Tympanometry
Principle: When sound strikes the tympanic membrane (TM), some energy is absorbed and some reflected.
- Stiffer TM: Reflects MORE sound energy.
- Compliant TM: Reflects LESS sound energy.
Goal: To measure the compliance/stiffness of the tympano-ossicular system by changing pressure in the sealed canal, thus identifying middle ear pathology.
Equipment
A probe is fitted snugly into the external auditory canal. It has three channels:
1. Tone Delivery (220 Hz)
+
2. Microphone (Picks up reflected sound)
+
3. Pressure Pump (Changes pressure: Positive → Normal → Negative)
Types of Tympanograms
The graph charting compliance against pressure changes.
| Type | Description | Clinical Condition |
|---|---|---|
| Type A | Normal peak compliance at ambient pressure. | Normal Middle Ear |
| Type As | Compliance is LOWER (Shallower peak) at/near ambient pressure. | Fixation of Ossicles: • Otosclerosis • Malleus Fixation |
| Type Ad | Compliance is HIGH (Deep peak) at/near ambient pressure. | Disruption: • Ossicular discontinuity • Thin/Lax TM |
| Type B | Flat or Dome-shaped. No compliance change with pressure. | Fluid/Thickening: • Middle Ear Fluid (OME) • Thick TM |
| Type C | Max compliance at negative pressure (> -100 mm H2O). | Retraction: • Retracted TM • Early fluid accumulation |
Testing Eustachian Tube Function
Tympanometry can assess ET function in both intact and perforated drums.
Procedure (Intact TM)
- Create negative or positive pressure (-200 or +200 mm H2O) in the middle ear.
- Ask patient to swallow 5 times in 20 seconds.
- Result: Ability to equilibrate pressure = Normal Tubal Function.
Other Uses
- Checking Patency of Grommet in Serous Otitis Media.
📚 Source: ENT Dhingra
đź’¬ Comments
No comments:
Post a Comment