Normative studies

Clinicians must consider normative data before interpreting the absorbance graph. Age, gender, ear, body size, and race can affect WBT values, attributable to differences in ear canal mobility, and the size and length of the outer and middle ear structures [16-19]. The use of data derived from studies differing in age, race, and sex improves diagnostic utility. The use of age- and ethnicity-specific norms are recommended when diagnosing otosclerosis [17]. Australian Aboriginal and Caucasian neonates require a broader set of normative data. Aboriginal neonates exhibit significantly lower absorbances than Caucasians, but equivalent pass rates [18]. WBT exhibits a multi-peak pattern in infants aged 0-2 months, but a single broadly peaked pattern in those aged 4-6 months [20]. Özgür, et al. [21] developed normative data for Turkish populations. The resonance frequency was low in those aged 0-1 months and the absorbance at 250 Hz was high in those aged 0-2 years. Aithal, et al. [22] derived normative WBT data for Caucasian neonates. WBT at 1-4 kHz was optimal when evaluating the outer and middle ear. Frequencies above 4 kHz yielded variable data. Polat, et al. [23] found that the use of different norms for males and females increased the diagnostic specificity and sensitivity of ossicular discontinuities and tympanic membrane perforations affecting high-frequency hearing. The side of the ear may also affect the results. Left ears exhibited greater energy reflectance at 1.0 and 2.0 kHz [24]. In addition, WBT performed at ambient or peak pressure affect the normative data and may be clinically valuable in patients with either negative or positive middle ear pressure. The differences between systems are not clinically significant [17]. Sun [25] reported normative adult WBT data; the test-retest reliability was excellent. Keefe, et al. [26] evaluated down- and up-swept tympanograms using acoustic stimulation of the ear canal to calculate reflectance. Ryu and Cho [27] derived normative data for Koreans. The WBT absorbances of those aged 17-29 years were higher at 1.6-3.2 kHz. Males exhibited higher absorbances at low frequencies and females at high frequencies, especially 4 kHz. The use of such data increased diagnostic precision.

Improvements in tympanometry

WBT improves tympanometry by yielding tympanograms of various frequencies, including resonance frequency tympanograms that determine whether the ear problem is mass- or stiffness-predominant. Some clinicians use such data to detect otosclerosis and ossicular chain abnormalities [8,28]. The average adult value is 375-2000 Hz, but 800-2000 Hz in infants; such frequency data are used to detect middle ear effusions. They are minimally noise-sensitive, yielding clean traces from even noisy patients such as on infants. A comparison between WBT at 1250 Hz and static admittance at 226 Hz found that WBT best distinguished between healthy ears and those with a middle ear effusion [29]. High-frequency tympanometry yields better results in younger infants, and low-frequency tympanometry better results in older infants. However, the optimal frequencies detecting middle ear problems in infants aged 4-8 months remain unclear. WBT yields tympanograms at both 226 and 1000 Hz, allowing clinicians to compare low- and high-frequency data. Terzi, et al. [13] found that the wideband acoustic absorbance rate (the 0.375-2-kHz average mean absorbance) was significantly lower in patients suffering from otitis media with effusion than in those with simple otitis media, or healthy subjects (p＜0.017 and 0.001, respectively).

Otosclerosis

Otosclerotic 226-Hz tympanograms are often very similar to normal tympanograms. Static immittance recorded at higher probe-tone frequencies is superior to that measured using standard low probe-tones in the diagnosis of otosclerotic ears [8]. Furthermore, it is not easy to monitor disease progression using only audiometric and acoustic reflex data. WBT absorbance and resonance data can be used to detect and monitor otosclerosis. The absorbance at peak pressure differs from that of normal ears. Otosclerosis is associated with low absorbance at ＜1 kHz [28,30]. In addition, changes in resonance frequency over time may indicate disease progression. Although the resonance frequencies differ significantly among individuals, the frequency should be stable in ears with normal middle ear function. As otosclerosis progresses, the middle ear stiffens, causing the resonance frequency to increase over time [8,28,30].

Middle ear problems in infants

Tympanometry using higher probe-tone frequencies yields more sensitive data than does conventional low probe-tone tympanometry when middle ear disease is suspected in newborn infants [12]. WBT adds high-frequency information. In addition, WBT yields a wideband-averaged tympanogram. In infants, tympanograms from 800 to 2000 Hz are averaged to yield a single curve. For patients older than 6 months, the appropriate range is 375 to 2000 Hz. An averaged curve is less sensitive to noise than are tympanograms recorded at single frequencies; averaging reduces noise. In addition, WBT can differenciate between an airfilled ear and an ear with complete otitis media with effusion (OME) using the absorbance graph [29,30].

Guan, et al. [31] described the factors affecting sound energy absorbance in a chinchilla model of acute otitis media. Middle ear pressure was the principal contributor to a reduction in sound energy absorbance in early-stage disease. Middle ear effusion reduced the sound energy absorbance at 6-8 kHz in early-stage disease and at 2-8 kHz on day 8 of disease. A loss of residual sound energy absorbance attributable to structural changes was evident over the entire frequency range on day 8 of disease, but only at high frequencies in early-stage disease. Aithal, et al. [14] reported that the 1-4-kHz region could be optimally used to evaluate the conductive status of newborns.

Newborn hearing screening (NHS)

WBT can be used for newborn hearing screening (NHS). WBT and wideband reflexes could be more accurate than 256 or 1000 Hz tympanometry. Power reflectance measurements are significantly different for ears that pass NHS and ears that refer with middle-ear transient condition [14,32,33].

Tympanic perforations

Conventional tympanometry detects tympanic perforations and pressure-equalization tube opening, but it yields no more middle ear information. WBT similarly detects perforations or open pressure- equalization tubes. In addition, WBT can be used to pre/post monitoring of pressure equalization tube. A perforation changes the absorbance pattern. In addition, the tympanographs and absorbance graphs yield middle ear data across the full frequency range. Perforated ears exhibit higher absorbances at low frequencies; interestingly, the smallest perforations have the largest effect [30].

Ossicular chain disarticulation

Eardrum thinning and ossicular chain disarticulation trigger high-level static compliance at 226 Hz. However, it is not easy to distinguish these diseases by conventional tympanography. The existence of a resonance frequency identifies a disarticulation; the absorbance peak in the lower-frequency region is reduced [28,34]. Ossicular discontinuity shows a prominent notch in wideband reflectance around 400-800 Hz [30,34].

Semicircular canal dehiscence (SCD)

Nakajima, et al. [34] reported that absorbance could be used to identify semicircular canal dehiscence (SCD) with 92% sensitivity and 72% specificity. SCD shows SCD notch. It is a notch around 1 kHz and smaller and not as sharp as the notch due to ossicular discontinuity [34].

Postoperative monitoring

It is not easy to evaluate a fragile middle ear after ear surgery; it is important to not apply pressure to the eardrum. WBT yields an absorbance graph in the absence of applied pressure. Middle ear status may thus be assessed immediately after surgery [30,34].

Others

Pitaro, et al. [35] investigated wideband reflectance in newborns; significant increases were evident when 70-80% of the ear canal diameter was occluded.

Significant differences in energy reflectance curves were evident in Down’s syndrome patients with middle ear pathologies [36].

Pucci, et al. [37] used WBT to analyze acoustic absorbance in neonates exposed to passive smoking during pregnancy. The absorbances at low frequencies were lower than those at high frequencies at both ambient and peak pressures, but no difference between the exposure and non-exposure groups was evident.

Voss, et al. [38] reported that WBT can be used to monitor intracranial pressure change.