New Hope for Hearing

More than 17 million Americans suffer from some degree of hearing loss. Many are older people whose deafness is caused by progressive nerve damage, which can often be corrected by artificial hearing aids. But a significant number are younger people whose impairment is triggered by disease or injury to the tympanum and ossicles (see diagram), the eardrum and tiny vibrating bones that transmit sound waves to the inner ear.

Until recently, surgeons had only one method of correcting damage to the eardrum--repair of the tympanum with tissue usually taken from the fibrous lining of the ear muscle. This operation sometimes thickened the eardrum and thus produced only questionable improvements in hearing efficiency. Now surgeons are perfecting a technique for replacing damaged eardrums and ossicles with healthy donor tissue. The operation offers some new hope for an escape from hearing impairment.

For years, doctors who tried eardrum transplants were hampered by their inability to preserve a donor's tissue until it was needed. One solution to their problem was developed by Dr. Rodney Perkins, of Palo Alto, Calif., who tried the buffered formaldehyde solution that has proved successful in the preservation of heart valves. The formaldehyde not only preserves the eardrum and helps retain its shape, but may even improve its tensile strength as well. As a result, doctors can now obtain healthy eardrums and ossicles from deceased donors and store them in an eardrum bank for up to seven months before they are used.

Although harvesting and storing eardrum tissue is no longer difficult, the transplant procedure remains delicate. Surgeons make an incision behind the recipient's ear and cut away any diseased or damaged portions of the hearing organs before replacing them with the donor tissue.,If only the donor's eardrum is used, it is fastened to the patient's ossicles with a nylon sling. If the donor's ossicles are used as well, they are connected to the patient's remaining ear bones so that sound vibrations can be conducted unimpeded to the inner ear.

The new ear parts, which take from one to five hours to implant, do not of themselves restore the patient's hearing. Instead, they serve as a scaffolding over which the patient's own ear-canal skin grows to form new ear tissue. The operation does, however, substantially reduce hearing loss. Most eardrum-damaged patients have moderately severe impediments. In most cases, the implants have improved their hearing to within the normal range.

Tissue rejection, which has led to the failure of other transplant operations, has yet to prove a problem in eardrum homografts. Nor have other complications arisen. Doctors across the country have performed about 70 such operations since 1968. Perkins, who has done 30 of them, reports that 90% of the new eardrums are still in place and intact.

When people have been deaf since birth, they often cannot reproduce speech because they have never heard sounds. To help them learn to speak, Ohio State University's Bio-Medical Engineering Coordinating Committee has developed a device called a visual vocoder that translates sounds into patterns of light. Soon to be used to teach children at a state school for the deaf, the machine features a display board containing 40 vertical rows of twelve lights each. Words spoken by a teacher into a microphone are converted into lights that march across the board from right to left, forming a recognizable pattern. Deaf children then try to duplicate the pattern. By comparing their own sound patterns with those of their teacher, the children can adjust both the pitch and volume of their voices and, through practice, learn to speak the words they cannot hear.

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