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Introduction to Tympanometry

This is an introduction to understanding and reporting on tympanometry measurements.

You should use this guide in conjunction with your own clinic’s protocols and current research in acoustic immittance testing.

Contents:

  1. What is tympanometry?
  2. What is a tympanogram?
  3. Terminology
  4. Tympanogram types
  5. Reasons for repeating tympanometry
  6. How to report results
 

What is tympanometry?

Tympanometry is a test where both negative and positive pressure is applied to the middle ear alongside a constant probe tone. Tympanometry assesses how much of the probe tone is absorbed into the middle and inner ear, and how much is reflected. This allows clinicians to form a picture of how the tympanic membrane acts and functions. 

 

What is a tympanogram?

A tympanogram is a graph produced by tympanometry. It shows the movement of the tympanic membrane and is most often cone-shaped. The peak of a tympanogram is where the eardrum is balanced between negative and positive pressure. By using a template such as Jerger’s classification, it is possible to determine if the tympanic membrane moves freely or if a disorder is present.

 

Tympanometry terminology

There are several terms you need to know when performing tympanometry and interpreting tympanograms:

  • Ear canal volume
  • Tympanometric peak pressure
  • Static compliance
  • Gradient

Let’s dive into each below.

 

Ear canal volume

Fowler & Shanks [1] define ear canal volume as “an estimate of the volume of air medial to the probe, which includes the volume between the probe tip and the tympanic membrane if the tympanic membrane is intact, or the volume of the ear canal and the middle ear space if the tympanic membrane is perforated.”

On average, children from 3-5 years of age have an ear canal volume of 0.4-1.0 cc, while the range is 0.6-1.5 cc for adults.

Ear canal volume can help to suggest what middle ear pathology is present.

For example, an ear canal volume >2.0 with a type B tympanogram in children would suggest a perforated tympanic membrane or a patent grommet.

Alternatively, a very small ear canal volume with a type B tympanogram would suggest wax interference.

 

Tympanometric peak pressure

Tympanometric peak pressure, also known as middle ear pressure, is the ear canal pressure at which the peak of the tympanogram occurs [2].

 

Static compliance

Onusko [3] defines static compliance as “the greatest amount of acoustic energy absorbed by the middle ear system (the vertical peak of the tympanic tracing).”

 

Gradient

Fowler & Shanks [1] define the gradient as “an objective measure that describes the steepness of the slope of the tympanogram near the peak.”

 

Tympanogram types

There are several tympanogram types, as proposed by Jerger:

  • Type A
  • Type B
  • Type C
  • Type As
  • Type Ad
  • Tympanic membrane perforation

Before covering each below, please note that the classification of tympanogram types differs between clinics and audiologists.

The below merely provides an overview of which tympanograms you may come across and what they may indicate.

 

Type A tympanogram

Figure 1 shows what a type A tympanogram looks like:

Type A tympanogram

Figure 1: Type A tympanogram.

Type A tympanograms exhibit the following characteristics:

  • Sharp peak
  • Middle ear pressure between -99 to +50 mmH2O
  • Static compliance between 0.3-1.6 cc in adults
  • Static compliance between 0.2-0.9 cc in children 3-5 years of age
  • Ear canal volume within normal range

 

Type B tympanogram

Figure 2 shows what a type B tympanogram looks like:

Type B tympanogram

Figure 2: Type B tympanogram.

Type B tympanograms exhibit the following characteristics:

  • No peak
  • Non-measurable or reduced middle ear pressure
  • Non-measurable or reduced static compliance
  • Ear canal volume within normal range

 

Type C tympanogram

Figure 3 shows what a type C tympanogram looks like:

Type C tympanogram

Figure 3: Type C tympanogram.

Type C tympanograms exhibit the following characteristics:

  • Sharp peak
  • Middle ear pressure below -99 mmH2O
  • Static compliance between 0.3-1.6 cc in adults
  • Static compliance between 0.2-0.9 cc in children 3-5 years of age
  • Ear canal volume within normal range

 

Type As tympanogram

Figure 4 shows what a type As tympanogram looks like:

Type As tympanogram

Figure 4: Type As tympanogram.

Type As tympanograms exhibit the following characteristics:

  • Sharp peak
  • Normal middle ear pressure
  • Static compliance below 0.3 cc in adults
  • Ear canal volume within normal range

 

Type Ad tympanogram

Figure 5 shows what a type Ad tympanogram looks like:

Type Ad tympanogram

Figure 5: Type Ad tympanogram.

Type Ad tympanograms exhibit the following characteristics:

  • Sharp peak
  • Normal middle ear pressure
  • Static compliance above 1.6 cc in adults
  • Ear canal volume within normal range

 

Tympanic membrane perforation

Figure 6 shows what a tympanogram would look like if the patient’s tympanic membrane is perforated:

Tympanic membrane perforation tympanogram

Figure 6: Tympanic membrane perforation tympanogram.

  • No peak
  • Non-measurable or reduced middle ear pressure
  • Non-measurable or reduced static compliance
  • Large ear canal volume
 

Reasons for repeating tympanometry

If you patient swallows, talks, laughs, coughs or similar during the test, then you may want to repeat the test for more reliable results.

If you get an odd result that does not look correct or does not match the audiogram findings, then you may want to repeat the test to see if the results are repeatable.

 

How to report on tympanometry results

You can find some common sentences used to report on tympanometry results below.

Please note that you should look at tympanometry results in conjunction with other audiological results in the test battery, such as tone audiometry or speech audiometry.

 

Type A

Tympanometry showed normal middle ear pressure and static compliance.

Type B

Tympanometry showed no measurable middle ear pressure or static compliance, consistent with middle ear pathology.

Type C

Tympanometry showed significant negative middle ear pressure in the presence of normal static compliance, consistent with Eustachian tube dysfunction or middle ear pathology.

Type As

Tympanometry showed normal middle ear pressure with decreased static compliance, consistent with a hypomobile tympanic membrane.

Type Ad

Tympanometry showed normal middle ear pressure with increased static compliance, consistent with a hypermobile tympanic membrane.

Large ear canal volume

Tympanometry showed a large ear canal volume, consistent with a tympanic membrane perforation or patent grommet.

 

References

[1] Fowler, C. G., & Shanks, J. E. (2002). Tympanometry. In J. Katz (Ed.), Handbook of clinical audiology (5th ed.). (pp. 175 – 204). Baltimore: Lippincott Williams & Wilkins.

[2] Margolis, R. H., & Hunter, L. L. (2000). Acoustic Immittance Measurements. In  R. J. Roeser, M. Valente & H. Hosford-Dunn (Ed.), Audiology diagnosis. (pp. 381 - 423). New York: Thieme Medical Publishers, Inc.

[3] Onusko, E. (2004). Tympanometry. American Family Physician, 70 (9), 1713 – 1720.

November 2013
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