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Impedance Audiometry & BERA

A Clinical Presentation

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PART 1: IMPEDANCE AUDIOMETRY

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1. Introduction

• Impedance: Opposition to flow of sound energy
• Admittance (Immittance): Ease with which sound energy flows through the middle ear system (the reciprocal of impedance)
• Modern instruments measure acoustic immittance (admittance-based)

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2. Components of the Impedance Audiometry Battery

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3. Instrumentation

• Probe tip — sealed in the external ear canal
• Probe tone generator — delivers a 226 Hz probe tone (85 dB SPL) in adults; 1000 Hz in infants < 6 months
• Air pressure pump — varies canal pressure from +200 to –400 daPa
• Microphone — detects reflected sound
• Manometer — measures ear canal air pressure
• Bridge meter — measures and displays compliance

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4. Tympanometry

"Tympanometry measures the impedance of the middle ear to sound and is useful in diagnosis of middle-ear effusions. A tympanogram is the graphic representation of change in impedance or compliance as the pressure in the ear canal is changed." — Harrison's Principles of Internal Medicine, 21st Ed. (p. 1039)

1. Ear canal is sealed with probe tip
2. Air pressure is varied from +200 to –400 daPa
3. Compliance changes are plotted as a tympanogram

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5. Tympanogram Types (Jerger's Classification)

"Compliance that does not change with change in pressure suggests middle-ear effusion (Type B). With negative pressure in the middle ear, as with Eustachian tube obstruction, the point of maximal compliance occurs with negative pressure (Type C)." — Harrison's (p. 1039)

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6. Acoustic Reflex

Reflex Arc:

Loud Sound → Cochlea → CN VIII → Cochlear Nucleus
→ Superior Olivary Complex → Facial Nerve Nucleus (CN VII)
→ Stapedius Muscle contraction (bilateral)

Types of Acoustic Reflex Testing:

Acoustic Reflex Threshold (ART):

• Normal: 70–100 dB HL above pure tone threshold
• Absent reflex → suggests conductive loss, severe SNHL, CN VII palsy, or brainstem lesion
• Elevated reflex → seen in moderate SNHL

Clinical Significance:

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7. Acoustic Reflex Decay (ARD)

• Stimulus: Sustained tone at 10 dB above ART for 10 seconds
• Positive decay (>50% amplitude reduction in 5 seconds) = retrocochlear lesion (acoustic neuroma, CN VIII lesion)
• Tested at 500 Hz and 1000 Hz
• Normal: reflex sustained for full 10 seconds

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8. Static Acoustic Compliance

• Measured in milliliters (ml) or cm³
• Normal: 0.3–1.6 ml
• Reduced (<0.3 ml): Otosclerosis, middle ear effusion
• Increased (>1.6 ml): Ossicular discontinuity, flaccid TM

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9. Clinical Applications of Impedance Audiometry

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PART 2: BERA (Brainstem Evoked Response Audiometry)

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1. Introduction

• ABR — Auditory Brainstem Response
• BAER — Brainstem Auditory Evoked Response
• BAEP — Brainstem Auditory Evoked Potential

"Brainstem auditory-evoked responses (BAERs)... are useful in differentiating the site of sensorineural hearing loss. In response to sound, five distinct electrical potentials arising from different stations along the peripheral and central auditory pathway can be identified using computer averaging from scalp surface electrodes." — Harrison's Principles of Internal Medicine, 21st Ed. (p. 1041)

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2. Neural Generators of BERA Waves

Waves I, III, and V are the most consistent and clinically important.

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3. BERA Waveform — Clinical Example

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4. Instrumentation and Procedure

• Surface electrodes (Ag-AgCl)
• Signal averager (computer)
• Earphones (insert or standard)

• Active (non-inverting): Vertex (Cz) or forehead
• Reference (inverting): Ipsilateral mastoid/earlobe
• Ground: Contralateral mastoid/forehead

• Click stimulus (broadband, 0.1 ms duration) — most commonly used
• Tone pip/burst — frequency-specific testing
• Rate: 10–90 clicks/second (typically 11.1/sec)
• Intensity: 60–90 dB nHL for threshold search; 80–90 dB for neurodiagnosis
• Polarity: Rarefaction, condensation, or alternating

• 1000–2000 sweeps averaged to extract the tiny neural signal (0.1–1 µV) from background noise

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5. BERA Parameters Measured

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6. Interpretation of BERA

A. Conductive Hearing Loss

• All waves present but with increased absolute latencies (shift to the right)
• Inter-peak intervals normal (I–III, III–V, I–V unchanged)
• Wave I most affected

B. Cochlear (Sensory) Hearing Loss

• Absent or poorly formed Wave I at low intensities
• Remaining inter-peak intervals normal
• Threshold elevated

C. Retrocochlear (CN VIII / Acoustic Neuroma)

• Prolonged I–III inter-peak interval (> 2.3 ms)
• Absent waves beyond Wave I, or wave V absent
• Interaural latency difference Wave V > 0.4 ms
• Positive acoustic reflex decay on impedance audiometry

D. Brainstem Pathology (e.g., MS, tumor)

• Prolonged III–V interval (> 2.3 ms)
• Abnormal waveform morphology
• Waves I and III present, but Wave V delayed/absent

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7. Clinical Applications of BERA

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8. Factors Affecting BERA

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9. Advantages and Limitations

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PART 3: COMBINED INTERPRETATION

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Summary

• Impedance Audiometry evaluates the middle ear (tympanometry), stapedial reflex arc (CN VII, CN VIII, brainstem), and helps localize conductive vs. sensorineural pathology.
• BERA evaluates the entire auditory pathway from cochlea to midbrain — it is the gold standard for objective hearing threshold estimation and retrocochlear lesion detection.
• Together, they form a powerful objective audiological test battery essential in ENT, Neurology, Pediatrics, and Audiology practice.

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• Slides 1–6: Impedance Audiometry — principles, instrumentation, tympanometry types, and acoustic reflex with full reflex arc
• Slides 7–9: Special tests — Recruitment, SISI, Threshold Tone Decay
• Slides 10–11: ECoG
• Slides 12–15: BERA — waves, generators, normal latencies, clinical uses — with a real ABR image
• Slides 16–17: ASSR and OAEs
• Slides 18–19: Summary and key exam points

• I will give you a ready-to-import slide outline (already done above), and
• I can now provide a VBA macro or Google Slides Apps Script that auto-creates the full deck in one click on your system.

1. Microsoft PowerPoint VBA macro (best if you use desktop PowerPoint)
2. Google Slides script (best if you use Google Drive)

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HOW TO USE

1. Go to script.google.com
2. Click New Project
3. Delete all existing code
4. Paste the entire script below
5. Click Run (▶) → it will ask for permissions → click Allow
6. Go to your Google Drive — the presentation will be saved there as "Impedance Audiometry & BERA"

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    "• Seen in COCHLEAR lesions: Ménière's disease, Presbycusis",
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    "• Intensity in affected ear adjusted to match loudness perceived in normal ear",
    "• Test starts at 20 dB above threshold of deaf ear → repeated every 20 dB",
    "• Conductive / Neural deafness: initial difference maintained throughout",
    "• Cochlear lesion: Partial, Complete or OVER-RECRUITMENT seen"
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  // ══════════════════════════════════════════════════════════
  // SLIDE 10 — SISI TEST
  // ══════════════════════════════════════════════════════════
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    "• Every 5 seconds: tone is increased by 1 dB (a 'blip')",
    "• 20 such blips are presented",
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  // ══════════════════════════════════════════════════════════
  // SLIDE 11 — THRESHOLD TONE DECAY TEST
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    "4. Result expressed as: number of dB of decay needed"
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  // ══════════════════════════════════════════════════════════
  // SLIDE 12 — EVOKED RESPONSE AUDIOMETRY INTRO
  // ══════════════════════════════════════════════════════════
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    "• Requires special equipment with an AVERAGING COMPUTER",
    "• Two types have gained wide clinical acceptance:"
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    ["(2)", "BERA / ABR / BAER", "Measures brainstem response to auditory stimuli\nWaves produced in first 10 ms\nUseful in: acoustic neuroma, infant screening, malingerers, intraoperative monitoring"]
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    "• Recording electrode: thin needle through tympanic membrane → PROMONTORY",
    "• Adults: local anaesthesia  |  Children / anxious: general anaesthesia",
    "• Sedation does NOT interfere with responses (advantage)",
    "• Uses: (i) Hearing threshold in young infants  (ii) Diagnosis of MÉNIÈRE'S DISEASE",
    "         — enlarged SP:AP ratio (>0.4) is diagnostic of Ménière's"
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  // SLIDE 14 — BERA INTRODUCTION
  // ══════════════════════════════════════════════════════════
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    "• Noninvasive, objective electrophysiological test",
    "• Differentiates lesions of COCHLEA from CN VIII (VIIIth nerve)",
    "• Elicits brainstem responses to auditory stimulation by CLICKS or TONE BURSTS",
    "• Electrical potentials generated along brainstem pathways → picked up from VERTEX",
    "   by surface electrodes (Ag-AgCl)",
    "• Uses COMPUTER AVERAGING of 1000–2000 sweeps to extract signals (0.1–1 µV)",
    "• Waves produced in first 10 ms after stimulus",
    "• Measures hearing sensitivity in range of 1000–4000 Hz",
    "• First, Third, and Fifth waves (I, III, V) are most stable and clinically used",
    "• Studied for: ABSOLUTE LATENCY (between waves I and V) and AMPLITUDE"
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  // ══════════════════════════════════════════════════════════
  // SLIDE 15 — BERA WAVE GENERATORS
  // ══════════════════════════════════════════════════════════
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    ["Wave II",      "Proximal part of CN VIII near brainstem",           "~2.5 ms"],
    ["Wave III",     "Cochlear Nucleus",                                  "~3.5 ms"],
    ["Wave IV",      "Superior Olivary Complex",                          "~4.5 ms"],
    ["Wave V",       "Lateral Lemniscus",                                 "~5.5 ms"],
    ["Waves VI–VII", "Inferior Colliculus",                               "~6–7 ms"]
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  // SLIDE 16 — BERA LATENCIES & NORMAL VALUES
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    ["Brainstem Pathology (MS, tumor)", "Prolonged III–V interval (> 2.3 ms)\nWaves I & III present but Wave V DELAYED or ABSENT"]
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    ["(ii)", "Determine Hearing Threshold", "In infants, adults who cannot cooperate, and MALINGERERS"],
    ["(iii)", "Retrocochlear Pathology", "Diagnose ACOUSTIC NEUROMA (vestibular schwannoma) — prolonged I–III interval"],
    ["(iv)", "Intraoperative Monitoring", "Monitor CN VIII during surgery of cochlear neuroma / skull base tumours"],
    ["(v)", "Brainstem Lesions", "Detect subclinical brainstem demyelination in Multiple Sclerosis"],
    ["(vi)", "Brain Death", "All BERA waves absent except Wave I = confirmation of brain death"]
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    "Type B tympanogram = Middle ear EFFUSION (Glue ear)",
    "Type C = Eustachian tube dysfunction / retracted TM",
    "Absent acoustic reflex + normal hearing = CN VII lesion proximal to stapedius",
    "Stapedial reflex DECAY = Retrocochlear lesion (CN VIII / acoustic neuroma)",
    "RECRUITMENT = COCHLEAR lesion  |  Tone DECAY = RETROCOCHLEAR lesion",
    "SISI score 70–100% = COCHLEAR  |  0–20% = Retrocochlear",
    "BERA Waves I, III, V are most clinically significant",
    "Prolonged I–III interval = Peripheral / CN VIII lesion",
    "Prolonged III–V interval = Central / Brainstem lesion",
    "OAEs present + absent ABR = Auditory Neuropathy Spectrum Disorder (ANSD)"
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---

WHAT YOU GET

• Navy & blue professional color theme with gold accents
• Fully formatted tables (tympanogram types, BERA wave generators, latency values, etc.)
• Acoustic reflex arc diagram
• All interpretation tables
• Summary key-points slide

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---

IMPEDANCE AUDIOMETRY & BERA

Assessment of Hearing - Special Tests

1. Introduction

• Tympanometry
• Acoustic reflex measurements

---

2. Impedance Audiometry - Principle

• Sound striking tympanic membrane is partly absorbed and partly reflected.
• Stiff tympanic membrane reflects more sound.
• Compliant tympanic membrane reflects less sound.
• By changing canal pressure and measuring reflected sound, middle ear compliance is assessed.

---

3. Instrumentation

1. Oscillator: delivers probe tone (usually 220 Hz)
2. Microphone: records reflected sound
3. Air pump: varies pressure (+200 to -400 daPa)

---

4. Tympanometry

Types of Tympanograms

• Type A: Normal peak near 0 daPa - normal middle ear
• Type As: Shallow peak - otosclerosis/malleus fixation
• Type Ad: High peak - ossicular discontinuity/flaccid TM
• Type B: Flat - middle ear effusion/perforation/wax
• Type C: Peak at negative pressure - Eustachian tube dysfunction

---

5. Acoustic Reflex

Clinical Uses

• Objective hearing estimate in infants
• Detection of malingerers
• Cochlear pathology (recruitment)
• Facial nerve lesions
• Retrocochlear lesion detection (reflex decay)
• Brainstem pathway assessment

---

6. Acoustic Reflex Arc

---

7. Recruitment

• Soft sounds not heard
• Loud sounds become rapidly intolerable Seen in cochlear lesions (e.g., Ménière's disease, presbycusis).

---

8. SISI Test (Short Increment Sensitivity Index)

• High score (70-100%): cochlear lesion
• Low score (0-20%): retrocochlear lesion
• Conductive loss usually low (<15%)

---

9. Threshold Tone Decay Test

• Significant decay (>25 dB) suggests retrocochlear lesion.

---

10. Evoked Response Audiometry

1. Electrocochleography (ECoG)
2. BERA/ABR

---

11. Electrocochleography (ECoG)

• Cochlear microphonics
• Summating potential (SP)
• Action potential (AP)

• Ménière's disease
• Infant threshold estimation

---

12. BERA (ABR/BAER)

• Records brainstem auditory potentials after click/tone stimuli
• Waves occur in first 10 ms
• Waves I, III, V are most useful clinically

Wave Generators

• Wave I: Distal CN VIII
• Wave II: Proximal CN VIII
• Wave III: Cochlear nucleus
• Wave IV: Superior olivary complex
• Wave V: Lateral lemniscus / inferior colliculus pathway

---

13. BERA Normal Values (approx.)

• Wave I: 1.5 ms
• Wave III: 3.5 ms
• Wave V: 5.5-5.7 ms
• I-III: ~2.0 ms
• III-V: ~2.0 ms
• I-V: ~4.0 ms
• Interaural Wave V difference: <0.4 ms

---

14. BERA Interpretation

• Conductive loss: delayed absolute latencies, normal interpeak intervals
• Cochlear loss: elevated threshold, relatively preserved interpeak intervals
• Retrocochlear lesion: prolonged I-III, delayed/absent Wave V
• Brainstem lesion: prolonged III-V

---

15. Clinical Uses of BERA

• Newborn/infant hearing screening
• Threshold estimation in uncooperative patients
• Acoustic neuroma evaluation
• Intraoperative CN VIII monitoring
• Brainstem lesion assessment
• Brain death support (when applicable protocols used)

---

16. Otoacoustic Emissions (OAE)

• Sounds generated by outer hair cells
• Useful in neonatal hearing screening
• Helps distinguish cochlear from retrocochlear pathology
• OAE present with absent ABR may suggest auditory neuropathy spectrum disorder

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17. Summary

• Impedance audiometry evaluates middle ear and reflex pathways.
• BERA evaluates neural conduction from cochlea to brainstem.
• Combined use improves localization of hearing pathology and objective diagnosis in difficult-to-test patients.

---

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Slide 1. Title

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Slide 2. Impedance Audiometry: Overview

• Objective, non-invasive middle ear test
• Useful in children and uncooperative patients
• Based on sound reflection and compliance changes
• Assesses tympano-ossicular stiffness/compliance

1. Tympanometry
2. Acoustic reflex measurements

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Slide 3. Instrumentation

• Oscillator: delivers probe tone (usually 220 Hz)
• Microphone: picks reflected sound
• Air pump: changes pressure (+200 to -400 daPa)

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Slide 4. Tympanometry: Principle

• Ear canal is sealed with probe
• Pressure swept from positive to negative
• Compliance recorded as pressure changes
• Peak compliance indicates middle ear pressure

• Children: up to ~1.5 ml
• Adults: up to ~2 ml

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Slide 5. Types of Tympanograms

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Slide 6. Acoustic Reflex

• Loud sound triggers bilateral stapedius contraction
• Produces measurable compliance change

• Ipsilateral reflex
• Contralateral reflex

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Slide 7. Acoustic Reflex Arc

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Slide 8. Uses of Acoustic Reflex

• Infant hearing assessment
• Detecting malingerers
• Cochlear lesion clues (recruitment)
• Facial nerve lesion localization
• Retrocochlear clues (reflex decay)
• Brainstem pathway assessment

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Slide 9. Recruitment (Special Test)

• Abnormal loudness growth in cochlear pathology
• Soft sounds poorly heard, loud sounds rapidly intolerable
• Seen in cochlear SNHL (e.g., Ménière's, presbycusis)

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Slide 10. SISI Test

• Detects ability to hear 1 dB increments

• 70-100%: cochlear lesion likely
• 0-20%: retrocochlear lesion likely
• Conductive loss often low score

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Slide 11. Threshold Tone Decay Test

• Assesses auditory nerve fatigue
• 4000 Hz tone, sustained hearing checked over time
• Needing major intensity increase suggests decay

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Slide 12. Evoked Response Audiometry

1. Electrocochleography (ECoG)
2. BERA/ABR/BAER

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Slide 13. Electrocochleography (ECoG)

• Cochlear microphonics
• Summating potential (SP)
• Action potential (AP of CN VIII)

• Ménière's disease support
• Objective threshold estimation in infants

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Slide 14. BERA: Introduction

• Also called ABR / BAER / BAEP
• Records brainstem responses to clicks/tone bursts
• Waves occur within first 10 ms
• Waves I, III, V are most clinically robust

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Slide 15. BERA Wave Generators

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Slide 16. BERA Normal Values

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Slide 17. BERA Interpretation

• Conductive loss: delayed absolute latencies, interpeak often normal
• Cochlear loss: threshold elevation, relative interpeak preservation
• Retrocochlear lesion: prolonged I-III, delayed/absent wave V
• Brainstem lesion: prolonged III-V, abnormal morphology

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Slide 18. Clinical Uses of BERA

• Newborn/infant hearing screening
• Threshold estimation in non-cooperative patients
• Acoustic neuroma (retrocochlear) evaluation
• Intraoperative monitoring of CN VIII
• Brainstem dysfunction evaluation

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Slide 19. Key Exam Points (Take Home)

• Type B tympanogram -> middle ear effusion
• Type C -> ET dysfunction
• Reflex decay suggests retrocochlear pathology
• Recruitment suggests cochlear pathology
• SISI high -> cochlear; low -> retrocochlear
• BERA waves I, III, V are most useful
• OAE present with absent ABR may indicate auditory neuropathy

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