Biomedical subjects

Yvonne Chan

Publications and source records attributed to Yvonne Chan.

6 recordsLinked to original sources

PubMed2006

Intraoperative cone-beam CT for guidance of temporal bone surgery.

OBJECTIVES: To describe our preclinical experience with Cone Beam CT (CBCT) in image-guided surgery of the temporal bone. STUDY DESIGN AND SETTINGS: A mobile isocentric C-arm (PowerMobil, Siemens Medical Systems, Erlangen, Germany) modified to include a flat-panel detector (Varian Imaging Products, Palo Alto, CA) and a motorized orbit was developed to acquire multiple projections in rotation about a subject. Initial experiments imaging steel wire in air were used to investigate the system's spatial resolution in 3D image reconstruction. Subsequently temporal bone dissection was performed on five cadaver heads using the modified C-arm as an image guidance system. RESULTS: We obtained a spatial resolution of 0.85 mm. The image acquisition time was 120 seconds and the radiation dose approximately one-tenth of a conventional CT scan. CONCLUSION: CBCT provided submillimeter accuracy at high speed with low radiation dosage to offer utility as an intraoperative imaging system. SIGNIFICANCE: CBCT offers technology that approximates "near-real-time" image guidance. EBM RATING: C-4.

Cadaver↗

PubMed2005

Definition of genetically distinct attenuation mechanisms in naturally virulence-attenuated Listeria monocytogenes by comparative cell culture and molecular characterization.

Listeria monocytogenes is a foodborne pathogen able to cause serious disease in humans and animals. Not all isolates are equally pathogenic, however, and several isolates have been characterized as naturally virulence attenuated. We sought to identify the genetic basis of natural virulence attenuation using cell culture assays and molecular techniques. By comparing the phenotypes of naturally virulence-attenuated isolates to those of defined virulence gene mutants in plaque, cytotoxicity, and hemolysis assays and by characterizing selected virulence genes and their expression using DNA sequencing and TaqMan reverse transcriptase PCR, we classified virulence-attenuated isolates into four categories. Both group A and group B isolates were noncytotoxic and nonhemolytic; however, group A isolates underexpressed listeriolysin O (LLO, encoded by hlyA), while group B isolates produced LLO proteins that were inactive. The single isolate in group C was fully cytotoxic, had higher than wild-type hemolytic activity, and was, therefore, likely virulence attenuated due to overexpression of LLO. Group D isolates were characterized by normal cytotoxicity, hemolytic activity, and hlyA expression but had reduced intracellular growth. The genetic mechanisms causing virulence-attenuated phenotypes among the group D isolates could not be determined definitively but may involve defects in the expression of actA or the function of the ActA protein. Our results show (i) that the combination of cell culture assays and molecular techniques used in this study allows for identification and characterization of naturally virulence-attenuated isolates and (ii) that multiple distinct genetic mechanisms are responsible for natural virulence attenuation in L. monocytogenes.

Animals↗

PubMed2004

The cell-specific expression of endothelial nitric-oxide synthase: a role for DNA methylation.

The basis for the endothelial cell-restricted expression of endothelial nitric-oxide synthase (eNOS) is not known. While transgenic promoter/reporter mice demonstrated endothelium cell-specific eNOS expression, we found robust expression of episomal eNOS promoter/reporter constructs in cell types that do not express the native eNOS transcript. To explore the mechanism underlying this differential activity pattern of chromatin-versus episome-based eNOS promoters, we examined the methylation status of 5'-regulatory sequences of the human eNOS gene. DNA methylation differed dramatically between endothelial and nonendothelial cell types, including vascular smooth muscle cells. This same cell type-specific methylation pattern was observed in vivo in endothelial and vascular smooth muscle cells of the mouse aorta at the native murine eNOS promoter. We addressed the functional consequences of methylation on eNOS transcription using transient transfection of in vitro methylated promoter/reporter constructs and found that methylated constructs exhibited a marked decrease in the synergistic action of Sp1, Sp3, and Ets1 on eNOS promoter activity. The addition of methyl-CpG-binding protein 2 further reduced the transcriptional activity of methylated eNOS constructs. Importantly, chromatin immunoprecipitation demonstrated the presence of Sp1, Sp3, and Ets1 at the native eNOS promoter in endothelial cells but not in vascular smooth muscle cells. Finally, robust expression of eNOS mRNA was induced in nonendothelial cell types following inhibition of DNA methyltransferase activity with 5-azacytidine, demonstrating the importance of DNA methylation-mediated repression. This report is the first to show that promoter DNA methylation plays an important role in the cell-specific expression of a constitutively expressed gene in the vascular endothelium.

Animals↗

PubMed2004

Smoking cessation in patients diagnosed with head and neck cancer.

OBJECTIVE: To determine patients' smoking status after the diagnosis and treatment of squamous cell carcinoma of the head and neck (SCCHN) and to identify factors associated with smoking cessation. DESIGN: Cross-sectional survey study conducted over a 2-year period. SETTING: Head and neck surgery clinic of an academic tertiary care hospital. METHODS: Two hundred thirteen consecutive patients diagnosed with SCCHN were interviewed to ascertain patients' smoking status and the incidence of smoking cessation. Information on demographics, tobacco and alcohol history, disease characteristics, and treatment modality was also collected. MAIN OUTCOME MEASURES: The rate of smoking cessation was evaluated, in which smoking cessation is defined as the use of no cigarettes at least 1 month prior to the interview. Possible predictors of smoking cessation were evaluated. RESULTS: One hundred twenty-five patients were found to be smoking at the time of diagnosis. Among these patients, 53.6% stopped smoking after diagnosis or during treatment. In the univariate analyses, tumour site (p = .01), concurrent alcohol use (p = .03), and number of attempts to quit pre- (p = .03) and postdiagnosis (p = .001) were found to be highly predictive of patient smoking cessation. Multivariable modelling showed that gender, tumour site, and number of attempts to quit smoking were significantly and independently related to smoking cessation. CONCLUSIONS: Although smoking cessation would be presumed to be high after cancer diagnosis, this study has identified patient subgroups in which postdiagnosis smoking cessation intervention programs need to be made more effective.

Adult↗

PubMed2002

Patient education and informed consent in head and neck surgery.

OBJECTIVE: To examine the effects of an educational intervention, in the form of printed material, on patient knowledge and recall of possible risks from parotidectomy or thyroidectomy. DESIGN: Prospective, randomized, controlled study conducted during a 9-month period. SETTING: Head and neck surgery clinic of an academic tertiary care hospital. PATIENTS: One hundred twenty-five consecutive patients older than 16 years who were undergoing thyroidectomy or parotidectomy at the head and neck surgery clinic were recruited. Four patients were excluded from analysis because their follow-up interview was not within the required limits. INTERVENTION: At the preoperative visit during the routine consent process, both groups received a verbally delivered checklist of risks specific for the surgery to be performed. The intervention group was also given a pamphlet with written information accompanied by illustrations. MAIN OUTCOME MEASURES: The effectiveness of the educational intervention was determined by comparing the average rate of risk recall between the intervention and control groups. The effects of age, sex, level of education, and time between the consent and recall interviews on recall rate were also assessed. RESULTS: The overall risk recall rate for both procedures was 39.1%. The recall rate of the intervention group was 50.3% compared with 29.5% for the control group (P<.001). CONCLUSIONS: The intervention consistently improved risk recall for all patients regardless of age, sex, and level of education. Patients' ability to recall potential risks was significantly increased by an educational intervention; all patients would benefit from this intervention.

Adolescent↗

PubMedDate not supplied

Effective hand function assessment after burn injuries.

This study compared two methods of hand function assessment, the Michigan Hand Outcomes Questionnaire (MHQ) and the Test d'Evaluation des Membres Supérieurs des Personnes Agées (TEMPA) in 20 patients discharged from a regional adult burn center (1995-1999). Spearman's rank correlation coefficient analysis was used to compare the MHQ and TEMPA scores, with P <.05 considered significant. The MHQ revealed that 68% of patients reported hand function deterioration, mainly with the nondominant hand (65%). Activities of daily living (76%) and work (59%) were the most affected. According to the MHQ, patient satisfaction correlated with work performance (r =.66, P =.002), aesthetics (r =.64, P =.003), pain (r =.59, P =.008), and activities of daily living (r =.54, P =.017). The MHQ indicated more hand function deterioration than the TEMPA. There was a significant correlation between the MHQ and TEMPA total scores (r =.68, P =.001). This study supports using the MHQ to determine which patients would benefit from the more resource-consuming TEMPA.

Activities of Daily Living↗