Understanding Tympanogram Classifications and Measurements

3. Ear Canal Volume (ECV)

ECV measures the physical size of the external auditory canal. This is measured in mL or cc.

• Small Volume (< 0.3 mL): May indicate a blockage, such as earwax.
• Large Volume (> 2.0 mL in adults): Suggests a significant opening, such as a perforated (holed) eardrum or a patent PE tube.

Jerger Classifications: Interpreting the Tracing

Clinicians use the Jerger classification system to categorize the shape of the tympanogram based on the relationship between pressure and compliance.

Type A: Normal Results

A Type A tympanogram shows a healthy "mountain" shape with a peak within the normal pressure range (-100 to +100 daPa). There are two common subtypes:

• Type As (Shallow): Characterized by hypocompliance. The peak is present and the pressure is normal, but the eardrum moves less than expected.
• Type Ad (Deep): Characterized by hypercompliance. The peak is very high (often exceeding 1.5 mmho), indicating a very mobile or flaccid eardrum. This is sometimes seen in children who have had multiple ear infections or PE tubes.

Type B: Flat Tracing

A Type B tympanogram shows no peak at all, meaning there is no measurable compliance. To determine the cause, you must look at the Ear Canal Volume:

• Normal Volume + Type B: Suggests fluid in the middle ear (e.g., an ear infection).
• Small Volume + Type B: Suggests a blockage like wax.
• Large Volume + Type B: Suggests a perforated eardrum.

Type C: Negative Pressure

A Type C tympanogram shows a peak that occurs at a pressure more negative than -100 daPa. This is often associated with Eustachian tube dysfunction.

Connecting Tympanometry to Hearing Loss

Tympanometry is a vital tool for differentiating between types of hearing loss.

• Conductive Hearing Loss: This occurs when sound is blocked from reaching the cochlea by issues in the outer or middle ear (like fluid, wax, or a perforation). This is typically associated with Type B or Type C tympanograms.
• Sensorineural Hearing Loss: This occurs when the problem is located in the cochlea or the auditory nerve. Because the middle ear system is functioning correctly, these patients typically present with a normal Type A tympanogram.

Acoustic Reflexes

The final component of immittance testing is the measurement of acoustic reflexes. This is a reflexive contraction of the stapedius muscle in the middle ear in response to a sufficiently loud sound.

When this muscle contracts, it causes ossicular chain stiffening, which reduces the compliance of the middle ear. The immittance bridge records the difference in compliance caused by this contraction.

It is important to remember that the acoustic reflex is a bilateral phenomenon. In a healthy auditory system, presenting a loud sound to one ear will trigger a reflexive response in both ears.

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Summary Table of Normative Values