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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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IMPEDANCE AUDIOMETRY & BERA

Assessment of Hearing — Special Tests

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SLIDE 1: IMPEDANCE AUDIOMETRY — Overview

• An objective test, widely used in clinical practice
• Particularly useful in children
• Based on a simple principle: when sound strikes the tympanic membrane, some energy is absorbed while the rest is reflected
• A stiffer tympanic membrane reflects more sound; a compliant one reflects less
• By changing pressure in a sealed ear canal and measuring reflected sound energy, we can assess the compliance or stiffness of the tympano-ossicular system → determines healthy or diseased status of the middle ear

1. (a) Tympanometry
2. (b) Acoustic Reflex Measurements

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SLIDE 2: INSTRUMENTATION

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SLIDE 3: TYMPANOMETRY — Principle

• Measures the physical volume of air between the probe tip and tympanic membrane
• Normal ear canal volume: up to 1.5 ml in children, 2 ml in adults
• Any increase in volume → perforation of the tympanic membrane (because middle ear volume is added to external ear canal volume)
• This is also used to find patency of the ventilation tube

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SLIDE 4: TYPES OF TYMPANOGRAMS

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SLIDE 5: ACOUSTIC REFLEX

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SLIDE 6: ACOUSTIC REFLEX ARC

LOUD SOUND
     ↓
   Cochlea
     ↓
  CN VIII (Distal part)
     ↓
 Cochlear Nucleus
     ↓
Superior Olivary Complex (bilateral)
     ↓
CN VII Nucleus (both sides)
     ↓
Stapedius Muscle Contraction (bilateral)

• Ipsilateral reflex: CN VIII → Ventral cochlear nucleus → CN VIII → Ventral cochlear nucleus → Superior olivary complex → CN VII (same side) → Stapedius
• Contralateral reflex: Crosses brainstem via contralateral medial superior olivary nucleus → contralateral CN VII → Stapedius

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SLIDE 7: SPECIAL TESTS OF HEARING

1. Recruitment

• Phenomenon of abnormal growth of loudness
• Ear does not hear low intensity sounds but hears greater intensity sounds as loud or even louder than normal
• A loud sound tolerable in normal ear → intolerable in recruiting ear
• Patients with recruitment are poor candidates for hearing aids
• Seen in cochlear lesions (e.g. Ménière's disease, presbycusis)
• Helps differentiate cochlear from retrocochlear sensorineural hearing loss

• Tone played alternately to normal and affected ear
• Intensity in affected ear adjusted to match loudness in normal ear
• Test starts at 20 dB above threshold of deaf ear → repeated every 20 dB
• In conductive and neural deafness: initial difference maintained throughout
• In cochlear lesions: partial, complete or over-recruitment may be seen

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SLIDE 8: SHORT INCREMENT SENSITIVITY INDEX (SISI Test)

• Cochlear lesion patients distinguish smaller intensity changes better than normal persons
• SISI differentiates cochlear from retrocochlear lesions
• Method: Continuous tone 20 dB above threshold sustained for 2 min; every 5 sec, tone increased by 1 dB (20 such blips presented)
• Patient indicates blips heard
• SISI Score:
  • Conductive deafness: seldom >15%
  • Cochlear deafness: 70–100%
  • Nerve deafness: 0–20%

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SLIDE 9: THRESHOLD TONE DECAY TEST

• Measures nerve fatigue — detects retrocochlear lesions
• Normally a person hears a tone continuously for 60 seconds
• In nerve fatigue: patient stops hearing earlier
• Method:
  • Tone of 4000 Hz presented at 5 dB above threshold continuously for 60 sec
  • If patient stops hearing → intensity increased by 5 dB → continued till patient can hear for full 60 sec
  • Result expressed as number of dB of decay
  • Decay >25 dB = diagnostic of retrocochlear lesion

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SLIDE 10: EVOKED RESPONSE AUDIOMETRY (ERA)

1. Electrocochleography (ECoG)
2. Brainstem Auditory Evoked Response (BAER/BERA/ABR)

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SLIDE 11: ELECTROCOCHLEOGRAPHY (ECoG)

• Measures electrical potentials arising in the cochlea and CN VIII within first 5 ms of auditory stimulus
• Response in three forms:
  • Cochlear microphonics
  • Summating potentials (SP)
  • Action potential (AP) of the VIIIth nerve
• Recording electrode: usually a thin needle passed through the tympanic membrane onto the promontory
• Done under local anaesthesia in adults; general anaesthesia in children or anxious persons
• Sedation does not interfere
• Useful: (i) find hearing threshold in young infants and children; (ii) diagnosis of Ménière's disease (raised SP:AP ratio)

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SLIDE 12: BERA (Brainstem Auditory Evoked Response)

• Differentiates lesions of cochlea from VIIIth nerve (Figure 4.9)
• Noninvasive technique
• Elicits brainstem responses to auditory stimulation by clicks or tone bursts
• Electrical potentials generated in response to several brainstem pathways, picked up from vertex by surface electrodes
• Measures hearing sensitivity in range of 1000–4000 Hz
• Waves are produced in first 10 ms
• First, third, and fifth waves are most stable and used in measurements
• Studied for absolute latency (usually between waves I and V) and amplitude

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SLIDE 13: BERA — WAVE GENERATORS

Mnemonic: E COLI MA — Eight nerve, Cochlear nucleus, Olivary complex Lateral, Inferior colliculus, Medial geniculate, Auditory cortex

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SLIDE 14: BERA — NORMAL WAVEFORM & LATENCIES

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SLIDE 15: USES OF BERA / ABR

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SLIDE 16: AUDITORY STEADY STATE RESPONSE (ASSR)

• Conducted with tone bursts of various frequencies
• Can produce frequency-specific thresholds of hearing
• Detects hearing in infants to profound levels even at young age
• Modulated rapidly in amplitude and frequency → gives frequency-specific audiogram
• Hearing losses >80 dB can be detected
• Useful in cochlear implant selection in severe to profoundly deaf infants

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SLIDE 17: OTOACOUSTIC EMISSIONS (OAEs)

• Low-intensity sounds produced by outer hair cells of normal cochlea
• Elicited by very sensitive microphone placed in external ear canal, analyzed by computer
• Sound produced by outer hair cells travels: outer hair cells → basilar membrane → perilymph → oval window → ossicles → ear canal
• OAEs are absent when hearing loss does not exceed 30 dB; may be absent in 50% of normal persons

• (a) Screening test in neonates, uncooperative/mentally challenged individuals after sedation
• (b) Distinguish cochlear from retrocochlear lesions — OAEs absent in cochlear SNHL; OAEs present in auditory neuropathy (ANSD) and CN VIII lesions
• (c) Detect ototoxic sensorineural hearing loss early
• (d) Diagnose retrocochlear pathology — abnormal or absent auditory brainstem response with normal OAEs = auditory neuropathy
• (e) OAEs are also useful to diagnose retrocochlear pathology including acoustic neuroma; impaired speech discrimination score, absent/abnormal brainstem response — OAEs are normal

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SLIDE 18: SUMMARY TABLE — OBJECTIVE HEARING TESTS

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SLIDE 19: KEY POINTS TO REMEMBER

• Impedance audiometry is objective — no patient cooperation required
• Type B tympanogram = middle ear effusion (glue ear)
• Absent acoustic reflex with normal hearing = CN VII lesion proximal to stapedius
• Stapedial reflex decay = retrocochlear (CN VIII / acoustic neuroma)
• BERA waves I, III, V are the 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)
• Recruitment = cochlear lesion; Tone decay = retrocochlear lesion

• 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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    "• This stiffens the ossicular chain → detectable as a change in compliance by tympanometry",
    "• The reflex is mediated through CN VIII (afferent) and CN VII (efferent)"
  ], 30, 100, 660, 70, 13, DARK_TEXT);

  addRect(s, 20, 172, 680, 3, HEADER_BG, null);
  addText(s, "Types of Acoustic Reflex", 30, 178, 400, 25, 14, true, HEADER_BG, "left");
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    ["Type", "Probe Ear", "Stimulus Ear", "Tests"],
    ["Ipsilateral\n(Uncrossed)", "Same ear", "Same ear", "CN VIII + lower brainstem + CN VII (same side)"],
    ["Contralateral\n(Crossed)", "Opposite ear", "Stimulus ear", "CN VIII + full brainstem pathway + CN VII (probe side)"]
  ];
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  addText(s, "Normal Acoustic Reflex Threshold (ART)", 30, 378, 500, 22, 13, true, HEADER_BG, "left");
  addBulletBox(s, ["• 70–100 dB above the pure tone threshold (hearing level)"], 30, 400, 660, 30, 13, DARK_TEXT);

  // ══════════════════════════════════════════════════════════
  // SLIDE 7 — ACOUSTIC REFLEX ARC
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(6);
  setSlideBackground(s, ACCENT);
  headerBar(s, "Acoustic Reflex Arc");
  slideNum(s, 7);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  var arcSteps = [
    "LOUD SOUND (70–100 dB)",
    "Cochlea",
    "CN VIII (Distal)",
    "Cochlear Nucleus",
    "Superior Olivary Complex (bilateral relay)",
    "CN VII Nucleus — both sides",
    "Stapedius Muscle Contraction (bilateral)"
  ];
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    }
    ayPos += 56;
  });

  addText(s, "Mnemonic: E COLI MA", 30, 430, 660, 28, 13, true, HEADER_BG, "center");
  addText(s, "Eight nerve → Cochlear nucleus → Olivary complex Lateral → Inferior colliculus → Medial geniculate → Auditory cortex", 30, 452, 660, 25, 10, false, DARK_TEXT, "center");

  // ══════════════════════════════════════════════════════════
  // SLIDE 8 — USES OF ACOUSTIC REFLEX
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(7);
  setSlideBackground(s, ACCENT);
  headerBar(s, "Uses of Acoustic Reflex Testing");
  slideNum(s, 8);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  var uses = [
    ["(i)", "Hearing in infants & young children", "Objective — patient does not need to respond"],
    ["(ii)", "Detecting malingerers", "Person feigning deafness will show positive stapedial reflex on pure tone stimulation"],
    ["(iii)", "Cochlear pathology (Recruitment)", "Stapedial reflex present at 40–60 dB (not 70 dB) = Recruitment = cochlear lesion"],
    ["(iv)", "Stapedial Reflex Decay", "Sustained tone for 10 s — amplitude falls >50% = CN VIII / retrocochlear lesion"],
    ["(v)", "CN VII / Facial nerve lesion", "Absent reflex with normal hearing = CN VII lesion proximal to nerve to stapedius"],
    ["(vi)", "Brainstem lesion", "Ipsilateral reflex present but contralateral absent = lesion in brainstem"]
  ];
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    addText(s, u[2], 273, uy+5, 419, 50, 11, false, DARK_TEXT, "left");
    uy += 62;
  });

  // ══════════════════════════════════════════════════════════
  // SLIDE 9 — RECRUITMENT & ABLB TEST
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(8);
  setSlideBackground(s, ACCENT);
  headerBar(s, "Special Tests — Recruitment & ABLB");
  slideNum(s, 9);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  addText(s, "Recruitment", 30, 73, 400, 25, 15, true, HEADER_BG, "left");
  addBulletBox(s, [
    "• Abnormal growth of loudness — ear does NOT hear low intensity sounds",
    "• But hears high intensity sounds as LOUD or even LOUDER than normal",
    "• A sound tolerable in normal ear becomes INTOLERABLE in the recruiting ear",
    "• Seen in COCHLEAR lesions: Ménière's disease, Presbycusis",
    "• Patients with recruitment are POOR CANDIDATES for hearing aids",
    "• Helps differentiate cochlear from retrocochlear sensorineural hearing loss"
  ], 30, 100, 660, 120, 13, DARK_TEXT);

  addRect(s, 20, 225, 680, 3, HEADER_BG, null);
  addText(s, "Alternate Binaural Loudness Balance (ABLB) Test", 30, 231, 600, 25, 14, true, HEADER_BG, "left");
  addBulletBox(s, [
    "• Tone (e.g. 1000 Hz) played alternately to normal and affected ear",
    "• 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"
  ], 30, 258, 660, 110, 13, DARK_TEXT);

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  addText(s, "KEY: Recruitment = COCHLEAR lesion (NOT retrocochlear)", 30, 380, 660, 35, 13, true, "#c0392b", "center");

  // ══════════════════════════════════════════════════════════
  // SLIDE 10 — SISI TEST
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(9);
  setSlideBackground(s, ACCENT);
  headerBar(s, "SISI Test — Short Increment Sensitivity Index");
  slideNum(s, 10);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  addText(s, "Principle", 30, 73, 400, 25, 14, true, HEADER_BG, "left");
  addBulletBox(s, [
    "• Cochlear lesion patients detect smaller changes in intensity BETTER than normal",
    "• SISI differentiates COCHLEAR from RETROCOCHLEAR lesions"
  ], 30, 100, 660, 50, 13, DARK_TEXT);

  addRect(s, 20, 152, 680, 3, HEADER_BG, null);
  addText(s, "Method", 30, 158, 400, 25, 14, true, HEADER_BG, "left");
  addBulletBox(s, [
    "• Continuous tone presented 20 dB above threshold for ~2 minutes",
    "• Every 5 seconds: tone is increased by 1 dB (a 'blip')",
    "• 20 such blips are presented",
    "• Patient indicates how many blips are heard → expressed as percentage"
  ], 30, 185, 660, 90, 13, DARK_TEXT);

  addRect(s, 20, 278, 680, 3, HEADER_BG, null);
  addText(s, "SISI Score Interpretation", 30, 284, 400, 25, 14, true, HEADER_BG, "left");
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    ["Conductive Deafness", "Seldom > 15%"],
    ["Cochlear Deafness", "70 – 100%  ✓ HIGH"],
    ["Nerve (Retrocochlear) Deafness", "0 – 20%"]
  ];
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  // ══════════════════════════════════════════════════════════
  // SLIDE 11 — THRESHOLD TONE DECAY TEST
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(10);
  setSlideBackground(s, ACCENT);
  headerBar(s, "Threshold Tone Decay Test");
  slideNum(s, 11);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  addText(s, "Principle", 30, 73, 500, 25, 14, true, HEADER_BG, "left");
  addBulletBox(s, [
    "• Measures NERVE FATIGUE — used to detect RETROCOCHLEAR lesions",
    "• Normal: person hears a tone continuously for 60 seconds",
    "• Nerve fatigue: patient stops hearing the tone EARLIER"
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  addText(s, "Method", 30, 174, 400, 25, 14, true, HEADER_BG, "left");
  addBulletBox(s, [
    "1. Tone of 4000 Hz presented at 5 dB above patient's threshold continuously for 60 s",
    "2. If patient stops hearing → intensity increased by 5 dB → procedure continued",
    "3. Continued until patient hears for full 60 seconds (or audiometer limit reached)",
    "4. Result expressed as: number of dB of decay needed"
  ], 30, 201, 660, 90, 13, DARK_TEXT);

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  addText(s, "Interpretation", 30, 301, 400, 25, 14, true, HEADER_BG, "left");
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  addText(s, "Decay > 25 dB  =  RETROCOCHLEAR LESION (diagnostic)", 83, 340, 554, 35, 15, true, "#c0392b", "center");
  addBulletBox(s, ["• Decay < 25 dB = Normal / cochlear lesion"], 30, 392, 660, 30, 13, DARK_TEXT);
  addBulletBox(s, ["• Simple, inexpensive test requiring only a standard audiometer"], 30, 422, 660, 30, 13, DARK_TEXT);

  // ══════════════════════════════════════════════════════════
  // SLIDE 12 — EVOKED RESPONSE AUDIOMETRY INTRO
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(11);
  setSlideBackground(s, ACCENT);
  headerBar(s, "Evoked Response Audiometry (ERA)");
  slideNum(s, 12);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  addText(s, "What is ERA?", 30, 73, 400, 25, 14, true, HEADER_BG, "left");
  addBulletBox(s, [
    "• Objective test measuring ELECTRICAL ACTIVITY in auditory pathways in response to stimuli",
    "• Requires special equipment with an AVERAGING COMPUTER",
    "• Two types have gained wide clinical acceptance:"
  ], 30, 100, 660, 65, 13, DARK_TEXT);

  addRect(s, 55, 172, 620, 3, HEADER_BG, null);

  var eraTypes = [
    ["(1)", "Electrocochleography (ECoG)", "Measures cochlea + CN VIII potentials within first 5 ms\nRecording electrode at the PROMONTORY\nUseful in: Ménière's disease, infant thresholds"],
    ["(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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    addText(s, et[1], 75, ey+5, 615, 30, 14, true, HEADER_BG, "left");
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  });

  // ══════════════════════════════════════════════════════════
  // SLIDE 13 — ECoG
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(12);
  setSlideBackground(s, ACCENT);
  headerBar(s, "Electrocochleography (ECoG)");
  slideNum(s, 13);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  addText(s, "Principle", 30, 73, 400, 25, 14, true, HEADER_BG, "left");
  addBulletBox(s, [
    "• Measures electrical potentials arising in the COCHLEA and CN VIII within first 5 ms",
    "• Response comes in three forms:"
  ], 30, 100, 660, 50, 13, DARK_TEXT);

  var ecoForms = [
    ["Cochlear Microphonics (CM)", "AC electrical response of outer hair cells mimicking the stimulus waveform"],
    ["Summating Potential (SP)", "DC shift — baseline displacement; enlarged in Ménière's disease"],
    ["Action Potential (AP)", "Compound action potential of CN VIII — most clinically used component"]
  ];
  var ef = 153;
  ecoForms.forEach(function(row, i) {
    var bg = i % 2 === 0 ? "#dce8f5" : WHITE;
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    addText(s, row[1], 268, ef+6, 424, 33, 11, false, DARK_TEXT, "left");
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  });

  addRect(s, 20, 295, 680, 3, HEADER_BG, null);
  addText(s, "Procedure & Uses", 30, 301, 400, 25, 14, true, HEADER_BG, "left");
  addBulletBox(s, [
    "• 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"
  ], 30, 328, 660, 110, 13, DARK_TEXT);

  // ══════════════════════════════════════════════════════════
  // SLIDE 14 — BERA INTRODUCTION
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(13);
  setSlideBackground(s, ACCENT);
  headerBar(s, "BERA — Introduction");
  slideNum(s, 14);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  addText(s, "Also known as: ABR  |  BAER  |  BAEP", 30, 73, 660, 25, 13, true, "#c0392b", "center");

  addRect(s, 20, 100, 680, 3, HEADER_BG, null);
  addBulletBox(s, [
    "• 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"
  ], 30, 108, 660, 220, 13, DARK_TEXT);

  addRect(s, 20, 332, 680, 3, HEADER_BG, null);
  addText(s, "Electrode Placement", 30, 338, 400, 25, 14, true, HEADER_BG, "left");
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    ep += 35;
  });

  // ══════════════════════════════════════════════════════════
  // SLIDE 15 — BERA WAVE GENERATORS
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(14);
  setSlideBackground(s, ACCENT);
  headerBar(s, "BERA — Wave Generators (Jewett Waves)");
  slideNum(s, 15);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  var wRows = [
    ["Wave", "Generator (Anatomical Site)", "Approximate Latency"],
    ["Wave I",       "Distal part of CN VIII (cochlear nerve)",          "~1.5 ms"],
    ["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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  var wTc = [WHITE, DARK_TEXT, DARK_TEXT, DARK_TEXT, DARK_TEXT, DARK_TEXT, DARK_TEXT];
  var wW  = [80, 350, 150];
  var wX  = [25, 105, 455];
  var wy  = 72;
  wRows.forEach(function(row, ri) {
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  addText(s, "★  Waves I, III, V are the most clinically significant (most stable)", 30, 440, 660, 30, 13, true, HEADER_BG, "center");

  // ══════════════════════════════════════════════════════════
  // SLIDE 16 — BERA LATENCIES & NORMAL VALUES
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(15);
  setSlideBackground(s, ACCENT);
  headerBar(s, "BERA — Normal Latencies & Inter-peak Intervals");
  slideNum(s, 16);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  addText(s, "Normal BERA Values", 30, 73, 500, 25, 14, true, HEADER_BG, "left");
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    ["Parameter", "Normal Value", "Clinical Significance"],
    ["Absolute Latency — Wave I",    "~1.5 ms",    "Peripheral (cochlea / CN VIII)"],
    ["Absolute Latency — Wave III",  "~3.5 ms",    "Lower brainstem"],
    ["Absolute Latency — Wave V",    "~5.5–5.7 ms","Upper brainstem / Midbrain"],
    ["Inter-peak Interval I–III",    "~2.0 ms",    "Peripheral to lower brainstem conduction"],
    ["Inter-peak Interval III–V",    "~2.0 ms",    "Lower to upper brainstem conduction"],
    ["Inter-peak Interval I–V",      "~4.0 ms",    "Total brainstem conduction time"],
    ["Interaural Wave V difference", "< 0.4 ms",   "Asymmetric lesion (e.g. acoustic neuroma)"]
  ];
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  // ══════════════════════════════════════════════════════════
  // SLIDE 17 — BERA INTERPRETATION
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(16);
  setSlideBackground(s, ACCENT);
  headerBar(s, "BERA — Interpretation by Lesion Type");
  slideNum(s, 17);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  var interp = [
    ["Conductive HL", "All waves present but SHIFTED RIGHT (prolonged absolute latencies)\nInter-peak intervals NORMAL — only absolute latencies affected"],
    ["Cochlear (Sensory) HL", "Absent/poor Wave I at low intensities\nInter-peak intervals NORMAL once waves appear\nThreshold elevated"],
    ["Retrocochlear (CN VIII / Acoustic Neuroma)", "Prolonged I–III interval (> 2.3 ms)\nAbsent waves beyond Wave I, or Wave V absent\nInteraural latency difference Wave V > 0.4 ms"],
    ["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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    iy += 93;
  });

  // ══════════════════════════════════════════════════════════
  // SLIDE 18 — USES OF BERA
  // ══════════════════════════════════════════════════════════
  s = presentation.insertSlide(17);
  setSlideBackground(s, ACCENT);
  headerBar(s, "Uses of BERA / ABR");
  slideNum(s, 18);
  addRect(s, 20, 65, 680, 415, WHITE, HEADER_BG);

  var beraUses = [
    ["(i)", "Neonatal & Infant Hearing Screening", "Objective threshold — no cooperation needed; used in Universal Newborn Hearing Screening (UNHS)"],
    ["(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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    addRect(s, 260, buy, 435, 62, bg, "#aec6e8");
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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

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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.

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3. Instrumentation

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

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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

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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

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6. Acoustic Reflex Arc

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7. Recruitment

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

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8. SISI Test (Short Increment Sensitivity Index)

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

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9. Threshold Tone Decay Test

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

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10. Evoked Response Audiometry

1. Electrocochleography (ECoG)
2. BERA/ABR

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11. Electrocochleography (ECoG)

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

• Ménière's disease
• Infant threshold estimation

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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

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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

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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

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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)

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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)

---

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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