Biomedical subjects

M B Bush

Publications and source records attributed to M B Bush.

3 recordsLinked to original sources

PubMed2006

A pinch elastometer for soft tissue.

A prototype compression elastometer suited to the characterisation of soft tissue is analysed and tested by application to various elastomers. The test material is pinched between two rigid cylinders and the compression force and displacement interpreted to yield a measure of "effective" stiffness or to calibrate a simple non-linear-elastic material model (Neo-Hookean). This deformation suits the testing of bulk soft tissue since it effectively isolates the test material from boundary conditions such as other soft tissue, ligaments and bones. These can be highly variable in the body and can affect results greatly when employing other types of tests to determine the elastic nature of tissue. A simple linear-material analysis, based on established solutions to two-dimensional problems, is extended to take into account various geometrical complexities. This analysis permits immediate inversion of the readings from the device to yield the elastic properties of the material, without the need for complex numerical analysis. Finite element analysis is also employed to determine the range of reliable application of the linear-elastic model. In particular, this analysis permits the extension of the linear-elastic analysis to include simple forms of non-linear-material behaviour. The method is demonstrated using three elastomers having significantly different material properties. A viable range of application of the device is identified in which it yields results with reasonable precision and accuracy. The prototype device was able to measure the effective elastic modulus of the test materials with a maximum error of 13% for three material types (N=25). Repeatability error was less than 7% in all cases. Further refinement of the device and measuring system will reduce this uncertainty.

Biomechanical Phenomena↗

PubMed1998

A mathematical model for micturition gives new insights into pressure measurement and function.

Our objective was to analyze the factors contributing to the development of detrusor pressure during micturition in the female with reference to a mathematical model. One hundred patients with predominantly stress incontinence were investigated with micturition pressure studies. Frictional and dynamic losses were estimated at various flow rates using a mathematical model. Almost 25% of patients recorded a micturition pressure below 11 cmH2O at peak flow (mean 23 cmH2O, range 0-91). Large inter- and intrapatient variations in micturition pressures were recorded on retesting. The low pressures were explained by a recently described external opening mechanism, backward stretching of the vagina during micturition by the muscles of the pelvic floor. This opened out the outflow tract and created the potential for a falsely high P(abd). The large variability in micturition pressures on retesting was attributed to changes in urethral radius being magnified to the fourth power. It was concluded that, micturition itself, and the components for pressure generation, are complex non-linear entities which appear to be greatly modified by the external striated pelvic floor opening mechanism. Addressing anatomical defects in this mechanism may be a fruitful route of future enquiry in females with emptying problems.

Adult↗

PubMed1997

On the flow through the human female urethra.

The flow characteristic for a human female urethra is determined by direct measurement of flow rate and pressure difference data. The measurements are made on a full-scale physical model of a urethra in its open state, which was created using dimensional information taken from video cystograms. The measured data therefore include viscous dissipation effects associated with developing flow, changes in cross-sectional area and changes in flow direction. These effects are often ignored in mathematical models of this system. The data may therefore assist in the development and testing of more realistic models for urine flow. The measured characteristic is compared with a mathematical model of the flow based on a straight tube of uniform diameter carrying fully developed turbulent flow. When the diameter of the model tube is chosen to be equal to the distal diameter of the urethra, it is observed that the predicted flow characteristic provides a good first approximation to the measured characteristic, despite the substantial differences in geometry and flow regime between the mathematical model and the actual system.

Female↗