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

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↗