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Biomedical subjects

W T Peake

Publications and source records attributed to W T Peake.

At least 19 recordsLinked to original sources
PubMed2002

Mammalian ear specializations in arid habitats: structural and functional evidence from sand cat (Felis margarita).

To test whether structural specializations of sand-cat ears are adaptations to their desert habitats we measured structural and acoustic features of their ears. The area of the external ear's pinna flange is similar to that of domestic cat. The dimensions of the ear canal are about twice domestic cat's, as is the volume of the middle-ear air space. The magnitude of the acoustic input-admittance at the tympanic membrane is about five times larger than that of domestic cat; both the middle-ear cavities and the ossicular chain contribute to the increase. Structure-based models suggest the acoustic admittance looking outward through the external ear is generally larger for sand cat than for domestic cat; the radiation power-efficiency is also larger in sand cat for frequencies below 2 kHz. Hearing sensitivity (estimated from measurements and model calculations) in sand cat is predicted to be about 8 dB greater than in domestic cat for frequencies below 2 kHz. Analysis of attenuation of sound in deserts implies that the increased sensitivity extends sand cat's hearing range beyond domestic cat by 0.4 km at 0.5 kHz. Thus, the structural specializations may provide habitat-specific survival value.

Acoustic Stimulation↗
PubMed2001

How do tympanic-membrane perforations affect human middle-ear sound transmission?

Although tympanic-membrane (TM) perforations are common sequelae of middle-ear disease, the hearing losses they cause have not been accurately determined, largely because additional pathological conditions occur in these ears. Our measurements of acoustic transmission before and after making controlled perforations in cadaver ears show that perforations cause frequency-dependent loss that: (1) is largest at low frequencies; (2) increases as perforation size increases; and (3) does not depend on perforation location. The dominant loss mechanism is the reduction in sound-pressure difference across the TM. Measurements of middle-ear air-space sound pressures show that transmission via direct acoustic stimulation of the oval and round windows is generally negligible. A quantitative model predicts the influence of middle-ear air-space volume on loss; with larger volumes, loss is smaller.

Ear, Middle↗
PubMed2001

Middle-ear function with tympanic-membrane perforations. I. Measurements and mechanisms.

Sound transmission through ears with tympanic-membrane (TM) perforations is not well understood. Here, measurements on human-cadaver ears are reported that describe sound transmission through the middle ear with experimentally produced perforations, which range from 0.5 to 5.0 mm in diameter. Three response variables were measured with acoustic stimulation at the TM: stapes velocity, middle-ear cavity sound pressure, and acoustic impedance at the TM. The stapes-velocity measurements show that perforations cause frequency-dependent losses; at low frequencies losses are largest and increase as perforation size increases. Measurements of middle-ear cavity pressure coupled with the stapes-velocity measurements indicate that the dominant mechanism for loss with TM perforations is reduction in pressure difference across the TM; changes in TM-to-ossicular coupling generally contribute less than 5 dB to the loss. Measurements of middle-ear input impedance indicate that for low frequencies, the input impedance with a perforation approximates the impedance of the middle-ear cavity; as the perforation size increases, the similarity to the cavity's impedance extends to higher frequencies. The collection of results suggests that the effects of perforations can be represented by the path for air-volume flow from the ear canal to the middle-ear cavity. The quantitative description of perforation-induced losses may help clinicians determine, in an ear with a perforation, whether poor hearing results only from the perforation or whether other pathology should be expected.

Acoustic Stimulation↗
PubMed2001

Middle-ear function with tympanic-membrane perforations. II. A simple model.

A quantitative model of the human middle ear with a tympanic-membrane (TM) perforation is developed. The model is constrained by several types of acoustic measurements made on human cadaver ears, which indicate that perforation-induced changes in transmission result primarily from changes in driving pressure across the TM and that perforation-induced change in the structure of the TM and its coupling to the ossicles contributes a substantially smaller component. The model represents the effect of a perforation on the pressure difference across the TM by inclusion of a path for sound coupling through the perforation from the ear canal to the middle-ear cavity. The model implies that hearing loss with perforations depends primarily on three quantities: the perforation diameter, sound frequency, and the volume of air in the middle-ear cavity. For the conditions that produce the largest hearing loss (low frequency and large perforation), the model yields a simple dependence of loss on frequency, perforation diameter, and middle-ear cavity volume. Predictions from this model may be useful to clinicians in determining whether, in particular cases, hearing losses are explainable by the observed perforations or if additional pathology must be involved.

Deafness↗
PubMed2000

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.

Animals↗
PubMed2000

Acoustic responses of the human middle ear.

Measurements on human cadaver ears are reported that describe sound transmission through the middle ear. Four response variables were measured with acoustic stimulation at the tympanic membrane: stapes velocity, middle-ear cavity sound pressure, acoustic impedance at the tympanic membrane and acoustic impedance of the middle-ear cavity. Measurements of stapes velocity at different locations on the stapes suggest that stapes motion is predominantly 'piston-like', for frequencies up to at least 2000 Hz. The measurements are generally consistent with constraints of existing models. The measurements are used (1) to show how the cavity pressure and the impedance at the tympanic membrane are related, (2) to develop a measurement-based middle-ear cavity model, which shows that the middle-ear cavity has only small effects on the motion of the tympanic membrane and stapes in the normal ear, although it may play a more prominent role in pathological ears, and (3) to show that inter-ear variations in the impedance at the tympanic membrane and the stapes velocity are not well correlated.

Acoustic Impedance Tests↗
PubMed2000

Middle ear pathology can affect the ear-canal sound pressure generated by audiologic earphones.

OBJECTIVE: To determine how the ear-canal sound pressures generated by earphones differ between normal and pathologic middle ears. DESIGN: Measurements of ear-canal sound pressures generated by the Etymtic Research ER-3A insert earphone in normal ears (N = 12) were compared with the pressures generated in abnormal ears with mastoidectomy bowls (N = 15), tympanostomy tubes (N = 5), and tympanic-membrane perforations (N = 5). Similar measurements were made with the Telephonics TDH-49 supra-aural earphone in normal ears (N = 10) and abnormal ears with mastoidectomy bowls (N = 10), tympanostomy tubes (N = 4), and tympanic-membrane perforations (N = 5). RESULTS: With the insert earphone, the sound pressures generated in the mastoid-bowl ears were all smaller than the pressures generated in normal ears; from 250 to 1000 Hz the difference in pressure level was nearly frequency independent and ranged from -3 to -15 dB; from 1000 to 4000 Hz the reduction in level increased with frequency and ranged from -5 dB to -35 dB. In the ears with tympanostomy tubes and perforations the sound pressures were always smaller than in normal ears at frequencies below 1000 Hz; the largest differences occurred below 500 Hz and ranged from -5 to -25 dB. With the supra-aural earphone, the sound pressures in ears with the three pathologic conditions were more variable than those with the insert earphone. Generally, sound pressures in the ears with mastoid bowls were lower than those in normal ears for frequencies below about 500 Hz; above about 500 Hz the pressures showed sharp minima and maxima that were not seen in the normal ears. The ears with tympanostomy tubes and tympanic-membrane perforations also showed reduced ear-canal pressures at the lower frequencies, but at higher frequencies these ear-canal pressures were generally similar to the pressures measured in the normal ears. CONCLUSIONS: When the middle ear is not normal, ear-canal sound pressures can differ by up to 35 dB from the normal-ear value. Because the pressure level generally is decreased in the pathologic conditions that were studied, the measured hearing loss would exaggerate substantially the actual loss in ear sensitivity. The variations depend on the earphone, the middle ear pathology, and frequency. Uncontrolled variations in ear-canal pressure, whether caused by a poor earphone-to-ear connection or by abnormal middle ear impedance, could be corrected with audiometers that measure sound pressures during hearing tests.

Acoustic Impedance Tests↗
PubMed2000

A noninvasive method for estimating acoustic admittance at the tympanic membrane.

The acoustic admittance at the tympanic membrane (TM), Y(TM), describes the linear acoustic properties of the ear. Here, a noninvasive measurement procedure is developed for estimating Y(TM) in intact ears. The method consists of (1) measuring the admittance in the ear canal Y(EC) with a commercially available earphone-and-microphone system, and (2) estimating Y(TM) via a uniform-tube approximation of the space between the measurement point and the TM. The dimensions of this space are estimated from Y(EC) via an area-estimation algorithm [Keefe et al., J. Acoust. Soc. Am. 91, 470 (1992)] and measurements made with controlled static pressures in the canal. Measurements in artificial loads are used to test the accuracy of the measurement system and to determine sources of error. For accurate admittance measurements: (1) extension of the microphone tube medially beyond the earphone's port is necessary for frequencies above 2 kHz; (2) the acoustic system must be calibrated in known loads with diameters within 15% of the canal diameter, because the source's output characteristics vary with load diameter. The method is applied to intact ears of anesthetized domestic cats; for frequencies below 5 kHz, the estimated Y(TM) in four ears have features that are similar to those of previous measurements made at the cat TM. Sources of error include nonuniform waves generated at the earphone's narrow port, inaccuracy in estimation of canal dimensions, irregular geometry of the canal, and earphone-microphone cross talk.

Acoustics↗
PubMed2000

Tests of some common assumptions of ear-canal acoustics in cats.

The accuracy of ear-canal admittance and reflectance as measures of the ear's properties depends on the acoustic effects of the canal. Here, measurements of acoustic admittance at different canal locations in domestic cats are used to test three common assumptions. (1) Can a uniform-tube model of the canal represent spatial variations in admittance? Data from cats support this assumption for frequencies below 3 kHz, where the admittance inferred at the tympanic membrane (TM) based on a uniform-tube model differs by less than 3 dB in magnitude and 0.07 periods in angle from the admittance measured at the TM; for higher frequencies greater differences occur. (2) Do large static air pressures in the canal make the middle ear rigid without affecting the properties of the canal space? The measurements reported indicate that large negative static pressures reduce the low-frequency compliance of the cat middle ear to about 10% of the compliance of the canal air volume. Static displacements of the acoustic probe, TM, and canal walls with static pressure may affect estimates of the canal volume and middle-ear compliance by as much as 15% to 20%. (3) Is the acoustic-reflectance magnitude constant with position along the canal? Reflectance data from cat ear canals generally support this idea, except within a frequency region near 0.5 kHz for which there is evidence of energy loss. These results demonstrate that noninvasive measurements in the canal describe middle-ear acoustic properties to within tolerances that depend on the effects of the canal.

Acoustics↗
PubMed2000

Acoustic mechanisms that determine the ear-canal sound pressures generated by earphones.

In clinical measurements of hearing sensitivity, a given earphone is assumed to produce essentially the same sound-pressure level in all ears. However, recent measurements [Voss et al., Ear and Hearing (in press)] show that with some middle-ear pathologies, ear-canal sound pressures can deviate by as much as 35 dB from the normal-ear value; the deviations depend on the earphone, the middle-ear pathology, and frequency. These pressure variations cause errors in the results of hearing tests. Models developed here identify acoustic mechanisms that cause pressure variations in certain pathological conditions. The models combine measurement-based Thévenin equivalents for insert and supra-aural earphones with lumped-element models for both the normal ear and ears with pathologies that alter the ear's impedance (mastoid bowl, tympanostomy tube, tympanic-membrane perforation, and a "high-impedance" ear). Comparison of the earphones' Thévenin impedances to the ear's input impedance with these middle-ear conditions shows that neither class of earphone acts as an ideal pressure source; with some middle-ear pathologies, the ear's input impedance deviates substantially from normal and thereby causes abnormal ear-canal pressure levels. In general, for the three conditions that make the ear's impedance magnitude lower than normal, the model predicts a reduced ear-canal pressure (as much as 35 dB), with a greater pressure reduction with an insert earphone than with a supra-aural earphone. In contrast, the model predicts that ear-canal pressure levels increase only a few dB when the ear has an increased impedance magnitude; the compliance of the air-space between the tympanic membrane and the earphone determines an upper limit on the effect of the middle-ear's impedance increase. Acoustic leaks at the earphone-to-ear connection can also cause uncontrolled pressure variations during hearing tests. From measurements at the supra-aural earphone-to-ear connection, we conclude that it is unusual for the connection between the earphone cushion and the pinna to seal effectively for frequencies below 250 Hz. The models developed here explain the measured pressure variations with several pathologic ears. Understanding these mechanisms should inform the design of more accurate audiometric systems which might include a microphone that monitors the ear-canal pressure and corrects deviations from normal.

Audiometry↗
PubMed1998

Toynbee Memorial Lecture 1997. Middle ear mechanics in normal, diseased and reconstructed ears.

A review of the structure-function relationships in normal, diseased and reconstructed middle ears is presented. Variables used to describe the system are sound pressure, volume velocity and acoustic impedance. We discuss the following: (1) Sound can be transmitted from the ear canal to the cochlea via two mechanisms: the tympanoossicular system (ossicular coupling) and direct acoustic stimulation of the oval and round windows (acoustic coupling). In the normal ear, middle-ear pressure gain, which is the result of ossicular coupling, is frequency-dependent and smaller than generally believed. Acoustic coupling is negligibly small in normal ears, but can play a significant role in some diseased and reconstructed ears. (2) The severity of conductive hearing loss due to middle-ear disease or after tympanoplasty surgery can be predicted by the degree to which ossicular coupling, acoustic coupling, and stapes-cochlear input impedance are compromised. Such analyses are used to explain the air-bone gaps associated with lesions such as ossicular interruption, ossicular fixation and tympanic membrane perforation. (3) With type IV and V tympanoplasty, hearing is determined solely by acoustic coupling. A quantitative analysis of structure-function relationships can both explain the wide range of observed post-operative hearing results and suggest surgical guidelines in order to optimize the post-operative results. (4) In tympanoplasty types I, II and III, the hearing result depends on the efficacy of the reconstructed tympanic membrane, the efficacy of the reconstructed ossicular chain and adequacy of middle-ear aeration. Currently, our knowledge of the mechanics of these three factors is incomplete. The mechanics of mastoidectomy and stapedectomy are also discussed.

Biomechanical Phenomena↗
PubMed1997

The middle ear of a lion: comparison of structure and function to domestic cat.

Acoustic and anatomical measurements were made on the middle ear of a deceased lion and compared with measurements from the domestic cat. The acoustic input impedance and sound-transmission ratios measured in the two species have similar features but differ quantitatively. Three-dimensional anatomical reconstructions show that the middle-ear structures of the lion and cat are similarly arranged but have large differences in absolute and relative size. In all fields, a bony septum divides the middle-ear air space into two cavities that are coupled through a small opening. A six-element analog-circuit model based on this distinctive structure captures the main features of both sets of middle-ear frequency responses, except at high frequencies. The element values are consistent with the structural dimensions of the cavities. The results suggest that quantitative measures of middle-ear cavity structure could allow prediction of frequency-dependent features of acoustic sensitivity for the entire cat family.

Acoustic Impedance Tests↗
PubMed1997

Sound-pressure measurements in the cochlear vestibule of human-cadaver ears.

The middle-ear pressure gain for the 50-Hz to 12-kHz range was determined from the ratio of sound pressures measured in the vestibule and the ear canal of four human-cadaver ears. The magnitude of the middle-ear pressure gain is 20 dB for frequencies between 500 Hz and 2 kHz. Above 4 kHz, the gain changes as a function of frequency at a rate of approximately -8 dB/octave and below 400 Hz at 4 dB/octave. The standard error of the mean magnitude across the four ears is typically less than 3 dB. The phase angle of the pressure gain also changes with frequency. Interruption of the ossicular chain decreases the vestibule pressure by at least 20 dB. It is shown that air bubbles in the inner ear can diminish the vestibule pressure; procedures are used to remove bubbles. From these pressure measurements and previous measurements of stapes motion, the frequency dependence of behavioral thresholds for tones was tested to discover whether it corresponds to the constancy of a physiological variable at the cochlear input. Among pressure, power, or stapes-motion measures, the vestibule pressure is most nearly constant with frequency at the behavioral "minimum audible pressure."

Adult↗
PubMed1997

Analysis of middle ear mechanics and application to diseased and reconstructed ears.

OBJECTIVE: To review current concepts of the mechanical processes of the human middle ear, and to apply them to practical issues in clinical otology and tympanoplasty surgery. BACKGROUND: The wide range of conductive hearing losses associated with middle ear pathology and reconstruction cannot be adequately explained by simple models of middle ear function. METHODS: Variables used to describe the system are sound pressure, volume velocity, and acoustic impedance. The relationship between specific middle ear structures and these variables is described such that inferences can be drawn regarding sound conduction in the normal, diseased, and reconstructed middle ear. RESULTS AND CONCLUSIONS: Sound can be transmitted from the car canal to the cochlea via two mechanisms: the tympano-ossicular system (ossicular coupling) and direct acoustic stimulation of the oval and round windows (acoustic coupling). Acoustic coupling is negligibly small in normal ears, but can play a significant role in some diseased and reconstructed ears. In the normal ear, middle ear pressure gain (which is the result of ossicular coupling) is frequency-dependent and less than generally believed. The severity of conductive hearing loss due to middle-ear disease or after tympanoplasty surgery can be predicted by the degree to which ossicular coupling, acoustic coupling, and stapescochlear input impedance are altered. Hearing after type IV and V tympanoplasty is determined solely by acoustic coupling. The difference in magnitude between the oval- and round-window pressures is more important than the difference in phase in determining cochlear input. In tympanoplasty types I, II, and III, adequate middle-ear and round-window aeration is necessary and the tympanic membrane-ossicular configuration may be less crucial.

Acoustics↗
PubMed1996

Is the pressure difference between the oval and round windows the effective acoustic stimulus for the cochlea?

The assumption that the pressure difference between the cochlear windows is the stimulus that produces cochlear responses is tested experimentally in the ears of anesthetized cats. Cochlear potential is used as a measure of cochlear response. The sound pressures at the oval and round windows are individually controlled with both pressures at the same frequency and amplitude. When the angle difference between the two pressures is varied over one cycle, cochlear-potential magnitude varies by about 40 dB, with a sharp minimum occurring with the angle difference near zero. A linear model of the response to the two input pressures estimates a complex common-mode gain C and a complex difference-mode gain D; magnitude of D is about 35 dB greater than magnitude of C over the frequency range that was tested (75 to 1000 Hz). Thus, except for conditions that make the common-mode input much larger than the difference-mode input, the pressure difference between the oval and round windows is, to a good approximation, the effective acoustic stimulus for the cochlea.

Acoustic Stimulation↗
PubMed1994

Measurements of the acoustic input impedance of cat ears: 10 Hz to 20 kHz.

The acoustic input impedence of the ear is a useful measure of the behavior of the middle ear and of its effect on the acoustics of the external ear. A high-impedance acoustic source with an integral microphone was designed for acoustic-impedance measurements. The source's Norton equivalent circuit was determined from measurements of the sound pressure it generated in known acoustic loads. Tests on simple acoustic configurations show errors in impedance measurements of less than 10% in magnitude and 7 degrees in angle over a frequency range from 10 Hz to 10 kHz with increasing errors at higher frequencies. Measurements at the tympanic membrane (TM) on five cat ears with widely opened middle-ear cavities show an impedance that is compliance-like below 0.3 kHz and approximately resistive above 2 kHz. With the cavities intact the impedance magnitude is somewhat larger for low frequencies, has a sharp maximum near 4 kHz, and at the highest frequencies is little affected by the state of the cavities. Impedance magnitude varies among ears by a factor of 3. The pressure reflection-coefficient that is determined from the impedance is frequency dependent with magnitude between 0.2 and 1. To characterize the motion transformation of the TM we calculate the ratio of tympanic-membrane volume velocity to the velocity of the mallear umbo, called here the kinematic area ATK. This complex quantity is constant with an angle of zero for frequencies below 0.6 kHz, but at higher frequencies both magnitude and angle of ATK vary with frequency.

Acoustic Impedance Tests↗
PubMed1992

Middle-ear transmission: acoustic versus ossicular coupling in cat and human.

Otologic surgeons consider the action of sound pressure on the cochlear windows to be of major importance in certain cases of middle-ear pathology, yet previously published network models of mammalian middle ears do not include such a mechanism. A unified middle-ear model is developed in which it is assumed that the difference of acoustic pressures acting on the windows adds to the ossicular-chain pressure to produce cochlear input. From a network model of the cat middle-ear cavities we estimate the contributions of pressures on the cochlear windows for both normal and abnormal cat ears. For the human ear we use the model of Kringlebotn (1988) and measurements of Békésy (1947). We determine that the pressure difference across the cochlear windows is negligibly small in normal cat and human ears. Thus, it is a reasonable approximation to ignore this mechanism in normal ears. For ears with a drastically altered tympanic membrane and/or ossicular chain, acoustic coupling to the cochlear windows can--to a considerable extent--explain residual hearing in human. The model predicts hearing levels for type IV tympanoplastic reconstructions that agree with the best results obtained surgically.

Acoustic Stimulation↗