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Biomedical subjects

W R Funnell

Publications and source records attributed to W R Funnell.

At least 19 recordsLinked to original sources
PubMed1996

Low-frequency coupling between eardrum and manubrium in a finite-element model.

The mechanical coupling between the eardrum and the manubrium was studied by means of a finite-element model of the cat eardrum. Previous calculations of the effect of varying the eardrum curvature were extended, demonstrating the critical role of curvature in the behavior of the eardrum. A new procedure was developed for directly studying the coupling of forces from different points on the eardrum to the manubrium, and the distribution of load-coupling values over the eardrum surface was calculated. A geometrically simplified eardrum with a circular outline was also studied. It was found that certain regions of the eardrum are more effective in driving the manubrium than can be explained on the basis of their distance from the axis of rotation. This enhanced coupling depends on the curvature of the eardrum but, unlike the mechanism hypothesized by Helmholtz, requires neither tension nor anisotropy.

Animals↗
PubMed1996

Finite-element modeling of the normal and surgically repaired cat middle ear.

In this work, three-dimensional finite-element models of the normal and surgically repaired cat middle ear were developed. The normal middle-ear model was formed by adding explicit representations for the footplate and cochlear load to an existing model of the cat eardrum. The footplate was modeled as a thin plate with a thickened rim. The cochlear load was represented by springs attached along the footplate's periphery. The model is valid for frequencies below 1 kHz and for physiological sound levels. Eardrum and manubrium displacement, and out-of-plane displacements of the footplate's center, were found to compare well with experimental results. The normal model was modified to simulate the effects of two types of middle-ear surgery, both of which are used to repair a discontinuous ossicular chain. Bulging of the footplate was found to occur when a prosthesis made direct contact with the footplate. The location of the prosthesis along the manubrium did not affect the motion of the footplate as long as the joints were all rigid. When the joints were flexible, the largest displacements occurred when the prosthesis was positioned near the upper end of the manubrium.

Animals↗
PubMed1996

On the incorporation of moiré shape measurements in finite-element models of the cat eardrum.

The mechanical behavior of the eardrum has previously been shown to depend critically on its shape, but accurate shape measurements have been difficult to make. Phase-shift moiré topography provides a valuable technique for measuring such shapes, and measurement in the presence of large static pressures facilitates the determination of the boundaries of the pars tensa, pars flaccida, and manubrium. New measurements of the shape of the cat eardrum are presented. The presence of hysteresis in the pressure-displacement response is demonstrated. The shapes are incorporated in individualized finite-element models for four different ears, and the variability between and within animals is examined. Fixed-manubrium low-frequency displacements are simulated and compared for the different models.

Animals↗
PubMed1994

A method for determining three-dimensional vibration in the ear.

In the classical concept of the middle ear function the malleus rotates around a fixed axis which implies that at small amplitudes of vibration its displacement is essentially one dimensional. As a consequence malleus vibrations have been measured previously along a single viewing axis. As a first step in the study of the complete malleus motion we determined the three dimensional components at a single point (umbo) of the manubrium. To define 3-D motion it is in principle necessary to measure the vibrations from widely different observation angles. The viewing angles are limited however in our case by the ear canal geometry to about +/-15 degrees. In order to resolve the 3-D components under these conditions it is necessary to measure the vibration components with high accuracy. Amplitude and phase of the umbo vibrations were measured with a heterodyne interferometer over a wide frequency range (100 Hz to 20 kHz). The system included a two axis goniometer with the axes of rotation positioned at the focal plane of the interferometer objective lens. It was therefore possible to change the viewing angle in small increments around two orthogonal axes while keeping the same point in focus. From a redundant set of measurements the three orthogonal components of vibration were calculated by least squares fitting. The vector sum of the three components gives the three dimensional motion of the observed point. The vibration of the point on the umbo was found not to follow a straight line but an elliptical path instead. The shape of the ellipse and the inclination of the plane of the ellipse with respect to the stationary malleus position changed with frequency. These observations are consistent with our earlier findings that the mode of malleus vibration changes with frequency [Decraemer et al. (1991) Hear. Res. 54, 305-318].

Acoustic Stimulation↗
PubMed1992

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 Young's 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.

Animals↗
PubMed1991

Shape and derived geometrical parameters of the adult, human tympanic membrane measured with a phase-shift moiré interferometer.

The shape of the tympanic membrane is fairly complex and seems to be of significant importance in the coupling of the acoustic sound pressure in the external ear canal to the motion of the middle ear ossicles. A moiré shift interferometer was used to measure with great precision the shape of the external surface of human tympanic membrane. The dense matrix of z(x,y) values thus obtained is used to calculate different geometrical parameters (area, curvature, ...). We show further how the same data can be used to specify exactly the shape of the tympanic membrane in a mathematical finite-element model of the middle ear.

Adult↗
PubMed1991

Malleus vibration mode changes with frequency.

The mode of vibration of the cat manubrium is investigated by measuring its vibration in response to sound stimulus at four locations between the umbo and the processus lateralis with a heterodyne interferometer. The determination of mode requires high precision in measurement because amplitude differences between the points are small (about 20% at low audio-frequencies). Changes in the frequency response with time have been reported in an earlier paper. The nature and magnitude of this time change is analysed in detail: over a period of 1 h the average change in amplitude is about 5% and in phase 5 degrees. The malleus vibration at some frequencies is purely translational, it is rotational at others and mixed at most frequencies. When the motion is rotational the position of the axis of rotation shifts with frequency, the shifts are so large that the axis can lie near the umbo so that amplitudes at the processus lateralis are larger than at the umbo. The classical concept of the malleus rotating around a fixed axis running from the anterior mallar to the posterior incudal ligament fits our measurements only at low frequencies.

Animals↗
PubMed1990

Heterodyne interferometer measurements of the frequency response of the manubrium tip in cat.

A heterodyne interferometer proved to be a very accurate tool to measure amplitude and phase of the malleus response during acoustical stimulation. It was shown that to obtain equal accuracy in the acoustical pressure measurements, pressure response must be remeasured at short time intervals. At frequencies above 4 kHz various gross resonances are apparent on the frequency response curves. The resonances are, depending on the animal, more or less pronounced. As a result of the improved accuracy changes of the malleus vibration response with time could clearly be discriminated. These changes can be related to shifts in frequency of the position of these resonances. Comparison of experimental frequency response and lumped parameter model predictions from literature shows that these resonances are not present in the model responses.

Acoustics↗
PubMed1990

Three-dimensional reconstruction and quantitative evaluation of devascularizing cortical lesions in the rat.

The use of a reconstruction method suitable for three-dimensional (3-D) representations of the cortex for the quantitative evaluation of unilateral devascularizing cortical lesions is reported, demonstrating that 3-D reconstructions can be used for quantitative evaluation of the extent of cortical lesions, in addition to simply visualizing shapes. The procedure allowed the definition of precise quantitative parameters characterizing the volumes and surface areas of the cortical regions involved. It was shown that digitized serial sections from atlases can be utilized for multiple correlation studies by superimposing morphological and biochemical parameters. More specifically, the enzymatic activity of choline acetyltransferase (ChAT) in the nucleus basalis magnocellularis (NBM), and morphological parameters (number and cross-sectional areas) of the ChAT-positive immunoreactive cholinergic neurons, were related to the numerical values for the volume and surface area of the cortical lesions. The applicability of this method goes beyond the scope illustrated in this study. For example, various morphological anomalies in the brain could be quantified; changes in various cortical and subcortical structures could be followed during development; and the 3-D size, shape and position of a graft could be related to the number of viable foetal cells.

Animals↗
PubMed1989

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.

Animals↗
PubMed1988

Body surface isopotential mapping of permanent cardiac pacemaker spike amplitudes: a noninvasive method for detecting and localizing insulation failure.

Cardiac pacing systems produce cardiac contractions by delivering electrical charges to the myocardium. Reliable cardiac pacing, and the longevity of pacemakers depends on the absence of electrical leaks. Electrical leaks often do not cause symptoms and if suspected, there are few methods which are able to identify their location and none suited to small or intermittent leaks. We surface mapped the pacemaker spike amplitudes over the pockets of 29 patients with unipolar pacemakers, several of which had suspected pacemaker leaks. For each patient, pacer voltage spikes were recorded with an optical ECG recorder from sixty-three positions on the skin over the pacemaker. The spike voltages were interpolated with a 2-D Fourier transform, contoured, and plotted by a computer. Electrical leaks were readily detected and their positions indicated by the resulting maps. The operative findings confirmed the map guided prediction in all six patients sent for pacemaker revision. Pacemaker spike amplitude surface mapping detects and locates pacing system insulation failures.

Electrocardiography↗
PubMed1987

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.

Acoustics↗
PubMed1984

On the calculation of surface areas of objects reconstructed from serial sections.

This paper concerns certain aspects of the calculation of the surface area of objects reconstructed from serial sections. The main points discussed are (1) the relative importance of the number of sections compared to the number of segments taken around the contour in each section; and (2) the fact that the error in the estimated surface area may actually become worse as the number of sections increases. The number of sections should be made large enough to reproduce the three-dimensional shape of the object, but not too much larger; the number of segments around the contours should then be made large enough that the segment size is similar to or smaller than the section thickness.

Anatomy↗
PubMed1983

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.

Acoustics↗
PubMed1982

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 Békésy's capacitive-probe measurements with this picture.

Animals↗
PubMed1978

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.

Acoustic Stimulation↗
PubMed1977

On the visualisation of nonstationarities in point processes.

A method is described for graphically presenting interval data, such as neural interspike intervals or electrocardiographic R-R intervals, in a form that facilitates the identification of nonstationaries. The method is essentially a plot of isoprobability contours of the cumulative interval histogram, as functions of time. A sequential algorithm is used for updating the contour-line positions. This display is used in an interactive system for visually identifying nonstationarities, and for subsequently comparing selected segments of the data quantitatively using the Kolmogorov-Smirnov test.

Computers↗