Track 20. Biomechanics of Organs 20.3. Urinary Tract $389

In order to study the implementation of prosthesis, it is very important to achieve a correct modelling of the vibro-acoustic behaviour of middle ear [3]. In this work, a finite element modelling of the middle ear was made. For this proposes, a dynamic study will be presented by using the ABAQUS program. The model will include the different ligaments of the support structure. Hyperelastic behaviour of the components will be taken into account [2]. The connection between ossicles will be done by using contact formulation, which can be interpreted as a simulation of the capsular ligaments.

References [1] D. Falvo. Medical and psychosocial aspects of chronic illness and disability,

Jones and Bartlett Publishers 2005(3); 5. [2] EA.L.S. Martins, R.M. Natal Jorge, A.J.M. Ferreira, M. Figueiredo, R.A.A. Fer-

nandes, M. Figueiredo, R. Silva. Modelling the mechanical behavior of soft tissues using hyperelastic constitutive models. In: ICCB2005, H Rodrigues et al.(Eds.), Lisbon 2005; pp. 403-410.

[3] EJ. Prendergast, E Ferris, H.J. Rice, A.W. Blayney. Vibro-acoustic modeling of the outer and middle ear using the finite element method. Audiol Neurootol 1999; 4: 185-191.

6672 Mo, 16:15-16:30 (P13) Biomechanics o f ot i t is media with ef fus ion in human ear R.Z. Gan, C. Dai, X. Wang. School of Aerospace and Mechanical Engineering and Bioengineering Center, University of Oklahoma, Norman, Oklahoma, USA

The middle ear, which includes tympanic membrane (or eardrum) and three ossicular bones (i.e., malleus, incus and stapes) suspended in an air-filled cavity (i.e., middle ear cavity) by suspensory ligaments/muscles, is an ex- tremely small structure with complex shape. Changes of middle ear structure, material properties of ear components, and dynamic environment of middle ear cavity in disease states such as otitis media with effusion (OME) directly affect the sound transmission from the air-filled external ear canal to the fluid- filled cochlea, and thus, result in conductive hearing loss. The amount and rheological property of the fluid found inside middle ear cavity are primary variables describing the state of OME and reflecting different resistance on the moving parts of the middle ear. In this paper, we report our recent study on effects of fluid in middle ear cavity and the middle ear air pressure on movements of the tympanic membrane (TM) and/or stapes footplate in human cadaver ears. Displacement of the TM at the umbo in response to sound pressure (e.g., 90dB SPL) at ear canal was first measured with laser Doppler vibrometer, while the middle ear air pressure was varied, and saline or silicone fluids were introduced into the middle ear cavity. Next, the OME was simulated in a 3-D anatomic finite element (FE) model of human ear. The multi-field of a i r - structure-fluid coupled FE analysis was performed in the model to determine influence of the fluid in middle ear cavity on acoustic-mechanical transmission. The results include: (1) frequency response curves of displacements at the TM and/or stapes footplate over frequency range of 100-10 kHz in response to changes of middle ear air pressure and various middle ear fluid levels; and (2) effect of combined fluid and air pressure on TM movement. The results have quantitatively demonstrated how the fluid level, viscosity, and middle ear air pressure affect transfer function of middle ear for sound transmission.

4693 Mo, 16:30-16:45 (P13) Calculat ion o f the stra in-stress state of the reconstructed middle ear after inserting a malleus-incus prosthesis

G. Mikhasev 1 , S. Ermochenko 1 , M. Bornitz 2. 1Department efMathematics, Vitebsk State University, Vitebsk, Belarus, Russia, 2 HNO Clinic, Dresden University of Technology, Dresden, Germany

Sound transfer through a reconstructed middle ear is strongly dependent on the geometrical characteristics of the prosthesis and its position with respect to an eardrum. In this paper the modeled reconstructed middle ear consists of a thin annular plate made from cartilage, the intact stapes, and a T-type prosthesis replacing the malleus-incus chain and interposed between the stapes head and the reconstructed eardrum. Inserting the prosthesis leads inevitably to an initial pretension in the reconstructed ear. This pretension can be generated by a prosthesis longer than the distance between the stapes head and the eardrum. A high pretension can lead to a stiffening of the ligaments and a significant shift of the eigen-frequency spectrum of the middle ear system. Only a small amount of pretension ensures satisfactory sound transmission. A model of the reconstructed middle ear will be presented which enables the initial strain-stress state of the sound conducting system to be determined. Deformations of the thin annular plate are described by differential equations in cylindrical co-ordinates. Rigid and elastic boundary conditions are consid- ered on the edges of the annular plate. The prosthesis and the stapes are considered as two linked beams. The stapes footplate experiences two kinds of forces: the annular ligament forces and the forces from part of the cochlea fluid. The equilibrium of the prosthesis and stapes is described by four vector equations.

It is supposed that the optimal position of the prosthesis plate is close to the centre of the eardrum. In this case, inclined positions of the prosthesis with respect to the eardrum are considered, in order to avoid a high pretension. Introducing a small parameter ,~ characterizing the eccentricity between pros- thesis plate and eardrum, the perturbation method and Fourier series are used for solving the equation for the plate with an eccentric cut. The influence of the parameter ~, the inclination angle of the prosthesis and its geometrical dimensions on the stresses in the "prosthesis-stapes" coupling as well as on the pretension of the annular ligament are analyzed in the paper.

20.3. Urinary Tract 5222 Tu, 08:15-08:30 (P17) Development of a device for measurement of leak point pressure in anesthet ized rats M.S. Damaser 1,2,3, P. Zaszczurynski 1,2,3, B.E. Schwartz 3, D.L. Lin 1,2,3, N. Esparza 3. 1Cleveland Clinic Foundation, Cleveland, OH, USA, 2Louis Stokes Cleveland VA Medical Center, Cleveland, OH, USA, 3Hines VA Hospital, Hines, IL, USA

Introduction: We have previously used a manual method to measure leak point pressure (LPP) in rodent models of urinary incontinence. This method mimics the clinical test used diagnostically but has the potential for high inter- and intra-individual variation. The goal of this project was to develop and evaluate a device to standardize LPP testing in rats. Methods: Six female rats underwent suprapubic bladder catheter implantation. For LPP testing two days later, the rats were anesthetized and the bladders were filled with saline while bladder pressure was measured via the bladder catheter. For the manual method, the experimenter applied a gradually in- creasing vertical force over the bladder, increasing abdominal pressure. The force was rapidly removed when a leak was observed at the urethra. The peak pressure was taken as LPP, a measure of urethral resistance to flow. The LPP device applied the vertical force using a rounded tip driven by a linear actuator with force and displacement sensors. For each rat, an expert and a novice (of manual LPPs) each performed 3 manual, then 3 with the device and finally 3 more manual LPPs. Results: We found a linear relationship between force and pressure and a nonlinear relationship between both these variables and displacement. The novice demonstrated higher variability in rate of change of bladder pressure using the manual method than the expert. In contrast, the novice did not demonstrate a high variability of LPP, indicating relative insensitivity to rate of change of bladder pressure. There were no significant differences between the LPP results obtained using the device or the manual method, suggesting that either could be used to study LPE Conclusions: Our findings suggest that the manual LPP method gives repeat- able results with little intra- or inter-individual variability. The training phase, important for the manual LPP method, could be eliminated by use of the LPP device.

4847 Tu, 08:30-08:45 (P17) Flow dynamics in a stented ureter S.L. Waters, J.H. Siggers, J.A.D. Wattis, L.J. Cummings. Division efApplied Mathematics, University of Nottingham, University Park, Nottingham, UK

Vesicorenal reflux is a major complication in patients with ureteric stents. Typically the bladder pressure is fairly low, but during bladder twitches or voiding it rises, driving reflux (or back flow) of urine up the ureter and into the renal pelvis, which, in turn, may lead to infections or scarring in the renal pelvis. We develop a mathematical model to examine urine flow in a stented ureter. We treat the ureter as a long, thin, vertical, axisymmetric tube, and model its wall as a membrane with nonlinear elastic properties. The stent is modelled as a rigid, permeable, hollow circular cylinder lying coaxially inside the ureter. The renal pelvis is treated as an elastic bag, whose volume increases in response to increased internal pressure. Fluid enters the renal pelvis from the kidney with a prescribed flux. The stent, ureter and renal pelvis are filled with urine, which is assumed to be an incompressible Newtonian fluid, and the pressure in the bladder is prescribed. We use the model to calculate the total volume of reflux generated during voiding and twitches, and investigate how it is affected by the stent and ureter properties. Finally we discuss the implications of our results for the optimisation of stent design to minimise reflux.

4514 Tu, 08:45-09:00 (P17) Simulat ion of urine flow through the male lower urinary tract I. Korkmaz, B. Rogg. Chair of Fluid Mechanics, Ruhr-University of Bochum, Germany

Regarding the diagnosis and the introduction of new surgical working methods, for the urologist the understanding of urine flow in the two urinary organs - urinary bladder und urethra - is of great importance. In this context, the