Firearms are a common source of impulse noise that may potentially damage a hearing organ. It is not easy to predict soldiers' personal susceptibility to noise exposure.
The purpose of this study was to evaluate of the transient evoked otoacoustic emission (TEOAE) and distortion-product otoacoustic emission (DPOAE) before and after shooting and compare it with conventional pure tone audiometry. Standard pure tone audiometry, tympanometry, TEOAE and DPOAE measurements were recorded before and 10-15 minutes after shooting.
Ten male soldiers (20 ears) were exposed to impulse noise from automatic gunfire (15 single rounds of live ammunition). They did not use any earplugs. The reduction in amplitude of the TEOAE after shooting was 3.1 and 5.1 as SPL for 3 and
4 kHz respectively for the right ear and 4.3 dB SPL for 1 kHz and 0.6 dB SPL at 2 kHz for the left ear.
The greatest reduction in DPOAE occurred at frequencies of 1.0 kHz (3.8dB SPL) and 3.0 kHz (2.9 dB SPL) for the left ear. There were no differences in the audiometric thresholds before and after shooting. Emissions appear to be more sensitive for monitoring early cochlear changes after shooting, than pure tone audiometry.
Keywords: otoacoustic emissions (TEOAE, DPOAE) firearms, shooting
|How to cite this article:|
Konopka W, Zalewski P, Pietkiewicz P. Evaluation of transient and distortion product otoacoustic emissions before and after shooting practice. Noise Health 2001;3:29-37
The discovery of otoacoustic emission (OAE) has given a new possibility in early diagnosis of the auditory system. Since 1978 OAE has played an important role in clinical practice as a method of universal neonatal screening and monitoring of micromechanical function of the cochlea (Kemp et al.,1993). Transient evoked otoacoustic emission (TEOAE) and distortion product otoacoustic emission (DPOAE) are noninvasive, objective and frequency specific tests for evalua-ting hair cell damage caused by noise and other etiological factors (Franklin et al., 1991; Schmiedt et al., 1986).
|How to cite this URL:|
Konopka W, Zalewski P, Pietkiewicz P. Evaluation of transient and distortion product otoacoustic emissions before and after shooting practice. Noise Health [serial online] 2001 [cited 2020 Feb 23];3:29-37. Available from: http://www.noiseandhealth.org/text.asp?2001/3/10/29/31760
Sounds of high intensity often cause damage to the organ of Corti. Many publications have described the pattern of cellular damage or their loss. It is well known that the outer hair cells often get damaged first (Zenner, 1997). There are data that OAEs in humans and in animals become weaker after short exposures to noise (Lonsbury-Martin et al., 1991; Sliwinska -Kowalska et al., 1993) and OAE measurements appear to be a sensitive method of monitoring the early cochlear changes after noise-induced trauma (Hotz et al., 1993).
The published results about hearing loss caused by industrial noise, show that TEOAE and DPOAE provide the possibility of monitoring the development of noise- induced trauma (CEliwiflska-Kowalska 1998). According to Oeken (1998) measuring the DPOAE upon acute acoustic trauma could be relevant to prognosis for therapy.
Noise induced hearing loss is usually measured as temporary threshold shifts (TTS) or permanent threshold shifts (PTS) by pure tone audiometry but very seldom by OAEs.
Firearms are a common source of impulse noise that may potentially damage the hearing organ. Especially in countries where military service is compulsory, a large portion of the population is exposed to such noise. It is very important for soldiers to identify their individual susceptibility to noise exposure. It is difficult to predict temporary or permanent damage to hearing sensitivity (Henderson et al., 1993).
The aims of this study were to evaluate transient evoked otoacoustic emissions and distortionproduct otoacoustic emission before and after shooting and compare with conventional pure tone audiometry.
| Material and Methods|| |
Our material comprises 10 male soldiers (20 ears) who were in obligatory military service, with an average age of 20 years. There were in military service for 3 months and it was their shooting training. Written consent was obtained from all subjects and the project was approved by the local University Ethics Committee. The soldiers were exposed to impulse noise from automatic gunfire. The shooting range included 15 single rounds ( 150-165 dB peak level measured at the ear ) of live ammunition. They did not use any hearing protectors.
Conventional pure tone audiometry, tympanometry, evoked transient and distortion product otoacoustic emissions, were recorded before and about 10-15 minutes after shooting practice.
All the testing was performed in a relatively quiet room in a building on the grounds of the military installation.
In the same group OAE and PTA were measured twice with a 10-minute pause without noise exposure.
Otoacoustic emissions were recorded using an ILO 292 Echoport version 5.0. TEOAE recordings of 260 sweeps were collected for every subject at a stimulus level of 80 + 2dB SPL using 80 s duration clicks. An artefact rejection level of 4.6 mPa (47.3 dB SPL) was used throughout the recording session. Each response was windowed from 2.5 to 20 ms post stimulus and bandpass filtered from 500 to 6000 Hz. DPOAE were recorded with the DP- Gram procedure. The 2f1-f2 DPOAE were recorded at a single level of 70 dB SPL. The f2 /f1 ratio was held constant at 1.22 while f1 and f2 varied from 0.8 to 5.2 kHz and from 1.0 to 6.3 kHz. Averaging was used until the "noise floor" did not change any more. Only responses with an amplitude at least two standard deviation above the noise were used in the results. The statistical analysis was done with the Wald-Wolfowitz test with a significance level set as p< 0.05.
| Results|| |
All subjects had bilateral audiometric thresholds from 10 to 20 dB HL for the audiometric frequencies to 3 kHz, and 25-30 dB HL for 4 to 8 kHz. [Table - 1],[Table - 2] before and after shooting. We did not notice any significant differences.
The tympanograms were normal (type A, with middle-ear pressure between -80 and +50 daPa) and the presence of acoustic reflex at normal levels.
The results were separately analysed for each ear immediately after noise exposure. The mean change in TEOAE level was calculated separately for each frequency band. Significant reduction in amplitude of the TEOAE after shooting was found for the frequencies 1, 1.5, 2, 3 and 4, kHz for the right ear with a mean change of 2.6 dB SPL and for 3 kHz, 3.1 dB SPL (p<0.02 ) and for 4 kHz, 5.1 dB SPL (p<0.03).
The decrease in amplitude of the TEOAE was significant for the left ear for only 1 kHz (4.3 dB SPL, p<0.01) and 2 kHz (0.6 dB SPL, p<0.05) after noise exposure.
DPOAE alteration as a amplitude reduction was seen in 19 of the 20 tested ears. The mean amplitude of the DPOAE was decreased over the whole range. The mean change for the right ear was 0.8 dB SPL, and for the left ear 2.0 dB SPL for the frequencies 1, 2, 2.5, 3, 4, 5 and 6 kHz. The greatest reduction occurred for 1.0 kHz -(3.8 dB SPL, p<0.01) and 3.0 kHz - ( 2.9 dB SPL, p<0.04 ) for the left ear .
| Discussion|| |
Exposure to impulse noise during compulsory military service depends on the number of shots, or explosion impulses, distance of injured ear from causal firearm as well as on hearing protectors usage.
Changes induced by moderate or severe noise exposure that give rise to TTS, have been shown to alter the amplitude or frequency composition of transient evoked otoacoustic emissions (Kemp, 1982), distortion product otoacoustic emissions (Schmiedt, 1986; Martin et al. 1987; Sutton et al 1994) and spontaneous otoacoustic emissions, (Norton et al. 1989; Furst et al. 1992). Hotz et al. (1993) used OAEs to monitor changes in cochlear function resulting from exposure to firearms, among military personnel after a 17week training period. Significant bilateral changes in click evoked OAE amplitudes were observed in the frequency range 2-4 kHz. No preponderance of the left ears was noted.
Attias et al. (1996) found reduced click evoked OAE levels for the frequencies 1, 2, 3 and 4 kHz in patients with normal audiograms, after noise exposure (10 minutes exposure to white noise at 90 dB SL).
In our group, reduction of the TEOAE amplitude was found especially for 3 and 4 kHz for the right ear and for 1 and 2 kHz for the left ear. The amplitude reduction of the TEOAE was actually greater in the right ear than in the left one for most frequencies.
The greatest effect of noise exposure on the DPOAE amplitude concerned left ear for 1.0 and 3.0 kHz.
All our shooters were right-handed and probably the asymmetrical effect resulted from the shooting posture depending on the shadow effect of the body.
We did not notice any differences between audiometric threshold before and after shooting.
Reduced TEOAE and DPOAE levels in noise exposed soldiers may be the first early indication of potential hearing loss. Clinical experience with otoacoustic emissions indicates that OAE may play a role as a screening method for the soldiers exposed to noise and as a tool for monitoring early changes in the cochlea. TTS measurement is still the most widely used method for investigating reversible cochlear effects in the human. In our opinion small changes in the function of the cochlea can be monitored by measuring TEOAE and DPOAE especially in cases where classical audiometry is less sensitive.
| Conclusions|| |
- The effect of noise exposure on TEOAE was seen especially for 3 and 4 kHz and on DPOAE for 1.0 and 3 kHz.
- The amplitude reduction of the TEOAE was often greater in the right ear while DPOAE showed changes in the left ear. 3. Emissions seem to be more sensitive for monitoring cochlear changes than pure tone audiometry.
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Department of Otolaryngology Military Medical University, Zeromskiego 113, 90-549 Lodz
Source of Support: None, Conflict of Interest: None
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5]
[Table - 1], [Table - 2]