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Biomedical subjects

R Probst

Publications and source records attributed to R Probst.

At least 73 records · Page 4Linked to original sources
PubMed1993

Transiently evoked and distortion-product otoacoustic emissions. Comparison of results from normally hearing and hearing-impaired human ears.

Evoked otoacoustic emissions can be measured after a transient stimulus or as distortion products of two pure tones. Measurements of both emission types are being used more frequently as the techniques become easier to implement and the clinical benefits are realized. In addition, comparisons between the two types of emissions from the same ear provide information about cochlear mechanisms. We have measured transiently evoked otoacoustic emissions (TEOAEs) stimulated with clicks and distortion-product otoacoustic emissions (DPOAEs) from 166 ears of individuals with and without hearing impairment. The TEOAE and DPOAE amplitudes were compared with each other and with corresponding audiometric thresholds by frequency. Results revealed a high correspondence between the two emission types (r = .78) and between the distribution of the energy for each emission and audiometric threshold levels at corresponding frequencies (DPOAE, Spearman p = -.84; TEOAE, p = -.77). The DPOAEs were present more often than were TEOAEs when hearing levels across frequency were greater than 30-dB hearing level. The results suggest that both TEOAEs and DPOAEs are derived largely from similar mechanisms. The differences between the occurrence of the two emissions by audiometric threshold level would suggest that TEOAEs may be preferable for screening purposes, whereas DPOAEs may be more valuable for monitoring cochlear changes clinically.

Adult↗
PubMed1993

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.

Acoustic Stimulation↗
PubMed1993

A comparison of transiently evoked and distortion-product otoacoustic emissions in humans.

The measurement of transiently evoked otoacoustic emissions (TEOAEs) can identify a hearing loss exceeding 25-30 dB HL with high sensitivity. However, further quantification of the hearing loss is not possible, and the frequency specificity of TEOAEs has been questioned. Distortion-product otoacoustic emission (DPOAE) measurements are being developed for clinical use in the hope that they will be more frequency-specific than are TEOAEs. We have compared TEOAEs and DPOAEs in both normally hearing and hearing-impaired subjects with the purpose of learning more about the frequency specificity of these two types of emissions. In a first investigation, toneburst-evoked OAEs were compared to DPOAEs stimulated at 1, 2 and 4 kHz in ten ears without spontaneous otoacoustic emissions of ten normally hearing subjects. Input/output (I/O) functions of DPOAEs at frequency regions of 1 and 2 kHz were characterized by roll-overs and irregularities that were not present in either DPOAE I/O functions at 4 kHz or in TEOAE I/O functions at 1, 2 and 4 kHz. Mean slopes of the I/O functions increased with increasing frequency for DPOAEs and decreased for TEOAEs. In a second investigation, click-evoked OAEs and DPOAEs (stimulated by pure tones in the frequency range of 0.75-6 kHz) were measured in 42 ears of 21 normally hearing subjects and 128 ears of 64 subjects with varying degrees of sensorineural hearing loss. Results from both investigations revealed that the amplitude ratio between DPOAEs and TEOAEs changed systematically with frequency. DPOAE amplitudes became larger with increasing frequency and TEOAE amplitudes became smaller.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

[Results of a prospective open study of therapy of sudden deafness with flunarizine].

The treatment effect of the lipophilic calcium antagonist flunarizine on the recovery of sudden hearing loss was evaluated in a prospective phase-II study. Thirty-seven patients presenting with recent and sudden onset of unilateral sensorineural hearing loss were treated with 50 mg flunarizine intravenously for the first two days followed by 10 mg flunarizine orally for four weeks. Pure-tone audiometry was done before the beginning of the treatment and after one and four weeks. The absolute and relative hearing gains after one and four weeks were compared to those of 67 similar patients previously treated with saline infusions and placebo tablets in the same institutions during a double blind study (Probst et al. Acta Otolaryngol. 112 (1992) 435-443). The mean absolute hearing gains of the flunarizine group was 17 dB and 21 dB, after one and four weeks respectively (placebo group: 16 dB and 24 dB). The corresponding relative hearing gains (defined as absolute gain divided by initial hearing loss) were 35% and 43% for the flunarizine group and 33% and 42% for the placebo group. We conclude that flunarizine treatment does not improve the recovery of sudden hearing loss.

Administration, Oral↗
PubMed1993

Silicone stents in the management of inoperable tracheobronchial stenoses. Indications and limitations.

BACKGROUND: Various stent models have been developed for the treatment of inoperable stenoses of the central airways caused by external compression. Increasing use is made of the silicone stents designed by Dumon. We tested their technical feasibility, tolerance, and long-term efficacy in relieving respiratory symptoms in patients referred for endoscopic palliation of malignant disease. METHODS: All procedures were performed under general anesthesia with the use of the rigid bronchoscope. We inserted 38 stents in 31 patients (median age, 67 years; 25 men and 6 women) whose airways showed residual obstruction of > 50 percent of the lumen after laser resection of endobronchial tumor and/or mechanical dilatation of extrinsic compressions. RESULTS: Stent placement and removal--where necessary--were easy in all patients, but five stents inserted in three patients with short (< or = 2.5 cm) and conical stenoses migrated, necessitating emergency removal. In 27 of the remaining 28 patients, stent tolerance was excellent; 1 proximal tracheal stent (< 1 cm below the vocal cords) had to be removed because of otalgia and dysphagia. One lethal hemoptysis occurred within hours after a repeated laser therapy and removal of an indwelling stent. No other serious complications occurred. Immediate and lasting relief of dyspnea and improvement in performance status (Karnofsky scale, activity index) was achieved in 90 percent (28/31) of patients (p < 0.01). The influence of adjuvant radiotherapy on local tumor recurrence and survival was analyzed in a subgroup of ten patients with stage IIIB squamous cell carcinoma with comparable performance status. Five did not undergo adjuvant radiotherapy (group A) and five did (group B). In group A, four of five stents were occluded by tumor recurrence above or below the stent after a median follow-up of 2 months; in group B, zero of five were occluded (p < 0.05) after 4 months. Median survival was 4 months in group A and 6 months in group B; the difference did not reach significance. CONCLUSIONS: The silicone stents designed by Dumon are easily inserted and removed; they are also well tolerated and very efficacious in relieving respiratory symptoms caused by extrinsic airway compression. Short and conical stenoses present limitations for their use due to increased risk of migration. Combined treatment with laser resection, stent insertion, and subsequent radiotherapy is necessary to prevent local tumor recurrence and may improve survival.

Adult↗
PubMed1993

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.

Adult↗
PubMed1993

Clinical monitoring using otoacoustic emissions.

Damaging influences to the cochlea are a leading cause of sensorineural hearing loss. Examples include acute or chronic noise exposure and cochleotoxic drugs such as aminoglycosides. Typically, once damage has occurred, the cochlea cannot recover. Therefore, prevention is critical. If damaging influences cannot be avoided, then secondary prevention or early detection of cochlear hearing loss becomes important. Ideally, methods for the detection of cochlear damage should be as specific and as sensitive as possible. Otoacoustic emissions satisfy these criteria and offer a means of testing aspects of cochlear function in a non-invasive and objective way. Evoked otoacoustic emissions measured either after transient stimuli or during two-tone stimulation (distortion-product otoacoustic emissions) are the types most commonly used for clinical purposes. They are stable over time within individual ears and their repeatability has been established under conditions of clinical testing using commercial equipment. Thus, they are well suited as an effective means of monitoring subtle changes in cochlear status. The possibility of making non-invasive repeated measures of cochlear function has led to the widespread use of otoacoustic emissions in animal experiments. Influences of development, anoxia, anaesthesia, noise, and drugs have been monitored. Preliminary studies in humans demonstrate that cochlear damage due to ototoxic drugs such as aminoglycosides or cisplatin and due to noise exposure can be detected using otoacoustic emissions. Comparison of such results to those available using pure-tone audiometry indicates a greater sensitivity of otoacoustic emissions for detecting early cochlear damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1993

[Sudden deafness].

Sensorineural hearing loss with rapid onset occurring without obvious reasons is considered a clinical entity called sudden hearing loss. Such hearing dysfunctions must be rated as severe handicaps, comparable to a sudden loss of vision. Neither the patient nor the physician should regard sudden deafness as a minor incident. An immediate and meticulous search for possible causes is mandatory. As a first step, an otoscopic examination should be carried out, and the hearing loss must be documented by an audiometric evaluation. Further steps of management will be tailored according to the results of these examinations. In some cases, immediate therapeutic measures must be taken to improve the patient's hearing loss. Therefore, an emergency referral of the patient to an otologist is to be recommended in all cases of sudden hearing loss.

Brain Stem↗
PubMed1993

[Use of acoustic distortion products in clinical diagnosis. The site of origin of otoacoustic emissions in the inner ear].

Distorsion product otoacoustic emissions (DPOAE) are generated by a continuous bitonal stimulation of the cochlea. The resulting emissions are measurable in a definite mathematical function of the primaries (mf1 +/- nf2; f1 < f2). In humans sound emission at the frequency 2f1-f are usually detectable. To determine if a disturbance of DPOAE-amplitude is associated with a cochlear lesion in the frequency region of the evoked emissions or the primaries, we performed suppression experiments using normal-hearing, healthy probands (n = 14). DPOAE were measured in the frequency range between 800 Hz and 8 kHz with different sound-pressure levels for the primaries. Evoked emissions for each proband were measured with these different stimulus parameters to determine baseline values. In suppression experiments sound emissions were evoked continuously with different stimuli between 800 Hz and 8 kHz, disturbed simultaneously with a third tone of 1, 2 and 4 kHz and then compared with baselines. Suppressor tones (1, 2, 4 kHz) reduced significantly the DPOAE amplitudes in the frequency region of the geometric mean of the primaries. This indicates that a reduction of the emission amplitude in associated with a cochlear lesion near the generation site of the DPOAE. The suppression curves exhibit a sharp and steep graph, indicating their relation to cochlear frequency selectivity.

Acoustic Stimulation↗
PubMed1992

[Palliative measures in tumor-induced obstruction of the airways].

Local stenoses of the central airways in malignant inoperable disease are sometimes present at the time of diagnosis or develop over time after the completion of systemic palliative treatment. These stenoses should be relieved by local means in order to prevent the development of atelectasis and poststenotic pneumonia. Otherwise, patients will develop progressive dyspnea, and their general condition will decline rapidly. Various methods aimed at the relief of local obstructions exist and are often used in combination. Most procedures are performed under general anaesthesia using the rigid bronchoscope. Intraluminal obstructions can be relieved by laser-, cryo- and brachytherapy (endobronchial radiation). Extrinsic stenoses caused by airway compression from outside or by thickening of the airway wall through submucosal tumor growth must be dilated. At the end of these procedures, the insertion of silicone stents is ideally suited to maintain airway patency in dilated extrinsic stenoses and to prevent recurrent intraluminal tumor growth after laser therapy. The various methods aimed at the relief of malignant local airway obstructions are discussed, with emphasis on the recently developed silicone stents.

Airway Obstruction↗
PubMed1992

Stapedius reflexes to electrical stimulation in the rabbit for the assessment of hearing.

The possibility of using electrically induced stapedius reflexes as a means of objective hearing evaluation was investigated in the rabbit as an animal model. The contralateral stapedius reflex to acoustic and electrical stimulation was measured in anesthetized rabbits. For electrical stimulation, the middle ear was opened surgically and stimulation was applied by a monopolar electrode placed at or into the round window. Contraction of the middle ear muscle was monitored by digital sampling and averaging of the impedance changes in the contralateral ear. Acoustically evoked reflexes were recorded within expected limits despite anesthesia. The level of the electrical stimulus was raised until mass reflexes of the neck muscles were observed. A contralateral stapedius reflex to electrical stimulation could not be demonstrated. In our experiment, monopolar electrical stimulation at the round window could not elicit contralateral stapedius reflexes.

Acoustic Stimulation↗
PubMed1992

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.

Acoustic Stimulation↗
PubMed1992

Postprandial pattern of triglyceride-rich lipoprotein in normal-weight humans after an oral lipid load: exaggerated triglycerides and altered insulin response in some subjects.

In 13 healthy, male nonsmokers (mean age: 25.7 +/- 2.4 years) with normal fasting triglycerides we investigated postprandial changes of triglycerides in several lipoprotein fractions. After a 12-hour overnight fast they ingested a standardized lipid load (1,017 kcal) including 30,000 IU retinyl palmitate. Postprandially, total triglycerides increased significantly (p < 0.001) to a peak value of 221 +/- 81 mg/dl at 5 h. Two subjects had an exceptionally strong triglyceride response (peak values: 363 and 390 mg/dl). They had the highest levels of retinyl palmitate in the chylomicron and the nonchylomicron fraction, and one of them showed elevated intermediate-density lipoprotein values throughout the test period. In addition, they showed an altered early and an increased late postprandial insulin response. Thus, our data provide evidence that an exaggerated postprandial triglyceride response may point to an increased atherogenic risk even in healthy subjects with normal fasting triglycerides.

Adult↗
PubMed1992

Influence of general anesthesia on transiently evoked otoacoustic emissions in humans.

The influence of general anesthesia (GA) on transiently evoked otoacoustic emissions (TEOAEs) was studied in 19 normally hearing women undergoing surgery. Emissions were measured on the day before the operation, after premedication but before the beginning of the operation, and during and after the operation. There were no significant differences in TEOAE amplitude or in reproducibility between results obtained the day before the operation and after premedication. Ten patients received nitrous oxide (N2O) during GA (N2O group), and 9 patients did not (non-N2O group). The amplitude of TEOAEs was reduced during GA in 9 of 10 patients in the N2O group and in 7 of 9 patients in the non-N2O group. However, the average decrease of amplitude after the first 10 minutes was greater in the N2O group (4 +/- 3.4 dB) than in the non-N2O group (0.18 +/- 1.4 dB). The corresponding mean reproducibility of the response decreased in 9 of 10 patients of the N2O group (29% +/- 24%) and was nearly unchanged in the non-N2O group (2.3% +/- 7.2%). The time course of the amplitude reduction was similar in both groups. The smallest amplitudes were reached on an average by 19.3 +/- 11.4 minutes in the N2O group and by 17 +/- 13.6 minutes in the non-N2O group. Preoperative and postoperative TEOAEs were comparable in level and reproducibility. Differential frequency effects imply a middle ear effect for the greater reduction of TEOAE amplitudes in the N2O group due to gas diffusion into the middle ear.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustics↗
PubMed1992

Transiently evoked otoacoustic emissions in patients with Menière's disease.

Transiently evoked otoacoustic emissions (TEOAEs) were stimulated using clicks or 1-kHz tone bursts in both ears of 31 patients with unilateral Meniere's disease. Using click stimuli, responses were present in 29/31 of the non-Meniere's ears and in 26/31 of the Meniere's ears. Stimulation using 1-kHz tone bursts produced responses in 30/31 of the non-Meniere's ears and in 28/31 of the Meniere's ears. Audiometric configuration strongly influenced the presence of TEOAEs in the affected ears. In all but 2 ears with average hearing sensitivity (0.5, 1, 2 kHz) poorer than 25 dB HL, responses were present only when accompanied by at least one pure-tone threshold better than 30 dB HL from 0.75 to 2 kHz. In the opposite ears, all of which had essentially normal hearing, responses were approximately 5 dB lower in level and contained fewer spectral peaks in comparison with results obtained from a normative database. Neither age nor pure-tone results could account for these differences. Thus, TEOAEs obtained from patients with Meniere's disease manifest features that may be considered as atypical either in comparison to results from ears with normal hearing or from ears with relatively flat sensorineural hearing losses due to other etiologies.

Adult↗
PubMed1992

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.

Acoustic Stimulation↗
PubMed1991

[Silicone endoprosthesis in the treatment of tracheobronchial stenosis. Report of the first 12 patients treated with this method].

Inoperable tracheobronchial stenoses are most often due to malignant disease. Apart from systemic therapy, various local treatment modalities such as laser resection, cryotherapy and endobronchial radiation therapy have been designed to maintain airway patency. Recently, various models of tracheobronchial stents (or endoprostheses) have been designed to maintain airway patency. They prevent recurring endobronchial tumor growth or progressive extrinsic compression of dilated airways. Silicone stents are highly suitable for this purpose. We treated 12 patients (11 males, 1 female, median age 68,5 years) suffering from bronchial carcinoma (6), esophageal carcinoma (4), metastatic colon carcinoma (1) and metastatic osteosarcoma (1). One stent per patient was inserted at the following sites: 6 in the right main bronchus, 4 in the trachea, 1 in the left main bronchus and 1 tracheobronchial left. We observed 2 complications: one obstruction of a bronchial stent by secretions which could be managed by fiberbronchoscopy and one short fire to a bronchial stent on repeat laser therapy. Rapid and lasting relief of dyspnea was observed in all patients. Our initial experience with a median follow-up of 2 months confirmed the easy insertion technique, the excellent effect and tolerance as well as the simple postoperative care of these silicone stents. Their use immediately after relief of a tracheobronchial obstruction by local means can be recommended.

Aged↗