Intraoperative determination of coupling efficiency of Carina® middle ear implant by means of auditory evoked potentials

A novel coupling quality index to estimate the coupling efficiency in Vibrant Soundbridge

BACKGROUND

The objective-based methods for intraoperative monitoring have been suggested to assess the coupling and the outcomes of Vibrant Soundbridge (VSB). Although several techniques were proposed, they have not been widely adopted due to their complexity and invasiveness.

PURPOSE

This study aimed to investigate the accuracy of a new coupling quality index using an intraoperative ABR threshold via AcoustiAP and its correlation with the perioperative measures.

METHODS

This is a prospective study conducted at a tertiary center. The medical records were retrieved for all patients who underwent VSB implantation and had an intraoperative objective assessment for the coupling efficiency. AcoustiAP was used to evaluate the intraoperative ABR thresholds, which were assessed directly after the floating mass transducer (FMT) placement using acoustic CE-Chirp signals. The Vibrogram was used for the postoperative audiological evaluation. A new coupling quality index was calculated based on the intraoperative ABR thresholds.

RESULTS

Ten patients were eligible for the present study. The ABR thresholds for good coupling ranged from 35 to 60 dBnHL. The loose coupling thresholds ranged considerably from 40 to 100 dBnHL. Overall, the median intraoperative ABR threshold at good coupling was 42.5 (40-60) dBnHL and 60 (40-100) dBnHL at loose coupling. The analysis showed that there was a significant change in the coupling quality index at the good and loose coupling points (24.3 ± 14 vs 38.8 ± 18.2, respectively, p < 0.001). At a cut-off value of 22.6 dB, the coupling quality index had a sensitivity of 70%  and specificity of 90% for discriminating good and loose coupling.

CONCLUSION

This study provides evidence for the utility of intraoperative ABR measurements in predicting the coupling efficiency in patients with VSB. Our results showed that the coupling quality index had an acceptable accuracy in discriminating between good and poor coupling, which can help clinicians optimize the fitting process for individuals and may ultimately lead to improved patient outcomes.

Battery Lifespan of an Implantable Middle Ear Device

Background: The Carina system (Cochlear Ltd., Sydney, Australia) is a totally implantable device providing acoustic amplification in adult patients with moderate-to-severe sensorineural or mixed hearing loss. One of the main concerns about such a totally implantable device has been represented by the subcutaneous battery lifespan. The aim of this article is to report the analysis of battery performances in a series of Carina-implanted patients after a long follow up. Methods: In this retrospective study, the technical data of a series of patients implanted with the Carina middle ear implant in our clinic have been analysed, extracting the data from the log of telemetric measures. Results: The mean lifespan cutback was 0.43 h/years (from 0 to 0.71 h/year), with a strong negative significant correlation between the follow-up period and the percentage of battery residual lifespan. Conclusion: The lifespan of the Carina’s battery seems consistent with the manufacturer statement of a pluri-decennial lifespan, avoiding the need of an early surgical substitution and providing a full day of use of the system even after up to 12 years from the implantation.

In-vivo characterisation of an implanted microphone and totally implantable active middle ear implant

OBJECTIVE

To objectively evaluate acoustic sensitivity of the implanted microphone, and maximum stable gain of a totally implantable active middle ear implant.

DESIGN

Prospective, single centre evaluation.

STUDY SAMPLE

Fourteen adult patients.

RESULTS

Microphone sensitivity is approx. 10 dB lower than an externally worn conventional hearing aid, at frequencies up to 4000 Hz, and substantially lower at higher frequencies. The masking level due to microphone noise, which determines the softest test tones that can be detected, is estimated at <20 to <30 dB HL up to 1000 Hz, and <40 dB HL at higher frequencies. Maximum stable effective gain is the maximum amplification achievable without causing feedback whistling. In sensorineural hearing loss (SNHL) cases, it is 30-40 dB at frequencies up to 2000 Hz, allowing to compensate for even the maximum recommended hearing loss (60-70 dB HL). In both SNHL and mixed hearing loss (MHL) cases, maximum stable effective gain is lower (+20 to -30 dB) around 3000-6000 Hz.

CONCLUSIONS

Microphone sensitivity is high enough to achieve aided thresholds of 20-40 dB HL. A strong correlation between actuator coupling efficiency and maximum stable effective gain implies that any effort to improve actuator efficiency should also increase the available gain.