Comparison of studies on bone conduction thresholds and the HAIC interim standard for bone conduction audiometry.
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Air↗
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Bone-conducted auditory brainstem-evoked responses and skull vibratory velocity measurement in rats at frequencies of 0.5-30 kHz with a new giant magnetostrictive bone conduction transducer.
CONCLUSIONS: A new giant magnetostrictive bone conduction transducer (GMT) measuring 8 mm (length) by 2 mm (diameter) is capable of outputting sounds over a wider range of frequencies than conventional electromagnetic transducers (EMTs). The GMT can vibrate the rat skull about 3-100 times faster than the EMT, especially above 2 kHz. OBJECTIVES: Since the GMT can generate high sound quality and output sounds above 10 kHz, we investigated the width of the frequency response of the GMT and evaluated its mechanical performance. MATERIALS AND METHODS: We chose Wistar rats to estimate the GMT performance by measuring the bone-conducted ABR and the skull vibratory velocity because their hearing frequency range extends from 0.15 kHz to 67 kHz. We also measured the bone-conducted auditory brainstem responses (ABRs) and the skull vibratory velocity of rats with the EMT. Skull vibratory velocity was measured with a laser Doppler vibrometer (LDV). RESULTS: The skull vibratory velocity at the ABR threshold obtained with each transducer was within the -35 to -50 dB range (0 dB re 1 mm/s). When 1 Vpp was applied to each transducer, the GMT had a higher velocity at frequencies of 2-30 kHz, and the EMT at frequencies of 0.5-1 kHz.
Animals↗
Middle ear conduction deafness and bone conduction.
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Bone Conduction↗
Communicate with bone conduction.
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Bone Conduction↗
High-frequency air-conduction and electric bone-conduction audiometry. Comparison of two methods.
Threshold values for 147 subjects (9-43 years old) were measured with a high-frequency (HF) air-conduction (AC) (Interacoustics AS 10 HF) and an electric bone-conduction (EBC) (Audimax 500) audiometer. In addition, the reproducibility of these methods was studied in another group of 24 subjects. The results confirmed the previous findings of Okstad et al. (1988) that the electric current (i) used as a stimulus in the Audimax 500 audiometer can be converted into decibels with a correction factor of 40 log (i) re 1 mA as Tonndorf & Kurman (1984) have proposed. However, an additive frequency-dependent correction is needed to obtain similar loudness sensation increases with these audiometers. Reproducibility with the EBC audiometer was better than with the AC audiometer, especially in the HF range.
Adult↗
Quantifying air-conducted acoustic radiation from the bone-conduction vibrator.
Sound pressure levels in the external auditory canals of 50 subjects were measured at 2000 and 4000 Hz with a bone-conduction vibrator on the forehead, the mastoid ipsilateral to the probe microphone, and the mastoid contralateral to the probe microphone. A plug was placed in the external auditory canal to minimize sound pressure levels in the external auditory canal produced by the osseotympanic mode of bone conduction. Results suggest that clinically significant false air-bone gaps (greater than 10 dB) due to acoustic radiation into the concha from the bone-conduction vibrator are most likely to occur at 4000 Hz when the bone-conduction vibrator is placed on the mastoid of the test ear. To minimize the possible confounding effects of acoustic radiation, the bone-conduction vibrator may be placed on the forehead or the mastoid contralateral to the test ear while masking the nontest ear.
Acoustics↗
High-frequency air-conduction and electric bone-conduction audiometry. Age and sex variations.
208 subjects representing both sexes and five age groups (15-70 years) were examined to obtain age-related threshold values for high-frequency (HF) electric bone-conduction (EBC) audiometry. The measurements also included conventional pure-tone audiometry and air-conduction (AC) HF (8-18 kHz) audiometry. The measured EBC thresholds were comparable to the values obtained with AC audiometers, and were equal to ISO standards at the frequencies of 0.5-6 kHz. The 15- and 20-year-old groups' EBC thresholds at 8 kHz were equivalent to thresholds of 15-year-old people from a cross-sectional material in Northern Finland. Thresholds deteriorated as a function of age, particularly in the HF range. The males had poorer thresholds than the females, especially in the age groups of 40 and 60 years. This could be attributed mainly to their greater noise exposure. The EBC method is quite practical and reliable for routine clinical measurements, but the dynamic range of the audiometer limits its use to relatively young subjects.
Adolescent↗
Force threshold for hearing by direct bone conduction.
The bone-anchored hearing aid is connected, by means of a skin-penetrating bayonet coupling, to an implanted titanium fixture. Hence, direct bone conduction (dbc) excitation is used. Since no international standard of audiometric zero for dbc force threshold exists, it is of general interest to determine the dbc force threshold for normal hearing subjects. Two different methods have previously been applied to estimate the relation between bone conduction (bc) and dbc thresholds. One preliminary problem was to make a measurement of the output-force level of dbc transducers, which is equivalent to the situation in situ. A skull simulator, TU-1000, has been designed for measuring the output-force level of dbc transducers. The skull simulator does, in an adequate way, reflect the mechanical point impedance of the human skull. This opportunity to determine equivalent dbc force thresholds has motivated the present study in which a linear relation between the dbc force threshold and the bc force threshold was estimated. The estimate found in the present study conforms fairly well with the two previously found estimates. It is suggested that the estimate found in the present study be used as the reference equivalent threshold force level for dbc.
Adolescent↗
A comparison of auditory brain stem response thresholds and latencies elicited by air- and bone-conducted stimuli.
Auditory brain stem responses (ABRs) were measured for stimuli presented both by air conduction and by bone conduction. Stimuli included clicks and tone bursts at octave frequencies from 250 to 4000 Hz. ABR thresholds were comparable for air- and bone-conducted stimuli. Wave V latencies were longer for bone-conducted stimuli compared to similar responses for air conduction. This effect was evident for both clicks and tone bursts. The fact that these latency differences were largely independent of stimulus spectrum suggests that they are not due to differences between the frequency responses of air and bone conduction transducers. This finding is expected when one considers the interaction between output, threshold, and frequency for both transducer types. These data also suggest that there are inherent differences in transmission by air and bone conduction that affect response latency but are unrelated to the amplitude spectrum in the signal.
Acoustic Stimulation↗
Auditory brain stem evoked responses to bone-conducted signals.
Auditory brain stem evoked responses to air-conducted and bone-conducted signals were recorded in subjects with normal hearing and in subjects with conductive hearing loss. In normal subjects, the latency to wave V for bone-conducted signals was approximately 0.5 ms longer than the latency for air-conducted signals delivered at the same sensation level. In conductive hearing loss, the separation of the latency-intensity functions for air conduction and bone conduction (corrected for the 0.5-ms delay) provided a valid estimate of the behavioral air-bone gap in the 1,000- to 4,000-Hz region.
Audiometry, Evoked Response↗
Bone conduction experiments in humans - a fluid pathway from bone to ear.
Animal experiments in this laboratory have led to the suggestion that a major pathway in bone conduction stimulation to the inner ear is via the skull contents (brain and CSF). This hypothesis was now tested in humans. Auditory nerve brainstem evoked responses could be recorded in neonates to bone conduction stimulation over the fontanelle and audiometric responses were obtained in neurosurgical patients with the bone vibrator on the skin over a craniotomy. There were no differences in threshold between these responses and those obtained to bone conduction stimulation over skull bone in the same subjects. Audiometric thresholds in response to bone vibrator stimulation of the eye (a 'natural craniotomy') were no different from those to bone stimulation delivered to several sites on the head. Thus there is no need to vibrate bone in order to obtain 'bone conduction' responses. Bone vibrator thresholds to stimulation at the head region with thinnest bone (temporal) were better than those to stimulation at the forehead region which has much thicker bone, implying that the vibrations penetrate the skull at the site of the vibrator. In addition, the magnitude of vibration (acceleration) measured at various sites around the head in response to bone vibrator stimulation at a fixed point on the forehead generally decreased with distance from the point of vibration. Therefore it seems that the vibrations produced by a bone vibrator at a point on the head are also able to penetrate the skull, setting up audio-frequency pressures in the CSF which spread by fluid communications to the inner ear fluids, exciting the ear.
Adolescent↗
The masked threshold to noise ratio in brainstem electric response audiometry: assessment of the conductive loss component by bone-conducted masking.
The aim of this study was to assess the conductive loss component (CLC) by brainstem electric response audiometry. A bone-conducted noise was used to mask out the response to a conventional air-conducted click stimulus. The difference between the levels of the click and the noise is defined as the masked threshold to noise ratio (MTNR). This MTNR was determined for 21 normal ears (MTNR = -13 +/- 5 dB). The increase in MTNR compared to this normative value is a measure of the CLC. For 10 ears with an artificially induced purely conductive loss, the increase in MTNR is in good agreement with the results of conventional pure-tone and brainstem electric response audiometry.
Acoustic Stimulation↗
Bone conduction threshold levels for different bone vibrator types.
This study determined if bone conduction (BC) thresholds were influenced by vibrator type. BC thresholds were obtained for 100 subjects using mastoid placement of Radioear B-71 and B-72 and Pracitronic KH 70 bone vibrators. The nontest ear was masked (30 dB EL) and the ear ipsilateral to the vibrator was open except when testing at 3000 and 4000 Hz when the ear canal was occluded with an earplug to guard against acoustic radiation. BC thresholds at 250 Hz obtained with the B-72 and KH 70 were significantly (p less than .05) higher by 10.5 dB and at 500 Hz were significantly (p less than .05) lower by 5.5 dB than for the B-71. BC thresholds at other frequencies (1000, 2000, 3000, and 4000 Hz) were not significantly different among vibrator types. The findings indicated that reference equivalent threshold force levels (RETFLs) for BC audiometry should be specified by bone vibrator type.
Adult↗
Aided free-field thresholds in children with conductive hearing loss fitted with air- or bone-conduction hearing aids.
Although conductive hearing loss is often found in children, few reports have appeared on the fitting of hearing aids in these children. In the present study, aided thresholds were determined in 40 children and 30 adults with pure conductive hearing loss (bone-conduction thresholds of 20 dB HL or less) who were successfully fitted with hearing aids. The patient group was split into subgroups according to the type of hearing aid used (bone-conduction hearing aid, binaural or monaural air-conduction hearing aids). Within each subgroup, the aided thresholds proved to be comparable between the adults and children and were nonconsistently related to the degree of (air-conduction) hearing loss. In the patients with a bone-conduction hearing aid, the aided free-field thresholds at the most important frequencies for speech perception (1, 2 and 4 kHz) were found to be between 20 and 30 dB HL, while in the patients with an air-conduction hearing aid, irrespective of whether it was applied monaurally or binaurally, these thresholds were between 15 and 20 dB HL. It is suggested that these values should be considered as target thresholds when fitting hearing aids in children with conductive hearing loss.
Adolescent↗
High-frequency audiometry. Masking of air- and bone-conduction signals.
Interaural attenuation has been investigated for both air-conduction and bone-conduction signals in the frequency ranges 0.25-18 and 0.25-16 kHz respectively. Ear canal occlusion is recommended when using the Koss HV/1A earphone for BC masking, as acoustic transmission occurs through the headset in the high-frequency range. Minimum masking levels for 1/3-octave filtered white noise were established for bone-conduction signals in the frequency range 8-16 kHz. Central masking of bone-conduction signals proved to be of the same order of magnitude in the conventional- and high-frequency ranges, while the cross-masking level was approximately 10-15 dB lower above 6 kHz. Recommendations are made for a masking procedure in the high frequency range.
Acoustic Stimulation↗
The balanced electromagnetic separation transducer a new bone conduction transducer.
Conventional bone conduction transducers, which are relatively large, suffer from poor performance at low frequencies. A new type of electro-dynamic transducer, the balanced electromagnetic separation transducer (BEST), was developed to improve the performance of the conventional transducers. By using a balanced suspension principle, the quadratic distortion forces, as well as the static forces between the vibrating parts, are principally counterbalanced. Both the distortion and the size of the transducer can therefore be considerably reduced. Moreover, the static and dynamic magnetic fluxes are separated, except in the air gap regions, giving a more efficient transducer. For example, in comparison with a conventional B71 transducer, a prototype of the BEST has: Lower total harmonic distortion (THD), by 20-25 dB, and improved sensitivity by 10-20 dB for 100 to 1000 Hz and by 2-10 dB for 1 to 10 kHz. From a clinical point of view, the BEST offers a chance to measure bone thresholds, at 250 and 500 Hz, which are reliable at hearing levels not possible before. For example, at 250 Hz the BEST has 23 dB higher sensitivity than the B71; the THD is improved from 61% (B71) to 3.3% (BEST) at 40 dB HL (ISO 389-3, 1994).
Audiometry, Pure-Tone↗
[Otoacoustic emission cochleogram evoked by bone conducted stimulation].
As bone conducted stimulation, tone bursts of different frequencies were applied through the forehead in 7 normal-hearing subjects. Binaural evoked otoacoustic emissions (EOAE) were then recorded simultaneously, which saved one half of the time required for conventional monaural recording. Analysed with autoregressive modeling, the main echo of EOAE was a narrow-band sound with a stimulus dependent central frequency. It was suggested that the generation site of EOAE was near to that cochlear portion stimulated by the corresponding frequency. The latency of EOAE, although independent of the stimulus intensity, tended to be shorter at higher stimulus frequencies. This was possibly due to the differences in the distances from the generation sites of the otoacoustic emissions to the tympanic membrane. Recordable otoacoustic emissions were evoked by tone bursts of 1.0, 2.0, 3.0 and 4.0 kHz in all the 14 normal ears except one at 4.0 kHz, and 10 and 7 ears by tone bursts of 0.5 and 6.0 kHz, respectively. Emission cochleogram was obtained when the means of EOAE detection thresholds were plotted in an audiogram format. The lowest threshold was found at 1.0 kHz. This might be related to the middle ear resonance frequency of 1100 +/- 230 Hz. The technique of simultaneous recording of binaural EOAE and plotting of emission cochleogram described in this paper is clinically useful as a means of objective evaluation of hearing.
Adult↗
Binaural interaction of bone-conducted auditory brainstem responses.
Bone-conducted auditory brainstem responses (ABRs) elicited by monoaural stimulation are very useful for evaluating hearing in children with congenital atresia of both ears. In a previous study of sound lateralization in children with congenital atresia of both ears, using bilateral bone-conducted stimuli, we found that most of the children could sufficiently retain binaural hearing ability in terms of both intensity and time differences. In this study we attempted to record bilateral bone-conducted ABRs in normal subjects in order to explore binaural interaction objectively. The study revealed that binaural interaction exists in bone-conducted ABRs. This can be taken as neurophysiological evidence that sound lateralization can be detected by children with bilateral microtia and atresia.
Adult↗