Amplification is the best rehabilitative strategy if the hearing loss cannot be treated medically or surgically. A sensorineural hearing loss does not preclude benefit from a hearing aid. Likewise, audiometric configuration (pattern of loss across frequencies), decreased speech discrimination, and the presence of recruitment (an abnormally rapid rise in perceived loudness with increased signal level) do not exclude the possibility of successful hearing aid use.
A person with a sharply sloping pattern on audiometric tracings, severely decreased speech discrimination ability, or greatly reduced dynamic range (difference between the threshold of sensitivity and the threshold of discomfort) may have difficulty adapting to amplification devices. However, no single finding in the history, physical examination, or audiometric evaluation can accurately predict how well a patient with presbycusis will be rehabilitated with amplification. Factors that contribute to successful accommodation to amplification include the patient’s desire to communicate (socially and vocationally), expectations and motivation, manual dexterity, and audiometric characteristics. Audiologists experienced in interacting with elderly persons and in dealing with physical and psychologic limitations are most likely to succeed in arranging appropriate amplification.
AMPLIFICATION
Certain guidelines help when communicating with any hearing-impaired person. Communication is most effective when competing environmental sound is absent or minimal. The speaker must first ensure that his face is well illuminated and that the listener is attentive. Optimally, the speaker should be about 3 ft from the listener’s better or aided ear, lips and facial expression should be visible, and speech should be slow and clear. Shouting is not necessary and may worsen the patient’s ability to discriminate. If the person misunderstands a statement, it should not be repeated word for word; instead, the original statement should be paraphrased.
Assistive Listening Devices
These devices help hearing-impaired persons overcome problems using the telephone, television, or radio and communicating in small or large groups. Portable and nonportable amplifiers boost telephone speaker output, and special devices signal an incoming call with either a louder ring or a flashing light. Other devices can sufficiently amplify television and radio signals for the hearing-impaired person while family members listen at normal volume levels. Telecaptioning may benefit those with good vision whose residual hearing is not sufficient to benefit from amplified sound signals.
For small-group communication (eg, in card games), relatively inexpensive devices that have a portable microphone, amplifier, and headset can be used. For large-group communication (eg, in a concert hall or church), many public facilities have group amplification systems such as infrared transmission, and the person can borrow a special portable receiver.
Hearing Aids
Amplification with hearing aids can help persons with conductive or sensorineural hearing losses. Although hearing aids vary in size and power, they share certain features. A microphone receives the sound, transforms it into electrical energy, and sends this signal to an amplifier that increases its energy. How much the incoming signal is amplified, as manifested in the output of the hearing aid speaker, is known as gain. The earmold channels the hearing aid output into the ear canal and affects the acoustic characteristics of the delivered signal.
The hearing aid evaluation matches the patient’s auditory thresholds across the frequency band and speech discrimination ability with the type of hearing aid recommended for those characteristics. Some patients with relatively normal pure-tone thresholds demonstrate very poor speech discrimination and are less likely to benefit from a hearing aid. Some patients with hearing loss and recruitment will require a hearing aid with input automatic gain control and output limiters, technologic advances that prevent pain from overamplification.
When the type of hearing aid is selected, the patient should be taught how to adjust the device and how to keep it clean and functional. Important factors in determining whether a patient will be a successful hearing aid user include motivation, the need to communicate, and appropriate expectations for what can be achieved with the hearing aid. The social stigma as well as the expense of the hearing aid may be difficult to overcome.
For a time, the most widely used hearing aid was the behind-the-ear or postauricular version. The bulk of the device is hooked above and posterior to the pinna; it is connected to the earmold by flexible tubing. Improvements in technology have made it possible to assemble all the required components into a shell small enough to be inserted in the ear; these in-the-ear aids have become popular, in part because they are so unobtrusive. Generally, the smaller the device, the less powerful it is. More important, inserting and adjusting these small devices may be difficult for some elderly persons. Eyeglass-mounted aids have diminished in popularity, although they remain useful for some.
The contralateral routing of signals (CROS) aid is for those whose hearing is totally lost in one ear and relatively normal in the other. A microphone directs sound from the poorer-hearing to the better-hearing ear. If the better-hearing ear is also impaired, the signal from the poorer-hearing ear can be amplified; this type of device is called a BiCROS aid. Originally, the two devices were connected by cords, but newer models can communicate via FM signals.
A body aid, the most powerful type available (ie, producing the highest gain), may be concealed in a pocket or worn with a body strap and is connected by wires to the earpiece, which is connected to the earmold. The elderly, particularly those with impaired fine motor skills, may find it easier to manage the controls of a body aid. Alternatives include geriatric molds, designed for easier handling, and remote controls similar to a credit card to facilitate adjusting settings.
Hearing aids have various modifications, according to individual need. The T switch enables telephone communication through the hearing aid. Circuitry modifications include automatic gain control, automatic signal processing, and multiple signal processing. Automatic gain control automatically adjusts loud or soft sounds to about the same volume. Automatic signal processing and multiple signal processing attempt to improve the signal (human speech)-to-noise ratio and thus ameliorate hearing ability.
In contrast to air-conduction aids, which require an earmold, the bone-conduction aid is placed in direct contact with the head, usually over the mastoid, with a headset. Bone-conduction aids may be appropriate when an in-the-ear aid is contraindicated, as in persistent, uncontrollable otorrhea or canal atresia.
Cochlear Implants
The cochlear implant is approved for profoundly deaf adults who derive no benefit from the most powerful hearing aid. A microphone picks up the incoming sound and sends it to a speech processor; the processor modifies the signal and transmits it to external circuitry, which then relays the information to the receiver in the implanted device. From the internal circuitry, one or more electrodes implanted in the cochlea stimulate the remaining neural elements of hearing.
Implantation generally requires mastoid surgery and brief hospitalization. The device is expensive, and insurance coverage varies. Although it serves a limited population, the cochlear implant can make a tremendous difference in the life of a totally deaf and otherwise isolated person.
Vibrotactile Devices
Vibrotactile devices are alternative modes of rehabilitating profoundly deaf persons; vibrators placed either on the wrist or sternum or around the waist transform speech and environmental sounds into vibrations that can be perceived on the skin. With appropriate training, patients can learn to identify and localize sounds and can use the vibrotactile information to communicate better.
AUDITORY REHABILITATION
The goal of rehabilitation is to achieve the best hearing possible by using a combination of amplification, speech reading, and auditory training.
Speech Reading
The term speech reading has replaced lip reading because linguistic information is obtained not only by watching the speaker’s lips but also by following facial expressions and gestures. Such visual cues may be an adjunct or an alternative to hearing aids. Decreasing visual acuity and poor short-term memory may militate against mastering speech reading.
Auditory Training
Auditory training is often combined with an amplification device to maximize benefit. Auditory training can help patients discriminate between distinctly differing sounds with hearing alone, eventually enabling them to develop schemes for making fine distinctions, particularly between similar speech sounds. In essence, such training makes the patient more aware of subtle auditory clues.
With auditory training, as with any aspect of auditory rehabilitation, having interested family members accompany the geriatric patient is helpful. Family members not only can provide encouragement and support but also may prompt the older patient when short-term memory fails.