Rudolf Probst

A randomized, double-blind, placebo-controlled study of dextran/pentoxifylline medication in acute acoustic trauma and sudden hearing loss

The effectiveness of any therapy in acute acoustic trauma or sudden hearing loss of unknown origin has not been demonstrated convincingly. The assessment is difficult because of a relatively high rate of spontaneous recovery. Nevertheless, many different forms of treatment are recommended. We tested one form, treatment with rheoactive substances, in a prospective, randomized, double-blind trial and compared treatment with (a) infusions of dextran-40 with pentoxifylline, (b) saline infusions with pentoxifylline, and (c) saline infusions with placebo medication. Pure-tone hearing thresholds served as control parameters and were taken before treatment and at 1 and 4 weeks after the onset of therapy. Three hundred eighty-two patients were included in the trial, 331 (87%) could be analyzed, 184 patients were treated because of sudden hearing loss, 147 because of acute acoustic trauma. The three treatment groups were comparable in their basic characteristics including the amount of initial hearing loss. In patients with sudden hearing loss, no significant differences of hearing recovery were detected between the three treatment groups. Hearing recovery was also similar in patients with acute acoustic trauma. A power analysis of the study revealed that possible true treatment differences of a hearing recovery of 10 dB would have lead to significance with a probability of over 90%. It is concluded that there were, in fact, no clinically relevant differences in hearing gains of sudden hearing loss or acute acoustic trauma between treatments with saline infusions together with placebo medication and treatment with dextran-40 and/or pentoxifylline.

Otoacoustic emissions: an approach for monitoring aminoglycoside-induced ototoxicity.

Ototoxic drugs, such as aminoglycosides, affect outer hair cell integrity in the inner ear. Transiently evoked otoacoustic emission (TEOAE) characteristics are related to outer hair cell function and can be expected to reflect the influence of ototoxic agents. Transiently evoked otoacoustic emissions were measured during amikacin sulfate therapy in nine patients. The duration of treatment for individual patients ranged from 9 to 33 days. A reversible decrease of overall TEOAE level, occurring after a treatment period longer than 16 days, was found in the majority of patients. The monitoring of TEOAEs is proposed as a method for early identification and, as a result, prevention of aminoglycoside‐induced ototoxicity.

Suppression of the 2f1−f2 otoacoustic emission in humans

Suppression of the 2f1-f2 distortion-product otoacoustic emission (DPOAE), stimulated with primaries, f1 and f2, in the frequency regions of 1, 2, and 4 kHz was measured in one ear of 14 human subjects with normal hearing. Suppression rate functions were generated with a suppressor at either 1, 2, or 4 kHz increasing in level from 30 to 76 dB SPL for the corresponding f1 and f2 combinations. Stimulus levels for DPOAEs were L1 = 70 dB SPL and L2 adjusted to produce the highest amplitude DPOAE for each ear (range, 0 to 6 dB below L1). Results indicated that DPOAEs were reduced 3 dB in amplitude for a mean suppressor level of 61 dB SPL. Maximum amplitude reduction occurred at a mean suppressor level of 69 dB SPL. These levels varied little for the three stimulus frequency regions. Mean slopes of the rate functions decreased as stimulus frequency region increased. Suppression tuning curves (STCs) were generated in the same three frequency regions and with L1 at either 70 or 55 dB SPL and L2 adjusted individually for each ear. The tips of the STCs were at frequencies associated with f1 and f2. The tip regions of the STCs for the 4-kHz stimulus condition were more complex in that they contained more multiple minima than did those for the 1- and 2-kHz regions. Results confirm that optimal suppression of the 2f1-f2 DPOAE occurs for frequencies in the vicinity of f1 and f2 rather than at 2f1-f2.

Effects of atmospheric pressure variation on spontaneous, transiently evoked, and distortion product otoacoustic emissions in normal human ears ☆

The effects of atmospheric pressure changes on the frequency and amplitude of spontaneous (SOAEs), transiently evoked (TEOAEs) and distortion product (DPOAEs) otoacoustic emissions in normally hearing humans were compared. The purpose was to determine if the transmission of each form of OAE was influenced differently by the middle ear. Sixty-one subjects were tested in a pressure chamber. Twenty-seven SOAEs with a frequency range between 535 to 4729 Hz from 21 subjects were examined. Transiently evoked OAEs were studied in 20 subjects using clicks and tone-bursts at 0.5, 1, 2, 3, and 4 kHz. Distortion-product OAEs were generated at seven geometric mean frequencies between 1 and 8 kHz in another 20 subjects. Spontaneous OAEs were examined by applying atmospheric pressure up to 9 kPa and down to -2.5 kPa, for the measurement of TEOAEs and DPOAEs the pressure was varied from 0 kPa up to 8 kPa. In spite of large interindividual differences, results suggest that the influence of pressure on the three OAEs is frequency specific. The frequency and amplitude change of SOAEs, the modification of the amplitude and spectra of TEOAEs, and the amplitude change of DPOAEs are more influenced by changes in middle ear pressure below 4 kHz than are OAEs in the range at 4 kHz and above.

Monitoring the effects of noise exposure using transiently evoked otoacoustic emissions

One possible alternative to conventional pure-tone testing for screening and monitoring cochlear changes is the measurement of otoacoustic emissions. The aims of this study were to determine the feasibility of using transiently evoked otoacoustic emission (TEOAE) measurements as an objective field procedure and to compare the sensitivity of the measurements indirectly to pure-tone thresholds. The test groups were 117 male recruits and 30 male career cadets in compulsory military service in Switzerland. Transiently evoked otoacoustic emissions were measured before and at the end of a 17-week training period that included exposure to noise from firearms. Results revealed significant changes in response amplitudes in the frequency range from 2 to 4 kHz, whereas changes in the frequency range from 0.5 to 2 kHz were not significant for either group. The changes in relative amplitude did not exceed 15% when spectra containing the lower frequencies were considered. However, they were always greater than 83% within the higher-frequency range. All mean changes were in the direction expected from cochlear damage. Comparison of TEOAE results with pure-tone thresholds measured for a similar sample of subjects indicated that TEOAE testing may be more sensitive than pure-tone audiometry in detecting early cochlear damage from noise. The testing of TEOAEs is feasible as a screening procedure. It offers objective and repeatable information and is substantially less time consuming than pure-tone audiometry.

Noninvasive Tracking of Patient's Head Movements During Computer-Assisted Intranasal Microscopic Surgery

A noninvasive system designed for patient tracking during image‐guided intranasal sinus surgery is described. It is based on optical digitizing with a custom‐made registration and reference system, locatable surgical instruments, and a self‐localizing operating microscope. Experimental and clinical results reveal a high degree of accuracy for the system. A mean spatial error of 0.82 ± 0.31 mm was determined for repositioning of the reference system in a plastic model of the skull. For the positioning of the microscope, a mean error of 2.3 ± 0.83 mm was calculated. Measurements of repositioning accuracy in 24 patients who received surgery for various sinus diseases had a mean spatial error of 1.56 ± 0.76 mm. The 95% error interval for locating intranasal structures using the surgical instrument was 2.05 mm, and it was 4.92 mm using the microscope. These results suggest that the use of our noninvasive registration and reference system may be effective, accurate, and useful for noninvasive tracking of patient movements in computer‐assisted intranasal surgery.

Preoperative and postoperative auditory and facial nerve function in cerebellopontine angle meningiomas.

Preoperative and postoperative facial nerve and auditory function were reviewed retrospectively in 13 cases of cerebellopontine angle meningiomas. According to their location within the posterior fossa and with special reference to the internal auditory canal, they were classified into a premeatal and a retromeatal group. All the tumors were removed by an otoneurosurgical team by use of a retrosigmoid approach. Postoperative results (1 year after operation) were compared within the two groups with respect to preservation of hearing (normal hearing in 31% and preservation of preoperative hearing in 69% of the cases) and facial nerve function (no or mild postoperative impairment in 69% of the cases). Both preoperative and postoperative impairment of facial nerve and auditory function prevailed in the premeatal group. For preservation of vital vascular and central nervous structures, subtotal resection with consecutive fractionated radiation therapy had to be performed in 30% of the cases. Our results provide substantial evidence that in cerebellopontine angle meningiomas a precise preoperative study of tumor location will assist in improving individual operative strategy and thus postoperative functional results.

Repeatability of transiently evoked otoacoustic emissions in normally hearing humans

Transiently evoked otoacoustic emissions (TEOAEs) were stimulated using clicks. Responses were measured in each ear of 10 adult subjects during three test sessions separated by 3-day intervals. The purpose was to determine the amount of short-term variability in the amplitude of the emissions when measured under similar test conditions. For each of two modes of determining the stimulus level, mean overall response levels varied approximately 1 dB with repeated measurements. The spectra of the responses were analyzed in discrete frequency bands from 0.7 to 5.8 kHz. Response energy peaked at 1.2 kHz and was reduced markedly above 4 kHz. Variability within individual spectral bands was approximately 1 dB from 0.9 to 4.1 kHz and was slightly greater for 0.7 kHz. The amplitude of TEOAEs is stable over successive short-term measurements. The technique can be used as a sensitive means of monitoring cochlear function.

Reporting click-evoked and distortion-product otoacoustic emission results with respect to the pure-tone audiogram.

Measurement of transiently evoked otoacoustic emissions, elicited primarily using click stimuli, and distortion-product otoacoustic emissions is gaining prominence as a clinical technique. One proposed application is the estimation of hearing levels. In this report, several formats for describing otoacoustic emission test results obtained from adult subjects are discussed. Descriptive analyses involve comparisons of individual results with normative data obtained from a group of normally hearing adults.

Reverse middle-ear transfer function in the guinea pig measured with cubic difference tones

Otoacoustic emissions are increasingly useful for determining cochlear function noninvasively. It is widely agreed that these acoustic signals reflect micromechanical processes in the cochlea. However, their quantitative interpretation requires knowledge of the ways in which vibrations travelling back to the ear canal from the cochlea are shaped by the middle ear. An intracochlear source is needed to derive the reverse middle-ear transfer function (rMETF) by comparing pressure in the external ear canal to the corresponding pressure in scala vestibuli. In the present study, the rMETF was obtained in vivo in the guinea pig using as intracochlear sound source the cubic difference tones (CDTs) generated by a pair of external pure tones. With a closed ear canal and open bulla, the rMETF was found to be flat (-35 dB) over a broad frequency range (1.5-8 kHz). The differences between forward and reverse METF could be explained by different loads acting on the middle ear network, which depends on the direction of signal transmission. With knowledge of the rMETF, it becomes possible to quantify CDTs within the cochlea by measuring them noninvasively in the ear canal.