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Biomedical subjects

W F Decraemer

Publications and source records attributed to W F Decraemer.

At least 19 recordsLinked to original sources
PubMed1995

Shape and displacement patterns of the gerbil tympanic membrane in experimental otitis media with effusion.

This study assesses the visco-elastic properties of the tympanic membrane (TM) in isolated gerbilline temporal bones as a function of time after inducing experimental otitis media with effusion (OME). To do this we measured the TM displacements produced by application of sequences of static pressures across the TM, with a high resolution, real-time, differential moiré interferometer, and the results were compared with measurements on healthy ears. Two methods of producing OME were used: in one group tubal plugging was performed to produce mild OME (the 'TP group'); in the other group electro-cauterization of the nasopharyngeal orifice of the Eustachian tube was used to cause a severe form of OME (the 'EC group'). The measurements were performed from one day up to ten weeks after surgery. In the TP group the displacement fringe patterns were normal, i.e. qualitatively they resembled the patterns of the control group. Quantitatively there was a significant decrease of displacement for a given pressure on the first day after surgery, followed by a trend of increase with time; after seven to ten days the displacement was larger than in the control group. In the EC group the displacement was significantly reduced after half a week, followed by a trend of increase with time, similar to what was found in the TP group; at one week the displacement was larger than in the control group, and at ten weeks the largest displacement was recorded. In the EC group the displacement patterns were often irregular; in some cases with changes suggesting the presence of weak spots in the TM where retraction pockets most likely could develop. OME seems to affect the stiffness of the TM promptly so that it is a potential parameter for early diagnosis. The stiffness changes may, if measurable in the clinical situation, become prognostic parameters in the treatment of OME.

Acoustic Stimulation↗
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↗
PubMed1994

Modelling the malleus vibration as a rigid body motion with one rotational and one translational degree of freedom.

Vibration of a set of points distributed along the manubrium of cat was measured with a heterodyne interferometer in response to sinusoidal acoustic signals. The observed motion did not fit pure rotation of the malleus around a fixed axis coinciding with the anterior mallar and posterior incudal ligament as is classically assumed. As a first approximation a model of motion consisting of a rotational and a translational component was used. At low frequencies the rotation is mostly predominant, but the situation may be entirely reversed at mid and high frequencies. The presence of a translation besides rotation was also found at some frequencies in the motion of the human malleus.

Acoustic Stimulation↗
PubMed1992

Area change and volume displacement of the human tympanic membrane under static pressure.

Direct measurements are presented of the area change and volume displacement of a human tympanic membrane under static pressures in the range of -1.6 KPa to +1.6 kPa. The area change is given separately for the pars tensa and the pars flaccida. For the pars tensa a strong asymmetry in area change under positive and negative pressure is observed. The volume displacement is also given separately for the pars tensa and the pars flaccida. The volume displacement of the entire TM agrees very well with volume displacement data in literature on tympanometry. It is shown further that a linear relationship between umbo displacement and volume displacement exists. The compliance of the tympanic membrane under static pressure load is compared to acoustic compliance measurements at low frequencies, and found to be a factor 2.5 higher than the compliance at 500 Hz.

Acoustic Impedance Tests↗
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

Human tympanic membrane deformation under static pressure.

The effect of static pressures in the range of plus and minus 1.6 kPa on the shape of tympanic membrane is measured using a non-contacting optical technique on a fresh human temporal bone. Full field data of the deformation are presented as well as cross-sections along two major directions. Strong asymmetry between medial and lateral movements is demonstrated. The displacement of the umbo is compared to other work. The rotation angle of the manubrium in function of pressure is calculated and also compared to other work. It is demonstrated that the rotation angels can not account for the measured movement of the umbo, which leads to the conclusion that for static high pressure levels the classical hypothesis of rotation around a fixed axis has to be abandoned. The comparison with data of TM displacement under dynamic stimuli is discussed.

Adult↗
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↗
PubMed1989

A thermodynamically consistent constitutive equation for the elastic force-length relation of soft biological materials.

Starting from the laws of thermodynamics of reversible processes, a temperature-dependent constitutive equation is derived for the elastic force-length relation of soft biological tissues. These tissues are composed of a network of fibres (mainly collagen). The equation is based on a model which uses a simplified two-dimensional representation of the alpha-helix of collagen.

Collagen↗
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↗
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

Tympanometric middle-ear pressure determination with two-component admittance meters.

Exact tympanometric determination of the middle-ear pressure based on the location of the (central) extremum of susceptance, conductance, admittance, impedance, reactance or phase-angle tympanograms is not possible. None of these immittance components reaches its extremum exactly at middle-ear pressure neither at 220 nor at 660 Hz, due to the hysteresis caused by the viscoelastic behaviour of the soft biological tissue of the middle-ear structures. These effects cannot be avoided by lowering the rate of the pressure change during the recordings. The error on the middle-ear pressure determinations using a tympanometric method can be estimated to be of the order of 15 daPa.

Acoustic Impedance Tests↗
PubMed1983

A search for the most suitable imminent components and probe tone frequency in tympanometry.

The relative occurrence of bell-shaped and various types of W-shaped susceptance-conductance and admittance-phase tympanograms at a probe-tone frequency of 660 Hz was determined from registrations on normal ears. The diagnostic value of the susceptance-conductance versus the admittance-phase representation of tympanograms was studied on pathological middle-ear systems. Using probe-tone frequencies from 510 Hz up to 910 Hz, tympanograms for all four imminent components were recorded on 10 pathological ears and the diagnostic value compared. From the combination of these studies we conclude that the admittance-phase approach at a probe tone frequency between 500 and 700 Hz is a good choice.

Acoustic Impedance Tests↗