Trajectory of the Aging Cochlea Sumitrajit (Sumit) Dhar Professor & Chair Roxelyn & Richard Pepper Department of Communication Sciences and Disorders Fellow, Hugh Knowles Center for Hearing Science Northwestern University Evanston, IL IHS, September 2016
Learning Objectives Identify early signs of age-related hearing loss. Select the best tools for diagnosing agerelated hearing loss. Counsel patients about the likely trajectory of age-related hearing loss.
Cochlear mechanics and OAEs The life of the inner ear Clinical strategies for data quality Clinical parameters for data acquisition Case studies
Cochlear mechanics and OAEs The life of the inner ear Midlife crisis The elderly inner ear
Transient/Click Evoked Otoacoustic Emissions (TEOAE) Distortion Product Otoacoustic Emissions (DPOAE) Stimulus Frequency Otoacoustic Emissions (SFOAE) Spontaneous Otoacoustic Emissions (SOAE)
SFOAE 40 Level (db SPL) 30 20 10 0 P Total at 40 db SPL P Total at 40 db SPL w/ suppressor Phase (cycles) -10 1.0 1.5 2.0 0-5 -10 1.0 1.5 2.0 - = PSFOAE P Stimulus P SFOAE = P Total P Stimulus
Mechanics, Mechanisms, Modalities
Lessons from Kemp, 1978 Random noise recorded when closed cavity is stimulated with a click. Same stimulus in human ear shows response lasting beyond 10 ms TEOAE. We have to wait for the speaker to stop ringing. Continues to be the case; early TEOAE is not recorded. Different delays for responses to tone bursts of different frequencies cochlear origin.
Site of Generation Cochlea: observed delay in OAEs; recordings from BM & auditory nerve. Outer Hair Cells: concomitant ablation of OAEs and OHC (e.g., Davis et. al., 2002); loss of OAEs due to other insults associated with OHC damage (salicylate, noise, etc.). But where in the OHC?
Prestin KO Liberman et al., 2004
Verpy et. al., (2008); Nature Liberman et al., 2004
Cochlea Outer Hair Cell Stereocilia (transducer) Soma (?amplifier) Olivocochlear efferents Middle ear transmission
Frequency/Place Specificity
Idealized Spread of Excitation fp Stapes base apex
DPOAEs f2 f1 Stapes base apex
SFOAE/CAP-STC IT fs fp fs Stapes base apex Damage
IT Experiments
Tone Exposure Experiments
Normal Hearing Human Ears Charaziak, Souza, and Siegel, 2013
The Good News: SFOAE generation region in the chinchilla is much more localized at and above 3 khz. In humans, OAE generation regions appear to even be more restricted.
DPOAEs f2 f1 2f1-f2 Stapes base apex
65 db SPL 75 db SPL
The Good News: DPOAE generation area appears to be narrower in humans as compared to other laboratory animals. Stimulus levels up to 65 db SPL should yield place specific estimates of cochlear health.
OAEs are primarily produced by the outer hair cells. DPOAEs are most likely produced by steriociliary nonlinearities. OAE generation is generally frequency (place) specific. OAE generation is more place specific in the apical half of the cochlea. OAE generation appears to be more place specific in humans as compared to other species.
Cochlear mechanics and OAEs The life of the inner ear Clinical strategies for data quality Clinical parameters for data acquisition Case studies
30 20 10 0-10 -20-30 1 2 Frequency (khz) OAEs are vital signs of the life of the inner ear and allow exquisite monitoring of cochlear health.
Age related changes progress from the base to the apex of the cochlea. But when they start and how they progress is not established to our sa:sfac:on.
Stevens et al., 1987
with Jonathan Siegel Steve Zecker David Klodd Vickie Hellyer Rebecca Abel Jungmee Lee Gayla Poling Funding: National Institutes of Health [R01 DC008420]
Lee#et#al.,# 12 Ear#&#Hearing Poling# et#al.,# 14 JASA Souza#et#al.,# 14 JASA
Data from ongoing project att NU and UI Hospital clinics. Full sample stands at ~1199 individuals (10-65 yrs). 316 otologic normal individuals from phase I. 661 individuals with average thresholds across 0.5-4 khz 20 db HL from phase II. Behavioral Thresholds DPOAEs SFOAEs 0.125-20 khz; Different calibration in two phases. 0.75-20 khz; 55/40, 65/55, 75/75 db FPL 0.75-20 khz, 40 db FPL
Thresholds between 0.125 and 20 khz. DPOAE: Stereociliary nonlinearity boosted by electromotility. stapes input base apex Evoked OAEs between 0.75 and 20 khz SFOAE: Roughness in the cochlear impedance gradient causing reflection.
*
N=661; At least 35 in each bin. 25-29 yrs 45-49 yrs 6-12 khz
DPOAE Ear canal Middle ear Cochlea f 1 f 2 DPOAE base 1 f 2 f 1 2f 1 -f 2 2 apex Total DPOAE 1 2
Phase I & II: 5-yr bins starting at 10 yrs old; at least 55 in each bin N=997 55/40 db FPL
Phase I & II: 5-yr bins starting at 10 yrs old; at least 55 in each bin N=997 65/55 db FPL
Phase I & II: 5-yr bins starting at 10 yrs old; at least 55 in each bin N=997 75/75 db FPL
N=997; DPOAE Loss;75/75
N=997; DPOAE Loss;75/75 25-29 yrs 45-49 yrs 4-16 khz
55/40 65/55 75/75
Change in DPOAE levels with age (75/75 db FPL)
Change in DPOAE levels with age (75/75 db FPL)
10-14 yrs old 75/75 65/55 55/40
10-14 yrs old 40-44 yrs old 75/75 65/55 55/40
40 SFOAE Level (db SPL) 30 20 10 0 P Total at 40 db SPL P Total at 40 db SPL w/ suppressor Phase (cycles) -10 1.0 1.5 2.0 0-5 -10 1.0 1.5 2.0 - = PSFOAE P Stimulus P SFOAE = P Total P Stimulus
Phase I & II: 5-yr bins starting at 10 yrs old; at least 55 in each bin N=997 40 db FPL
N=997; SFOAE Loss; 40 db FPL
N=997; SFOAE Loss; 40 db FPL 40-yr plateau
Change in SFOAE levels with age (40 db FPL)
SFOAE Total Stimulus Jitter possible source of variability.
After mid life changes
Funding: National Institutes of Health [R01 DC003552]
Less reflection DP phase accumulation for older age groups.
Does this signify broadening cochlear tuning with age?
CLUES con ions
Behavioral Behavioral thresholds and DPOAEs show clinically significant shift as early as 25 years of age. Loss evident across a wider frequency range in DPOAEs. DPOAEs Largest shift in thresholds and DPOAEs between 30 and 49 years old. These age-related changes are visible slightly above the traditionally measured frequency range (6-12 khz for thresholds, 4-16 khz for DPOAEs).
DP Th 1.5 khz In the approximate middle of the cochlea (1.5 khz), DPOAE and behavioral thresholds show signs of decline with age. DP Th 12.5 khz At the cochlear base (>12.5 khz) both behavioral thresholds and DPOAEs show accelerated declines. Th Th DP DP A second faster phase of threshold decline might represent neural loss. Age related changes in DPOAEs are evident at all stimulus levels.
SF DP Th Global Observations Age- or life-related decline starts early, perhaps as soon as developmental changes are complete. The central nervous system is able to largely compensate for these peripheral changes for significant portions of our life span.
outer & middle ears dominantly cochlear, outer hair cells with others all hell breaks loose
Thank You NIH/NIDCD; American Hearing Research Foundation; ASHA Foundation; Deafness Research Foundation.