[Objective frequency-specific measurement of hearing threshold using narrow-band chirp stimuli with level-adaptive simultaneous masking]. / Objektive frequenzspezifische Hörschwellenbestimmung mittels schmalbandiger Chirp-Reize mit pegeladaptiver simultaner Maskierung.

BACKGROUND: In the past, various simulation and measurement paradigms have been introduced and evaluated in order to improve frequency-specific measurement of the hearing threshold using early auditory evoked potentials (EAEP). A promising approach for improvement of detection of stimulus response is the usage of frequency-modulated chirp signals, which optimize the temporal synchrony of neuronal responses along a region of the basilar membrane. AIM OF THE STUDY: This study validated the performance of three generated narrow-band chirp stimuli in combination with a level-adaptive simultaneous masker on a collective of normally hearing subjects. MATERIAL AND METHODS: In this study 25 normal hearing subjects took part after undergoing pure tone audiometry as well as an objective estimation of the auditory threshold using low, middle and high chirp stimuli. The characteristic EAEP parameters were visually identified before statistical analysis. The characteristic latency level function was conducted using measurements within a stimulus level range from 80 to 0 dB HL. Afterwards a comparison of objectively verified auditory threshold and subjective auditory threshold was conducted. RESULTS: All objectively determined thresholds of the frequency-specific evoked EAEP were on average below 10 dB HL: low chirp at 8.2 dB HL, middle chirp at 5.8 dB HL and high chirp at 5.4 dB HL. The mean difference compared to subjectively determined auditory thresholds at all frequencies was below 3 dB and was not significant. CONCLUSION: Brainstem evoked response audiometry (BERA) using a band-limited and level-specific masked chirp stimulus is an efficient method for the determination of frequency-specific excitation thresholds in the clinical routine. The small, insignificant difference compared to the subjectively determined auditory thresholds makes usage of correction factors mostly redundant. Confirming the study results concerning low chirp stimuli so far, the low chirp BERA currently seems to be the method of choice for estimation of auditory threshold at low frequency ranges around 500 Hz.

[Early acoustic evoked potentials in patients with "small" vestibular schwannomas]. / Frühe akustisch evozierte Potenziale bei Patienten mit "kleinem" Vestibularisschwannom.

BACKGROUND: The prognostic potential of click-evoked early acoustic evoked potentials (EAEP) for vestibular schwannoma (VS) diagnostics is considered insufficient for tumors small than approximately <1.5 cm in diameter. However, up until now, the derivations at higher sound pressure levels have mainly been used for EAEP evaluation. The aim of this study was to examine whether registered EAEP are more sensitive to pathological changes at low sound pressure levels and with smaller tumors. METHODS: Comparative examinations (pair-matched) were conducted with 34 patients. An appropriate patient with an identical hearing level threshold - either a purely cochlear hearing deficiency or a normal hearing level - was matched to each tumor patient. EAEP were registered at 80, 60, and 40 dB HL. The characteristic parameters where assessed visually and evaluated statistically, both in respect to patient groups and in bilateral comparisons. Furthermore, the relationship between the level-dependent wave V latency differences in bilateral comparison and tumor size were evaluated. RESULTS: Low-level cochlear hearing deficiencies did not cause a change in wave V latency, such that the pathological side differences at 40 dB HL in patients with VS can be considered a "purely" retrocochlear hearing deficiency. The sensitivity of EAEP registered at 40 dB HL decreases only with tumors under about <5 mm in diameter. Combining the values of wave V latency and interaural wave V latency difference effectively reduces false-positive findings at 40 dB HL to zero. CONCLUSION: Beyond the suprathreshold derivations, potential registrations at 40 dB HL can also be diagnostically useful to differentiate cochlear from retrocochlear lesions. In the case of small VS and good hearing levels, these registrations may also be used for intraoperative monitoring to allow better evaluation of level-dependent changes in the auditory nerve.

[Examination of a training effect in the Freiburg monosyllabic test]. / Untersuchung zum Trainingseffekt des Freiburger Einsilbertests.

BACKGROUND: The Freiburg monosyllabic test (FBE) was introduced into clinical routine almost 60 years ago. Recently, there has been renewed scientific interest in the FBE. Nevertheless, neither the earlier nor the later publications showed any evidence for a training effect. For this reason, this aspect is examined in more detail in the present study. METHODOLOGY: All 20 test lists of the FBE were presented in a fixed, predetermined order to 40 suitable otologically normal subjects. According to DIN 45626-1, the 50 % speech discrimination score is expected at a level of 29.3 dB SPL (Sound Pressure Level). In this study, the test material was presented at a level of 29 dB SPL. The speech discrimination scores were analyzed depending on the particular test run. RESULTS: The mean speech recognition score (43.2 %) depended on the test run. An increase in speech recognition by 13 percent points was observed in the first three test runs. After two test runs, no further increase in speech recognition was observed. CONCLUSION: When using the FBE in clinical routine, two test lists should be heard by the patients before the actual test starts. This procedure helps to improve the quality of the FBE.

[Evaluation of the perceptual equivalence of test lists in the Freiburg monosyllabic speech test]. / Untersuchungen zur perzeptiven Äquivalenz der Testlisten im Freiburger Einsilbertest.

BACKGROUND: In the past, the perceptual balance of test lists for the Freiburg monosyllabic speech test (FBE) was frequently evaluated without producing consistent results. Until now, the studies used very diverse methods and did not accurately follow the standardized specifications. In this study, therefore, the perceptual equivalence of test lists was verified with a large group of participants according to the standard ISO EN 8253-3. METHODS: A total of 160  suitable otologically normal subjects were recruited at two institutions, each of whom listened to all test lists of the FBE using predefined measurement conditions. The subjects were divided in three groups depending on the transducer used for test list presentation (headphones "HDA 200" and "TDH 39", as well as free-field loudspeaker, "FF"). Lists that deviated were identified using the approaches specified in the standard. RESULTS: The reference curve for FBE was not met by any group. While the "HDA 200" group indicated 4.6 dB lower thresholds, results for the "TDH 39" and "FF" groups showed 1.2 and 2.5 dB higher thresholds, respectively. For an average speech recognition score of 44.3 %, test lists 5, 11, 12, and 15 lay outside the calculated tolerance range of 4.5 to -4.4 percent points. The same lists also deviated when calculating discrimination functions and therefore do not fulfill the criteria for perceptual equivalence. DISCUSSION: In the future, lists identified as deviating from the norm should not be used. The results of this study only partly agree with results from former studies.

[Discrimination of Hearing Disorder by Means of CLS and OAE in Vestibular Schwannoma]. / KLS und OAE zur Differenzierung der Hörstörung bei Vestibularisschwannom.

INTRODUCTION: Currently a sensitive early diagnosis of small vestibular schwannoma is only possible by using magnetic resonance imaging (MRI). OBJECTIVES: The main objective was a differentiation of the cochlear and retrocochlear component of small vestibular schwannoma with the help of categorial loudness scaling (CLS) and the growth function of otoacoustic emissions (DPOAE I/O-functions). MATERIAL AND METHODS: 34 patients (gr. 1: 17 patients with vestibular schwannoma ≤15 mm, gr. 2: 17 matched patients with an inner ear hearing disorder) were examined. Besides audiological standard procedures they also underwent CLS according to the Würzburger auditory field and a generation of DPOAE I/O-functions was conducted on the probands. RESULTS: The gradients of the loudness growth function as part of the CLS and the DPOAE I/O-functions showed with few exceptions [500 Hz at 0-10 dB HL during CLS (p=0,040)] no significant differences between the groups (all p>0.05). A recruitment verification with the help of CLS was possible for tumors starting at a size of 5.45,mm at 3,000 and 4,000 Hz, respectively for tumors exceeding the size of 6.85 mm at 6,000 Hz with 100% sensitivity but only low specificity. CONCLUSIONS: A differentiation between a vestibular schwannoma and a mere cochlear hearing disorder with only the help of CLS and DPOAE I/O-functions is not possible. The results corroborate the thesis of an additional cochlear component even in small vestibular schwannoma. The implementation of CLS to determine cochlear deficits linked to vestibular schwannoma seems to be medically sensible if the tumor size exceeds 5 mm. According to the diagnostic method used to determine vestibular schwannoma MRI remains the first choice procedure.