Measurements of ear-canal geometry from high-resolution CT scans of human adult ears.

Description of the ear canal's geometry is essential for describing peripheral sound flow, yet physical measurements of the canal's geometry are lacking and recent measurements suggest that older-adult-canal areas are systematically larger than previously assumed. Methods to measure ear-canal geometry from multi-planar reconstructions of high-resolution CT images were developed and applied to 66 ears from 47 subjects, ages 18-90 years. The canal's termination, central axis, entrance, and first bend were identified based on objective definitions, and the canal's cross-sectional area was measured along its canal's central axis in 1-2 mm increments. In general, left and right ears from a given subject were far more similar than measurements across subjects, where areas varied by factors of 2-3 at many locations. The canal areas varied systematically with age cohort at the first-bend location, where canal-based measurement probes likely sit; young adults (18-30 years) had an average area of 44mm2 whereas older adults (61-90 years) had a significantly larger average area of 69mm2. Across all subjects ages 18-90, measured means ± standard deviations included: canals termination area at the tympanic annulus 56±8mm2; area at the canal's first bend 53±18mm2; area at the canal's entrance 97±24mm2; and canal length 31.4±3.1mm2.

Absorbance Measurements From Normal-hearing Ears in the National Health and Nutrition Examination Survey, 2015-2016 and 2017-2020.

OBJECTIVE: To summarize absorbance and impedance angles from normal-hearing ears within the 2015-2016 and 2017-2020 US National Health and Nutrition Examination Surveys (NHANES). DESIGN: Two publicly available NHANES datasets were analyzed. Ears meeting criteria for normal hearing and valid absorbance and impedance angle measurements were identified. Measurements were summarized via descriptive statistics within categories of age cohort, race/ethnicity cohort, sex (male, female), and ear (left, right). RESULTS: A total of 7029 ears from 4150 subjects, ages 6 to 80 years, met inclusion criteria. Differences between subgroups within all categories (age, race/ethnicity, sex, and ear) were fractions of the sample SDs. The largest differences occurred between age cohorts younger than 20 years. CONCLUSIONS: The NHANES absorbance and impedance angle measurements are consistent with published literature. These results demonstrate that trained professionals, using the Titan instrument in a community setting inclusive of all demographics, produce comparable measurements to those in laboratory settings.

Measurements of ear-canal cross-sectional areas from live human ears with implications for wideband acoustic immittance measurements.

Wideband acoustic immittance (WAI) measures are noninvasive diagnostic measurements that require an estimate of the ear canal's area at the measurement location. Yet, physical measurements of the area at WAI probe locations are lacking. Methods to measure ear-canal areas from silicone molds were developed and applied to 169 subjects, ages 18-75 years. The average areas at the canal's first bend and at 12 mm insertion depth, which are likely WAI probe locations, were 63.4 ± 13.5 and 61.6 ± 13.5 mm2, respectively. These areas are substantially larger than those assumed by current FDA-approved WAI measurement devices as well as areas estimated with acoustical methods or measured on cadaver ears. Left and right ears from the same subject had similar areas. Sex, height, and weight were not significant factors in predicting area. Age cohort was a significant predictor of area, with area increasing with decade of life. A subset of areas from the youngest female subjects did not show an effect of race on area (White or Chinese). Areas were also measured as a function of insertion depth of 4.8-13.2 mm from the canal entrance; area was largest closest to the canal entrance and systematically decreased with insertion depth.

Distortion Product Otoacoustic Emissions and Intracranial Pressure During CSF Infusion Testing.

BACKGROUND: A noninvasive method to monitor changes in intracranial pressure (ICP) is required for astronauts on long-duration spaceflight who are at risk of developing the Visual Impairment/Intracranial Pressure syndrome that has some, but not all of the features of idiopathic intracranial hypertension. We assessed the validity of distortion product otoacoustic emissions (DPOAEs) to detect changes in ICP. METHODS: Subjects were eight patients undergoing medically necessary diagnostic cerebrospinal fluid (CSF) infusion testing for hydrocephalus. DPOAE measurements were obtained with an FDA-approved system at baseline and six controlled ICP levels in ∼3 mmHg increments in random order, with a range from 10.8 ± 2.9 mmHg (SD) at baseline to 32.3 ± 4.1 mmHg (SD) at level 6. RESULTS: For f2 frequencies between 800 and 1700 Hz, when ICP was ≥ 12 mmHg above baseline ICP, DPOAE angles increased significantly and DPOAE magnitudes decreased significantly, but less robustly. DISCUSSION: Significant changes in DPOAE angle and magnitude are seen when ICP is ≥ 12 mmHg above a subject's supine baseline ICP during CSF infusion testing. These results suggest that the changes in DPOAE angle and magnitude seen with change in ICP are physiologically based, and suggest that it should be possible to detect pathological ICP elevation using DPOAE measurements. To use DPOAE for noninvasive estimation of ICP during spaceflight will require baseline measurements in the head-up, supine, and head-down positions to obtain baseline DPOAE values at different ICP ranges. Williams MA, Malm J, Eklund A, Horton NJ, Voss SE. Distortion product otoacoustic emissions and intracranial pressure during CSF infusion testing. Aerosp Med Hum Perform. 2016; 87(10):844-851.

Reflectance Measures from Infant Ears With Normal Hearing and Transient Conductive Hearing Loss.

OBJECTIVE: The objective is to develop methods to utilize newborn reflectance measures for the identification of middle-ear transient conditions (e.g., middle-ear fluid) during the newborn period and ultimately during the first few months of life. Transient middle-ear conditions are a suspected source of failure to pass a newborn hearing screening. The ability to identify a conductive loss during the screening procedure could enable the referred ear to be either (1) cleared of a middle-ear condition and recommended for more extensive hearing assessment as soon as possible, or (2) suspected of a transient middle-ear condition, and if desired, be rescreened before more extensive hearing assessment. DESIGN: Reflectance measurements are reported from full-term, healthy, newborn babies in which one ear referred and one ear passed an initial auditory brainstem response newborn hearing screening and a subsequent distortion product otoacoustic emission screening on the same day. These same subjects returned for a detailed follow-up evaluation at age 1 month (range 14 to 35 days). In total, measurements were made on 30 subjects who had a unilateral refer near birth (during their first 2 days of life) and bilateral normal hearing at follow-up (about 1 month old). Three specific comparisons were made: (1) Association of ear's state with power reflectance near birth (referred versus passed ear), (2) Changes in power reflectance of normal ears between newborn and 1 month old (maturation effects), and (3) Association of ear's newborn state (referred versus passed) with ear's power reflectance at 1 month. In addition to these measurements, a set of preliminary data selection criteria were developed to ensure that analyzed data were not corrupted by acoustic leaks and other measurement problems. RESULTS: Within 2 days of birth, the power reflectance measured in newborn ears with transient middle-ear conditions (referred newborn hearing screening and passed hearing assessment at age 1 month) was significantly greater than power reflectance on newborn ears that passed the newborn hearing screening across all frequencies (500 to 6000 Hz). Changes in power reflectance in normal ears from newborn to 1 month appear in approximately the 2000 to 5000 Hz range but are not present at other frequencies. The power reflectance at age 1 month does not depend significantly on the ear's state near birth (refer or pass hearing screening) for frequencies above 700 Hz; there might be small differences at lower frequencies. CONCLUSIONS: Power reflectance measurements are significantly different for ears that pass newborn hearing screening and ears that refer with middle-ear transient conditions. At age 1 month, about 90% of ears that referred at birth passed an auditory brainstem response hearing evaluation; within these ears the power reflectance at 1 month did not differ between the ear that initially referred at birth and the ear that passed the hearing screening at birth for frequencies above 700 Hz. This study also proposes a preliminary set of criteria for determining when reflectance measures on young babies are corrupted by acoustic leaks, probes against the ear canal, or other measurement problems. Specifically proposed are "data selection criteria" that depend on the power reflectance, impedance magnitude, and impedance angle. Additional data collected in the future are needed to improve and test these proposed criteria.

Intrasubject variability in power reflectance.

BACKGROUND: Power reflectance measurements are an active area of research related to the development of noninvasive middle-ear assessment methods. There are limited data related to test-retest measures of power reflectance. PURPOSE: This study investigates test-retest features of power reflectance, including comparisons of intrasubject versus intersubject variability and how ear-canal measurement location affects measurements. RESEARCH DESIGN: Repeated measurements of power reflectance were made at about weekly intervals. The subjects returned for four to eight sessions. Measurements were made at three ear-canal locations: a deep insertion depth (with a foam plug flush at the entrance to the ear canal) and both 3 and 6 mm more lateral to this deep insertion. STUDY SAMPLE: Repeated measurements on seven subjects are reported. All subjects were female, between 19 and 22 yr old, and enrolled at an undergraduate women's college. DATA COLLECTION AND ANALYSIS: Measurements on both the right and left ears were made at three ear-canal locations during each of four to eight measurement sessions. Random-effects regression models were used for the analysis to account for repeated measures within subjects. The mean power reflectance for each position over all sessions was calculated for each subject. RESULTS: The comparison of power reflectance from the left and right ears of an individual subject varied greatly over the seven subjects; the difference between the power reflectance measured on the left and that measured on the right was compared at 248 frequencies, and depending on the subject, the percentage of tested frequencies for which the left and right ears differed significantly ranged from 10% to 93% (some with left values greater than right values and others with the opposite pattern). Although the individual subjects showed left-right differences, the overall population generally did not show significant differences between the left and right ears. The mean power reflectance for each measurement position over all sessions depended on the location of the probe in the ear for frequencies of less than 1000 Hz. The standard deviation between subjects' mean power reflectance after controlling for ear (left or right) was found to be greater than the standard deviation within the individual subject's mean power reflectance. The intrasubject standard deviation in power reflectance was smallest at the deepest insertion depths. CONCLUSIONS: All subjects had differences in power reflectance between their left and right ears at some frequencies; the percentage of frequencies at which differences occurred varied greatly across subjects. The intrasubject standard deviations were smallest for the deepest probe insertion depths, suggesting clinical measurements should be made with as deep an insertion as practically possible to minimize variability. This deep insertion will reduce both acoustic leaks and the effect of low-frequency ear-canal losses. The within-subject standard deviations were about half the magnitude of the overall standard deviations, quantifying the extent of intrasubject versus intersubject variability.

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

BACKGROUND: There 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. OBJECTIVE: We hypothesized that changes in ICP may be reflected by altered DPOAE responses via an associated change in perilymphatic pressure. METHODS: We measured the ICP and DPOAEs (magnitude and phase angle) during opening and closing in 20 patients undergoing lumbar puncture. RESULTS: We 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. CONCLUSION: We 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. ABBREVIATIONS: DPOAE, distortion product otoacoustic emissionICP, intracranial pressureIIH, idiopathic intracranial hypertensionLP, lumbar punctureTBI, traumatic brain injury.

Assessment of ear disorders using power reflectance.

This article describes the effect of various pathologies on power reflectance (PR) and absorbance measured in human adults. The pathologies studied include those affecting the tympanic membrane, the middle-ear ossicles, the middle-ear cavity, the inner ear, and intracranial pressure. Interesting pathology-induced changes in PR that are statistically significant have been reported. Nevertheless, because measurements of PR obtained from normal-hearing subjects have large variations and some pathology-induced changes are small, it can be difficult to use PR alone for differential diagnosis. There are, however, common clinical situations without reliable diagnostic methods that can benefit from PR measurements. These conditions include ears with a normal-appearing tympanic membrane, aerated middle-ear cavity, and unknown etiology of conductive hearing loss. PR measurements in conjunction with audiometric measurements of air­bone gap have promise in differentiating among stapes fixation, ossicular discontinuity, and superior semicircular canal dehiscence. Another possible application is to monitor an individual for possible changes in intracranial pressure. Descriptions of mechanisms affecting PR change and utilization of PR measurements in clinical scenarios are presented.

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 test­retest data must be described and quantified. Contributors to variability in ear-canal absorbance­based 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, test­retest data from the literature are reviewed.

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.

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

OBJECTIVE: 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. DESIGN: 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. RESULTS: 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. CONCLUSIONS: 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.

Normative reflectance and transmittance measurements on healthy newborn and 1-month-old infants.

OBJECTIVE: Ear-canal-based wideband reflectance (WBR) measurements may provide objective measures to assess and monitor middle-ear status in young babies. This work presents WBR measurements of power reflectance and transmittance on populations of healthy newborn babies (3 to 5 days) and healthy 1-mo-old babies (28 to 34 days). Thus, this work determines how power reflectance and transmittance vary between newborn and 1-mo-old babies and characterizes the range of these measures in normal populations. DESIGN: Power reflectance and transmittance were calculated from pressure measurements made in the ear canals of seven newborn (12 ears) and eleven 1-mo-old (19 ears) babies. Permutation tests, t tests, and regression (random effects) models were used to test the effects of age (newborn versus 1 mo), gender, and ear side (right versus left). RESULTS: The power reflectance and transmittance did not differ significantly for the age comparison (newborn versus 1 mo), although the results suggest a possible difference between newborn and 1-mo-old ears near 2000 Hz. There were no differences between the male and female ears. There are small but significant differences between left and right ears in three frequency bands encompassing 500 to 4000 Hz, where the predicted power reflectance mean for the left ear differs from the right ear by 0.02 to -0.07 depending on the frequency band. CONCLUSIONS: At most frequencies, power reflectance and transmittance are indistinguishable for newborn and 1-mo-old healthy babies, with limited or no differences between the two age groups and the males and females. There were small differences in some frequency bands for left and right ears. The measurements made here are similar to other published results in some frequency ranges but differ in other frequency ranges; differences among other studies from neonatal intensive care unit babies, healthy newborn babies, and healthy 1-mo-old babies are discussed.

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 subject's multiple measurements, were generally smaller in the upright position relative to the tilted position.

Sources of variability in reflectance measurements on normal cadaver ears.

OBJECTIVES: The development of acoustic reflectance measurements may lead to noninvasive tests that provide information currently unavailable from standard audiometric testing. One factor limiting the development of these tests is that normal-hearing human ears show substantial intersubject variations. This work examines intersubject variability that results from measurement location within the ear canal, estimates of ear-canal area, and variations in middle-ear cavity volume. DESIGN: Energy reflectance (ER) measurements were made on nine human-cadaver ears to study three variables. (1) ER was measured at multiple ear-canal locations. (2) The ear-canal area at each measurement location was measured and the ER was calculated with the measured area, a constant area, and an acoustically estimated area. (3) The ER was measured with the middle-ear cavity in three conditions: (1) normal, (2) the mastoid widely opened (large air space), and (3) the mastoid closed off at the aditus ad antrum (small air space). RESULTS: Measurement-location effects are generally largest at frequencies below about 2000 Hz, where in some ears reflectance magnitudes tend to decrease systematically as the measurement location moves away from the tympanic membrane but in other ears the effects seem minimal. Intrasubject variations in reflectance due to changes in either measurement location within the ear canal or differences in the estimate of the ear-canal area are smaller than variations produced by large variations in middle-ear cavity air volume or intersubject differences. At frequencies below 2000 Hz, large increases in cavity volume systematically reduce the ER, with more variable changes above 2000 Hz. CONCLUSIONS: ER measurements depend on all variables studied: measurement location, ear-canal cross-sectional area, and middle-ear cavity volume. Variations within an individual ear in either measurement location or ear-canal cross-sectional area result in relatively small effects on the ER, supporting the notion that diagnostic tests (1) need not control for measurement location and (2) can assume a constant ear-canal area across most subjects. Variations in cavity volume produce much larger effects in ER than measurement location or ear-canal area, possibly explaining some of the intersubject variation in ER reported among normal ears.

Non-ossicular signal transmission in human middle ears: Experimental assessment of the "acoustic route" with perforated tympanic membranes.

Direct acoustic stimulation of the cochlea by the sound-pressure difference between the oval and round windows (called the "acoustic route") has been thought to contribute to hearing in some pathological conditions, along with the normally dominant "ossicular route." To determine the efficacy of this acoustic route and its constituent mechanisms in human ears, sound pressures were measured at three locations in cadaveric temporal bones [with intact and perforated tympanic membranes (TMs)]: (1) in the external ear canal lateral to the TM, P(TM); (2) in the tympanic cavity lateral to the oval window, P(OW); and (3) near the round window, P(RW). Sound transmission via the acoustic route is described by two concatenated processes: (1) coupling of sound pressure from ear canal to middle-ear cavity, H(P(CAV) ) identical withP(CAV)P(TM), where P(CAV) represents the middle-ear cavity pressure, and (2) sound-pressure difference between the windows, H(WPD) identical with(P(OW)-P(RW))P(CAV). Results show that: H(P(CAV) ) depends on perforation size but not perforation location; H(WPD) depends on neither perforation size nor location. The results (1) provide a description of the window pressures based on measurements, (2) refute the common otological view that TM perforation location affects the "relative phase of the pressures at the oval and round windows," and (3) show with an intact ossicular chain that acoustic-route transmission is substantially below ossicular-route transmission except for low frequencies with large perforations. Thus, hearing loss from TM perforations results primarily from reduction in sound coupling via the ossicular route. Some features of the frequency dependence of H(P(CAV) ) and H(WPD) can be interpreted in terms of a structure-based lumped-element acoustic model of the perforation and middle-ear cavities.

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

INTRODUCTION: Intracranial 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. METHODS: DPOAE magnitudes were measured on seven normal-hearing, healthy subjects at four postural positions on a tilting table (angles 90 degrees , 0 degrees , - 30 degrees , and - 45 degrees to the horizontal). At these positions, it is expected that ICP varied from about 0 (90 degrees ) to 22 mm Hg ( - 45 degrees ). DPOAE magnitudes were measured for a set of frequencies 750 < f2 < 4000, with f2/f1 = 1.2. RESULTS: For the low-frequency range of 750

Determinants of hearing loss in perforations of the tympanic membrane.

BACKGROUND: Although tympanic membrane perforations are common, there have been few systematic studies of the structural features determining the magnitude of the resulting conductive hearing loss. Our recent experimental and modeling studies predicted that the conductive hearing loss will increase with increasing perforation size, be independent of perforation location (contrary to popular otologic belief), and increase with decreasing size of the middle-ear and mastoid air space (an idea new to otology). OBJECTIVE: To test our predictions regarding determinants of conductive hearing loss in tympanic membrane perforations against clinical data gathered from patients. STUDY DESIGN: Prospective clinical study. SETTING: Tertiary referral center. INCLUSION CRITERIA: Patients with tympanic membrane perforations without other middle-ear disease. MAIN OUTCOME MEASURES: Size and location of perforation; air-bone gap at 250, 500, 1,000, 2,000, and 4,000 Hz; and tympanometric estimate of volume of the middle-ear air spaces. RESULTS: Isolated tympanic membrane perforations in 62 ears from 56 patients met inclusion criteria. Air-bone gaps were largest at the lower frequencies and decreased as frequency increased. Air-bone gaps increased with perforation size at each frequency. Ears with small middle-ear volumes, < or = 4.3 ml (n = 23), had significantly larger air-bone gaps than ears with large middle-ear volumes, > 4.3 ml (n = 39), except at 2,000 Hz. The mean air-bone gaps in ears with small volumes were 10 to 20 dB larger than in ears with large volumes. Perforations in anterior versus posterior quadrants showed no significant differences in air-bone gaps at any frequency, although anterior perforations had, on average, air-bone gaps that were smaller by 1 to 8 dB at lower frequencies. CONCLUSION: The conductive hearing loss resulting from a tympanic membrane perforation is frequency-dependent, with the largest losses occurring at the lowest sound frequencies; increases as size of the perforation increases; varies inversely with volume of the middle-ear and mastoid air space (losses are larger in ears with small volumes); and does not vary appreciably with location of the perforation. Effects of location, if any, are small.

How does the sound pressure generated by circumaural, supra-aural, and insert earphones differ for adult and infant ears?

OBJECTIVE: To determine how the ear canal sound pressure levels generated by circumaural, supra-aural, and insert earphones differ when coupled to the normal adult and infant ear. DESIGN: The ratio between the sound pressure generated in an adult ear and an infant ear was calculated for three types of earphones: a circumaural earphone (Natus Medical, ALGO with Flexicoupler), a supra-aural earphone (Telephonics, TDH-49 with MXAR cushion), and an insert earphone placed in the ear canal (Etymoup and down arrow tic Research, ER-3A). The calculations are based on (1) previously published measurements of ear canal impedances in adult and infant (ages 1, 3, 6, 12, and 24 months) ears (Keefe et al., 1993, Acoustic Society of America, 94:2617-2638), (2) measurements of the Thévenin equivalent for each earphone configuration, and (3) acoustic models of the ear canal and external ear. RESULTS: Sound-pressure levels depend on the ear canal location at which they are measured. For pressures at the earphone: (1) Circumaural and supra-aural earphones produce changes between infant and adult ears that are less than 3 dB at all frequencies, and (2) insert earphones produce infant pressures that are up to 15 dB greater than adult pressures. For pressures at the tympanic membrane: (1) Circumaural and supra-aural earphones produce infant pressures that are within 2 dB of adult ears at frequencies below 2000 Hz and that are 5 to 7 dB smaller in infant ears than adult ears above 2000 Hz, and (2) insert earphones produce pressures that are 5 to 8 dB larger in infant ears than adult ears across all audiometric frequencies. CONCLUSIONS: Sound pressures generated by all earphone types (circumaural, supra-aural, and insert) depend on the dimensions of the ear canal and on the impedance of the ear at the tympanic membrane (e.g., infant versus adult). Specific conclusions depend on the location along the ear canal at which the changes between adult and infant ears are referenced (i.e., the earphone output location or the tympanic membrane). With circumaural and supra-aural earphones, the relatively large volume of air within the cuff of the earphone dominates the acoustic load that these earphones must drive, and differences in sound pressure generated in infant and adult ears are generally smaller than those with the insert earphone in which the changes in ear canal dimensions and impedance at the tympanic membrane have a bigger effect on the load the earphone must drive.

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.