Assessment Tools: Introduction and Practical Use of Tympanometry Measurements in a Hearing Conservation Program

The following is a brief description of the anatomy and physiology that is measured during tympanometry testing, the importance of incorporating tympanometry measurements in a hearing conservation program, and how tympanograms are measured.

The Auditory Pathway

A full description on how the auditory system works can be found in a previous article entitled Introduction to the Anatomy and Physiology of the Auditory System.

What is Tympanometry?

Tympanometry provides information about the compliance (mobility) of the middle ear system by using equipment called a tympanometer. Results from the tympanometer are placed on a tympanogram which plots the compliance (mobility) of the eardrum on the Y axis versus the air pressure of the ear, which is measured in dekapascals (daPa) on the X axis.

Why are they important?

• Tympanometry is fast, objective and does not require employee participation.
• Tympanometry can aid in the determination of work-relatedness on the OSHA 300 Log and is seen as a legally binding tool.
• Tympanometry can be used during the Audiologist plant visit to evaluate employees being held for plant visits and medical referrals.
• Gives employees more validity for following-up with incomplete medical referrals.

How are tympanograms recorded?

The tympanometer is comprised of three small plastic tubes that are attached to a metal probe. The three plastic tubes are connected to (1) a miniature loudspeaker, which emits a pure tone; (2) a tiny microphone, which picks up the sound of the ear canal; and (3) an air pump which can create either positive or negative pressure within the ear canal (Martin, 2000). The metal probe is then covered with a removable probe tip that is varied in size to accommodate most ears. This probe tip is placed into the ear canal where a pressurized seal is formed. The tympanometer can be started manually or automatically when a pressurized seal is formed within the ear canal. The eardrum is then displaced from its resting position by positive pressure that is inserted from the probe tip to the ear canal. Once the initial pressure has reached 0 daPa, the positive pressure is changed to negative pressure, which gives the appearance of a "mountain peak" on the tympanogram. These results are seen in a normal functioning middle ear system.

What do the results indicate?

Results from this evaluation can help the audiologist to understand whether the employee has a possible middle ear infection, a pressure-equalizing tube that may be clogged, a possible problem with the bones of the middle ear, or problems with middle ear muscle reflex. The following chart is an indication of how tympanograms are classified.

Example of a Type A Tympanogram.
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Example of a Type B Tympanogram.

Example of a Type C Tympanogram.

Before drawing conclusions from tympanometry results in reference to hearing loss diagnoses, a variety of audiologic evaluations should be performed.

Summary

Tympanometry is to serve as a supplement to the hearing tests performed by the OHC in determining the eardrum mobility of the employee. No single test in the assessment of hearing will tell the audiologist all that is needed to identify and provide direction for treatment and rehabilitation of hearing loss. A variety of tests will provide information about the functioning of different sites of injury along the auditory pathway. Testing for eardrum mobility, can aid in screening medical referrals and employees who show a non work-related OSHA recordable hearing loss in the plant.

References & Additional Resources

• Hall, J.W. & Mueller, H.G. (1997). Audiologists’ Desk Reference Volume I: Diagnostic Audiology Principles, Procedures, and Practices. San Diego, CA: Singular Thomson Learning.
  
  
• Martin, F.N. & Clark, J.G. (2000). Introduction to Audiology, 7th Edition. Boston: Allyn and Bacon.
  
  
• The American Academy of Audiology
  
  
• The American Speech Language and Hearing Association.
  
  
• Grason Stadler Instruments