1. Phenotyping Noise Induced Hearing Loss with Audiometry and DPOAEs
Ishan Bhatt, Ph.D., NAU
Susan L. Phillips, Ph.D., UNCG
Mohsin Ahmed Shaikh, Ph.D. candidate, UNCG

2. Disclosure
Dr. Susan Phillips, Mr. Mohsin Ahmed Shaikh and I have no relevant financial or nonfinancial relationships to disclose.
The material presented today is based on audiometric and otoacoustic emissions (OAEs) data collected from the School of Music, University of North Carolina at Greensboro. The study was approved by the Institutional Review Board, UNCG ( ).

3. Key Factors in Noise-induced Hearing Loss
Globally growing hearing health concern
NIHL is a complex disorder
Some individuals are more susceptible than others
Gene
Environment
Gene-environment
interaction

4. Importance of Phenotyping NIHL
Success of gene mapping lies on the ability to define the target phenotype (i.e. trait of a disease) with accuracy and precision
(Schulze & McMahon, 2004)

5. Early Efforts: Phenotyping NIHL
Definition: Absolute audiometric thresholds at high frequencies (3 to 8 kHz)
Industrial population
Confounding variables
(Sliwinska-Kowalska & Pawelczyk, 2013; Van Laer et al., 2006)

6. Recent Efforts: Phenotyping NIHL
Definition: Bilateral audiometric notch within 4 to 6 kHz
Collage-aged student musicians
Better control over confounding variables
Potential NIHL Phenotypes
(Phillips et al., 2012)

7. Purpose of the Study
To evaluate the 4-6 kHz audiometric notch using a test battery of Distortion-Product Otoacoustic Emissions (DPOAEs)
Hypothesis: Musicians with 4-6 kHz audiometric notch will exhibit reduced DPOAEs compared to musicians without the notch

8. Method Sample 77 musicians 18-31 years
Normal otoscopic examination and tympanometric findings
DPOAE measured in the left ear
Online Survey
Primary instruments
Participation in ensembles
Exposure to music

9. DPOAE Test Battery DPOAE I/O function (ILO 292-II V6):
2 f1 - f2 DP frequency at 2, 3, 4 and 6 kHz
L2 ranging from 75 to 30 dB SPL in 5 dB steps
Formula-based approach: L1 = (0.4)L2+39
2f1 - f2 DPgram was measured from 2 to 8 kHz in 9 data points/octave with L1 and L2 were 60 and 40 dB SPL respectively

10. Statistical Analysis Repeated measure ANOVA
Within subject factors: 10 DP data points,
Between subject factors: Audiometric groups and music exposure
Covariate: Gender

11. Results 55/77(23 females and 32 males) participants completed survey
18/55 showed 4-6 kHz audiometric notch
5/55 showed high frequency drop

12. Results continue… DPOAE I/O function:
Main effect of exposure to music was statistically significant (p= 0.029)
Main effect of audiometric groups was not statistically significant (p>0.05) 1 2 3 4

13. Results continue… Main effect of music exposure: DPgram
Frequency range (2-4 kHz): F (3, 44) = 4.78, p= 0.006
Frequency range (4-8 kHz): F (3, 44) = 2.884, p= 0.046
Main effect of audiometric groups: No statistically significant effect found 1 2 3 4

14. DPOAEs in 3 Audiometric Configurations
DPgram: 2-8 kHz (9 data points/octave)

15. Standing Waves in the Ear Canal
Discussion
No effect of audiometric configurations on DPOAEs
Observation can be attributed to:
DPOAE recording limitations and/or
Physiological basis
Standing Waves in the Ear Canal

16. Damage to Stria Vascularis
Damage to OHCs
Damage to Stria Vascularis
Elevated audiometric thresholds and comparatively poor DPOAEs
Elevated audiometric thresholds and comparatively better DPOAEs
(Bhagat et al., 2010; Hofstetter, Ding, Powers, & Salvi, 1997; Ozturan, Jerger, Lew, & Lynch, 1996)
(Mills, Norton, & Rubel, 1993; Gates et al., 2002)

17. Conclusion
Musicians with higher music exposure are likely to show reduction in DPOAE amplitude
Further research in required to investigate DPOAEs in musicians with the 4-6 kHz audiometric notch

18. Future Research DPOAE recording using advance calibration technique
A well-defined control group of non-musicians may improve sensitivity of the future studies
Animal study to validate potential sub-phenotypes
Validate the music exposure survey

19. References
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