Immittance

Immittance

Diagram of the osseous labyrinth, an important structure in the study of immittance.

Immittance is a term used in audiology and otology to describe the ease or difficulty with which energy flows through the middle ear. It is a combination of the terms "impedance" and "admittance," which are used to describe the opposition to energy flow and the ease of energy flow, respectively. Immittance measurements are crucial in diagnosing middle ear disorders and assessing hearing loss.

Components of Immittance

Immittance is composed of two main components:

Impedance

Impedance is the opposition that a system presents to the flow of acoustic energy. It is measured in ohms and is influenced by the mass, stiffness, and resistance of the middle ear structures. Impedance is a critical factor in determining how sound is transmitted through the ear.

Admittance

Admittance is the measure of how easily energy flows through a system. It is the reciprocal of impedance and is measured in siemens. Admittance provides information about the compliance and conductance of the middle ear.

Measurement of Immittance

Immittance is typically measured using a device called a tympanometer. This device assesses the function of the middle ear by varying the air pressure in the ear canal and measuring the reflected sound energy. The key measurements obtained from tympanometry include:

Tympanometry

Tympanometry is a test that evaluates the movement of the tympanic membrane in response to changes in air pressure. It provides a tympanogram, which is a graph that shows the compliance of the middle ear as a function of air pressure. Tympanometry helps in identifying conditions such as otitis media, eustachian tube dysfunction, and perforated eardrum.

Acoustic Reflex Testing

Acoustic reflex testing measures the contraction of the stapedius muscle in response to loud sounds. This reflex helps protect the inner ear from damage due to loud noises. The presence or absence of the acoustic reflex can provide information about the integrity of the auditory pathway.

Clinical Applications

Immittance testing is used in various clinical settings to:

• Diagnose middle ear effusion and otitis media.
• Evaluate eustachian tube function.
• Assess ossicular chain integrity.
• Monitor hearing aid performance.

Related Pages

• Audiometry
• Hearing loss
• Middle ear
• Otology