Middle-ear Air Space Research Articles

Office-based Eustachian tube endoscopy

The Eustachian tube is a conduit between the middle ear and the nasopharynx, allowing the aeration and drainage of the middle ear air space while protecting the ear from contaminants from the nasopharynx. In-office Eustachian tube endoscopy can be a powerful tool to aid in the diagnosis and management of obstructive and patulous Eustachian tube dysfunction. In this chapter, we review the background and technique for Eustachian tube endoscopy, illustrated with clinical cases.

A lumped-element model of the chinchilla middle ear.

An air-conduction circuit model was developed for the chinchilla middle ear and cochlea. The lumped-element model is based on the classic Zwislocki model of the same structures in human. Model parameters were fit to various measurements of chinchilla middle-ear transfer functions and impedances, using a combination of error-minimization-driven computer-automated and manual fitting methods. The measurements used to fit the model comprise a newer, more-extensive data set than previously used, and include measurements of stapes velocity and inner-ear sound pressure within the vestibule and the scala tympani near the round window. The model is in agreement with studies of the effects of middle-ear cavity holes in experiments that require access to the middle-ear air space. The structure of the model allows easy addition of other sources of auditory stimulation, e.g., the multiple sources of bone-conducted sound-the long-term goal for the model's development-and mechanical stimulation of the ossicles and round window.

Correlation of Site and Size of Tympanic Membrane Perforation and Middle Ear Air Space Volume with Magnitude of Hearing Loss

Abstract Introduction The effects of tympanic membrane perforations on middle ear sound transmission are not well characterized, largely because ears with perforations typically have additional pathological changes. It has been established that the larger the perforation, the greater is the hearing loss (HL). Aim This study aimed to correlate the location and size of tympanic membrane perforation and middle ear air space volume with the magnitude of HL in patients with tubotympanic or inactive mucosal type of chronic otitis media (COM). Materials and Methods A prospective clinical study of patients with tympanic membrane perforations due to COM and without any other ear disease and who attended the Otolaryngology services at our institute between July 2010 and December 2011 was conducted. A total of 300 ears were evaluated by performing otoendoscopy, followed by photo documentation and audiological investigations (pure-tone audiometry and tympanometry). Tympanic membrane perforations were categorized based on their size and location, and the mean air-bone (AB) gap between the various types of perforations was compared and statistically analyzed with significance level of p < 0.05. Results Out of 300 ears, maximum number of ears (n = 124, 41.3%) had large-sized perforations (> 30 mm2) that had a maximum mean AB gap of 26.43 dB, and minimum number of ears (n = 60, 20%) had small-sized perforations (0–9 mm2) that had minimum mean AB gap of 9.12 dB. The remaining were medium-sized perforations that had mean AB gap of 16.13 dB. Depending on the location, maximum were central perforations (n = 198, 66%) and minimum were anterosuperior (AS) perforations (n = 9, 3%). Based on the middle ear volume on tympanometry, maximum ears were of low-volume group (n = 246, 92%) that had larger mean AB gap of 19.96 dB HL when compared with the high-volume group (n = 24, 8%) with 11.80 dB HL. AB gap was maximum at lower frequencies and decreased with increase in frequencies except at 4,000 Hz, that is, 56.9 dB HL at 250 Hz, 42.6 at 500 Hz, 41.5 at 1,000 Hz, 32.4 at 2,000 Hz, and 49.5 at 4,000 Hz. Conclusion HL increases as the area of tympanic membrane perforation increases. There is an inverse relationship between HL and middle ear air space volume. Comparing the small-sized perforations at different sites with the middle ear volume being low, it was found that posterosuperior (PS) perforations had 4 to 7 dB greater HL than AS and anteroinferior (AI). However, the relationship was statistically insignificant. The phase cancellation effect of round window causing greater HL in posteroinferior (PI) perforations does not exist in small- and medium-sized perforations. HL is greater at lower frequencies and less at higher frequencies.

Effects of middle-ear disorders on power reflectance measured in cadaveric ear canals.

Reflectance measured in the ear canal offers a noninvasive method to monitor the acoustic properties of the middle ear, and few systematic measurements exist on the effects of various middle-ear disorders on the reflectance. This work uses a human cadaver-ear preparation and a mathematical middle-ear model to both measure and predict how power reflectance R is affected by the middle-ear disorders of static middle-ear pressures, middle-ear fluid, fixed stapes, disarticulated incudostapedial joint, and tympanic-membrane perforations. R was calculated from ear-canal pressure measurements made on human-cadaver ears in the normal condition and five states: (1) positive and negative pressure in the middle-ear cavity, (2) fluid-filled middle ear, (3) stapes fixed with dental cement, (4) incudostapedial joint disarticulated, and (5) tympanic-membrane perforations. The middle-ear model of Kringlebotn (1988) was modified to represent the middle-ear disorders. Model predictions are compared with measurements. For a given disorder, the general trends of the measurements and model were similar. The changes from normal in R, induced by the simulated disorder, generally depend on frequency and the extent of the disorder (except for the disarticulation). Systematic changes in middle-ear static pressure (up to 6300 daPa) resulted in systematic increases in R. These affects were most pronounced for frequencies up to 1000 to 2000 Hz. Above about 2000 Hz there were some asymmetries in behavior between negative and positive pressures. Results with fluid in the middle-ear air space were highly dependent on the percentage of the air space that was filled. Changes in R were minimal when a smaller fraction of the air space was filled with fluid, and as the air space was filled with more saline, R increased at most frequencies. Fixation of the stapes generally resulted in a relatively small low-frequency increase in R. Disarticulation of the incus with the stapes led to a consistent low-frequency decrease in R with a distinctive minimum below 1000 Hz. Perforations of the tympanic membrane resulted in a decrease in R for frequencies up to about 2000 Hz; at these lower frequencies, smaller perforations led to larger changes from normal when compared with larger perforations. These preliminary measurements help assess the utility of power reflectance as a diagnostic tool for middle-ear disorders. In particular, the measurements document (1) the frequency ranges for which the changes are largest and (2) the extent of the changes from normal for a spectrum of middle-ear disorders.

Comment on “When an Air-Bone Gap is not a Sign of a Middle-Ear Conductive Loss” By Sohmer et al.

Comment on “When an Air-Bone Gap is not a Sign of a Middle-Ear Conductive Loss” By Sohmer et al.

Structures that contribute to middle-ear admittance in chinchilla.

We describe measurements of middle-ear input admittance in chinchillas (Chinchilla lanigera) before and after various manipulations that define the contributions of different middle-ear components to function. The chinchilla's middle-ear air spaces have a large effect on the low-frequency compliance of the middle ear, and removing the influences of these spaces reveals a highly admittant tympanic membrane and ossicular chain. Measurements of the admittance of the air spaces reveal that the high-degree of segmentation of these spaces has only a small effect on the admittance. Draining the cochlea further increases the middle-ear admittance at low frequencies and removes a low-frequency (less than 300 Hz) level dependence in the admittance. Spontaneous or sound-driven contractions of the middle-ear muscles in deeply anesthetized animals were associated with significant changes in middle-ear admittance.

Acoustics of the human middle-ear air space

The impedance of the middle-ear air space was measured on three human cadaver ears with complete mastoid air-cell systems. Below 500 Hz, the impedance is approximately compliance-like, and at higher frequencies (500-6000 Hz) the impedance magnitude has several (five to nine) extrema. Mechanisms for these extrema are identified and described through circuit models of the middle-ear air space. The measurements demonstrate that the middle-ear air space impedance can affect the middle-ear impedance at the tympanic membrane by as much as 10 dB at frequencies greater than 1000 Hz. Thus, variations in the middle-ear air space impedance that result from variations in anatomy of the middle-ear air space can contribute to inter-ear variations in both impedance measurements and otoacoustic emissions, when measured at the tympanic membrane.

Mechanisms of hearing loss resulting from middle-ear fluid

Fluid in the middle ear, a defining feature of otitis media with effusion (OME), is commonly associated with a 20- to 30-dB conductive hearing loss. The effects and relative importance of various mechanisms leading to conductive hearing loss were investigated in a human temporal bone preparation. Umbo velocity in response to ear-canal sound was measured with a laser vibrometer while saline and silicone fluids of viscosity 5–12,000 cSt were introduced into the middle ear to contact part or all of the tympanic membrane (TM) and fill part or all of the middle ear. At low frequencies, reductions in umbo velocity (Δ V U) of up to 25 dB depended on the percentage of the original middle-ear air space that remained air-filled, which suggests that the primary mechanism in hearing loss at low frequencies is a reduction of the admittance of the middle-ear air space due to displacement of air with fluid. At higher frequencies, Δ V U (of up to 35 dB) depended on the percentage of the TM contacted by fluid, which suggests that the primary mechanism at high frequencies is an increase in tympanic membrane mass by entrained fluid. The viscosity of the fluid had no significant effect on umbo velocity. Δ V U for the fluid-filled middle ear matched hearing losses reported in patients whose middle ear was believed to be completely filled with fluid. The difference between Δ V U for a partly-filled middle ear and hearing losses reported in patients whose middle ear was believed to be incompletely fluid-filled is consistent with the reported effect of middle-ear underpressure (commonly seen in OME) on umbo velocity. Small amounts of air in the middle ear are sufficient to facilitate umbo motion at low frequencies.

Changes in auditory sensitivity with depth in a free-diving California sea lion (Zalophus californianus).

All current data on underwater hearing in pinnipeds are based on tests conducted in small tanks, and may not accurately represent the auditory functioning of free-ranging animals, especially if hearing sensitivity changes with water depth. Underwater auditory thresholds were determined for a California sea lion at depths ranging from 10 to 100 meters. The following results were obtained: (1) False alarm probabilities (responding in the absence of a signal) decreased significantly with depth, indicating that the sea lion adopted a more conservative response criterion in deeper water. (2) Hearing sensitivity generally worsened with depth. (3) There was a significant interaction between depth and frequency, the depth effect being most pronounced at 10 kHz and reversing at 35 kHz. Increasing pressure related to diving probably alters the impedance characteristics of the pinniped ear, in particular affecting the size of the middle-ear air space via expansion of cavernous tissue in the middle-ear cavity. These results show that the middle ear plays a functional role in underwater sound detection in sea lions. However, contrary to previous speculation, the presence of cavernous tissue in the sea lion middle ear does not appear to enhance sensitivity at depth.

Relating middle-ear acoustic performance to body size in the cat family: measurements and models.

Is the acoustic performance of the mammalian middle ear dependent on body size? We focus on the cat family, because of its qualitatively uniform (and distinctive) middle-ear structure, large size range, and the extensive data available from domestic cats which provide a framework for relating middle-ear acoustics to structure. We report measurements of acoustic admittance in 17 live adult ears of 11 exotic species, ranging in size from sand cat (3 kg) to tiger (180 kg). For low frequencies, the middle-ear response is compliant for all species and generally increases with size. The compliance of the middle-ear air space increases with size, but the compliance of the tympanic membrane and ossicular chain is not correlated with size. Structure-based rules are developed to represent some features of middle-ear performance: (1) low-frequency sensitivity increases with size; and (2) the frequency of a prominent notch in admittance decreases with size. Although some species deviate from the rules, the data generally support the idea that in larger felids the middle-ear response is shifted to lower frequencies. Thus, in the cat family, body size partly describes variations in auditory features. More speculatively, ethological pressures which might influence hearing performance are discussed.

Measurements of Middle-Ear Function in the Mongolian Gerbil, a Specialized Mammalian Ear

The middle ear of the Mongolian gerbil is thought to be specialized so that it can hear the 3,000-Hz and lower sounds produced by approaching predators. Evidence in the literature suggests several specializations: (1) an effect of the large middle-ear air spaces in the gerbil is to increase the sensitivity of this ear to sounds of 3,000 Hz and lower in frequency; (2) the combined action of the middle-ear cavity and the significant pars flaccida of the tympanic membrane in the gerbil ear reduces the sensitivity to sounds of frequencies below 500 Hz. This paper describes anatomical and functional measurements of stapes motion and suggests that the stiffness of the gerbil ossicular system also acts to reduce sensitivity to low-frequency sounds. The primary conclusion is that the frequency dependence of the gerbil middle ear is the result of the interaction of multiple factors, thereby complicating the relationship between single structural specializations and overall function.

Acoustic mechanisms: Canal wall-up versus canal wall-down mastoidectomy

The contribution of the middle ear air spaces to sound transmission through the middle ear in canal wall-up and canal wall-down mastoidectomy was studied in human temporal bones by measurements of middle ear input impedance and sound pressure difference across the tympanic membrane for the frequency range 50 Hz to 5 kHz. These measurements indicate that, relative to canal wall-up procedures, canal wall-down mastoidectomy results in a 1 to 5 dB decrease in middle ear sound transmission below 1 kHz, a 0 to 10 dB increase between 1 and 3 kHz, and no change above 3 kHz. These results are consistent with those reported by Gyo et al. (Arch Otolaryngol Head Neck Surg 1986;112:1262-8), in which umbo displacement was used as a measure of sound transmission. A model analysis suggests that the reduction in sound transmission below 1 kHz can be explained by the smaller middle ear air space volume associated with the canal wall-down procedure. We conclude that as long as the middle ear air space is aerated and has a volume greater than 0.7 ml, canal wall-down mastoidectomy should generally cause less than 10 dB changes in middle ear sound transmission relative to the canal wall-up procedure. (Otolaryngol Head Neck Surg 1998;118:751-61.)

The caloric stimulus: mechanisms of heat transfer

This review is concerned with the physical processes involved in thermal stimulation of the vestibular end-organ. A brief outline of the anatomy of the end-organ is given with particular reference to the horizontal semicircular canal, followed by a description of end-organ hydrodynamics. The neurophysiological mechanisms of thermal stimulation are then considered. Finally, routes of heat transfer from outer to inner ear are discussed.

Sound-power collection by the auditory periphery of the Mongolian gerbil Meriones unguiculatus. I: Middle-ear input impedance.

This is the first paper of a series dealing with sound-power collection by the auditory periphery of the gerbil. The purpose of the series is to quantify the physiological action of the gerbil's relatively large tympanic membrane and middle-ear air cavities. To this end the middle-ear input impedance ZT was measured at frequencies between 10 Hz and 18 kHz before and after manipulations of the middle-ear cavity. The frequency dependence of ZT is consistent with that of the middle-ear transfer function computed from extant data. Comparison of the impedance and transfer function suggests a middle-ear transformer ratio of 50 at frequencies below 1 kHz, substantially smaller than the anatomical value of 90 [Lay, J. Morph. 138, 41-120 (1972)]. Below 1 kHz the data suggest a low-frequency acoustic stiffness KT for the middle ear of 970 Pa/mm3 and a stiffness of the middle-ear cavity of 720 Pa/mm3 (middle-ear volume V MEC of 195 mm3); thus the middle-ear air spaces contribute about 70% of the acoustic stiffness of the auditory periphery. Manipulations of a middle-ear model suggest that decreases in V MEC lead to proportionate increases in KT but that further increases in middle-ear cavity volume produce only limited decreases in middle-ear stiffness. The data and the model point out that the real part of the middle-ear impedance at frequencies below 100 Hz is determined primarily by losses within the middle-ear cavity. The measured impedance is comparable in magnitude and frequency dependence to the impedance in several larger mammalian species commonly used in auditory research. A comparison of low-frequency stiffness and anatomical dimensions among several species suggests that the large middle-ear cavities in gerbil act to reduce the middle-ear stiffness at low frequencies. A description of sound-power collection by the gerbil ear requires a description of the function of the external ear.

High-resolution CT of temporal bone trauma

Computed tomographic (CT) findings in 18 patients with temporal bone trauma were reviewed. Eight patients suffered longitudinal fractures of the petrous bone, which were associated with ossicular dislocation in two patients. Transverse fractures were detected in six patients, with a contralateral mastoid fracture in one patient. In four patients, the fractures were restricted to the mastoid region. Of the 14 patients in whom adequate neurologic evaluation was available, seven had a permanent facial nerve or hearing deficit while five suffered at least a transient neurologic deficit related to the temporal bone trauma. Routine head CT (10 mm sections) demonstrated only eight of 19 petrous bone injuries. Clues to such injury included opacification of the mastoid air cells (10 patients), sphenoid sinus (11 patients), external canal and middle ear air space (10 patients), and local pneumocephalus (five patients). Evidence of brain trauma or extraaxial hematoma was seen in 12 patients. In 13 cases, high-resolution CT was also performed, demonstrating temporal bone injuries in all. This latter technique allows rapid and detailed evaluation of temporal bone trauma. Reports of radiographic evaluation of temporal bone trauma tend to deal with a somewhat skewed population, selected on the basis of clinical symptomatology. In a major trauma center equipped with high-resolution CT, it was found that temporal bone fractures may be seen incidentally, or in patients in whom symptomatology related to temporal fracture is obscured by much more serious neurologic compromise.

Reconstruction of the Middle Ear With Fascia and Bone

THIS PAPER will confine itself to a discussion of surgical problems in reconstructing deficiencies of the middle ear sound conduction system. There will be no mention of preoperative workup and of treatment and selection of patients, which are so important to success. We have already covered this rather fully 1-3 in previous publications. However, we are all prone to slight this important area, and in our office we routinely go through a check list to make sure that each patient has a complete evaluation before surgery: Ear drainage Culture and sensitivity Drainage controlled Hearing tests Air-bone gap adequate Discrimination score adequate Eustachian tube function Politzerization Examination of upper respiratory tract 1. Nasopharynx Nasal fossae Sinuses Allergy Condition of the middle ear Air space Condition of middle ear mucosa Squamous epithelium in middle ear Tympanosclerosis (extent) Mobility malleus Mastoid x-rays Tissues for Tympanic Grafting Over the past 12

A new operation to restore hearing in conductive deafness of chronic suppurative origin.

The purpose of this paper is to present a new operation, designed to be a standard operation, to eradicate infection and to restore hearing in deafness caused by chronic otitis media. The operation is performed as a one-stage surgical procedure. For convenience of description, however, it will be divided into three stages: (1) the elimination of diseased tissue, (2) the plastic technique for rebuilding a middle-ear air space, and (3) the reestablishment of a new conductive mechanism. Each stage will be presented in turn; the technique will be illustrated, and the advantages will be described. First Stage To eliminate diseased tissue, in what may be called the curative part of the operation, I have used the radical mastoidectomy. The steps in the execution of this familiar procedure require no explanation except in relation to the preservation of the skin of the auditory canal. This skin is needed to carry

FUNDAMENTALS OF BONE CONDUCTION

Sound vibrations conducted to the ear by way of the cranial bones are distributed to and through all parts of the head and reach the inner ear mainly in two ways: 1. By immediate transmission through the solid structures. (Thus the petrous bone is set in motion. The stapes relatively remaining still, the endolymph vibrations act on the oval and round windows in opposite phases, that is, one goes in while the other goes out, the same as in air conduction). 2. By mediate conduction through the solid structures to the external meatus and middle ear air spaces, and thence by secondary excitation of the tympanum and ossicles to the labyrinth. The difference between the paths traversed by bone conduction and by air conduction depends somewhat on frequency, and is one purely of degree, as by air conduction sound reaches the ear not only through the air in the meatus,