Biomedical subjects

V A Coveney

Publications and source records attributed to V A Coveney.

5 recordsLinked to original sources

PubMed2001

Is the behaviour of the leg during oscillation linear?

The linear behaviour of the human leg was studied using a free oscillation method. The lower leg is represented by a simple mass, spring and dashpot model. Forty-five subjects underwent free vibration tests on their right legs. The force amplitude and the time period, for successive oscillations enabled calculation of the stiffness to mass ratio values. It was found that the time period of the second oscillation cycle was significantly lower than that of the first, implying a corresponding increase in stiffness. The experimental data consistently exhibits these non-linear characteristics, indicating that the use of non-linear models could be of benefit for future free oscillation studies.

Adult↗

PubMed2001

An abdominal wall simulator for testing suprapubic urinary catheters.

Urinary catheters (drainage tubes) are in widespread use. The most common type of long-term catheter is the Foley, which is made from natural or synthetic rubber. Foley catheters are passed into the bladder via the urethra or the suprapubic puncture channel (through the abdominal wall). A simulator for the abdominal wall has been developed to simulate aspects of the interaction between it and a suprapubic catheter. The simulator is based on a slab of ultrasoft elastomer with tensionable reinforcing polyamide filaments. The behaviour of the simulator has been compared with data published. A soft membrane (contact pressure) transducer (SMT) was used and novel instrumented 'tongs' for lateral indentation of the puncture track giving indentation stiffness. Slab materials were used with shear moduli of 0.1 and 0.021 MPa. Two filament-tensioning methods were used: by clamping to a winding mechanism and by weights. The combination of the softer slab material and tensioning by weights gave good conformity to physiological data; other combinations did not.

Abdominal Muscles↗

PubMed2001

A servo-mechanical bladder dynamic simulator.

A method is described for the physical simulation of the dynamic behaviour of the urinary bladder. It has been found that the model can be controlled to an arbitrary pressure-volume characteristic essentially independent of the properties of the bladder material. Characteristic relationships between pressure and flow rate have also been observed in studies of the bladder, and this behaviour is also amenable to simulation.

Animal Testing Alternatives↗

PubMed2001

Optimization of debris removal during bladder irrigation.

Debris build-up within the bladder is one of the main problems encountered by patients undergoing long term catheterization. One of the methods of ameliorating this is to wash out the bladder at regular intervals. In this paper, an alternative method of bladder irrigation is investigated experimentally. The effectiveness of several possible catheter designs has been examined, together with other relevant variables such as the proximity and alignment of the tube tip to the debris and the irrigation flow rate. Results show that debris removal is very sensitive to tube design, with best designs achieving almost complete removal and the worst practically none. The proprietary continuous irrigation catheter used was particularly poor for the type of debris used. Removal is insensitive to the distance of the tube tip from the bladder base up to a limiting value, above which it reduces rapidly. Where misalignment causes the inlet jet to miss the debris, removal rates are very low. Increasing flow rate increases removal up to a limiting value, above which it remains constant. Although the results show the general trends, to optimize the system requires further understanding of the detailed flow patterns within the bladder. A theoretical study using computational fluid dynamics is thus being undertaken.

Administration, Intravesical↗

PubMed2001

Suprapubic track pressure and force--deformation measurements in a (live) human subject and in animal models post-mortem.

Tests have been performed on animal models shortly post-mortem and on a healthy human subject in order to obtain estimates of the forces which act on suprapubic urinary catheters and similar devices and to develop an abdominal wall simulator. Such data and test methods are required for the systematic design of suprapubic devices because of the dual need to maintain the functionality of devices and to avoid excessive pressure on soft body tissue which could lead to ischaemia and in turn necrosis. In the post-mortem animal models, electrical excitation was applied to the abdominal wall in order to stimulate muscle activity. Two types of transducers were used: a soft membrane transducer (SMT) for pressure measurement and novel instrumented 'tongs' to determine indentation stiffness characteristics in the suprapubic track or artificial pathway created for a device. The SMT has been extensively used in the urethras and bladders of human subjects while the tongs were built specifically for these tests. Only the well-established SMT was used with the human subject; a peak pressure of 22 kPa was obtained. In the animal models the pressure profile given by the SMT had a peak whose position corresponded well with the estimated location of the rectus muscle measured on the fixed tissue section. The peak value was 5.5 kPa, comparable with values likely to cause necrosis if maintained for more than 1 day. Remarkably consistent indentation stiffness values were obtained with the instrumented tongs; all values were close to 0.45 N/mm (33 kPa/mm).

Abdominal Muscles↗