Biomedical subjects

T C Fung

Publications and source records attributed to T C Fung.

8 recordsLinked to original sources

PubMed2006

Instability of the two-layered thick-walled esophageal model under the external pressure and circular outer boundary condition.

The mucosal folding is a phenomenon observed for some biological tissues, including the pulmonary airway and gastrointestinal tract. In order to understand the mechanism of the formation of mucosal folding, a thick-walled two-layered cylindrical mathematical model was developed to investigate the buckling behavior under the external pressure and circular outer boundary condition. With the finite element method, the validity and accuracy of the proposed model was verified. The results showed that the fold number was in the range of 4-6, which was agreed with the experimental observation for the mucosal folding of a porcine esophagus. The fold number was found to decrease with the increase in the ratio of the inner to outer material stiffness. The increase in the thickness of inner layer also caused a slight declination of the fold number. Since the effects of both the material and geometrical nonlinearities have been accounted for, this model is more general to be used for the prediction of the buckling behavior of the layered structure with a wide range of thickness ratios and/or stiffness ratios.

Animals↗

PubMed2006

Directional, regional, and layer variations of mechanical properties of esophageal tissue and its interpretation using a structure-based constitutive model.

The esophagus, like other soft tissues, exhibits nonlinear and anisotropic mechanical properties. As a composite structure, the properties of the outer muscle and inner mucosal layer are different. It is expected that the complex mechanical properties will induce nonhomogeneous stress distributions in the wall and nonuniform tissue remodeling. Both are important factors which influence the function of mechanosensitive receptor located in various layers of the wall. Hence, the characterization of the mechanical properties is essential to understand the neuromuscular motion of the esophagus. In this study, the uniaxial tensile tests were conducted along two mutually orthogonal directions of porcine esophageal tissue to identify the directional (circumferential and axial), regional (abdominal, thoracic, and cervical), and layer (muscle and mucosa) variations of the mechanical properties. A structure-based constitutive model, which took the architectures of the tissue's microstructures into account, was applied to describe the mechanical behavior of the esophagus. Results showed that the constitutive model successfully described the mechanical behavior and provided robust estimates of the material parameters. In conclusion, the model was demonstrated to be a good descriptor of the mechanical properties of the esophagus and it was able to facilitate the directional, layer, and regional comparisons of the mechanical properties in terms of the associated material parameters.

Animals↗

PubMed2006

3D Mechanical properties of the layered esophagus: experiment and constitutive model.

The identification of a three dimensional constitutive model is useful for describing the complex mechanical behavior of a nonlinear and anisotropic biological tissue such as the esophagus. The inflation tests at the fixed axial extension of 1, 1.125, and 1.25 were conducted on the muscle and mucosa layer of a porcine esophagus separately and the pressure-radius-axial force was recorded. The experimental data were fitted with the constitutive model to obtain the structure-related parameters, including the collagen amount and fiber orientation. Results showed that a bilinear strain energy function (SEF) with four parameters could fit the inflation data at an individual extension very well while a six-parameter model had to be used to capture the inflation behaviors at all three extensions simultaneously. It was found that the collagen distribution was axial preferred in both layers and the mucosa contained more collagen, which were in agreement with the findings through a pair of uniaxial tensile test in our previous study. The model was expected to be used for the prediction of stress distribution within the esophageal wall under the physiological state and provide some useful information in the clinical studies of the esophageal diseases.

Animals↗

PubMed2006

Viscoelasticity of esophageal tissue and application of a QLV model.

The time-dependent mechanical properties of the porcine esophagus were investigated experimentally and theoretically. It was hypothesized that the viscoelasticity was quasilinear, i.e., the time and strain effects were independent. In order to verify the separability of time and strain effects, the stress-relaxation test was conducted at various strains and the data were fitted with the Fung's quasilinear viscoelastic (QLV) model. By using the material parameters obtained from the stress relaxation test, the cyclic peak stress and hysteresis were predicted. Results showed that the stress relaxed by 20-30% of the peak stress within the first 10 s and stabilized at approximately 50% at the time of 300 s. The relative stress relaxation R(2) (i.e., the difference of stress at a particular time to the final equilibrium stress normalized by the total difference of the peak and final stress) was not different significantly for various strains. It was also found that, by using the stress-time data during both the ramp and relaxation phases, the correlation between parameters was substantially reduced. The model could also predict the cyclic peak stress and hysteresis except for the underestimate of valley stress. We conclude that the QLV model could be used as the material characterization of the esophageal tissue.

Animals↗

PubMed1994

Effect of thyroxine administration on serum thyrotropin receptor antibody and thyroglobulin levels in patients with Graves' hyperthyroidism during antithyroid drug therapy.

Graves' hyperthyroidism is due primarily to overproduction of antibodies to thyrotropin receptors (TR-ab), which stimulate the thyroid gland and cause hyperthyroidism. Antibody production during antithyroid drug therapy is an important determinant of the course of the disease. We therefore observed the changes of serum TR-ab, thyroglobulin (Tg) and thyroid hormone levels in response to administration of L-thyroxine (T4) in Graves' hyperthyroid patients during antithyroid drug therapy. Serum levels of TR-ab, Tg and other thyroid hormones were measured by radioimmunoassay (RIA) during either methimazole treatment alone or in combination with thyroxine in 60 Graves' hyperthyroid patients. The patients initially were treated with 30 mg of methimozole daily for 3 months, which was then reduced to 15 mg daily for the following 3 months. All patients were euthyroid 6 months after the start of antithyroid therapy and the TR-ab level decreased from 61 +/- 11% (+/- SD) to 28 +/- 7% (p < 0.01). Patients then were divided into three groups: group A (N = 25), whose TR-ab level was 10% or more (the cut-off value for positivity), received 0.1 mg of T4 and 10 mg of methimazole daily for 6 months; group B (N = 15), whose TR-ab level also was 10% or more and was age- and thyroid function-matched with group A, received only 10 mg of methimazole daily for 6 months; group C (N = 20), with a TR-ab level of less than 10%, received 10 mg of methimazole alone daily for 6 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1979

The role of the cholinergic system in the central control of thermoregulation in rats.

Systemic and central administration of methacholine (a synthetic choline derivative) both produced dose-dependent decreases in rectal temperature in rats at all the ambient temperatures studied. Both at room temperature (22 degrees C) and in the cold (8 degrees C), the hypothermia in response to methacholine application was brought about by both a decrease in metabolic heat production and an increase in cutaneous circulation. In the heat (29 degrees C), the hypothermia was due solely to an increase in respiratory evaporative heat loss. Furthermore, the methacholine-induced hypothermia was antagonized by central pretreatment of atropine (a selective blocker of cholinergic receptors), but not by the central administration of either 6-hydroxydopamine (a relative depletor of catecholaminergic nerve fibers) or 5,6-dihydroxytryptamine (predominately a serotonin depletor). The data indicate that activation of the cholinergic receptors within brain with methacholine decreases heat production and (or) increases heat loss which leads to hypothermia in rats.

5,6-Dihydroxytryptamine↗

PubMedDate not supplied

Predictors of neonatal mortality in 1,500-1,999 g premature infants with respiratory failure. Basis for ECMO Therapeutic Trial.

Despite the introduction of new ventilation techniques and surfactant therapy, some premature infants still experience severe respiratory failure and either die or survive with severe bronchopulmonary dysplasia. Extracorporeal membrane oxygenation is currently not offered for preterm infants with a birth weight less than 2,000 g, mainly because of the potential high risk for intracranial hemorrhage. The aim of this study was to determine risk predictors for mortality alone and for mortality or major lung morbidity in 1,500-1,999 g premature infants with respiratory failure. We reviewed the medical records of all preterm infants (n = 459) with respiratory failure and a birth weight of 1,500-1,999 g treated at five medical centers from 1989 to 1991. Of those infants, 23 (5%) had severe respiratory failure, defined as a requirement for ventilatory support with the fraction of inspired oxygen > or = 0.8 or peak inspiratory pressure > or = 30 cmH2O for > or = 3 hr in the 1st week of life. A mortality of > or = 75% was associated with a single arterial/alveolar oxygen ratio < or = 0.04; pulmonary air leak alone or pulmonary air leak with a mean airway pressure > or = 12 cmH2O; and arterial oxygen tension < or = 50 mmHg. These risk predictors may provide a basis for the selection of patients for future clinical trials of extracorporeal membrane oxygenation in this high-risk group of 1,500-1,999 g premature infants with severe respiratory failure.

Body Weight↗

PubMedDate not supplied

Comparison of gentamicin bioassay values utilizing three different indicator organisms.

Gentamicin serum concentrations were monitored via bioassay with three indicators, to determine if assay results were influenced by the testing organism. When mean assay values, from seven samples, were compared to mean target values, there was no significant differences with Staphylococcus epidermidis, Bacillus subtilis or Klebsiella pneumoniae. However, levels from one of the seven samples yield dramatically lower concentrations, for all three indicators, than the target. This suggests the presence of a bioassay inhibitor substance. Additional testing of the organisms, versus serum without gentamicin, revealed Bacillus subtilis to be much more serum-sensitive than the others.

Bacillus subtilis↗