Abstract:
The study aimed to determine the relationship between the medial olivocochlear (MOC) efferent reflex strength and susceptibility to noise-induced hearing loss (NIHL). This was evaluated by measuring the efferent suppression (ES) results from the contralateral suppression of Transient Evoked Otoacoustic Emissions (TEOAEs). It was predicted by several researchers that the strength of the MOC efferent reflex could determine the susceptibility to hearing loss (HL). The prediction was that an individual with a stronger MOC efferent reflex was less susceptible to developing a HL and an individual with a weaker MOC efferent reflex was more susceptible to developing a HL.
The design used in the study was a categorical independent comparative design. The independent values used in the study were the results from the contralateral suppression of the TEOAEs and the thresholds obtained from each participant’s pure tone audiogram. A quantitative research approach was used as different numerical values were collected from each participant. The numerical results obtained for each participant were objectively compared between the two identified groups.
Forty-one participants between the ages of 30 and 45 years, who had been exposed to noise levels between 89.3 dBA and 101.6 dBA at a Platinum mine in the North West Province, were used for the study. Twenty participants presented thresholds within normal limits of 0 to 15 dB and 21 participants presented with a permanent minimal NIHL with thresholds of 16 to 40 dB at 3000 Hz, 4000 Hz and 6000 Hz averaged. The data was analysed using the Statistical Package for the Social Sciences (SPSS) program version 25 (IBM Inc.). Non-parametric tests were used with the Mann-Whitney U test, where the ES of the two independent groups were compared.
The results showed no statistically significant difference in the ES of the normal hearing participants compared to the participants with a minimal HL. However, participants with normal hearing presented, on average, with a slightly stronger ES than the participants with a minimal HL. The lowest p-values in this study were calculated at 2000 Hz and 4000 Hz, with a p-value of 0.085 at 4000 Hz for the age category 30 to 35 years and a p-value of 0.086 at 2000 Hz for the age category 41 to 45 years. This suggests that it could be possible that the MOC reflex strength may predict the degree of HL. It is recommended that more research be done on contralateral suppression of TEOAE measurements on participants who present with permanent NIHL to possibly use the MOC reflex to predict susceptibility to HL in clinical practice.
