Biomedical subjects

S Puria

Publications and source records attributed to S Puria.

9 recordsLinked to original sources

PubMed2001

Human middle-ear sound transfer function and cochlear input impedance.

The middle-ear pressure gain, defined as the ear canal sound pressure to cochlear vestibule pressure gain, GME, and the ear canal sound pressure to stapes footplate velocity transfer function, SVTF, simultaneously measured in 12 fresh human temporal bones for the 0.05 to 10 kHz frequency range are reported. The mean GME magnitude reached 23.5 dB at 1.2 kHz with a slope of approximately 6 dB/octave from 0.1 to 1.2 kHz and -6 dB/octave above 1.2 kHz. From 0.1 to 0.5 kHz, the mean GME phase angle was 51 degrees, rolling off at -78 degrees /octave above this frequency. The mean SVTF magnitude reached a maximum of 0.33 mm s(-1)/Pa at 1.0 kHz with nearly the same shape in magnitude and phase angle as the mean GME. The ratio of GME and SVTF provide the first direct measurements of Z(c) in human ears. The mean Z(c) was virtually flat with a value of 21.1 acoustic GOmega MKS between 0.1 and 5.0 kHz. Above 5 kHz, the mean Z(c) increased to a maximum value of 49.9 GOmega at 6.7 kHz. The mean Z(c) angle was near 0 degrees from 0.5 to 5.0 kHz, decreasing below 0.5 kHz and above 5 kHz with peaks and valleys.

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↗

PubMed1998

Measurements and model of the cat middle ear: evidence of tympanic membrane acoustic delay.

In order to better understand the mechanics of tympanic membrane (TM) transduction at frequencies above a few kHz, the middle-ear (ME) impedance measured near the tympanic membrane is studied for three anesthetized cat ears after widely opening the ME cavities (MEC). Three conditions were measured: intact ossicles, drained cochlea, and disarticulated stapes. When the cochlear load is removed from the ME by disarticulating the stapes, the impedance magnitude varies by about +/- 25 dB in the 5- to 30-kHz range, with peaks and valleys at intervals of approximately 5 kHz. These measurements suggest middle-ear standing waves. It is argued that these standing waves reside in the TM. In contrast, the magnitude of the impedance for the intact case varies by less than +/- 10 dB, indicating that for this case the standing waves are damped by the cochlear load. Since the measurements were made within 2 mm of the TM, standing waves in the ear canal can be ruled out at these frequencies. Although the ME cavities were widely opened, reflections from the ME cavity walls or surrounding structures could conceivably result in standing waves. However, this possibility is ruled out by model predictions showing that such large standing waves in the ME cavity space would also be present in the intact case, in disagreement with the observation that standing waves are damped by cochlear loading. As a first-order approximation, the standing waves are modeled by representing the TM as a lossless transmission line with a frequency-independent delay of 36 microseconds. The delay was estimated by converting the impedance data to reflectance and analyzing the reflectance group delay. In the model the ossicles are represented as lumped-parameter elements. In contrast to previous models, the distributed and lumped parameter model of the ME is consistent with the measured impedance for all three conditions in the 200-Hz to 30-kHz region. Also in contrast with previous models, the ear-canal impedance is not mass dominated for frequencies above a few kHz. Finally, the present model is shown to be consistent, at high frequencies, with widely accepted transfer functions between (i) the stapes displacement and ear-canal pressure, (ii) the vestibule pressure and ear-canal pressure, and (iii) the umbo velocity and ear-canal volume velocity. An improved understanding of TM mechanics is important to improve hearing aid transducer design, ear-plug design, as well as otoacoustic emissions research.

Acoustics↗

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

Olivocochlear reflex assays: effects of contralateral sound on compound action potentials versus ear-canal distortion products.

The strength of the olivocochlear reflex has been assayed by comparing ipsilateral cochlear responses with and without contralateral sound. In humans, ipsilateral cochlear responses have usually been inferred by measuring otoacoustic emissions (OAEs), whereas, in animal work, they have been assessed by measuring compound action potentials (CAPs). Thus reports that the reflex strength is smaller in humans than in animals cannot be interpreted until the differences between the two tests are better understood. The present study directly compares reflex assays using distortion-product (DP) OAE and CAP measures in the same animals. For ipsilateral frequencies of 2-8 kHz and levels from 25 to 80 dB SPL, efferent reflex strength was computed from the CAP or DPOAE amplitude-versus-level curves measured with and without contralateral noise. The "effective attenuation" produced by efferent activation was, with few exceptions, greater when measured with the CAP than with the DPOAE assay. Differences between the two measures increased as frequency increased, with differences as large as 10 dB observed. These results, coupled with previous measurements on humans and animals, suggest that the efferent reflex is at least as strong in humans as has been shown in animal experiments.

Acoustic Stimulation↗

PubMed1996

The ipsilaterally evoked olivocochlear reflex causes rapid adaptation of the 2f1-f2 distortion product otoacoustic emission.

The onset behavior of the distortion product otoacoustic emission (DPOAE) at 2f1-f2 in anesthetized cats was measured with temporal resolution finer than 70 ms. The amplitude of the DPOAE adapts after onset of the primary tones by as much as 6 dB for monaural stimulation and 10 dB when the primaries are presented binaurally. DPOAE adaptation consists of a large, rapid component, with a time constant of roughly 100 ms, and a small, slower component with a time constant of roughly 1000 ms. The rapid component disappears when only the crossed olivocochlear bundle (OCB) is cut, whereas the slow adaptation persists after complete OCB section. The loss of rapid adaptation upon OC section is accompanied by a concomitant increase in the steady-state amplitude of the DPOAE. Thus an intact OC reflex can significantly alter DPOAEs obtained during routine measurement. Rapid adaptation of the monaurally evoked 2f1-f2 DPOAE is probably mediated by reflex activity in ipsilaterally responsive OC neurons innervating outer hair cells. The effects of this ipsilateral reflex on DPOAE amplitudes are typically twice as large as those of the contralateral reflex, presumably because there are twice as many ipsilaterally responsive OC neurons. Tests for the ipsilateral OC reflex based on the phenomenon of rapid adaptation should be both feasible and useful in human subjects.

Acoustic Stimulation↗

PubMed1991

A parametric study of cochlear input impedance.

In this paper various aspects of the cat cochlear input impedance Zc (omega) are implemented using a transmission line model having perilymph viscosity and a varying cross-sectional scalae area. These model results are then compared to the experimental results of Lynch et al. [J. Acoust. Soc. Am. 72, 108-130 (1982)]. From the model, the following observations are made about the cochlear input impedance: (a) Scalae area variations significantly alter the model Zc (omega); (b) the use of anatomically measured area improves the fits to the experimental data; (c) improved agreement between model and experimental phase is obtained when perilymph viscosity and tapering are included in the cochlear model for frequencies below approximately 150 Hz; (d) when model scalae tapering and perilymph viscosity are chosen to match physiological conditions, the effect of the helicotrema impedance on Zc (omega) is insignificant; and (e) the cochlear map, which is defined as the position of the basilar membrane peak displacement as a function of stimulus frequency, can have an important effect on Zc (omega) for frequencies below 500 Hz. A nonphysiological cochlear map can give rise to cochlear standing waves, which result in oscillations in Zc (omega). Scalae tapering and perilymph viscosity contribute significantly to the damping of these standing waves. These observations should dispel the previous notion that Zc (omega) is determined solely by parameters of the cochlea close to the stapes, and the notion that Zc (omega) is dominated by the helicotrema at low frequencies.

Acoustic Impedance Tests↗