Hearing Aids
- Author: Suzanne H Kimball, AuD, CCC-A/FAAA; Chief Editor: Arlen D Meyers, MD, MBA more...
Products
Hearing aids can be defined as any devices that amplify the acoustic signals to a degree that enables individuals with hearing loss to use their remaining hearing in a useful and efficient manner.
Category
Hearing aids
Device details
Body hearing aid
The photograph below is an example of a body hearing aid.
Body hearing aid. Image courtesy of Wikimedia Commons. Rexton
- Fusion PP Body Aid
- Model-HA 20-DX Body Aid
Behind the ear (BTE)
The images below depict behind-the-ear hearing aids.
Behind-the-ear (BTE) hearing aid. Image courtesy of the National Institutes of Health (NIH). 
Open-fit behind-the-ear (BTE) hearing aid. Image courtesy of the National Institutes of Health (NIH). This list of current hearing aid manufacturers and products, shown below in alphabetical order, is not exhaustive. Other products are available for consumers.
Oticon
- RISE 2 Platform Series
Phonak
- Spice Generation
Resound
- Alera Series
Siemens
- BestSound Technology
Starkey
- Wi Series
Widex
- Clear Series
In the ear (ITE)
The images below depict in-the-ear hearing aids.
In-the-ear hearing aid (ITE). Image courtesy of the National Institutes of Health (NIH). 
Completely in-the-canal (CIC) hearing aid. Image courtesy of the National Institutes of Health (NIH). Design Features
The first hearing aids were mechanical resonating devices that included tubes and horns of various sizes. In the early 1900s, electrical instruments replaced mechanical hearing aids. The first truly wearable electrical hearing aid was manufactured in the 1930s; in the 1950s, transistors were introduced into hearing aids. Since the 1950s, hearing aids have become smaller, and battery cost has lessened.[1]
According to the Better Hearing Institute, nearly all hearing aids currently sold in the United States are digital.
Analog vs digital
The foundation for today's digital hearing aids was developed around the time of World War II; however, the first wearable digital aid was not produced until the mid 1980s. In the 1990s, programmable digital hearing aids were developed, which allowed for clearer sound quality and precise fitting paradigms.
The development of digital hearing aid technology has been the most significant advancement with these devices since the introduction of the earlier electric hearing aids. Current digital technology is able to address listener needs that previous technology was not able to accommodate, such as reducing acoustic feedback, increasing the audibility of speech sounds, and reducing background noise.[2] Digital aids can also provide for connectivity with devices such as cell phones, computers, televisions, and MP3 players.[3]
Some analog hearing aids can be digitally programmed; the digital programmer can adjust the gain, frequency response, and output of the analog circuit. Some analog hearing aids also may have multiple channels (frequency bands) that can be digitally programmed. Although programmable analog aids are still on the market, 90% of current hearing aid technology is digital.
The difference between a digital signal processing (DSP) hearing instrument and an analog aid is that the analog signals from the microphone are converted into a digital form by an analog-to-digital converter. Once in the digital form, the signals are manipulated by sophisticated processing algorithms and then converted back to analog form by digital-to-analog conversion.
The digitally controlled hearing aids usually use an external programming unit that the dispenser uses to adjust the gain, output, and frequency response of the unit. Many of these aids have multiple channels that allow the dispenser to program individual gain, output, and compression for each frequency channel. Up to 15 channels are available in current high-end digital hearing aids.
Most of the digital hearing aids and some of the digitally programmed analog hearing aids use a common computer platform database called NOAH. This database can carry the audiometric information and office-based information on each patient. Software from each manufacturer can be installed on the platform. The aids are connected to a common interface (HI-PRO or NOAH link) that allows the software from the manufacturer to interface with the hearing aid. The fitting paradigms vary with each manufacturer. Wireless programming options are now available with current hearing aid technology.[4]
See also Implantable Hearing Devices, Bone-Anchoring Hearing Aids, Surgical Placement of Bone-Anchored Hearing Systems, and Hearing Impairment.
Basic components and functions of hearing aids
The basic components of a contemporary hearing aid include a microphone, an amplifier, a receiver, and a power supply.
Microphones
A microphone is a transducer that converts the sound signal into electrical energy. The amplifier is a transformer that increases the amplitude of the electrical signal that is sent to the receiver. The receiver then changes the modified electrical signal back into sound energy that is directed into the ear. Power is supplied to the hearing aid via a battery.
Various microphones, amplifiers, and receivers are used, depending on the type and degree of hearing loss. The American National Standard Institute's (ANSI) American National StandardSpecification of Hearing Aid Characteristics specifies the electroacoustic tests that a manufacturer must perform and publish for each hearing aid before the instrument is shipped.[5] The standard states the tolerance allowed so that the audiologist can perform the same tests to verify the performance of an instrument against specifications.
Currently used hearing aid microphones are primarily electrical devices that have good linear behavior over a frequency range of 50-6000 Hz. This range can be modified to be more appropriate for specific hearing losses.
Directional microphones have been developed that can vary with both the amplitude and the direction of the sound source relative to the microphone. They can reduce the sounds coming from the back of a hearing aid wearer compared with the sounds coming from the front by as much as 15 decibels (dB). This change can greatly improve the signal-to-noise ratio (SNR) of the listener and, thus, the understanding of speech in the presence of noise. Directional microphones have been used as early as the 1970s as a way to improve speech understanding in noisy surroundings.
In recent years, digital signal processing (DSP) has been incorporated into the design of directional hearing aids, and hearing aids with adaptive directional microphones have been introduced. With adaptive directional microphones, the directional pattern changes depending on the signal azimuth, intensity level, and duration. In other words, adaptive directional microphones are designed to ensure the best SNR for the wearer regardless of the location of the sound source. This technology has also been shown to improve speech intelligibility in the presence of background noise.[6]
Amplifiers
Hearing aid amplifiers are transformers primarily composed of transistors that are built into an integrated circuit. These transistors provide a current source and serve a variety of functions. In these transistors, the primary function of the amplifier is to increase the power of the electrical signal received from the microphone.
Typically, hearing aids have 2 or more stages of amplification. The first stage is the preamplifier, which is at the level of the microphone. The preamplifier helps to amplify the initial input signal. At this level, the gain is relatively low.
Most amplification is supplied by the power amplifier. These amplifiers are typed in a particular class. The most common are referred to as class A, class B, and class D. They are distinguished by their power consumption, gain, and output abilities.[7]
Each amplifier can be modified to limit the maximum output of the hearing aid. For linear amplification, the amplifier may be limited by peak clipping, which occurs when the electrical signal exceeds the maximum output of some component of the hearing aid circuit. This type of limiting causes various forms of distortion that have been found to reduce the intelligibility and the subjective quality of speech.
A hearing aid that has some type of level-dependent signal processing is termed a nonlinear hearing aid. Most nonlinear hearing aids reduce gain as input or output levels increase.
Nonlinear hearing aids are designed to amplify a wide range of sounds so that they are audible to the hearing-impaired listener without becoming uncomfortably loud. These aids usually use some form of compression circuit that reduces the gain of the instrument when either the input to the device or the output of the device exceeds a predetermined level. This process results in comfortable amplification for the wearer and prevents the hearing aid from saturating.
Compression hearing aids can provide amplification of the speech components that are essential for intelligibility and can reduce impulsive or high-level sounds that normally cause discomfort.
Receivers
The hearing aid receiver is an output transducer and handles more power than a microphone. Receivers in hearing aids are very small because of cosmetic considerations.
In general, larger receivers can supply larger output signals. Therefore, the small receivers on hearing aids may be taxed to their output capabilities.
The receiver must also be chosen to match its amplifier. A mismatch in design produces limited output and increases distortion.
Current advances in receiver technology have allowed hearing aids to amplify much higher frequencies than previous generation hearing aids, which is beneficial for individuals with high-frequency hearing loss.
Because of the receiver's open position in the external ear canal for in-the-ear and receiver-in-the-canal hearing aids, it is vulnerable to damage from debris in the ear canal and from the receiver being dropped. Manufacturers state that approximately 40% or more of hearing aids returned for service have damage or blockage to the receiver.
Power supply
The power supply to the hearing aid is derived from its battery. Mercury- or silver-based batteries were used to supply power to hearing aids for many years; however, most hearing aid batteries in use today are zinc-air cells.
The primary feature of the zinc-air cell is its longer shelf life compared with the mercury- or silver-based hearing aid batteries. Zinc-air cells are not activated until a tape seal is removed from the positive side of the battery. This side contains small holes through which air enters to initiate activation. In most situations, the zinc-air cells last longer than their mercury counterparts.
Hearing aid batteries have a relatively flat discharge rate, and the battery's capacity is rated in milliampere hours (mAh). If the current drain of a hearing aid is known, an estimate of the expected life of the battery can be calculated by dividing the battery's capacity by the current drain measured in milliamperes (mA).
In general, digital hearing aids require more battery power than analog aids; therefore, battery life is shortened relative to the previous-generation hearing aids. Solar-powered hearing aids and rechargeable nickel-metal hydrate batteries may become options at some time in the future.[3]
Technical considerations
Effects on sound quality
With any digital hearing aid, sound quality can be affected at any stage, including the microphone, the A/D converter, the signal processor, or the receiver. Bandwidth and input saturation level can affect microphone performance; input saturation level, sampling rate, and bit resolution can affect the A/D converter; the number of channels, algorithms, compression characteristics, directionality, and feedback all can have an effect on signal processing; and bandwidth and output saturation level can affect the receiver.
Recent hearing aid technologies
Among recent technologies for hearing aids are linear frequency transposition and music synthesizers, as well as potential tinnitus maskers.
Some hearing aids are equipped with linear frequency transposition capabilities, which are used in individuals with precipitous high-frequency hearing losses or dead regions in the basal end of the cochlea. These individuals often miss high-frequency information, such as consonant sounds like /s/, /f/, and /th/ or environmental sounds, such as birds chirping. Linear frequency transposition "lowers" the high-frequency input sounds to an audible frequency for the wearer. For example, if someone has audible hearing only up to 3000 Hz, then sounds that occur above that range are transposed into the frequency range below 3000 Hz so that the higher frequency sounds are heard.[8, 9]
With regard to music synthesizers, at least one hearing aid currently available on the market has a patented relaxation program that uses fractal technology to generate soothing harmonic tones and chimes that can aid the patient in relaxation and concentration. This technology is also currently being tested for use as a tinnitus masker.[10]
Hearing aid sizes and styles
Body hearing aid
The first wearable electronic hearing aid was the body hearing aid (see image below). This type of aid included a variably sized case that was worn on the body of the user and contained the microphone, amplifier, battery, on/off switch, and volume control. Leading from the case were the receiver cord and the receiver. Attached to the receiver was an ear mold that was fitted to the wearer's ear. Because of the size of the aid and the placement of the microphone on the body rather than in the ear, very few body aids are currently dispensed.
Body hearing aid. Image courtesy of Wikimedia Commons. Behind-the-ear (BTE) hearing aid
The behind-the-ear (BTE) hearing aid is worn behind the pinna (see image below). The body of the instrument contains the microphone, amplifier, receiver, on/off switch, and volume control. Leading from the receiver is the ear hook, which loops around the ear and carries the amplified sound to the tubing attached to the ear mold.
Behind-the-ear (BTE) hearing aid. Image courtesy of the National Institutes of Health (NIH). The BTE hearing aid was the most common aid dispensed from the early 1960s until the early 1980s. Beginning in 1983, in-the-ear (ITE) type hearing aids captured the largest part of the hearing aid market. In 1987, approximately 80% of hearing aids dispensed in the United States were ITE instruments; most of the remaining hearing aids were BTE instruments. Currently, however, BTE hearing aids have regained much of the market share owing to the availability of open-fit BTE aids.
These BTE aids are very small and are nearly invisible when fit behind the ear. The longer thin tubing and fitting software allow access to higher frequency amplification with increased bandwidth from 6000-8000 Hz.[11] These open-fitting hearing aids provide excellent sound quality, better directional microphone placement, and less occlusion compared with many ITE hearing aids. The earpiece of an open fit hearing aid is a small, soft rubber or silicone cap, known as a dome. This type of aid is normally suitable for patients with mild or moderate hearing loss. The fitting time is usually shorter because earmold impressions are not needed, because the dome fits into the ear canal (as shown in the image below). These new, thin-tube (open-fit) varieties of BTE hearing aids made up over 50% of the total market as of 2007.
Open-fit behind-the-ear (BTE) hearing aid. Image courtesy of the National Institutes of Health (NIH). In 2010 (as of September), 67.3% of hearing aids sold in the United States were BTE hearing aids, of which 40.4% were of the receiver-in-the-canal type.[12]
One variety of these open-fit hearing aids, called receiver-in-the-canal aids (RIC), allows the placement of the receiver into the ear canal of the wearer. This allows for a smoother frequency response and increased gain before feedback occurs.
In-the-ear hearing aids
ITE hearing aids can be broken down into full-shell, half-shell, canal, and completely in-the-canal (CIC) instruments. The faceplate of the instrument includes the battery door, on/off switch, volume control (if available), and microphone opening. Most of the shells for each of these aids are manufactured using ear mold impressions taken from the individuals in whom these aids are to be fitted.
The full-shell instrument fills the concha of the individual (see the image below) and is the largest of the ITE hearing aids. This device can typically address more severe hearing losses with greater ease because of its ability to fill the canal and the concha of the external ear. It thus can reduce the chance of feedback from the hearing aid.
In-the-ear hearing aid (ITE). Image courtesy of the National Institutes of Health (NIH). The half-shell is an instrument that fills only the concha cavum and the canal and is approximately half the size of a full-shell instrument. Because of its smaller size, this device is cosmetically more appealing and is appropriate for moderate to severe hearing losses.
The canal-sized ITE aid (ITC) primarily fits within the concha and in the outer half of the canal. The faceplate of this aid is accessible to the user to allow changing the volume control and turning the aid on and off. This hearing aid provides some advantage in gain at higher frequencies because of its depth of insertion and the acoustic resonance in the unblocked concha.
The completely in-the-canal aid (CIC), or what may be termed a peritympanic hearing aid, is fitted deep into the ear canal and is the smallest of all hearing aids (see the image below). It typically fits entirely within the ear canal, and the deepest portion of the hearing aid is in close proximity to the tympanic membrane. The faceplate is usually not accessible to the user. This device also needs a short cord or wire attached to the faceplate for the wearer to use while removing the aid.
Completely in-the-canal (CIC) hearing aid. Image courtesy of the National Institutes of Health (NIH). The CIC aids are regarded as the most cosmetically pleasing, and, because of the close proximity to the tympanic membrane, they can reduce or eliminate the occlusion effect or the barrel sound experienced by many hearing aid users. Additionally, individuals with this type of aid can use the telephone like those without hearing aids. Owing to the size limitations of the internal components of the aid and the physical limitations of the ear canal itself, these hearing aids are most appropriate for individuals with mild to moderate hearing loss.
Ear mold impressions
For BTE fittings, ear mold impressions of the patient are taken, and these impressions are sent to a manufacturer who makes the ear mold that will be fit to the chosen BTE instrument.[13] The manufacturer is instructed on the type of material to be used, the type of mold to be made, and any modifications, venting, and tubing that is to be included with the mold.
For ITE instruments, ear mold impressions are sent to the hearing aid manufacturer, who makes the casing of the ITE hearing aid from the impression.
Hearing aid manufacturers are also instructed by the dispenser regarding the type of ITE aid that is to be made and the type of microphone, amplifying circuits, and receivers that are most appropriate for the patient.
In recent years, hearing aid manufacturers have provided dispensers the technology that allows for ear mold impressions to be digitally scanned in the office and electronically sent to the manufacturer. This process allows for a more accurate ear mold or custom-fitted hearing aid, eliminate the shipping of ear mold impressions, and reduces turnaround time by several days.[14]
Hearing aid accessories
Many different types of remotes can control programs and the volume of a hearing aid if a volume wheel or program button is not on the aid itself. They come in many different styles such as watches, pens, key chains, or those about the size of an MP3 player. Any of these may be deemed necessary for the wearer as his or her lifestyle dictates.
Another accessory available for hearing aids is an FM system. FM systems improve the signal-to-noise ratio (SNR) by allowing a speaker to talk directly into a microphone and, with the use of harmless radio waves, the speech signal is sent directly to a tiny FM receiver that is coupled to the BTE aid of the listener. Many of the newer FM receivers extend only a short distance from the bottom of the BTE. Traditionally, FM systems were used in school classroom settings but are now commonly used in various other situations or activities, such as lectures, concerts, restaurants and in the car.[15]
Indications
A variety of factors must be taken into account before an individual is considered to be a candidate for a hearing aid.[16, 17, 18, 19, 20] These factors also depend on whether the individual is an adult or a child.
One major misconception concerning the candidacy of hearing aid use revolves around the type of hearing loss. In the past, some physicians were trained to believe that hearing aids were not helpful for sensorineural hearing losses. However, most patients fitted with hearing aids have sensorineural hearing loss, and those who are fitted properly have reported increased communication abilities from the use of hearing aids, especially with current hearing aid technology.
Tests
The following tests are used to determine the frequency response curve, gain, and maximum output of the individual's hearing aid.
Audiologic test results are primarily used to determine the hearing aid candidacy for adults. Other factors, such as motivation, perceived handicap, and social needs, are also considered.
Audiologic results including pure-tone thresholds (PTA), speech recognition thresholds (SRS), and word recognition scores (WRS) in quiet and in noise are used to define the type, degree, and configuration of hearing loss and the ability to discriminate between various speech sounds.
In addition, most comfortable loudness and uncomfortable loudness levels help in determining the patient's dynamic range. The dynamic range for speech can be defined as the difference in decibels between the speech recognition threshold and the uncomfortable loudness level, or the softest level at which a word can be just understood and the point at which sounds are uncomfortably loud.
In addition to the above tests, which are completed under earphones, sound-field versions of these tests can help determine the binaural hearing abilities of the individual and help with fitting verification of the hearing aid.
Motivational factors
Motivation and the amount of perceived handicap are major factors in determining the candidacy for hearing aid use in adults.
Motivational factors can be determined by interviewing the individual and obtaining information regarding the impact of the hearing loss on everyday life and the perceived need for amplification. Individuals who are highly motivated and perceive that they will hear better with hearing aids or that their understanding of speech will improve with hearing aids are most likely to adapt to and obtain maximum use from the aid.
A variety of hearing-handicap scales can be used to measure the self-perceived hearing handicap of a patient. Several self-report scales, including the Hearing Handicap Inventory for the Elderly (HHIE),[21] the Client Oriented Scale of Improvement (COSI),[22] and the Abbreviated Profile of Hearing Aid Benefit (APHAB) are relatively short and assess the areas of hearing handicap, including the social and emotional effects of hearing loss. These scales also can be used after fitting of the hearing aid to determine the benefit of its use.
Infants and Children
Any child with a verifiable hearing loss of any extent is a candidate for amplification. A combination of objective electrophysiologic tests and behavioral tests are usually needed to determine the degree, type, and configuration of the hearing loss when evaluating a young child.
Infants who are identified with sensorineural hearing loss can be fit with amplification when younger than 6 months. Because behavioral test results at this age are limited, electrophysiologic test results are primarily used to determine hearing aid candidacy.
With all very young children, the hearing aid evaluation and fitting process should be ongoing. Children need to be monitored on a regular basis to determine if the fit of the hearing aid is appropriate and if the aid is set for maximum aided results.
Clinical Trial Evidence
Monaural vs binaural amplification
After reviewing the test results and determining the type and degree of loss to each ear, a decision must be made whether to recommend one hearing aid (monaural amplification) or 2 hearing aids (binaural amplification). For most binaural hearing losses, 2 hearing aids are recommended.[23, 24]
One of the primary reasons for this recommendation is the mounting clinical evidence that indicates that failure to fit hearing aids on both ears of patients with binaural hearing loss can result in temporary and perhaps permanent decrease in the auditory function in the unaided ear. The deterioration over time of auditory perceptual function in the unaided hearing-impaired ear has been referred to as the "auditory deprivation" effect.[24, 25, 26]
Clinical Implementation
In addition to the hearing evaluation and the patient profile obtained regarding the patient's hearing handicap and motivation (see Indications), other testing may be completed in the sound field, especially speech recognition in the presence of noise. These tests can help determine the type of hearing aid to be chosen. They also serve as nonaided pretests that will be compared with aided posttesting.
Monaural vs binaural amplification
After reviewing the test results and determining the type and degree of loss to each ear, a decision must be made whether to recommend one hearing aid (monaural amplification) or 2 hearing aids (binaural amplification). For most binaural hearing losses, 2 hearing aids are recommended.[23, 24]
One of the primary reasons for this recommendation is the mounting clinical evidence that indicates that failure to fit hearing aids on both ears of patients with binaural hearing loss can result in temporary and perhaps permanent decrease in the auditory function in the unaided ear. The deterioration over time of auditory perceptual function in the unaided hearing-impaired ear has been referred to as the "auditory deprivation" effect.[24, 25, 26]
In addition to avoiding the possible deprivation effects, other advantages exist to binaural amplification, including better sound localization, improvement of speech recognition in the presence of noise, improved speech clarity, and more natural and less stressful listening.
Besides determining the size of the hearing aid and whether to fit monaurally or binaurally, the determination of frequency response, gain, and overall output of the hearing aid must be decided. In many settings, Real Ear measurements are made to help select the proper characteristics of the hearing aid.
Specifications
Specifications of hearing aids from manufacturers are produced using the American National Standards Institute (ANSI) S3.22 standards concerning the gain, output, and frequency response of the hearing aid.[5] These measurements are made in a 2-cm3 coupler. This coupler is used to simulate the condition of the aid in an ear, but many differences exist between a metal 2-cm3 coupler and the volume and texture of a real ear canal and eardrum, and many individual differences exist between ears. Because of these differences, a Real Ear probe-tube measurement is used to reveal the exact frequency response, gain, and maximum output of the hearing aid in the ear of the individual at the site of the eardrum.
Real Ear measurements
Using the Real Ear equipment, the audiologist places a probe microphone into the ear canal and presents a known auditory signal to the individual. The information from the microphone when the stimulus is present yields a Real Ear unaided response (REUR). This response reveals the resonating characteristics of the ear canal without the aid in place and can assist in formulating the best 2-cm3 coupler response for a patient at the time a hearing aid is ordered.
A variety of prescriptive techniques for fitting hearing aids use information from Real Ear measures. These techniques include the half-gain rule and the prescription of gain and output (POGO).[27, 28]
National Acoustics Laboratory technique
One of the most popular prescriptive techniques for adults is the procedure developed by the National Acoustics Laboratory (NAL) in Australia for selecting gain and frequency response of a hearing aid.[29, 30] The NAL algorithm is used to calculate the most appropriate Real Ear gain. The NAL method is based on comfort, whereas a prescriptive method such as Desired Sensation level (DSL) (commonly used in pediatric fittings) is based on audibility of sounds.[31] Each method has its own strengths and rationale for providing goals and targets to guide the hearing aid fitting.
From the algorithm, a hearing aid is selected with the required frequency response and gain characteristics, and comparisons are made between the predicted gain and the Real Ear measurements obtained from the hearing-impaired client.
This can be obtained by measuring the real-ear aided response (REAR). The REAR is taken with the hearing aid and the probe microphone in the ear, and the aid's gain is turned to match the calculated Real Ear gain. The REAR is the gain in decibels relative to the stimulus level presented to the patient.
The real-ear insertion gain (REIG) is the difference between the REAR and the REUR and is used to verify that the predetermined target insertion gain has been achieved.
Hearing aid fitting and orientation
After the hearing aid has been ordered and sent to the hearing aid dispenser, it is ready to be fitted to the patient.
Fitting
Some dispensers may have open-fit behind-the-ear (BTE) aids on hand, which can be fitted to the patient immediately. In either case, the hearing aid is inserted into the patient's ear, and the acoustic performance of the aid is evaluated. This can be accomplished by using Real Ear equipment or by sound field–aided test results.
With the Real Ear equipment, a Real Ear–aided response can be obtained, and the insertion gain of the aid can be measured. This gain can be compared with the target gain generated by a particular prescriptive method chosen by the dispenser (eg, NAL or DSL), and the hearing-aid settings can be adjusted until a reasonable match is observed. In addition to the gain, similar adjustments are made to the total output of the aid to ensure that the aid does not exceed the patient's loudness discomfort levels.
After Real Ear measurements are taken, the patient may be placed in a sound booth where aided sound-field testing of the speech recognition threshold and the word recognition in quiet and in noise can be made. The difference between the aided and the unaided measures (ie, functional gain) provides a general indication of the benefit provided by the hearing aid.
Orientation
Once the hearing aid has been fitted and evaluated, the patient is given a general orientation concerning the hearing aid, including all the components of the device, how to insert and remove the aid, the care and maintenance of the aid, and how and when to change batteries.
During the orientation, the patient is counseled about the use of the aid in various settings, common problems faced by individuals using hearing aids in these settings, and strategies to maximize hearing aid benefit.
Questions that the patient may have concerning wearing and using the aid are answered. If the patient appears to understand how to insert and remove the hearing aid and understands how to turn the aid on and off and adjust the volume control, he or she is allowed to leave with the aid.
Follow-up/Monitoring
During the past decade, hearing aids have progressed from rather simple linear analog amplifiers to hearing aids with sophisticated digital programmable analog circuits and digitally programmable digital circuits. These digital devices can contain a variety of channels and programs to function in various listening situations.
Although the digital technology provides a more precise fit, complete counseling during the fitting and orientation sessions remains necessary to maximize the communication abilities of the individual with a hearing loss. Keep in mind that face-to-face hearing aid dispensing remains the most effective means to verify an appropriate hearing aid fit, even though many digital hearing aids can be purchased over the counter or by mail order.[32, 33]
In most settings, the hearing aid is dispensed with a trial period of at least 30 days, and the dispenser sets up 2-3 appointments with the patient during this time. During these follow-up visits, the patient's ear mold may need to be modified for a more comfortable fit or to reduce feedback problems.
Near the end of the trial period, the dispenser may retest the patient in the sound field to obtain aided sound-field measures. The dispenser also may obtain aided measures of the patient's self-assessed hearing handicap to assess the patient's subjective perception of the benefits of the hearing aid. Numerous other factors can also be considered to determine whether the hearing aid fitting is successful. These include the actual hearing aid use time, which is recorded via data logging within the aid itself; the impact that the hearing aid fitting has had on the individual's significant others; and the overall improvement in quality of life.[3]
If the patient decides to purchase the hearing aid, then the warranty for the aid begins. Most hearing aids come with at least a 1-year warranty. Extended warranties (up to 3 y) are also available. These types of warranties are most appropriate for children or other individuals who may be at risk of damaging the hearing aid.
Berger KW. The hearing aid, its operation and development. In: The Hearing Aid. 3rd ed. Thieme Medical Publishers; 1984.
Kochkin S. Customer satisfaction with hearing instruments in the digital age. Hearing Journal. 2005;58 (9):30-43.
Paul PV, Whitelaw GM. Hearing and Deafness: An Introduction for Health and Education Professionals. Sudbury, Mass: Jones and Bartlett; 2011.
Lindley, G. Unleash the power of wireless communication. Adv for Audiologist. 2007;9(4):59-62.
American National Standards Institute (ANSI), Acoustical Society of America (ASA). American National Standard Specification of Hearing Aid Characteristics, Includes 2007 Erratum. New York; NY: ANSI/ASA; 2009:S3.22-2009.
Valente M, Mispagel K. Performance of an Automatic Adaptive Dual-Microphone ITC Digital Hearing Aid. Hearing Review. February 2004;11(2):42-46, 71.
Potts LG, Valente M, Agnew J. Sound quality judgments: Class A versus class D output stages. Poster presented at: AAA Annual Meeting. Richmond, Va: 1994.
Kuk F, Korhonen P, Peeters H, Keenan D, Jessen A, Andersen H. Linear Frequency Transposition: Extending the Audibility of High-Frequency Information. Hearing Review. October 2006;13(11):42, 44, 44-46, 48.
Kuk F, Keenan D, Korhonen P, Lau CC. Efficacy of linear frequency transposition on consonant identification in quiet and in noise. J Am Acad Audiol. Sep 2009;20(8):465-79. [Medline].
Kuk F, Peeters H. The Hearing Aid as a Music Synthesizer. Hearing Review. October 2008;15(10):28, 30, 32-33, 36-38.
Kochkin S. Thin tube mini-BTE survey. Alexandria, Va: Better Hearing Institute; September 11, 2006..
Kirkwood D. In troubled economic times, the hearing aid industry remains an island of stability. The Hearing Journal. 2010;63(12):11-6.
Byrne D, Sinclair S, Noble W. Open earmold fittings for improving aided auditory localization for sensorineural hearing losses with good high-frequency hearing. Ear Hear. Feb 1998;19(1):62-71. [Medline].
Taylor B, Younk R. The lost art and new science of ear mold selection and modification. The Hearing Review. 2005;12 (12):24-28.
Nelson J. Achieving Hearing Aid and FM System Transparency. Hearing Review. May 2002;9(5):14, 18-20.
Berger KW. Prescription of hearing aids: a rationale. J Am Audiol Soc. Nov-Dec 1976;2(3):71-8. [Medline].
Cox RM, Alexander GC, Gray GA. Who wants a hearing aid? Personality profiles of hearing aid seekers. Ear Hear. Feb 2005;26(1):12-26. [Medline].
Hornsby BW, Mueller HG. User preference and reliability of bilateral hearing aid gain adjustments. J Am Acad Audiol. Feb 2008;19(2):158-70. [Medline].
Palmer CV. Quantifying and responding to patient needs and expectations. J Am Acad Audiol. Nov-Dec 2005;16(10):789-808. [Medline].
Staab WJ. Peritympanic instrument: Fitting rationale and test results. Hearing J. 1992;42:21-26.
Newman CW, Weinstein BE. The Hearing Handicap Inventory for the Elderly as a measure of hearing aid benefit. Ear Hear. Apr 1988;9(2):81-5. [Medline].
Dillon H, James A, Ginis J. Client Oriented Scale of Improvement (COSI) and its relationship to several other measures of benefit and satisfaction provided by hearing aids. J Am Acad Audiol. Feb 1997;8(1):27-43. [Medline].
Briskey R. Binaural hearing aids and news innovations. In: Katz J, ed. Handbook of Clinical Audiology. Lippincott Williams & Wilkins; 1978:501-507.
Silverman CA, Silman S. Apparent auditory deprivation from monaural amplification and recovery with binaural amplification: two case studies. J Am Acad Audiol. Oct 1990;1(4):175-80. [Medline].
Hurley RM. Onset of auditory deprivation. J Am Acad Audiol. Nov-Dec 1999;10(10):529-34. [Medline].
Silman S, Silverman CA, Emmer MB, et al. Adult-onset auditory deprivation. J Am Acad Audiol. Nov 1992;3(6):390-6. [Medline].
Cornelisse LE, Seewald RC, Jamieson DG. The input/output formula: a theoretical approach to the fitting of personal amplification devices. J Acoust Soc Am. Mar 1995;97(3):1854-64. [Medline].
McCandless G, Lyregaard P. Prescription of gain/output (POGO) for hearing aids. Hearing Instruments. 1983;1:12-16.
Byrne D, Dillon H. The National Acoustic Laboratories' (NAL) new procedure for selecting the gain and frequency response of a hearing aid. Ear Hear. Aug 1986;7(4):257-65. [Medline].
Dillion H. NAL-NL1: A new procedure for fitting non-linear aids. Hearing J. 1999;52(10):12-16.
Cornelisse L, Seewald R, Jamieson D. Fitting wide-dynamic range compression hearing aids; The DSL I/O approach. Hearing J. 1994;47(10):23-29.
Sweetow R. Hearing aid delivery models: Part I. Audiology Today. Sep/Oct 2009;21(5):49-58.
Lesiecki W. Does the in-office electronic scanning of impressions really change everything?. Hearing Review. 2006;13 (1):32-35.
Burton P. Consumer segmentation research yields a personalized way to select hearing aids. Hearing Journal. October 2006;62:24, 26-27.
Chisolm TH, Johnson CE, Danhauer JL, Portz LJ, Abrams HB, Lesner S, et al. A systematic review of health-related quality of life and hearing aids: final report of the American Academy of Audiology Task Force On the Health-Related Quality of Life Benefits of Amplification in Adults. J Am Acad Audiol. Feb 2007;18(2):151-83. [Medline].
Cox R. Using loudness data for hearing aid selection: The IHAFF approach. Hearing J. 1995;48:38-45.
Cox RM, Xu J. Short and long compression release times: speech understanding, real-world preferences, and association with cognitive ability. J Am Acad Audiol. Feb 2010;21(2):121-38. [Medline].
Fllynn MC. New design focus yields a hearing device that people actually want. The Hearing Review. 2006;13 (4):58-63.
Fortune TW, Preves DA. Hearing aid saturation and aided loudness discomfort. J Speech Hear Res. Feb 1992;35(1):175-85. [Medline].
Gittles T, Niquette D. FIG6 in ten. Hearing Review. 1995;2(10):1995;2(10):28-30.
Hamilton AM, Munro KJ. Uncomfortable loudness levels in experienced unilateral and bilateral hearing aid users: evidence of adaptive plasticity following asymmetrical sensory input?. Int J Audiol. Sep 2010;49(9):667-71. [Medline].
Hickson L, Clutterbuck S, Khan A. Factors associated with hearing aid fitting outcomes on the IOI-HA. Int J Audiol. Aug 2010;49(8):586-95. [Medline].
Johnson EE, Ricketts TA. Dispensing rates of four common hearing aid product features: associations with variations in practice among audiologists. Trends Amplif. Mar 2010;14(1):12-45. [Medline].
Kirkwood DH. Survey: Dispensers fitted more hearing aids in 2005. Hearing Journal. 2006;59 (4):40-50.
Kirkwood, D. Survey probes the economic realities of the dispensing business. Hearing Journal. March 2006;59:19-32.
Kochkin S. MarkeTrak VIII: The impact of the hearing healthcare professional on hearing aid user success. Hearing Review. 2010;17(4):12-34.
Kuk F, Keenen D. How do vents affect hearing aid performance. The Hearing Review. 2006;13 (2):33-42.
Kuk F, Peeters H, Keenan D, Baekgaard L. Timing is (Almost) Everything: Verifying the Performance of Fully Adaptive Directional Microphones. Hearing Review. August 2005;12(8):24-29.
Köbler S, Lindblad AC, Olofsson A, Hagerman B. Successful and unsuccessful users of bilateral amplification: differences and similarities in binaural performance. Int J Audiol. Sep 2010;49(9):613-27. [Medline].
O'Brien A, Yeend I, Hartley L, Keidser G, Nyffeler M. Evaluation of frequency compression and high-frequency directionality. Hearing Journal. 2010;63(8):32-7.
Sarampalis A, Kalluri S, Edwards B, Hafter E. Objective measures of listening effort: effects of background noise and noise reduction. J Speech Lang Hear Res. Oct 2009;52(5):1230-40. [Medline].
Stelmachowicz P, Lewis D, Hoover B, Nishi K, McCreery R, Woods W. Effects of digital noise reduction on speech perception for children with hearing loss. Ear Hear. Jun 2010;31(3):345-55. [Medline]. [Full Text].
Valente M, Fabry DA, Potts LG. Recognition of speech in noise with hearing aids using dual microphones. J Am Acad Audiol. Nov 1995;6(6):440-9. [Medline].
Wu YH. Effect of age on directional microphone hearing aid benefit and preference. J Am Acad Audiol. Feb 2010;21(2):78-89. [Medline].
Wu YH, Bentler RA. Impact of visual cues on directional benefit and preference: Part II--field tests. Ear Hear. Feb 2010;31(1):35-46. [Medline].
Print
