Pressure transfer between intracranial and cochlear fluids in patients with Meniere's disease.

OBJECTIVES: To elucidate the pressure transfer between intracranial and labyrinthine fluids in patients with well-defined unilateral Meniere's disease. STUDY DESIGN: Eleven patients previously exposed to hypobaric pressure agreed to be investigated further with the tympanic membrane displacement (TMD) technique. TMD was used to indirectly analyze perilymph pressure changes as the result of changes in body position. METHODS: Repeated measurements for both the diseased and the healthy ears were made with the patients supine and then in a sitting position. The TMD parameters for the maximum inward displacement, the Vi, and the mean volume displacement, the Vm, were calculated and compared. RESULTS: The paired comparison showed statistically significant larger Vi values for both ears in the supine position. A similar tendency was observed for the Vm value. This difference of the Vi was significantly larger for the diseased ear compared with the currently healthy ear. The results were compared to the audiometric and electrocochleographic results previously obtained on the same patients when they were subjected to hypobaric pressure. Patients who experienced the largest differences in hearing level thresholds in the lower frequencies also showed the greatest differences in TMD values as the result of postural changes. CONCLUSIONS: Despite the limited number, the statistically supported results suggest a relation between the efficiency of the routes of pressure transfer and the observed effect of hypobaric exposure. The results also indicate that for the patients tested, the routes of communication are more effective in the diseased ear than in the healthy ear--a condition that may relate to the pathogeneses of Meniere's disease.

The relationship between the acoustic reflex threshold and levels of loudness categories in hearing-impaired listeners.

When applied as a tool for hearing aid fitting, categorical loudness scaling (CLS) is time consuming and not feasible in all subjects. It is therefore desirable to use objective measures for accurate prediction of loudness categories among hearing-impaired individuals. The present study aimed at exploring whether loudness perception at the ART is constant with varying hearing threshold. Seventy-five subjects with various degrees of hearing impairment, measurable acoustic reflex and normal middle ear function participated. The HTLs, ARTs and the levels of six loudness categories at frequencies 0.5, 1, 2 and 4 kHz were determined for all subjects. Loudness at the ART was found to be correlated with the amount of hearing loss. On the basis of these results, it is concluded that the ART cannot be used for accurate estimation of loudness in hearing-impaired subjects.

The acoustic reflex threshold: not predictive for loudness perception in normally-hearing listeners.

The working hypothesis of an ongoing study is that the quick and reliable procedure of acoustic reflex threshold (ART) determination in conjunction with measurements of HTL may yield accurate estimates of loudness. The aim of this study was to investigate whether differences in loudness in normally-hearing subjects are reflected in the ARTs and to collect normal material with respect to pure-tone elicited ART and loudness categories. Categorical loudness scaling (CLS) and ART measurements were performed at frequencies of 0.5, 1, 2 and 4 kHz in 60 normally-hearing subjects (HTL<20 dB HL, 26 males, 34 females, aged 21-63 years) with no history or sequelae of middle ear disease. Subjects reporting disturbing tinnitus were excluded. The results show that the ART is not a predictor of individual loudness perception for normally-hearing subjects. Using a numerical scale (HTL=0, 'very soft'=5, 'soft'=15, 'OK'=25, 'loud'=35, 'very loud'=45 and 'too loud'=50) loudness for pure tones grows almost linearly at approximately 0.4 arbitrary loudness units per dB below the 'loud' category. Above the 'loud' category the slope is around 1 unit per dB. The median ART was 85 dB HL at frequencies of 0.5, 1, 2 and 4 kHz. No differences in loudness perception across frequencies were found.

Loudness perception is influenced by long-term hearing aid use.

The aim of this study was to explore possible differences in the perception of loudness between long-term hearing aid full-time users and non-users. Categorical loudness scaling using pure-tone stimuli was carried out by hearing-impaired subjects. The mean levels of loudness categories at one frequency (hearing threshold: 50-75 dB HL) in a group of 18 hearing aid users (daily use < or = 15 hours per day) were compared with the corresponding levels found in 18 hearing-impaired non-users with the same distribution of hearing thresholds. The results show that, for hearing losses of 50-75 dB HL, the mean level rated as 'loud' by long-term full-time users of hearing aids is 4.5 dB above the mean level of the corresponding category rated by non-users. This difference is statistically significant (P<0.05). No significant differences were found for the lower categories. Among those subjects who had been wearing hearing aids for at least six months, no significant correlation was found between the levels of the 'loud' category and the length of time that hearing aids had been used.

Long-term test-retest reliability of category loudness scaling in normal-hearing subjects using pure-tone stimuli.

The present study investigates the test-retest reliability of category loudness scaling with pure tones for each of the scaling categories: 'very soft', 'soft', 'OK', 'loud', 'very loud' and 'too loud' at the audiometric frequencies 0.5, 1 kHz, 2 kHz and 4 kHz. Category loudness scaling at two sessions separated by between 1 and 4 weeks was obtained from 16 normal-hearing subjects who all had normal otoscopy, present acoustic reflexes at audiometric frequencies 0.5-4 kHz and middle ear pressure within +/-50 daPa. Intra-subject between-session reliability was found not to be frequency dependent, and comparison with other studies revealed that reliability is not dependent on the applied stimulus signal. Test-retest reliability varied between the different categories: In the categories 'very soft', 'loud', 'very loud' and 'too loud' the test reliability is in the same range as found for hearing thresholds determination, whereas for the 'soft' and 'OK' categories it is poorer. The greater uncertainty for intermediate levels should be considered when using category loudness scaling, e.g. for calculating hearing aid parameters.

Neonatal hearing screening using otoacoustic emissions elicited by maximum length sequences.

The aim of this study was to provide statistical information on otoacoustic emission (OAE) measurements in new-born infants, which could be useful in the interpretation of results and could add some clinical parameters that might be used for future objective and automatic response evaluations. Transient evoked OAEs (TEOAEs) using maximum length sequences (MLS) were recorded in 129 full-term new-born infants between 48 and 72 hours of age. The use of MLS enabled stimulus rates of up to 2000/sec to be utilized. The analysis comprised five main issues: (1) signal to noise ratio (S/N); (2) derived non-linear responses; (3) a combination of derived non-linear emissions called compound non-linear emissions; (4) time/frequency analysis and (5) signal power analysis. The result of the analysis were as follows. (1) The largest S/N ratio was obtained when more than 60% of the recordings were rejected. (2) The derived non-linear emissions comprised level non-linear and rate non-linear responses, the latter obtained by subtraction of recordings at fixed stimulus level, but at different stimulus rates. The rapid suppression of emission amplitude as the stimulus rate increases is the basis for this non-linear response which also features stimulus cancellation. (3) The compound non-linear emissions, consisting of a sum of derived non-linear responses may prove efficient by proper selection of stimulus parameters, but did not in the present form show the expected improvements of amplitude and stimulus cancellation. (4) The time/frequency analysis, however, based on calculations of the instantaneous frequency as a function time after stimulus onset, showed a consistent tendency of falling frequency versus time after stimulus onset as a basic characteristic feature of OAE. (5) The analysis of the emission power as a function of time after stimulus onset showed that linear recordings in new-born infants are reliable, with stimulus ringing fully decayed 3 ms after the stimulus onset. The findings may prove useful in future attempts to develop screening equipment with automatic response evaluation for new-born infants. From a clinical point of view the MLS technique was successful when measuring emissions in neonates, owing to the fast recording time and the utilization of an efficient noise rejection paradigm.