What is tympanometry?
First developed in the 1950's, tympanometry is an objective measurement used to evaluate the condition of the middle ear eardrum and the conduction bones by creating variations of air pressure in the ear canal (1Terkildsen et al.). Since then, the test technique has further developed and become a common part of the audiological test routine.
1Terkildsen, K. and K.A. Thomsen (1959). The influence of pressure variations on the impedance measuring bridge for clinical use. J. Laryngol. Otol. 73, 409-418.
What is an acoustic reflex measurement?
Just like tympanometry measurements, a probe is inserted into the ear canal. While playing a continues probe tone, short test signals (e.g. 0.5, 1 or 2kHz) are presented at levels of 70 - 100dB, triggering the stapes muscle to contract.
Through this contraction, the ossicular chain and ear drum stiffens as well, leading to a measurable decrease of compliance in the ear canal. The acoustic reflex is measurable in both ears (ipsilateral and contralateral).
Why measure acoustic reflexes?
Acoustic reflexes are regularly used in audiological testing and measure the stapedius and the tensor tympani reflex generated eardrum movement in response to intense sound. Acoustic reflex measurements provide feedback on:
- Type and degree of hearing loss (conductive, sensory, neural)
- Injury of the facial nerve or vestibulocochlear nerve