Interpretation of results

• in measuring middle ear compliance, four patterns are commonly seen:
  • normal - greatest compliance - as indicated by the amount of sound absorbed - occurs when the pressure in the middle ear equals that in the external ear, which is atmospheric
  • increased - greatest compliance occurs when the pressure in the middle ear canal is positive relative to that in the external ear; this indicates a floppy ear drum e.g. from disruption of the ossicular chain
  • decreased - compliance maximum when pressure in middle ear is negative relative to the external ear; this indicates eustachian tube dysfunction
  • flat - very little sound is absorbed because the middle ear is incompressible - eg. from glue ear
• in infants and the mentally handicapped, tympanometry may be used to assess the threshold for the stapedius muscle reflex and hence, hearing loss. Normally, contraction occurs at 75 decibels but greater stimulation is required if hearing is impaired. Contraction of the stapedius muscle is indicated by a sudden decrease in the sound absorbed and thus, an increase in the amount reflected
• it is not reliable in infants younger than seven months because the ear canals of infants are highly compliant.(1)
• using pneumatic otoscopy with tympanometry improves the accuracy of diagnosis (1)

Reference:

• (1) Edward Onusko. Tympanometry.Am Fam Physician 2004;70:1713-20