**Wideband Tympanometry Wideband Tympanometry**

Thais Antonelli Diniz Hein, Stavros Hatzopoulos, Piotr Henryk Skarzynski and Maria Francisca Colella-Santos Thais Antonelli Diniz Hein, Stavros Hatzopoulos, Piotr Henryk Skarzynski and Maria Francisca Colella-Santos Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67155

#### **Abstract**

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The wideband tympanometry (WBT) assesses the middle ear function with a transient wideband stimulus in order to capture the middle ear behavior at a wide range of frequencies. Data in the literature suggest that the WBT has more sensibility to detect middle ear disorders than the traditional tympanometry. In this context, pathologies, which might be more easily identified/monitored by WBT, include otosclerosis, flaccid eardrums, ossicular chain discontinuity with semicircular canal dehiscence, and negative middle ear pressure with middle ear effusion. The chapter presents information on classical tympanometry, the multifrequency tympanometry equivalent coded as WBT, clarification of terms used in WBT measurements, and a short overview of clinical applications in infants and adults.

**Keywords:** acoustic immitance, tympanometry, wideband tympanometry, acoustic reflectance, acoustic absorbance

#### **1. Introduction to tympanometry**

Sound stimuli can be modified by alterations of the middle ear functionality; therefore, an assessment of the middle ear function is fundamental for a proper evaluation of hearing impairment. Acoustic immittance is a general term referring to measurements related to tympanometry and acoustic stapedial reflexes, which can provide information about the middle ear (ME) status. Tympanometry measurements represent alterations in the sound absorbance characteristics of the ME system (composed by the tympanic membrane + the middle ear), as the pressure in the external acoustic canal is modified. Clinically, these pressure values range from +200 to -400 daPa. According to Shanks and Lilly [1], the most accurate measurements are those in the low pressure end.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The ME ossicular structures drive the incoming sound stimuli from the eardrum (maleus) to the inner ear (footplate of the stapes). In terms of acoustic energy transmission, there is a physical problem interfacing the middle and the inner ear. The middle ear propagation medium is gaseous while the inner ear medium is liquid. To optimize the propagating stimulus energy, it is necessary to adjust the ME impedance so that the stimulus at the stapes undergoes an "*optimal power transference into the inner ear*" also called "*minimum impedance reflection*." This operation is termed as "*the middle ear impedance matching transformer*" [2, 3] and describes the efficiency by which the acoustic sound energy at the stapes is transformed into an acoustic pressure wave inside the helix structures of the inner ear, without significant energy losses.

There is a specific terminology in the ME measurements: There is an excellent review of these terms by Block and Wiley [4] and by Hall and Chandler [5]. Most of the ME measurements refer to *acoustic immittance* values, which describe the *easiness* by which a sound stimulus can propagate across a medium (air or liquid). Most media impose a resistance to any type of propagation energy. According to this concept, the structures of the ME impose a *resistance* to the propagation of the sound energy, and this opposition/resistance is termed as *acoustic impedance Z*(*ω*). By definition, the reciprocal value of acoustic impedance is *acoustic admittance Y*(*ω*). In this context an acoustic immittance measurement can refer to either *Z*(*ω*) or *Y*(*ω*) and the measurement is conducted with the same manner. The *Z*(*ω*) and *Y*(*ω*) variables are complex and they are characterized by a real and an imaginary part. In clinical terms, this characteristic means that the values of these depend on the frequency (*ω*) of the propagating stimulus. There is another measurement called "static immittance" which refers to measurement under a normal atmospheric pressure (i.e., not varying) and according to Hall and Chandler [5] clinically this can be measured at 226 Hz.

Traditional tympanometry assesses the impedance of the middle ear at the frequency of 226 Hz. The measurement modality is described in **Figure 1**, and it is conducted with a sensitive probe, which seals completely the ear of the patient. Once the 226 Hz tone is emitted, the pressure variation in the external acoustic meatus displaces the eardrum. This causes the tone absorption of the ME to vary, and a sensitive microphone incorporated in the probe evaluates the total admittance of the system [2].

Tympanometry provides quantitative information about the presence of fluid in the ME, about the mobility of the tympanic-ossicular system, and about the volume of the external acoustic meatus. While it is an effective procedure to identify ME changes in children, adults, and seniors, it has its limitations. For example, there are reported cases in the literature of myringotomy surgeries where the 226 Hz tympanometric data were reported as normal [6]. Assessment outliers like these myringotomy cases, are probably caused by a lack of specific norms for the different types of populations under assessment. It is well known that the eardrum and the external acoustic meatus of neonates and children are anatomically different than those from adult subjects. In this context, the ME impedance norms of one population do not describe well the norms of the other.

Data in the literature suggest that in infants of approximately 6 months of age, the high-frequency ME transmission is more efficient. Tympanometry measurements with a high‐frequency tone (1000 Hz) can be more sensitive to identify ME changes than those conducted with a 226 Hz probe tone [6–8]. High frequency tympanometry has been shown to be reliable and highly reproducible. But the data in the literature also suggest that the 1000 Hz protocol cannot always identify all children with ME alterations. As a result, discrepant data between studies are reported, as well as reports describing an interpretation difficulty of the 1000 Hz impedance tracing [9, 10]. The 1000 Hz tympanometry trace is different than the traditional trace of 226 Hz. For many subjects the 1000 Hz trace presents a double peak and its clinical interpretation can be quite complicated [11].

**Figure 1.** The tympanometry probe (shown with three major components) seals the ear of the patient. The components shown include the microphone, the pressure regulation system, and a speaker transducer.

A differential diagnosis for the evaluation of middle ear function is essential for infants presenting ME disorders, as in the case of temporary conductive hearing losses. This aspect is critical, because there is high incidence of unsuccessful results (FAIL) in neonatal hearing screening programs. These results are frequently caused by changes in the ME status and affect significantly the time and spectral characteristics of the transiently evoked otoacoustic emissions (TEOAEs), which are routinely used in the hearing screening protocols [12–15].
