Download Audiometric Requirements for the Neuromonics Tinnitus Treatment

Neuromonics Tinnitus Treatment: Audiometric Requirements
AUDIOMETRIC CONSIDERATIONS
Essentially, the main audiometric requirement is the ability to measure hearing thresholds in a
calibrated fashion across the range from 250 Hz to 12.5 kHz. While the 250 Hz to 8 kHz is
standard for audiometry, this is insufficient for tinnitus clinic purposes, as many of those patients
who were thought to have normal hearing actually have a loss restricted to the very high
frequencies. An important study of very high frequency audiometry in tinnitus sufferers found that
there was an almost universal incidence of hearing loss in frequencies greater than 8 kHz
(Domenech, et al., 1991). Recent evidence indicates that the high frequency audiometric hearing
thresholds are valid and reliable, and constitute a better early indicator of noise-induced hearing
loss and acoustic trauma than the lower frequencies (Ahmed, et al, 2001). That report also noted
that these frequencies are rarely tested in the usual clinic assessments, despite actually
constituting a very large proportion of human frequency sensitivity. It concluded that the very high
frequencies were an accurate indicator of any damage to the auditory system, even if the hearing
loss was very limited.
Recent animal studies of the neurophysiological response to noise trauma found that it leads to a
high frequency hearing loss, particularly worse in the frequencies greater than 8 kHz (Norena &
Eggermont, 2005). It was found that this loss can lead to a strongly reorganized tonotopic map,
but this was also able to be prevented by providing an enriched acoustic environment in the
frequency range of the hearing loss. Lower frequency sound enrichment clearly did not work as
well as sounds that matched the high frequency loss. As a result of this objective evidence, those
researchers have subsequently recommended that tinnitus treatments provide acoustic signals
that are tailored to correct for hearing loss, so that stimulation is provided across the broadest
possible range of neurons (Eggermont, 2005).
These experimental findings of the role of the higher frequencies in tinnitus are also consistent with
clinical experience with patient descriptions of their tinnitus, and the greater incidence of a more
conclusive pitch match when the higher frequencies are offered as an option (Vernon & Meikle,
1988). In a sample of 90 consecutive tinnitus clinic patients, it was found that the substantial
hearing loss was generally only apparent in the frequencies greater than 8 kHz (Davis, Wilde and
Steel, 1999). That study also found that mean pitch match was 8 kHz, and so many patients fell
above that average. Thus, without those higher frequencies to offer as a comparison with their
tinnitus, it is not possible to check for octave confusion.
Clinical measurement of tinnitus seems to have had less attention in recent years, perhaps
because the reasons for audiometric measurement may not have been clear to early TRT
researchers. Evidence for this was that the early noise generators were called white noise
generators, even though they did not produce an equal frequency response across the full hearing
range. One study of actual ear-level output showed that most patients with a typical hearing loss
only received a narrow band of noise centered around 2 kHz (Sheldrake, Coles & Foster, 1995).
Other prominent European tinnitus researchers have subsequently proposed that the efficiency of
TRT might be improved by modifying acoustic stimuli to account for each individual’s hearing loss
(Baguley, Beynon, and Thornton, 1997). In keeping with this, the Neuromonics treatment aims to
provide the broadest possible frequency range of acoustic output to ensure maximal stimulation of
all corresponding acoustic pathways.
Another of the aims of the Neuromonics Tinnitus Treatment is to provide a stimulus that is able to
be effective at the lowest possible sensation level, and so enable a relaxation response to be
maximized. This is in keeping with experimental comparisons of the effects of masker bandwidth
by Kemp and George (1992), who found that the broadest of the bandwidths tested (0.1 to 15 kHz)
tended to mask at the lowest sensation level, and that the additional high frequency response
©Neuromonics Pty Ltd
Page 1 of 6
DocNo 0_W01 Rev 0.2
Neuromonics Tinnitus Treatment: Audiometric Requirements
tended to most benefit those with higher pitched tinnitus. As the long term spectral average of
relaxation music has a low frequency emphasis, it is the antithesis of what is required for those
with a high frequency hearing loss, and considerable spectral modification is required to counter
this (Davis, Wilde & Steed, 2002). Neuromonics also aims to maximize perception of natural
musicality across the whole range of frequencies that normal hearing listeners take for granted.
To enable this, the hearing thresholds across the full frequency range of human hearing need to
be reliably measured so that the output of the Neuromonics Processor can be individualized
accordingly.
Calibration Considerations
The lack of calibration standards for defining dB HL in the higher frequencies had previously
retarded their practical measurement, but in 1998, consensus was reached and an international
standard was published (ISO/TR 389-5:1998). Prior to that, the USA (ANSI) and European Union
(EU) homogenized several audiometric equipment standards. As there was no ANSI standard for
equipment for the high frequencies, the USA adopted the EU standard, referred to as: IEC 6454:1994 Audiometers. Part 4: equipment for extended high-frequency audiometry. This standard
specifies the need for equipment to provide pure tones at 10 kHz, as well as at 9, 11.2 and 14 kHz.
This is because the physical dimensions of the higher frequencies are acoustically quite distinct,
and the tonotopic representation in the cortex can be expected to be arranged equally as distinctly.
A practical reason to determine hearing thresholds at least around 10 kHz is that many tinnitus
patients with significant hearing loss across the speech range have no residual hearing left at
equipment limits at 12.5 kHz (typically limited to 80 dBHL). Additionally, when the mean hearing
thresholds in a tinnitus clinic sample at 8, 10 and 12.5 kHz (Davis, 1998) are graphically plotted, an
extrapolation of average values at 10 kHz underestimates the actual mean thresholds by more
than 5 dB. As the standard deviations were also greater for the high frequencies than for the
speech frequencies, some individual’s variations would even be greater, and so directly measured
(rather than extrapolated) thresholds are much more empirically accurate.
Audiometry for the >8 kHz region requires special headphones. The standard audiometric
headphones have changed little in the last half century, and were not constructed with the
measurement of the high frequencies in mind. The standard covers three styles. The insert type is
the Etymotic Research ER-2, the closed supra-aural type earphone is the Sennheiser HDA 200.
The open type supra-aural earphone is the Koss HV/1A, but it is now out of production (Frank,
2001).
The test/retest reliability of high frequency audiometry has been shown in several controlled
studies to be acceptable once the purpose-built earphones are used (ISO/TR 389-5:1998).
Because of the dimensions of the very high frequency sound waves, partial canal collapse has a
greater effect than for the < 8 kHz frequencies, and so all high frequency earphones are either
insert style or supra-aural to reduce pinna-induced collapse. Additionally, since partial wax
occlusion has a greater effect in high frequencies than it does for the < 8 kHz frequencies, this
may need greater care. It is also a reason why we have a preference for the supra-aural type. The
insert phones also have the disadvantage of being less robust and requiring refill eartips, and they
produce a sense of occlusion that reduces the validity of tinnitus pitch/loudness matching.
Some audiometers offer pure tones at 12.5 kHz while others do so at 12 kHz; practically speaking,
these two are considered to be interchangeable as far as calibration is concerned, due to the
purpose-built high frequency headphones having a flat frequency response in that region.
Maximum output of audiometers for the higher frequencies can also be much lower than the
speech range frequencies. For example, the Maico MA53 maximum output at 12.5 kHz is 80
©Neuromonics Pty Ltd
Page 2 of 6
DocNo 0_W01 Rev 0.2
Neuromonics Tinnitus Treatment: Audiometric Requirements
dBHL. Thresholds obtained at higher intensities than that might be erroneous due to distortion
(Fausti 2002, Personal Communication).
Other Tinnitus Clinic Measurement Considerations
There are several audiometer features required to provide the Neuromonics Tinnitus Treatment.
Some of the recommended audiometric testing procedures bear much resemblance to earlier
tests, but are now advocated for somewhat new reasons. For example, residual inhibition testing is
now advocated, not so much as a prognostic indicator, but instead primarily to dampen down any
tinnitus exacerbation that may arise from performing Loudness Discomfort Level (LDL)
assessments. To perform Residual Inhibition assessments properly, the audiometer needs to be
able to provide Narrow Band Noise in both ears simultaneously, and so it is included in the
following list of audiometric requirements.
The ability to provide all hearing thresholds through the same headphones is required to be able to
quickly provide two-alternative-forced-choice pitch match comparisons across the full frequency
range. Pitch matching is performed these days more for counseling than psychophysical reasons.
Having the one set of headphones also saves clinician time by not having to constantly open the
booth door to change headphones.
The loudness growth typically displayed in tinnitus patients is markedly steeper than those with a
matched sensorineural loss but no tinnitus (Davis, 1998). This greatly reduced dynamic range is
consistent with a central gain-type of phenomenon. Consequently 2 dB steps are required for
many tinnitus measurements, and so easy access to changing dB steps is helpful, particularly for
LDL testing.
The high-frequency pack’s broad band noise output is generally broader than the pink-type
(speech) noise that other audiometers actually provide, and so covers more of the range of
frequencies relevant to tinnitus. The true white noise Minimum Masking Level is more
representative of the effect that the Neuromonics Tinnitus Treatment can provide.
Upgrading Your Audiometer, or Choosing a New One
The high frequency pack can be retro-fitted to most existing audiometers listed here. The
headphones are typically the most expensive component, at around $US 1,000. The kit (including
headphones), installation and calibration cost between $US 1,500 - $US 2000. Once the
equipment is set up, the Tinnitus Clinic can also now offer an ototoxicity monitoring service for
agencies such as Oncology departments (Frank, 2001).
Neuromonics’ own clinics in Australia currently use Maico MA 53 audiometers with HDA200
earphones. However, the Maico 53 is not available in the United States and purchasing a used unit
from the internet is not recommended. The MedRx Avant Audiometer is a PC based audiometer
that is quite portable and includes all necessary features. The Interacoustics Equinox is a PCbased audiometer with all of the necessary features though decibel step sizes are set at only 5dB
and 1dB. The popular GSI 61 does not allow all frequencies to be accessed through one set of
headphones unless properly modified. The modification to the Sennheiser headset can be made
by most calibration technicians. It is important to specify that this modification be made when the
appointment for calibration is made as the modification is not usually done on-site. Additionally,
gold plated stereo patch cables are necessary with the GSI 61. If the headphone modification is
not done the GSI 61 is quite cumbersome switching from headset to headset during pitch match
testing. The Madsen Itera II is good value, but the lack of ability to perform proper residual
inhibition procedures is a limitation. It can be somewhat clumsily circumvented by using a binaural
CD recording of all the narrow band noises, and playing this back through an auxiliary input.
©Neuromonics Pty Ltd
Page 3 of 6
DocNo 0_W01 Rev 0.2
Neuromonics Tinnitus Treatment: Audiometric Requirements
Table 1 Feature Requirements*
The following table assumes that the high frequency option has been installed and the audiometer
has been calibrated to the high frequency earphones as per ISO 389-5 (1998).
Hearing
threshold
assessment
Minimum
Masking
Level
assessment
Loudness
Discomfort
Level
assessment
Residual
Inhibition
assessment
Graphing
Requirements
MedRx
Avant
Stealth
GSI
61
Interacoustic
Equinox
Madsen
Itera II
Siemen
UNITY
PC
Essential
Ability to measure 10 kHz and 12 kHz (or 12.5 kHz)
√
√
√
√
√
Preferable
Preferable
Preferable
Ability to test all frequencies through the HF headphones
Easy access to change dB steps
Ability to also provide 11.2 kHz, 14 kHz and 16 kHz for pitch
matching
Ability to provide Broad Band Noise greater than pink noise
(speech range)
√
√
√
√2
√
√
√
√
√
√1
√
√
√
√
√
√
√
√
√
√
Preferable
Essential
Ability to provide white noise that includes the 8-12 kHz range
Ability to provide pure tones in 2 dB steps
?
√
?
√
?
X 1dB step
?
√
?
√
Essential
Ability to provide Narrow Band Noise (NBN) at each of the
frequencies 0.25 to 12 kHz
√
√
√
√
√
Preferable
Essential
Ability to provide NBN in left and right channels simultaneously
Use of a paper audiogram that depicts the 10, 12 and 14 kHz
thresholds.
Ability to graph (on paper) tinnitus measures in terms of
sensation level and across time periods
Use of an electronic audiogram that depicts the 10, 12 and 14
kHz thresholds
The ability to electronically send test results to a database such
as NOAH3, and to be able to network with other computers
√
√
√
√
√
√
X
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
Essential
Essential
Preferable
Preferable
Legend:
√1= currently non-standard, so special request at factory required to hand-carry it though production
√2= currently non-standard, but can be done by calibrating agencies
*The provided chart was derived from spec sheets and inquiry to each manufacturer- Please check with your special instrument
dealer to ensure the audiometer meets the requirements needed to perform the proper testing.
Other Recommendations
For tinnitus assessments, it is recommended that stapedius reflex assessments not be
performed, as in some cases this has the potential to exacerbate tinnitus, or otherwise lose the
trust of the tinnitus patient that the clinician understands their particular tinnitus-related concerns.
Calibration:
The calibration agencies need to have the appropriate ear simulators, couplers and adapters to
calibrate the very high frequencies, so this does limit the number of agencies who can perform the
task. Those who have invested in the couplers (IEC 318 coupler and type 1 or type 2 adaptor for
the HDA200) should thus have the relevant calibration standards to hand to calibrate your
audiometer. If buying a new audiometer with the high frequency pack installed, it should be precalibrated from the factory, but it is worth checking this before committing to it. Some audiometers,
such as the Interacoustics, might need to be specially ordered to ensure they are set up optimally
for tinnitus clinic requirements.
Table 2. dBSPL to HL Transfer Values for the Higher Frequencies
©Neuromonics Pty Ltd
Page 4 of 6
DocNo 0_W01 Rev 0.2
Neuromonics Tinnitus Treatment: Audiometric Requirements
kHz
8
9
10 11.2 12.5 14
16
Sennheiser HDA200 17.5 18.5 22 23
28
36
56
Koss HV/1A
15.5 19.5 24 23
25
34.5 52
ER-2
18.5 14
20 28.5 36
41.5 55
Please note that this document presents only those audiometers that are sufficiently well known to
Neuromonics to be able to comment on. There may be others that are appropriate that we are not
yet aware of. Specifications can also change too.
If you would like any more information, or electronic versions of audiograms, etc, please do not
hesitate to contact Neuromonics.
©Neuromonics Pty Ltd
Page 5 of 6
DocNo 0_W01 Rev 0.2
Neuromonics Tinnitus Treatment: Audiometric Requirements
References
Ahmed, Dennis, Badra, Ismail, Ballal, Ashoor, & Jerwood, (2001). High frequency (10-18 kHz)
hearing thresholds: reliability, and effects of age and occupational noise exposure. Occup. Med.
Vol.51 No.4, pp. 245-258.
Baguley, D. M., Beynon, G. J., and Thornton, F. (1997). A consideration of the effect of ear canal
resonance and hearing loss upon white noise generators for tinnitus retraining therapy. The
Journal of Laryngology and Otology, 111(September), 810-813.
Davis, P.B., (1998). Music as Therapy in Rehabilitation of Tinnitus Patients: Effects of Spectral
Modification and Counselling. PhD Thesis. School of Speech and Hearing Science, Curtin
University of Technology, Perth, Western Australia.
Davis, P.B., Wilde, R.A., and Steed, L. (1999).Changes in tinnitus distress over a four month notreatment period: Effects of audiological variables and litigation status. Proceedings of the Sixth
International Tinnitus Seminar, Cambridge, UK. Published by the Tinnitus and Hyperacusis Centre,
London. p384-390.
Davis, P. B., Wilde, R.A., & Steed, L. (2002). Neurophysiologically-Based Tinnitus Rehabilitation
Using Tinnitus Desensitisation Music. In R. Patuzzi (Ed.), Seventh international tinnitus seminar
(pp. 188-190). Fremantle, Australia: University of Western Australia.
Domenech, J., Fuste, J., Traserra, G., & Traserra, J. (1991). High-frequency audiometry in the
clinical evaluation of tinnitus patients. In J.-M. Aran, & R. Dauman, (Eds.), Proceedings of the
fourth international tinnitus seminar, (pp. 49-51): Kugler Publications, Amsterdam / New York.
Eggermont, J. (2005). Cortical Tonotopic Map Reorganization and its implications for the treating
of tinnitus. Presented at the VIII International Tinnitus Seminar, Pau, France. 7 September 2005
Frank, T. (2001). High Frequency (8 to 16 kHz) Reference Thresholds and Intrasubject Threshold
Variability Relative to Ototoxicity Criteria Using a Sennheiser HAD 200 Earphone. Ear & Hearing,
April 2001, 161-168.
International Standards Organisation (1998). ISO/TR 389-5:1998(E) Acoustics — Reference zero
for the calibration of audiometric equipment —Part 5:Reference equivalent threshold sound
pressure levels for pure tones in the frequency range 8 kHz to 16 kHz
IEC 645-4:1994. Audiometers. Part 4: equipment for extended high-frequency audiometry.
Kemp, S. G., George, R. N. (1992). Masking of tinnitus induced by sound. Journal of Speech and
Hearing Research, 35, 1169-1179.
Norena, A.J. & Eggermont, J. (2005) Enriched Acoustic Environment after Noise Trauma Reduces
Hearing Loss and Prevents Cortical Map Reorganization. The Journal of Neuroscience, January
19, 2005 25(3):699-705.
Sheldrake, J. B., Coles, R. R. A., & Foster, J. R. (1995). Noise generators ("maskers") for tinnitus.
In G. E. Reich, & J. A. Vernon, (Eds.), Proceedings of the fifth international tinnitus seminar, (pp.
351-352). Portland, Oregon, USA: American Tinnitus Association.
Vernon, J. A., & Meikle, M. B. (1988). Measurement of tinnitus. In M. Kitahara (Ed.), Tinnitus :
Pathophysiology and management, (pp. 36-52). Tokyo: Igaku-Shoin.
©Neuromonics Pty Ltd
Page 6 of 6
DocNo 0_W01 Rev 0.2