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Audiologic Rehabilitation

Sharon A. Sandridge and Craig W. Newman

The primary goal of audiologic rehabilitation (AR) is to help patients overcome the communication and psychosocial consequences of hearing loss. In routine clinical practice, hearing aid (HA) dispensing often represents the beginning and end of audiologic intervention. Yet the fitting of amplification is just one step in the process. Included in the process is a complete audiologic evaluation, assessment of individual listening needs, determination of appropriate amplification devices (i.e., HAs, assistive listening devices [ALD], a bone-anchored hearing aid [Baha®] system, or cochlear implants) and follow-up services (i.e., communication strategy training, auditory listening training, or more intensive speech and language therapy). This chapter describes a service delivery model of AR (Fig. 30–1) primarily for patients with adult-onset sensorineural hearing loss (SNHL). Given the majority of individuals with conductive hearing loss are treated successfully through medical intervention, this population will not be addressed. Likewise, infants and children with congenital or acquired SNHL will not be addressed, although the main difference in the AR model between children and adults is the need for more intensive follow-up. Before discussing the AR model shown in Fig. 30–1, an overview of the psychosocial impact of hearing loss is presented.

Consequences of Hearing Loss

Within the framework of the most recent World Health Organization (WHO)¹ model, health conditions are examined under three domains: body or body condition (impairment), whole person (activity limitations), and person in society (participation restrictions). Using this systems approach, the impact of a hearing loss on the psychosocial functioning can be assessed.

Following is a brief description of each component of the WHO¹ model as it relates to auditory function. Impairment is the measurable loss of hearing function. For example, the loss of hair cell function at the basal end of the cochlea causes a high-frequency hearing loss. Activity limitation (formerly referred to as disability), on the other hand, is the impact of the hearing loss on the person’s ability to communicate or hear sounds. For example, high-frequency hearing impairment decreases the ability to perceive consonant sounds (e.g., /t/, /s/, /v/, /f/) important for speech understanding. In addition to decreased audibility, SNHL loss produces alterations in (1) dynamic range (i.e., the level difference between uncomfortable listening levels and threshold of audibility); (2) frequency resolution (i.e., separating sounds of different frequencies); and (3) temporal resolution (i.e., intense sounds masking weaker sounds that immediately proceed or follow). The result of each of the aforementioned aspects of hearing loss is reduced speech intelligibility especially in background noise. Participation restriction (formally referred to as handicap) represents the nonauditory problems faced by the patient in everyday situations. For example, the individual with high-frequency SNHL no longer attends social functions because it is too difficult to follow conversations. Accordingly, participation restriction represents the social (e.g., withdrawal from communication situations) and emotional (e.g., frustration) manifestations resulting from hearing impairment and activity limitation.

In general, individuals do not seek audiologic services when their hearing loss exists within the impairment domain only. Individuals seek audiologic services when their hearing impairment moves into the participation domain. That is, individuals get medical and audiologic help when hearing loss causes significant difficulty in their day-to-day activities.

Communication Needs Assessment

The first step in the AR process, as shown in Fig. 30–1, is to document hearing impairment through the audiometric evaluation (see Chapter 8). The results from the audiologic assessment serve as the basis for defining the patient’s hearing loss (degree, type, and configuration), establishing the need for medical intervention, assisting in the decisions regarding specific amplification devices (i.e., the electroacoustic parameters of the devices), planning appropriate treatment intervention, setting realistic expectations from amplification, and evaluating improvements following intervention.

Although pure-tone and speech audiometric tests provide information regarding maximum auditory function in optimal listening situations, these tests do not assess how well the patient performs in everyday life. Patients’ communication needs must be assessed using more ecologically valid tools. A few such tools, as described briefly here, should be included in the hearing needs assessment:

• Speech Perception in Noise (SPIN)2 involves the presentation of 50 sentences in which patients repeat the last word of each sentence. Twenty-five of the sentences are considered high-predictability sentences, that is, the last word is predictable from the context of the sentence (e.g., “The baby slept in the crib”). In contrast, the last word for the remaining 25 sentences cannot be predicted from the sentence context (e.g., “She has known about the drug”) and are considered low-predictability sentences. The test sentences can be presented in quiet or in the presence of multitalker speech babble at various signal-to-noise ratios (SNRs). For example, sentences can be presented at 50 dB HL, and the multitalker babble presented 8 dB less intensely, yielding a +8 SNR.

• Quick Speech in Noise (QuickSIN)³ is a speech-in-noise test that measures the ability to understand sentences in a background noise by presenting six sentences at different SNRs. The test is quick (it takes less than 1 minute), easy to administer and score, has high face validity, and can be useful for patient counseling.

• Hearing in Noise Test (HINT)⁴ uses sentence-length material to obtain a sentence reception threshold obtained in quiet and again in background noise. An SNR is computed and can be used to demonstrate the effectiveness of amplification by comparing aided and unaided HINT sentence reception thresholds as well as SNRs.

In addition to objective measures, self-report questionnaires have gained widespread use for quantifying activity limitation and participation restriction. These tools are especially useful when administered in a pre- and posttest format to document AR benefit. Here are a few of the more commonly used psychometrically robust questionnaires:

• Abbreviated Profile of Hearing Aid Benefit (APHAB)⁵ quantifies the level of difficulty/activity limitation caused by the hearing impairment in given situations as well as documents the reduction in the difficulty through the use of amplification. The questionnaire consists of 24 questions that are divided into four subscales: Ease of Communication, Background Noise, Reverberation, and Aversiveness to Sounds. Patients quantify the level of difficulty on a 7-point scale ranging from “always” (99%) to “never” (1%).

• Hearing Handicap Inventory for the Elderly/Adult (HHIE/A)^6,7 assesses self-perceived hearing handicap (participation restriction) for older (HHIE; ≥65 years old) and younger (HHIA; <65 years old) adults. These instruments are 25-item questionnaires measuring social and emotional consequences of hearing loss. Patients respond to each statement with “yes,” “sometimes,” or “no.”

In addition to assessing the patient’s communication needs, several biopsychosocial factors require consideration when determining HA candidacy. Among the primary physical variables are the patient’s visual status, manual dexterity, shape and dimension of the pinna and external auditory canal, and overall health. Important psychological factors affecting HA candidacy and benefit include motivation, cognitive status, and personality. In fact, motivation is critical to the success of the HA fitting and is a multivariate process incorporating acknowledgment of hearing loss, communication needs, self-image, and expected benefit. The relationship between patients’ acknowledgment of hearing loss and motivation has been found to be strongly correlated with HA use and satisfaction.⁸ From a social perspective, key variables to consider when evaluating HA candidacy include the patient’s lifestyle, family support, and financial factors.

Hearing Device Selection

During this phase (Fig. 30–1), the audiologist engages in a complex decision-making process of determining which hearing devices will be the most appropriate. The devices could include HAs, ALDs, or a combination of technology. Selfassessment questionnaires allow the audiologist to best determine which device (or devices) is the most appropriate for the patient.

• Client Oriented Scale of Improvement (COSI)⁹ allows patients along with the audiologist to isolate up to five specific areas of listening difficulties. The situations are listed and prioritized and can be compared with established norms.

• Hearing Aid Selection Profile (HASP)¹⁰ is a 40-item instrument assessing patient’s motivation for using amplification, expectations for amplification use, communicative needs, manual dexterity, cosmesis as well as attitudes toward cost and technology. The HASP was designed to be used as a prefitting tool at the outset of AR services to provide the clinician with a general sense of the patient’s expectations and perceptions toward technology, in general, and hearing aids, specifically. A profile is generated from the eight categories useful in specific device selection, counseling for realistic expectations, and as an outcome tool for documenting quality improvements.

• Characteristics of Amplication Tool (COAT), which we developed, is an eight-item questionnaire that assesses eight key areas (see Appendix 30–1). Responses to each item assist the audiologist in selecting the most appropriate HA style, options, and level of technology for a given patient.

Figure 30–2 A block diagram representing the basic components of an HA. Signal processing could be either analog or digital. Amp, amplifier.

Hearing Aids

Choosing the most appropriate HA involves selecting an instrument with the particular combination of characteristics (electroacoustic and nonelectroacoustic) that will meet the needs (listening, communicative, cosmetic, and financial) of the patient. Before discussing those characteristics, Fig. 30–2 diagrams the basic components of the HA.

Basic Components

Microphone: The microphone is a transducer that converts the acoustic sound entering the HA into an electrical signal. Several types of microphones can be found in HAs. Omnidirectional microphones are equally sensitive to sounds from all directions (Fig. 30–3). Directional microphones, on the other hand, are more sensitive to sounds originating from specific angles, as seen in Fig. 30–3. Utilizing more than one microphone within the same device is referred to as multimicrophone technology. Combining multiple omnidirectional microphones or an omnidirectional and a directional microphone has been shown to increase speech intelligibility by increasing the SNR.^11,12

Amplifier: The amplifier is responsible for modifying and increasing the gain of the incoming signal. There are two types of signal processing amplifiers: analog signal processing (ASP) and digital signal processing (DSP). The electrical signal from the microphone in the ASP system is altered through the use of filters. In the DSP system, the electrical signal is converted to a binary code and modified through a set of mathematical algorithms. The incorporation of DSP technology into hearing devices over the past 10 years has expanded the clinical efficacy of amplification through increased fitting flexibility, improved fidelity, feedback management schemes, advanced noise reduction, and use of artificial intelligence. In just 10 years, DSP instruments essentially took over the market going from 0% in 1995 to more than 80% in 2005.¹³ It is predicted that in a few years, ASP instruments will command less than 1% of the market share.

Receiver: The receiver functions to convert the amplified electrical signal to an acoustic signal heard by the ear. It is a microphone in reverse.

Battery: Five sizes of batteries are available ranging from a size 5 (5.7 mm in diameter) to a size 675 (11.4 mm in diameter). Generally, as seen in Table 30–1, as the size of the HA increases, so does the size of the battery. The larger battery sizes have more battery capacity so they last longer (220 to 350 hours). Regardless of the size, the majority of the batteries today are zinc air. Zinc air batteries use air as the oxidizing agent and remain inactive until the paper tab is removed from the top of the battery.

Additional Hearing Aid Features

• Telecoil (t-coil): Some HAs contain a coil of wire that, when activated, creates an electromagnetic field. When the HA electromagnetic field crosses the electromagnetic field emitted by the telephone receiver, the signal from the telephone is transferred to the HA. The advantage of using a telecoil is the elimination of feedback when the telephone receiver is placed close to the HA.

• Channels: If the frequency response (i.e., the response of the HA across low to high frequencies) is divided into smaller units, the HA is considered to have multiple channels or bands. The division of the entire frequency response into smaller units allows more precise adjustment of the frequency response. As the number of bands/channels increases, theoretically, so does the programming precision.

• Programs: Many HAs have multiprograms, that is, they offer different programs for different listening situations. For example, an HA can be programmed to maximize listening in quiet situations, whereas an alternative program provides maximum benefit in noisy situations. Changing programs can be accomplished through the use of remote controls, HA switches, or in some cases the programs change automatically dependent on the listening situation.

Figure 30–3 Polar plots of omnidirectional and directional microphones are illustrated. Note that the omnidirectional microphone, represented by the dotted line, is equally sensitive to sounds originating from the entire 360-degree plot. The directional microphone, represented by the solid line, shows greater sensitivity to sounds originating from 0-degree azimuth (sounds coming from the front of the listener) and least sensitive to sounds at 180-degree azimuth (sounds coming from the back of the listener). The solid line to the right of the head represents the placement of the HA.

Gain refers to the amount or magnitude of amplification. It is the difference between the input and output level of the device. For example, if a 50-dB signal is picked up by the HA and is delivered to the patient’s ear at 80 dB, then the gain would be 30 dB. This is graphically illustrated in Fig. 30–4.

Frequency response curve is a graphic representation of the amount of gain (in dB) as a function of frequency (Fig. 30–4

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