infection by several echoviruses.

Animals↗
PubMed1994

T cells and natural killer cells regulate human IgG subclass concentrations in SCID mice.

Cytokine regulation of human IgG subclass production is not well understood. Since T cells and natural killer (NK) cells produce IL-4 and/or IFN-gamma, we examined the effect of these cells on human IgG subclass concentration in reconstituted severe combined immunodeficient (SCID) mice. SCID mice receiving only B-cell-enriched splenocyte preparations had significantly decreased IgG concentrations and significantly decreased IgG1/IgG2 ratios compared to mice receiving B cells plus T cells (P = 0.02). IgG2 represented 58% of the total IgG at 28 days in mice receiving B-cell-enriched preparations compared to 19% of the total for the group receiving both B cells and T cells (P = 0.013). The effect of natural killer cells (CD16+) on IgG subclass was also studied in this model. IgG2 concentrations were twofold higher in mice receiving CD16-depleted cells compared to controls (P = 0.004). No significant differences were noted for IgG1, IgG3, or IgG4 subclass concentrations. In conclusion, T cells and natural killer cells influence human IgG subclass regulation in the SCID mouse model. We propose that the regulation of human IgG subclass production can be further examined in the SCID model.

Animals↗
PubMed1994

Experience with the management of ovarian germ cell tumors in Chinese patients.

Treatment results of 37 consecutive patients with primary ovarian germ cell tumors (OGCTs) were analyzed. Thirty-three were referred after initial laparotomy and four were first seen at relapse. Four patients with stage I dysgerminoma and grade 1 immature teratoma were observed after operation without recurrence. There was also no relapse in eight patients with dysgerminoma given postoperative irradiation (whole abdomen, median 30 Gy). Twenty-five patients (3 dysgerminomas, 11 immature teratomas, 9 endodermal sinus tumors, and 2 mixed germ cell tumors) received short-term cis-platinum-based chemotherapy. Six out of eight measurable tumors treated by chemotherapy had complete remission. Complete follow-up information was obtained in 35 out of 37 patients. The 4-year actuarial survival rates of the whole group and those referred immediately after initial surgery were 94.1 and 100%, respectively. cis-Platinum was substituted by carboplatin in eight cases but this did not affect treatment result. Nonetheless, deaths occurred in two of four patients referred at relapse with extensive disease and initially treated with suboptimal regimens. Chemotherapy-induced side effects were common but mostly tolerable and were related to cis-platinum and bleomycin. The results of this series show that cis-platinum-based chemotherapy is so effective that nearly 100% cure can be achieved in OGCTs and suggest that it is important to institute optimal chemotherapy from the start. On the other hand, common side effects of treatment and possible late toxicities make it desirable for future studies to see whether chemotherapy intensity could be reduced in patients with good prognosis.

Adolescent↗
PubMed1994

Determination of tumour vascularity using selective hepatic angiography as compared with intrahepatic-arterial technetium-99m macroaggregated albumin scan in hepatocellular carcinoma.

A total of 51 patients with hepatocellular carcinoma (HCC) were studied to determine the tumour vascularity as determined by selective hepatic angiography (HAG) and by intrahepatic-arterial technetium-99m-labeled macroaggregated albumin (Tc99m-MAA) scan. The tumour vascularity was graded on the HAG films by an interventional radiologist using a scale ranging from 1 (hypovascular) to 4 (extremely hypervascular). The grades of vascularity on HAG were grade 1 in 5 patients, grade 2 in 13 patients, grade 3 in 24 patients and grade 4 in 9 patients. The tumour vascularity on scintigraphy was determined by quantifying the count rates over the tumour and normal liver areas by an analog/digital gamma-camera, and the resultant tumour-to-normal ratio (T/N ratio) gave a quantitative measure of the vascularity. The range of the T/N ratio was 0.9 to 11.1, with a median of 3.7. There was no correlation between the tumour vascularity grading on HAG and the T/N ratio on the Tc99m-MAA scan (Wilcoxon rank test, P = 0.83). Thus, we conclude that HAG cannot reveal the true vascularity nor reflect the T/N ratio in HCC.

Angiography↗
PubMed1994

Cytoreductive surgery for hepatocellular carcinoma.

A prospective study was conducted on 26 patients for cytoreductive surgery of inoperable hepatocellular carcinoma. These patients underwent cytoreduction with liver resection, cryosurgery, microwave tissue coagulation and/or absolute alcohol injection. In-hospital mortality was 7.7%. The symptomatic relief and quality of survival were excellent. The median survival of patients after cytoreduction was 10.0 months and the survival was much better than those of 26 patients matched by sex, age, tumour size, Child-Pugh grading and Karnofsky scores who received systemic chemotherapy during the same period of the study (log rank test, P = 0.0001). There was no statistical difference between the survival curves of those patients who received (19 patients) and those who did not receive (7 patients) additional treatment by chemotherapy or selective internal radiation therapy after cytoreduction. This suggests that the gained survival benefit could have been derived mainly from the cytoreductive surgery rather than the additional treatments.

Adolescent↗
PubMed1994

Treatment of inoperable hepatocellular carcinoma with intrahepatic arterial yttrium-90 microspheres: a phase I and II study.

Eighteen patients with inoperable hepatocellular carcinoma (HCC) were treated with intrahepatic arterial yttrium-90 microspheres. All these patients showed a lung shunting below 15% and a tumour-to-normal ratio higher than 2 as determined by diagnostic technetium-99m macroaggregated albumin (Tc-MAA) gamma scintigraphy. The treatment was given through an arterial port placed during laparotomy. The radiation doses to the liver and tumour were determined intraoperatively with a beta probe and liquid scintillation counting of multiple liver biopsies. The treatment was well tolerated without major complications. In all patients the tumour marker fell to a level which ranged from 41% to 0.2% of the pretreatment level. Tumour regression was found to be dose related. Progressive or static disease occurred in a higher proportion of patients whose tumours received < 120 Gy (P = 0.005). Survival was better in those whose tumours received > 120 Gy (median survival = 55.9 weeks) than those whose tumours received lower doses (median survival = 26.2 weeks). This difference is statistically significant with P = 0.005. We conclude that yttrium-90 microsphere therapy is safe and that tumour response is dose related. A tumour dose of > 120 Gy is recommended.

Adolescent↗
PubMed1994

Carbon dioxide absorption is not linearly related to intraperitoneal carbon dioxide insufflation pressure in pigs.

BACKGROUND: Carbon dioxide absorption into the blood during laparoscopic surgery using intraperitoneal carbon dioxide insufflation may lead to respiratory acidosis, increased ventilation requirements, and possible serious cardiovascular compromise. The relationship between increased carbon dioxide excretion (VCO2) and intraperitoneal carbon dioxide insufflation pressure has not been well defined. METHODS: In 12 anesthesized pigs instrumented for laparoscopic surgery, intraperitoneal carbon dioxide (n = 6) or helium (n = 6) insufflation pressure was increased in steps, and VCO2 (metabolic cart), dead space, and hemodynamics were measured during constant minute ventilation. RESULTS: VCO2 increases rapidly as intraperitoneal insufflation pressure increases from 0 to 10 mmHg; but from 10 to 25 mmHg, VCO2 does not increase much further. PaCO2 increases continuously as intraperitoneal insufflation pressure increases from 0 to 25 mmHg. Hemodynamic parameters remained stable. CONCLUSIONS: By considering Fick's law of diffusion, the initial increase in VCO2 is likely accounted for by increasing peritoneal surface area exposed during insufflation. The continued increase in PaCO2 without a corresponding increase in VCO2 is accounted for by increasing respiratory dead space.

Absorption↗
PubMed1994

Intracellular expression of toxic shock syndrome toxin 1 in Saccharomyces cerevisiae.

In order to search for an occult cytotoxic enzymatic activity of the toxic shock syndrome toxin 1 (TSST-1), we placed the gene encoding TSST-1 (tstH) under the control of an inducible promoter in the eukaryotic yeast Saccharomyces cerevisiae. Under similar circumstances, the known bacterial enzymatic cytotoxins Shiga-like toxin and diphtheria toxin are both highly lethal to the yeast host. Although full-length stable TSST-1 was demonstrated within the yeast cells and although it retained mitogenicity for human T cells, it had no apparent effect on the yeast cells' growth kinetics or on their gross morphology. Retrieval and sequencing of the toxin gene revealed the wild-type sequence throughout, thus demonstrating that the apparent lack of toxicity for the yeast cells was not due to a serendipitous attenuating mutation within the coding region of the toxin gene. Similar results obtained after a second transformation of the same strain and after transformation of an unrelated strain demonstrate that neither chance permissive host mutation nor intrinsic host resistance was likely to have obscured an existing cytotoxic property of TSST-1. We conclude that TSST-1 probably does not possess a discrete enzymatic property cytotoxic for eukaryotic cells.

Animals↗
PubMed1994

Diagnostic pharmaco-scintigraphy with hepatic intra-arterial technetium-99m macroaggregated albumin in the determination of tumour to non-tumour uptake ratio in hepatocellular carcinoma.

Between October 1990 and March 1993, 124 patients who had hepatocellular carcinoma (HCC) underwent diagnostic pharmaco-scintigraphy with hepatic intraarterial technetium-99m macroaggregated albumin (TcMAA) to determine the tumourous to non-tumourous liver tissue uptake ratio (T/N ratio). There were 110 males and 14 females. Ages ranged from 16 to 73 with a median of 55 years. The range of T/N ratio was 0.7 to 19.3 with a median of 3.8. 12 patients with inoperable HCC were subsequently selected by predetermined criteria to undergo treatment with hepatic intraarterial yttrium-90 microspheres and the T/N ratios in these patients were validated by beta probe dosimetry and liquid scintillation count of multiple liver biopsies. The T/N ratio determined by preoperative diagnostic TcMAA scan correlated well with intraoperative beta probe dosimetry, with coefficient of correlation r = 0.82. Preoperative TcMAA scan also correlated well with liquid scintillation count of biopsy specimens, with r = 0.96. We conclude that TcMAA scan can be used to determine the T/N ratio in patients with HCC, thus allowing better selection of patients with inoperable tumours for loco-regional therapy.

Adolescent↗
PubMed1994

Selective internal radiation therapy with intra-arterial iodine-131-Lipiodol in inoperable hepatocellular carcinoma.

UNLABELLED: From August 1990 to June 1993, 26 patients with inoperable hepatocellular carcinoma were treated with intra-arterial iodine-131-Lipiodol (131I-L). METHODS: Iodine-131-Lipiodol was given through either an implantable arterial port (9 patients) or during hepatic angiography (17 patients). All 26 patients had multiple lesions, 3 had involved resection margin after surgical resection and 1 had diffuse infiltrative lesions. The median size of the largest tumor among 22 patients with a measurable lesion was 4.5 cm (2-9.5 cm). The end points are tumor response in terms of tumor size, change in serum alpha-fetoprotein level, toxicity of treatment and overall survival. RESULTS: Twenty-three patients received a single treatment of 1.11-2.22 GBq (30-60 mCi)131I-L. Three patients received 2.22-4.44 GBq (60-120 mCi)131I-L in three fractions. Considering both radiological regression and reduction in serum alpha-fetoprotein level as objective response criteria, the overall response rate was 52% (13 out of 25 patients with evaluable disease). Ten out of 15 patients who had raised alpha-fetoprotein levels had more than 50% reduction and 8 patients had more than 90% reduction in alpha-fetoprotein level. Since analysis, 19 patients have died and 7 remain alive, giving a minimum median survival of 6 mo (range 1.2-16.6 mo), with 4 surviving more than 1 yr calculated from the day of treatment. There was only one patient who had late deterioration of liver function compatible with radiation hepatitis. There was no bone marrow toxicity documented in any patients. CONCLUSION: Treatment with intra-arterial 131I-L was well tolerated in patients with inoperable hepatocellular carcinoma and produced an objective response of 52% with median survival of 6 mo. A fractionated dose of 131I-L was feasible and the radiation dose could be escalated safely.

Carcinoma, Hepatocellular↗
PubMed1994

Acute median nerve dysfunction from wheelchair propulsion: the development of a model and study of the effect of hand protection.

Carpal tunnel syndrome is prevalent among individuals who are wheelchair dependent. Maximal electrophysiologic median nerve dysfunction has been isolated to the proximal part of the carpal tunnel--the site of hand-wheel interface during wheeling. The objective of this study was to determine if measurable median nerve dysfunction (conduction slowing or block) results from a single session of vigorous wheeling and, if so, if protection for the hand with a glove (padded over the region of the carpal tunnel) could minimize the dysfunction. Thirty-five subjects (16 wheelchair dependent; 19 able-bodied) propelled a roller-mounted wheelchair at maximal rate of 2,000 hand strikes. A protective glove was worn on 1 hand only. Immediately before and after the wheeling, hand surface temperatures and bilateral median motor and sensory conductions were performed, and across-carpal tunnel conduction velocity and conduction block were calculated. Another group of 11 able-bodied subjects underwent similar electrodiagnostic testing before and after one half hour of vigorous stationary cycling (no hand trauma). Results were analyzed using a three-way analysis of covariance for repeated measures and demonstrated that (1) significant increases (5.2% to 8.5%) in across carpal tunnel conduction block occurred as a result of wheelchair propulsion but not cycling; (2) the wheeling-induced conduction block was not altered by using a protective glove. This study has demonstrated a model for measuring acute median nerve dysfunction resultant from wheeling but raises doubts regarding the protective effect of glove use on median nerve function.

Adolescent↗
PubMed1994

Measuring lung shunting in hepatocellular carcinoma with intrahepatic-arterial technetium-99m macroaggregated albumin.

UNLABELLED: With increased use of intraarterial administration of chemotherapeutic and radioactive particulate agents, it is necessary to assess agent delivery in the lung. METHODS: Technetium-99m-labeled macroaggregated albumin (99mTc-MAA) delivered through the hepatic artery was used to determine the degree of lung shunting in 125 patients with hepatocellular carcinoma (HCC). RESULTS: The percentage of lung shunting varied among patients and it ranged from less than 1% to 67.2%, with a median of 8.1%. The degree of shunting depended on the vascularity of the tumors but not on the tumor size. The effect of angiotensin II on lung shunting was tested on six patients and there was no significant difference found between those patients who were pre-treated with angiotensin II and those who were not. One patient who underwent a liver resection, had a significant decrease in lung shunting from 28.5% to less than 1% after surgery. CONCLUSION: The lack of effect of angiotensin II together with the almost complete ablation of lung shunting by tumor resection suggested neoplastic blood vessels were responsible for the shunting.

Angiotensin II↗