Clinical applications of otoacoustic emissions in Industry Prof. Dr. B. Vinck, MSc, PhD University of Ghent, Belgium
The 25th anniversary of the discovery of otoacoustic emissions (OAEs) [sounds that can be measured in the external ear canal following the presentation of an acoustic stimulus] was celebrated in 2003.
The past Cochlea is a passive system GEORG VON BEKESY
The past. Kemp s discovery that the ear makes sound while listening to sound had difficulty getting published Nature rejected his manuscript on the grounds that otoacoustic emissons would doubtless prove of little interest outside the community of clinicians concerned with the diagnosis of hearing impairment. The discovery of otoacoustic emissions (OAEs) sparked a revolution in our understanding of the physical basis of hearing. Ironically, it has been precisely in the area of clinical utility that the full potential of OAEs has yet to be realized.
Otoacoustic emissions Where are we today?
4 types of OAEs were described Otoacoustic Emissions Spontaneous OAE Evoked Otoacoustic Emissions (EOAE) Poststimulatory OAE Perstimulatory OAE Transient OAE SFOAE DPOAE
existing models of cochlear function were modified significantly to acknowledge the reality of active processing several studies tried to relate OAEs to several neural and psychoacoustical phenomena. emitted responses were described in a number of experimental species commonly used as research models of hearing impairment
OAE generation Exactly how OAEs arise and how they are propagated in the cochlea is still in debate Experimental and theoretical evidence demonstrates two different mechanisms of generation
Mechanism based taxonomy of OAEs Otoacoustic Emissions OAEs that arise by Linear Reflection OAEs that arise by Non-linear distortion Reflection Emissions due to coherent reflection from random impedance perturbations Distortion Emissions due to nonlinearities acting as sources of traveling waves SOAEs Due to standing waves caused by coherent reflection Evoked Emissions mechanisms Shera, 2004 A mixture of both mechanisms
OAE generation Exactly how OAEs arise and how they are propagated in the cochlea is still in debate Experimental and theoretical evidence demonstrates two different mechanisms of generation OAEs are generated as a by-product of the electromotile vibrations of the OHCs Presence of OAEs demonstrates that the cochlea act as a cochlear amplifier that enhances the sensitivity and frequency tuning of the vibration of the cochlear partition
Clinical applications From the beginning : three major applications of OAE testing in clinical settings became apparent : differential diagnosis of hearing loss hearing screening in difficult-to-test patients such as newborns serial monitoring of progressive hearingimpairment conditions
AUDITORY SCREENING Auditieve screening
AUDITORY NEUROPATHY
Since this recognition of the major clinical applications of OAEs, other uses have emerged : resolving the legitimacy of medico-legal claims involving compensatory payments for hearing loss based on the sensitivity of OAEs to the intactness of the OHC system and its susceptibility to noise-induced damage the use of emissions to measure the functional intactness of the descending auditory nervous system.
Since this recognition of the major clinical applications of OAEs, other uses have emerged : resolving the legitimacy of medico-legal claims involving compensatory payments for hearing loss based on the sensitivity of OAEs to the intactness of the OHC system and its susceptibility to noise-induced damage the use of emissions to measure the functional intactness of the descending auditory nervous system.
Relationship noise and OHC damage
IHC ROW 3 ROW 2 ROW 1 Evolution damage
Literature data Hall & Lutman (1999) : the various OAE measures have the potential to distinguish small changes in cochlear function from measurement uncertainty, and hence show promise for monitoring cochlear function in ears exposed to noise or other hazards.
Study : TTS : Growth & Recovery pattern assessed by OAE Protocol Vinck et al, 1999 Pre-stimulatory evaluation 60 minutes exposure 60 min. postobservation interval Post evaluation Audiometry Oto-admittance evaluation TEOAE s DPOAE s (DP-GRAM Every 10 minutes TEOAEs DPOAES Every 4 minutes TEOAEs DPOAES
Study : TTS : Growth & Recovery pattern assessed by OAE Results Transient OAE s 90 90 Repro :: Globaal 90 Repro : 4 Khz 80 80 70 60 No difference 70 60 50 50 40 30 20 40 30 20 10 1 3 5 7 9 11 13 15 17 19 21 PER POST 10 76 0 5 10 15 20 25 0 5 10 15 20 25
Study : TTS : Growth & Recovery pattern assessed by OAE Results DPOAE s 10 8 6 4 2 0 DP-GRAM 1538 Hz 1 3 5 7 9 11 13 15 17 19 21 0 DP-GRAM 4004 16 14 16 15 15 12 14 14 10 13 13 12 12 8 11 11 6 10 10 4 9 9 1538 Hz 4004 Hz 4358 Hz 4761 Hz 8 8 2 7 7 1 4 7 6 1 4 DP-GRAM 4358 Hz 7 10 13 16 19 22 6 1 4 DP-GRAM 4761 Hz 7 10 13 16 19 22 DPOAE response levels : TTS growth and recovery 18 16 14 12 10 8 DP-GRAM 5188 Hz 10 13 16 19 22 5188 Hz 6 1 4 7 10 13 16 19 22
Literature data Plinkert (1999) : The results suggest that TEOAE provides a more sensitive and more objective method of detecting a subtle noise-induced disturbance of cochlear function than do PTA.
Literature data Konopkwa (2000) : The purpose of this study was evaluation of the click evoked otoacoustic emission (TEOAE) and distortion-product otoacoustic emission (DPOAE) before and after shooting and comparison with conventional pure tone audiometry. Emissions seem to be more sensitive for monitoring early cochlear changes after shooting than pure tone audiometry.
Literature data Sliwinska et al. (2002) : The results of the study suggest that OAEs, are likely to become a valuable method for assessing early hearing damage caused by exposure to noise.
Literature data Lapsey-Miller (2004) : otoacoustic emissions show promise in detecting noise-induced inner ear changes
AUDIOMETRY OTOTACOUSTIC EMISSIONS Measures Hearing threshold Measures OHC damage Both are fruit!!!
60% Damage 1 ROW UHC No damage AUDIOGRAM Altschuler, 1992
Follow-up OAE study in industry (Vinck et al., submitted for publication, 2006)
Study population 626 employees (571 males, 71 females) Mean age : 43.3 yrs (SD = 9.4 yrs)
120 100 AGE DISTRIBUTION NOISE POPULATION 16% n = 626 18% n = 571 n = 55 er e Number of employees 80 60 40 20 0 13% 12% 11% 10% 7% 2% 1% 0% 0% 15 20 25 30 35 40 45 50 55 60 65 70 3% 3% 1 % 1% 1% 1% 0% 0% 0% 0% 0% 15 20 25 30 35 40 45 50 55 60 65 70 Sex : Male Age (years) Sex : Female
Study population : A. Test population 626 employees (571 males, 71 females) Mean age : 43.3 yrs (SD = 9.4 yrs) Mean exposure duration : 15 yrs (SD= 11.4 yrs)
120 100 80 60 40 Number of employees Number of employee 20 0 0 10 20 30 40 50 120 100 80 60 40 < 30 years 0 10 20 30 40 50 30-40 years 20 0 0 10 20 30 40 50 0 10 20 30 40 50 40-50 years Exposure duration (in years) 50-60 years
Study population 626 employees (571 males, 71 females) Mean age : 43.3 yrs (SD = 9.4 yrs) Mean exposure duration : 15 yrs (SD= 11.4 yrs) Mean exposure level : 83.3 dba (SD = 9) [60-93 dba]
Study population : B. Control population 3500 Males and 440 Females Mean age : 44.2 years (SD = 8.3 years) Not exposed to industrial noise Used as a reference population for OAEs
Methods Dosimetry Pure-tone audiometry (2006 only) Otoacoustic Emissions (2005 and 2006) transient OAE & Distortion Product OAE
OAE - gram Reference population was used to construct an OAE gram, based on TEOAE and DPOAE measurements Reproducibility % are used as key parameter
Results 1. Influence of age
Pure-tone audiometry OAE-gram Hearing loss (db HL) 5 10 15 20 25 30 +60 yrs < 30 yrs 30-40 yrs 40-50 yrs 50-60 yrs Repro loss in % (re: controls) 100 90 80 70 60 50 40 30 20 < 30 yrs 30-40 yrs 40-50 yrs 50-60 yrs 35 10 +60 yrs 40 2 50Hz 500 Hz 1000Hz 2000Hz 4000Hz 8000Hz 0 1.0Khz 2.0Khz 3.0Khz 4.0Khz 5.0Khz 6.0Khz 1.5Khz 2.5Khz 3.5Khz 4.5Khz 5.5Khz 6.5Khz Age Frequency in Hz
Pure-tone audiometry OAE-gram Hearing loss (db HL) 5 10 15 20 25 30 +60 yrs < 30 yrs 30-40 yrs 40-50 yrs 50-60 yrs Repro loss in % (re: controls) 100 90 80 70 60 50 40 30 20 < 30 yrs 30-40 yrs 40-50 yrs 50-60 yrs 35 10 +60 yrs 40 2 50Hz 500 Hz 1000Hz 2000Hz 4000Hz 8000Hz 0 1.0Khz 2.0Khz 3.0Khz 4.0Khz 5.0Khz 6.0Khz 1.5Khz 2.5Khz 3.5Khz 4.5Khz 5.5Khz 6.5Khz Age Frequency in Hz
20 15 DP-GRAM < 30 yrs 10 5 0 40-50 yrs 30-40 yrs -5 50-60 yrs -10-15 +60 yrs -20 DP @ 841Hz DP @ 1189Hz DP @ 1682Hz DP @ 2378Hz DP @ 3364Hz DP @ 4757Hz DP @ 6727Hz DP @ 1000Hz DP @ 1414Hz DP @ 2000Hz DP @ 2828Hz DP @ 4000Hz DP @ 5657Hz DP @ 8000Hz
TEOAE Band repro 100 90 80 < 30 yrs Repro in % 70 60 50 30-40 yrs 40-50 yrs Same tendency for SNR & Response levels 40 30 20 REPRO1K REPRO1.5K REPRO2K REPRO3K REPRO4K 50-60 yrs +60 yrs
Results 1. Influence of age 2. Influence of exposure duration (corrected for age)
AUDIO 45 40 Hearing Loss in db (HL) at 4 khz 35 30 25 20 15 (1) (2) (3) (4) (5) < 5 yrs 5-10 yrs 10-20 yrs 20-30 yrs 30-40 yrs 10 5 Exposure time 1 2 3 4 5 e xpcode
OAE-GRAM 70 65 Repro loss in % (re: Control) at 4 khz 60 55 50 45 40 35 30 25 20 15 (1) (2) (3) (4) < 5 yrs 5-10 yrs 10-20 yrs 20-30 yrs 10 (5) 30-40 yrs 5 1 2 3 4 5 e xpcode
Pure-tone audiometry OAE-gram Hearing loss (db HL) 5 10 15 20 25 30 35 40 45 50 < 5 yrs 5-10 yrs 10-20 yrs 20-30 yrs 30-40 yrs A250Hz A500Hz A10 00H z A2000 Hz A4000H z A80 00H z Repro loss in % (re: controls) 90 80 70 60 50 40 30 20 10 0 1.0Khz 2.0Khz 3.0Khz 4.0Khz 5.0Khz 6.0Khz 1.5Khz 2.5Khz 3.5Khz 4.5Khz 5.5Khz 6.5Khz Exposure time Frequency in Hz
Results 1. Influence of age 2. Influence of exposure duration (corrected for age) 3. Influence of exposure level
Influence of exposure level No significant difference on OAEs and Audiometry
Results 1. Influence of age 2. Influence of exposure duration (corrected for age) 3. Influence of exposure level 4. Follow-up 2005-2006
Repro loss in % (re: controls) 100 90 80 70 60 50 40 30 20 10 p < 0.001 Deterioration of 3-10 % esp. Low-Mid frequencies OAE-gram 2005 2006 0 1.0Khz 2.0Khz 3.0Khz 4.0Khz 5.0Khz 6.0Khz 1.5Khz 2.5Khz 3.5Khz 4.5Khz 5.5Khz 6.5Khz
Results 1. Influence of age 2. Influence of exposure duration (corrected for age) 3. Influence of exposure level 4. Follow-up 2005-2006 2006 5. Relation audiometry - OAE
1kHz 2kHz 4kHz 8kHz 1kHz -0,56* 2kHz -0,59* 4kHz -0,61* 8kHz -0,58* * Significant at p < 0.05 level
Conclusions OAEs have proven useful in monitoring the effects of agents, such as loud sounds on cochlear function There is accumulating evidence that it is possible to detect such adverse effects of noise on OHC function using OAEs before a related hearing loss can be detected by pure-tone audiometry. OAEs supply unique information about cochlear function in the presence of hearing problems It is this capability that make this technique valuable to use in a hearing conservation program for the early detection and as a complementary technique to the audiometric-test battery