Classification of hearing aids by technological features

The HA market offers a multiplicity of HA with sometimes very few differences between HA characteristics. The variations in HA characteristics could be compared to all possible options of a car. In order to understand the HA market, we propose two types of HA classifications:

• A first classification, using four levels of complexity, is used by HA producers and is described.

• A second classification is developed and proposed by our team. It is more precise and assigns a weight to each aspect of the HA. It should be discussed and validated by producers, retailers, audiologists and ear-nose-throat specialist physicians (ENT). We built this classification proposal because we did not find a HA classification based on technological complexity in the scientific literature nor on the internet. This classification is limited to the HA technological complexity (the physical facts) but includes elements from the literature described in this report and also elements from our own clinical experience. It does not take into account the HA prices.

Contacted audiologists working in other countries had additional information so that we have been informed of the existence of French (Table 14) and German (not received) classifications towards the end of our study.

46 Hearing Aids KCE Reports 91 Table 14: French classification: ‘liste des produits et prestations’.

Old French Classification A. Efficacy evaluation

Peak clipping 0-2-4

H-tonality 0-2-4 L-tonality 0-2-4

Compression procedures 0 to 6

Audio input 0/2

Induction coil 0/2

Total A 22

B. Particular characteristics

Full gain 0-2-4-6-8-10

Gain without distortion 0-2-4-6-8-10

Internal noise 1-2-4-6-8-10

(Position de la pastille ?) (unclear) 10

Battery consumption 0/2

Total B 42

C. Supplementary possibilities

Programmable ?

> 2 bands ?

Gain progression < 5 dB ?

Recovery frequencies between channels ?

≥ 2 programs ?

Remote control ?

Dual microphone ?

Anti-feedback ? Auto-adaptative system ? (unclear) ?

New Classification * Group A (5 points)

Group B (8 points, ≥1 suppl possibilities) Group C (9 points, ≥3 suppl possibilities) Group D (10 points, ≥ 5 suppl possibilities)

* This classification, developed by an experts panel, will appear soon in the French Law.

4.2.2.1 Four-level classification

This is a classification of HA in four categories with progressive technological complexities, available from the internet and used by different HA producers.

Level I product: basic analogue or digital instruments

The standard analogue or digital hearing aids have linear amplification. The fitting may regulate the maximum output and the amplification of the low and high frequencies.

There is generally one channel of treatment. The microphone is omnidirectional.

Level II product: middle-level analogue or digital HA with non-linear amplification.

These hearing aids have compression circuits that automatically adjust the loud sounds coming into the analogue or digital hearing aid (AGC). They provide a non-linear amplification: K-amp, WDRC. They may have two or three spectral channels. There is one microphone with sometimes two openings (omnidirectional or more directional).

They may be programmed by a computer, or by trimmers. They allow more flexible utilization than Level I products.

Level III product: advanced instruments

These systems are exclusively digital, allowing the audiologist more fine-tuning capabilities. They may have multiple memories the patient can select depending on the listening situation (restaurant, TV, telephone, music). They may adjust incoming sounds automatically without a volume control. They have two microphones with fixed directionality. They may include noise reduction and fixed feedback corrections systems. They may automatically detect wireless phone, FM systems.

Level IV product: more complex digital technology

These systems include the newly developed systems of microphones with adaptive directionality, complex noise reduction systems, speech recognition systems, adaptive feedback correction systems, adaptive automatic fitting taking account of the usual environment conditions, wireless communication between the two fitted hearing aids, etc…

4.2.2.2 New proposed classification: complexity scale

This classification is more precise than the four-level classification described above.

Indeed, the four ordinal categories classification is not always easy to implement because the options offered by the HA are not always comparable and present in one category. These options may be compared to those offered in cars, and it is not always possible to classify various brands of cars.

To limit this difficulty, we propose to give an empirical, albeit arbitrary, value to each technical feature proportionally related to its importance for hearing recovery quality. A weight is assigned to each characteristic and these weights are based on the literature review and on our own clinical experience.

A higher weight is given to the characteristic with the most important impact on hearing recovery quality: amplification types, microphone, noise reduction, feedback reduction.

Non discriminant parameters receive a lower weight: the maximum output, the maximum distortion rate. The number of channels received a low weight because the ideal number of channels in not yet clearly defined. The sum of the different weights determines the HA complexity “index”. The maximum possible value for this index is 61.

This complexity scale is a first proposal that may serve as a tool to compare the different HA taking into account their functionality for the patients’ quality of hearing.

This scale should be finalised with the producers, the importers, the audioprothesists, and the users (the patients) in a subsequent stage.

This scale must also be completed by a clear definition of mandatory characteristics that must absolutely be present to define the HA complexity index. Indeed, all the parameters do not present the same importance. This scale must also be compared to the official French HA classification. Until now in France, each HA received a number of points calculated on items A and B of Table 14. This number of points defined the HA official price. This classification is going to be modified. The HA will be classified in 4 groups. The French classification is used to define the HA reimbursement amount for children. For adults, it is also used for reimbursement by complementary insurances.

48 Hearing Aids KCE Reports 91

Table 15 shows the empirical values we have given to the different parameters.

Table 15: Empirical value given to the different parameters to construct the complexity scale.

HEARING AID CHARACTERISTICS points

Amplification Linear (with peak clipping or compression limiter) 5

Non-linear 10

Multiband adaptative directionability 10

Noise reduction 6

Voice enhancement 4

Feedback reduction

Static 2 Dynamic 4 Average maximum output 90 dB (2cc coupler)

110-120dB 1

Environment automatic adaptation 1

Induction coil 1

Audio input 1

Second micro to allow M and T together 1

Automatic coil or audio detection 1

Battery life

<150h 1 150-199h 2 200-250h 3

>250 4 Optimised solution for binaural fitting or wireless detection 2

Music detection and adaptation 2

Wind noise reduction 1

4.3 RESULTS