Perfecting the balance of Bimodal

How it began

I remember it vividly. In April 1988, the head professor of the ENT university clinic where I had been studying audiology for merely two weeks told me that they had just implanted two patients with multichannel cochlear implants and I had to do the mapping. There was hardly a single word in that sentence that I understood.

So the adventure began. Fitting CI’s before dealing with hearing aids or even mastering audiometry. The world felt upside down, but it was also the best educational experience one can imagine. Computers were simple machines with floppy discs and monochrome screens. No textbooks on CI’s or courses were available – it was learning by doing. More than thirty years later, the world of cochlear implants has developed tremendously. Half a million ears have been implanted and the procedure is performed 65’000 times per year. The technology is impressive and fascinating. Most interestingly, CI’s and hearing aids have come closer together than ever before. Not only in technology, but also in fitting.

For optimal outcomes and acceptance of hearing aids, the fitting formula chosen by the hearing care professional plays an important role. Next to APD Contrast for severe to profound hearing losses (see my previous blog), there is another great fitting formula dedicated to this special target group that all fitters should know: the Adaptive Phonak Digital Bimodal Fitting Formula (APDBFF).

What is this about?

In many cases, unilaterally implanted CI patients continue to use a hearing aid on the contralateral ear. It is widely accepted that such a bimodal solution makes sense. There is literature showing substantial benefit for among other things speech understanding in noise, localization and music perception.¹ The fitting of a bimodal hearing aid however is different from fitting a hearing aid if there is no CI on the other side. We need a special fitting formula for this case.

Why is a special fitting formula needed?

The CI is (for most bimodal listeners) the dominant source of sound information and speech understanding. Therefore, the hearing aid should be programmed to support the CI. Traditional fitting formulae do not align acoustic and electric processing so selecting any hearing aid and any fitting formula whilst ignoring the other ear is not good enough. After all, the sound from the CI in one ear and from the hearing aid in the other ear will meet in the brainstem. For all kinds of different and rapidly changing listening situations, these two auditory streams need to merge and give the auditory cortex an opportunity to recreate a truthful representation of the acoustic environment. In my opinion, the auditory streams should not collide head on. This is the very reason why APDBFF was developed. It was designed to maximize the benefit of Advanced Bionics Naida CI’s when a contralateral hearing aid is worn.

How is this different?

APDBFF can be selected only for Phonak Naída Link, the bimodal hearing aid portfolio from Phonak. This fitting formula option will appear once you connect a Phonak Naída Link to Phonak Target.

It differs from other fitting formulae in three ways:

1. The frequency response is different. For most audiograms, it gives more emphasis on the low frequencies (< 1 kHz) and it minimizes amplification into dead regions.
2. The loudness growth is similar to that of the CI by using a high compression kneepoint (63 dB SPL) and high compression ratio (12:1).
3. The dynamic behavior is similar to that of the CI, by using long time constants, instead of syllabic compression.

 

APDBFF saves the hearing care professional the time-consuming iterative process of aligning the response of the hearing aid to the CI. And as long as one does not have direct access to knee points, compression ratios and attack- and-release times in the fitting software of hearing aids, the outcome of such hard work remains questionable anyhow.

For patient benefits, there is a growing body of evidence showing that a bimodal hearing aid makes clinical sense and using APDBFF makes even more sense.² Most recently, at the 10^th European Investigators Conference in Venice, Italy, Dr. Talma Shpak from Bnai Zion Medical Center in Haifa, Israel, reported interim results from a large study which included (among other benefits) an enhanced identification of monosyllabic words in a natural listening environment and more ease of listening in a group conversation. In the majority of study participants, APDBFF was the better than the patients’ own hearing aids or to Naída Link with a conventional fitting formula.

When is it needed?

For individuals likely to benefit from the combined input of a CI and contralateral hearing aid, choose AB for the implant and Phonak Naída Link as the bimodal hearing aid with the Adaptive Phonak Digital Bimodal Fitting Formula. This was not a consideration in 1988 when I began in audiology. Only patients who did not benefit at all from acoustic amplification were considered candidates for CI in those days. Hearing aids and CI’s were miles apart. Today they are powerfully connected.

For more information on the Bimodal, visit our product page.

 

 

References

¹ Dorman, M.F., Gifford, R.H., Spahr, A.J., McKarns, S.A. (2008) The benefits of combining acoustic and electric stimulation for the recognition of speech, voice and melodies. Audiology and Neurotology. 13:105-112.

² Veugen, L.C., Chalupper, J., Snik AF, van Opstal, A.J., Mens, L.H. (2016) Matching automatic gain control across devices in bimodal cochlear implant users. Ear and Hearing. 37: 260-270.