Susan E. Voss

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.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.

Posture-induced changes in distortion-product otoacoustic emissions and the potential for noninvasive monitoring of changes in intracranial pressure

IntroductionIntracranial pressure (ICP) monitoring is currently an invasive procedure that requires access to the intracranial space through an opening in the skull. Noninvasive monitoring of ICP via the auditory system is theoretically possible because changes in ICP transfer to the inner ear through connections between the cerebral spinal fluid and the cochlear fluids. In particular, low-frequency distortion-product otoacoustic emissions (DPOAEs), measured noninvasively in the external ear canal, have magnitudes that depend on ICP. Postural changes in healthy humans cause systematic changes in ICP. Here, we quantify the effects of postural changes, and presumably ICP changes, on DPOAE magnitudes.MethodsDPOAE magnitudes were measured on seven normal-hearing, healthy subjects at four postural positions on a tilting table (angles 90°, 0°, −30°, and −45° to the horizontal). At these positions, it is expected that ICP varied from about 0 (90°) to 22 mm Hg (−45°). DPOAE magnitudes were measured for a set of frequencies 750<f2<4000, with f2/f1=1.2.ResultsFor the low-frequency range of 750≤f2≤1500, the differences in DPOAE magnitude between upright and −45° were highly significant (all p<0.01), and above 1500 Hz there were minimal differences between magnitudes at 90° versus −45°. There were no significant differences in the DPOAE magnitudes with subjects at 90° and 0° postures.ConclusionsChanges in ICP can be detected using the auditory-based measurement of DPOAEs. In particular, changes are largest at low frequencies. Although this approach does not allow for absolute measurement of ICP, it appears that measurement of DPOAEs may be a useful means of noninvasively monitoring ICP.

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.

Consensus statement: Eriksholm workshop on wideband absorbance measures of the middle ear

The participants in the Eriksholm Workshop on Wideband Absorbance Measures of the Middle Ear developed statements for this consensus article on the final morning of the Workshop. The presentations of the first 2 days of the Workshop motivated the discussion on that day. The article is divided into three general areas: terminology; research needs; and clinical application. The varied terminology in the area was seen as potentially confusing, and there was consensus on adopting an organizational structure that grouped the family of measures into the term wideband acoustic immittance (WAI), and dropped the term transmittance in favor of absorbance. There is clearly still a need to conduct research on WAI measurements. Several areas of research were emphasized, including the establishment of a greater WAI normative database, especially developmental norms, and more data on a variety of disorders; increased research on the temporal aspects of WAI; and methods to ensure the validity of test data. The area of clinical application will require training of clinicians in WAI technology. The clinical implementation of WAI would be facilitated by developing feature detectors for various pathologies that, for example, might combine data across ear-canal pressures or probe frequencies.

Posture systematically alters ear-canal reflectance and DPOAE properties.

Several studies have demonstrated that the auditory system is sensitive to changes in posture, presumably through changes in intracranial pressure (ICP) that in turn alter the intracochlear pressure, which affects the stiffness of the middle-ear system. This observation has led to efforts to develop an ear-canal based noninvasive diagnostic measure for monitoring ICP, which is currently monitored invasively via access through the skull or spine. Here, we demonstrate the effects of postural changes, and presumably ICP changes, on distortion product otoacoustic emissions (DPOAE) magnitude, DPOAE angle, and power reflectance. Measurements were made on 12 normal-hearing subjects in two postural positions: upright at 90 degrees and tilted at -45 degrees to the horizontal. Measurements on each subject were repeated five times across five separate measurement sessions. All three measures showed significant changes (p<0.001) between upright and tilted for frequencies between 500 and 2000 Hz, and DPOAE angle changes were significant at all measured frequencies (500-4000 Hz). Intra-subject variability, assessed via standard deviations for each subjects multiple measurements, were generally smaller in the upright position relative to the tilted position.

Intracranial pressure modulates distortion product otoacoustic emissions: a proof-of-principle study.

BACKGROUNDnThere is an important need to develop a noninvasive method for assessing intracranial pressure (ICP). We report a novel approach for monitoring ICP using cochlear-derived distortion product otoacoustic emissions (DPOAEs), which are affected by ICP.nnnOBJECTIVEnWe hypothesized that changes in ICP may be reflected by altered DPOAE responses via an associated change in perilymphatic pressure.nnnMETHODSnWe measured the ICP and DPOAEs (magnitude and phase angle) during opening and closing in 20 patients undergoing lumbar puncture.nnnRESULTSnWe collected data on 18 patients and grouped them based on small (<4 mm Hg), medium (5-11 mm Hg), or large (≥15 mm Hg) ICP changes. A permutation test was applied in each group to determine whether changes in DPOAEs differed from zero when ICP changed. We report significant changes in the DPOAE magnitudes and angles, respectively, for the group with the largest ICP changes and no changes for the group with the smallest changes; the group with medium changes had variable DPOAE changes.nnnCONCLUSIONnWe report, for the first time, systematic changes in DPOAE magnitudes and phase in response to acute ICP changes. Future studies are warranted to further develop this new approach.nnnABBREVIATIONSnDPOAE, distortion product otoacoustic emissionICP, intracranial pressureIIH, idiopathic intracranial hypertensionLP, lumbar punctureTBI, traumatic brain injury.

Factors that introduce intrasubject variability into ear-canal absorbance measurements.

Wideband immittance measures can be useful in analyzing acoustic sound flow through the ear and also have diagnostic potential for the identification of conductive hearing loss as well as causes of conductive hearing loss. To interpret individual measurements, the variability in test–retest data must be described and quantified. Contributors to variability in ear-canal absorbance–based measurements are described in this article. These include assumptions related to methodologies and issues related to the probe fit within the ear and potential acoustic leaks. Evidence suggests that variations in ear-canal cross-sectional area or measurement location are small relative to variability within a population. Data are shown to suggest that the determination of the Thévenin equivalent of the ER-10C probe introduces minimal variability and is independent of the foam ear tip itself. It is suggested that acoustic leaks in the coupling of the ear tip to the ear canal lead to substantial variations and that this issue needs further work in terms of potential criteria to identify an acoustic leak. In addition, test–retest data from the literature are reviewed.

Function and Acoustics of the Normal and Diseased Middle Ear

The middle ear helps convert compressional sound waves in the ear canal into transverse traveling waves in the cochlea. This chapter presents a conceptual framework for understanding middle ear function. The framework is first developed for the normal middle ear and then modified to include several pathological conditions. Data describing energy transfer between the ear canal and the cochlea are reviewed, including impedance measures, ossicular motions, and cochlear pressure measurements. The functions of individual parts of the normal middle ear are discussed for the tympanic membrane, the malleus and incus complex, the stapes, and the middle ear cavity. The effects of specific middle ear pathologies are discussed, including those affecting the middle ear cavity, the tympanic membrane, and the ossicles. Whenever possible, the diseases are represented by modifying the conceptual model of the normal middle ear.