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Deafness and ‘miracle’ of cochlear implants

By on September 23, 2019 in Columnist with 0 Comments
Jim Brown

How we hear seems like science fiction, overcoming hearing loss seems even more amazing

By Jim Brown M.D.

In the United States there are 10 million people who are hard of hearing and 1 million who are functionally deaf. 

About 25 percent of U.S. adults 65-74 and 50 percent of those over 75 have disabling hearing loss. About 2 out of 1,000 newborns are born deaf and 90 percent of these are born to hearing parents. 

The average age of first time hearing aid users is 70. This subject is very personal to my wife and me who also use hearing aids and without them would be functionally deaf. 

The subject of hearing impairment became even more personal when our daughter-in-law recently underwent cochlear implant surgery. She had become completely deaf in one ear and was rapidly losing her hearing in her other ear. Hearing aids were not helping her. 

Untreated hearing loss is associated with a lower quality of life, depression, social isolation and cognitive decline. It can affect employment, earning ability, as well as can become a factor in accidents. 

There are many causes of hearing loss, but the main one seems to be aging. In addition to that, exposures to excessive noise, viral infections such as mumps, measles and shingles as well as meningitis and diabetes are suspect. 

Some medications can damage the ear and are considered to be “ototoxic,” including a few antibiotics that fortunately are not used that much currently. Some readily available medications like aspirin (8 to 12 pills taken daily for a long period of time), as well as anti-inflammatory meds like ibuprofen and naproxen if used in higher than recommended doses for a long time can cause ear damage. 

In addition, some autoimmune diseases can damage the auditory nerve. Rarely, a tumor of the auditory nerve can cause hearing loss in the affected ear. 

Our ability to hear is a very complex process. 

There are two main types of hearing loss. The most common is sensory-neuro hearing loss, which is permanent. This is caused by damage to the tiny hair-like cells in the inner ear or damage directly to the auditory nerve. This nerve carries the information about loudness, pitch and the understanding of speech to our brain. 

Sensory-neuro loss can also result in difficulty understanding speech even if it is loud enough to be heard. 

The other, conductive hearing loss, can be caused by a mechanical problem or injury in the outer or middle ear. It can even occur in the ear canal by earwax blocking the sounds from getting to the eardrum. 

How we hear seems to me quite miraculous. 

Sounds enter our outer ear where they vibrate our tympanic membrane (eardrum). This moves three tiny bones in the inner ear and vibrates them back and forth. 

The stapes bone vibrates against the cochlea that causes the fluid in the cochlea to move gently back and forth. The cochlea is a spiral shaped organ in our middle ear that looks somewhat like a small snail shell. The term cochlea comes from ancient Greek meaning snail. 

This movement of fluid releases chemical signals that stimulate the nerve fibers near the cochlea that then transmit signals to the auditory nerve and thus to the brain which then interprets them as sounds, words, music, and the like. 

This all seems to me like science fiction, but it is how we are made. 

In patients with deafness like my daughter-in-law’s, amplifying sound no longer helps the deaf ear to hear. Her only option was to get a cochlear implant before she was totally deaf in both ears. 

A cochlear implant is a neuro-prosthetic device that is surgically implanted in the skull.

Cochlear implants differ from hearing aids in two key ways. First, electrical signals are transmitted directly to nerve fibers in the auditory nerve, bypassing the outer and middle ear entirely. 

That means that the brain can detect signals from the implant even if the ear bones, cochlea, and hair cells are non-functioning, making implants effective, even for people with profound hearing loss. 

Second, unlike hearing aids, which are fitted and worn externally, the receiver and electrode of a cochlear implant must be surgically placed under the skin, into the cochlea itself.

A microphone that is worn on the back of the ear detects sounds and converts them to electrical signals. These signals are sent to a microcomputer processor that selects and amplifies certain frequencies to make speech easier to interpret. 

Those signals are passed to a transmitter attached to the outside of the head with a magnet. The transmitter sends the signals to a receiver that has been surgically placed under the skin, above the ear. The receiver sends signals to the inner ear, along a tiny cable, to a series of electrodes implanted directly in the cochlea. The signals generate electrical impulses along the electrodes that stimulate the nerve fibers surrounding the cochlea that in turn stimulate the auditory nerve, sending nerve signals to the brain. 

This is very complex, but it was necessary to try to explain how these implants work. It still seems like a miraculous mystery to me. 

As of 2017, it is estimated that 325,000 cochlear implants have been implanted worldwide. There were 96,000 implanted in the U.S., including 38,000 in children. 

It is estimated that the average cost can range from $30,000-$50,000 which includes the pre and post op doctor visits, the actual implant, surgical and hospital charges. In some cases insurance covers some of the cost of the implant. In Britain and Australia their National Health Service covers the total cost. 

After her surgery our daughter -in-law said her joy was “over the moon” when she started hearing out of her totally deaf ear. 

She said that the words sounded “robotic” at first and that it will take some time for the brain to adapt as it is now learning to convert different electrical signals into sounds and words. There obviously is a learning curve to all this, and she has exercises that eventually will get her there. 

As I write this, she texted me that it is getting better and better. She just had dinner in a noisy restaurant and she was able to hear and it has only been three weeks since her surgery. 

Her doctor said it will take three to six months to “hit the sweet spot.” She is well on her way already. 

Our joy for her is also “over the moon” thanks to modern surgery and this advanced technology. 

Jim Brown, M.D., is a retired gastroenterologist who has practiced for 38 years in the Wenatchee area. He is a former CEO of the Wenatchee Valley Medical Center.

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