What characteristic defines a Type Ad tympanogram?

A Type Ad tympanogram is characterized by normal middle ear pressure with high compliance, which indicates a hypermobile tympanic membrane. This suggests that the eardrum moves excessively due to low impedance, often associated with conditions such as a thinning or abnormality of the tympanic membrane, or potentially ossicular chain dislocation.

The key aspect of Type Ad is that while the pressure is normal, the compliance measure reflects a more mobile response than typical, suggesting that the eardrum's ability to transmit sound is impaired but allows for increased movement in the absence of pressure change. Understanding this helps in the diagnosis of middle ear conditions and assessing the structural integrity of the tympanic membrane.

Other types of tympanograms indicate different conditions, such as reduced compliance or abnormal pressure, which do not apply to Type Ad. In Type A tympanograms, for instance, both pressure and compliance would be within normal limits, while Type As indicates normal pressure but reduced compliance, reflecting a stiff tympanic membrane.