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National Guideline Centre (UK). Hearing loss in adults: assessment and management. London: National Institute for Health and Care Excellence (NICE); 2018 Jun. (NICE Guideline, No. 98.)
16.1. Introduction
The most common complaint of adults with hearing loss is difficulty understanding speech in the presence of background noise or competing speech. Because hearing aids cannot improve deficits in frequency, temporal and spatial resolution, an adult with hearing loss may continue to experience some difficulties, even when wearing hearing aids. The perception, and acceptance, of hearing aids is likely to be improved if they can be shown to improve listening to speech in the presence of background noise.
One hearing aid option that has been developed to distinguish speech from noise, and improve the speech-to-noise ratio (SNR), is the implementation of directional microphones. In contrast to omnidirectional microphones, which respond equally well to sounds arriving from all directions, a directional microphone is more sensitive to sounds from one direction (for example, speech coming from directly in front of the hearing aid user) and less sensitive to other directions (for example, background noise from the side or behind the hearing aid user). Directional microphones have the potential to benefit all hearing aid users. A disadvantage is that the signal of interest to the hearing aid user may come from a location where the microphone is least sensitive (for example, from behind). Modern hearing aids generally have microphones that can be enabled as omnidirectional or directional, usually involving the user selecting a different setting or programme on the hearing aid. Directional microphones have been shown to be efficacious in the research laboratory although their effectiveness in the real world is less clear.
Background noise can be reduced using adaptive (or digital) noise reduction. The aim of a hearing aid that has adaptive noise reduction is to provide less amplification to noise than to speech. This is achieved by identifying the frequencies (or time) where noise is particularly intense, relative to speech, and applying less amplification. Since the noise and the signal will be reduced in this frequency range, the speech-to-noise ratio remains unchanged, but there is the potential to improve listener comfort, reduce listening effort and achieve sustained performance throughout the day. Again, users often have the option of enabling or disabling the noise reduction setting on the hearing aid by selecting a different listening programme.
The benefits of directional microphones and adaptive noise reduction are based largely on theoretical advantages and studies of efficacy. The intention of this chapter is to review the evidence on the clinical and cost effectiveness of these hearing aid technologies and to develop recommendations for their use in adults with hearing loss.
16.2. Review question: What is the clinical and cost effectiveness of directional versus omnidirectional microphones?
For full details see review protocol in appendix C.
Table 92
PICO characteristics of review question.
16.2.1. Clinical evidence
A search was conducted for systematic reviews and randomised controlled trials comparing the effectiveness of hearing aids with directional microphones versus hearing aids with omnidirectional or disabled microphones to improve listening for adults with hearing loss in the presence of background noise.
One study was included in the review;103 and is summarised in Table 93 below. Evidence from this study is summarised in the clinical evidence summary below (Table 94). See also the study selection flow chart in appendix E, forest plots in appendix K, study evidence tables in appendix H, GRADE tables in appendix J and excluded studies list in appendix L.
Table 93
Summary of studies included in the review.
Table 94
Clinical evidence summary: Directional microphones compared with Omnidirectional microphones for hearing loss.
The aim of the study was to determine the impact of hearing aids with directional microphones on self-perceived localisation disability and concurrent handicap among older individuals with impaired hearing.
16.2.2. Economic evidence
No relevant health economic studies were identified.
See also the health economic study selection flow chart in appendix F.
16.2.3. Evidence statements
Clinical
Directional compared with omnidirectional microphones
- There was no clinically important difference in localisation disability and localisation handicap (very low quality evidence, 1 study).
Economic
- No relevant economic evaluations were identified.
16.2.4. Recommendations and link to evidence
| Recommendations |
|
| Relative values of different outcomes | The guideline committee agreed that the following critical outcomes should be included in the review: speech recognition in noise, ease of listening, and hearing-specific health-related quality of life including the Hearing Handicap Inventory for the Elderly (HHIE). The committee agreed that the following important outcomes should be included in the review: outcomes reporting restricted participation or activity limitation and social interactions, employment and education, health-related quality of life including the Health Utilities Index Mark 3 (HUI-3), and other outcomes such as safety, adverse effects and adherence. |
| Quality of the clinical evidence | One study comparing hearing aids with directional microphones to hearing aids with omnidirectional microphones was included in this review. This study reported on ‘localisation disability’ defined as self-perceived level of ability to tell the direction of sounds, and on ‘localisation handicap’ defined as self-perceived amount of withdrawal from activities of daily living, at 3 months post-fitting. The committee considered the potential for hearing aids, particularly those with directional microphones to reduce localisation skills, relative to the unaided condition. There was a high risk of bias in the selection of participants, lack of blinding and imprecision. The participants’ gender, average age, average duration of hearing loss and duration of hearing loss range are given. However comparability of these factors between groups has not been analysed and no other potential confounding factors have been explored. Therefore, the evidence for these outcomes was rated as very low. The committee noted that although the included paper was published in 2007, microphone technology has not improved in a significant way since then apart from some improvements in processors. Therefore, it was agreed that the evidence is still useful to consider. |
| Trade-off between clinical benefits and harms | Directional microphones have been shown to markedly improve the signal-to-noise ratio, compared with omnidirectional microphones, in many lab-based studies where the signal of interest is presented from directly in front of the listener and the noise is presented from other locations. The committee noted that there may be some occasions in real life when omnidirectional microphones may be more helpful such as being able to hear traffic approaching from different directions. No studies investigating signal-to-noise ratio in real life met the inclusion criteria. An important auditory ability is to localise sound. If hearing aids interfere with this ability this could result in a safety issue such as not being able to locate a warning sound. The evidence from the review is that hearing aids did not introduce localisation problems but there is a need for self-report to be verified empirically by directly measuring localisation abilities. The evidence from this review showed no difference between directional or omnidirectional microphones for the outcomes measuring ability to tell the direction of sounds, and activity limitation through withdrawal from activities of daily living, however the committee noted that the 1 study included in the review was very small and underpowered. Given the lack of evidence the committee was unable to recommend one type of microphone over another, but agreed it was important to highlight the benefits microphones can provide and the different settings for different situations and environments should be explained to people. The committee confirmed that all hearing aids provided through the NHS have both directional and omnidirectional microphones. Audiologists are able to activate the microphones when setting the hearing aid programmes for individuals’ needs. Hearing aids have several programmes for different listening situations such as ‘party’ or ‘quiet’ and the microphone setting is an important factor. The hearing aid user can select different programmes once they have been activated by the audiologist. The audiologist also ensures that the user knows how and when to activate the settings. If the audiologist does not set up these microphone options when the hearing aid is first prescribed and fitted, a further face-to-face appointment will be required at a later date. The committee considered that some people may not be aware that there is capacity to change the microphone programmes available on their hearing aids or the different modes available in order to improve listening in different acoustic situations. Current good practice is to provide the person with information on the features available and to work with the person to select the appropriate programmes that meet individual needs. The committee also stressed that the follow-up appointment should include a review of the person’s experience in using the microphone features and any changes required. The committee based its recommendations on its experience and knowledge. |
| Trade-off between net clinical effects and costs | No health economic evidence was identified for this question. The recommendations made for this review concern the content of advice given to hearing aid users in their fitting and follow-up appointments. These appointments are already necessary or recommended, and are discussed further in other chapters of this guideline. The nature of the advice given in these appointments will not give rise to any additional costs given that the appointments will be taking place and will be of fixed cost. The advice relates to the use of functions that can already be found on standard hearing aids prescribed in the NHS. Giving advice on how hearing aids can be used more effectively will increase the effectiveness of hearing aid use for no additional cost and so will be cost effective compared with not giving such advice, and may be cost saving if it reduces any need for additional subsequent appointments. |
| Other considerations | The committee stressed that directional microphones can be helpful for listening and speaking situations where filtering out sound around the person is needed. |
16.3. Review question: What is the clinical and cost effectiveness of noise reduction algorithms?
For full details see review protocol in appendix C.
Table 95
PICO characteristics of review question.
16.3.1. Clinical evidence
The aim of this study was to determine the impact of digital or adaptive noise reduction algorithms in a hearing aid without concomitant directional microphone use in both laboratory and field settings.
A search was conducted for randomised controlled trials that estimate the clinical effectiveness of noise reduction algorithms used to improve listening in the presence of background noise.
No studies were identified for inclusion in this review. See study selection flow chart in appendix E and the excluded studies list in appendix L.
16.3.2. Economic evidence
No relevant health economic studies were identified.
See also the health economic study selection flow chart in appendix F.
16.3.3. Evidence statements
Clinical
- No relevant clinical evidence was found.
Economic
- No relevant economic evaluations were identified.
16.3.4. Recommendations and link to evidence
| Recommendations | Please see the recommendations in section 16.2.4. |
| Research recommendation | What is the most suitable outcome measure to use when investigating the clinical and cost effectiveness of directional microphones and digital (adaptive) noise reduction? |
| Relative values of different outcomes | The guideline committee considered the following outcomes to be critical for this review: ease of listening, reduced listening effort and hearing-specific health-related quality of life including the Hearing Handicap Inventory for the Elderly (HHIE). The following outcomes were considered important: speech recognition in noise, outcomes reporting restricted participation or activity limitation and social interactions, employment and education, health-related quality of life including the Health Utilities Index Mark 3 (HUI-3), and other outcomes such as safety, adverse effects and adherence. |
| Quality of the clinical evidence | No clinical evidence was identified. |
| Trade-off between clinical benefits and harms | A noise reduction mode is provided as standard on most hearing aids. A follow-up appointment may be required to adjust settings as individuals assess their needs in different environments. For example, a person living in a care home may require different settings to a person living in their own home. Having multiple settings is not appropriate for all people. Those who have physical or cognitive impairments may not be able to manage switching between settings. Hearing aid features should be set up based on individual need. As no evidence was found, the committee based its recommendations on its knowledge and experience of noise reduction features being underutilised in some cases. This is due to users not being aware of noise reduction functions available on their devices or not knowing how to use them. The committee noted that noise reduction algorithms are not helpful for all people. Some do not like the quality of the sound when noise reduction is turned on and therefore there is a trade-off between reducing overall sound level to improve listening comfort but losing other qualities of the sound. Since no evidence was identified for this clinical question, the committee agreed that further research is needed to assess the benefit of the noise reduction function and decided to make a research recommendation in this area. |
| Trade-off between net clinical effects and costs | No health economic evidence was identified for this question. The recommendations made regarding noise reduction algorithms can be found in the reviews regarding the use of microphones (section 16.2.4) and interventions to support the use of hearing aids (section 18.2.4). They concern the content of advice given to hearing aid users in their fitting and follow-up appointments. These appointments are already necessary or recommended, and are discussed further in other chapters of this guideline. The nature of the advice given in these appointments will not give rise to any additional costs given that the appointments will be taking place and will be of fixed cost. The advice relates to the use of functions that can already be found on standard hearing aids prescribed in the NHS. Giving advice on how hearing aids can be used more effectively will increase the effectiveness of hearing aid use for no additional cost and so will be cost effective compared with not giving such advice, and may be cost saving if it reduces any need for additional subsequent appointments. |
| Other considerations | The committee agreed that all hearing aids currently provided by the NHS have a noise reduction feature available. However, these need to be enabled by an audiologist. There are different modes of noise reduction available, which the audiologist will programme together with other features, for example directional or omnidirectional microphones. All hearing aid features should be set up with the individual and based on individual needs and preferences. The committee agreed that the option to review these settings following a trial period in the real world is important so that features can be adjusted, added or removed based on user experience. Functionality can be limited because the technology does not allow the user to be able to control or adjust modes themselves, and they need to seek help from audiology services. |
- Hearing aid microphones and noise reduction algorithms - Hearing loss in adultsHearing aid microphones and noise reduction algorithms - Hearing loss in adults
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