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ORIGINAL ARTICLE
Year : 2014  |  Volume : 1  |  Issue : 2  |  Page : 87-96

Clinical diagnosis of middle ear disorders using wideband energy reflectance in adults


Department of Otorhinolaryngology, Audiology Unit, Zagazig University, Zagazig, Egypt

Date of Submission13-Oct-2014
Date of Acceptance01-Aug-2014
Date of Web Publication9-Jan-2015

Correspondence Address:
Walied M Ibraheem
Audiology, Department of Otorhinolaryngology, Audiology Unit, Zagazig University, Zagazig
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2314-8667.149017

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  Abstract 

Accurate diagnosis of middle ear disorders in adults is a challenging task because of the complexity of disorders. The wideband energy reflectance (WBER) technique provides simplicity and accuracy in diagnosing middle ear disorders across a wide frequency range. This research is expanding the studies of WBER to investigate the middle ear function in normal and pathological conditions of the middle ear in adults. Several specific WBER patterns were established in a variety of middle ear disorders among adults that should help in early diagnosis of such pathologies. The energy reflectance (ER) pattern included significantly higher ER in the control group of children than the control group of adults at 0.5 and 1 kHz, abnormally high or shallower ER in otosclerotic ears with a characteristic Carhart notch at 2 kHz, abnormally low ER in ears with tympanic membrane (TM) perforation, and abnormally low ER with a deep notch in ears with hypermobile TM. In the presence of negative middle ear pressure, elevated ER at ambient pressure was also observed. Results also showed that standard tympanometry was less sensitive in diagnosing middle ear disorders compared with WBER, especially in otosclerotic cases. Further studies are still required to validate the clinical use of ER in larger numbers of individuals with confirmed middle ear disorders.

Keywords: eustachian tube dysfunction, otitis media with effusion, otosclerosis, tympanometry, wideband energy reflectance


How to cite this article:
Ibraheem WM. Clinical diagnosis of middle ear disorders using wideband energy reflectance in adults. Adv Arab Acad Audio-Vestibul J 2014;1:87-96

How to cite this URL:
Ibraheem WM. Clinical diagnosis of middle ear disorders using wideband energy reflectance in adults. Adv Arab Acad Audio-Vestibul J [serial online] 2014 [cited 2017 Aug 16];1:87-96. Available from: http://www.aaj.eg.net/text.asp?2014/1/2/87/149017


  Introduction Top


The hearing process consists of the transmission of sound energy through the external auditory meatus to the tympanic membrane (TM). The sound energy results in vibration of the TM with equal atmospheric pressure on both sides of the TM. The mechanical vibrations are then transmitted from the TM to the air-filled middle ear space and ossicles, which further amplify the sound energy and transmit the energy to the fluid-filled inner ear. At the inner ear, the mechanical vibration is converted into electric waves and transmitted as nerve signals that are interpreted by the brain as sounds.

The movement of the stapes footplate is directly proportional to the frequency and amplitude of the sound waves. This route of sound transmission is called the 'ossicular route'. 'Acoustic route' is another way of transmitting sound waves directly from the TM and the oval window to the cochlea. The direct acoustic stimulation of the oval and round windows, by passing the ossicles (acoustic route), plays a part in sound transmission. In normal ears, most of sound energy are transmitted through ossicular route rather than acoustic route. (Voss et al., 2007) [26] .

From the above information, it appears that the middle ear plays an important role in the hearing process. The middle ear mainly helps to correct the impedance mismatching between the air medium of the middle ear and the fluid medium of the inner ear. It also helps to transform the acoustic energy at the TM into mechanical energy that will eventually be transferred to the cochlea [1] . Accordingly, middle ear disorders are expected to affect the normal transmission of sound, resulting in a conductive hearing loss.

The middle ear system is a vibrating mechanical system. Such a system is composed of three elements: mass, stiffness, and friction. When the mass and stiffness components cancel each other (equal), the so-called middle ear resonant frequency, it is expected that the amplitude of vibration of the air-filled middle ear is at its maximum.

However, when the mass increases without change in stiffness or friction, the resonant frequency is lowered and the amplitude of vibration is lowered at frequencies above the resonant frequency. In contrast, when the stiffness component of the middle ear increases, the resonant frequency increases and the magnitude of vibration reduces for frequencies below the resonant frequency (Roeser et al., 2000) [27] .

Middle ear disorders are a variable group of pathological conditions that include middle ear infection (otitis media with effusion), chronic otitis media with perforation of the TM, eustachian tube dysfunction (ETD), ossicular disruption or dislocation, and/or otosclerosis. Such middle ear disorders may lead to a conductive hearing loss because of its effect on mass, stiffness, and/or frictional elements of the normal middle ear.

Several objective measurements of middle ear function have been developed over the last four decades. Various anatomical structures of the middle ear represent a complex network system that affects the sound presented to the ear. Not all the sound represented to the middle ear is delivered to the cochlea; a small amount of the power is absorbed by the bony structure of the middle ear [2] . Acoustic immittance, using tympanometry, assesses the middle ear status by measuring the transmitted sound energy to the middle ear.

Acoustic immittance provides objective information about the mechanical transfer function in the outer and middle ear. Acoustic immittance is defined as the velocity with which an object moves in proportion to an applied force, whereas acoustic impedance (Za ) is the opposition offered by the middle ear and the TM to the flow of energy. Mathematically, acoustic admittance (Ya ) of a system is the reciprocal of impedance. Acoustic immittance refers collectively to acoustic admittance, acoustic impedance, or both [3] . Investigators have found that abnormalities in the middle ear transmission might be reflected in the acoustic condition of the TM [4] . Acoustic immittance can be measured using a single probe-tone frequency (single-frequency tympanometry) or using a series of multiple probe frequencies [multifrequency tympanometry (MFT)].

Since 1970, single-frequency tympanometry has remained the most conventional clinical middle ear measure because it is a noninvasive, objective, and inexpensive indicator of many middle ear pathologies in children and adults. Unfortunately, low-frequency probe-tone tympanometry has a high rate of false negatives in infants younger than seven months old [5] . This is explained by the movement of the infant's ear canal wall with pressure changes in the external ear canal because of immaturity of the bony part of the external auditory canal. In addition, tympanometry was found to be more or less insensitive to many middle ear lesions that affect the ossicular chain [6] . Furthermore, Keefe and Levi (1996) [28] investigated false-positive tympanometry results and compared their results with energy reflectance (ER), a recent middle ear function measure. They found normal middle ear ER at higher frequencies in infants who showed a flat low probe-tone tympanometry.

MFT, which was first introduced by Colletti [7] , measures middle ear impedance using multiple frequency probe tones ranging from 226 to 500 Hz and up to 2000 Hz. Similar to the previous discussion on the three elements of the mechanical system of the middle ear, admittance of the middle ear has three components: stiffness (compliant susceptance), mass susceptance, and conductance (resistance).

Because measurement of middle ear function is more accurate when several probe-tone frequencies are used, MFT is considered superior to single-frequency tympanometry in detecting high impedance, pathological conditions of the middle ear such as middle ear effusion, otosclerosis, and chronic otitis media. Such pathological conditions were not detected by conventional tympanometry [7],[8] (Keefe and Levi, 1996). Several studies have shown that MFT has higher sensitivity and specificity in detecting middle ear pathologies such as a TM mass or adhesions [9] . Also, MFT is more sensitive than single-frequency tympanometry in identifying normal and pathological middle ear conditions in neonates [10] .

Wideband energy reflectance

Wideband energy reflectance (WBER) is a new technique that has been introduced recently to evaluate middle ear dysfunction [11] . WBER introduces an incident sound into the ear and is transmitted through the ear canal and TM. Some of the sound energy is absorbed through the middle ear and the cochlea and a portion of it is reflected back [Figure 3]. ER is defined as the square magnitude of pressure reflectance ǀR(f2 , which represents the ratio of the sound energy reflected from the TM to the incident sound energy at a specific frequency (f). The ER ratio ranges from 1 to 0 (1.0 = all incident sound energy is reflected and 0.0 = all sound energy is absorbed) [4] . ER is an indicator of the middle ear power to transfer sound [12] .

WBER measures middle ear function using a chirp stimulus at 65 dB SPL over a wide frequency range, typically 0.2-8 kHz and at a fixed ambient pressure [12] . Normative data have shown that most incident acoustic power is reflected back to the ear canal (ER ratio close to 1) at frequency ranges below 1 kHz or above 10 kHz that also show poor hearing thresholds at frequencies below 1 kHz and above 4 kHz (less efficient middle ear function) [11] . More specifically, 50% of the acoustic power is transmitted to the middle ear between the 1 and 5 kHz frequency range, indicating that the most effective middle ear transfer function (ER is at its lowest values, closer to 0) occurs around 1-5 kHz [4],[11],[13] .

WBER has been used to measure normal middle ear function and middle ear disorders using ambient pressure [4],[8],[12] . In other studies, the researchers used pressure to measure the acoustic stapedial reflex [13],[14] . Development of the middle ear in infants was also investigated using WBER [11],[15] (Keefe and Levi, 1996).

Although MFT may be helpful in the diagnosis of otosclerosis, it adds little information to the diagnosis [16] . However, WBER responses in the ears of patients with otosclerosis fell outside the 5th-95th percentile of the normative data and presented a distinctive pattern for the disease [12] , which suggests that WBER is a sensitive middle ear measure. In a recent study, WBER was found to be useful in distinguishing 28 otosclerotic ears from normal and/or other causes of a conductive hearing loss. A significantly higher ER was found in otosclerotic ears at frequency ranges between 0.4 and 1 kHz as compared with normal ears. In the same study, WBER was found to be more sensitive in diagnosing otosclerosis than the conventional 226 Hz tympanometry and MFT [8] .

Wideband energy reflectance in other middle ear pathologies

Hunter et al. [17] found higher sensitivity of WBER in the detection of otitis media of the middle ear in infants and children with a cleft palate. Feeney et al. [12] studied WBER using ambient pressure in 13 ears with different middle ear disorders and compared their results with normative data. The different middle ear disorders that were involved in this study were as follows: four ears with otitis media with effusion, one ear with ossicular discontinuity, two ears with otosclerosis, two ears with a hypermobile TM, two ears with a perforated TM, and one participant with bilateral sensorineural hearing loss. The results suggested a distinctive WBER pattern in different pathologies of the middle ear [12] .

There are several advantages to measuring ER of the middle ear function using the WBER measure: (i) WBER is not affected by the external auditory canal properties and is also not sensitive to probe location in the external auditory canal; (ii) WBER is more closely related to hearing sensitivity than acoustic immittance; (iii) in contrast to tympanometry, WBER can be carried out at ambient (atmospheric) pressure, and thus, it can be used in young infants because it is unaffected by the floppy ear canal wall; and (iv) ER is not affected by the probe position and standing waves in the outer ear canal, whereas admittance or impedance measurements are affected by these variables [4],[18] .


  Participants and methods Top


Two main groups of adult volunteers were recruited to participate in this study. The experimental group of adults included 22 participants (10 men, 12 women), whose age ranged from 20 to 57 (mean ± SD 6.7 ± 11.7) years. This group was further subdivided into subgroups on the basis of their middle ear disorder: otosclerosis, ETD, hypermobile TM, and TM perforation. A matched control group of adults was included in the study, ranging in age from 20 to 62 (mean ± SD 35.2 ± 10.8) years. A comparison was performed between the control group of adults and a matched group of normal children, age range 1-5 (mean ± D 3.8 ± 1) years. All volunteers of the control group had a clear otoscopic examination without any gross eardrum abnormalities or excessive cerumen; negative history of head trauma, hearing loss or middle ear diseases; normal hearing sensitivity 25 dB HL or less at octave frequencies between 0.25 and 8 kHz and normal 226-Hz tympanometry [18] .

All participants underwent the following procedures:

Otoscopic examination of the ear canal and tympanic membrane

Standard tympanometry

0GSI-TympStar tympanometer (Chicago, USA): 226 Hz tympanometry was used to evaluate the middle ear status in adults. The TympStar was calibrated according to the American National Standards Institute [19] standards at atmospheric pressure to verify probe-tone frequencies and intensity before data collection.

To determine the shape of tympanograms, Jerger classifications [20] were used (type A, B, C). Also, we used Feldman's [21] subtypes Ad and As for abnormally high-peaked and low-peaked type A tympanograms.

Pure-tone audiometry

Pure-tone audiometry (Standard Hearing Test) was performed using a Madsen Grason Stadler GSI-61 (Chicago, USA) audiometer calibrated according to the American National Standards Institute (ANSI) standards (re: S3.6.1989). Pure-tone audiometry was carried out in a single-walled booth using TDH-39 headphones.

Wideband energy reflectance

WBER is another measure of middle ear function. WBER is a computerized system for research that is used to measure the wideband evoked aural responses in the ear canal. Two WBER systems were used: Reflwin version 1.9 (Interacoustics, Denmark) was used to measure the middle ear function in children groups, whereas Reflwin version 2.0 was used for adult groups. Both systems include a desktop computer with a data acquisition sound card. However, version 1.9 has an Etymotic Research Probe system (ER-10C) with a 20 dB receiver gain, whereas the version 2.0 has a different probe system (see below). Recording was performed in a sound booth (version 1.9) or in a quiet room (version 2.0). Calibration was completed daily before testing.

Wideband energy reflectance hardware and software configuration

The WBER instrument included the following components [Figure 1]:
Figure 1Wideband energy reflectance research system. (a) The wideband Interacoustics AT235 device modified for computer control (tympanometry/pump controller). (b) Windows PC, which includes the card sound and the in and out channels (http://www.interacoustics.com).

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  1. A CardDeluxe (Denmark) professional sound card drives the probe and records the microphone output from the probe. The CardDeluxe sound card has two channels that go in and out, at a 22.05 kHz sample rate, and a 24-bit voltage resolution.
  2. Interacoustics probe: two receiver ports, one microphone port, and a static pressure coupled to the port.
  3. A dedicated PC with monitor holds the CardDeluxe sound card that is installed and a serial port to communicate with the AT235 middle ear analyzer. The PC ran the Reflwin software under the Windows XP operating system.
  4. Interacoustics tympanometry pump/controller (version 2.0): an Interacoustics AT235 Middle Ear Analyzer was modified to allow control by Reflwin software for wideband tympanometry measurements in the ear. A new dedicated probe was designed to allow for a wideband absorbance measurement and wideband tympanometry, which is a pressurized wideband absorbance test.
  5. Reflwin holds a Matlab code as a utility library of analysis, plotting, and database routines, which allow the user to create electronic (pdf) documents with measurement results and create a computerized database readable by commercial spreadsheet software (i.e. Excel).


Wideband energy reflectance calibration

WBER is initially calibrated at the factory. The machine was calibrated each day before the testing procedure and two sets of calibration tubes were used. Each set included a long and a short tube. One tube set had a large diameter (0.794 cm) appropriate for testing adult-sized ear canals; the second set had a small diameter (0.476 cm) set of tubes appropriate for testing infant-sized ear canals. Each set of large or small tubes had a long and a short tube that were closed at one end. The calibration was started by inserting the probe tip with a suitable ear tip attached to it into the large long tube and then the large short tube. If the recordings were satisfactory, it could be saved to a file. Re-recording was performed if the results were unsatisfactory. The same calibration steps were repeated for the small tubes.

Wideband energy reflectance testing procedure

The probe tip, with a suitable-size foam ear tip (version 1.9) or reusable plastic ear tip (version 2.0), was placed securely in the participant's ear canal. Chirp sounds were presented at a moderate stimulus level (65 dB SPL) under ambient pressure into the ear. The patient was instructed to sit quietly during the test, which took less than 2 min of testing per ear. An averaged response was obtained at 32 sweeps and measured to the sixth octave frequency. The probe was reinserted if a leak was observed according to the model suggested by Keefe et al. [22] .

The ER ratio was measured over a wideband of frequencies ranging from 0.25 to 8 kHz generated by the probe receiver. Results were recorded and automatically saved on the provided software. ER results ranged from 0.0 to 1.0; high reflectance values close to 1.0 indicate low absorbance by the middle ear and that the majority of the sound energy is reflected back, and vice versa.


  Results Top


The data for WBER were analyzed using several one-way analyses of variance (ANOVAs) to compare the control groups (adults vs. children) and the corresponding pathological groups (otosclerosis, TM perforation, hypermobile TM, ETD) as a function of octave frequency 0.25, 0.5, 1, 2, 4, and 8 kHz.

Control groups (adults and children)

Tympanometric results showed that the entire adult control group had normal type A tympanograms with normal ear canal volume (Yec ) values (0.9-1.8 cm³) and admittance at the TM level (Ytm ) values (0.4-1.2 mmho). Similarly, all children in the control group had normal type A tympanogram with the Yec values ranging from 0.4 to 0.9 cm³, and the Ytm values ranged from 0.3 to 1 mmho. Pure-tone thresholds were less than 25 dB HL for all participants.

The ER patterns were similar between the two control groups as shown in [Figure 2]. The mean ER (50th percentile) was high in the low frequencies, decreased as a function of frequency to a minimum (the most absorbed energy), and then increased gradually at higher frequencies. The main difference between the two control groups was the presence of the lowest ER between 1.5 and 3.5 kHz in normal adults compared with 2-3.8 kHz in normal children [Figure 2] and [Table 1]. The ANOVA analysis showed a statistically significant difference between the two control groups only at 0.5 kHz [F(1,36) = 16.973; P = 0.000] and 1 kHz [F(1,36) = 5.489; P = 0.025]. This difference was mainly because of higher ER for the groups of children (0.908) than the adult groups (0.792) at 0.5 kHz. Also at 1 kHz, the ER was higher (0.557) than the adult group (0.447) as shown in [Table 2].
Figure 2: Energy reflectance in normal adults and normal children. The lines represent the 10th, 25th, 50th, 75th, and 90th percentile of the energy reflectance of the control adults (a) and control children (b). fx1-Green, 10th percentile; fx2-Dashed red, 25th percentile; fx3-Black, 50th percentile; fx4-Dashed blue, 75th percentile; fx5-Blue, 90th percentile.

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Control adults versus otosclerotic patients
Table 1 Summary of energy reflectance mean, SD, and one-way analysis of variance analysis between control children and adults


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Table 2 Summary of energy reflectance mean, SD, and one-way analysis of variance analysis between control adults and otosclerosis


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Similar to the normal tympanometric findings from the control adults, all otosclerotic ears had normal type A tympanograms. Their Yec volumes were 0.6-1.1 cm³ and Ytm magnitudes were 0.3-1.0 mmho. The average pure-tone hearing thresholds were less than 25 dB HL for the control group and 51-60 dB HL for the otosclerotic group. The average air-bone gap for the otosclerotic group was 28.5-46 dB. The mean ER for the otosclerosis group (n = 10) was shallower, with a restricted minimum ER around 2.8 kHz compared with the control adults [Figure 3]. Although the ANOVA results show that there was no statistically significant difference between the two groups, the mean ER (50th percentile) were higher at frequencies 0.5, 1, 2, and 4 kHz [Table 2].
Figure 3: Energy reflectance in normal adults and adults with otosclerosis. The lines represent the 10th, 25th, 50th, 75th, and 90th percentile of the energy reflectance of the control adults (a) and adults with otosclerosis (b). fx1-Green, 10th percentile; fx2-Dashed red, 25th percentile; fx3-Black, 50th percentile; fx4-Dashed blue, 75th percentile; fx5-Blue, 90th percentile

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Control adults versus patients with perforated tympanic membrane

Compared with the normal type A tympanogram of the control adult group, individuals with TM perforation had type B flat tympanograms with abnormally high Yec (3.4-5.9 cm³). Air conduction hearing thresholds ranged between 15 and 55 dB HL for the perforated TM group compared with less than 25 dB HL for the control group. A lower ER ratio was observed in patients with TM perforation (n = 7) than that of the adult control group (n = 17). The mean ER was low in the lower frequencies, increased as a function of frequency to a maximum at 1.8 kHz, decreased gradually to a maximum at 3.5 kHz, and then increased again at higher frequencies [Figure 4]. The ANOVA results show statistically significant differences between the two groups at all frequencies, except at 8 kHz [F(1,22) = 2.837; P = 0.106]. These significant differences occurred mainly because the control group had higher ER than the TM perforated group at 0.25 kHz (0.993 vs. 0.577) and 0.5 kHz (0.792 vs. 0.566). The reverse pattern occurred at higher frequencies where the TM perforated group (0.717) had higher ER than the control group at 1 kHz [0.717 control adults (a) and adults with perforated TM (b)].
Figure 4: Energy reflectance in normal adults and adults with perforated tympanic membrane (TM). The lines represent the 10th, 25th, 50th, 75th, and 90th percentile of the energy reflectance of the control adults (a) and adults with perforated TM (b). fx1-Green, 10th percentile; fx2-Dashed red, 25th percentile; fx3-Black, 50th percentile; fx4-Dashed blue, 75th percentile; fx5-Blue, 90th percentile.

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Control adults versus patients with hypermobile tympanic membrane

All control adult groups had normal type A tympanograms with Yec of 0.9-1.8 cm³ and Ytm were 0.4-1.2 mmho, whereas the hypermobile TM group had abnormal type Ad tympanograms with abnormally high admittance (Ytm 1.8-1.9 mmho) and normal Yec volumes (0.7-0.9 cm³). Pure tone thresholds ranged between 5 and 30 dB HL for the hypermobile TM group compared with the thresholds for the control group (<25 dB HL). As shown in [Figure 5] and compared with normal ER, the mean ER for the hypermobile TM group was abnormally low in the low frequencies up to around 2.8 kHz before it increased to a maximum above 6 kHz. Also, the figure shows that the ER is more variable in the low-frequency range in the hypermobile group than the control group.
Figure 5: Energy reflectance in normal adults and adults with hypermobile tympanic membrane (TM). The lines represent the 10th, 25th, 50th, 75th, and 90th percentile of the energy reflectance of the control adults (a) and adults with hypermobile TM (b). fx1-Green, 10th percentile; fx2-Dashed red, 25th percentile; fx3-Black, 50th percentile; fx4-Dashed blue, 75th percentile; fx5-Blue, 90th percentile.

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The ANOVA results between the control adult group (n = 17) and the hypermobile TM group (n = 7) showed statistically significant differences between the two groups at 0.25 kHz [F(1,22) = 93.528; P = 0.000], 0.5 kHz [F(1,22) = 96.176; P = 0.000], and at 1 kHz [F(1,22) = 13.255; P = 0.001]. The ER was not statistically different between groups at frequencies higher than 1 kHz. [Table 5] and [Figure 5] shows that the differences between the two groups were mainly because of a higher ER for the control group than the hypermobile group at 0.25 kHz (0.993 vs. 0.420), 0.5 kHz (0.792 vs. 0.273), and 1 kHz (0.447 vs. 0.203).

Control adults versus patients with eustachian tube dysfunction

The ETD group had type C tympanograms with an abnormally negative tympanometric peak pressure (TPP), which ranged from -155 to - 318 daPa. Their Yec and Ytm were within the normal range (0.6-0.9 cm³ and 0.6-0.8 mmho, respectively). The air conduction thresholds ranged from 5 to 25 dB HL (at 8 kHz) for the ETD group. The ANOVA findings are presented in [Table 3]. Summerize ER mean, SD and one way anova of control adults and adults with etd. Statistically significant differences between the two groups (control adults and the ETD group) were observed only at 0.25 kHz [F(1,18) = 8.956; P = 0.00]. This difference was mainly because of the higher ER for the control group (0.993) than the ETD group (0.823) at that particular frequency [Table 3].
Table 3 Summary of energy reflectance mean, SD, and one-way analysis of variance analysis between control adults and adults with eustachian tube dysfunction


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  Discussion Top


WBER measurement has the potential to provide valuable information on middle ear function across a wide frequency range and can distinguish abnormal from normal middle ear function. This research is expanding the studies of WBER to investigate the middle ear function in normal and pathological conditions of the middle ear in adults. Overall, the study included 17 adult ears. The experimental groups with middle ear disorders included 27 adult ears (10 otosclerosis, seven TM perforations, seven hypermobile TM, and three ETD). The relatively large numbers of cases make our study more comprehensive than previously published work by Feeney et al. [12] and Allen et al. [4] , who studied fewer numbers of ears (13 in Feeney et al. [12] and four in Allen et al. [4] ) with variable middle ear pathological conditions.

Control groups (adults and children)

Normative data were collected from two control groups: a group of adult (mean ± SD age 35.2 ± 10.8 years) and a group of children (mean ± SD age 3.8 ± 1 years). In the presence of normal pure-tone thresholds, tympanometry results showed that all adults and children control groups had normal type A tympanograms with normal ear canal volume. The current findings of acoustic admittance values were within the normal range for the control adults (0.3-1.7 mmho) [23] .

The mean adult ER measured over one-sixth octaves showed a normal ER pattern. This pattern, consisting of high ER in the low frequencies, decreased to a minimum (the most absorbed energy) between 1.5 and 3.5 kHz, and then increased gradually at higher frequencies. Our finding, as shown in [Figure 2], also shows that most of the incident power is reflected back to the ear canal at frequencies below 1 kHz, whereas at frequencies from 1 to 5 kHz, most of the incident sound energy is absorbed by the middle ear. The reflected power below 1 kHz can be explained by the increased impedance mismatching at the TM (reactance is greater than resistance), whereas between 1 and 5 kHz, the impedance of the TM is equal to the impedance of the ear canal (reactance is canceled), resulting in transmission of most of the sound energy to the middle ear [4] . Using the same ER measuring equipment, several researchers have reported a similar normal ER pattern in adults [11],[12],[18] . In another study that used different ER equipment (Reflectance Measurement System IV; Mimosa Acoustics Inc.), Allen et al. [4] tested a 50-year-old woman with normal hearing. They reported a similar ER pattern [high ER at low frequencies, minimum ER level (40-50%) between 1 and 3 kHz, and then high ER above 50% at a higher frequency].

On comparing the ER pattern between the two control groups, our findings showed a similar ER pattern between the two groups [Figure 2]. However, the minimum ER extended over a wider frequency range (2-3.8 kHz) in normal children compared with normal adults (1.5-3.5 kHz). In addition, the control group of children had a statistically significantly higher ER than the control group of adults at 0.5 and 1 kHz [Figure 2] and [Table 1]. Below 1 kHz, the middle ears of children have lower compliance than the ears of adults [24] . This might explain the lower power transfer by the middle ear of children at lower frequencies. Hunter et al. [17] studied ER patterns in children ranging in age from 6 months to 4 years and found that the lowest ER was between 1.5 and 4 kHz. Despite the age difference in children between the two studies, younger children in the Hunter and colleagues' study compared with the current study, the ER results are still comparable. This normal pattern of ER supports the presence of a normal type A tympanogram and hence normal middle ear function.

Patients with otosclerosis

As shown in [Figure 3], the mean ER for the otosclerosis group was shallower, with a restricted minimum ER around 2.8 kHz compared with the control adults. Testing a young female adult with bilateral otosclerosis, Allen et al. [4] reported a higher ER pattern below 0.8 kHz compared with normal. A similar pattern is shown in [Figure 3] for the 50th and 90th percentiles below 0.8 kHz. In addition, Feeney et al. [12] measured ER in only two otosclerotic patients. One of them was 49-year-old woman who had right ear otosclerosis for eight years. This patient had higher ER below 1 kHz than normal. The second case was a 26-year-old woman with bilateral otosclerosis, who also showed a higher ER ratio than normal below 1 kHz; ER was within the normal range at higher frequencies for both cases.

Although the mean ER ratios (50th percentile) in our study were higher at frequencies 0.5, 1, 2, and 4 kHz [Table 2], there were no statistical differences between the otosclerosis and the control groups. The lack of a significant difference between the two groups may be because of the relatively small sample size used in this study, the air-bone gap, and the stage of the disease. However, the presence of Carhart notch at 2 kHz [Figure 3] is characteristic for otosclerosis in an early stage of the disease before it stabilizes. In a larger study of ER in otosclerotic patients, Shahnaz et al. [8] examined 28 cases with surgically confirmed otosclerosis (8 men and 20 women, age range 24-56 years). They found that compared with normal controls, otosclerotic ears had higher ER between 0.4 and 1 kHz in 71% of cases and above 1.5 kHz in 10% of cases. In contrast, 18% of cases showed lower ER data than normal above 1 kHz. The authors concluded that the pattern of change in the ER pattern among all otosclerotic ears reported was not consistent [8] . The inconsistent ER patterns may be explained by the presence of otosclerosis at different stages of the disease process. For example, Zhao et al. [25] classified otosclerosis into three pathological stages: normal stiffness, low stiffness, and high stiffness. In addition, increased stiffness of the middle ear in otosclerosis, the annular ligament in particular, was shown to increase impedance mismatch below 2 kHz and lead to a consequent increase in the reflected energy [4] . The difference in the ER pattern in our otosclerotic group compared with the previous studies can be attributed to the variability of the ER pattern reported by Shahnaz et al. [8] and the different pathological stages proposed by Zhao et al. [25] . For example, our finding of high ER at a low frequency may suggest stiffness of the ossicles of the middle ear and/or stiffness of the annular ligament because of otosclerosis. In contrast to Shahnaz et al. [8] , our cases were diagnosed only clinically, but were not confirmed surgically.

Patients with tympanic membrane perforation

In the present study, the presence of a low ER ratio was observed in seven patients with TM perforation in comparison with the control group of adults. The mean ER in the TM perforation patients was mainly low in the lower frequencies [Figure 4], with statistically significant differences between the two groups at all frequencies except at 8 kHz [Table 4]. This abnormally low ER pattern is characteristic of TM perforation. These findings are similar to the results of Feeney et al. [12] . They studied two ears (right and left ear) of two patients with perforated TM and found lower ER values than normal at frequencies below 0.8 kHz, but higher ER than normal at higher frequencies. Allen et al. [4] reported a lower than normal ER below 1.5 kHz in a single right ear with perforated TM. Despite the similar pattern, the results of Feeney et al. [12] and Allen et al. [4] , and our findings show a highly variable ER curve. The presence of low ER indicates that the incident energy, mainly at low frequencies, is highly absorbed into the middle ear because of the large volume of the middle ear space (ear canal volume and the middle ear) caused by the TM perforation.

Patients with hypermobile tympanic membrane
Table 4 Summary of energy reflectance mean, SD, and one-way analysis of variance analysis between control adults and adults with perforated tympanic membrane


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The tympanometric evaluation of the entire group with hypermobile TM (four women and three men, mean±SD age 33.1±7.7 years) had abnormal type A d tympanograms with abnormally high admittance and normal ear canal volume. In contrast to the ER pattern in the TM perforation and compared with normal, the mean ER for the hypermobile TM group showed an abnormally low notch in the low frequencies, mainly at 0.25 and 1 kHz, before it increased to a maximum above 6 kHz. The ER ratios were not statistically different between the two groups at frequencies higher than 1 kHz [Table 5] and [Figure 5].
Table 5 Summary of energy reflectance mean, SD, and one-way analysis of variance analysis between control adults and adults with hypermobile tympanic membrane


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In comparison with previous studies, the deep notch at 0.5-0.6 kHz described by Feeney et al. [12] was not showen in the mean (50th percentile) ER curve (black curve in [Figure 5] of the current study, but could still be detected in the 90th percentile curve (blue curve in [Figure 5]. In addition, the abnormally high peak ER between 3 and 4 kHz was apparent in our hypermobile TM group [Figure 5], in agreement with the finding of Feeney et al. [12] . As shown in [Figure 5], the ER curve of the hypermobile group is more variable in the low frequency. This variability may be because of the variation in the size and the site of the scarred part of the TM, and the absence of the mass effect of the TM.

Patients with eustachian tube dysfunction

The ETD group had a type C tympanogram with abnormally negative TPP, which ranged from -155 to -318 daPa. The ETD group also showed normal ear canal volume (0.6-0.9 cm³³) and acoustic admittance (0.6-0.8 mmho). The overall ER patterns in ears with ETD showed a high ER ratio at low and mid frequencies. The affected frequency range depends on the TPP. The ear with the lowest negative TPP (-155 daPa) has high ER at 1, 1.6, 2.2, and 4 kHz, whereas the ear with TPP -190 daPa has high ER from 1.6 to 2.2 kHz. For the ear with the highest negative TPP(-318 daPa), the ER pattern was abnormally high at low frequencies, mid frequencies up to 4 KHz., consistent with the results reported by Feeney et al. [12] . They reported abnormally high ER at 3.34 and 8.91 kHz in the right ear and 2.5-2.97 kHz in the left ear of the same individual, and abnormally low ER from 2 to 4 kHz. A missed underlying pathology besides the ETD might be the cause of the different ER pattern. Given that there is no specific explanation, the high ER at different frequency range is dependent on TPP. Further study of large numbers of ears with ETD and different negative TPP is needed.


  Conclusion Top


WBER is an objective, safe measure for the assessment of different middle ear pathologies.

A normal pattern of ER was confirmed in the control group. The normal ER pattern was potentially useful in differentiating normal from middle ear disorders. Several specific WBER patterns have been established in a variety of middle ear disorders that will help in early diagnosis of such pathologies. The ER patterns included significant higher ER in the control group of children than the control group of adults at 0.5 and 1 kHz, abnormally high in otosclerotic ears with the presence of a Carhart notch at 2 kHz, abnormally low in ears with TM perforation, and abnormally low ER with a deep notch in ears with hypermobile TM. In the presence of negative middle ear pressure, elevated ER at ambient pressure is also expected. Results also showed that standard tympanometry was less sensitive in diagnosing middle ear disorders compared with WBER especially in otosclerotic cases. Findings also show that WBER not only can distinguish abnormal from normal middle ear function but can also characterize different middle ear disorders. Further studies are required to validate the clinical use of ER in larger numbers of individuals with confirmed middle ear disorders. Because of the relatively high variability of ER measured at mid-frequency and high-frequency regions and insufficient data, other ER measures should be included such as power transmittance and power absorption data in interpreting the ER results. Until further improvement in ER measurements, middle ear status should be assessed by standard tympanometry and supported with ER measures to provide additional information about the middle ear status across a wide frequency range.


  Acknowledgements Top


Conflicts of interest

None declared.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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