Introduction
Wideband acoustic immittance or wideband tympanometry (WBT) is an emerging tool used to examine the middle ear condition, ossicular chain, and tympanic membrane mobility [1]. A single wide spectrum stimulus “click” instead of the traditional 226 Hz probe tone is presented to the ear canal and hundreds of tympanograms from 226 to 8000 Hz could be visualized in a 3D format. This method permits complete analysis of middle ear conditions over a wide range of frequencies that encompass the full range of speech signals. Moreover, the acoustic energy absorbance of the middle ear and resonance frequency (RF) will be calculated [2]. Therefore, the clinical advantage of WBT is to increase the diagnostic precision of middle ear disorders and conditions and to increase the sensitivity and specificity of the test compared to traditional immittance measurements. Recent results show that different middle ear pathologies can affect the normal energy absorbance and RF in different ways [3]. Although several studies reported their normative values of WBT [4, 5], some other reports show that ethnic, gender, and age differences are a source of variability to the norms, and utilizing the same norm can cause erroneous results [6, 7]. For instance, according to Shahnaz et al., Caucasians have a higher peak pressure, larger ear canal, and narrower tympanic cavity than Asians [7]. Hunter and Shahnaz also reported that the Chinese population mainly had smaller admittance and ear canal volume, a more positive tympanogram peak pressure (TPP), and larger track width (TW) values [8]. Hence, the current study was conducted to investigate and collect the normal characteristics of clinical WBT measurement in the Iranian young adult population. Having our ethnic-specific norms can help clinicians to determine the middle ear conditions and disease more accurately. This report will provide preliminary data from a larger study conducted at Iran University of Medical Sciences to explore the sequel of various middle ear pathologies on WBT normative data. 

Materials and Methods
Twenty healthy students from the School of Rehabilitation Sciences, Iran University of Medical Sciences (8 females, and 12 males) with a Mean±SD age of 26.9±6.21 years were registered to participate in this descriptive cross-sectional study. All subjects had a clear history of auditory, learning, and neurologic function. All had normal otoscopic examinations, and well-functioning middle ear status (confirmed with traditional immittance results) and had normal pure tone thresholds (air conduction thresholds of better than 20 dB HL in the range of 250–8000 Hz). Subjects gave written consent to take part in the study. All the participants enrolled in the study had Iranian ethnic origin. 
The Interacoustics Titan version 3.1 (IMP440, Denmark) was first calibrated as specified by IEC 60645-5/ANSI S3.39, type 1 standards. Afterward, an appropriate probe tip (CIR 55-INSERT) was inserted in the external auditory meatus and 100 dB peSPL (almost equal to 65 dB nHL) click stimulus was presented to the ear in a quiet audiometry cabin to calculate the wideband acoustic immittance parameters in the frequency range of 226 to 8000 Hz. Participants were asked to stay still and pressure inside the ear canal was changed from +200 to -400 dapa, with 200 dapa/s pump speed. WBT estimations included RF of the middle ear, power absorbance, and other tympanometric data. Power absorbance is the total energy entered into the middle ear. The measured RF is the resonance frequency of the middle ear and is recorded at middle ear pressure. The average tympanograms, which are a flat trace showing the amount of energy absorbance in the range of 375–2000 Hz were also calculated. The benefit of taking wideband-averaged tympanograms is to include information for numerous frequencies, and also less sensitivity to noise or patient movement. Therefore, the wideband-averaged tympanograms build a more consistent and clearer view of the middle ear status.

Results
Quantitative parameters of wideband acoustic immittance, including compliance (mL), external ear canal volume (cc), tympanogram gradient (dapa), and tympanogram peak pressure (TPP) at 226, 678, 800, and 1000 Hz were extracted and descriptive statistics were summarized in Table 1.



Besides, Table 2 presents the measurement of resonance frequency and dedicated immittance parameters.



Figure 1 shows the spread of power absorbance values over a range of frequencies.



This Figure shows both pressurized and non-pressurized amounts of energy absorbance and percent ratios of all subjects in the frequency range of 226–8000 Hz. Figure 2 shows wideband-averaged tympanograms in the frequency range of 375–2000 Hz. 



Discussion
The results of previous studies show significant differences in WBT parameters, including resonance frequency, middle ear energy absorbance curve, and other quantitative tympanometric parameters in different populations. Also, WBT (absorbance over a range of pressure) carries crucial data that is not present in single-frequency tympanometry. Therefore, it is necessary to measure clinical normative values ​in different ethnicities to make a more appropriate clinical judgment about the status of the middle ear and also to increase diagnostic accuracy in middle ear pathologies. Therefore, in the present study, wideband acoustic immittance values ​​were measured and reported in the young Iranian population. The observed differences in various parameters of WBT between the current research and other papers can be attributed to the different ethnicities of the tested population. For example, the mean RF of the human middle ear system with air conduction excitation is between 0.8–1.2 kHz [8, 9], while the average resonance frequency of the middle ear in the Iranian ethnicity is lower and was measured in the range of 632 to 932 Hz. In another comparison, the range of the normative acoustic admittance in the adult population is traditionally considered between 0.3 and 1.6 mmho [8, 10], but the present study showed that this range is in the range of 0.2 to 1.3 mmho in the Iranian population. Therefore, the results of this study highlight the importance of using specific clinical normative values ​​of Iranian individuals, which can be used as a part of the basic clinical evaluations in audiology. Also, paying attention to the normative values increases the power of differential diagnosis of middle ear disorders, including otitis media, ossicular chain fixation, ossicular discontinuity, and tympanic membrane perforation, and makes it possible to check the progress of the disease or the process of its treatment.

Ethical Considerations

Compliance with ethical guidelines
The study method was approved by the deputy of research, Iran University of Medical Sciences, Tehran, Iran (Code: IR.IUMS.REC.1398.420).

Funding
This work was supported by the Iran University of Medical Sciences, Tehran, Iran (Code: 98-2-75-15036). 

Authors' contributions
All authors equally contribute to preparing all parts of the research.

Conflict of interest
The authors declared no conflict of interest. 

Acknowledgments
The authors like to convey our appreciation to all the individuals who participated in the study.




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