Bone Conduction Implant, a new approach for BAHA

In the 70's, the Swedish researchers at Sahlgrenska University Hospital and Chalmers University of Technology in Gothenburg developed original bone anchored hearing aids (known as BAHA for its acronym in English) which are used today by thousands of hearing impaired. Designed for those with a healthy cochlea in the inner ear, but with one of the several conditions that prevent the sound to reach it, the ​​original implants anchored in the bone use a small titanium screw implanted behind the ear to resonate against bones and send sound waves to the cochlea.

           

People behind the original BAHA decided that, thanks to the newly available technology, a new approach that would involve a totally implanted component could overcome the negative aspects of the bone anchored devices, such as infection and loose screws. The new bone conduction implant (BCI for its acronym in English) is placed directly into the bone behind the ear, and, using inductance, receives signals from an external component that has a microphone. A small speaker placed near the implant in the cochlea regenerates the sound picked up by the microphone, allowing the user to listen. The first patient who was implanted last month was fitted with the new device at the Sahlgrenska University Hospital already underway and new clinical trials.

Source:

http://www.chalmers.se/en/news/Pages/New-implant-replaces-impaired-middle-ear.aspx

The power of your ear

For the first time, scientists have managed to connect a medical implant and feed it with the energy of a natural battery that we all carry in our inner ear. Yes, all mammals have in their inner ear an "endocochlear potential" similar to a battery. It is located in a chamber filled with ions that, with the aid of sound waves, produce electricity gradients which become auditory nerve signals processed by the brain. In words of the discovers at MIT: 

"The ear converts a mechanical force — the vibration of the eardrum — into an electrochemical signal that can be processed by the brain; the biological battery is the source of that signal’s current. Located in the part of the ear called the cochlea, the battery chamber is divided by a membrane, some of whose cells are specialized to pump ions. An imbalance of potassium and sodium ions on opposite sides of the membrane, together with the particular arrangement of the pumps, creates an electrical voltage." 

"We have known for 60 years that this battery exists and that it’s really important for normal hearing, but nobody has attempted to use this battery to power useful electronics." says Konstantina Stankovic, a researcher at Harvard-MIT Division of Health Sciencies and Technology. 

So far, they have managed to use this source of electricity to power a tiny device without affect hearing.

Image: Patrick P. Mercier - MIT website

This technique could be used to power small ear implants which assist people with hearing loss, to deliver drugs to the body or to feed other sensors. At present, the voltage and power are so weak that scientists had to design a mini converter circuit so the electricity could be exploited by a small electronic device (see the image for a close view into the device size).

http://web.mit.edu/newsoffice/2012/biological-battery-1107.html

Cochlear implants... a successful history with a bright future ahead

A friend of mine said to me few days ago: cochlear implants are one of those things of medicine and technology which actually looks like "magic" or "a miracle". Indeed, cochlear implants made possible to connect deaf people with the world of sound, allowing them to converse with others and even to listen to music. A dream for deaf people which started to take shape for the first time in Dr. Graeme Clark's mind, an Australian otolaryngologist pioneer in the field. He was the first person to develop the multi-channel cochlear implant and to have successfully performed the world’s first implant procedure on Mr Rod Saunders in August 1978, at Melbourne’s Royal Victorian Eye and Ear Hospital.

 

But explaining the whole history of this hearing implants is not the purpose of today's post. I would ike just to mention some of the new technologies currently developped in this interesting field, just to show that there is still big room for improvement and that deaf people can hope for the best in upcoming years. Among others: 

- DACS: Direct Acoustical Cochlear Stimulation: implantable hearing device which bypasses the middle ear and applies powerful vibration directly at the oval window in order to stimulate the cochlea without significantly entering it. It replaces the function of the ear drum and ossicular chain with direct vibration at the oval window (take a look here for more information: http://www.acousticimplants.com/en/product/how-it-works.php)

- Increase number of electrodes: "hi fi" cochlear implant featuring 50 electrodes. It is hoped that the increased number of electrodes will enable users to perceive music and discern specific voices in noisy rooms.

- Laser stimulation: The laser stimulation produced more precise signals in that brain region than the electrical stimulation commonly used in cochlear implants. Laser stimulation is a promising technology for improving the auditory resolution of implants.

- Fully internal cochlear implant with an internal microphone system: a fully implanted system which can be worn all the time (sleeping, having a shower…). The ability to hear 24/7! As of April 2011, four people have undergone a trial of an internal microphone system, with two more yet to come. More information in this article: http://www.newscientist.com/article/mg21028064.800-ear-implants-for-the-deaf-with-no-strings-attached.html

- Liquid transmission means for transmitting acoustical energy to the cochlea, using a liquid filled tube which is surgically inserted through the middle ear to an orifice in the cochlea. The liquid filled tube acts as a transmission line with little losses because the liquid can be similar in acoustic properties to the perilymph in the cochlea and the impedance of the transmission line can be more closely matched to the acoustic impedance of the cochlea at the termination of the tube at the cochlea.

- Improvement speech processing strategies: In the n-of-m sound coding strategy, the signal is processed through m bandpass filters from which only the n maximum envelope amplitudes are selected for stimulation (m>n). While this maximum selection criterion, adopted in the advanced combination encoder strategy, works well in quiet, it can be problematic in noise as it is sensitive to the spectral composition of the input signal and does not account for situations in which the masker completely dominates the target. A new selection criterion could be based on the signal-to-noise ratio (SNR) of individual channels.
- Possibility of delivering drugs to the cochlea by means of the cochlear implant to develop a range of local pharmacologic interventions to prevent hearing degeneration.

I hope this is enough to arouse curiosity... see you in the next biomedipost.

If you want to know how the natural process of hearing works, click here... And also a nice video about cochlear implants from Cochlear Limited: