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Amplification strategies for people with poor hearing

2009; Lippincott Williams & Wilkins; Volume: 62; Issue: 5 Linguagem: Inglês

10.1097/01.hj.0000352176.56992.1e

2333-6218

Christine E. Jones, Robert L. Martin,

Hearing Loss and Rehabilitation

Some people need amplification that goes beyond hearing aids. We all see patients whose hearing loss is so severe they need all the help we can give them. And some children, like those Wendy Pearce discussed in the February Nuts & Bolts column on auditory neuropathy spectrum disorder (ANSD), need special hearing aid systems to help them develop language. This month we're going to discuss patients with markedly impaired hearing and recommend ways to provide them with the best possible amplification. Our goals are straightforward: Provide patients with clean, clear amplified sound to facilitate their learning and personal growth. Here are some suggestions on how to use FM systems to dramatically reduce the perceived background noise for children and adults with poor hearing. (1) Be extra careful with gain in the lower frequencies. Patients who use either hearing aids or FM systems often say, “I can't use them in restaurants, at parties, or while walking on the street. All I hear is noise—huge amounts of noise! I can't understand anyone because of al the noise.” When you hear this complaint from a patient, go out to a noisy street and listen to what the patient is using, whether it's an FM or hearing aids. A huge amount of noise can come through an FM system if the settings are not ideal. If we use a lot of compression, we unintentionally pump up the background noise. Reducing compression and gain in the lower frequencies can markedly reduce perceived background noise. In some modern hearing instruments, fine-tuning can be done specifically in an FM+M program so as not to affect other listening conditions. Possible noise-reduction adjustments include raising kneepoints, especially in the low frequencies, and using noise cancellation. Another strategy for reducing noise through the FM transmitter is to use the directional microphones and noise-reduction modes available on some FM transmitters. When fitting adults with FM, it is important to counsel them on the use of these settings in noisy environments to keep the transmitter focused on the signal of interest. Be very careful when you set the gain for soft sounds. The more compression you use (lower kneepoints, higher ratios), the more background noise you introduce into the system. (2) Use the boom mic for the FM transmitter, and place it close to the talker's mouth. Some older, body-worn FM microphones generate a lot of mechanical noise. They pick up the scraping sound caused when the transmitter slides across the speaker's clothes. Boom or head-worn microphones are much better for two reasons. First, they are closer to the speaker's mouth, which greatly improves the S/N ratio. Second, they don't touch the body of the speaker, so there's no mechanical noise. Boom microphones are relatively inexpensive, which makes them a good choice for use in schools. If you're a school audiologist who purchases equipment for your school, get a separate boom microphone for each teacher and each assistant. This helps prevent germs from being shared along with the mic. (3) Be very careful with your microphone settings. Huge amounts of noise reduction are possible with FM systems. Maximum reduction is achieved when the system operates in the FM-only mode and the transmission microphone is near the teacher's mouth. In some cases, perceived background noise is completely eliminated. Sometimes, though, you want to set the system to the FM+ hearing aid setting. This allows environmental noise (e.g., from a noisy classroom or a crowded restaurant) to enter the system through the microphones on the hearing aids. The improvement in S/N ratio created by the FM system can easily be negated by the noise of the school children or the customers in a restaurant. (4) Consider using multiple transmitters for each patient. The newest FM systems allow you to use several sets of transmitters for each receiver. This is a great improvement, which enables several people in different parts of a room to talk to the FM wearer. In the past, when two transmitters were used, they both broadcast to the listener simultaneously. The S/N ratio suffered. This has now changed. A modern solution, called a multi-talker network, enables up to 10 independent transmitters to be combined in a network that broadcasts out to a group of listeners. No special equipment is needed and only one transmitter broadcasts at a time. The system makes sure the network maintains the S/N ratio and clarity of speech with an FM system. The person wearing the receiver can choose who wears the “priority” transmitter. “Spare” transmitters can be used when several people are present. In a classroom, such a network allows students to hear both the primary teacher and the teaching assistant. (5) Pick durable FM units. An FM unit can be built into a hearing aid or it can be added onto an existing BTE hearing aid. When the FM receiver is built into the hearing aid, the system is an integrated unit. When the FM receiver is placed in a small separate package, it is plugged into a conventional BTE hearing aid by means of a small “boot,” called an “audio shoe.” This type of FM is usually called a universal receiver. The integrated units are more durable, less prone to breakdown. They are recommended for children and adults who spend most of their time listening with the FM system. When you use the “add on” type of FM receiver, be sure you purchase and give the patient an extra set of boots. They are the weakest link in the system and need to be replaced whenever the system starts to go on and off. (6) Make sure settings are correct, Older FM systems had toggle switches on the receiver units that patients often found confusing. The newest FM systems have eliminated these switches. Make sure all patients—parents, teachers, and family members—have simple, easy-to-read sheets showing all the critical switch positions. (7) Discover “dynamic FM.” The newest type of FM is called dynamic FM. It automatically adjusts the intensity of the FM signal—the level of the speaker's voice—when the level of the background changes. This maintains a large, positive S/N ratio and greatly improves word recognition. Some older FM systems were complicated and difficult for patients to use. The newest FM systems are easier to use and have the potential to greatly reduce perceived noise. Modern FM transmission technology helps us reach our goal of giving patients clean and clear amplified sound and large reductions in perceived background noise. PUTTING IT ALL TOGETHER Now, let's put the above suggestions and information to work: Suppose David and Sally come to see you. David currently has a pair of BTE hearing aids. However, even with his hearing aids he can't hear and understand Sally when she talks to him. They want your help. When David is fitted with the newest FM integrated system—set to the FM-only mode to maximize noise reduction—and Sally is wearing the FM transmitter (with the microphone close to her mouth, to maximize speech clarity), David has his best chance to hear and understand Sally. This type of fitting usually produces dramatically better results than a hearing aid fitting. David is likely to be a good candidate for a new type of hand-held microphone, the DynaMic (See Figure 2), which Phonak introduced last month at AudiologyNOW! It looks like a standard hand-held microphone and can be easily taken to parties, restaurants, church, etc. It can be handed to a friend, a waiter, or anyone else, who can use it to transmit to an FM wearer such as David. This new model addresses a major problem associated with older FM systems—that they work for only one speaker and one listener. With the DynaMic, multiple people can talk to multiple others in all types of listening environments and enjoy the benefits of clear, almost noise-free FM communication.Figure 2: The DynaMic is a new kind of microphone.NOTES FOR THE SCHOOL AUDIOLOGIST FM technology can be valuable for team-teaching in a school. Inspiro FM transmitters, a Phonak product (see Figure 1) that can be used independently, can also be brought into a network of up to 10 transmitters. Sometimes two teachers (or a teacher and an aide) might instruct in two different classrooms or small groups and then want to team up to work with the same group of children. To do this, both teachers wear an Inspiro and when they team up the child wearing the receiver will hear them both.Figure 1: An Inspiro FM transmitter.If one Inspiro is desired and there is no need for independently functioning transmitters, the new DynaMic microphones from Phonak, which look like traditional hand-held mics, can be used in the network. This would be ideal in classrooms where a pass-around mic is desired. The teacher would wear an Inspiro and the DynaMic would be placed on a table with multiple students. Now the child wearing the receiver can hear both the teacher and the student discussion. This is a less expensive way to set up a multi-transmitter network. Diagnosing ANSD Children with auditory neuropathy spectrum disorder (ANSD) are difficult to diagnose accurately. They can have mild/moderate hearing loss even though the ABR data suggest they have severe or profound impairment. Make sure to include the family's perspective—their estimate of the child's degree of hearing loss. Also, be sure to get access to a wide range of diagnostic information, including cortical auditory evoked potentials (CAEP) data, a new measurement. If either a child or an adult has a mild/moderate hearing loss, a well-fitted, open-style hearing aid may provide lots of speech information with minimal noise exposure.