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INFLUENCE OF THE EARDRUM STIFFNESS ON THE MIDDLE EAR SOUND FUNCTION TRANSFER
S182
Presentation 1115 − Topic 16. Ear biomechanics
INFLUENCE OF THE EARDRUM STIFFNESS ON THE MIDDLE EAR SOUND FUNCTION TRANSFER Luis Caminos (1), Antonio Garcia-Gonzalez (2), Antonio Gonzalez-Herrera (2)
1.Departamento de Ingeniería Mecánica, Universidad del Táchira Venezuela; 2.Departamento de Ing. Civil, Materiales y Fabricación, Universidad de Málaga España. 1
Introduction Some controversy exists about the influence of the eardrum stiffness on the middle ear sound transmission. Some studies suggest an increase of the membrane tympanic stiffness with age [Ruah et al, 1991], but other authors show a decrease of middle ear impedance with age in frequencies above 2500 Hz [Feeney et al, 2004]. Additionally, there exists a great uncertainty in the experimental determination of this property [Fay et al, 2005]. In this study, a Finite Element Model (FEM) of the human middle ear [Caminos et al, 2011] is used to analize the effect of eardrum stiffness on the stapes footplate velocity function transfer SVFT. The goal of this research is find a possible relation between the stiffness of eardrum and the impedance of middle ear in the high frequency range.
Methods The study has been developed by means of a FEM of the middle ear. This model was previously validated with experimental data. It is composed by the tympanic membrane, osicular chain, ligaments and tendons support. The cochlear load is simulated with a mechanical equivalent system (dampermass-damper), and the properties values of materials are taken from the literature according to commonly accepted values [Caminos, 2011]. A sound presure level of 80 dB is applied on the tympanic membrane and the stape footplate velocity is calculated using a harmonic analisys in a frecuency range from 100 to 10 KHz. SVFT is the ratio between the stape footplate velocity and pressure over the tympanic membrane. This parameter is directly proportional to the middle ear acoustic admittance. It is calculated with different values of eardrum Young´s modulus (YM), in the frequency range studied.
Figure 1:Comparison of SVFT with different YM and mean curve obtained by [Aibara et al, 2001].
Discussion Results obtained shows a clear reduction on SVFT with stiffness at low frequencies and an slight SVFT increase above 2.5 KHz. The model shows that the displacement of the tympanic membrane is more uniform across the surface with higher stiffness. In the high frequency range, this behavior at the eardrum increases the displacements of the footplate and therefore decreases the impedance. A possible relation of stiffness with age is observed comparing with the curve obtained by Aibara (Fig. 1). The mean age of the subjets is 67.9 years. These results are close to the curve corresponding to YM = 10E. This value (E = 0.3 GPa) is in concordance with the estimation made by [Fay et al, 2005] based on the dynamic behaviour of the membrane.
References
Results Fig. 1 shows the SVFT variation with the frequency for different values of the eardrum YM. E = 0.032 GPa is considered the reference value. A marked decreased of SVFT with the increase of YM below 2.5 KHz is observed. However, with YM=10E the footplate velocity is increased slightly above of 2.5 KHz. The peak value is 0.42 mms-1/Pa at 900 Hz with YM=E. This value is decreased to 0.22 mmsJournal of Biomechanics 45(S1)
/Pa with YM=10E at 1.3 KHz. Curves for 20E and 30E have a similar behaviour and SVFT is lower than the reference at low frequencies. Above 4 KHz the values are slightly increased. Additional calculations has been made analysing other parameter which may alter the eardrum stiffness, as the eardrum thickness. Similar effects are observed.
Aibara et al, Hear. Res., 152:100-109, 2001. Caminos et al, 11th Int. Mechanics of Hearing Workshop, 515-520, 2011. Caminos, PhD thesis, U. of Malaga (Spain), 2011. Fay et al, J Biomech, 38:1807-1815, 2005. Feeney et al, J Acoust. S. Am., 116:3546-58, 2004. Ruah et al, Arch. Otolaryngol. Head Neck Surg., 117: 627–634, 1991.
ESB2012: 18th Congress of the European Society of Biomechanics
Presentation 1115 − Topic 16. Ear biomechanics
INFLUENCE OF THE EARDRUM STIFFNESS ON THE MIDDLE EAR SOUND FUNCTION TRANSFER Luis Caminos (1), Antonio Garcia-Gonzalez (2), Antonio Gonzalez-Herrera (2)
1.Departamento de Ingeniería Mecánica, Universidad del Táchira Venezuela; 2.Departamento de Ing. Civil, Materiales y Fabricación, Universidad de Málaga España. 1
Introduction Some controversy exists about the influence of the eardrum stiffness on the middle ear sound transmission. Some studies suggest an increase of the membrane tympanic stiffness with age [Ruah et al, 1991], but other authors show a decrease of middle ear impedance with age in frequencies above 2500 Hz [Feeney et al, 2004]. Additionally, there exists a great uncertainty in the experimental determination of this property [Fay et al, 2005]. In this study, a Finite Element Model (FEM) of the human middle ear [Caminos et al, 2011] is used to analize the effect of eardrum stiffness on the stapes footplate velocity function transfer SVFT. The goal of this research is find a possible relation between the stiffness of eardrum and the impedance of middle ear in the high frequency range.
Methods The study has been developed by means of a FEM of the middle ear. This model was previously validated with experimental data. It is composed by the tympanic membrane, osicular chain, ligaments and tendons support. The cochlear load is simulated with a mechanical equivalent system (dampermass-damper), and the properties values of materials are taken from the literature according to commonly accepted values [Caminos, 2011]. A sound presure level of 80 dB is applied on the tympanic membrane and the stape footplate velocity is calculated using a harmonic analisys in a frecuency range from 100 to 10 KHz. SVFT is the ratio between the stape footplate velocity and pressure over the tympanic membrane. This parameter is directly proportional to the middle ear acoustic admittance. It is calculated with different values of eardrum Young´s modulus (YM), in the frequency range studied.
Figure 1:Comparison of SVFT with different YM and mean curve obtained by [Aibara et al, 2001].
Discussion Results obtained shows a clear reduction on SVFT with stiffness at low frequencies and an slight SVFT increase above 2.5 KHz. The model shows that the displacement of the tympanic membrane is more uniform across the surface with higher stiffness. In the high frequency range, this behavior at the eardrum increases the displacements of the footplate and therefore decreases the impedance. A possible relation of stiffness with age is observed comparing with the curve obtained by Aibara (Fig. 1). The mean age of the subjets is 67.9 years. These results are close to the curve corresponding to YM = 10E. This value (E = 0.3 GPa) is in concordance with the estimation made by [Fay et al, 2005] based on the dynamic behaviour of the membrane.
References
Results Fig. 1 shows the SVFT variation with the frequency for different values of the eardrum YM. E = 0.032 GPa is considered the reference value. A marked decreased of SVFT with the increase of YM below 2.5 KHz is observed. However, with YM=10E the footplate velocity is increased slightly above of 2.5 KHz. The peak value is 0.42 mms-1/Pa at 900 Hz with YM=E. This value is decreased to 0.22 mmsJournal of Biomechanics 45(S1)
/Pa with YM=10E at 1.3 KHz. Curves for 20E and 30E have a similar behaviour and SVFT is lower than the reference at low frequencies. Above 4 KHz the values are slightly increased. Additional calculations has been made analysing other parameter which may alter the eardrum stiffness, as the eardrum thickness. Similar effects are observed.
Aibara et al, Hear. Res., 152:100-109, 2001. Caminos et al, 11th Int. Mechanics of Hearing Workshop, 515-520, 2011. Caminos, PhD thesis, U. of Malaga (Spain), 2011. Fay et al, J Biomech, 38:1807-1815, 2005. Feeney et al, J Acoust. S. Am., 116:3546-58, 2004. Ruah et al, Arch. Otolaryngol. Head Neck Surg., 117: 627–634, 1991.
ESB2012: 18th Congress of the European Society of Biomechanics