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Biomedical subjects

M B Meikle

Publications and source records attributed to M B Meikle.

13 recordsLinked to original sources
PubMed2000

Psychoacoustic measures of tinnitus.

This report reviews research from the 1930s to the present that has extended our understanding by investigating the characteristics of tinnitus that can be studied using psychoacoustic techniques. Studies of tinnitus masking and residual inhibition began in the 1970s, leading to the therapeutic use of tinnitus masking and a consequent increase in research devoted to tinnitus measurement. In 1981, the CIBA Foundation symposium on tinnitus advocated general adoption of four tinnitus measures: (1) pitch, (2) loudness, (3) maskability, and (4) residual inhibition. Since then, psychoacoustic research into all four topics has proliferated, yielding many valuable insights and controversies concerning the details of measurement techniques. A consensus has emerged that neither the loudness nor other psychoacoustic measures of tinnitus bear a consistent relation to the severity or perceived loudness of tinnitus. Nevertheless, quantification is needed in clinical trials of proposed treatments and in a variety of other types of tinnitus research. Standardization of techniques for specifying the acoustic parameters of tinnitus thus continues to be an important research goal.

Humans↗
PubMed1999

Tinnitus severity, loudness, and depression.

Answers to questionnaires filled out by 436 patients who visited our tinnitus clinic were analyzed. Patients were asked to report the presence or absence of depression and to rate the loudness and severity of their tinnitus. Responses to questions about tinnitus loudness and severity from 121 patients who reported current depression were compared with responses from 285 patients who reported no history of depression. There was no significant difference in reported loudness of tinnitus between patients with and without depression. However, patients with current depression scored significantly higher than patients without depression on all 12 questions relating to tinnitus severity. We conclude that depression and tinnitus severity are linked in some patients. Treatment of depression with medications and psychotherapy is likely to reduce tinnitus severity for many of these patients.

Depression↗
PubMed1999

Pulsed versus continuous tones for evaluating the loudness of tinnitus.

Loudness balance techniques are commonly employed to match the loudness of tinnitus using either pulsed or continuous tones; however, it is not known whether the tone duration affects the observed loudness matches. In this study, hearing thresholds and tinnitus loudness matches were measured in 26 subjects with chronic tinnitus using both pulsed and continuous tones. Subjects' thresholds and loudness matches were determined at 11 frequencies between 0.5 and 10 kHz. No significant differences were found between pulsed versus continuous measures, either for thresholds or for loudness matches. There were, however, nine subjects (34.5% of the group) who showed relatively large differences (> or =10 dB) at one or more test frequencies. These "outlier" values did not show systematic trends; some were positive, some negative. In conclusion, studies employing group data appear to be comparable if group sizes are sufficiently large (e.g., > or =25 subjects). Studies employing smaller numbers of subjects may, however, be vulnerable to potential positive or negative biases introduced by one or more outliers.

Adult↗
PubMed1997

Electronic access to tinnitus data: the Oregon Tinnitus Data Archive.

The recently published Oregon Tinnitus Data Archive can be viewed by anyone with Internet access and World Wide Web browser software. A dynamically changing document to be amplified and upgraded in future versions, at present the Archive summarizes records from 1630 patients with tinnitus seen between 1982 and 1992 at the Tinnitus Clinic of the Oregon Health Sciences University. The Archive has many features of standard journal publications but also has added advantages of extensive appendixes and other background information, as well as the ease of use and flexibility offered by hypertext documents. The data in the Archive can be used for a variety of clinical and research purposes such as development of prevalence estimates for medical conditions or etiologic circumstances associated with tinnitus, testing of clinical impressions and other hypotheses, and efforts to identify risk factors and possible causal agents for tinnitus.

Computer Communication Networks↗
PubMed1984

The perceived severity of tinnitus. Some observations concerning a large population of tinnitus clinic patients.

Detailed information about tinnitus was obtained from over 1800 patients attending a tinnitus clinic. Patients rated their tinnitus severity on a scale from 1 to 10 and also provided information concerning the quality, duration, localization, and other attributes of their tinnitus. In addition to standard audiometric tests, patients received tests for tinnitus pitch, loudness, maskability, and residual inhibition, and provided a brief medical history. The severity ratings of over 90% were at or above the scale value of 5. There was no correlation between rated severity and the loudness of tinnitus (obtained by a loudness balance procedure using external sounds matching the tinnitus pitch), thus confirming earlier observations. The severity also was not related to the type, quality, or pitch of tinnitus sound heard. However, severity ratings were highly correlated with incidence of sleep disturbance. Additional observations concerning relationships between perceived severity and other patient characteristics are discussed.

Acoustic Impedance Tests↗
PubMed1981

Tinnitus masking:unresolved problems.

With care to provide properly chosen masking sounds, masking can help in 60-80% of clinically significant tinnitus cases. There is no universal masker; instead, an individual evaluation of each patient's tinnitus must be performed in order to match the masking sounds to the patient's audiogram and the spectral characteristics of the tinnitus. Successful long-term masking can usually be achieved in patients for whom (1) hearing impairment is not excessive. (2) the tinnitus frequency, FT, can be reliably located, and (3) the tinnitus can be completely masked by a band of noise at or near FT at a low sensation level. Such patients often experience residual inhibition (temporary suppression of tinnitus upon cessation of masking) which may accumulate with sustained use of masking, in some cases becoming permanent. Long-term masking is difficult or impossible for patients whose hearing is so impaired they cannot hear the masker, or those for whom the masking sounds must be presented at unacceptably loud levels to obtain adequate coverage of the tinnitus. There is a great need for additional work to determine what factors influence the effectiveness of masking, in order to improve our ability to provide appropriate masking stimuli even for the difficult cases.

Humans↗
PubMed1978

Neural correlates of auditory fatigue: frequency-dependent changes in activity of single cochlear nerve fibers.

1. These experiments were designed to test whether intense pure tones produced greater depression of cochlear nerve fibers tuned to the exposure frequency or of those tuned to frequencies above the exposure frequency. Spike discharges of single fibers were studied in anesthetized cats before, during, and after exposures lasting 1 min. Exposure frequency was varied relative to each fiber's characteristic frequency (CF), and was either at the CF or 1/2 octave above (+1/2 oct) or 1/2 octave below (-1/2 oct) the CF. Exposure levels were 85 or 90 dB SPL. Effects of the various exposures on driven discharge rates were evaluated using standard test stimuli at each fiber's CF. In addition, nonevoked discharges were measured during the brief quiet intervals between test stimuli ("interstimulus activity") as well as during extended quiet periods ("resting activity"). Major results were as follows: 2. All the exposures resulted in depression of the driven discharge rates; however, these effects were strongly dependent on the exposure frequency. The depression was greatest and endured the longest following -1/2 oct exposures at 90 dB. The CF exposures at 85 and 90 dB were much less depressant, as were exposures at -1/2 oct at 85 dB; these three exposures resulted in very similar recovery functions. The +1/2 oct exposures produced little or no depression, whether at 85 or 90 dB. 3. Interstimulus activity was depressed immediately following all exposures, but recovered to normal quickly than did driven discharge rates. Following exposures at -1/2 oct at 90 dB, recovery was non-monotonic in that an extended period of supernormality preceded the return to normal rates. During this period of elevated activity, the interstimulus activity approached but never exceeded the resting rate of the same fiber. 4. Resting activity recovered even more rapidly than interstimulus activity, being completely normal by 1 min following all exposures. 5. These results constitute the first demonstration that the CF is not necessarily the most depressant exposure frequency for a given cochlear nerve fiber. Further, the results imply that the half-octave (or greater) shifts of the point of maximum hearing loss, so characteristic of auditory fatigue, may be accounted for by frequency-dependent alterations in the responsiveness of cochlear nerve fibers.

Acoustic Stimulation↗
PubMedDate not supplied

Combined effects of noise and neomycin. Cochlear changes in the guinea pig.

Cochlear damage resulting from the combination of neomycin with acoustic overstimulation was investigated in guinea pigs. Four groups of animals received subcutaneous injections and exposure to broad band noise daily for 7 days, as follows: I. Neomycin (200 mg/kg) followed by 10 hours of noise at 115 dB SPL; II. Saline followed by 115 dB noise: III. Neomycin followed by low intensity noise (45 dB as an acoustic control); or IV. Saline followed by 45 dB noise. After a 30 day stabilization period, each ear was examined electrophysiologically and histologically. Measures of cochlear integrity included AC cochlear potentials from 100 Hz through 20 kHz as well as outer hair cell (OHC) counts. A marked interaction leading to augmentation of damage was found when neomycin was combined with 115 dB noise (Group I). Losses in cochlear sensitivity, averaged across all frequencies, amounted to 62 dB in Group I, whereas the averaged losses for Groups II and III were only 16 dB and 17 dB respectively. Loss of OHC's was close to 100% in Group I, while OHC losses were only 17% in Group II and 26% in Group III.

Acoustic Stimulation↗
PubMedDate not supplied

Reduction of acoustically induced auditory impairment by inhalation of carbogen gas. II. Temporary pure-tone induced depression of cochlear action potentials.

Guinea pigs were exposed to a 4.5 kHz pure-tone at 104 dB for 10 min during artificial ventilation with either carbogen gas (95% O2/5% CO2) or normal air. Mean N1 response amplitudes to tone bursts at 32 test frequencies extending from 2.1 kHz through 30 kHz were measured at standardized intervals before and after the acoustic overstimulation. All animals received normal air during recovery. Significant reduction of N1 response amplitude depression within a 3/8 to 1 octave frequency domain above the exposure frequency was found in the group which received the carbogen gas. Those frequencies found to be maximally depressed and the relative rate of recovery from the acoustic overstimulation were not affected by carbogen inhalation. The invariance of the "half-octave shift" following pure-tone acoustic overload was confirmed. Arterial blood gas analysis of guinea pigs respiring carbogen revealed a marked rise in PO2 and PCO2. Carbon dioxide is a potent stimulator of cerebral and cochlear vasodilatation. Sound-induced vasoconstrictive ischemia has been implicated in noise-induced cochlear pathology. The beneficial effects of elevated arterial PCO2 are suggested to have been mediated by reduction of acoustically induced vascular insufficiency within the inner ear.

Animals↗
PubMedDate not supplied

Comparison of electrically and acoustically evoked responses in the auditory cortex of the guinea pig: implications for a cochlear prosthesis.

Guinea pigs have been used to develop an animal model for evaluation of electric stimulation of the cochlea. Techniques were developed for recording from single neural units in the auditory cortex. Acoustic responses exhibit similar patterns of neural discharge ("on", "off", sustained excitation and inhibition, etc) to those reported for auditory neurons in other species. Similar response patterns are obtained when electric stimulation is used. However, cortical units display characteristic frequency tuning with acoustic stimulation, whereas it becomes increasingly difficult to evoke electric responses as stimulus frequency increases. Recording of gross evoked responses from the same cortical area indicates that the intensity function for electric stimulation is much steeper than that seen for acoustic stimulation.

Acoustic Stimulation↗