Search PubMed⌕ Search

Biomedical subjects

R Probst

Publications and source records attributed to R Probst.

At least 19 recordsLinked to original sources
PubMed2001

Mismatch negativity and psychoacoustic measures of gap detection in normally hearing subjects.

Temporal auditory processing deficits are thought to play an important role in some pathologies of speech understanding difficulties. The purposes of the present study were to determine whether short silent gaps within a pure tone can be used to elicit mismatch negativity (MMN) as an objective measure of temporal resolution, and to investigate the relation between MMN and performance on a behavioral gap-detection task. The stimuli used for both tasks were 1-kHz sinusoids presented in a low-pass masking noise. Behavioral gap-detection thresholds were determined using an adaptive three-alternative forced-choice procedure. To elicit MMN, a series of deviant stimuli with varying gap durations was generated and presented in an oddball paradigm among standard stimuli without a gap. Only the gaps larger than the mean behavioral gap-detection threshold evoked a clear MMN. There was no clear relation between psychoacoustic and MMN thresholds.

Acoustic Stimulation↗
PubMed2001

[Partially hydrogenated aryl-1,2/1,4-anthraquinone derivatives, 5-lipoxygenase inhibitors with arotinoid structure].

The combination of 5-LOX inhibition and retinoid activity in one molecule could be an interesting pharmacological tool to influence psoriasis. Thus we synthesized compounds with arotinoid structure by anellation of the 5-LOX inhibitors 1 and 2 with 1,1,4,4-tetramethylcyclohexane. A key step was the CuCl-MeCN-O2 oxidation of tetrahydroanthracenol 13 to the corresponding 1,2-anthraquinone 14 which could be converted to the analogous 2-hydroxy-1,4-anthraquinone 19 by Thiele-Winter reaction followed by oxidation. The halogenated quinones 9 and 21 were arylated with 2,6-di-tertbutylphenol and demethylated or hydrolyzed to the target compounds 3 and 4 which were tested in comparison with the non-anellated 5-LOX inhibitors 1 and 2 for LOX inhibition in activated human granulocytes and for antioxidative activity by the method of Popov with the chemiluminometer Photochem. The results are discussed in relation to the corresponding logP values. The 1,2-quinones 1 and 3 are more potent 5-LOX inhibitors than their 1,4-analogues 2 and 4, the tetrahydroanthraquinon derivatives 3 and 4 are less potent than the naphthoquinones 1 and 2. All compounds are devoid of any activity in cell differentiation as compared to retinoic acid as indicated by the NBT test with HL-60 leukemia cells.

Anthraquinones↗
PubMed2000

Cortical reorganization after acute unilateral hearing loss traced by fMRI.

Unilateral acoustic stimulation produces a functional MRI (fMRI)-blood-oxygenation-level-dependent (BOLD) response mainly in the contralateral auditory cortex. In unilateral deaf patients, the BOLD response is bilateral. We studied a subject with sudden hearing loss after cochlear nerve resection before and repeatedly after surgery. During normal bilateral hearing, contralateral cortical BOLD responses were found. Progressing compensatory reorganization with bilateral representation of unilateral stimulation was detected over a period of approximately 1 year.

Acute Disease↗
PubMed2000

Suppression of tone burst evoked otoacoustic emissions in relation to frequency separation.

Tone burst evoked otoacoustic emissions (TBEOAEs) were measured for two tone bursts presented separately and as a two-tone burst complex to examine the linearity of TBEOAE generators for different frequency separations of the stimuli. The stimuli were: (a) tone bursts of 5-ms duration and center frequencies of 1, 1.5, 2 and 3 kHz; (b) complex stimuli with the 1-kHz tone burst combined digitally with each of the other specified tone bursts. Signals were delivered at 70 dB SPL using a non-linear processing method and at 60 dB SPL using a linear method to 21 ears of normally hearing adults. Spectra of TBEOAEs obtained with single-tone bursts were superimposed (composite) and compared to those of the two-tone burst complex. A close correspondence between the composite and complex spectra was present in all ears. However, the components on the higher-frequency slope of the 1-kHz spectral peak were reduced in the complex spectra obtained with a frequency separation of 0.5 kHz when compared to the corresponding composite spectra. The reduction was greater at a stimulus level of 70 dB SPL than with 60 dB SPL. The effect was smaller for a frequency separation of 1 kHz, and almost absent for the tone burst separation of 2 kHz. Thus, suppression leads to weak non-linear frequency superposition for higher-level, closely spaced stimuli.

Acoustic Stimulation↗
PubMed2000

Changes in collagen I and collagen III metabolism in patients with generalized atopic eczema undergoing medium-dose ultraviolet A1 phototherapy.

Fourteen patients suffering from acute, exacerbated atopic eczema were screened for changes in collagen I and collagen III metabolism in serum (n = 11), urine (n = 11) and skin biopsies (n = 9) before and after medium-dose ultraviolet (UV) A1 phototherapy (15 exposures of 50 J/cm2 over a 3-week period, total dose 750 J/cm2). Mature collagen I and, to a lesser extent, mature collagen III were found to be decreased after the therapy in skin samples from the irradiated patients. As markers of collagen I degradation, the cross-links pyridoline and deoxypyridoline were analysed in urine using high-performance liquid chromatography. Both cross-links were found to be mildly increased after UVA1 phototherapy, without reaching statistical significance. As markers of de novo collagen synthesis we screened for the procollagen I-carboxyterminal peptide (PICP) and procollagen III-aminoterminal peptide (PIIINP) levels in serum and skin. The ratio of PICP to PIIINP in serum dropped significantly after the UVA1 phototherapy, suggesting a different impact of UVA1 on the two collagens. These findings were paralleled by a diminished ratio of PICP to PIIINP in tissue samples. Staining for matrix metalloproteinase 1 (MMP-1) and its specific counterpart, tissue inhibitor of MMP-1 (TIMP-1), showed slight increases for both proteins by therapeutic UVA1; this was also seen in serum for TIMP-1 but not MMP-1. In our study, high-energy UVA1 doses induced changes of the skin collagens in patients with atopic eczema which are measurable by their metabolites in serum and urine.

Chromatography, High Pressure Liquid↗
PubMed2000

[First results of a national hearing screening program in Switzerlans].

A Swiss study group was formed in summer 1998 with the aim of establishing a universal hearing screening programme in newborns following the recommendations of the "European Consensus Statement on Neonatal Hearing Screening" (Milan 1998). The aim of the group was to standardise and to introduce universal hearing screening in all infants born in Switzerland. Starting in June 1999, several hospitals in Switzerland began the screening programme using commercially available equipment for easy and highly automated measurement of transient evoked otoacoustic emissions. Up to March 2000, 6262 children were born in these hospitals and 5656 (90%) underwent neonatal hearing screening. 88 children of the 5656 did not pass the screening test. The measurement of otoacoustic emissions was repeated in a follow-up examination within 6 weeks. If otoacoustic emissions were again absent, evoked auditory brainstem potentials were measured. 48 children were found to have hearing within normal limits at the follow-up examination, 24 children have not been examined yet, 11 children were examined in other clinics or the follow-up examination was refused by the parents. 5 children were found to have bilateral hearing dysfunction and were referred to rehabilitation within the first 6 months of life.

Evoked Potentials, Auditory, Brain Stem↗
PubMed2000

[Extended high-frequency audiometry--reproducibility of two type of earphones].

Auditory thresholds in the frequency range of 0.5-6 kHz and in the extended high-frequency range (8-16 kHz, according to ISO 389-5) were measured for one ear of 139 otologically healthy persons (77 females, 62 males, mean age 25 years, range 12-54 years) using insert earphones ER-2 of Etymotic Research and circumaural earphones HDA 200 of Sennheiser. For each subject, two measures of the thresholds were obtained for both types of transducers during the same test session. Repeatability was significantly worse in the 8-16 kHz region (repeated thresholds were within +/- 5 dB for 90% of the thresholds of each frequency and within +/- 10 dB for 98%), compared to that in the 0.5-6 kHz region (+/- 5 dB for 97%, +/- 10 dB for 100%), as determined by paired t-test and Wilcoxon signed rank test. Repeatability was similar for both transducer types.

Adolescent↗
PubMed2000

[Is there clinical evidence for the aging of the peripheral vestibular organ?].

The ageing process of hearing is well known. Age-dependent normative data are established for pure tone audiometry. It seems logical to suppose that the peripheral vestibular system undergoes a similar ageing process. To support this hypothesis we investigated subjects aged 50-82 with presbyacusis demonstrated by pure tone audiometry. Asymmetry of the peripheral vestibular system was ruled out by symmetrical thermal excitation rate. Slow-phase velocity of nystagmus induced by rotating-chair stimulation was compared with pure tone audiometry. We found no significant correlation and thus our approach failed to bear out the hypothesis.

Aged↗
PubMed1999

[Instructor in the army and fortifications guard--risk occupations for acute acoustic trauma and for wearing a hearing aid].

In the Swiss army instructors and fortifications guards are exposed to firearms' noise which harms the ear. It was investigated whether the decline in the cases of acute acoustic traumas in non-professional soldiers serving in the army from 1987 to 1996 also was detectable in army instructors and fortifications guards (professional soldiers) and whether these persons were wearing hearing aids (as an indicator of hearing loss) more often than the average of the male Swiss population. First, we analyzed a historical time series of the incidence density of acute acoustic traumas in non-professional soldiers as well as in army instructors and fortifications guards. Second, we compared the prevalence rate of wearing a hearing aid in army instructors and fortifications guards with the male Swiss population. The incidence density for acute acoustic traumas in army instructors and fortifications guards observed over ten years showed no significant change whereas among non-professional soldiers a strong decline (-12% per year) was observed. The prevalence rate of wearing a hearing aid in army instructors and fortifications guards was significantly higher (RR 3.91 [95% CI 3.09-4.96]) than in the male Swiss population. These results suggest increased hearing impairment among army instructors and fortifications guards which is probably due to the high exposure to impulse noise events (occupational disease). It is recommended that these persons be subjected to a compulsory prevention program.

Accidents, Occupational↗
PubMed1999

[The usefulness of intraoperatively registered, electrically evoked stapedius reflex for the programming of cochlear implants in children].

The programming of a cochlear implant speech processor used by young children is often difficult, especially when the stimulus level associated with maximum auditory loudness (MAL) needs to be determined. Excessively high stimulation should be avoided as this can have a traumatic effect. The aim of this study was to determine if a relationship exists between the intraoperatively determined electrical stapedius reflex threshold (ESRT) and the postoperatively determined MAL and hearing threshold for 27 patients, each having one of three implant types. The question of whether the ESRT provides a practical technique to simplify, improve and accelerate speech processor programming was investigated. For the monopolar stimulation mode used for the Med-El and Clarion implant systems, the average MAL and threshold was expressed as a percentage of the average ESRT across all electrodes. For the "common ground" stimulation mode used for the Nucleus implant system, a parabolic transformation was used to relate MAL and ESRT to one another. These transformations between MAL values calculated from the ESRT and the actual MAL values, determined psychoacoustically, diverged considerably from one another. Therefore, it was not possible to determine the MAL from the ESRT with certainty. The ESRT does, however, provide a means to estimate an approximate upper boundary for the MAL, apart from its use to control implant function. The determination of the exact MAL will still need to be determined using behavioural techniques.

Adolescent↗
PubMed1999

Premeatal and retromeatal cerebellopontine angle meningioma. Two distinct clinical entities.

OBJECTIVE: Meningiomas represent the second most common type of neoplasm of the cerebellopontine angle (cpa). Their relationship to critical neural or vascular structures of the cpa is variable and they present with different signs and symptoms. MATERIALS AND METHODS: A retrosigmoid craniotomy was performed in 31 cpa-meningiomas from January 1981 to February 1997. The mean age of the 25 women (81%) and the 6 men (19%) was 53 +/- 13 years. According to their location within the posterior fossa and with special reference to the internal auditory canal (IAC), they were classified in 17 cases (55%) as retromeatal (posterior to the iac) and in 14 cases (45%) as premeatal (anterior to the iac). RESULTS: The retromeatal group showed a significantly larger tumour size (21 +/- 15 vs 29 +/- 20 mm) and the diagnosis was made later (2.7 +/- 3.2 vs 1.1 +/- 0.9 years) compared to premeatally located meningiomas. Before the operation, a reduction of the facial nerve function (64% vs 0%) and hearing function (100% vs 25%) was present significantly more often in premeatal meningiomas. The clinical appearance of the retromeatal group was dominated by cerebellar symptoms (44% vs 0%). Both preoperative and postoperative impairment of facial nerve and auditory function prevailed in the premeatal group. CONCLUSION: The topological classification of CPA-meningiomas according to their location anterior or posterior to the ICA is important, because the clinical presentation, the surgical strategy to be applied, and the functional outcome of critical neural structures differ between the two subtypes. Our results provide substantial evidence for the paradoxical observation that premeatal meningiomas have a significantly worse postoperative functional outcome compared to retromeatal meningiomas although premeatal meningiomas become symptomatic earlier and at smaller sizes.

Adult↗
PubMed1999

Trigeminocardiac reflex during surgery in the cerebellopontine angle.

OBJECT: In different experimental studies authors have analyzed the autonomic responses elicited by the electrical, mechanical, or chemical stimulation of the trigeminal nerve system. The trigeminocardiac reflex (TCR) is a well-recognized phenomenon that consists of bradycardia, arterial hypotension, apnea, and gastric hypermotility. It occurs during ocular surgery and during other manipulations in and around the orbit. Thus far, it has not been shown that central stimulation of the trigeminal nerve can also cause this reflex. METHODS: The TCR was defined as clinical hypotension with a drop in mean arterial blood pressure (MABP) of more than 20% and bradycardia lower than 60 beats/minute. Pre-, intra-, and postoperative heart rate (HR) and MABP were reviewed retrospectively in 125 patients who underwent surgery for tumors of the cerebellopontine angle (CPA), and they were divided into two groups on the basis of the occurrence of the TCR during surgery. Of the 125 patients, 14 (11%) showed evidence of the TCR during dissection of the tumor near the trigeminal nerve at the brainstem. Their HRs fell 38% and their MABPs fell 48% during operative procedures as compared with preoperative levels. After cessation of manipulation, the HRs and the MABPs returned to preoperative levels. Risk factors for the occurrence of the TCR were compared with results from the literature. CONCLUSIONS: The authors' results show the possibility of occurrence of a TCR during manipulation of the central part of the trigeminal nerve when performing surgery in the CPA.

Adolescent↗