Essential hearing aids features for LMICs

The WHO profile lists features for high-quality digital hearing aids in LMICs, emphasizing behind-the-ear hearing aids with earmoulds. This preference stems from their ease of fit, decreased susceptibility to malfunctioning due to ear-canal debris, and their cost-effectiveness, especially as earmoulds can be replaced individually as the ear canal grows. These features can be categorized across product design as well as suitability in LMICs (including cost and serviceability) which is equally critical. 107

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Table 30: Summary of essential product design features for LMICs as defined by WHO

Feature Rationale
Behind- the-ear Behind-the-ear hearing aids with earmoulds enable easy fit and lower risk of earwax-related malfunctions. In growing ear canals, only the earmould needs to be replaced, saving costs.
Digital Digital hearing aids offer increased adaptability in moulding the output signal to suit a broad spectrum of devices with a limited range; superior performance is achieved by allowing the utilization of an individual's remaining hearing capabilities.
Robust design Hearing aids should endure mild impact shocks, light rain, and dust, and should aim for a minimum of five years of continuous usage to be suitable for use in LMICs where access to professionals for repair is limited.
Compression Compression in hearing aids reduces the range of sound level in the environment to match the restricted hearing range. It enhances comfort for loud sounds, reduces distortion, and improves soft speech clarity. Proper management prevents amplification-induced hearing loss. Compression can be implemented as signal enters the device (input) or after the device amplifies the signal (output).
Feedback management Effective feedback management in hearing aids is vital to prevent acoustic loops that degrade the listening experience and drain the battery excessively. Common causes include loose earmoulds, prevalent in LMICs, and difficulties faced by new and elderly users during insertion. The effectiveness is measured by added stable gain (ASG), with a recommended ASG of 10 dB or more.
On–off switch Hearing aids must feature a dedicated on-off switch or a straightforward alternative for powering down, enabling user- friendly management and battery conservation.
Volume control A volume control, a prevalent user-directed feature, is crucial for wearer comfort, particularly when the amplified signal is too intense.

Proper validation of hearing-aid performance is vital to avoid insufficient amplification or over-amplification in all users, especially in children with small ear canals.

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Table 31: Preferred technical properties of the World Health Organization

Parameter Minimum requirement
Maximum Output Sound Pressure Level (OSPL) (90) 100-130 dB SPL +/- 4 dB
Maximum Output Sound Pressure Level (OSPL) (90) at 1 kHz 90-124 dB SPL +/- 4 dB
Maximum full-on acoustic gain 45-67 dB SPL +5/-0 dB
Full-on acoustic gain at 1 kHz 42-70 dB SPL +5/-0 dB
Basic frequency response

200-4,500 Hz

200-2,000 Hz +/- 4 dB SPL

2000-4,500 Hz +/- 6 dB SPL

Total harmonic distortion at 70 dB SPL input

500 Hz <8%

800 Hz <8%

1,500 Hz <2%

Equivalent input noise @ 1kHz ≤30 dB SPL @ 1 kHz
Battery current drain ≤1 mA
Battery life 2-3 weeks
Telecoil sensitivity ≥75 dB at 10 mA/m

Table 32: Summary of essential product design features for LMICs

Feature Rationale
Affordability Cost is a key barrier to hearing-aid uptake in LMICs. Hearing aids should be affordable for the majority of those in need in each community.
Labelling Hearing aids must bear permanent markings indicating the manufacturer or distributor's name, model name, serial number, and year of manufacture.
Robust packaging Packaging and labelling must endure exposure to high moisture levels and withstand impacts throughout the extended distribution chain common in LMICs. Additionally, the packaging should guarantee the safe storage of the hearing aid.
Technical data The hearing aid should be accompanied by technical specifications outlining electronic and acoustic performance expectations, including parameters detailed (see table 31).
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Feature Rationale
Contraindications Package covers must feature an advisory statement for hearing-aid dispensers. It should instruct dispensers to recommend that potential recipients seek clearance from healthcare personnel if any of the specified conditions, such as visible ear deformity or acute dizziness, are present.
User guide Every hearing aid should include clear usage instructions, featuring an illustration of the device, operational controls, user adjustments, and battery compartment. The guide should also cover accessory descriptions, maintenance procedures, and care instructions in the national language(s) of the purchase country, supported by easily comprehensible diagrams. Maintenance advice should consider local factors, like cost-effective dehumidification methods.
Obtainable power cells The hearing aid should be designed to accommodate a battery type readily available in the local region. This may include conventional hearing aid batteries, watch batteries (particularly accessible in some LMICs), or rechargeable cells.
Safe packaging of batteries Hearing aid batteries pose a danger, and ingestion may result in fatal consequences (Litovitz, Whitaker & Clark, 2010). Battery packaging must be explicitly labelled, emphasizing that batteries should be kept out of the reach of children and small animals. The design should make it challenging for a young child to open.
Appropriate earmoulds Earmoulds should align with the hearing aid type, device gain/output, and user preferences. Suitable options include stock earmoulds (pre-configured), custom earmoulds, instant earmould products, and disposable standard flexible dome moulds.
Sustainable production facilities for earmoulds If earmold production facilities are established, they should be designed to be sustainable within a local or regional context.
Hearing aid housing Design of the hearing aid should facilitate the opening of the housing for maintenance purposes and adjustment of pre-set controls (if provided) without risking damage to the housing or internal components.
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Feature Rationale
Post-fitting service As all hearing aids are prone to malfunction, service support from hearing-aid suppliers in LMICs is crucial. The nature and scope of service activities will vary based on the type of hearing aid. Facilities should be accessible for minor repairs, including device cleaning, ear hook replacement, battery contact adjustments, switch changes, and trimmer and volume control adjustments.

As the global hearing aid market continues to expand, understanding the nuanced dynamics of adoption, segmentation, and essential features becomes imperative for stakeholders shaping the future of hearing health. Along with access to hearing aids, implementation of appropriate service delivery approaches for the provision and maintenance of hearing aids is critical. WHO hearing-aid service-delivery approaches for LMIC settings provides guidance to develop and implement a national or subnational community-level programme for the delivery of hearing aid services. 108