Welcome to Cochlear Dead Regions and Implications for Fittings. Presenter: Audiologist, Speaker, Author. IHS Organizers: Housekeeping

Transcription

1 Welcome to Cochlear Dead Regions and Implications for Fittings Presenter: Ted Venema PhD Audiologist, Speaker, Author IHS rganizers: Fran Vincent Membership and Marketing Manager Ted Annis Senior Marketing Specialist Housekeeping This presentation is being recorded CE credit is available! Visit ihsinfo.org for details Note taking handouts are available at ihsinfo.org on the webinar page. Feel free to download now! 1

2 Agenda Describe cochlear dead regions in terms of cochlear hair cells and the cochlear traveling wave utline audiograms associated with cochlear dead regions Explain the rationale for the Threshold Equalizing (TEN) test State some examples and implications of cochlear dead regions for hearing aid fittings Q&A (enter questions in Question Box any time) CCHLEAR HAIR CELLS, THE TRAVELING WAVE & CCHLEAR DEAD REGINS 2

3 Cross Section of the Cochlea Spiral Ligament Helicotrema Temporal Bone Scala Vestibuli Scala Media Scala Tympani Basilar Membrane Spiral Ganglia Figure 1.2 Venema, T. Compression for Clinicians 2 nd edition, Cengage 2006 Normal Inner & uter Hair Cells Inner Hair cells Afferent Send sound information to the brain Figure 1.7 Venema, T. Compression for Clinicians, 2 nd edition, Cengage

4 Damaged uter Hair Cells uter Hair cells Efferent Receive sound information from the brain Figure 1.8 Venema, T. Compression for Clinicians, 2 nd edition, Cengage 2006 uter Hair Cells: The Active Cochlear Mechanism Note how embedded HCs actually pull tectorial membrane down 4

5 Cochlear Dead Regions Are Not Due to uter Hair Cell Damage HCs amplify & sharpen traveling wave peak Damage: reduces basilar membrane vibration Without HCs one would have about db SNHL This is the most common degree of HL (Presbycusis!) More severe SNHL means IHC damage as well HCs give about 50 db gain for lows; 65 db gain for highs Loss of sharpening traveling wave: Results in increased difficulty hearing in noise Slight drop in speech discrimination, but not much uter Hair Cell Contributions to the Traveling Wave HCs Sharpen Peak 1. Amplify 2. Sharpen Basilar Membrane Traveling Wave Envelope of Traveling Wave Basilar Membrane Displacement Figure 1.5 Venema, T. Compression for Clinicians, 2 nd edition, Cengage

6 The Traveling Wave: Naturally Sharpened vs Aided Natural traveling wave: 2 peaks from 2 tones close in Hz SNHL with HC damage: smaller rounded peaks Aided traveling wave: enlarges peaks but cannot sharpen Figure 1.2 Venema, T. Compression for Clinicians 2 nd edition, Cengage 2006 Cochlear Dead Regions However, Are Due to Inner Hair Cell Damage HCs tend to die before IHCs They are the moving part; more susceptible to aging and noise If HC damage causes about db SNHL More severe SNHL means IHC damage as well IHC damage really deteriorates Speech Discrimination! B/c garbled message is sent on to the brain Question: What audiograms suggests cochlear dead spots? To understand that, look at next few slides! 6

7 The Asymmetrical Traveling Wave Intense Low Hz traveling wave moves entire Basilar Membrane Intense High Hz traveling wave moves Basilar Membrane only at base Basilar Membrane Envelopes Basilar Membrane Displacement Upward Spread of Masking Intense Low Hz traveling wave (TW) moves entire Basilar Membrane Note that the Low Hz envelope covers a soft High Hz TW envelope Basilar Membrane Envelopes Basilar Membrane Displacement 7

8 It Doesn t Work the ther Way Around Soft Low Hz TW moves mainly the apical Basilar Membrane Intense High Hz traveling wave still moves Basilar Membrane only at base Basilar Membrane Envelopes Basilar Membrane Displacement AUDIGRAMS ASSCIATED WITH CCHLEAR DEAD REGINS 8

9 Low Hz Dead Regions Can Therefore Masquerade as Moderate Reverse HL Apex Base Low Hz Traveling wave In totally dead IHC region Will stimulate healthy hair cells In mid & high Hz regions Asymmetrical traveling wave Steep front; shallow, longer tail Total deafness in lows Looks like moderate low Hz SNHL High Hz Dead Regions However Have to Be Severe, Precipitous SNHL Apex Base High Hz Traveling wave In totally dead IHC region Will stimulate healthy hair cells In mid & low Hz regions Steep wave front must be intense For this to happen Due to asymmetrical TW shape Severe precipitous SNHL actually looks like mirror image of TW front 9

10 For example Apex Base For Example Apex Base 10

11 For Example Apex Base Cookie Bite Audiograms A Combination of the Above Apex Base 11

12 TESTING FR CCHLEAR DEAD REGINS: THE THRESHLD EQUALIZING NISE (TEN) TEST TEN Test Noise It is a broad band noise, delivered ipsilateral to tone Has unique spectral shape For normal HL, gives equal masked thresholds Eg. 50 db TEN gives 50 db HL across all Hz s So no, you cannot use your speech masking noise 12

13 TEN Noise Spectrum +10 Relative db Hz 10,000 Eg: 30 db TEN Gives 30 db HL Thresholds 13

14 Main Assumption Behind TEN Test Low Hz cochlear dead region resulting in 50 db HL thresholds Soft ipsilateral TEN noise (eg. 30 db HL) will elevate thresholds for low Hz tones. Apex (lows) Base (highs) Why? Because thresholds in dead region come from high Hz s They do not truly arise from the low Hz hair cells If the HL Is a True Moderate Low Hz SNHL (Not a Dead Region) The soft ipsilateral TEN will have little effect It will mask the healthy high Hz thresholds And elevate them as a result But the low Hz thresholds won t hear the TEN And the thresholds will be unchanged 14

15 Main Assumption Behind TEN Test Soft ipsilateral TEN noise (eg. 30 db HL) will elevate thresholds for high Hz tones. High Hz cochlear dead region resulting in 80 db HL thresholds Apex (lows) Base (highs) Why? Because thresholds in dead region come from low Hz s They do not truly arise from the high Hz hair cells If the HL Is a True Severe High Hz SNHL (Not a Dead Region) The soft ipsilateral TEN will have little effect It will mask the healthy low Hz thresholds And elevate them as a result But the high Hz thresholds won t hear the TEN And the thresholds will be unchanged 15

16 SME EXAMPLES AND IMPLICATINS FR FITTINGS Client with Mild Moderate SNHL Cochlear Dead Spots Not Suspected Figure 2.5 Venema, T. Compression for Clinicians, 2 nd edition, Cengage 2006 Masked symbols: thresholds with 30 db TEN 16

17 Client with Profound High Hz SNHL Cochlear Dead Spots Suspected Figure 2.6 Venema, T. Compression for Clinicians, 2 nd edition, Cengage 2006 Masked symbols: thresholds with 30 db TEN Client with Profound High Hz SNHL Cochlear Dead Spots Suspected Masked symbols: thresholds with 50 db TEN 17

18 Implications For Fitting Moderate Reverse SNHL Fit the transitions Not the worst thresholds! Severe precipitous high Hz SNHL Fit the transitions Not the worst thresholds! Apex Base Apex Base Fitting the Left Corner Audiogram?? Frequency Transposition X X X X X XXXXXX A bridge between Hearing Aids & Cochlear Implants 18

19 Ever Wonder What Sounds Are Like for People with Dead Regions? Recall testing those with reverse SNHL I suspect dead low Hz regions when reliability is poorer for lows, but I ve never asked them what the pure tones sounded like. Recall testing those with pronounced, precipitous SNHL These clients tell me the highs sound like a scratch, or that the highs feel like a tickle. thers have reports from their subjects as well They report tones in dead regions sound like noise however, this observation is inconsistent. Ratings of clarity Cannot be used as reliable indicators of dead cochlear regions. Keep It Simple You don t need a weatherman to tell you where the wind blows ~Bob Dylan Wet your finger and stick it in the air! If you see the suspicious audiograms, then suspect cochlear dead regions Present tone so client can hear it, then ask as to its quality If poor, then don t amplify in those Hz s! 19

20 References Moore, BCJ (2001). Dead regions in the cochlea: Diagnosis, perceptual consequences, and implications for the fitting of hearing aids. Trends in Amplification 5(1) Moore, BCJ (2001). Dead regions in the cochlea: Implications for the choice of high frequency amplification. In Seewald, RC & Gravel, JS, eds, A Sound Foundation through Early Amplification, Phonak AG Moore, BCJ (2004) New Version of the TEN test with calibrations in db HL. Ear & Hearing 25(5): Moore BCJ. Testing for Cochlear Dead Regions: Audiometer implementation of the TEN(HL) Test. Hearing Review. 2010;17(1):10 16,48. Venema, TH. Compression for Clinicians (2006); Ch 2 Cengage Publishing ISBN Questions Enter your question in the Question Box on your webinar dashboard 20

21 Contact Ted Venema, PhD: For more info on obtaining a CE credit for this webinar: THANK YU FR ATTENDING! 21