Updates in Hearing Technology

Not Your Grandparent's Hearing Aid

A hearing aid is essentially an amplifying device designed to compensate for a listener's loss of hearing acuity. Using computer software, a Doctor of Audiology (a health care professional who specializes in hearing and balance) programs the hearing aid to apply appropriate amounts of amplification at specific pitches. Best practice dictates that a small probe microphone be placed into the patient's ear canal during programming. The resulting measurement, called Real-Ear Verification or Speech Mapping, allows the Audiologist to “see” how the hearing aid is amplifying sound in real time, from within the ear itself. Whether the patient is a 6-month-old infant or a 103-year-old veteran, Real-Ear Verification leads to objective, accurate, and safe hearing aid programming.

Achieving audibility, however, is only the beginning. Hearing aids today analyze the surrounding environment and make advanced signal processing decisions in milliseconds. With binaural (ear-to-ear) communication between devices, hearing aids can even scan 360° around the patient's head to identify dominant speech patterns and reduce the effects of background noise. Higher levels of hearing aid technology can even recognize the presence of music, whether the listener is in a large reverberant space, or whether the listener is riding in the car—all based on the characteristic noise and spectral patterns of the acoustic environment.

Bluetooth/2.4 GHz Streaming

A technology that has received a great deal of attention in recent years is the ability to wirelessly stream audio signals from one device to another using Bluetooth. Initially used for hands-free mobile phone communication, Bluetooth streaming technology is now used to send audio signals (eg, from phones, MP3 players, television) into the patient's ears. The hearing aids, in essence, become personal headphones. Some hearing aid manufacturers utilize an intermediate device called a streamer that must be worn around the patient's neck. The streamer receives the Bluetooth signal, and, using a neckloop antenna, sends the signal via near-field magnetic induction (NFMI) to the hearing aids [1]. By streaming audio directly into the hearing devices, the streamer produces sound quality that does not suffer the effects of reverberation and distance. Often, these streamers double as remote controls, allowing the patient to adjust hearing aid volume and change listening programs. Unfortunately, the size and visibility of the streamer device deters some consumers.

Other hearing aid manufacturers do not require the intermediary streamer, but can send audio signals directly to the hearing aids from another device using a 2.4 GHz license-free Industry Science Medical (ISM) platform [1]. Sound sources may include manufacturer-specific remote microphones, TV transmitters, and, most popular of all, iPhones, iPads or other Apple devices. While very similar to Bluetooth, the 2.4 GHz protocol uses proprietary bandwidths for the communication of a designated set of devices. After downloading an application (app), patients can utilize their smart phones as a remote control in a fashion similar to the streamer. As many of us are rarely without our smart phones, 2.4 GHz streaming offers hearing aid users convenient and discrete control over their devices.

Lithium Ion Batteries

The vast majority of hearing aids run on small disposable zinc-air batteries. Depending on the size of the battery, it typically lasts 6 to 10 days and then is replaced. Some zinc-air batteries, used in the tiniest of hearing aids, last only 3-4 days. Unfortunately, disposable batteries are rarely recycled properly, a concern given that most zinc-air batteries contain mercury. A welcome alternative for many patients is rechargeable batteries. Offered by only a few hearing aid manufacturers, traditional rechargeable batteries utilize nickel-metal-hydride (NiMH) technology. Each night, the patient places the hearing aids in a charging unit that recharges them for use in the morning. For patients with dexterity or vision challenges, the convenience and ease of rechargeability go a long way toward independent maintenance of their aids. Drawbacks of NiMH batteries are their limited daily life span (12-16 hours) on a single charge and the need to still replace them once a year.

In the last year, a superior energy development was achieved using lithium-ion batteries. While perhaps best known for their challenges (exploding smart phones!), when managed for overheating, lithium-ion (Li-Ion) batteries offer many advantages to traditional disposable and previous generations of rechargeable hearing aid batteries. The patient using Li-Ion batteries avoids weekly battery changes and only needs to replace the battery every 3-4 years (see Figure 1). With an estimated 1.5 billion disposable hearing aid batteries entering landfills annually, Li-Ion boasts a greener solution [2]. Another great advantage is the length of Li-Ion battery life on a single charge—up to 24 hours. With hearing aid signal processing becoming more advanced, power consumption has also increased. Binaural communication between devices, as well as wireless audio streaming, places greater demands on battery consumption, so a quick charging Li-Ion battery with extended battery life is a real plus for patients connected to modern technology [3].

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FIGURE 1.

Lithium Ion Rechargeable Hearing Aids

Hybrid Devices: Half Cochlear Implant-Half Hearing Aid

For patients with severe cochlear damage and very poor speech understanding, even the most advanced hearing aid technology may not be able to overcome the degradation of neural structures in the ear. Instead, a cochlear implant may be the best treatment. A traditional cochlear implant uses electrical impulses to stimulate the auditory nerve through the cochlea, imitating the fine-tuned response of the cochlea's small hair cells. A cochlear implant has two main components: an external speech processor and an internal electrode array. The patient wears the external speech processor over the ear, which uses small microphones to pick up sound in the environment. The sound is then turned into an electronic signal that communicates via a magnetic coil to the internal electrode array, which is implanted directly into the cochlea. Following the tonotopic (pitch specific) layout of the cochlea, the electrode array can stimulate different regions at different rates, all of which is perceived by the patient as varying pitch and loudness.

Prior Food and Drug Administration regulation has limited cochlear implant candidacy to those with moderate to profound bilateral sensorineural hearing loss (what some describe as deafness). This meant that some patients found themselves in a hearing purgatory: having hearing too poor to be sufficiently helped by a hearing aid, but not yet poor enough to qualify for a cochlear implant. Additionally, cochlear implant surgery typically resulted in a loss of residual hearing due to cochlear trauma. With newer, improved surgical techniques and in some cases a shortened internal electrode array, both the candidacy and the methods of cochlear implantation have changed [4]. Surgeons are now able to preserve low frequency hearing, leaving the patient with the opportunity to integrate both acoustic and electrical hearing. Thus enters the hybrid cochlear implant, which utilizes a cochlear implant for the patient's damaged mid and high frequency hearing and a hearing aid for the preserved low frequency hearing.

Candidates for hybrid cochlear implants must be adults over 18 years old with “ski-slope” shaped audiograms, where hearing is normal to moderate in the low pitches but then steeply declines to a severe to profound hearing loss in the high pitches (see Figure 2). Candidates must also demonstrate poor speech understanding even in their best aided condition. Research shows that speech understanding outcomes are better for those with electro-acoustic hearing than those with a traditional cochlear implant or hearing aid alone [5]. Evidence also shows improved ability to hear in noise with a hybrid device compared to a traditional cochlear implant, largely due to the added sound cues found only in acoustic hearing [6]. With a hybrid cochlear implant, patients no longer have to wait for their hearing to worsen before accessing the significant benefits of a cochlear implant, while further improving their hearing with the combined power of a hearing aid.

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FIGURE 2.

Audiogram Candidacy for Hybrid Cochlear Implants