유모세포의 손상으로 인해 발생하는 감각신경성 난청 (sensorineural hearing loss, SNHL)의 특징은 누가현 상으로 인해 역동범위가 건청인에 비해서 좁아져 있다. 중도 난청 이하의 경우 쾌적수준(most comfortable level, MCL)은 청력역치(hearing threshold level, HTL)의 1/2 내외의 기울기를 가지고 증가하며, 불쾌수준 (uncomfortable level, UCL)은 변화가 거의 없거나, MCL에 비해서 낮은 기울기로 증가한다. 그러나 중도 난청 이상의 경우는 MCL 및 UCL이 좀 더 가파른 기울기를 가 지고 증가하며 이때에도 UCL의 기울기는 MCL에 비해서 낮게 나타난다(Schwartz et al., 1988). 결과적으로 SNHL의 HTL이 증가할 때 MCL과 UCL의 증가율이 낮 아서 역동범위가 더욱 감소하며, 이로 인해 SNHL의 음량 증가(loudness growth)의 특징은 건청(normal hearing, NH) 또는 전음성 난청에 비해 비정상적으로 빠르게 증가 하는 것으로 나타난다(Allen et al., 1990; Elberling, 1999; Punch et al., 2004; Sammeth et al., 1989). 이 러한 이유로 역동범위가 좁은 SNHL이 착용한 보청기에 대한 이득과 최대출력(SSPL90 또는 OSPL90)을 효과적 으로 산출하기 위해서는 HTL에 따른 MCL과 UCL의 변 화를 살피는 것이 효과적이다(이경원 & 김진숙, 2009; Byrne & Dillon, 1986; McCandless & Lyregaard, 1983).
The purpose of this study was to examine changes in the most comfortable level (MCL) and the uncomfortable level (UCL) depending on hearing threshold level (HTL) by investigating loudness growth among persons with normal hearing (NH) and sensorineural hearing loss (SNHL) at 500 Hz and 3,000 Hz. Based on the results, this study intended to provide useful data to calculate gain or frequency response curve and SSPL90 or OSPL90 of hearing aid that was used by Koreans with hearing loss. The NH group consisted of 17 persons (17 ears) in total who had the pure tone threshold average of 20 dB HL or less and who were 23-33 years old (average: 27.9 years, SD: 4.0 years). The SNHL group consisted of 117 persons (161 ears) in total who had the HTL of 40-75 dB HL at 500 Hz or 3,000 Hz and who were 19-78 years old (average: 55.1 years, SD: 15.4 years). As for presented tone, 5% frequency-modulated tone was used at 500 Hz and 3,000 Hz. Based on the results of study by Allen (1990), loudness category (LC) for loudness growth test was divided to 7 LCs before the HTL of 40-75 dB for NH and SNHL was divided by 5 dB interval at 500 Hz and 3,000 Hz. The results of this study were as follows. First, at 500 Hz and 3,000 Hz, the MCL of NH was 51.5 and 56.8 dB HL while the UCL was 88.5 dB HL and 88.7 dB HL. Consequently, the MCL at 3,000 Hz was found to be higher by 5.3 dB (p < .05). Second, the MCL and the UCL of SNHL persons increased as a function of the HTL. However, slope of regression equation was low in the order of the HTL, the MCL and the UCL. Therefore, it was confirmed that dynamic range became narrow according to increase in the HTL. Third, the MCL showed the higher correlation with the HTL than the UCL. This study was meaningful in that the study intended to measure loudness growth of Koreans with NH and SNHL. The results of this study are expected to have influences on development of hearing aid fitting formula for Koreans with hearing loss.
INTRODUCTION METHODS & MATERIALS RESULTS DISCUSSIONS CONCLUSIONS
