Ear Canal Pressure Research Articles

Influence of static middle ear pressure on transiently evoked otoacoustic emissions and distortion products.

Otoacoustic emissions (OAE) are influenced in their amplitude and frequency spectra by the middle ear. The effects of changes in the middle ear transmission mechanisms on transiently evoked OAE (TEOAE) and distortion product emissions (DPOAE) were investigated as a function of static ear canal pressure in 25 normal-hearing test persons aged 18-35 years. The ear canal pressure was varied stepwise between positive and negative values of 200 daPa. TEOAE and DPOAE amplitudes were attenuated significantly with changes of the static ear canal pressure, with greatest changes at low frequencies (< 2 kHz). The alterations of OAE amplitude were slightly dependent on the polarity of the pressure, with positive pressure producing a greater attenuation (0.6 dB). The results demonstrate that changes in middle ear impedance can cause a misinterpretation of OAE. To avoid this problem, tympanometry should always precede OAE measurements. Alternatively, both methods can be combined using one acoustic probe, so that the emissions can be evoked at the peak of middle ear compliance.

Pressure transfer function and absorption cross section from the diffuse field to the human infant ear canal.

The diffuse-field pressure transfer function from a reverberant field to the ear canal of human infants, ages 1, 3, 6, 12, and 24 months, has been measured from 125-10700 Hz. The source was a loudspeaker using pink noise, and the diffuse-field pressure and the ear-canal pressure were simultaneously measured using a spatial averaging technique in a reverberant room. The results in most subjects show a two-peak structure in the 2-6-kHz range, corresponding to the ear-canal and concha resonances. The ear-canal resonance frequency decreases from 4.4 kHz at age 1 month to 2.9 kHz at age 24 months. The concha resonance frequency decreases from 5.5 kHz at age 1 month to 4.5 kHz at age 24 months. Below 2 kHz, the diffuse-field transfer function shows effects due to the torsos of the infant and parent, and varies with how the infant is held. Comparisons are reported of the diffuse-field absorption cross section for infants relative to adults. This quantity is a measure of power absorbed by the middle ear from a diffuse sound field, and large differences are observed in infants relative to adults. The radiation efficiencies of the infant and the adult ear are small at low frequencies, near unity at midfrequencies, and decrease at higher frequencies. The process of ear-canal development is not yet complete at age 24 months. The results have implications for experiments on hearing in infants.

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.

The Effect of Middle Ear Pressure on Transient Evoked Otoacoustic Emissions

To determine the effect of middle ear pressure on transient evoked otoacoustic emissions (TEOAEs), emissions were recorded in ears with tympanometric peak pressures < or = -100 daPa and audiometric thresholds < or = 30 dB HL at 500 through 2000 Hz. TEOAEs were alternately recorded at ambient pressure and at the tympanometric peak pressure. As demonstrated for the 14 ears tested, equalization of the middle ear pressure increased TEOAE amplitude. Reproducibility was similarly improved in 12 of 14 ears. Unequalized middle ear pressure attenuated low frequency emissions more than high frequency emissions. These amplitude and spectrum differences were consistent with previously reported observations of the effects of ear canal pressure on otoacoustic emissions. Results suggest that unequalized middle ear pressure may increase the occurrence of false positive failures, if otoacoustic emission testing is used for hearing screenings without consideration of middle ear pressure.

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.

Differential effects of ear-canal pressure and contralateral acoustic stimulation on evoked otoacoustic emissions in humans

The effect of ear canal pressure variation (ECPV) on click evoked otoacoustic emissions (EOAEs) was compared to the suppressive effect observed with contralateral acoustic stimulation (CAS) in 11 healthy subjects. Both total EOAE amplitude and amplitude of 200 Hz frequency bands (22) were analyzed. Our results revealed that the ECPV as the CAS induced a decrease of the total EOAE amplitude; these two factors showed an additive effect when they are conjoint. The study of the EOAE frequency bands showed that the majority of them decreased under CAS and ECPV; however, a few bands are not affected. Moreover, it appeared that amplitude of the EOAE frequency bands were not modified in a similar way between the two factors: indeed some bands around 4.1 kHz did not decrease either by CAS or ECPV. These results suggest that these applied factors exert different actions on EOAEs. Moreover, the lack of a decrease effect for the same bands, both with CAS and ECPV, may explain the vulnerability of some cochlear locations.

Effect of ear-canal air pressure on evoked otoacoustic emissions.

The effect of ear-canal air pressure on click-evoked otoacoustic emissions was measured for pressures ranging from 200 to -200 daPa and stimulus levels ranging from 60-90 dB PeSPL. Positive and negative ear-canal pressures (relative to ambient pressure) reduced the emission amplitude by 3-6 dB. A spectral analysis of the emissions revealed that the effect of ear-canal air pressure is that of a high-pass filter with a cutoff frequency of 2600 Hz and a slope of 4 dB/oct. The spectral changes are the expected effect of an increase in stiffness of the middle ear and were independent of pressure polarity and click level. Ear-canal air pressure substantially reduced the reproducibility of the emission waveform, in many cases rendering the emission indistinguishable from background noise. The implication of these findings for hearing screening applications is that a high false alarm rate may occur in normal-hearing patients with intratympanic air pressures that are significantly different from ambient pressure.

External ear canal pressure regulating device and tinnitus suppression device

A tinnitus suppression device using an in-the-canal external ear canal pressure regulating device (125,136,144) to alter the pressure of the fluid of the external ear canal interior of the pressure regulating device. The device has (125,136,144) a body (126,133,146) which can be inserted into the external ear canal (14) and which seals the canal (14) from ambient pressure. An adjustably sized body (126,138,146) such as a collapsible bulbous portion (120) or a bellows type wall (128) provides a mechanism for altering the pressure in the canal (14). Either a valve (132,134) or a mechanical displacement device (152) maintains the pressure differential created.

Pressure transfer function from the diffuse field to the human infant ear canal

The diffuse field pressure transfer function H(f) to the ear canal of human infants was measured from 100–11 000 Hz. The diffuse field pressure and the ear canal pressure were simultaneously measured in a reverberant room using spatial averaging of source and microphones. The probe microphone tip was inserted 5 mm into the infant ear canal, and the parent was instructed to hold the infant while slowly walking around the room; an experimenter walked around the room with the other microphone. Results using KEMAR and in adult canals were consistent with the literature. H(f) for the 1-month-old infants has a strong peak (10–15 dB) at 4–5 kHz. The majority of the ten infants showed a twin peak structure, with the additional peak (8–12 dB) at 5–6 kHz, H(f) has a dip at 8–9 kHz and increases up to 11 kHz. A 5-dB peak at 1-2 kHz may be due to the proximity of the parent's torso to the infant's head. Additional results on older infants will be discussed. [Work supported by NIH.]

Shape and derived geometrical parameters of the adult, human tympanic membrane measured with a phase-shift moiré interferometer

The shape of the tympanic membrane is fairly complex and seems to be of significant importance in the coupling of the acoustic sound pressure in the external ear canal to the motion of the middle ear ossicles. A moiré shift interferometer was used to measure with great precision the shape of the external surface of human tympanic membrane. The dense matrix of z( x, y) values thus obtained is used to calculate different geometrical parameters (area, curvature). We show further how the same data can be used to specify exactly the shape of the tympanic membrane in a mathematical finite-element model of the middle ear.

Untersuchungen zur Bruchfestigkeit der Stapesfußplatte*

In a recent textbook concerning ear surgery, it is recommended to put some connective tissue on the stapes footplate before introducing a TORP. This should avoid penetration of the shaft of the TORP into the inner ear. Experimental studies were performed to estimate the pressure needed for pushing a TORP through the footplate. We found those pressures to be much higher than those which might occur by increasing pressure in the external ear canal or decreasing pressure in the middle ear. This means that perforations of the footplate are not due to one big event of changing pressure, but rather by chronic irritations or foreign body reactions. Anyhow, we consider the protection of the footplate by a layer of connective tissue to be very useful.

The acoustics of the external ear: Old problems and fresh perspectives

A coherent picture of the external ear, operating both in the free field and as an enclosed receiver, came into focus more than a decade ago though several troublesome problems remained, particularly at frequencies greater than a few kHz. These included uncertainty about the geometry and acoustical characteristics of the ear canal, uncertainty about the dynamics of the eardrum and the reflection of sound from the eardrum, uncertainty about the role of the external ear in sound localization and, above all, uncertainty about the acoustical interactions between earphones and ears. Considerable progress has been made in most of these areas during the past few years but some problems remain intractable. In the meantime, the scientific and technological advances of the 1970s and early 1980s have provided us with a legacy of valuable instruments: eardrum simulators, artificial heads especially the Knowles Electronic Manikin (KEMAR), microphones for probing ear canal pressure, and improved insert earphones.

Clinical evaluation of a new hand-held impedance audiometer

In order to evaluate the accuracy and clinical availability of MicroTymp (Welch Allyn) which was new, portable, cordless, and hand-held impedance audiometer, 64 normal subjects and 52 patients with otitis media with effusion were examined by use of MicroTymp and Amplaid 702 (Dana Japan). The types of tympanogram were agreed with each other in 87% of ears. Six cases of type C tympanograms in MicroTymp were shown to be type A by Amplaid 702, and the average of peak pressure of MicroTymp was more negative than Amplaid 702. The difference of peak pressure seemed to be influenced by the speed of ear canal pressure change, because the speed of MicroTymp was considerably higher than Amplaid 702; -200mmH2O/sec in MicroTymp, and -50mmH2O/sec in Amplaid 702. In the experimental study on 7 normal ears, negative shift of peak pressure was observed by increasing the rate of ear canal pressure change from -25mmH2O/sec to -50mmH2O/sec in Amplaid 702. These findings suggest that one should note in the judgment of type C tympanogram in MicroTymp having the peak pressure close to -100mmH2O.

Investigations into the nature of the association between threshold microstructure and otoacoustic emissions

Three studies are described which investigate the nature of the association between threshold microstructure and otoacoustic emissions. In the first study, threshold dips (similar in shape to those seen in threshold microstructure) are produced by introducing a low-level masker. Threshold microstructure is not abolished when tonal probes are replaced by narrowband-noise probes, while dips induced by external tonal maskers are eliminated. These findings rule out a simple interpretation of the microstructure dips as an instance of masking by otoacoustic emissions. In the second study, ear-canal measurements of the interactions of external tones with spontaneous emissions indicate that, although beating is often detected near threshold maxima, stimuli close to threshold minima are perceived as tonal because the emission is frequency locked by the external tone. The last study shows that reduction of the levels of otoacoustic emissions by aspirin consumption is associated with an initial reduction of thresholds in regions of threshold microstructure, with the greatest reduction occurring at threshold maxima. This suggests that threshold maxima may he due, at least in part, to interference or masking by the nearby otoacoustic emissions. A simple analog (driven Van der Pol oscillator) of an external tone interacting with a spontaneous emission is used to interpret ear-canal pressure waveforms and associated psychophysical percepts (including threshold detection), for tones close in frequency to emissions.

The mechanics of the middle-ear at static air pressures: the role of the ossicular joints, the function of the middle-ear muscles and the behaviour of stapedial prostheses.

In an experimental study, the mechanical behaviour of the ossicle-chain during changes of the static air pressure was analyzed microscopically and with a radiographic magnification technique in temporal bone preparations. Several preliminary experiments served to pinpoint methodological problems, like exsiccation-artifacts, storage procedures, preparation defects, missing air-cushion effect with the opened middle-ear cavity, absent labyrinthine pressure, relation of the optical axis to middle-ear structures and statistical reproducibility of the measured values. Variations of the static air pressure in the external ear canal ranging from 0 to +/- 400 mmH2O induce an inward-outward movement of the malleus. In the regular middle-ear, the direction of this movement is changed within the ossicular chain into a predominantly upward-downward direction of the lenticular process, due to a gliding function of the incudo-malleal (IM) joint. This results in a gliding movement of the surfaces of the incudostapedial joint (IS). In this way, the stapes and the inner-ear are decoupled from the excessive displacements of the drum membrane and malleus. This change in the mode of motion explains many former results of ossicle vibration, aroused by unphysiologically high sound pressures, like v. Békésy's description of the tilting footplate. This mode of motion, however, changes completely if the gliding function of the IM-joint is cancelled by experimental ankylosis. In that case, the predominant direction of movement at the incus and stapes is inward and outward, too. This mode of motion has been the generally accepted concept of the ossicle-chain mechanics up to now. This isodirectional motion also occurs with progressive exsiccation of the temporal bone preparations, explicable with drying and shrinking of the capsular ligament of the IM-joint. It is conceivable, therefore, that our concepts of the mechanics of the ossicle-chain were partly based on experiments with insufficiently moistened temporal bone preparations, as the methodological problem of the exsiccation became known only during recent decades. In further experiments with static air pressure, the mechanics of the reconstructed ossicle-chain, i.e. tympanoplasty and stapedial prostheses, were studied. In the columella-like chain reconstruction, the displacement of the stapes equals the values measured with the ankylosed IM-joint. This displacement is limited by the strength of the annular ligament, whose function, however, is eliminated in the case of stapedial prostheses. Now the displacement is limited by the friction of the piston at the perforation in the footplate.(ABSTRACT TRUNCATED AT 400 WORDS)

Pressure transmission properties from the externa ear canal to the inner ear. An experimental study using guinea pigs.

The inner ear pressure (PIE) in response to pressure changes in the external ear canal was measured in guinea pigs while alternatively opening and closing the perforation of the otic bulla. When the bulla was opened, only a transient degree of applied pressure was transmitted to the inner ear and the amplitude of the PIE was smaller than that of the corresponding PIE when the bulla was closed. This was because the applied pressure was exclusively transmitted to the inner ear via the ossicular chain. When the otic bulla was closed, the pressure was transmitted not only via the ossicular chain but also via the round window (RW) through the middle ear cavity. When the bulla was closed, the amplitude of PIE was larger by a positive pressure load than by the corresponding negative one. The amplitude of PIE showed a linear relationship to ear canal pressure of at least within the +/- 200 mmH2O range, as long as pressure was slowly applied to the ear canal. When the loading pressure was abruptly changed, a bouncing response, possibly reflecting elasticity of the RW, was evoked, which diminished or disappeared when the round window was artificially ruptured.

外耳圧の内耳への伝達に関する研究 内耳窓破裂の発症機転の検討

The inner ear pressure (PIE) in response to pressure changes in the external ear canal was measured in guinea pigs during opening and closing of the fenestrum of the otic bulla. Opening of the bulla caused only a transient change in the PIE, and the PIE was lower than when the bulla was closed, because the applied pressure was transmitted to the inner ear exclusively via the ossicular chain. When the otic bulla was closed, the pressure was transmitted not only via the ossicular chain but also via the round window through the middle ear cavity. When the bulla was closed, the PIE was increased more by a positive pressure load than by a corresponding negative one. The PIE showed a linear relationship to the ear canal pressure at least within ±200 mmH2O, as long as pressure was applied slowly to the ear canal. When the loading pressure was changed abruptly, a bouncing response, possibly reflecting elasticity of the round window, was evoked. It diminished or disappeared when the round window was ruptured artificially.

Two‐microphone measurement of acoustic intensity in the ear canal as a calibration of high‐frequency hearing

As an alternative to measures of ear canal pressure in the vicinity of the tympanic membrane, we propose an acoustic intensity measurement slightly downstream from the point of sound delivery as a convenient and meaningful calibration of high‐frequency hearing. If sound absorption in the air medium and at the walls of the ear canal is neglected, the power flow through any cross section of the ear canal would be equal to the power flow into the middle ear. A sound delivery and intensity measurement system has been built using a two‐port earmold. The tube of an Etymotic Research ER‐2 sound delivery system passes through one port and a pair of probe tubes (outer diameters = 1 mm, tip separation ≈ 3 mm) pass through the other. The latter are connected to ER‐7 microphones and used for acoustic intensity measurements based on a cross‐spectrum algorithm. Data are given on the sensitivity of measurement results with respect to the relative positions of the sound delivery point and probe tube tips. [Work supported by a grant from the Deafness Research Foundation.]

Diffuse field response of the ear

The ear canal pressure developed in a diffuse-field facility complying with ANSI S12.6-1984 was measured on 20 adult subjects (11 male and 9 female), with two replications on each ear for 19 of the 20 subjects. A soft 1-mm-o.d. silicone rubber probe tube was inserted until the subject reported the “thump” of the tube bumping the eardrum, and then withdrawn a couple of mm. Preliminary experiments indicated that this technique did not always produce the same results, with some curves on the same ear of the same subject showing substantially less “eardrum SPL” in the 8- to 20-kHz region than others. It was sometimes (but not always) possible to confirm with otoscopic examination that the lower-SPL curves corresponded to probe-tube locations away from the eardrum. Based on the preliminary experiments, data from the “best run of the best ear” (i.e., highest level above 8 kHz) were averaged. The resulting curve was similar to the curve obtained on a KEMAR manikin in the same sound field.

Effects of direction and rate of ear-canal pressure changes on tympanometric measures.

The effects of the direction (ascending and descending) and rate (12.5, 25.0, and 50.0 daPa/s) of ear-canal pressure changes on three tympanometric measures (peak static admittance, shape, and tympanometric peak pressure) were studied in 24 adults with normal middle-ear transmission systems. Susceptance, conductance, admittance, and phase angle data for the six conditions both at 226 and 678 Hz were obtained using a general purpose computer. Peak static admittance was significantly affected by both the rate and direction of pressure change as evidenced by a decrease in phase angle for ascending and for fast rates of ear-canal pressure change. Tympanometric shape was broader for descending pressure changes with less frequent notching both for descending and for slow rates of pressure change. Finally, the difference in peak pressure for the two directions of pressure change increased with the rate of ear-canal pressure change.