Dynamic properties of round window membrane in guinea pig otitis media model measured with electromagnetic stimulation

Abstract

The round window, one of two openings into the cochlea from the middle ear, plays an important role in hearing and is known to be structurally altered during otitis media. However, there have been no published studies systematically describing the changes in biomechanical properties of the round window membrane (RWM) that accompany bacterial otitis media. Here we describe the occurrence of significant changes in the dynamic properties of the RWM between normal guinea pigs and those with acute otitis media (AOM) that are detectable by electromagnetic force stimulation and laser Doppler vibrometry (LDV) measurements. AOM was induced by transbullar injection of streptococcus pneumoniae into the middle ear, and RWM specimens were prepared three days after challenge. Vibration of the RWM induced by coil-magnet coupling was measured by LDV over frequencies of 0.2–40 kHz. The experiment was then simulated in a finite element model, and the inverse-problem solving method was used to determine the complex modulus in the frequency domain and the relaxation modulus in the time domain. Results from 18 ears (9 control ears and 9 AOM ears) established that both the storage modulus and loss modulus of the RWM from ears with AOM were significantly lower than those of RWM from uninfected ears. The average decrease of the storage modulus in AOM ears ranged from 1.5 to 2.2 MPa and the average decrease of the loss modulus was 0.025 to 0.48 MPa. Our findings suggest that middle ear infection primarily affects the stiffness of the RWM due to the morphological changes that occur in AOM ears. We also conclude that the coil-magnet coupling method for assessment of RWM function may provide a valuable new approach to characterizing the mechanical response of the RWM when reverse driving is selected for middle ear implantable devices.

Complex modulus of round window membrane over auditory frequencies in normal and otitis media chinchilla ears

“…The experimental setup was similar to that used for guinea pig studies by Gan et al (2013). Figure 2 shows a schematic diagram of the experimental setup and indicates that the vibration of the magnet at the centre of RWM was measured by LDV along the vertical direction.…”

“…The vibration amplitude of the RWM was directly calculated from the voltage output of the LDV velocity decoder. The specimens were preconditioned before tests following the procedure described by Gan et al (2013). Because of the extremely small size and fixed bony boundary, the RWM specimen was difficult to conduct standard preconditioning in a material testing system.…”

“…To quantitatively evaluate the dynamic parameters of the chinchilla RWM, we compared the results obtained in this study with the data of human RWMs and guinea pig RWMs reported by Zhang and Gan (2013) and Gan et al (2013), respectively. Note that the human data were obtained from acoustic stimulation as the loading source.…”

“…Dynamic properties of the infectious RWM in AOM ears were measured first time by Gan et al (2013) in guinea pigs. The results from nine guinea pig RWMs in AOM ears showed that the mean resonance frequency of the RWM with a magnet of 0.03 mg decreased by 13.88%, which was almost the same as that of chinchilla RWMs measured in this study.…”

“…AOM induces morphological changes of the middle ear tissues, including the tympanic membrane (TM), stapedial annular ligament and RWM, which have been observed in patients and experimental animal models (Sahni et al, 1987;Goycoolea, 1995;Schachern et al, 2008;Yoon and Hellstrom, 2002). Recently, an AOM model of guinea pig induced by Streptococcus pneumonia was created and the changes of RWM mechanical properties were reported by Gan et al (2013). However, the biomechanical changes of RWM in other animal models of normal and pathological ears have rarely been reported.…”