Clinical trial of a low-cost, solar-powered hearing aid

Abstract

ObjectiveIn July 2001 the World Health Organization (WHO) launched their "Guidelines for hearing aids and services fordeveloping countries". The objective of this study was to evaluate the clinical outcome of an analogue, low-cost, behind-theearhearing aid (BTE-HA) that met the minimum technical requirements outlined by the WHO.Material and MethodsA total of 25 subjects (17 males, 8 females; median age 74 years; range 50–86 years) were recruitedamong patients referred for audiological evaluation who consented to participate in the trial. All subjects had a hearing lossof ≤60 dB HL at 2 kHz, were mobile and mentally unimpaired; 13 were experienced users of HAs, 3 suffered from mixedconductive/sensorineural hearing impairment (HI) and the remainder had pure sensorineural HI. Based on pure-tone, speechand impedance audiometry the BTE-HAs were fitted, using the National Acoustic Laboratories-R (NAL-R) prescriptionrule, 21 binaurally and 4 monaurally. All fittings were validated by insertion gain measurements, and the immediate benefitwas measured by means of the speech recognition score in background noise (SRSN; signal:noise ratio = 10 dB) without andwith the HA. After a 6-week trial period a structured interview based on the International Outcome Inventory for HearingAids (IOI-HAs) was performed.ResultsThe results showed that the amplification of the HA deviated significantly from the NAL-R target at allfrequencies, giving significantly more amplification at 500 and 1000 Hz despite maximum bass-cut, whenever relevant, andsignificantly less amplification as required at 2, 3 and 4 kHz. The median SRSN without HAwas 48% (range 0–96%), whichimproved significantly to 80% (range 24–100%) with HA. The median individual difference in SRSN without and with HAwas 20% (range 0–72%). The total IOI-HA score with the test HA was 4.1 (range 2.6–4.6), showing that it offeredsubjectively high satisfaction and reduction in limitations of activity.ConclusionThe low-cost HA: (i) provides benefit to the hearing-impaired person; (ii) offers poor amplification in the highfrequencies; and (iii) gives subjective satisfaction similar to that for modern available HAs.