Ultra-Fine Wire Plays Key Role in Cochlear Implant Design.

New hope for the profoundly deaf

Modern science continues to develop hearing aids of reduced size and increased complexity to provide clear amplified sound for the hearing impaired. But what options are available to profoundly deaf patients who face a world of silence when these conventional hearing aids no longer work? The answer for many is cochlear implants -- electronic devices that depend on micro-fine wire electrodes to bridge the gap between man and machine and restore hearing to the totally deaf.

Cochlear implants differ from typical hearing aids in that they do not amplify sound, but rather convert it to electrical signals that are sent directly to the cochlea, the snail-shaped part of the inner ear. Normally, sound waves enter the ear and vibrate the eardrum, which causes a chain reaction through tiny bones connecting the eardrum to the cochlea. The cochlea is filled with fluid and lined with thousands of tiny sensory receptors called hair cells. As fluid within the cochlea vibrates, hair cells convert vibrations into electrical impulses that are sent to the brain via the auditory nerve.

In a profoundly deaf ear, the majority of hair cells are so damaged that even amplified sound cannot be processed. Cochlear implants bypass these damaged hair cells and directly stimulate hearing nerves with electrical impulses, allowing the brain to receive sonic information. Implant candidates must have a profound sensorineural hearing loss in both ears that is unresponsive to high-powered hearing aids, and they should have some speech and language experience.

The CLARION cochlear implant system by Advanced Bionics Corporation, Sylmar, CA, includes a cochlear stimulator/receiver that is surgically implanted under the skin behind the ear. External components include a sound processor box, cable and headpiece that incorporates a microphone and transmitter. The implant's critical component is the spiral-shaped electrode array, which extends from the stimulator/receiver and fits inside the cochlea. The array consists of 16 ultra-fine platinum/iridium wires. These ultra-fine wires deliver electrical signals to hair cells within the cochlea that correspond to the sounds' frequencies. Higher sounds are sensed near the cochlea's entrance, whereas lower sounds are sensed further in.

To manufacture this simple yet vital component, CLARION chose California Fine Wire (CFW), a Grover Beach, CA-based supplier of specialty wire products for industrial, military and scientific applications. The company has a long-standing relationship with Advanced Bionics' founder and CEO Alfred Mann, a world-renowned developer of medical products such as the first implantable and rechargeable pacemaker and implantable insulin pumps for diabetics. The cochlear implant array's effectiveness is heavily dependent on CFW's ability to maintain a high degree of consistency and quality in their production processes. Initially, large-diameter wire is drawn through a series of progressively smaller dies and rewound onto spools. Each pass through a die further reduces its diameter and dramatically increases its length. The wire quality and die condition is extremely important, as even a microscopic burr could produce an unacceptable scratch in the finished wire.

A patient speaks, hears

"At CFW the ends of the wires to be used in the arrays are formed into very small balls. These balls focus and direct the electrical current toward the interior of the cochlea where the nerve fibers are," explains Doug Lynch of Sylmar, CA. "The more focused you make the electrical signals, the more control you have over the patient's ability to receive and formulate signals." While neither a doctor nor design engineer himself, Lynch has a very personal interest in the device and is a living testament to its success.

Lynch's life changed drastically in 1992 when he suddenly became deaf. His immune system turned on itself, attacking his left inner ear and rendering him totally deaf on that side. Eight months later, in just one day, his right ear also failed. "My body attacked my own inner ears -- as if I were allergic to myself," he recounts. "My treatment at the time included very aggressive chemotherapy, which restored a little bit of hearing in one of my ears. Then, after weaning myself off of medication and using powerful hearing aids, the disease struck again and wiped out what I had struggled to regain through chemotherapy." Searching for solutions, Lynch soon discovered cochlear implant technology.

Upon implantation, an audiologist uses a computer to "tune" the implant to the individual patient's needs. Each patient's implant is programmed to provide the exact amount of electrical stimulation required, depending on the viability of the hair nerve fibers.

"When the device was first programmed. I was completely shocked and amazed that I could hear quite well," Lynch enthused. "In my own personal experience, and in almost every single situation, things sound just like they did before I lost my hearing. It's as pure and rich and beautiful as it was before," Lynch added that there has been a near complete restoration of his hearing, adding an appreciation for the CFW wire -- the interface between processor and cochlea responsible for transmitting signals that make these new lifetime experiences possible.