A comparison of ear-canal-reflectance measurement methods in an ear simulator.

Ear-canal reflectance has been researched extensively for diagnosing conductive hearing disorders and compensating for the ear-canal acoustics in non-invasive measurements of the auditory system. Little emphasis, however, has been placed on assessing measurement accuracy and variability. In this paper, a number of ear-canal-reflectance measurement methods reported in the literature are utilized and compared. Measurement variation seems to arise chiefly from three factors: the residual ear-canal length, the ear-probe insertion angle, and the measurement frequency bandwidth. Calculation of the ear-canal reflectance from the measured ear-canal impedance requires estimating the ear-canal characteristic impedance in situ. The variability in ear-canal estimated characteristic impedance and reflectance due to these principal factors is assessed in an idealized controlled setup using a uniform occluded-ear simulator. In addition, the influence of this measurement variability on reflectance-based methods for calibrating stimulus levels is evaluated and, by operating the condenser microphone of the occluded-ear simulator as an electro-static speaker, the variability in estimating the emitted pressure from the ear is determined. The various measurement methods differ widely in their robustness to variations in the three principal factors influencing the accuracy and variability of ear-canal reflectance.

An anti-barotrauma system for preventing barotrauma during hyperbaric oxygen therapy.

In the present study, a tympanometry-based anti-barotrauma (ABT) device was designed using eardrum admittance measurements to develop an objective method of preventing barotrauma that occurs during hyperbaric oxygen (HBO2) therapy. The middle ear space requires active equalization, and barotrauma of these tissues during HBO2therapy constitutes the most common treatment-associated injury. Decongestant nasal sprays and nasal steroids are used, but their efficacy is questionable to prevent middle ear barotrauma (MEB) during HBO2 treatment. Accordingly, a tympanometry-based ABT device was designed using eardrum admittance measurements to develop an objective method for preventing MEB, which causes pain and injury, and represents one of the principal reasons for patients to stop treatment. This study was conducted to test a novel technology that can be used to measure transmembrane pressures, and provide chamber attendants with real-time feedback regarding the patient's equalization status prior to the onset of pain or injury. Eardrum admittance values were measured according to pressure changes inside a hyperbaric oxygen chamber while the system was fitted to the subject. When the pressure increased to above 200 daPa, eardrum admittance decreased to 16.255% of prepressurization levels. After pressure equalization was achieved, eardrum admittance recovered to 95.595% of prepressurization levels. A one-way repeated measures analysis of variance contrast test was performed on eardrum admittance before pressurization versus during pressurization, and before pressurization versus after pressure equalization. The analysis revealed significant differences at all points during pressurization (P⟨0.001), but no significant difference after pressure equalization was achieved. This ABT device can provide objective feedback reflecting eardrum condition to the patient and the chamber operator during HBO2 therapy.

Cribado auditivo mediante potenciales evocados auditivos de estado estable obtenidos por estimulación simultánea de la vía aérea y la ósea / Hearing screening using auditory steady state responses obtained by simultaneous air- and bone-conduction stimuli

Introducción y objetivos: Minimizar los falsos positivos constituye un objetivo de los programas de cribado auditivo universal. Una manera de lograrlo sería diferenciar entre los trastornos neurosensoriales (verdaderos positivos) y los conductivos transitorios (falsos positivos) mediante un método que permita estudiar la respuesta del sistema auditivo ante la estimulación tanto por vía aérea como por vía ósea. El objetivo de este trabajo es evaluar la eficiencia diagnóstica de una prueba automatizada de cribado basada en el registro de potenciales evocados auditivos de estado estable obtenidos por estimulación simultánea de vía aérea y vía ósea. Métodos: Se estudiaron 80 bebés menores de 2 meses de edad. A todos se les realizó la prueba de cribado, siendo posteriormente citados para el estudio confirmatorio, cuyo resultado se consideró como criterio de verdad del estado audiológico del bebé. Resultados: Con esta prueba se obtuvo una eficiencia diagnóstica equivalente (un 100% de sensibilidad y un 97,7% de especificidad) a la reportada para otras pruebas utilizadas en el cribado (emisiones otoacústicas y potenciales evocados de tronco cerebral), con la ventaja adicional de que la introducción de la vía ósea en el cribado permitió reducir la cifra de falsos positivos del 13,3 al 2,2%. La duración de la prueba fue de 5,3 (± 1,9) min, siendo suficiente en el 34% de los casos una sola repetición para llegar al resultado. Conclusiones: Esta prueba automatizada de cribado basada en el registro de potenciales evocados auditivos de estado estable permitió discriminar entre los trastornos conductivos transitorios y los neurosensoriales, reduciendo así los falsos positivos y elevando la eficiencia diagnóstica de esta metodología (AU)

Introduction and objectives: Minimising false positives rates is an important goal of universal newborn hearing screening programmes. An adequate way for reaching that goal could be differentiating between transient conductive hearing losses (false positives) and permanent sensorineural hearing impairments (true positives) by means of a methodology that studies electrophysiological responses obtained using both air- and bone-conduction stimuli. Our objective was to evaluate the efficiency of an automated hearing screening test based on auditory steady state responses obtained using simultaneous air- and bone-conduction stimuli. Methods: A sample of 80 high risk babies lees than 2 months of born were screened using the automatic screening test. A confirmatory clinical and electrophysiological evaluation was used as the gold standard. Results: The estimated diagnostic efficiency of this screening test was equivalent (100% sensitivity and 97.7% specificity) to the efficiency reported for otoacoustic emissions and automated auditory brainstem responses. The introduction of bone conduction in the screening reduced the false positive rate from 13.3% to 2.2%. The test duration was 5.3 (± 1.9) min. In 34% of babies only one repetition of the test was needed to raising the result. Conclusions: The screening test performed quite well in this initial clinical trial, differentiating transient conductive hearing losses from permanent neurosensory impairments and improving the diagnostic efficiency of auditory steady state responses (AU)

Choice of probe tone and classification of trace patterns in tympanometry undertaken in early infancy.

Tympanometry using 226 Hz, 678 Hz, and 1000 Hz probe tones was undertaken on two groups of babies, age 2 to 21 weeks. A group of 104 babies with normal ABR thresholds or TEOAEs were compared with a second group of 107 babies who had evidence of temporary conductive hearing loss based on the findings of a test battery, which included air and bone conduction ABR. The tympanograms were classified by Method 1, a simple visual classification system, and Method 2, adapted from a system described by Marchant et al (1986). The majority of tympanograms recorded in both groups using the 226 Hz probe tone were 'normal' Type A, with no significant difference in middle ear pressure or static admittance. However, both classification methods demonstrated significant differences between the two groups using the higher frequency probe tones, with Method 2 being the preferred system of classification. Tympanometry using 226 Hz is invalid below 21 weeks and 1000 Hz is the frequency of choice.

Normative multifrequency tympanometry in infants and toddlers.

Multifrequency tympanometry data were measured multiple times between the ages of four weeks and two years from 33 infants/toddlers. Tympanograms were also measured from 33 adult participants. Tympanograms recorded with five probe-tone frequencies (226, 400, 630, 800, and 1000 Hz) were classified using the Vanhuyse et al model classification system (Vanhuyse et al, 1975). Admittance at +200 daPa (Y200) and middle ear admittance (Y(ME)) were calculated. The proportion of Vanhuyse et al patterns in infants and toddlers was different than in adults, especially for younger ages. Y(ME) and Y200 both increased with age. Y(ME) and Y200 data for all infant/toddler groups were significantly lower than adult values at all of the tested probe-tone frequencies. These data can be used as a guide in the clinic to assess normal tympanometric values for infants and toddlers.

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.

[Noninvasive assessment of intracochlear pressure and patency of the cochlear aqueduct in normal probands with TMD (tympanic membrane displacement) analysis]. / Nicht-invasive Beurteilung des intracochleären Druckes und der Durchgängigkeit des Aquaeductus cochleae bei Normalpersonen mittels TMD-Analyse.

The intracochlear pressure cannot yet be evaluated in patients with certain audiological neuro-otological diseases. However, it seems to be of importance in the diagnosis and pathogenesis of Ménière's disease and related disorders. The present paper is aimed at introducing a setup to indirectly assess intracochlear and intracranial pressure changes and the design and philosophy of this technique. It is possible to describe a normal range of the measured values in healthy controls although large interindividual variations occur. In addition, the positional changes of the registered parameters enable assessment of the patency of the cochlear aquaeduct. This seems to be important in some diseases, such as stapes gusher.

Coupler-related real ear gain. Interaction between subject and hearing aid type.

In order to select hearing aids with a highly predictable real ear gain, in situ gain and compliance through the individual ear mould were measured on 8 normal-hearing subjects. The latter were chosen in order to reduce gain variation caused by various pathological conditions of the ear. All behind-the-ear aids commonly used in Sweden and one in-the-ear aid were studied. One sample of each hearing aid type was tested and the subjects had identical ear moulds. Hence, the variables were hearing aid type and subject. The study showed wide intra-subject coupler-related real ear gain variation (30 dB). Most of the aids showed a distinct correlation between coupler-related overall gain, and mould compliance. Some of the aids gave more uniform real ear gain, i.e. low interaction between subject and frequency-dependent gain. These results are elucidated by measuring the aid's acoustic output impedance.

Daily impedance audiometric screening of children. Validity of impedance tympanoscope ZS331 compared with impedance audiometer AZ7.

The purpose of the present study was to test a fully automated screening impedance tympanoscope against a clinical impedance audiometer. Previous studies have indicated a relatively high incidence of type B tympanograms when using the tympanoscope and in addition shown a surprisingly large number of type B curves of one day's duration. The present study was based on 51 otherwise healthy children attending kindergartens (100 ears) who underwent daily tympanometric screening with both the impedance tympanoscope ZS331 and the impedance audiometer AZ7. The tympanoscope indicated a significantly larger number of type B tympanograms, and in 16 cases the type B curves could be demonstrated on only one day, resulting in significantly higher point and period prevalences of type B tympanograms. The difference is mainly attributable to the different ways in which a type B tympanogram is defined by the two instruments. On the basis of the present study we conclude that the impedance tympanoscope is not well suited for this type of study.

Sweep-frequency tympanometry: its development and diagnostic value.

This reports a newly developed tympanometric system using a sweep-frequency probe tone. For a sweep-frequency tone ranging from 220 to 2 000 Hz, measurements of sound pressure (P) and phase were performed at ear canal pressures of 0 and -200 mm H2O. The results were expressed as a sound pressure curve (P0-P-200 in decibels), a phase curve (formula: see text) and a polar curve (formula: see text) against probe tone frequency. Both the frequency at which the sound pressure curve crossed the 0-dB difference line and the peak frequency of the phase curve shifted lower than normal for ossicular disruption and higher than normal for ossicular fixation. Changes in the sound pressure curve and in the phase curve were exaggerated for ossicular disruption and limited for fixation. As the result of these, the polar curve showed an expanded type for disruption and a compressed type for fixation. A review of 220-Hz tympanograms and of the polar curves for 10 patients demonstrated that the latter permitted a better discrimination among ossicular disorders.

Real-ear calibration of ipsilateral acoustic reflex stimuli from five types of impedance meter.

The Hearing Level scale has been established in national and international standards for tones presented via supra-aural earphones. However, the standards do not encompass stimuli from the probes of ipsilateral impedance meters. This study transfers the calibration of standardised earphones to the probes of five types of impedance meter and therefore enables the intensities of their ipsilateral stimuli to be defined in terms of Hearing Levels. The method used for transfer of calibration is based on equality of acoustic reflex responses elicitied by the impedance meter probe and by a standardised earphone. Ten subjects were tested with all five instruments to ensure comparability between instruments. The resultant calibration data are expressed in terms of Reference Equivalent Threshold Sound Pressure Levels measured in both 2 cc and Zwislocki couplers. The results indicate a considerable variation amongst instruments emphasising the need for a set of calibration data for each design of probe. This variation is less marked for the Zwislock coupler than for the 2 cc coupler.

Comments on the acoustic-reflex response for bone-conducted signals.

Previous studies which have measured acoustic-reflex responses to bone-conducted signals have not effectively differentiated reflex responses from artifacts. A convenient method for identifying such artifacts was developed and employed on some acoustic-reflex measures for bone-conducted signals. The findings indicated that artifacts result when a frequently-used acoustic admittance meter (Grason-Stadler 1720B) and a conventional bone vibrator were used to measure reflex responses for tonal and noise-activating signals. It was suggested that the method be employed in future studies which investigate the acoustic reflex in response to bone-conducted signals.

Bone-conducted stimulation in electrocochleography.

The mechanical vibration patterns close to the cochlea in intact skulls of human cadavers have been studied by means of a miniature accelerometer. A Radioear B70A vibrator and a Brüel & Kjaer Mini Shaker have been used, fed with filtered clicks and with short tone bursts. The tone bursts were found to be superior to the clicks with regard to the vibration spectrum. At 500 Hz a considerable distortion was observed in the accelerometer signal, also when using tone bursts. This distortion was presumably due to resonant vibrations in the skull itself, and may be a source of error not only when using stimuli of short duration as in bone-conduction ECoG but also in conventional bone-conduction audiometry. When the vibrations were applied to the exposed bone surface of the mastoid, vibration levels increased by 10-25 dB compared with when soft tissues covered the point of application. This could be of advantage in bone-conduction ECoG performed at ear surgery.

Tympanometric asymmetry.

Tympanometric asymmetry was investigated in 17 normal adult subjects. Experimental variables included transmission quantity, probe frequency, direction of pressure change, and type of probe tip. Tympanograms were characterized by systematic asymmetries that appeared to be related predominantly to middle-ear effects, although ear canal effects probably contributed to the asymmetries as well. Implications for the standardization of measurement procedures are discussed.