The influence of ventilation tube design on the magnitude of stress imposed at the implant/tympanic membrane interface

Acoustical Effects of Tympanostomy Tube Attachment to Human Tympanic Membrane

PURPOSE

Several therapeutic approaches for hearing disorders involve attaching medical devices to the tympanic membrane. The attachment of these devices can change the mechanical and acoustical properties of the middle ear, affecting the middle-ear vibrations. The alteration of passive mechanical properties results from the mass, stiffness, and geometry of the attached device. Additionally, procedures like tympanostomy tube attachment create perforations on the tympanic membrane, altering both the mechanical and acoustical properties of the middle ear. This study examined the acoustical effects of these as well as the combination of acoustical and mechanical effects of the attached devices on middle-ear vibrations.

METHODS

A finite-element model of the middle ear, including the middle-ear cavity, was used to systematically study the effects of perforation size and location on vibration outputs. Experimental data from the literature were used to tune the model. This model was then employed to investigate the combined mechanical and acoustical effects of tympanostomy tubes on vibration outputs.

RESULTS

In presence of both the mechanical effects of the device (due to its mass and stiffness) and the acoustical effects of it (due to perforations), the reduction in the motion of the stapes footplate resulting from the acoustical effects is more remarkable at low frequencies (below about 1 kHz). However, at higher frequencies, the mechanical effects of the device are dominant.

CONCLUSION

The findings of this study provide insights into the optimal design of the shape, location, and other characteristics of medical devices implanted on the tympanic membrane.

RESEARCH ON THE TYMPANIC MEMBRANE FREE VIBRATION MODEL BASED ON THIN PLATE THEORY

Myringoplasty is one of the routine surgeries in the treatment of tympanic membrane (TM) perforation. Since the anatomic structure of the middle ear cannot be simulated in clinical treatment, the surgery is mainly directed by experiences. Based on the mechanical properties of TM in the anatomy, four hypotheses are presented and TM is simplified as a sectorial annulus plate with fixed boundary condition. This paper proposes a free vibration model of TM. Its natural frequencies of free vibration are obtained by variables separation method and Bessel function. The system of fundamental solutions of fourth-order homogeneous equations can be solved for the analytical expressions of corresponding natural vibration mode. The theoretical model is proved to be valid since the natural frequency of the model is consistent with the experimental data. The effect of geometric parameters and material parameters on TM natural frequency is subsequently discussed in the numerical examples. Especially, the diameter and thickness of TM will cause different natural frequency errors above 40%, while the Young’s modulus and density of TM cause errors below 15% as well.

Fatigue analysis of tympanic membrane after ossiculoplasty

CONCLUSION

A tentative conclusion was made that the finite element method can be used to investigate the fatigue life of the tympanic membrane after ossiculoplasty; the main reason of the extrusion of the tympanic membrane may not be blamed to the fatigue mechanism under normal sound pressure.

OBJECTIVE

This study was to investigate the extrusion of the prosthesis from the tympanic membrane at post-ossiculoplasty by finite element method.

METHODS

A finite element model of the human middle ear has been constructed and used as the model of the constructed middle ear at post-ossiculoplasty. Then the fatigue life of the tympanic membrane was calculated under different sound pressure level using this model.

RESULTS

The tympanic membrane would not be extruded under normal sound pressure level. The sound pressure level which caused the tympanic membrane to crack in less than 3 years was higher than 145.17 dB (362.5 Pa).

Motion of tympanic membrane in guinea pig otitis media model measured by scanning laser Doppler vibrometry

Otitis media (OM) is an inflammatory or infectious disease of the middle ear. Acute otitis media (AOM) and otitis media with effusion (OME) are the two major types of OM. However, the tympanic membrane (TM) motion differences induced by AOM and OME have not been quantified in animal models in the literature. In this study, the guinea pig AOM and OME models were created by transbullar injection of Streptococcus pneumoniae type 3 and lipopolysaccharide, respectively. To explore the effects of OM on the entire TM vibration, the measurements of full-field TM motions were performed in the AOM, OME and untreated control ears by using scanning laser Doppler vibrometry (SLDV). The results showed that both AOM and OME generally reduced the displacement peak and produced the traveling-wave-like motions at relatively low frequencies. Compared with the normal ear, OME resulted in a significant change of the TM displacement mainly in the inferior portion of the TM, and AOM significantly affected the surface motion across four quadrants. The SLDV measurements provide more insight into sound-induced TM vibration in diseased ears.

Mesh morphing and response surface analysis: quantifying sensitivity of vertebral mechanical behavior

Vertebrae provide essential biomechanical stability to the skeleton. In this work novel morphing techniques were used to parameterize three aspects of the geometry of a specimen-specific finite element (FE) model of a rat caudal vertebra (process size, neck size, and end-plate offset). Material properties and loading were also parameterized using standard techniques. These parameterizations were then integrated within an RSM framework and used to produce a family of FE models. The mechanical behavior of each model was characterized by predictions of stress and strain. A metamodel was fit to each of the responses to yield the relative influences of the factors and their interactions. The direction of loading, offset, and neck size had the largest influences on the levels of vertebral stress and strain. Material type was influential on the strains, but not the stress. Process size was substantially less influential. A strong interaction was identified between dorsal-ventral offset and dorsal-ventral off-axis loading. The demonstrated approach has several advantages for spinal biomechanical analysis by enabling the examination of the sensitivity of a specimen to multiple variations in shape, and of the interactions between shape, material properties, and loading.