Tympanograms

Tympanograms are graphs produced by tympanometry, a test of middle-ear function that measures the mobility of the tympanic membrane (eardrum) and the ossicular chain as the air pressure in the ear canal is varied. A probe delivers a small tone and the air pressure in the ear canal is changed from positive to negative while a microphone records the reflected sound. The resulting tympanogram plots tympanic membrane admittance (or compliance) against ear-canal pressure, with the horizontal axis in decaPascals (daPa) and the vertical axis in milliliters or millimhos.

A normal pattern, Type A, shows a peak in compliance near atmospheric pressure, indicating normal middle-ear pressure and mobility. Type As shows a shallow peak, suggesting a stiff middle ear (for example due to retracted drum or scarring). Type Ad shows a tall peak, indicating hypermobile or flaccid tympanic membranes. Type B is flat with little or no peak; if the ear-canal volume is normal, this often reflects middle-ear effusion, whereas a large volume suggests a perforated tympanic membrane or a patent tympanostomy tube. Type C has a peak shifted toward negative pressure, indicating eustachian tube dysfunction and negative middle-ear pressure.

Clinically, tympanometry assists in diagnosing otitis media with effusion, eustachian tube dysfunction, barotrauma, and other middle-ear conditions, and it is used in pre-surgical assessment and pediatric as well as adult evaluations. Limitations include dependence on a good seal, ear-canal volume, and proper probe placement; results reflect middle-ear mobility rather than disease alone and can be affected by age and measurement frequency. High-frequency tympanometry (around 800–1000 Hz) may be more informative in infants, whereas standard 226 Hz is commonly used in adults. Typical normal values place the peak around 0 daPa with a peak compliance of roughly 0.3–1.7 mL.