Understanding Middle Ear & Tympanometry

Middle Ear Anatomy Quick Review:

• Eardrum (Tympanic Membrane): Thin membrane, outer ear से middle ear separate करता है
• Middle Ear Cavity: Air-filled space
• Ossicles: 3 tiny bones (malleus, incus, stapes) – sound को inner ear तक पहुंचाते हैं
• Eustachian Tube: Middle ear को throat से connect करती है – equalizes pressure

Normal Function:

• Eardrum vibrates when sound hits
• Vibrations ossicles के through inner ear जाते हैं
• Middle ear pressure = atmospheric pressure (Eustachian tube के through)
• Optimal vibration के लिए pressure balance जरूरी

What Can Go Wrong:

• Fluid in middle ear: Vibration dampens (मफल हो जाता है)
• Eustachian tube blockage: Negative pressure creates (vacuum effect)
• Eardrum perforation: No vibration
• Ossicular fixation: Bones don’t move properly

Tympanometry कैसे काम करता है?

Principle:

Tympanometry eardrum की compliance (लचीलापन/movement capability) measure करता है जब ear canal में pressure changes होते हैं।

Procedure:

Step 1: Probe Insertion

• एक small soft rubber tip (probe) ear canal में insert होता है
• Airtight seal बनता है

Step 2: Tone Delivery

• Probe एक 226 Hz tone (low frequency sound) deliver करता है

Step 3: Pressure Changes

• Probe ear canal में pressure vary करता है (+200 to -400 daPa)
• Positive pressure (pushing in) → Negative pressure (pulling out)

Step 4: Measure Reflection

• Different pressures पर, कितनी sound eardrum से reflect back होती है vs absorb होती है
• Maximum absorption = Maximum compliance = Eardrum moves best
• यह point note किया जाता है

Step 5: Graph (Tympanogram)

• Result एक graph है – pressure (X-axis) vs compliance (Y-axis)
• Shape of curve diagnosis बताता है

Duration:

• 2-3 minutes per ear
• Patient को कुछ नहीं करना – just sit still
• Babies में भी easily हो सकता है

Tympanogram Types – Result Interpretation

Type A (Normal):

• Shape: Inverted bell curve, peak at/near 0 daPa
• Meaning: Normal middle ear pressure, normal eardrum mobility
• Indicates: Middle ear healthy

Type As (Shallow):

• Shape: Peak present but reduced height
• Meaning: Reduced compliance (stiff eardrum/ossicles)
• Causes: Otosclerosis, tympanosclerosis

Type Ad (Deep):

• Shape: Very tall peak
• Meaning: Excessive compliance (hyper-mobile eardrum)
• Causes: Ossicular discontinuity (chain broken)

Type B (Flat):

• Shape: Flat line, no peak
• Meaning: No eardrum movement
• Causes:
  • Middle ear fluid (most common – OME/glue ear)
  • Eardrum perforation
  • Impacted wax (blocking probe)
• Differentiation: Otoscopy + ear canal volume measurement

Type C (Negative Pressure):

• Shape: Peak present but shifted left (negative pressure side)
• Peak at: -100 daPa या more negative
• Meaning: Negative middle ear pressure
• Cause: Eustachian tube dysfunction (blocked/not opening properly)
• Clinical: Ear fullness, mild hearing loss, may progress to fluid

Common Conditions Diagnosed

1. Otitis Media with Effusion (OME) – “Glue Ear”:

• Definition: Fluid in middle ear without active infection
• Very common in children (2-5 years peak)
• Symptoms: Hearing loss, ear fullness, speech delay (if chronic)
• Tympanogram: Type B (flat)
• Importance: Tympanometry best way to detect – otoscopy sometimes misses
• Treatment: Observation (many resolve), grommets if persistent >3 months

2. Eustachian Tube Dysfunction (ETD):

• Cause: Allergies, colds, adenoid enlargement
• Symptoms: Ear pressure, fullness, popping sensation, mild hearing loss
• Tympanogram: Type C (negative pressure)
• Treatment: Decongestants, nasal steroids, treat underlying cause

3. Eardrum Perforation:

• Tympanogram: Type B + increased ear canal volume
• Why volume increases: Probe measuring middle ear cavity also (normally just canal)
• Confirms: Perforation present

4. Otosclerosis:

• Definition: Stapes bone fixation (can’t move)
• Progressive conductive hearing loss
• Tympanogram: Type As (shallow – reduced compliance)
• Treatment: Hearing aid या stapedectomy surgery