W. Robert J. Funnell

Can virtual reality improve anatomy education? A randomised controlled study of a computer‐generated three‐dimensional anatomical ear model

Introduction  The use of computer‐generated 3‐dimensional (3‐D) anatomical models to teach anatomy has proliferated. However, there is little evidence that these models are educationally effective. The purpose of this study was to test the educational effectiveness of a computer‐generated 3‐D model of the middle and inner ear.

Modeling of the cat eardrum as a thin shell using the finite‐element method

A finite-element model of the cat eardrum is presented which includes the effects of the three-dimensional curved conical shape of the drum. The model is valid at low frequencies (below 1-2 kHz) and within the range of linear vibration amplitudes. The material properties used are based on a review of the literature. The critical material parameters are the stiffness (2 times 10(8) dyn cm(-2)) and thickness (40 micrometer) of the pars tensa. The model exhibits a vibration pattern and amplitude very similar to those observed experimentally using laser holography. A number of parameters are varied in order to study their relative importance in the model.

On the damped frequency response of a finite‐element model of the cat eardrum

This article presents frequency responses calculated using a three-dimensional finite-element model of the cat eardrum that includes damping. The damping is represented by both mass-proportional and stiffness-proportional terms. With light damping, the frequency responses of points on the eardrum away from the manubrium display numerous narrow minima and maxima, the frequencies and amplitudes of which are different for different positions on the eardrum. The frequency response on the manubrium is smoother than that on the eardrum away from the manubrium. Increasing the degree of damping smooths the frequency responses both on the manubrium and on the eardrum away from the manubrium. The overall displacement magnitudes are not significantly reduced even when the damping is heavy enough to smooth out all but the largest variations. Experimentally observed frequency responses of the cat eardrum are presented for comparison with the model results.

On the degree of rigidity of the manubrium in a finite-element model of the cat eardrum

It has always been assumed that the manubrium is in effect perfectly rigid. In this paper, a more realistic model of the manubrium is incorporated into an existing finite-element model of the cat eardrum. The manubrial thickness is based on a three-dimensional reconstruction from serial histological sections. After a review of the literature, a value of 2 x 10(11) dyn cm-2 is adopted for the Youngs modulus of the bone. The mode of vibration of the model is investigated for different manubrial-thickness values and it is found that a significant degree of manubrial bending occurs in the model for realistic values of manubrial thickness. As a result of the bending, the frequency response at the umbo at high frequencies displays much higher amplitudes and larger phase lags than when the manubrium is rigid. The bending will also affect the displacements transmitted to the ossicular load, and introduce significant errors into estimates of such displacements based on measurements of umbo displacement even at frequencies as low as a few kHz. Recent measurements of manubrium vibrations in the cat ear provide experimental evidence of bending.

A critical review of experimental observations on ear-drum structure and function.

This paper presents a review of the experimental data available concerning ear-drum structure, properties and behaviour, in order to provide a basis for quantitative modelling and to identify areas where further information is required. The review of anatomy and structure indicates a lack of quantitative data about thickness, fibre distribution, three-dimensional curvature, and post-natal development. The mechanical properties of the ear-drum and attached structures are very poorly known, particularly with respect to isotropy, uniformity and damping. A historical review of observations of ear-drum vibration patterns shows general agreement that at low frequencies the displacements of the manubrium are smaller than those of the surrounding drum. Possible reasons are suggested for the apparent incompatibility of Békésys capacitive-probe measurements with this picture.

Interferometric measurement of the amplitude and phase of tympanic membrane vibrations in cat.

The amplitude and phase of the tympanic membrane and malleus vibrations were measured over a wide frequency range with a homodyne interferometer. When sound pressure was maintained constant near the tympanic membrane, the malleus frequency response followed the typical pattern up to 10 kHz as measured by previous investigators. At higher frequencies the response changes dramatically. Instead of decreasing with frequency, between 10 and 20 kHz the vibration amplitude oscillates around a value which is only about 20 dB lower than the low frequency plateau level. Measurements of malleus vibration at several points along its length indicate that its mode of vibration changes at high frequencies, and no longer consists of a simple rotational component. All points on the tympanic membrane vibrate in phase with the malleus up to a frequency of 1 kHz. Above 5 kHz discrete resonances are observed, and the response varies strongly with position on the tympanic membrane.

On the undamped natural frequencies and mode shapes of a finite‐element model of the cat eardrum

This paper presents a three-dimensional finite-element model of the cat eardrum which includes inertial effects. The model is implemented using a hierarchical modeling scheme which permits the mesh resolution to be varied. The static behavior of the model is calculated as a function of mesh resolution in order to check the validity of an earlier model. The first six undamped natural frequencies, and the corresponding modal vibration patterns, are then calculated. They are found to lie between about 1.8 and 3.2 kHz for the standard values chosen for the model parameters. The effects on the natural frequencies of varying seven parameters of the model are described.

On the Coupling Between the Incus and the Stapes in the Cat

The connection between the long process and the lenticular process of the incus is extremely fine, so much so that some authors have treated the lenticular process as a separate bone. We review descriptions of the lenticular process that have appeared in the literature, and present some new histological observations. We discuss the dimensions and composition of the lenticular process and of the incudostapedial joint, and present estimates of the material properties for the bone, cartilage, and ligament of which they are composed. We present a preliminary finite-element model which includes the lenticular plate, the bony pedicle connecting the lenticular plate to the long process, the head of the stapes, and the incudostapedial joint. The model has a much simplified geometry. We present simulation results for ranges of values for the material properties. We then present simulation results for this model when it is incorporated into an overall model of the middle ear of the cat. For the geometries and material properties used here, the bony pedicle is found to contribute significant flexibility to the coupling between the incus and the stapes.

Comparison of the mechanical performance of ossiculoplasty using a prosthetic malleus-to-stapes head with a tympanic membrane-to-stapes head assembly in a human cadaveric middle ear model

Hypothesis: Ossiculoplasty using prosthetic reconstruction with a malleus assembly to the stapes head will result in better transmission of vibrations from the eardrum to the stapes footplate than reconstruction with a tympanic membrane assembly to the stapes head. Both types of reconstruction will be affected by tension of the prosthesis. Background: Theories (and some clinical studies) that the shape of the normal tympanic membrane is important suggest that prosthetic reconstruction to the malleus performs better than reconstruction to the tympanic membrane. This has not been previously tested by directly measuring vibration responses in the human ear. Our previous work suggests that tympanic membrane assembly to the stapes head type prostheses performed best under low tension. This had not been previously tested for malleus assembly to the stapes head type prostheses. Methods: Hydroxyapatite prostheses were used to reconstruct a missing incus defect in a fresh cadaveric human ear model. Two types of prostheses were used, one from the stapes head to the malleus (malleus assembly to the stapes head), the other from the stapes head to the tympanic membrane (tympanic membrane assembly to the stapes head). Stapes footplate center responses were measured using a laser Doppler vibrometer in response to calibrated acoustic frequency sweeps. Results: Tension had a very significant effect on both types of prostheses in the lower frequencies. Loose tension was best overall. The malleus assembly to the stapes head type prostheses consistently performed better than the tympanic membrane assembly to the stapes head type prostheses when stratified for tension. Conclusion: Tension has a significant effect on prosthesis function. Malleus assembly to the stapes head type prostheses generally result in better transmission of vibrations to the stapes footplate than tympanic membrane assembly to the stapes head type prostheses.

A nonlinear finite-element model of the newborn ear canal

A three-dimensional nonlinear finite-element model of a 22-day-old newborn ear canal is presented. The geometry is based on a clinical x-ray CT scan. A nonlinear hyperelastic constitutive law is applied to model large deformations. The Youngs modulus of the soft tissue is found to have a significant effect on the ear-canal volume change, which ranges from approximately 27% to 75% over the static-pressure range of +/-3kPa. The effects of Poissons ratio and of the ratio C10: C01 in the hyperelastic model are found to be small. The volume changes do not reach a plateau at high pressures, which implies that the newborn ear-canal wall would not be rigid in tympanometric measurements. The displacements and volume changes calculated from the model are compared with available experimental data.