Changes in Wide-band Tympanometry Absorbance Following Cochlear Implantation

Post-surgical changes in wideband absorbance in paediatric cochlear implant users after mastoidectomy and posterior tympanotomy

BACKGROUND

Although Cochlear implantation (CI) is effective in restoring hearing for children with severe-to-profound sensorineural hearing loss, it may influence the middle ear mechanics, potentially causing an air-bone gap and altering middle ear stiffness, which is not detected by traditional 226 Hz tympanometry.

AIMS/OBJECTIVES

To investigate the effect of mastoidectomy posterior tympanotomy (MPTA) on wideband absorbance (WBA) in children with CI.

MATERIALS AND METHODS

The study included 20 normal-hearing children (normal group) and 10 children with CIs who underwent MPTA (CI-MPTA group), aged 3-10 years. WBA at peak and ambient pressure, resonance frequency, and 226 Hz tympanometry were measured.

RESULTS

The normal group showed maximum absorbance at 1250 and 3000 Hz, whereas the CI-MPTA group had a single peak at 3000 Hz. The CI-MPTA group exhibited reduced absorbance at low and mid-frequencies (250-1500 Hz), with significant differences (p < 0.05) observed at 800-1250 Hz for peak pressure and 1000-1250 Hz for ambient pressure. No significant differences were found in resonance frequency or 226 Hz tympanometry.

CONCLUSIONS AND SIGNIFICANCE

CI with MPTA changes middle ear absorbance patterns, affecting the low- and mid-frequency regions. These findings indicate the importance of using WBA tympanometry to monitor middle and inner ear mechanics post-CI.

Evaluating Wideband Tympanometry Absorbance Changes in Cochlear Implant Recipients: Mechanical Insights and Influencing Parameters

Background: Cochlear implant (CI) electrode insertion can change the mechanical state of the ear whereby wideband tympanometry absorbance (WBTA) may serve as a sensitive tool to monitor these mechanical changes of the peripheral auditory pathway after CI surgery. In WBTA, the amount of acoustic energy reflected by the tympanic membrane is assessed over a wide frequency range from 226 Hz to 8000 Hz. The objective of this study was to monitor changes in WBTA in CI recipients before and after surgery. Methods: Following otoscopy, WBTA measurements were conducted twice in both ears of 38 standard CI recipients before and in the range of 4 to 15 weeks after CI implantation. Changes from pre- to postoperative absorbance patterns were compared for the implanted as well as the contralateral control ear for six different frequencies (500 Hz, 750 Hz, 1000 Hz, 2000 Hz, 3000 Hz, 4000 Hz). Furthermore, the influence of the time point of the measurement, surgical access, electrode type, sex and side of the implantation were assessed for the implanted and the control ear in a linear mixed model. Results: A significant decrease in WBTA could be observed in the implanted ear when compared with the contralateral control ear for 750 Hz (p < 0.01) and 1000 Hz (p < 0.05). The typical two-peak pattern of WBTA measurements was seen in both ears preoperatively but changed to a one-peak pattern in the newly implanted ear. The linear mixed model showed that not only the cochlear implantation in general but also the insertion through the round window compared to the cochleostomy leads to a decreased absorbance at 750 and 1000 Hz. Conclusions: With WBTA, we were able to detect mechanical changes of the acoustical pathway after CI surgery. The implantation of a CI led to decreased absorbance in the lower frequencies and the two-peak pattern was shifted to a one-peak pattern. The result of the linear mixed model indicates that WBTA can detect mechanical changes due to cochlear implantation not only in the middle ear but also in the inner ear.

The Effects of Middle-ear Stiffness on the Auditory Brainstem Neural Encoding of Phase

The middle-ear system relies on a balance of mass and stiffness characteristics for transmitting sound from the external environment to the cochlea and auditory neural pathway. Phase is one aspect of sound that, when transmitted and encoded by both ears, contributes to binaural cue sensitivity and spatial hearing. The study aims were (i) to investigate the effects of middle-ear stiffness on the auditory brainstem neural encoding of phase in human adults with normal pure-tone thresholds and (ii) to investigate the relationships between middle-ear stiffness-induced changes in wideband acoustic immittance and neural encoding of phase. The auditory brainstem neural encoding of phase was measured using the auditory steady-state response (ASSR) with and without middle-ear stiffness elicited via contralateral activation of the middle-ear muscle reflex (MEMR). Middle-ear stiffness was quantified using a wideband acoustic immittance assay of acoustic absorbance. Statistical analyses demonstrated decreased ASSR phase lag and decreased acoustic absorbance with contralateral activation of the MEMR, consistent with increased middle-ear stiffness changing the auditory brainstem neural encoding of phase. There were no statistically significant correlations between stiffness-induced changes in wideband acoustic absorbance and ASSR phase. The findings of this study may have important implications for understanding binaural cue sensitivity and horizontal plane sound localization in audiologic and otologic clinical populations that demonstrate changes in middle-ear stiffness, including cochlear implant recipients who use combined electric and binaural acoustic hearing and otosclerosis patients.

The effects of cochlear implantation on middle ear function: A prospective study

OBJECTIVES

Although sound conduction mechanisms may influence by cochlear implantation (CI), it is not very clear whether, how, and to what extent these mechanisms may be influenced the pediatric population. Wideband tympanometry (WBT) is a sensitive tool to evaluate alternations in the middle ear mechanics in a wide frequency range. The current study aimed to explore CI's impacts on sound conduction across the middle ear cavity using WBT in pediatrics.

METHODS

In a prospective design, 35 unilaterally implanted children (<24 months of age) with normal temporal bone anatomy were included in this study. Traditional tympanometry (226-Hz) and WBT measures were compared for each child in the implanted and non-implanted ears preoperatively and three months postoperatively.

RESULTS

No significant changes in the "static acoustic admittance" and "peak pressure" parameters were observed between the pre-CI and post-CI conditions in the implanted and non-implanted ears in the 226-Hz tympanometry test. Wideband absorbance recordings before CI surgery exhibited a double-peaked pattern over a frequency range of 250 to 8000 Hz. The pre- and postoperative acoustic energy absorbance comparisons indicated a significantly reduced mid-frequency (1260 to 3175 Hz) and high-frequency (5040 to 8000 Hz) absorbance in the implanted ears. However, our results indicated no significant differences in sound absorbance between the pre- and postoperative conditions in non-implanted ears.

CONCLUSION

Our findings suggested that WBT is a more sensitive method than traditional tympanometry for monitoring the mechanical status of the middle ear after cochlear implantation in pediatrics. Cochlear implantation in young children can significantly reduce mid- and high-frequency acoustic absorbance measured by WBT.

Wideband Acoustic Absorbance in Otosclerosis: Does Stapedotomy Restore Normal Tympanic Cavity Function?*

Introduction Otosclerosis is characterized by the fixation of the stapes to the oval window, thereby impairing acoustic signal absorbance. A commonly used surgical technique for improving hearing in cases of otosclerosis is stapedotomy. However, it is unclear whether this surgery restores all the physical characteristics of the tympano-ossicular system.

Objective To evaluate the tympano-ossicular system in individuals with fenestral otosclerosis pre and poststapedotomy using wideband tympanometry.

Method A total of 47 individuals and 71 ears were assessed. The subjects were divided into three groups: presurgery otosclerosis; postsurgery; and a control group of normal-hearing adults. A handheld tympanometer with a wideband module (226–8,000 Hz) was used to take measurements at ambient pressure and under pressurized conditions. The level of statistical significance adopted was p ≤ 0.05.

Results Acoustic absorbance at 226 Hz was low for all groups. At frequencies in the range 630 to 5,040 Hz, each group had a characteristic absorbance curve, allowing them to be distinguished from one another. In the presurgery group, absorbance values were below normal levels, with energy absorbance below 10%. Low energy absorbance was most evident at 1,000 Hz in the presurgery group, but this was not observed in the postsurgery group. Although there was an improvement in hearing, the surgery failed to restore the tympano-ossicular system to normal.

Conclusion Wideband acoustic absorbance proved able to differentiate normal ears and otosclerotic ears pre and postsurgery, under both ambient pressure and pressurized conditions.

Changes in Acoustic Absorbance Pre- and Post-Cochlear Implantation

PURPOSE

Until recently, there has been little investigation on the effects of cochlear implantation on the transmission of acoustic stimuli through the middle-ear system. Recent studies have shown that cochlear implantation decreases low-frequency acoustic absorbance, consistent with a stiffer middle-ear system postsurgery. The objectives of this study are (a) to investigate the time course of changes in acoustic absorbance post-cochlear implantation in the implanted ear and (b) to compare changes in acoustic absorbance between implanted and nonimplanted ears over time.

METHOD

Seventeen adult cochlear implant (CI) recipients within 6 months of device activation participated in this study. Wideband acoustic absorbance was measured in both ears at one to six different time points from pre-implantation up to 6-month postactivation. Analyses examined (a) changes in acoustic absorbance as compared to pre-implantation and (b) differences in acoustic absorbance between implanted and nonimplanted ears over time.

RESULTS

Acoustic absorbance in the implanted ear decreased postsurgery for frequencies lower than 1.5 kHz and persisted through at least 6-month postactivation. We also observed that the spectral range of decreased acoustic absorbance in the implanted ear decreased with longer time postsurgery. Differences in acoustic absorbance between implanted and nonimplanted ears occurred over a broad spectral range at the activation time point and persisted through at least 3-month postactivation, though for a narrower spectral range at the later time point.

CONCLUSIONS

Cochlear implantation increased middle-ear stiffness as indicated by decreased acoustic absorbance of low-frequency acoustic power. The findings of this study are consistent with those of previous studies and may have important implications toward understanding spatial hearing and programming of acoustic components for CI-combined electric and binaural acoustic stimulation patients.

Wideband tympanometry in ears with superior canal dehiscence before and after surgical correction

OBJECTIVES

Wideband tympanometry (WBT) has been shown to be sensitive to mechanical changes in the ear. This study investigated the effect of surgical correction of superior canal dehiscence (SCD) on WBT (i.e. absorbance and middle ear resonance frequency) compared to those on common surgical outcomes such as symptom resolution, vestibular evoked myogenic potentials (VEMP), and hearing thresholds.

STUDY SAMPLE AND STUDY DESIGN

Seven patients (eight ears with SCD) who underwent surgical correction of SCD underwent WBT in addition to pure-tone audiometry and VEMP assessment.

RESULTS

Postoperatively, all ears showed normalised/decreased absorbance at low frequencies and slightly enhanced absorbance in the middle frequency range (7/8 ears). The middle ear resonance frequency, which was initially lower than normal in most patients, increased in 6/8 operated ears, and decreased in two ears with no/partial symptom relief. In comparison, complete symptom control was observed in 6/8 operated ears, VEMP amplitudes reduced or normalised in all ears, and hearing thresholds remained stable or improved in 6/8 ears and worsened in two ears.

CONCLUSIONS

Surgery seems to change the response to WBT in patients with SCD. The results of WBT may represent mechanical changes induced by SCD, and should be considered when evaluating surgical outcomes.