Ear Canal Volume Research Articles

The effect of middle ear resonant frequency, ear canal resonance, and ear canal volume on TEOAE

It is well known that there is a large inter-individual variability in the size of the TEOAE. Quantifying the sources of variability can help to determine the influences of some of the factors that can affect test results. The difference found in TEOAE may be due to the difference in size and shape of the ear rather than cochlear mechanics. The effect of ear canal volume between the probe and the tympanic membrane influences the intensity and spectrum of the stimulus as well as the characteristics of the response. A small ear canal volume should result in a higher stimulus sound-pressure level. This can determine both the effectiveness of the evoking stimulus as well as the response that is measured. We will report results of the study of the relation between ear canal volume, ear canal resonant frequency, and resonant frequency of the middle ear on TEOAE for 20 normal hearing young adults. The purpose is to determine if the characteristics associated with TEOAE are influenced by middle ear resonance and ear canal resonance and volume. By quantifying some of the variables that can effect TEOAE the test interpretation may be clarified.

Correlation between ear canal resonance and tympanic membrane impedance in relation to age and body mass and postmortem changes

The human temporal bone preparation is an acknowledged model for research of the physical processes affecting the outer ear canal and eardrum. Changes affecting the oscillation and resonance behavior of the tympanic membrane and ear canal between death and temporal bone preparation presently exist in only a few studies. Since the influence of age and physique, as well as the width of ear canal on the ear canal resonance may be important, we prepared two separate studies to analyze these questions. The goal of our first test series involved children and was devised to determine if changes in the outer auditory canal resonances differed according to age. In so doing, canal resonance was recorded with a real ear measurement system. Further, we recorded middle ear pressure, impedance of the tympanic membrane, ear canal volume, height, weight and surface of the body, head and ear size. We found a significant decrease in the resonance frequency of the outer ear which was age-dependent and was 2.75 kHz in the 7-year-old child. In a separate study we wanted to know if results found in the postmortem temporal bone reflected in vivo relationships. A tympanometer and real ear measurement system was used to test the resonance behavior of the auditory canal as well as the vibration of the eardrum in dependence on temperature and the time after death for 9 h. We then proved the absence of significant changes in the auditory canal and eardrum oscillation in this time period before possible postmortem changes occurred. Our findings show that the method of bone preservation after its preparation is decisive for the validity of measurements in the isolated human temporal bone.

Individual differences of transient evoked otoacoustic emissions: Effects of gender and ear canal volume

Transient evoked otoacoustic emissions (TEOAE) are an objective means for measuring cochlear hearing loss in newborn infants. TEOAEs are low-intensity sounds produced by the normal cochlea that are elicited by acoustic stimuli and then recorded in the outer ear canal. Protocols are being developed for clinical use, and pass/fail criteria are usually based on the size of the emission. The common practice is to wait until an emission of 6 dB is achieved before recording a positive result. Within subject, stimulus-related characteristics may influence the results. Quantifying the sources of variability can effect the analysis of the results. This study will investigate the effects of gender and ear canal volume on TEOAE size. Five male and five female young adult volunteers will serve as subjects. None of the volunteers will have a history of otologic disease or use of medication. All subjects will have normal hearing and normal middle ear function. Pure-tone audiometry and single frequency immittance testing (226 Hz probe tone) will be made. TEOAE will be measured using ILO88 hardware controlled by an IBM PC.

Real-ear to coupler differences in children with grommets.

Real-ear to coupler differences (RECDs) are important for the selection of appropriate amplification characteristics for hearing impaired children. The aim of this study was to investigate the effects of patent grommets on RECDs in children. Subjects were 32 children aged between 4 and 7 years, 16 had a patent grommet in one or both ears as confirmed by otoscopy and large equivalent ear canal volumes on tympanometry. There was no evidence of middle ear pathology in the remaining 16 who comprised the control group. All real-ear and coupler measures showed good test-retest repeatability across the whole frequency range. The mean difference in RECDs between the two groups in the frequency range 0.125-0.75 kHz was 15 dB. The differences in RECDs were statistically significant (P < 0.01) for all frequencies below 0.75 kHz. There was a strong correlation between the mean RECD and equivalent ear canal volume at all frequencies between 0.125 and 0.5 kHz, and a moderate correlation at 0.75 kHz. Large inter-subject variability was found, with a maximum standard deviation of 6.6 dB at 4.0 kHz. Therefore, this study supports the need for individual RECD measures to be made, particularly for subjects with grommets, rather than using averaged transformation figures. It suggests that more low frequency gain should be given to hearing aid users with patent grommets to overcome the reduced SPL in the ear canal, due to leakage through the vented tympanic membrane.

A longitudinal investigation of duration and temporal variability in children's speech production: Smith B.L.; Kenney M.K.; Hussain S.J. Acouts. Soc. Am. (USA) (1996) 99/4 I (2344–2349)

To assess if young subjects affected by Williams syndrome (WS) with normal middle ear functionality and normal hearing thresholds might have subtle auditory dysfunctions that could be detected by using clinically available measurements.Otoscopy, acoustic reflexes, tympanometry, pure-tone audiometry, and distortion product otoacoustic emissions (DPOAEs) were measured in a group of 13 WS subjects and in 13 age-matched, typically developing control subjects. Participants were required to have normal otoscopy, A-type tympanogram, normal acoustic reflex thresholds, and pure-tone thresholds ≤15 dB HL at 0.5, 1, and 2 kHz bilaterally. To limit the possible influence of middle ear status on DPOAE recordings, we analyzed only data from ears with pure-tone thresholds ≤15 dB HL across all octave frequencies in the range 0.25–8 kHz, middle ear pressure (MEP) > −50 daPa, static compliance (SC) in the range 0.3–1.2 cm3, and ear canal volume (ECV) in the range 0.2–2 ml, and we performed analysis of covariance to remove the possible effects of middle ear variables on DPOAEs.No differences in mean hearing thresholds, SC, ECV, and gradient were observed between the two groups, whereas significantly lower MEP values were found in WS subjects as well as significantly decreased DPOAEs up to 3.2 kHz after adjusting for differences in middle ear status.Results revealed that WS subjects with normal hearing thresholds (≤15 dB HL) and normal middle ear functionality (MEP > −50 daPa, SC in the range 0.3–1.2 cm3, ECV in the range 0.2–2 ml) might have subtle auditory dysfunctions that can be detected by using clinically available methods. Overall, this study points out the importance of using otoacoustic emissions as a complement to routine audiological examinations in individuals with WS to detect, before the onset of hearing loss, possible subtle auditory dysfunctions so that patients can be early identified, better monitored, and promptly treated.

A computational model for tympanometry

A computational model for tympanometry was developed by describing the ear canal with the impedance theory of a tube and by representing the middle ear with the Zwislocki electroacoustic analog. Changes in ear-canal length and acoustic properties of the middle ear with ear-canal pressures during a tympanometric procedure were mimicked by manipulating relevant model parameters. Tympanograms of different patterns of the normal ear and the ear with a disarticulation of the ossicular chain were reproduced with the model and were in agreement with experimental observations reported by other investigators. The model demonstrated the relationship between various patterns of admittance tympanograms and middle ear impedance predicted by the Vanhuyse theory. The effects of the ear canal on the estimates of middle ear admittance using compensation procedures for ear-canal volume were also predicted with the model. The model can provide a better understanding of the mechanism of tympanometry and a framework for further modeling study.

Immittance findings in school-aged children.

The purpose of the present study was to obtain the median values and distributions of tympanometric variables and the distributions of acoustic reflex thresholds for three age groups of unselected school-aged children. Furthermore, the investigation was undertaken to provide normative immittance data for selected, otologically normal 7-, 10-, and 14-yr-old children. A total of 687 children, aged 6 to 15 yr, were thoroughly examined clinically, audiometrically, and tympanometrically. The same examinations were made in 471 otologically normal children, selected from the total population on the basis of the findings that both tympanic membranes were otomicroscopically healthy, and the hearing thresholds were better than or equal to 25 dB HL at all frequencies. The results showed that the median equivalent ear canal volume (Vec) increased from 0.65 ml to 1.00 ml with increasing age both in the unselected and selected populations. The median peak admittance values (Ytm) were between 0.55 and 0.5 mmho in the respective study groups, somewhat higher in older than in younger children. The same tendency was also seen in gradient and tympanometric peak pressure (TPP) results. Depending on the age, the median tympanometric peak pressures were 5 to 10 daPa higher in otologically normal children than in the unselected population. The median TPP was -10 daPa in a group of unselected children, and -5 daPa in a group of otologically normal children. The distribution of ipsi- and contralateral acoustic reflex thresholds is presented. Thresholds were higher in younger than in older children. The obtained results give new information on immittance findings in an unselected sample of school-aged children who were representative of children in the general population. Furthermore, the results are useful as normative immittance values in 7-, 10-, and 14-yr-old children when the limitations relating to the equipment are taken into account.

The relationship between sound transfer functions and hearing levels

The effects of individual differences in sound transfer function (STF) from free sound field to the tympanic membrane on hearing levels was studied in the right and left ears of 55 young male and 45 young female subjects. Furthermore, canal volumes and lengths have been recorded. STFs were measured in 1 3- octave bands using a miniature microphone and an attached probe. STF measurements were performed in the 0.5–16 kHz frequency range. Audiograms were registered with linear frequency sweep from 0.25 to 8 kHz. Transfer function spectra and magnitudes as well as ear canal dimensions were compared to hearing levels. There was a significant relationship between the dimensions of the ear canal and hearing levels. Large, compared to small, ear canal volumes resulted in a shift of STFs towards lower frequencies. STF spectra and magnitudes had a significant effect on hearing levels. Subject with low-frequency-dominated STFs have higher hearing thresholds than subjects with lower magnitude STFs.

Effect size on resonance of the outer ear canal by simulation of middle ear lesions using a temporal bone preparation

By means of a model of the external and the middle ear it is possible to simulate various, exactly defined pathological conditions of the middle ear and to describe their influence on ear canal resonance. Starting point of the investigations are fresh postmortem preparations of 8 human temporal bones with an intact ear drum and a retained skin of the ear canal. The compliance of the middle ear does not significantly differ from the clinical data of probands with healthy ears. After antrotomy it is possible to simulate pathological conditions of the middle ear one after the other at the same temporal bone. The influence of the changed middle ear conditions on ear drum compliance, ear canal volume and on the resonance curve of the external ear canal was investigated. For example, the middle ear was filled with water to create approximately the same conditions as in acute serous otitis media. In this middle ear condition a significant increase of the sound pressure amplification was found, on an average by 4 decibels compared to the unchanged temporal bone model. A small increase in resonance frequency was also measured. The advantages of this model are the approximately physiological conditions and the constant dimensions of the external and middle ear.

Multifrequency tympanometry in normal adults.

Multifrequency tympanograms were recorded from 56 ears of 28 normal-hearing adult subjects to obtain normative data and to determine abnormal criteria for tympanometric measures. Static admittance, tympanometric width, and tympanometric peak pressure at 226 Hz were analyzed along with eight different estimates of the resonant frequency of the middle ear. Based on test-retest reliability and normal distribution characteristics, preferred methods for clinical estimation of resonant frequency were determined. The sweep pressure mode (ear canal pressure is swept while probe frequency is held constant) is preferred for detection of abnormally high resonant frequencies. The sweep frequency mode (probe frequency is swept while ear canal air pressure is held constant) is preferred for identification of abnormally low resonant frequencies. Compensation for ear canal volume at +200 daPa was preferred over other compensation methods for estimation of middle ear resonant frequency.

Quantifying ear-canal geometry with multiple computer-assisted tomographic scans

Several audiological tests require knowledge of the sound-pressure spectrum at the eardrum. However, microphone readings are typically made at another, more-accessible position in the auditory canal. Recordings are then "adjusted" to the plane of the eardrum via mathematical models of the ear canal and eardrum. As bandwidths of audiological instruments have increased, ear-canal models have, by necessity, become more precise geometrically. Reported herein is a noninvasive procedure for acquiring geometry of the ear canal in fine detail. The method employs a computer-assisted tomographic (CAT) scanner in two steps to make radiographic images of parasagittal cross sections at uniform intervals along the lateral length of the canal. Accuracy was evaluated by comparing areas of cross sections appearing in radiographic images of a cadaver ear canal to cross sectional areas of corresponding michrotome slices of an injection mold of the same canal. Percent differences between these two areas had a mean value of 9.65% for 26 different cross sections of the one ear canal studied. Ear canal volume estimated from the CAT images was 6.12% different from the estimated volume of the injection mold: an improvement over the reported 39% maximum error of conventional acoustic volume measurements.

Multiple Frequency Tympanometry

Three methods for compensating multiple frequency acoustic admittance measurements for ear canal volume were studied in 26 men with normal middle ear transmission systems. Peak compensated static acoustic admittance (magnitude of y) and phase angle (phi) were calculated from sweep frequency tympanograms (226-1243 Hz in 113 Hz increments). Of the procedures used to compensate for volume in rectangular form, the ear canal pressure used to estimate volume had the largest effect on the estimate of middle ear resonance. Median resonance was 800 Hz for admittance measurements compensated at 200 daPa versus 1100 Hz for measurements compensated at -350 daPa. The remaining two methods, compensation of susceptance only versus both susceptance and conductance and compensation using the minimum volume versus separate volumes at each frequency, did not affect estimates of middle ear resonance. Estimates of middle ear resonance from compensated phase angle measurements also were compared with estimates of resonance from admittance and phase difference curves. Although resonance could not be estimated from the phase difference curve, resonance estimated from the admittance difference curve agreed with the estimate from compensated phase angle.

Possible role for glucan produced by streptococcus sanguis in Kawasaki disease

Universal newborn hearing screening (UNHS) has significantly reduced the age of children undergoing audiological examinations. Middle ear function is usually evaluated with tympanometry using a probe tone of 226 Hz, although higher frequencies are recommended in infants. The aim of this study was to compare the feasibility of 226 and 1000 Hz tympanometry for different trace classification systems in relation to age, risk factors for hearing loss and ear canal volume.Data from 577 infants (915 ears) <1 year were analyzed. Tympanograms were classified according to the classification systems of Jerger [16], Marchant et al. [4] and Kei et al. [5] and correlated with ear microscopy as the gold standard. Test quality parameters of tympanometry with probe tones of 226 and 1000 Hz were compared in four different age groups.The trace classification following Kei et al. presented the best correlation to ear microscopy and reduced the number of unclassified tympanograms. The use of probe tones of 226 Hz in infants below the age of nine months showed a poor level of sensitivity.We recommend the use of a 1000 Hz probe tone in infants at least up to the age of nine months. In this age group, 226 Hz tympanometry is inappropriate. In children with craniofacial abnormalities and smaller ear canal volumes, 1000 Hz tympanometry could be taken into consideration, even for older children. High-frequency tympanograms should be evaluated according to the classification system of Kei et al., which differentiates between peaked (normal) and flat (abnormal) curves.

Peripheral gangrene associated with Kawasaki disease

Universal newborn hearing screening (UNHS) has significantly reduced the age of children undergoing audiological examinations. Middle ear function is usually evaluated with tympanometry using a probe tone of 226 Hz, although higher frequencies are recommended in infants. The aim of this study was to compare the feasibility of 226 and 1000 Hz tympanometry for different trace classification systems in relation to age, risk factors for hearing loss and ear canal volume.Data from 577 infants (915 ears) <1 year were analyzed. Tympanograms were classified according to the classification systems of Jerger [16], Marchant et al. [4] and Kei et al. [5] and correlated with ear microscopy as the gold standard. Test quality parameters of tympanometry with probe tones of 226 and 1000 Hz were compared in four different age groups.The trace classification following Kei et al. presented the best correlation to ear microscopy and reduced the number of unclassified tympanograms. The use of probe tones of 226 Hz in infants below the age of nine months showed a poor level of sensitivity.We recommend the use of a 1000 Hz probe tone in infants at least up to the age of nine months. In this age group, 226 Hz tympanometry is inappropriate. In children with craniofacial abnormalities and smaller ear canal volumes, 1000 Hz tympanometry could be taken into consideration, even for older children. High-frequency tympanograms should be evaluated according to the classification system of Kei et al., which differentiates between peaked (normal) and flat (abnormal) curves.

Validity and Reliability of Tympanometric Measures for Pediatric Patients

Sensitivity and specificity of static acoustic admittance (SAA) and tympanometric width (TW) were assessed for 116 pediatric patients. Otologic examination was the validation criterion. Reliability of immediate repeat tympanometric measures (SAA, TW, peak pressure, and estimate of ear canal volume) was also evaluated. A statistically significant change in SAA, with a larger SAA on measure two than measure one, was observed. No significant change across the two sequential measures was observed for TW, peak pressure, or the estimate of ear canal volume. The sensitivity and specificity data collected are discussed with respect to assisting clinicians in selecting tympanometric criteria suitable to their own clinical situation.

Probe-tube microphone measures in hearing-impaired children and adults.

This study was designed to investigate the reliability of real-ear measurements of sound pressure level (SPL) and to compare these values with two coupler measures of SPL. A commercially available probe tube microphone system was used to measure real ear SPL in both children and adults. Test-retest reliability decreased as a function of frequency for both groups and, in general, was slightly poorer for the children. For both groups, coupler to real ear differences were larger for the 2 cm3 coupler than for the reduced volume coupler; however, no significant differences were observed between groups. In addition, a measure of ear canal volume was not found to be a good predictor of coupler to real ear discrepancies.

Acoustic impedance measurement on normal ears of children.

In order to provide the fundamental knowledge on outer and middle ear of children, acoustic impedance measurements were performed on 205 subjects. They ranged from 3 years old to 11 years old and had normal hearing. We utilized the acoustic inverse method for reconstruction of the ear canal area functions. The results show (a) the children have smaller ear canal radius than the adults and (b) the ear canal volume and the ear canal radius increase as a function of the age. The acoustic impedance at the eardrum were calculated from the reconstructed area function of the ear canals and the measured reflection data. It is shown that (c) mean resistance of the eardrum impedance remains between 300 and 350 cgs acoustic ohms above 2 kHz, and the value is not so much different from the reported data on the adults. On the other hand, (d) middle ear of the children has small compliance and its values approach to the adults data as the age increases. This is evident in lower frequencies below 1 kHz.

Tympanometric diagnosis of the aditus block in chronic otitis media

Prior to the surgery of chronic otitis media it is desirable to know whether or not there is any pathology in the attic or aditus ad antrum that in blocking the aeration of the middle ear space peripheral to those areas, because if some pathology are present in the areas surgical intervention to them is often necessary. Various radiological methods including the tomography or CT have so far been used for this purpose.The authors described a simpler and less time consuming method using tympanometry. In an ear with a perforation, the height of base line (compliance) of a tympanogram which normally represents the external ear canal volume in non-perforated ear, indicates the sum of the air volume contained in the external ear canal and the middle ear. In 56 ears (43 cases) with central perforations of the tympanic membranes (51 chronic otitis media, 5 traumatic perforations) a comparison was made between the compliance value and the CT findings of the ears. A very good correlation was found between the compliance value and the extent of the middle ear aeration estimated by the CT. While all the 33 ears with compliance values exceeding 2.0 cc were found to have clear attic and aditus ad antrum, 19 of 23ears with compliance values below 2. Occ and 17 of 18 ears with those below 1.5cc, were found to have aditus block.It is concluded that tympanometry, less time consuming and simpler than radiological methods, is very effective in the preoperative screening of the patency of the attic and aditus ad antrum in chronic otitis media with perforation.

Ear canal volume and variability in the patterns of temporary threshold shifts.

Ear canal resonance is thought to be responsible for the prominent loss of hearing in the 3.0 to 6.0 kHz region caused by over-exposure to noise. Relationships were identified between frequency-of-maximum temporary threshold shift (TTS) and physical measurements of the ear canal in 56 subjects. TTSs were produced by two separate exposures to broadband noise of either 2 hr or 20 minute duration. Ear canal volume was estimated from admittance tympanograms, diameter of the canal opening was measured, and canal length was calculated. Thirty subjects suffered the greatest TTS at 4.0 kHz, while 17 and 9 subjects had the greatest shift at 3.0 and 6.0 kHz, respectively. With subjects grouped according to frequency-of-maximum TTS, mean ear canal volume was found to be significantly different. Subjects with larger volumes were more likely to suffer the greatest loss at 3.0 kHz. Accordingly, subjects with smaller ear canal volumes suffered peak hearing loss at 6.0 kHz. Significant correlations were identified between ear canal volume and calculated length (resonance). Also, modest correlations were noted between frequency-of-maximum TTS and volume as well as TTS and length.

Screening tympanometry: criteria for medical referral.

Tympanograms were obtained from normal preschool and adult subjects with a prototype hand-held tympanometer to obtain normative values for four tympanometric variables: static admittance, equivalent ear canal volume, tympanometric peak pressure, and gradient. Effects of age group, sex, and pump speed (200 or 400 daPa/s) were determined. The results were incorporated into a four-part screening protocol (history, visual inspection, audiometry, and tympanometry) designed to reduce the excessive error rates associated with screening strategies that rely exclusively on tympanometry.