MANHASSET, NY -- A proof-of-concept prototype microphone implanted in the middle ear promises to partly offset the need for wearing an outer hearing aid.
The device would still require patients to wear a charger behind the ear while sleeping to recharge an implanted battery.
The current prototype of the packaged, middle-ear microphone measures 2.5 x 6.2 mm and weighs 25 mgrams, or less than a thousandth of an ounce.
The package is to be reduced to 2 x 2 mm, according to researchers Darrin J. Young, associate professor of electrical and computer engineering at the University of Utah and USTAR, the Utah Science Technology and Research initiative.
The National Institutes of Health says almost 220,000 people worldwide with profound deafness or severe hearing impairment have received cochlear implants, about one-third of them in the United States, where two-fifths of the recipients are children.
A microphone and related electronics worn outside the head raises reliability issues, prevents patients from swimming and creates social stigma.
The system developed by Young implants all the external components. Sound moves through the ear canal to the eardrum, which vibrates as it does normally. An attached accelerometer sensor detects the vibration at the umbo part of the ear and thru processor converts them into electrical signals that are sent to the electrodes in the cochlea.
“Everything is the same as a conventional cochlear implant, except we use an implantable microphone that uses the vibration of the bone,” Young explained.
Young conducted the study with Mark Zurcher and Wen Ko, who are his former electrical engineering colleagues at Case Western Reserve University in Cleveland, and with ear-nose-throat physicians Maroun Semaan and Cliff Megerian of University Hospitals Case Medical Center.
The study was funded by the National Institutes of Health (NIH-DC-006850).
The device has been successfully tested in the ear canals of four cadavers. Tests in people are about three years away, according to Young.
Research without a real purpose: This middle ear microphone reinvents the wheel, as it duplicates the microphone used in the Envoy Esteem implanted hearing aid, like the ones Sarah Churman has implanted in her, as we all saw in the viral video last fall:
What's more, this particular mic system does a rather poor job, compared to the piezo mic in the Esteem:
"To demonstrate the microphone, Young also used it to record the start of Beethoven’s Ninth Symphony while implanted in a cadaver ear. It is easily recognizable, even if somewhat fuzzy and muffled."
Finally, the whole concept of using the tympanic membrane as a microphone diaphragm is flawed, as when there is suppurative or non-suppurative otitis media (middle ear fluid), the sound is no longer crystal clear, and becomes badly muffled. Furthermore, there is the issue of instability ("feedback") when a tympanic membrane microphone is occupying the same pea-sized space in the middle ear cavity as a mechanical transducer coupled to the oval or round window to provide mechanical/acoustic stimulation to the perilymph in the scala vestibule & scala tympani. [Of course, this does not occur when electrical hearing is being used, as the spiral ganglion is being stimulated by the electrodes in the cochlear implant.]
But implanting the microphone directly under the skin, like as is done with the Otologics Carina, has its' own issues, due to head noises and also the loss of any directionality and resonances from the pinna & canal.
Editor, The Hearing Blog
You have a rich blog and know a lot. My own pedestrian opinion is that any research project that integrates electronics so that hearing-impaired people can be helped is a good thing. Hopefully from all the research we will manage to arrive at a cheap, reliable and socially acceptable implantable acoustic amplifier that may make it possible for impaired people to hear. Is there a more commercially ready device out there now?
This is very new good news. This will greatly benefit the 220,000 people worldwide and will help them lead a normal life. Can't we re-charge this device by generating electricity using head movements ?
How about stereophonic microphones on glasses frames (right and left sides)? Transcutaneous transmission of the signals from antennae in the glasses temples (the supporting arms on either side of the head) to receivers embedded within the person's temples would avoid the need for intact middle ear structures.