Source – Children’s hospital, Boston
Hearing Aids
What are hearing aids?
More than three million children in the US have hearing loss. Hearing aids can help improve hearing and speech, especially in children with sensorineural hearing loss (hearing loss in the inner ear due to damaged hair cells or a damaged hearing nerve). Sensorineural hearing loss can be caused by noise, injury, infection, certain medications, birth defects, tumors, and problems with blood circulation.
Hearing aids are electronic or battery-operated devices that can amplify and change sound. A microphone receives the sound and converts it into sound waves. The sound waves are then converted into electrical signals. Children as young as 2 months can be fitted with hearing aids.
Although the hearing aid can amplify sounds to achieve a “comfort level” of loudness for listening, the hearing aid can not correct for distortion of sounds caused by damage to the delicate hair cells in the inner ear or to the nerve endings which are stimulated by the hair cells. For many mild or moderate hearing losses, the hearing aid can make almost normal clarity of speech possible in a quiet room. However, for many severe or profound hearing losses, the speech heard through a hearing aid may not be clear enough to understand completely; it may sound like a weak, distorted telephone connection. Therefore, the listener uses lipreading or sometimes sign language to add to the understanding of speech through a hearing aid.
Although hearing aids do not provide perfect correction for hearing loss in the manner in which eyeglasses can correct some vision losses, the hearing aids combined with proper training in language and listening are enormously important for communication skills in a child with impaired hearing. In fact, the consistent use of properly functioning hearing aids, fitted as early as possible in infancy, is the single most important factor in the development of spoken language in a hearing-impaired child. However, the hearing aids must be used in the context of good language and listening stimulation in order for the child to learn to make sense of the amplified sounds.
What are the different types of hearing aids?
The type of hearing aid recommended for your child will depend on several factors, including his/her physical limitations, medical condition, and personal preference. There are many different types of hearing aids on the market, with companies continuously inventing newer, improved hearing aids. However, there are four basic types of hearing aids available today. Consult your child’s physician for additional information on each of the following types:
Who may be a candidate for hearing aids?
Nearly all children who have a hearing loss that may be improved with hearing aids can benefit from these devices. The type of hearing aid recommended may depend on several factors, including, but not limited to, the following:
the shape of the outer ear (deformed ears may not accommodate behind-the-ear hearing aids)
depth of depression near the ear canal (too shallow ears may not accommodate in-the-ear hearing aids)
the type and severity of hearing loss
the manual dexterity of the child to remove and insert hearing aids
the amount of wax build-up in the ear (excessive amounts of wax or moisture may prevent use of in-the-ear hearing aids)
ears that require drainage may not be able to use certain hearing aid models
Wearing a hearing aid:
Once the hearing aids have been fitted for the ears, your child should begin to gradually wear the hearing aid. Because hearing aids do not restore normal hearing, it may take time to get used to the different sounds transmitted by the device. The American Academy of Otolaryngology recommends the following when beginning to wear hearing aids:
Be patient and give your child time to get used to the hearing aid and the sound it produces
Start in quiet surroundings and gradually build up to noisier environments.
Experiment where and when the hearing aid works best for your child.
Keep a record of any questions and concerns you have, and bring those to your child’s follow-up examination.
Taking care of hearing aids:
Hearing aids need to be kept dry. Methods for cleaning hearing aids vary depending on the style and shape. Other tips for taking care of hearing aids include the following:
Keep the hearing aids away from heat.
Batteries should be replaced on a regular basis.
Avoid the use of hairspray and other hair products when the hearing aid is in place.
Considerations when purchasing a hearing aid:
A medical examination is required before purchasing a hearing aid. Hearing aids can be purchased from an otolaryngologist (a physician who specializes in disorders of the ear, nose, throat, and related structures of the head and neck), an audiologist (a specialist who can evaluate and manage hearing and balance problems), or an independent company. Styles and prices vary greatly. The National Institute on Deafness and other Communication Disorders recommends asking the following questions when buying hearing aids:
Can the hearing loss be improved with medical or surgical interventions?
Which design will work best for my child’s type of hearing loss?
May my child test the hearing aids for a certain period of time?
How much do hearing aids cost?
Do the hearing aids have a warranty and does it cover maintenance and repairs?
Can my child’s audiologist or otolaryngologist make adjustments and repairs?
Can any other assistive technological devices be used with the hearing aids?
Hearing aids typically need to be replaced after about five years. New, programmable and digital hearing aids, that can be adjusted as the level of hearing changes, may reduce the need for replacement.
What are the parts of a hearing aid?
The MICROPHONE changes sounds into electrical energy. Its location on the hearing aid is important, because the sounds closest to the microphone will be picked up most readily. The microphone of a body-level aid should not be covered by loose, bulky, or starched clothing, and should be protected from food or water falling onto it.
The AMPLIFIERS boost the electrical signal coming from the microphone. The amplifiers are located inside the hearing aid, and you will never see them, except in an aid taken apart for demonstration.
The RECEIVER changes the amplified electrical signal back into sound. For a body-level hearing aid, the receiver looks like a button and snaps onto the earmold. For an ear-level (behind-the-ear or in-the-ear) hearing aid, the receiver is inside the case of the aid and is not visible.
The BATTERY supplies power to the hearing aid.
The EARMOLD carries the sound into the ear canal, holds the hearing aid in place, and (when properly fitted) prevents acoustic feedback or squealing by not allowing the amplified sound to get back to the microphone.
The TUBING (of a behind-the-ear hearing aid) carries the sound from the receiver outlet through the earmold.
The CORD (of a body-level hearing aid) carries the electrical signal from the amplifier to the receiver.
Which is better, one hearing aid or two?
A hearing aid with a receiver going into just one ear is called a monaural hearing aid fitting. A binaural fitting consists of separate receivers going into each ear. A binaural fitting can be accomplished by using two separate hearing aids (one for each ear) or by using a body-level hearing aid which has two microphones, one on each side of the aid, with separate receivers for the two ears. When a Y-cord is used with a body-level aid, then the input from a single microphone is amplified and fed to both ears, so that both ears receive the same signal.
When there is some residual hearing present in each ear, two hearing aids are better than one. With only one hearing aid, it is nearly impossible to tell what direction a sound is coming from. Two hearing aids also help the listener to “tune in” to one voice in a noisy room. Two hearing aids are recommended for nearly all young children with hearing impairment unless it is proven that one of the ears has no residual hearing or can not benefit from amplified sound.
Which hearing aids are best for my child?
Your audiologist will decide which model of hearing aid suits your child’s hearing loss. The decision is based on several factors including the degree of loss, the slope (frequency response) of the audiogram, the possible need for future adjustments in amplification, and the size and fit of the aid on the ear.
What switches and controls are on the hearing aid?
Some hearing aids have several switches and controls on the hearing aid. Others have a remote control to change the settings on the aids, much like changing the channel and volume on your television set. Others have very few controls because they are programmed by a computer to adjust to the listening environment automatically.
Some hearing aids have an on-off switch which is separate from the volume control. Others have an on-off switch which is part of the volume control or the battery compartment, or part of the input selection (MTO) switch (see below). Some aids, however, can be turned off only by removing the battery from the battery contacts.
The input selection switch (if present) should be set to the “M” (microphone) position for normal use, and to the “T” (telephone coil) for using the telephone. If the input selection switch has an “MT” position, then both the sounds in the room and the telephone conversation can be amplified at once. The “O” position, if present, turns off the hearing aid.
If the hearing aid has a volume control (gain control), it is a toggle switch or rotating wheel which can be adjusted for comfortable listening in different situations. A volume control setting will be recommended by the audiologist.
On hearing aids that are not programmed by a computer, there may be two, three or four internal screw controls (potentiometers) on the hearing aid, hidden under a panel. The tone control de-emphasizes certain pitch ranges of the amplified sound, to suit the individual hearing loss. The output control insures that the amplified sound never surpasses the maximum intensity which the ear can use and tolerate. Although you should not change the screw settings on your child’s hearing aid, you should know the recommended settings in order to check the screw positions after any hearing aid repair.
How is hearing aid amplification measured?
Intensity is measured in decibels (dB). The more intense the sound, the more decibels it has. We hear changes in intensity as changes in loudness of the sound. Hearing loss can be measured in decibels; the loss of hearing for a particular sound is expressed as the number of decibels required for the individual with the hearing impairment to hear the sound as compared to the number of decibels required for someone with normal hearing to hear the sound.
Frequency refers to the “low” (bass) or “high” (treble) quality of the sound, or its pitch. Frequency is measured in Hertz (Hz), which means cycles per second (cps). Most hearing aids amplify sounds which fall into a frequency range of about 300-4000 Hz. This range covers most of the frequencies present in human speech, and covers slightly more than the frequency range transmitted by a telephone.
The gain of the hearing aid, expressed in decibels, is the amount by which the hearing aid amplifies sounds. For example, a hearing aid which takes an input level of 60 dB (about the level of an average conversation) and amplifies it so that the receiver puts out a level of 105 dB would be said to have a gain of 45 dB (because 105 dB – 60 dB = 45 dB). When you turn up the volume control of the hearing aid, you are increasing its gain. Most hearing aids have a full-on gain (the amount of gain provided when the volume control is all the way up) somewhere between 30 and 70 dB, depending upon the severity of the hearing loss.
Now what happens when an intense sound — for example, a 100 dB fire siren — comes into a hearing aid which has a gain of 60 dB? Surely the hearing aid does not feed a level of 160 dB into the ear, for this would exceed the pain threshold of the ear. Every hearing aid has a maximum power output (saturation level) beyond which the hearing aid simply will not amplify sounds. Most hearing aids have a maximum power output between 100 and 138 dB, again depending upon the severity of the loss and the ear’s ability to use and tolerate intense sound. For example, if the aid has a maximum power output of 127 dB, then the 100 dB fire siren will be amplified only to 127 dB even though the aid may have a gain of 60 dB for weaker sounds. Some hearing aids with advanced circuitry amplify soft sounds to a comfortable level without amplifying loud sounds to the point of distortion.
Unfortunately, no hearing aid can amplify and reproduce sound perfectly, without distorting it a little bit. A two-ounce hearing aid can not produce the sound quality of forty pounds of stereo equipment! The way in which the hearing aid changes the sound quality in an undesirable manner is called distortion. When the distortion level is high, speech reproduced by the aid sounds slurred, harsh, or unnatural. Sometimes a high level of distortion is the fault of the receiver, which may have been dropped once too often. In a body-level aid, the receiver can be replaced easily. In a behind-the-ear aid, high distortion levels necessitate a factory repair of the aid.
Why do hearing aids cost so much?
Each hearing aid costs from several hundred dollars to over two thousand dollars. The high cost reflects the technology used to develop the miniaturized components of the aid, and the mark-up to cover the dispenser’s services. If hearing aids were sold as often as calculators, the price would drop consi-derably; however, they are a low-volume item as markets go. Hearing aids can be covered entirely by Medicaid if your child is eligible for a Medicaid card. For families who are not eligible for Medicaid, there is an income-dependent state program in Massachusetts to cover the cost of hearing aids; your audiologist will tell you how to apply. A very few health insurance policies cover part of the cost of hearing aids; check with your insurance company. There are various charitable organizations to which you may apply if you can not pay for your child’s hearing aids.
How long will a hearing aid last?
A hearing aid lasts three to six years on a child, although the type of aid may need to be changed sooner if the child’s needs change. The hearing aid itself is not outgrown but begins to need frequent repairs as it gets older. The earmolds, however, need to be remade every few months as the child’s ears grow.
Occasionally a hearing aid is lost. First, look for it everywhere, enlisting the child’s help. Most manufacturers do offer damage or loss/damage coverage for at least one year after the date of the fitting. Find out about this coverage from the vendor, and be sure to purchase separate loss/damage insurance when the manufacturer’s policy runs out.
How are hearing aid batteries kept and checked?
Learn the type of battery used in the aid (both the size and the type).
Store unused batteries in a cool, dry place. Keep extras on hand. The refrigerator is not a good place to keep batteries, because it is too accessible to children. A battery should be at room temperature and dry when it is inserted into a hearing aid. If you are using zinc-air batteries, remove the tab on the back of a new battery and let it breathe for a few minutes before inserting it into the aid.
Have a battery tester and discard (or recycle) batteries when the voltage drops below the specified range. If you have no battery tester handy, the battery is dead if you hear no feedback (squeal) from the aid when it is on but not in the ear. Check batteries at night after a day’s use. A nearly dead battery will recover a bit overnight and may seem fine in the morning, but may only last a few minutes.
Keep batteries out of reach of children, like medicines or household chemicals.
How should we take care of hearing aids?
The hearing aid is a delicate electronic instrument. These simple rules will extend its life and lessen the frequency of repairs:
Do not leave the hearing aid on a radiator, stove, windowsill, glove compartment, car seat, dashboard of the car, or any other hot or cold place.
Leave the aid off the child when drying the child’s hair with a hair dryer.
Keep the aid dry. Keep it out of a steamy bathroom. Take the aid off the child for bathing, showering, or swimming. In rain or snow, take the aid off or cover it with a hood or umbrella. If the aid gets wet, dry it immediately with a soft cloth, remove the battery, and dry it with a hair dryer on the lowest setting from a distance of two feet. If your child perspires heavily, store the aid overnight in a tightly closed container with a silica gel packet to absorb the moisture. Condensation in the tubing from perspiration or earmold washing should be blown out with an infant’s nasal syringe, with the earmold and tubing detached from the aid.
Never spray the child’s hair with hair spray when the aids are being worn.
If there is visible corrosion on the battery contacts, take the aid to the hearing aid dispenser to be cleaned.
Open the battery compartment of the aid or remove the batteries overnight, to prevent corrosion and improve battery life.
How can I check my child’s hearing aid?
The following items are helpful for checking and maintaining a hearing aid: a hearing aid stethocope (“stethoset”) to listen to the aid (or an earmold custom-made for a parent); a battery tester which will test batteries in the 1.3-1.5 volt range; and a baby’s nasal syringe or earmold squeeze bulb.
A child’s hearing aid must be checked daily, because the child may be too young to tell you when something is wrong. If you perform a systematic check of the hearing aid’s function, you can find the cause of many simple malfunctions causing dead, weak, squealing, intermittent, or scratchy sound. Use a fresh battery when checking the aid.
First look at the aid carefully. Is the aid turned on? Is the input selection switch on “M,” not “T”?”
Are the battery contacts clean? Is the battery inserted properly and the compartment clicked shut all the way?
For a behind-the-ear aid, is the tubing free of cracks or holes? Does it fit snugly onto the aid? Is the earmold channel free of wax or moisture? Remove the tubing from the tone hook and use a squeeze bulb to blow out any moisture you see in the earmold or tubing.
For a body-level aid, look at the receiver and cord carefully. Is the insulation worn? Do both plugs fit firmly into the receiver and the aid? Is the receiver cracked or its casing loose? Is the earmold clean, and does it have a metal ring which snaps tightly to the receiver (with plastic washer if used)?
Put the aid to your ear, using an earmold or hearing aid stethoset. If the hearing aid has a volume wheel, are there any sudden jumps in loudness as you turn the volume control wheel? (The volume should increase smoothly as you turn the wheel.) Does the wheel itself turn smoothly? Is the sound scratchy as you turn the wheel, as though dust has entered the control? Leaving the volume at one level, listen for gross distortion of the sound and for the level of background noise (hum or hiss) from the aid itself.
For a body-level aid, roll the cord in your fingers at several places as you listen, to check for scratchiness or “cut-out” due to worn insulation. Wiggle the connections of the cord at each end; the sound should not cut out.
Check the source of any whistling by removing the aid and holding a thumb firmly over the canal opening of the earmold, with the aid full on. If you hear whistling, remove the tubing from the aid (for a behind-the-ear aid) or the earmold from the receiver (for a body-level aid) and now hold your thumb over the sound outlet. If there is no whistling now, the cause was a leak in the tubing or its connection (for a behind-the-ear aid) or between the earmold and receiver (for a body-level aid). If whistling persists, and the receiver is not cracked, then the aid probably has internal feedback and must be serviced by a repair facility.
With the aid on your child and adjusted to its customary volume setting, is there feedback (squealing) as the wearer moves his head back and forth and moves his jaw? If so, and earlier steps have yielded no problems, then the earmold is too small. The wearer should be able to turn the volume up at least a little beyond the customary volume setting without feedback, so that the volume setting is never dictated by the level at which feedback occurs.