True about tympanic membrane: (PGI Dec 2007)
Ans. D (Otosclerosis reduces compliance) Tympanometry Tympanometry is an objective test1, widely used in clinical practice & is particularly useful in children. It is based on the principle that when a sound strikes tympanic membrane, some of the sound energy is absorbed while the rest is reflected. A stiffer tympanic membrane reflects more sound energy than a complaint one "by changing the pressures in a sealed external auditory canal & then measuring the reflected sound energy, it is possible to find the compliance or stiffness of the tympano-ossicular system & thus find the healthy or diseased status of the middle ear. By chatting the compliance of tympano -ossicular system against various pressure changes, different types of graphs called tympanogram are: Type - A : Normal Tympanogram ' Type - As: Compliance is lower at or near ambient air pressure. Seen in fixation of ossicles e.g. otosclerosis or malleus fixation. Types AD- High compliance at or near ambient pressure. Seen in the ossicular discontinuity or thin & lax tympanic membraneQ. Type - B :A flat or dome-shaped graph. No Change in compliance with pressure changes. Seen in middle ear fluid or thick tympanic membrane Type - C: Maximum compliance occurs with negative pressure in excess of 100 mm of H20. Seen in retracted tympanic membrane & may show fluid in middle ear(r) Fig.: Types of tympanogram
Tympanosclerosis with increased compliance
Ossicular disruption with intact tympanic membrane and increased compliance
Fluid in middle ear cavity increases compliance
Otosclerosis reduces compliance
Otosclerosis