Immittancemetric Analysis

Immittance tests play a critical role in audiology for evaluating the functions of the middle ear. The health of the middle ear is usually determined by analyzing energy transmission and reflection. While the traditional 226 Hz tympanometry method detects conditions such as fluid accumulation or Eustachian tube dysfunction, Wideband Acoustic Immittance (WAI) tests provide comprehensive information over a broader frequency range. WAI enables more precise diagnosis of conditions such as otitis media and increases evaluation accuracy compared to traditional methods. These advances offer significant advantages to healthcare professionals in providing accurate diagnosis and effective treatment to patients.

What Is Immittance and How Is It Defined?

Immittance is a comprehensive term that encompasses both the concepts of impedance and admittance. Impedance is the resistance a system offers to alternating current and includes both resistance (the ohmic component) and reactance (the capacitive or inductive component). Admittance, on the other hand, is the reciprocal of impedance and defines how easily current flows through a system. Unlike impedance, admittance represents a measure of fluidity and is measured in siemens (S). Immittance brings these two parameters together within a common framework, offering a holistic approach for analyzing complex systems.

This term is frequently used in both engineering acoustics and the medical field. For example, in electrical engineering, immitance is critical for evaluating the impedance-admittance relationship in circuit design and analysis. In acoustics, it is used to understand how sound waves interact with different media, with tympanometry tests in audiology being an excellent example. Tympanometry evaluates middle ear function by measuring acoustic immittance and serves as an important tool in the diagnosis of conditions such as otitis media.

The historical origin of the term immitance dates back to 1945 when engineer Hendrik Wade Bode introduced it. Bode created this combined term to emphasize the complementary nature of impedance and admittance in electrical circuit analysis. Although it was initially called “adpedance,” the term “immitance” quickly gained broader acceptance and was rapidly adopted. In particular, Bode’s work, Network Analysis and Feedback Amplifier Design, helped standardize the concept of immitance in the engineering field.

Today, the concept of immitance is indispensable not only in engineering and acoustics but also in bioacoustics and medical research. In medicine, immitance measurements have led to the development of more precise diagnostic methods and have improved clinical applications.

What Is the Role of Immittance in Audiology?

Acoustic immittance tests are a critical tool in audiological practice for evaluating middle ear functions. These tests provide important information by analyzing how sound energy is transmitted or obstructed from the middle ear to the inner ear. Measurements such as tympanic membrane mobility, middle ear pressure, and acoustic reflex responses offer a detailed assessment of various components of the hearing system.

Tympanometry is one of the fundamental procedures in immittance testing and provides information about the overall health of the middle ear structures. For example, a Type B tympanogram may indicate pathologies such as fluid accumulation in the middle ear, while a Type C tympanogram may suggest Eustachian tube dysfunction. These findings not only aid in diagnosing hearing loss but also help identify underlying causes such as infections or anatomical abnormalities.

Acoustic reflex testing, on the other hand, evaluates the neural components of the hearing system. By measuring the stapedius muscle reflex in response to high-intensity sounds, the integrity of structures such as the cochlear nerve and facial nerve is examined. Abnormalities in the reflex response provide clues regarding neural pathologies or middle ear dysfunctions.

The clinical importance of these tests is substantial. They play a critical role in the early diagnosis of common middle ear disorders such as otitis media and guide treatment planning. They are also effective in diagnosing less common conditions such as ossicular chain abnormalities. Thus, immittance measurements have become an integral component of audiological evaluations.

Why Are Immittance Tests Important in Diagnosing Middle Ear Disorders?

Immittance tests are indispensable tools for diagnosing pathologies by evaluating the mechanical properties of the middle ear. These tests include measurements of impedance (the resistance to sound waves) and admittance (the transmission of sound waves). By specifically examining the energy transmission and reflection of the middle ear, conditions such as fluid accumulation, negative pressure, Eustachian tube dysfunction, and ossicular abnormalities can be detected.

Although traditional 226 Hz tympanometry has long been used as a fundamental method, its operation over a limited frequency range may be insufficient for detecting certain pathologies. For example, it has limited sensitivity in differentiating between types of otitis media or in accurately diagnosing ossicular chain anomalies. In contrast, Wideband Acoustic Immittance (WAI) evaluates energy transfer over a broad frequency range—from 226 Hz to 8000 Hz—providing more detailed and reliable information.

WAI not only increases diagnostic accuracy but also stands out due to its applicability in patient groups with limited cooperation, as it does not require active participation. The ability to obtain reliable results in infants and individuals with special needs enhances the importance of this test in pediatric audiology. Additionally, the normative data provided by WAI allows for standardization of evaluations across different age groups.

What Are the Challenges and Considerations in Immittance Measurements?

Immittance measurements require precision and accuracy in evaluating middle ear functions. However, various factors can affect the accuracy of these measurements and lead to misinterpretation of the results. Therefore, it is vital to be aware of the key elements that must be considered during the measurement process.

• Kulak Kanalı Hacmi (ECV):

Accurate measurement of the ear canal volume ensures that the immittance data are interpreted correctly. Deviations in volume—such as larger volumes indicating tympanic membrane perforation or smaller volumes suggesting blockage—must be taken into account.

• Selection of Probe Tone Frequency:

The probe tone frequency directly affects the reliability of the measurement results. While a 226 Hz probe tone provides reliable results for adults, higher frequencies such as 1000 Hz are recommended for infants. This selection is critical for understanding the different dynamics of the middle ear system in infants.

• Measurement Techniques in Infants and Adults:

The compliant structure of infants’ ear canals and the differing characteristics of their middle ear systems require different measurement approaches. The appropriate probe tone must be used in this age group to avoid misleading results.

• The Importance of Calibration:

Regular calibration of the equipment is indispensable for obtaining accurate measurement results. Calibration procedures guarantee the accuracy of the probe tone frequency and the reliability of the air pressure settings. Adherence to standards such as ANSI is essential for achieving consistent and reliable data.

Dr. Ody. Emel Uğur

Dr. Audiologist Emel Uğur was born in 1982 in Çanakkale. She worked for 15 years at Istanbul Training and Research Hospital, specializing in Pediatric Audiology, Otologic Diseases, and Vestibular System Disorders. In 2015, she joined the Acıbadem Healthcare Group. She currently works as a Dr. Audiologist at Acıbadem Altunizade Hospital and also serves as a faculty member and program director of the Audiometry Department at Acıbadem University Vocational School of Health Services.