Otoacoustic emissions of distortion products (DPOAE's) were recorded in normal and hearing-impaired human ears using relatively straightforward methods. Two pure-tone stimuli at fixed frequency levels of 73 dB HL for f1 and of 67 dB HL for f2 were used. The frequencies of the two primaries were chosen so that their geometric mean represented standard audiometric frequencies. Measurements of the emission amplitudes at 2f1-f2 and the adjacent noise floor were achieved by spectral averaging. A total of 101 subjects (199 ears) were tested. Seventy-seven ears in 46 subjects had normal hearing (hearing levels less than or equal to 20 dB at standard audiometric frequencies; average hearing levels, less than or equal to 10 dB). Thirty-six ears in 25 subjects had near-normal hearing (no hearing complaints, hearing levels less than or equal to 40 dB; average hearing levels, less than or equal to 20 dB). No significant differences in mean DPOAE values were apparent between these two groups of ears. All but two of these 113 ears (98%) showed emissions at three or more of the six frequencies tested between 1 and 6 kHz. Emissions were detected in more than 75% at each frequency between 1 and 6 kHz and in more than 85% between 1 and 4 kHz. A further 86 ears in 44 subjects exhibited varying degrees of sensorineural hearing loss caused by different pathologies. In general, emission amplitudes approximated the shapes of the audiograms, and a highly significant correlation between hearing thresholds and emission amplitudes was demonstrated in the frequency range of 1 to 4 kHz.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗

PubMedDate not supplied

Otoacoustic emissions in ears with hearing loss.

Fifty ears of 37 patients demonstrating several common types of hearing impairment were examined for the presence of spontaneous and evoked otoacoustic emissions to investigate the relationship of acoustic emissions to hearing pathology. Of the 50 ears, 44 exhibited various degrees of sensorineural hearing loss. Evoked otoacoustic emissions to clicks were detected in 34 of 35 sensorineural hearing loss ears with a subjective click threshold less than 55 dB SPL (25 dB nHL). None of nine ears with sensorineural hearing impairment and a subjective click threshold greater than 55 dB SPL demonstrated click-evoked emissions. Spectral analyses revealed that the constituent frequency components of evoked emissions were always within the frequency range where audiometric thresholds were less than 35 dB HL, and in the majority (94%) of cases, thresholds were less than 25 dB HL. In ears with relatively well-preserved hearing within the frequency range of click or 1.5-kHz toneburst stimuli, the basic features of evoked emissions were similar to those described for normal ears. Similarly, for ears demonstrating spontaneous otoacoustic emissions, estimated audiometric thresholds at the emitted frequencies were always less than 20 dB HL. The influence of the type of otologic pathology on acoustic emissions was studied in a subset of ears exhibiting typical high-frequency hearing losses. Ears with a noise-induced impairment showed a significant reduction in the incidence of both spontaneous emissions and spectral peaks in evoked emissions that was not evident in ears with similar patterns of hearing loss caused by other factors.

Acoustic Stimulation↗

PubMedDate not supplied

Intracochlear acoustic pressure measurements: transfer functions of the middle ear and cochlear mechanics.

Direct intracochlear acoustic pressure recordings (from 20 to 20,000 Hz) are used to measure the middle-ear transfer functions (forward and reverse) and to better understand the cochlear mechanics in the guinea pig. In the forward direction, the middle-ear transfer function is strongly dependent on the frequency and presents a maximum of +30 dB at 1,000 Hz (bulla open). In the reverse direction, the middle-ear transfer function looks like an ideal reverse middle-ear pressure transformer with -35 dB gain and 0 degrees phase lag from 20 to 8,000 Hz (bulla open, closed ear canal). Passive cochlear mechanics is studied with the help of intracochlear pressure measurements and differential cochlear microphonic potential recordings in the different turns.

Acoustic Stimulation↗

PubMedDate not supplied

Investigation of the nasopharyngeal bacterial flora in children with otitis media with effusion.

Explore the source record for details and available documents.

Child↗

PubMedDate not supplied

Acute acoustic trauma. A retrospective study of influencing factors and different therapies in 268 patients.

The files of 268 patients with acute acoustic trauma acquired during military service were analysed in a retrospective study. The following factors were examined: age, profession, degree of hearing loss, audiometric contour, and drug treatment. No influence of age or profession on recovery of hearing loss could be detected. The absolute hearing gain, defined as the difference between the hearing loss at onset and, on average, 7 days later, was dependent on the degree of initial hearing loss. The relative hearing gain, defined as absolute hearing gain divided by initial hearing loss, was independent of the degree of initial injury. The audiometric contour after the acoustic trauma had no prognostic relevance. Nine different types of drug treatment were compared in a subgroup of patients (n=199), in all of whom treatment was started within 2 days of the acoustic trauma. There were no significant differences in relative hearing gain between the nine types of treatment. Patients receiving early treatment had significantly better hearing one week after the acoustic trauma, as compared with the group of patients (n=69) not receiving treatment during the first 7 days. However, it was not possible to determine retrospectively whether this difference was due to treatment effects, or whether it was due to the exclusion of spontaneous remissions among those who were neither examined nor treated within the first 7 days.

Adult↗

PubMedDate not supplied

Repeatability of distortion product otoacoustic emissions in normally hearing humans.

Distortion product otoacoustic emissions (DPOAEs) at the frequency of 2f1-f2 were measured in one or both ears of 12 young adults during 4 test sessions over a 6-week period. The purpose was to determine the variability in DPOAE amplitudes and 'detection thresholds' over repeated measurements using a computer-based time-averaging system. DPOAEs were generated with f1 and f2 relative to (f1f2)1/2 in two basic paradigms: (a) fixed levels of L1 = L2 of 70 and 55 dB SPL over a stimulus range from 0.8 to 8 kHz in 0.2-octave intervals; (b) input-output functions in stimulus regions of 0.8, 1, 1.5, 2, 3, 4 and 6 kHz, L1 from 35 to 70 dB SPL changing in 5-dB steps and L2 at 6 dB below the amplitude of L1. The mean variability of DPOAE amplitudes with equilevel stimuli was 1.8 dB (SD = 1.8) for L1 = 70 dB SPL and 2.9 dB (SD = 2.7) for L1 = 55 dB SPL. It was 1.7 dB (SD = 1.7) and 2.4 dB (SD = 2.0) for comparable levels of L1 with L2 at 6 dB below L1. Variability in amplitude of the DPOAEs for the fixed-level condition was greatest overall above 6 kHz and below 1 kHz and in the 2-kHz region for one third of the subjects. Neither individual differences in emission amplitudes nor the presence of spontaneous otoacoustic emissions had a significant influence on the amount of amplitude variability within ears. Variability was not influenced by the length of time between measurements from 1 to 6 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗

PubMedDate not supplied

Intensity discrimination, temporal integration and gap detection by normally-hearing subjects with weak and strong otoacoustic emissions.

It is unlikely that the overall status of a cochlea and middle ear which produces strong otoacoustic emissions (OAEs), i.e. high-level evoked emissions (EOAEs) and spontaneous emissions (SOAEs), has a generalized effect on peripheral auditory processing if the sensitivity is normal. Current data do not support the hypothesis that a weak OAE profile (low-level EOAEs and no SOAEs) is indicative of subclinical damage to the cochlea. Nevertheless, the ability of a subject to perform some psychoacoustical tasks may be influenced by the interaction between OAEs and test signals. The present experiments investigated the influence of strong or weak OAEs on: (1) intensity just-noticeable differences for pure tones; (2) temporal integration in the vicinity of SOAEs; (3) gap detection thresholds for broad-band noise bursts. The results show that OAEs can influence performance on these psychoacoustical tasks, especially for low-level stimuli with spectral components in the vicinity of high-level SOAEs.

Audiometry, Pure-Tone↗