[Effectiveness of hearing aid provision for severe hearing loss]

In practice, the unilateral monosyllabic speech recognition score with hearing aid (WRS₆₅(HA)) is often below the maximum word recognition score with headphones (WRS_max), in particular for subjects with severe hearing loss. The aim of this study was to evaluate the efficiency factor Q of hearing aid provision, the ratio WRS₆₅(HA)/WRS_max, in patients with severe to profound hearing loss.

Data from real-ear measurements (REM), pure tone and speech audiogram, and speech recognition with and without hearing aid of 93 ears in 64 patients were examined. The patients visited the authors' hearing center for hearing aid evaluation in 2019. Deviations of the real-ear measured frequency-dependent output level values from the prescription targets NAL-NL2 and DSL v5.0 were analyzed. Spearman correlation coefficients for the speech intelligibility index (SII) were calculated for the parameters WRS₆₅(HA) and Q.

In more than 67% of the hearing aid fittings, output level values matched the target curves of NAL-NL2 or DSL v5.0 in the range of ±5 dB for frequencies from 0.5 to 4 kHz at 65 dB SPL. Nevertheless, WRS_max was not achieved with hearing aid at conversational speech levels of 65 dB SPL (mean deviations: 34.4%). However, WRS₆₅(HA) and Q were best when target values for DSL v5.0 were achieved at 65 dB SPL, which is associated with a higher SII.

For patients with severe to profound hearing loss, the prescription targets of NAL-NL2 and DSL v5.0 do not provide sufficient amplification for WRS_max to be achieved at a normal speech level of 65 dB SPL. It remains to be investigated whether alternative prescriptions with better audibility for input levels of 50 and 65 dB SPL might improve the effectiveness of hearing aid provision.