In Tune with Cochlear Implants

From: Design News - Newton,MA,USA - May 14, 2007

Technical breakthroughs are making the quality of life much richer for individuals with moderately severe to profound hearing loss

Lawrence D. Maloney, Contributing Editor -- Design News, May 14, 2007

Who are the best candidates for cochlear implants?

The device can be an effective treatment option for several types of patients, particularly children 12 months of age or even younger who suffer moderately severe to profound sensorineural hearing loss. Hearing-impaired adults who receive little or no benefit from conventional amplification (hearing aids) are also good candidates. To achieve optimum benefit from a cochlear implant, adult candidates need to be highly motivated to learn how to use the device and must have realistic expectations. Of course, there should be no medical contra-indications. Certainly, the number of implants has increased steadily since we introduced our first commercial cochlear device in 1989. Thousands of our devices are being implanted each year in more than 80 countries worldwide.

What advances have made cochlear implant technology more viable?

Improved microchip technology makes it possible for us to design highly flexible and energy-efficient circuits. Implants can now stimulate at very high rates — beyond 50,000 pulses per second, with different pulse shapes and various stimulation modes. Thus, you can deliver more information per time unit to the auditory nerve. We also have seen major advances in electrode design. With MED-EL electrodes, which are capable of being inserted deeply into the cochlea, we have the ability to stimulate the entire length of the inner ear. As a result, there is a better matching between a person’s natural tonotopicity and the physical location of stimulation. This results in a faster learning curve in speech understanding with the cochlear implant. Better and less traumatic electrodes also leave the door open for new concepts, such as combined electrical and acoustic stimulation (EASTM).

How about new developments in the external speech processor?

MED-EL offers a modular, lightweight design that meets the needs of a wide range of patients, including very small children. We also have integrated powerful application specific integrated circuits (ASICs), designed for maximum energy efficiency. With this approach we can providing an average battery life of three to five days for the three 675 zinc air batteries (1.4V). In addition, these ASICs provide optimum flexibility for future innovations with regard to speech coding strategies.

How is your company addressing some of the challenges that face cochlear implants, such as music appreciation and speech recognition in noisy settings?

The custom-made ASIC in our new PULSARci100 implant addresses this problem by offering greater flexibility in stimulation modes, pulse shapes and stimulation rates (50,704 pulses per second). This enables the device to increase the information it delivers to the cochlea in a given time period. Together with our latest speech processor developments, OPUS 1 and OPUS 2, our implants can now deliver more low-frequency and temporal information, which is very important for music appreciation and for processing tonal languages, such as Chinese. This technological capability is called the FineHearingTM concept. Traditional cochlear implant systems only provide information on changes in the amplitude of a signal over time. This is referred to as the “envelope” of an incoming sound. At MED-EL, we have developed fine structure processing (FSPTM), which also uses temporal stimulation patterns to represent rapidly changing details in the frequency of a signal. Modifying implants to deliver this fine-structure information can improve music perception, as well as speech recognition in noisy settings like restaurants.

What other new concepts are you exploring?

As previously mentioned, cochlear implants have become so powerful that we can now deliver more than 50,000 pulses per second. But if you want to deliver these high stimulation rates — and at the same time retain the sequential stimulation used in standard speech coding strategies — you have to narrow the stimulation pulses and at the same time increase the stimulation amplitude to achieve nerve excitation. But you begin to run into technical limits, such as the amount of voltage an implant can supply. We addressed this challenge by developing what we call our Intelligent Parallel Stimulation (IPSTM) concept, which involves stimulating several electrodes simultaneously. We’ve developed some sophisticated algorithms to manage potential channel interaction. This technology is already implemented in our latest OPUS 1TM and OPUS 2TM speech processors, recently introduced in Europe.

What is the strategy for introducing these new features into your systems?

The PULSARci100, which is available in the U.S., can offer these new features. In general, we view the implanted components of our system as a future-ready constant. The powerful electronics can be incorporated into a ceramic or titanium housing. So, the implant can remain in the patient’s head for as long as a lifetime. This design philosophy allows our cochlear implant recipients to benefit from future developments without having to replace their implanted component. The external components, such as the ASIC that resides in the speech processor, can be upgraded with software as we develop new speech-coding technologies.

Looking further into the future, where is this technology headed?

We are involved in ongoing research into hybrid devices that combine technologies from hearing aids and cochlear implants, a concept currently under clinical trial in the U.S. This technology benefits people who can hear at low frequencies but not at high. Future implant systems could also integrate drug delivery systems. This could prevent further deterioration of the auditory system and also prevent tissue growth, which would keep electrode impedances and power requirements low. Moving forward, we expect to make increasing progress toward making these devices smaller and smaller. Ultimately, we hope to have a fully implantable device. In such a design, the entire system, including the external speech processor, would be placed in the same temporal bone area where the stimulator now resides. Already, we have achieved an important milestone in this design with our energy-efficient ASICs.

© 2007 Design News