Baha® for conductive, mixed, and unilateral loss

This is the authors' abstract. We don't add key points for this paper.

Increasingly, people with conductive, mixed, and single-sided sensorineural hearing losses are investigating the possibility of a bone-conduction hearing implant.* Bone-conduction hearing implants such as Baha® provide an excellent hearing solution for these types of hearing loss, and more than 45,000 people now use them. The Baha system consists of three parts: the osseointegrated implant, the sound processor, and the abutment, which connects the two. The sound processor is connected directly to the skull through an abutment attached to an osseointegrated titanium implant in the temporal bone. The sound vibrations are thereby passed through the titanium implant and vibrate the cochlea directly. Bone conduction addresses conductive hearing loss by bypassing the outer and middle ear and directing the sound to the cochlea. It can also compensate for a degree of sensorineural hearing loss in a mixed hearing loss with increased amplification. Additionally, Baha provides a solution for single-sided sensorineural deafness (SSD) as the skull can efficiently conduct the sound from one side of the head to the opposite normal-hearing cochlea. FOR CONDUCTIVE, MIXED LOSSes Baha is frequently selected in cases of permanent conductive and mixed hearing loss. Medically, conductive hearing loss is often concomitant with various outer and middle ear abnormalities (e.g., atresia) or pathologies (e.g., continuously draining ear) that preclude the wearing of hearing aids. Audiologically, the key benefit of Baha for people with mixed and conductive hearing loss is that sound is routed directly to the cochlea through bone conduction thereby bypassing the conductive component entirely. The conductive aspect of a hearing loss creates two difficulties for conventional hearing aids. First, the gain required by the hearing aid is double that required for a sensorineural loss.1,2 Second, amplifying sound through a conductive loss alters the sound picture. Both of these issues combine to make finding a conventional hearing solution difficult due to the high gain requirements, problems with feedback, and distortion. The result is that Baha provides a solution that requires less gain and produces a higher sound quality than conventional hearing aids.3 Flynn and colleagues recently compared the performance of Baha with conventional hearing aids on a group of adults (n=10) with mixed hearing loss.3 All subjects had a severe mixed hearing loss with sensorineural thresholds worse than 30 dB HL and at least a 30-dB air-bone gap. The test device used was the Baha Intenso™, which, as shown in Figure 1, provides 10 to 15 dB more gain than Baha Divino™, an older model, by combining active feedback cancellation with new bone transducer technologies.Figure 1: Increase in available gain with Baha Intenso over a head-worn Baha when the active feedback-cancellation system is implemented.The study reported on a series of measures, including aided thresholds, speech understanding in noise, and subjective reports of preference. As Figure 2 shows, performance with Baha provided a 2.5-dB improvement in speech understanding (SNR 50%) when compared with a digital super-power hearing aid.Figure 2: Comparison of adaptive speech test results showing the 2.5-dB SNR improvement available with Baha over conventional super-power hearing aids.To appreciate the magnitude of this improvement, note that Dillon reports that each dB of improvement in speech understanding provides 10% improved performance.1 Significantly improved speech understanding with Baha was reported for all participants. This confirms previous findings that Baha improves speech understanding and sound quality more than conventional approaches for this patient population.4-6 This is due to the greatly reduced gain requirements of Baha, which needs to compensate for only the sensorineural component of a hearing loss, while hearing aids must overcome the conductive loss as well. In summary, Baha provides an effective solution for conductive and mixed hearing losses when hearing aids are contraindicated. Moreover, the latest research indicates that clinicians should also consider the audiological criteria for Baha when the air-bone gap is greater than 30 dB. SINGLE-SIDED DEAFNESS Single-sided sensorineural deafness (SSD) provides significant communication difficulties, as mid- and high-frequency sounds are attenuated by up to 15 dB due to the head shadow effect. Apart from losing sound awareness due to this “shadow,” the patient has difficulty in situations where the noise is directed toward the good ear and speech is directed toward the deaf ear. In many situations (e.g., driving a car), the patient is unable to compensate by changing head position. Every year, there are approximately 200 new cases of SSD for every 1 million people. Unfortunately, many of them go untreated because of the perception that there is no effective solution. However, recent studies have demonstrated that Baha provides a unique benefit for people with SSD by enabling them to hear and understand sound from both sides where previously they could hear from only their good side.7–11 Patients with SSD wear the Baha processor on the deaf side and it transfers the signal directly across the skull to the good ear via bone conduction, thus eliminating the head shadow effect. With many patients, bone conduction transfers the sound seamlessly from one side to the other. However, a small number of patients require additional amplification to overcome an increased interaural attenuation and provide sufficient loudness in the good ear. For these patients, a more powerful sound processor, such as the Intenso, is recommended. Studies have compared the performance of Baha with that of the more traditional solution of CROS (contralateral routing of signal) hearing aids.7,8,11 These studies found significantly better speech understanding and subjective reports with the Baha than with CROS-based solutions. CONCLUSION Baha offers a proven treatment that complements conventional hearing aids and cochlear implants. Direct stimulation of the cochlea via bone conduction can provide an effective solution for people with conductive, mixed, or single-sided sensorineural hearing losses. Of the several implantable technologies for hearing loss, Baha is the only one that the patient can thoroughly evaluate before surgery. The use of a soft band or test rod permits the patient to evaluate the potential benefits of Baha. MORE NEXT MONTH Don't miss part two of this special section on the future of implantable hearing devices, which will run in the September issue. Edited by Marshall Chasin, part two will feature articles on the Otologics fully implantable system and TIHS, a totally implantable hearing system currently under investigation at the University of Oklahoma.