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Biomedical subjects

K Stephan

Publications and source records attributed to K Stephan.

At least 37 records · Page 2Linked to original sources
PubMed1990

Auditory brainstem response thresholds in a mouse mutant with selective outer hair cell loss.

Mutant animals with a particular type of cochlear pathology are an excellent model for studying the functional role of various cells of the cochlea. In homozygous WV/WV mutant mice we found a selective loss of outer hair cells as a constant defect with no progressive degeneration of the organ of Corti. The mice were followed throughout their lives and exhibited auditory brainstem responses that were elevated to about 50 dB SPL as compared to normal control animals. Sequential temporal bone studies showed that there was a selective loss of outer hair cells throughout the entire cochlea as seen in surface preparations. The inner hair cells were present in normal numbers and appeared to be essentially normal.

Aging↗
PubMed1990

Stapedius reflex growth function in cochlear implant patients.

The growth function of the contralateral stapedius reflex elicited by analog electrostimulation via cochlear implant was investigated in 9 patients and compared to reflex functions obtained for acoustic stimulation in 3 normal-hearing subjects. Sinusoidal signal bursts with the same time pattern were used for the two stimulation modes, the contraction of the middle ear muscle was monitored by sampling the compliance change in the contralateral ear. The reflex amplitudes were found to increase with increasing stimulus intensity in all individuals except in 1 with electrical stimulation. The slope of the intensity function for electrostimulation ranged between 5 and 85%/dB and in the acoustical mode between 2 and 4%/dB. In case of electrostimulation a frequency effect was observed.

Acoustic Stimulation↗
PubMed1990

Dynamic range of the contralateral stapedius reflex in cochlear implant patients.

The dynamic range of the contralateral Stapedius reflex elicited by analog electrostimulation via cochlear implant was investigated in 8 subjects supplied with a Vienna prosthesis. The study comprised patients fitted with intracochlear devices as well as patients with extracochlear devices. Sinusoidal bursts of 125, 500, 1,000 and 2,000 Hz were used as stimulation signals. Only in one patient was saturation of reflex amplitude observed. The dynamic range of the Stapedius reflex was defined either by the difference in stimulus level for reflex saturation or individual uncomfortable loudness level and reflex threshold. Two different methods were used, yielding values between 0.1 and 12 dB, with a median of 4 dB. The individual results were compared with individual psychoacoustic quantities, i.e. subjective dynamic range (difference between sensation threshold and uncomfortable loudness level) and residual dynamic range (difference between most comfortable loudness level and uncomfortable loudness level). The reflex dynamic range is located within the residual dynamic range of electrostimulation. Thus the Stapedius reflex dynamic range can be applied as a rough estimate of minimum residual dynamic range.

Acoustic Stimulation↗
PubMed1989

Hearing with selective inner hair cell loss.

In a comparative model study, the effect of selective inner hair cell loss on hearing threshold was investigated. Functional testing was related to a detailed morphological evaluation. Inner ears of homozygous Bronx waltzer mice (bv/bv) were investigated using light microscopy with Nomarski interference contrast optics and transmission electron microscopy. Hearing thresholds were determined using click evoked auditory brainstem responses at different ages. The histological evaluation was performed immediately after determination of the hearing threshold. The functional and histological findings were compared to the normal controls of the same age. Scattered loss of up to 70% of inner hair cells was found to cause only moderate elevation of hearing threshold.

Animals↗
PubMed1988

Stapedius reflex threshold in cochlear implant patients.

The contralateral stapedius reflex elicited by sinusoidal electrostimulation via cochlear implant was investigated in 12 patients. Contraction of the middle ear muscle was monitored by time-resolved synchronized digital sampling of the impedance change in the contralateral ear. The reflex was detected in all patients in whom the uncomfortable loudness level (UCLL) could be reached and who had intact middle ear function. Generally, the reflex threshold is located in the upper part of the dynamic range between the most comfortable loudness (MCL) and the UCLL. The demonstrated method may provide suitable assistance in speech processor adjustment in difficult-to-test patients.

Adult↗
PubMed1986

The benefit of hearing aids: influence of hearing loss and age.

The relation between accessible benefit and hearing loss in combination with age of the patient is analysed. The degree of hearing loss and improvement derived by hearing aid use as found in this work is based on the individually determined speech reception threshold (SRT) for the condition with and without hearing aid in a noiseless environment. It was found that a significant correlation exists between hearing loss and SRT gain by the hearing aid (difference between unaided and aided speech reception threshold) for a pure-tone hearing loss of less than 40 dB at 500 Hz, irrespective of age, whereas for a hearing impairment of 40-60 dB, the gain by using the hearing aid is dependent on the age of the patient. A multiple regression analysis was performed to study the relation between benefit and hearing loss for the two groups of hearing impairment and different age groups.

Age Factors↗
PubMed1980

Cystic fibrosis.

Explore the source record for details and available documents.

Adolescent↗
PubMed1976

Time course of changes in ventricular fibrillation threshold in myocardial infarction: characteristics of acute and slow occlusion with respect to the collateral vessels of the heart.

The time course of the changes in ventricular fibrillation threshold (VFT) was determined in 28 dogs by means of electrical stimulation, triggered from the R wave, with DC square wave pulse series (of 140 ms duration) inserted into the vulnerable period of the cardiac cycle. After acute coronary occlusion there was a sudden decrease in the VFT followed by a slow increase such that 30 min after the ligation pre-occlusion values of VFT were reached. The magnitude of the decrease in VFT depended upon the collateral blood supply. There were no other changes in VFT during the remaining course of the experiment. Following slow coronary occlusion the first arrhythmic phase was not detectable. Any decreases in VFT that occurred were smaller and of shorter duration than those occurring after acute occlusion and were independent of the extent of the collateral blood supply.

Angiocardiography↗