Otoacoustic Emissions Textbook Overview of otoacoustic emissions - - PowerPoint PPT Presentation

Update on Otoacoustic Emissions:

Basic Science to Clnical Application Morning Session

 Introductions  Historical evolution of OAEs  Cochlear physiology and OAEs  Prospects of clinical applications  Break  OAE types and taxonomy  Mechanisms of OAE generation  Complex generation of DPOAEs  DPOAEs and hearing thresholds  OAEs as early indicators of cochlear pathology

• Overview of otoacoustic emissions
• Anatomy and physiology
• Classification of OAEs
• Instrumentation and calibration
• Clinical measurement of OAEs: procedures
• OAE analysis
• OAE applications in children
• OAE applications in adults
• Efferent auditory system and OAEs
• New directions in research and clinical

application

Otoacoustic Emissions Textbook

Update on Otoacoustic Emissions: Basic Science to Clnical Application Afternoon Session

 General hardware and software orientation  Calibration and probe placement  Break  Measurements with various parameters in diverse

clinical populations

 Case studies: Participant cases

OAEs in AUDIOLOGY TODAY: Main Points

 OAEs are important in the diagnostic audiologic

assessment of children and adults.

 OAE findings and the audiogram do not always

agree … that‟s good … OAEs provide unique information on auditory status.

 Abnormal OAEs can be recorded with a normal

audiogram … and can detect cochlear dysfunction.

 OAEs should be a part of the basic audiologic test

battery.

Giuseppe Tartini (April 8, 1692 - February 26, 1770)

George von Bekesy (1899 - 1972)

Thomas Gold OAE Prophet

OAE: Classic Quote from Yesteryear by Thomas Gold

“I had discussed at length in 1948 with von Bekesy at Harvard that the observations he made on the dead cochlea were unrepresentative. But he wouldn‟t have that!” “It is shown that the assumption of a „passive‟ cochlea, where the elements are brought into mechanical

• scillation solely by means of the incident sound, is not

tenable.” “ … the nerve ending abstracts much energy from a mechanical resonator.”

William Rhode demonstrates cochlear nonlinearity in the squirrel monkey in 1971.

Data from Ruggero et al., 1982

David Kemp “Discoverer of OAEs”

Discovery of OAEs by David Kemp

(Kemp DT. Stimulated acoustic emissions from within the human auditory system. JASA 64: 1978.)

“A new auditory phenomenon has been identified in the acoustic impulse of the human ear… This component of the response appears to have its origin in some nonlinear mechanism probably located in the cochlea, responding mechanically to auditory stimulation, and dependent upon the normal functioning of the cochlear transduction process… It is tempting to suggest that one of the functions of the

• uter hair cell population is the generation of this

mechanical energy.”

David Kemp (1978)

Threshold Microstructure (Elliot, 1958) Spacing of Loudness Maxima (Kemp, 1979)

William Brownell: Discoverer of OHC Motility in Early 1980s

Music 1750s Audiology today Physics/Physiology 1978 – Psychoacoustics 1805 –

Historical Overview of OAEs: Major Events Since Discovery (1)

 1980s  Early studies of newborn hearing screening in UK and

Denmark

 Introduction of ILO 88 “auditory neuropathy”  1990s  Research on DPOAEs in animals and humans  NIH Consensus Conference recommends UNHS in

1993, including use of OAEs

 New DPOAE systems by major manufacturers in 1994  First CPT codes in 1995  OAEs in identification of ANSD  Automated OAE devices  Evidence on clinical applications grows

Historical Overview of OAEs: Major Events Since Discovery (2)

 2000 to present  Two textbooks on OAEs  OAEs recommended by JCIH for screening  New applications of OAEs including: Tinnitus Ototoxicity monitoring Noise/music cochlear dysfunction Preschool and school age screening  Combination technologies ABR and OAEs Tympanometry and OAEs  New CPT codes for OAEs

Update on Otoacoustic Emissions:

Basic Science to Clnical Application Morning Session

 Introductions  Historical evolution of OAEs  Cochlear physiology and OAEs  Prospects of clinical applications  Break  OAE types and taxonomy  Mechanisms of OAE generation  Complex generation of DPOAEs  DPOAEs and hearing thresholds  OAEs as early indicators of cochlear pathology

OAEs: Differences between inner and outer hair cells (1) Inner Hair Cells Outer Hair Cells

Single row 3 or 4 rows N = 3500 N = 12,000 to 20,000 On spiral lamina On basilar lamina Wine bottle shape Cylinder (test tube) shape) No contact bet/ stereocilia Tallest stereocilia contact tectorial and tectorial membrane membrane 95% of afferents innervate IHC 5% of afferents innervate OHCs

Not motile Motile Encompassed by support cells Supported only on top & bottom Central nucleus Nucleus at base of cell Single layer of endoplasmic Extensive subsurface reticulum cisternae Mitochondria scattered Mitochondria along throughout cell perimeter Efferents from lateral Efferents from medial superior olive superior olive

OAEs: Differences between inner and outer hair cells (2) Inner Hair Cells Outer Hair Cells

Hermann Ludwig Ferdinand von Helmholtz Overloading type nonlinearity in the middle ear.

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

• ther insults associated with OHC damage (salicylate,

noise, etc.).

 But where in the OHC?

Lessons from Kemp, 1978

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. Random noise recorded when closed cavity is stimulated with a click.

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

• ther insults associated with OHC damage (salicylate,

noise, etc.).

 But where in the OHC?

Cheatham et. al. (2004), J Physiol

Liberman et al., 2004

Prestin KO

Cheatham et. al., (2004); J. Physiol Verpy et. al., (2008); Nature

Cochlea Outer Hair Cell Stereocilia (transducer) Soma (?amplifier) Olivocochlear efferents Middle ear transmission

Why does it matter?

 No amplifier: Recordable DPOAEs at high input levels.

Good candidate for acoustic amplification.

 No transducer: DPOAEs not recordable. Good

candidate for electrical input.

Auditory Anatomy Involved in the Generation of OAEs

 Outer hair cell motility  Prestin motor protein  Stereocilia  Motion  Stiffness  Tectorial membrane  Basilar membrane mechanics  Dynamic interaction with outer hair cells  Stria vascularis  Middle ear (inward and outward propagation)  Medial efferent pathways  External ear canal  Stimulus presentation  OAE detection

Update on Otoacoustic Emissions:

Basic Science to Clnical Application Morning Session

 Introductions  Historical evolution of OAEs  Cochlear physiology and OAEs  Prospects of clinical applications  Break  OAE types and taxonomy  Mechanisms of OAE generation  Complex generation of DPOAEs  DPOAEs and hearing thresholds  OAEs as early indicators of cochlear pathology

OAEs in Early Detection of Outer Hair Cell Dysfunction: Rationale underlying many clinical applications

Abnormal OHC (OAEs) Normal OHC (OAEs)

CLINICAL APPLICATION OF OTOACOUSTIC EMISSIONS (OAE): General advantages

 Highly sensitive to cochlear (outer hair cell function)  Site specific (to outer hair cells)  Do not require behavioral cooperation or response  Ear specific  Highly frequency specific  Do not require sound-treated environment  Can be quick (< 30 seconds)  Portable (handheld devices)  Relatively inexpensive

CLINICAL APPLICATION OF OTOACOUSTIC EMISSIONS (OAE): Possible disadvantages

 Susceptible to effects of noise  Affected greatly by middle ear status  Provide cochlear information only about outer hair cells  May be abnormal or not detected with normal audiogram  Are not detectable with hearing loss > 40 dB HL  Cannot be used to estimate degree of hearing loss  Not a measure of neural or CNS auditory function  Not a test of hearing

Outer Hair Cells, Otoacoustic Emissions, and Auditory Function

 OHCs and OAEs are highly dependent on blood flow to

the cochlea, due to demands of metabolism

 OAEs are pre-neural and, therefore, not affected by

retrocochlear auditory dysfunction

 OHC motility contributes to:  enhanced auditory sensitivity  sharper tuning curves (increased frequency

selectivity or cochlear tuning)

 normal growth of loudness

OAEs after Sound Induced Damage

11 chinchillas exposed to 100 dBA for 5 days

Davis et al., 2005

And in humans…

Avan & Bonfils (2005) evaluated DPOAEs in 27 noise-exposed workers with clear notches in their audiograms. (in most ears)

still from Avan & Bonfils (2004)

(in 11 ears)

DPOAE Thd TEOAE

Recreational Exposure

• 21 participants listened to 1 hour of music from personal music players.

Repeated six times.

• No change in DPOAE or hearing thresholds even in those listening at >

75% of volume setting (97 – 102 dBA).

• TEOAE show statistically significant shift in these listeners of -0.47 dB

at 2 kHz and -0.70 dB at 2.8 kHz.

338 volunteers (US Navy) evaluated before and after 6-month training where they were noise exposed.

On average hearing thresholds did not change in a group of 75 volunteers.

Significant (-0.66 dB) change in TEOAE amplitude.

Significant (-1.28 dB) change in DPOAE amplitude. Greatest change at lowest stimulus level.

In 18 ears with PTS, the likelihood of PTS increased with decreasing OAE amplitude.

Hair cell response returns to normal; Long term synaptic loss and loss of neural amplitude; Loss of ganglion cells is delayed even more.

Six Reasons Why OAEs Will Never Replace the Audiogram nor Accurately Estimate Hearing Loss (1-3)

 OAEs measurement is dependent on inward and outward

propagation of energy through the middle ear (e.g., abnormal OAEs with normal hearing sensitivity)

 OAEs are more sensitive to cochlear dysfunction than

the audiogram (e.g., abnormal OAEs with normal hearing sensitivity)

 OAEs are electrophysiologic measures while the

audiogram is behavioral (e.g., normal OAEs with abnormal audiogram)

Six Reasons Why OAEs Will Never Replace the Audiogram nor Accurately Estimate Hearing Loss (4-6)

 OAEs are produced by OHCs, whereas the audiogram is

dependent on IHCs (e.g., normal OAEs with abnormal audiogram)

 OAEs are pre-neural, whereas the audiogram is

dependent on retrocochlear pathways (e.g., normal OAEs with abnormal hearing sensitivity)

 OAEs reflect OHC integrity, whereas the audiogram

measure hearing (e.g., normal OAEs with abnormal audiogram)

Otoacoustic Emissions in Audiology Today: Limitations in use of OAEs by clinical audiologists

 Over reliance on screening protocols, e.g.,  Recording within a limited frequency region  Simple “pass” versus “fail” outcome  Questionable techniques for measurement and analysis, e.g.,  Single trial or run (remember … “If your OAEs do not repeat, your test is not

complete!”

 Failure to achieve lowest possible noise levels (< 95%ile for adult normal

subjects)

 Analysis limited to “present” or “absent”  Not applied in a variety of patient populations  Only used as a screening technique for newborn infants  Not applied routinely in the initial diagnostic audiologic assessment of most

patients (children and adult)

 False assumption  OAEs will provide the same information that is available from the audiogram …

“I know the patient has a sensorineural hearing loss … why should I perform OAEs? …

Update on Otoacoustic Emissions:

Basic Science to Clnical Application Morning Session

 Introductions  Historical evolution of OAEs  Cochlear physiology and OAEs  Prospects of clinical applications  Break  OAE types and taxonomy  Mechanisms of OAE generation  Complex generation of DPOAEs  DPOAEs and hearing thresholds  OAEs as early indicators of cochlear pathology

But That’s Not the Entire Story (See Chapter 3 of Dhar & Hall, 2012)

Shera, 2009

Phase is a Factor in the Generation of OAEs

Regular Spacing of Spontaneous OAEs

base apex stapes input

Coherent Reflection Filtering

Zweig, Shera (1995 on)

Incoming signal is “reflected” randomly by outer hair cells; some reflections are coherent and contribute to the outward- traveling energy. Coherent reflectors near the peak region of the traveling wave have enough magnitude to contribute significantly to ear-canal OAE.

Inhibition (Suppression) of Otoacoustic Emissions: Role of the Efferent Auditory System

(See Chapter 9 of Dhar & Hall, 2012)

Classification

STIMULUS MECHANISM

Without stimulation Spontaneous Stimulated Transient,Distortion product,Stimulus frequency Distortion Reflection Spontaneous Mixed DPOAEs TEOAEs SFOAEs

Types of OAEs: Conventional Classification

Type Stimulus Prevalence Spontaneous none < 70% Evoked transient click or tone burst > 99% distortion product two pure tones > 99% stimulus frequency continuous tone ?? %

Transient Otoacoustic Emissions (TEOAE)

Distortion Product Otoacoustic Emissions (DPOAEs)

Update on Otoacoustic Emissions:

Basic Science to Clnical Application Morning Session

 Introductions  Historical evolution of OAEs  Cochlear physiology and OAEs  Prospects of clinical applications  Break  OAE types and taxonomy  Mechanisms of OAE generation  Complex generation of DPOAEs  DPOAEs and hearing thresholds  OAEs as early indicators of cochlear pathology

Update on Otoacoustic Emissions:

Basic Science to Clnical Application Morning Session

 Introductions  Historical evolution of OAEs  Cochlear physiology and OAEs  Prospects of clinical applications  Break  OAE types and taxonomy  Mechanisms of OAE generation  Complex generation of DPOAEs  DPOAEs and hearing thresholds  OAEs as early indicators of cochlear pathology

Update on Otoacoustic Emissions:

Basic Science to Clnical Application

Morning Session

 Introductions  Historical evolution of OAEs  Cochlear physiology and OAEs  Prospects of clinical applications  Break  OAE types and taxonomy  Mechanisms of OAE generation  Complex generation of DPOAEs  DPOAEs and hearing thresholds  OAEs as early indicators of cochlear pathology

f1 f2

• uter ear

middle ear

f2 f1

Mixed DPOAEs

• uter ear

middle ear

f2 f1

nonlinear reflection composite

model Talmadge, Long, Tubis & Dhar (1999); JASA

Talmadge, Long, Tubis & Dhar (1999); JASA

Hearing Level in dB HL

• 10 0 10 20 30 40 50 60

OAE Amplitude

WNL (Amplitude > 95%ile) No OAE (OAE – NF < 6 dB) Normal Present but not normal No OAE

Relation Between OAE Amplitude and Hearing Loss DPOAE 65/55 dB SPL TEOAE 80 dB SPL

Best bet for threshold prediction: Input/Output Functions

Improving Predictions Using I/O Functions

 Plot DPOAE pressure (in

Pascals not dB SPL).

 Fit linear function to first few

points reliably above the noise floor.

 Threshold is the stimulus level

that yields 0 Pa DPOAE amplitude per the fitted line. (Boege & Janssen, 2002)

 Two slope method (Neely et al.,

2009) leads to further improvement.

Neely et al., 2009

Gorga et al., 1997

Prediting thresholds from DPOAE levels has not been successful. Categorization of ears works to some extent. Screening works the best.

Gorga et al., 1997

Gorga et al., 1997

OAEs: Abnormal OHCs and loudness recruitment

“The phenomenon of loudness recruitment appears to be the psychoacoustic expression of the loss of a large component of outer hair cells and the concurrent preservation of a large component of inner hair cells and type I cochlear neurons.”

Schuknecht HF. Pathology of the Ear (2nd ed). 1993, p. 91

Diagnostic Application of OAEs: Findings for multiple frequencies vs. normal region

Normal region Noise floor Screening = pass (DP – NF = > 6 dB) Diagnostic = abnormal

Analysis of DPOAE Amplitude: Diagnostic Applications

Normal Present but Abnormal No OAE

Steps in Analysis of DPOAE Findings

 Perform analysis at all test frequencies  Verify adequately low noise floor (< 90% normal limits)  Verify replicability of DPOAE amplitude (+/- 2 dB) from at

least two runs

 Is DP - NF difference > 6 dB?  Yes? DPOAEs are present  No? There is no evidence of DPOAEs  Is DP amplitude within normal limits? Yes? DPOAEs are normal No? DPAOEs are abnormal (but present)

EAR CANAL FACTORS INFLUENCING OAE MEASUREMENT

 Non-pathologic  probe tip placement, size, or condition  probe insertion depth  standing waves  cerumen or debris  vernix casseous (healthy newborn infants)  Pathologic  stenosis  external otitis

CLINICAL APPLICATION OF OTOACOUSTIC EMISSIONS (OAE): Trouble-shooting

 Minimizing the effects of noise on OAE recordings  eliminate extraneous noise sources in test room  close door to test room  insert probe deeply  secure probe cord  instruct patient to remain quiet and still (if feasible)  position test ear away from equipment  modify protocol (to frequencies > 2000 Hz)

VENTILATION TUBES and OAEs

 Daya et al. (1966). Otoacoustic emissions: Assessment of hearing

after tympanostomy tube insertion. Clin Otolaryngol 21: 492-494.

 Owens, McCoy, Lonsbury-Martin, Martin. (1993). Otoacoustic

emissions in children with normal ears, middle ear dysfunction, and ventilating tubes. Amer J Otol 14: 34-40.

 Tilanus. Stenis, Snik.(1995). Otoacoustic emission measurements

in evaluation of the effect of ventilation tube insertion in children. Annals of ORL 104: 297-300.

 Richardson, Elliott, Hill. (1996). The feasibility of recording

transiently evoked otoacoustic emissions immediately following grommet insertion. Clin Otolaryngol 21: 445-448.

 Cullington, Kumar, Flood. (1998). Feasibility of otoacoustic

emissions as a hearing screen following grommet insertion. Brit J Audio 32: 57-62.

AUDIOGRAM & DPOAEs: Pre-ventilation tubes (5 y.o. girl)

20 40 60 80 .50 1K 2K 3K 4K 6K 8K

dB HL KHz

AC BC 20 40 60 80 8K 6K 4K 3K 2K 1K .50

Right Ear Left Ear

ST = 20 ST = 40

AUDIOGRAM & DPOAEs: Ventilation tubes (4 mos. later before APD eval.)

20 40 60 80 .50 1K 2K 3K 4K 6K 8K

dB HL KHz

AC BC 20 40 60 80 8K 6K 4K 3K 2K 1K .50

Right Ear Left Ear

ST = 15 ST = 15

Non-factors in OAE Interpretation

 Non-Factors

 diurnal effects (time of day)  genetics  body temperature  body position  anesthetic agents (w/ normal middle ear status)  state of arousal (attention to stimulus)

Hearing Level in dB HL

• 10 0 10 20 30 40 50 60

OAE Amplitude

WNL (Amplitude > 90%ile) No OAE (OAE – NF < 6 dB) Normal Present but not normal No OAE

Relation Between OAE Amplitude and Hearing Loss DPOAE 65/55 dB SPL TEOAE 80 dB SPL

Diagnostic Application of OAEs: Findings for multiple frequencies vs. normal region

Normal region Noise floor Screening = pass (DP – NF = > 6 dB) Diagnostic = abnormal

Analysis of DPOAE Amplitude: Diagnostic Application

Normal Present but Abnormal No OAE

Six Reasons Why OAEs Will Never Replace the Audiogram nor Accurately Estimate Hearing Loss (1-3)

 OAEs measurement is dependent on inward and outward

propagation of energy through the middle ear (e.g., abnormal OAEs with normal hearing sensitivity)

 OAEs are more sensitive to cochlear dysfunction than

the audiogram (e.g., abnormal OAEs with normal hearing sensitivity)

 OAEs are electrophysiologic measures while the

audiogram is behavioral (e.g., normal OAEs with abnormal audiogram)

Six Reasons Why OAEs Will Never Replace the Audiogram nor Accurately Estimate Hearing Loss (4-6)

 OAEs are produced by OHCs, whereas the audiogram is

dependent on IHCs (e.g., normal OAEs with abnormal audiogram)

 OAEs are pre-neural, whereas the audiogram is

dependent on retrocochlear pathways (e.g., normal OAEs with abnormal hearing sensitivity)

 OAEs reflect OHC integrity, whereas the audiogram

measure hearing (e.g., normal OAEs with abnormal audiogram)

2f1-f2

Otoacoustic Emissions: Current Research Topics (See Chapter 10. Dhar & Hall, 2011)

Lateral and Medial Efferent Auditory Pathways

Functional Role of Auditory Efferents

 Protection from noise.  Disrupted function in neuropathy.  Role in learning and learning

disability.

 Signal detection and localization in

noise.

Three categories of guinea pigs with varying MOC reflex strength. Animals with a strong reflex show least damage.

Hood et. al., 2003

Patients with auditory neuropathy have grossly reduced MOC reflex. TEOAE

Hood Hood Garinis et. al., 2008

Adults with learning disabilities have atypical pattern of MOC reflex. TEOAE

Efferent activation alters both basilar membrane vibration magnitude and phase.

Cooper & Guinan, 2006

Liberman et. al., 1996

CAS leads to reduction in SOAE magnitude and increase in SOAE frequency

Distortion Product OAEs

Siegel & Kim, 1982

Sun, 2008

Wagner et al., 2007

The lure of a change of greater magnitude has led to the suggestion of

• nly evaluating the “MOC

reflex” at dips.

General Methods

• 8 normal-hearing young adults.
• Best estimate of middle ear muscle reflex > 90 dB

SPL.

• DPOAE recorded using stimulus tones swept in

frequency between 1 and 4 kHz.

• Broad band noise (0.1 - 10 kHz) presented in

contralateral ear at 60, 70, and 80 dB SPL.

• +CAS conditions bracketed by two -CAS conditions.

• verlap

CF DPOAE

• CAS
• verlap

CF DPOAE

+CAS

Greater reduction in CF component could explain DPOAE enhancement in valleys.

The magnitude of the CF component is reduced more than the magnitude of the overlap component on efferent stimulation (also observed by Abdala et

al., 2009).

Purcell et al., 2008

Efferent stimulation also causes fine structure patterns to shift toward higher

• frequencies. (Mauermann & Kollmeier,

2004; Sun, 2005, 2008; Purcell et al., 2008, Abdala, 2009)

A differential reduction in DPOAE component magnitudes cannot account for frequency shifts in fine structure patterns.

Clinical Considerations

Stuck at one frequency

Large but inconsistent effects at valleys/dips/minima. Smaller but less inconsistent effects at peaks/maxima.

Following a peak

Consistent and systematic changes at peaks/maxima.

Tracking frequency shift

Practically speaking...

∆f f f / ∆f ≃ 16 f ± (f/4) f ± (f/8)

At least one of four strategically spaced measurements will be near peak/maximum.

Efferent modulation of OAEs can be

complex with changes in both magnitude and phase.

Both clinicians and scientists appear

to be interested in the phenomenon and its reliable measurement.

 Questions?