The fourth component was a vibrating piston in the middle ear, secured by four titanium bolts screwed to the skull. This was what actually delivered the sound. The middle ear consists of three tiny bones that conduct vibrations from the eardrum to the inner ear. The piston moved the bones more forcefully than the eardrum would, so it acted as an amplifier.
I peered at the skull, feeling like Hamlet contemplating a high-tech Yorick. The Carina was a strange-looking gadget. Big, too: at about five inches long, it stretched from behind the ear to just behind the temple. The surgery would involve opening a skin flap, drilling into the skull to countersink the components, and then drilling into the middle ear to install the piston. A lot of hardware to get into place.
“How long does the battery last?” I asked.
Each charge was good for about a day, Conn told me. The battery could go through enough charge cycles to last at least five years, and possibly 10 or more.
“And when the battery can’t hold a charge anymore?” I asked.
When that happened, Conn told me, the entire device, except for the piston, would be replaced. The microphone, coil, and processor had many connections to each other, so they had to be hermetically sealed together to keep body fluids out. The piston had only two connections, though, so a seal could be maintained between them. In any case, the surgery would be simple. Pull out the old unit. Snap in the new one.
“Wow,” I said to Yorick.
The $20,000 Question
Otologics arranged for me to speak with a Carina user in Hamburg, Germany, a 25-year-old medical student named Veronika Koch. I called her from the company’s conference room, aware that the situation was full of acoustical land mines. A totally deaf American was going to speak to a mostly deaf German through a speakerphone and across a language barrier.
But we understood each other with very little trouble. Veronika said she loved having a fully implanted device: “You don’t have to think about it. That’s the most important thing. When it was turned on, it was one of the most beautiful experiences I ever had. Nothing touching my ear. That natural feeling of hearing–it’s just beautiful.”
I asked her how the Carina sounded. “Sound quality is one of the biggest advantages,” she said. “Speech quality is good and more natural, and music is very beautiful.”
Veronika was clearly pleased. But I knew that Otologics would have given me its star patient. That’s why the FDA puts new products through clinical trials–to get an objective look at their performance. What do the Carina’s clinical trials show?
The device is now in phase II trials. (Phase I trials, conducted on a small group, test for safety; phase II, which involve a slightly larger group, tests for effectiveness; and phase III assesses both safety and effectiveness in a large group.) Results of the phase I trial had been ambiguous. In controlled hearing tests, its 20 subjects had scored somewhat worse with the Carina than they had with their own hearing aids, particularly in their ability to hear soft sounds. In a written survey to measure subjective impressions of the device, on the other hand, subjects had said, consistently, that they heard better with the Carina.
But still, the company wanted to see whether the phase II patients could get better results on the tests. They theorized that if the surgeons put the microphone in a specific spot behind the ear where there were fewer scalp muscles, soft sounds would not be masked so much.
So far, the phase II study has enrolled only 12 of the 70 to 80 users it needs, so its results are preliminary. But Herman Jenkins, the primary investigator, told me that the new microphone placement seems to be working. The phase II patients can hear a 3,000-hertz tone (a common frequency in speech) at a volume of 37 decibels, whereas the phase I subjects could hear it only at 55 decibels. This is a significant improvement; 37 decibels is about the ambient sound level of a library, whereas 55 decibels is the approximate level of conversational speech. And nine of the patients got word recognition scores that averaged 82 percent, statistically matching the 84 percent they got with their conventional hearing aids.