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Biomedical subjects

R W Chan

Publications and source records attributed to R W Chan.

10 recordsLinked to original sources
PubMed1998

Viscosities of implantable biomaterials in vocal fold augmentation surgery.

Vocal fold vibration depends critically on the viscoelasticity of vocal fold tissues. For instance, phonation threshold pressure, a measure of the "ease" of phonation, has been shown to be directly related to the viscosity of the vibrating mucosa. Various implantable biomaterials have been used in vocal fold augmentation surgery, with implantation sites sometimes close to or inside the mucosa. Yet their viscosities or other mechanical properties are seldom known. This study attempts to provide data on viscosities of commonly used phonosurgical biomaterials. Using a parallel-plate rotational rheometer, oscillatory shear experiments were performed on implantable polytetrafluoroethylene (Teflon or Polytef; Mentor Inc., Hingham, MA), collagen (Zyderm; Collagen Corp., Palo Alto, CA), glutaraldehyde crosslinked (GAX) collagen (Phonagel or Zyplast; Collagen Corp.), absorbable gelatin (Gelfoam; Upjohn Co., Kalamazoo, MI), and human abdominal subcutaneous fat. Samples of human vocal fold mucosal tissues were also tested. Under sinusoidal oscillatory shear at 10 Hz and at 37 degrees C, the dynamic viscosity was 116 Pascal-seconds (Pa-s) for polytetrafluoroethylene, 21 Pa-s for gelatin, 8-13 Pa-s for the two types of collagen, 3 Pa-s for fat, and 1 to 3 Pa-s for vocal fold mucosa. Results extrapolated to 100 Hz also show similar differences among the biomaterials, but all values are an order of magnitude lower because of the typical inverse frequency relation (shear thinning effect) for polymeric and biologic materials. The data suggest that the use of fat for vocal fold augmentation may be more conducive to the "ease" of phonation because of its relatively low viscosity, which is closest to physiologic levels. This implication is probably the most relevant in predicting initial outcome of the postoperative voice before there is any significant assimilation (e.g., resorption and fibrosis) of the implanted biomaterial.

Abdomen↗
PubMed1998

Psychosocial adjustment among children conceived via donor insemination by lesbian and heterosexual mothers.

This study examined the relations among family structure (e.g., number of parents, parental sexual orientation), family process (e.g., parents' relationship satisfaction, interparental conflict), and the psychological adjustment of children who had been conceived via donor insemination. The 80 participating families, all of whom had conceived children using the resources of a single sperm bank, included 55 families headed by lesbian and 25 families headed by heterosexual parents. Fifty families were headed by couples and 30 by single parents. Participating children averaged 7 years of age. Results showed that children were developing in normal fashion, and that their adjustment was unrelated to structural variables such as parental sexual orientation or the number of parents in the household. These results held true for teacher reports as well as for parent reports. Variables associated with family interactions and processes were, however, significantly related to indices of children's adjustment. Parents who were experiencing higher levels of parenting stress, higher levels of interparental conflict, and lower levels of love for each other had children who exhibited more behavior problems.

Adaptation, Psychological↗
PubMed1997

Further studies of phonation threshold pressure in a physical model of the vocal fold mucosa.

This paper reports results of further experimentation on a previously developed physical model of the vocal-fold mucosa [Titze et al., J. Acoust. Soc. Am. 97, 3080-3084 (1995)]. The effects of vocal-fold thickness, epithelial membrane thickness, and prephonatory glottal geometry on phonation threshold pressure were studied. Phonation threshold pressures in the range of 0.13 to 0.34 kPa were observed for an 11-mm-thick vocal fold with a 70-micron-thick "epithelial" membrane for different "mucosal" fluid viscosities. Higher threshold pressure was always obtained for thinner vocal folds and thicker membranes. In another set of experiments, lowest offset threshold pressure was obtained for a rectangular or a near-rectangular prephonatory glottis (with a glottal convergence angle within about +/- 3 degrees). It ranged from 0.07 to 0.23 kPa for different glottal half-widths between 2.0 and 6.0 mm. The threshold for more convergent or divergent glottal geometries was consistently higher. This finding only partially agrees with previous analytical work which predicts a lowest threshold for a divergent glottis. The discrepancy between theory and data is likely to be associated with flow separation from a divergent glottis.

Humans↗
PubMed1995

Osseointegrated implants for single tooth replacement in general practice: a 1-year report from a multicentre prospective study.

The single tooth implant is a treatment option for the replacement of missing single teeth and in many cases is the treatment of choice. It is, however, an expensive treatment requiring a co-ordinated approach to the surgical and restorative aspects of treatment. In this study, a group of dentists in general and restorative dental practice and with no previous experience in implant surgery underwent an intensive training course in all aspects of implant treatment for single teeth. Using a system of simplified instrumentation with a strict adherence to protocol, the group installed and restored single tooth implants ad modum Brånemark in a wide range of clinical situations. At the one year follow-up period following crown insertion, the success rate of treatment compared favourably with results reported from centres using the specialist team approach to treatment. The results of this study indicate that further consideration should be given to the training of general dentists so that improved delivery of dental health care can be provided at a more economic level.

Adolescent↗
PubMed1994

Does the voice improve with vocal hygiene education? A study of some instrumental voice measures in a group of kindergarten teachers.

This study investigated the efficacy of a program of vocal hygiene education designed for an occupational group at risk for dysphonia, namely, kindergarten teachers. Twelve female teachers explored concepts and knowledge of vocal abuse and vocal hygiene in a workshop session and attempted to practice vocal hygiene for 2 months. They showed significant voice improvement as assessed instrumentally in terms of three acoustic and electroglottographic parameters. There was no significant change of voice in a control group of 13 teachers. The results suggest that teachers were able to improve their voices if they significantly reduced vocal abuses in daily life and practiced specific strategies to maintain classroom order and reduce the use of voice in teaching.

Adult↗
PubMed1994

Single tooth replacement--expanded treatment options.

The aim of any prosthesis is to restore function and aesthetics by replacing the missing tooth with minimal risks to adjacent tissues. The options presently available to the patient for the replacement of a missing single tooth include the removable partial denture, partial and full coverage bridgework, resin-bonded bridgework and the single-tooth implant prosthesis. The relative merits and guidelines for successful application of these treatment modalities are presented.

Dental Implantation, Endosseous↗
PubMed1993

Computerized pattern recognition of EEG artifact.

Automated artifact classification of quantified EEG (QEEG) epochs from 9 males using linear discriminant analysis showed greater than 85% agreement with judges' opinions. These results were replicated (n = 600 epochs for each sample). Testing the entire sample (n = 5800) illustrated reliable eye artifact (94%) but reduced muscle artifact classification (70%) accuracy. Agreement was lowest in the case of more subtle forms of muscle artifact (i.e., low amplitude muscle), however, less than 4% of these were wrongly classified as non-artifact. Improved data collection techniques retaining high frequency energies are anticipated to improve muscle artifact recognition. Results indicate that low levels of artifact contamination would result when only those epochs classified as non-artifact were accepted for inclusion in further analysis.

Blinking↗