Middle Ear System Research Articles

A new method to identify the internal auditory canal during the middle cranial fossa approach: a preliminary report.

A new method which facilitates identification of the internal auditory canal during the middle cranial fossa approach is described. This method uses illumination of the external auditory meatus as a guide to the internal auditory canal. When the external auditory meatus is illuminated by a light source system such that used for a flexible fiberscope, areas of the middle ear air cell system are illuminated and observable through the plate of bone constituting the base of the middle cranial fossa. In the case of ordinary pneumatization of the middle ear system, the attic is the site of the most intense illumination. Knowledge of the exact location of the attic obtained by this new method is extremely useful when performing drilling to expose the internal auditory canal in the middle cranial fossa approach. This is because the internal auditory canal is located medial to the attic, and also because such knowledge is helpful in identifying the two conventional landmarks of this approach, i.e., the arcuate eminence and the greater superficial petrosal nerve, as the locations of these structures are intimately related to the attic. The method described is very simple, timesaving and inexpensive, and is very helpful in detecting the internal auditory canal. Further anatomical study is being undertaken to establish a method of pinpointing the internal auditory canal, starting from the attic which is readily identifiable by use of this method.

Tympanometric Hysteresis Effect and Errors in Middle Ear Pressure Determination - a Preliminary Study in Children with Secretory Otitis Media

Previous tympanometric studies on middle ear pressure (MEP) have revealed the hysteresis effect, which is illustrated in bidirectional tympanometries by the different peak pressures for either direction. This leads to an error in determination of MEP, which has been reported to be 10-25 daPa in normal ears, but experimental data have suggested that this error may be increased in ears with secretory otitis media (SOM). This was investigated in a group of 18 children with SOM by bidirectional tympanometries. The peak pressure difference (PPD) was calculated and found to be 75 daPa in the group of SOM, which was significantly larger than in normal ears (mean=3 daPa) ( p <0.001). The maximum PPD in the SOM group was 205 daPa, indicating an error in MEP determination of more than 100 daPa. Hysteresis is related to the viscous properties of the middle ear system, and the increased hysteresis in SOM ears can be explained by the additional viscosity of the middle ear effusion. In order to improve the accuracy of MEP estimation it is suggested that in ears with SOM, the mean pressure of bidirectional tympanometries should be applied.

Multiple-frequency tympanometry in children with acute otitis media

Multiple-frequency tympanometry (MFT) is a sweep-frequency method of acoustic immittance measurement, recently introduced in clinical practice. It provides values for the resonant frequency of the middle ear system. The purpose of this study was to use MFT to collect information about the mechanoacoustical changes occurring to the middle ear system after acute otitis media and to compare it with the results of conventional, low probe-tone tympanometry. Children with acute otitis media were followed up with both methods for 1 month after an episode of acute infection. Also, children with normal hearing were studied to establish normative data. Resonant frequency of the middle ear was found to be lower than normal even 1 month past the initial episode, for all types of 226-Hz tympanograms. MFT seemed to record changes in the middle ear after acute otitis media that 226-Hz tympanometry was unable to detect, implying persistence of pathology. More extended research will illuminate the clinical value of this method in the follow-up of acute otitis media. (Otolaryngol Head Neck Surg 1999;121:797-801.)

Mechanics of the middle ear system: computerized measurements of its pressure–volume relationship

A new method is described measuring the pressure–volume relationship of the middle ear system (MES). These measurements express the dynamic mechanical properties of the MES. Ear canal pressure changes are measured in response to tympanic membrane (TM) volume displacements in a material of 39 younger normal adults. During one recording procedure several displacements curves are obtained from which one curve is isolated representing the neutral position of the TM. From this curve the following variables are determined: hysteresis (μJ) describing the viscoelastic properties of the MES, compliance (mm 3/kPa) describing its elasticity, P range (kPa) describing the pressure range of the curve, and P ec0 (kPa) describing the ear canal pressure for the neutral position of the TM. Normative data are presented and compared with tympanometric measurements. Compliance correlates significantly to static admittance ( P<0.001), while P ec0 correlates significantly to middle ear pressure ( P<0.001). Further, data on repeatability and sources of measurement errors are reported, which support a high reliability of the method. Compared with tympanometry the method is more detailed and has several advantages, which are discussed, and it has been found valuable for future mechanical studies of the MES. These studies include possibilities for diagnostics of middle ear disorders and derivation of pressure–volume equations useful in modeling of the MES.

Mechanical Properties of the Middle Ear System Investigated by Its Pressure-Volume Relationship

A new method is presented for the measurement of ear canal pressure changes in response to tympanic membrane volume displacements, i.e. the pressure-volume relationship (PVR) of the middle ear system. This method has several advantages when compared to tympanometry; for example, it avoids phase delay and hysteresis can be used as a variable thanks to bidirectional recordings. Moreover, dynamic complicance is registered physically as changes in volume relative to pressure. Normative data for 39 subjects are summarized along with preliminary data from patients exhibiting various clinical conditions. The major findings are that secretory otitis media with middle ear effusion results in significantly increased hysteresis (leading to large errors when middle ear pressure is determined by tympanometry), two types of ossicular discontinuity may be distinguished by this method and that myringoplasty leads to a linear PVR in contrast to the nonlinearity found in normal subjects.

How body size affects middle-ear structure and function and auditory sensitivity in gekkonoid lizards.

Gekkonoid lizards increase in body size throughout life, and the present study investigates whether changes in auditory function accompany these increases. Middle-ear structures in four groups of animals, adults and juveniles of two gekkonoid species (Eublepharis macularius and Oedura marmorata), were examined. Tympanic membrane velocity and phase were also measured in all four groups. An indication of peripheral auditory function was obtained for each group by measuring compound action potentials (CAPs) from the round window membrane. The middle-ear contribution to CAP thresholds was obtained by comparing threshold levels of the CAP response with and without an intact middle-ear system. The results from these studies indicated that significant changes occurred in middle-ear structure, tympanic membrane velocity and CAP threshold between the younger and older animals. In addition, the adults of both species exhibited better auditory function when the acoustic stimulus was delivered to the tympanic membrane than when it was delivered to the columella footplate. The findings show clearly that increased body size (or age) is accompanied by functional changes in the auditory periphery.

Effect of anesthetic agents and middle ear pressure application on distortion product otoacoustic emissions in the gerbil

The functional status of the middle ear system has a crucial importance in the measurements of distortion product otoacoustic emissions (DPOAEs), because each emission signal has to be detected indirectly in the external canal. It was observed that DPOAEs were scarcely detectable in the gerbil anesthetized with pentobarbital. On the other hand, when ketamine was used as an anesthetic, the DPOAE levels were generally high. The differences in the effects of these anesthetic agents on the DPOAEs became less clear when the tympanic bulla was opened. This strongly suggests that the effects might be due to a modification of the middle ear pressure. This study was designed to elucidate the mechanisms of the effects of these anesthetics on the DPOAEs. Comparing the effects of pentobarbital and those of pressure application to the middle ear on the frequency characteristics of DPOAEs, the following conclusions emerged: (1) pentobarbital administration causes negative middle ear pressure in the gerbil; (2) the generated pressure strongly reduces DPOAE conduction through the middle ear; and thus (3) proper selection of anesthetic agents is very important in gerbil experiments that involve OAE measurements.

Sequelae of Secretory Otitis Media: Changes in Middle Ear Biomechanics

Gaihede M, Lildholdt T, Lunding J. Sequelae of secretory otitis media: changes in middle ear biomechanics. Acta Otolaryngol (Stockh) 1997; 117: 382-389.A new method previously introduced investigating the pressure-volume relationship of the middle ear system describes dynamic mechanical properties of the system: the variables measured are hysteresis, compliance, and Pec0 expressing the zero position of the tympanic membrane. The present study investigates the mechanical properties in 69 adolescents treated with ventilation tubes during childhood due to secretory otitis media. The tympanic membranes displayed various degrees of atrophy, sclerosis, and retraction of the pars flaccida. Atrophy was quantitatively related to decreasing hysteresis and increasing compliance, while myringosclerosis showed opposite effects. Pec0 was significantly lower for the group of former secretory otitis media than for normals (p < 0.001). This reflects a retraction pattern of the tympanic membrane, which may be explained by a low opening pressure of the eustachian tube or previous pressure load of the drum. Signs of retraction were not found by tympanometry. Treatment with ventilation tubes was associated with a dramatic increase of tympanic membrane pathology (66%) compared to untreated ears (12%), as assessed by otomi-croscopy (p < 0.001). However, these changes specific to treatment were not found in the corresponding mechanical variables of the middle ear system, as the effects of combined atrophy and myringosclerosis tend to counterbalance.

Fetal sheep in utero hear through bone conduction

Purpose: Although the air-conduction pathway is the principal mode of sound transmission to the inner ear, this may not be true for the fetus in utero. The fetus detects and responds to sounds in the maternal environment. Exogenous sounds can reach the fetal inner ear through the ear canal and middle ear system, bone conduction, or both. This study was designed to compare the effectiveness of these two routes of sound transmission by recording cochlear microphonic potentials from the fetus in utero in response to airborne sounds. Materials and Methods: Cochlear microphonics (CMs) recorded from one round window (RW) of fetal sheep in utero were obtained in three conditions: (1) head uncovered; (2) head covered with a neoprene hood; and (3) head covered with a neoprene hood fashioned with a hole that permitted the pinna and ear canal to be exposed. Tone bursts (0.5, 1.0, and 2.0 kHz) were delivered through a loudspeaker at high intensities (100 to 135 dB sound pressure level) to the flank of the ewe. CMs were detected with indwelling electrodes, amplified, and averaged. CM input-output functions were obtained from the fetus in each of the three conditions described above. Results: CMs recorded with the head uncovered were more sensitive than were the CMs recorded with the hood in place. There was no difference in sensitivity between the condition during which the head was completely covered and the condition in which the pinna and ear canal canal are exposed. Conclusion: The principal mode of sound transmission into the fetal inner ear is through bone conduction.

The fetal sound environment

The importance of understanding noise exposure effects on pregnant women and domestic animals was made apparent following findings that environmental sounds readily penetrate the abdominal wall, uterus, and fetal fluids. Relatively low-frequency sounds (&amp;lt;0.5 kHz) are transmitted, with sound pressure levels (dB re: 20 μPa) often higher in utero than SPLs in the air surrounding the abdomen. Overall shapes of intra-abdominal isosound pressure contours reveal important differences in the manner in which airborne and vibroacoustic sounds pass through the abdomen. Measurements of fetal cochlear microphonics show attenuation to be 10–15 dB for sounds 0.5 kHz and 40–45 dB for sounds between 0.5–2.0 kHz. Sound transmission is predominantly through bone conduction rather than through the fetal external and middle ear systems. Elevated thresholds for hearing can result from high-intensity noise exposure in fetal sheep. Nonauditory effects in humans include increases in heart rate and heart rate variability and body movements. Changes in behavioral state in the sheep fetus are easily induced with amplitude and frequency-modulated signals produced at the abdominal surface of the ewe. Stimulation in both REM and non-REM sleep led to a change in electrocortical activity, implying central arousal. [Work supported by NIH and March of Dimes Birth Defects Foundation.]

Fetal hearing: Characterization of the stimulus and response

Before sounds originating outside the abdomen of pregnant women can reach the inner ear of the fetus, they must first pass through the tissues and fluids surrounding the fetal head. Low-frequency sound energy easily penetrates to the fetal head, less than 5 dB attenuation for frequencies below 500 Hz, whereas higher frequencies are attenuated by up to 20 to 30 dB. The sound energy in amniotic fluid stimulates fetal hearing through a bone conduction route rather than through the external and middle ear systems. During passage through the bones of the skull, sound energy is slightly diminished for frequencies less than 250 Hz (10 to 20 dB), yet significantly reduced for frequencies from 500 to 2,000 Hz (40 to 50 dB). Thus, the fetus in utero can easily detect low-frequency sound energy (< 500 Hz) produced at levels that are comfortably loud for its mother, but probably cannot detect acoustic energy at frequencies higher than 500 Hz.

Multiple-frequency tympanometry in children with otitis media with effusion.

Multifrequency tympanograms were recorded from 76 ears of 43 children affected by otitis media with effusion (OME) and 90 ears of normal-hearing children to obtain data for resonance frequency (RF) and changes in phase angle. There was found to be a statistically significant decrease (p < 0.01) in both RF values and change in phase angle in ears with OME compared to normative data. This decrease may be interpreted by considering OME as a mass pathology. Multiple-frequency tympanometry seems to be a useful method for determining the effect of various middle-ear pathologies on the mechano-acoustical status of the middle-ear system.

Biomechanical characteristics of the middle ear system measured by a new method. III: Comparisons with tympanometric measurements.

A new method for studying middle ear mechanics is reported in which we measured ear canal pressure changes due to tympanic membrane volume displacements. One feature of this pressure-volume relationship (PVR) is the determination of dynamic compliance of the middle ear system (MES). We found a significant correlation between dynamic compliance expressed by the PVR and static acoustic compliance by tympanometry. Another feature of the PVR was determination of the mechanical zero position of the tympanic membrane (TM) defined in terms of minimum hysteresis, which correlated significantly with the neutral position of the TM determined by tympanometry, but indicates a retracted position of the TM relative to tympanometry. Finally the hysteresis effect of the MES measured with the PVR was compared and found to fall within the range of peak difference found in bidirectional tympanometric recordings, which is also influenced by phase delay and semi-dynamic conditions.

The biochemical characteristics of the middle ear system measured by a new method. I: Instrumentation.

A frequent finding in patients with earlier otitis media is the sequelae of tympanic membrane atrophy and sclerosis. A major number of these patients nevertheless present with normal audiometric and tympanometric findings. In search of an objective and quantitative description of these pathological changes a new instrument has been developed to measure pressure changes in the ear canal as a function of dynamic tympanic membrane volume displacement. This pressure-volume relationship of the middle ear system expresses non-linear behaviour and hysteresis, which is due to loss of energy under dynamic conditions. Hysteresis can be measured and is here introduced as a new mechanical variable of the middle ear system along with dynamic compliance. Hysteresis is expressed in microJ and compliance in microliter/cmH2O. Analytical measurements of the instrument were found to be small compared with clinical values (< 2.8%). This paper will be succeeded by another study presenting the clinical application of the method and a normal material.

The biomechanical characteristics of the middle ear system measured by a new method. II: Clinical application and normal material.

An instrument for measuring the pressure-volume relationship of the middle ear system was introduced earlier. This paper describes the practical application of the instrument and presents a normal material of 45 healthy young adults. Reflecting a slight increase in pressure in the ear canal during the measuring procedure, a series of curves is obtained, each representing a different position of the tympanic membrane. From these curves the zero curve is defined, representing the zero position of the drum. This curve is used to determine the variables of the pressure-volume relationship of the middle ear system: hysteresis, pressure range, Pec0, and compliance. The variables express objective and dynamic measures of the mechanical properties of the middle ear. The method had an acceptable repeatability and was found to be consistent with earlier investigations. It is easy to perform and causes the subject no discomfort. It is therefore considered useful for further investigation of middle ear physiology and pathophysiology.

Acoustic-reflex responses in patients with insulin-dependent diabetes mellitus

Purpose: patients with insulin-dependent diabetes mellitus (IDDM) are especially susceptible to microangiopathic complications such as nephropathy, retinopathy, and neuropathy. Microangiopathic changes are also the most important findings in histopathologic studies of the inner ear and central nervous systems in diabetic subjects. No previous studies have measured acoustic-reflex latencies (ARL) or amplitudes (ARA) in patients with IDDM. ARL and ARA reflect the function of the acoustic-reflex arch. Furthermore, possible changes in the tympanic membrane, ossicular chain, and stapedius muscle may affect the shape of acoustic-reflex. Subjects and Methods: Acoustic-reflex thresholds, latencies, and amplitudes were studied in 53 patients with IDDM and 42 randomly selected nondiabetic control subjects, aged between 20 and 40 years, using the Madsen Model ZO 73 Impedance Bridge (Madsen Electronics, Copenhagen, Denmark). Subjects with an abnormal tympanic membrane, conductive hearing loss, and known cause for hearing impairment eg, noise damage, were excluded from the study. Results: There were no differences between control and diabetic subjects in the contralateral acoustic-reflex thresholds. In contrast, patients with IDDM had longer ARLs and decreased ARAs compared with those of control subjects. ARA amplitude had linear correlation with the amplitude of tympanogram, whereas ARL had no linear correlation with auditory brainstem latencies in the same study subjects. Acoustic-reflex responses in insulin-dependent diabetic patients were not associated with the duration of diabetes, metabolic control, microangiopathy, or neuropathy. Concluslons: Prolonged ARLs and decreased ARAs in patients with insulin-dependent diabetes are probably caused more by the stiff middle ear system than disturbances in the brainstem.

Modeling and simulation of tympanograms

Tympanometry has become a standard evaluation procedure for children and adults in the audiological clinic. Because of the acoustical complexity of both the middle ear system and the testing device, there is a need to study tympanometry not only from an experimental but also a theoretical perspective to achieve a full understanding of the underlying mechanism. In the present study, a model has been developed for simulation of different type of tympanograms. In the model, the acoustic characteristics of the ear canal are described by a set of acoustic equations and those of the middle ear are described by the Zwislocki electric analog model. Model parameters corresponding to the ear canal length, the stiffness of the middle ear, and the resistance of the cochlea are manipulated to simulate the effects of the applied pressure in the ear canal during a tympanometric procedure. Typical tympanograms such as 1B1G, 3B1G, 3B3G, and 5B3G have been demonstrated with the model and are in good agreement with those actually recorded from the human ear. Some tympanograms seen under pathological and abnormal conditions are also simulated.

The Effects of Body Size on Functional Properties of Middle Ear Systems of Anuran Amphibians

Both tympanic and nontympanic pathways of sound reception are utilized by anuran amphibians. The relationship between body size and the acoustic responsiveness of various body surfaces that may serve as pathways for sound reception in anurans was analyzed. The motion of the different surfaces (tympanum, lateral body wall, lateral head surface, and dorsal shoulder surface) produced by sound was measured with a laser vibrometer in anuran species. The frequency response and amplitude levels of motion of these body surfaces clearly were linked with size. In all animals, nontympanic surfaces were most responsive to low frequencies, and the tympanum was most responsive to high frequencies. However, the responsiveness of nontympanic surfaces was greater, and extended to higher frequencies, in small anurans. In the smallest animals studied, nontympanic surfaces were often more responsive than the tympanum up to frequencies as high as 2500 Hz. In larger anurans, nontympanic responsiveness tended to decrease, and tympanic responsiveness tended to increase. In the largest animals studied, the tympanum was the most responsive surface at all except very low frequencies below about 200-300 Hz. These results suggest that small anurans can utilize nontympanic pathways for effective sound reception over a broad frequency range, whereas large anurans are more restricted to using a standard tympanic middle ear for hearing. This effect of body size on the utility of nontympanic sound reception may explain evolutionary patterns of tympanic ear reduction and loss observed in several small species of anurans.

Otoacoustic Emissions.

Otoacoustic emissions are low-intensity sounds that are produced in the cochlea and transmitted through the middle ear apparatus to the ear canal. They can be detected and extracted from the background noise in the ear canal through the use of a sensitive microphone and selective filtering or averaging techniques. The technical aspects of emission recording are very similar to those associated with the detection and capture of auditory evoked potentials. Emissions provide an acoustic link to a physiological window through which we can view the auditory periphery using frequency-specific stimuli that are presented at low and moderate intensities. The window provides an opportunity to examine cochlear activity that occurs prior to stimulation of the nervous system.Tonal emissions occur spontaneously in approximately 40% of people who have normal thresholds for pure-tone stimuli. SOAE and other types of emissions may be influenced by both ipsilateral and contralateral stimuli. One form of interaction results in suppression of the emission, and the tuning patterns associated with suppression of emissions by ipsilateral stimuli have characteristics that are similar to tuning patterns associated with single cochlear hair cells and individual neurons of the auditory nerve. These findings and other lines of evidence support the conclusion that an emission having tonal characteristics is produced from a very restricted region of the cochlear partition.Emissions may be evoked by brief click or tonal stimuli, and by continuous tonal stimuli, in virtually all individuals who have normal pure-tone thresholds and uncompromised middle ear systems. The EOAE are compromised by conditions that compromise the function of the cochlea, and they hold promise as tools that might be employed in screening for hearing loss. Preliminary findings suggest that screening employing TEOAE produces a yield that is similar to that produced by screening programs based on auditory brainstem responses. Emissions may offer advantages over current screening methods because of the ease with which they can be recorded and their apparent independence from neurological influence.Many questions regarding the origin and nature of emissions remain unanswered, but they appear to offer great sensitivity to the status of the auditory periphery. DPOAE provide an opportunity to scan the cochlear partition from base to apex with frequency-specific stimuli, and give the examiner a detailed view of the status of the end organ. The study of DPOAE holds great promise in refinement of site of lesion identification. It is exciting to witness the development of a tool to help clinical examiners probe the function of the previously inaccessible cochlea.

Primary ciliary dyskinesia and the middle ear

The middle ear cavity and the eustachian tube contain a well-functioning mucociliary clearance system. To learn more about the importance of this mucociliary clearance, we studied patients with primary ciliary dyskinesia, in whom mucociliary clearance is absent. Thirty-six patients were investigated by means of a questionnaire; in 16 of these patients, otological and audiological studies could be performed. In patients with primary ciliary dyskinesia, a discrepancy was found between subjective ear complaints and the actual middle ear function. Moreover, it appeared that for the middle ear system, mucociliary clearance is of importance only in the first 3 decades of life. With aging, however, a deficient mucociliary clearance system in the middle ear and eustachian tube can be fully compensated for.