While today’s MEI systems vary in many respects, they all involve the implantation of a transducer on or near the incudostapedial joint of the ossicular chain. That implantation allows the system to drive the middle ear directly rather than doing so by sending an amplified acoustic signal through the ear canal, as conventional devices do.
Explore This IssueMay 2011
Although Otologics LLC, based in Boulder, Colo., began with and still makes the partially implantable MET (middle ear transducer), CEO Jose Bedoya likened the evolution of MEIs to that of other medical implants. “They all start as external devices and then evolve to be implanted. The hurdle is the technology required to internalize them,” he said.
Until Envoy Medical’s Esteem product received FDA clearance in March 2010, every MEI made or marketed in the U.S. was electromagnetic. These devices contain an implanted magnet and an external coil coupled to the microphone. When the coil is energized by a signal, it causes the magnet to vibrate and move the ossicles.
The Esteem, on the other hand, uses piezoelectric technology. The mechanical signal is detected from a piezoelectric transducer at the head of the incus (the sensor) and converted to an electrical signal, which is then amplified, filtered and converted back to a vibratory signal that moves the ossicles.
The conventional air-conduction approach, said Bedoya, is an inefficient way of transmitting sound. Bedoya, whose company has developed two implantable systems, said that the thinking behind the MEI was, “Let’s see if surgically we can drive the middle ear directly and eliminate those inefficiencies and potential distortions.”
Once the device is successfully implanted and programmed, the wearer can essentially ignore it. “There is something very appealing to patients about not having to put something on to be able to hear,” Dr. Arriaga said. “They can leave it on 24 hours a day, swim or shower with it, and never worry about forgetting or losing it.”
Because it’s totally implanted, there is no issue of stigma or cosmetics. Maintenance is also minimal, with an implanted battery the manufacturer says will last for 4.5 to nine years.
“With a regular hearing aid, you take sound, you convert it into electricity, you manipulate it, and then you convert it back to sound, so there are two conversions,” Dr. Arriaga explained. “With an implantable device, you are taking sound, converting it to electrical energy, but you aren’t converting it back to sound. You’re leaving it as electrical energy that is moving the ossicular chain.”