Biomedical subjects
Publications and source records attributed to C Elberling.
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A method for the objective analysis of acoustically evoked brain stem potentials, BSER, is proposed. Recordings from 24 patients with pure cochlear hearing losses are adjusted in amplitude and time, and used to produce normative BSER waveforms serving as templates. The cross-correlation function between the individual, adjusted BSER recording and the corresponding template is calculated, yielding an objective measure of the BSER waveform and gross latency. Clinical application of the method has given encouraging results.
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An automatic method for critical band estimation from loudness summation data is presented. A mathematical model, based on a power function, is fitted to the data and the critical bandwidth is defined at the intersection of the asymptotes. The model is designed for clinical use, involving the treatment of the data from single test persons; it represents an operational solution to a difficult task. The model is able to describe data from normals and patients with a sensorineural hearing loss. Variability of the critical band estimates, intrasubject as well as intersubject, is larger than for visually obtained estimates. However, visual estimation is difficult, subjective, and probably heavily biased. The model produces estimates which in logarithmic form have a Normal distribution at medium loudness level, while visual estimation gives rise to irregular distributions at all levels. A normal range for model estimates from sets of data obtained at medium loudness level is defined by mean and standard deviation.
To overcome some of the problems involved in the application of brain stem evoked responses (BSER) in otoneurological diagnosis an approach is developed which combines cochlear and brain stem recordings. The activity of the cochlea and brain stem generators, as seen from the far-field recording electrode, is considered to be the output from a single system. The impulse response of this system can be derived through deconvolution of the brain stem evoked responses, BSER, with the compound action potential, AP, followed by appropriate filtering. This method is used on the recordings from 15 subjects with various degrees of cochlear hearing loss. The results show that the compound impulse response, CIR, for the brain stem consists of five recognizable peaks. From the individual subjects this response pattern is largely independent of intensity. By plotting the amplitude and latency of the individual peaks for all 15 subjects a set of normative data is retrieved. The variation in the data is small, probably because interfeerence from the periphery is eliminated and the separation of activity from the different brain stem generators is improved.
The physiological formation of the action potentials is presumed to be well-known and a method of decoding these potential is therefore based on this knowledge. The method uses the reverse process, i.e. deconvolution of the recorded AP's with a unit response, and a subsequent nonlinear transformation of the obtained waveforms (sigma PST-compound PST) from the time- into the location domain (distance along the coclear partition). The transformed waveforms are called excitation patterns. Stimulus polarity seems to have only a minor influence on the excitaton patterns and it is possible to produce frquency-specific information of the coclear function. A clinical case demonstrates the concordance between the excitation patterns and the puretone audiogram.
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3 patients with Norrie's diseas were examined with electrocochleography and brain-stem-evoked responses. The examination revealed a hearing loss of pure cochlear origin with no involvement of the brain stem. The disease is inherited as an X-linked recessive trait only affecting males with unaffected female carriers. The results are thus in agreement with previous investigations of the topical lesion in genetic hearing loss.
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