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Biomedical subjects

R Brix

Publications and source records attributed to R Brix.

15 recordsLinked to original sources
PubMed1991

Late cortical auditory potentials evoked by electrostimulation in deaf and cochlear implant patients.

Deaf or residually hearing patients without sufficient auditory communication by conventional hearing aids are candidates for the implantation of a cochlear prosthesis. In addition to objective audiometry (electrophysiological evaluation and assessment of the degree and type of hearing loss), preoperative electrostimulation tests should be performed. In so doing, it is reasonable to employ late cortical potentials for preoperative patient selection as well as for postoperative follow-ups. In contrast to early potentials (such as, brain stem evoked potentials), late cortical potentials offer technical, physiological, medical and psychological advantages. This approach to testing has been used successfully in 70 patients (including children over the age of 3 years).

Adult↗
PubMed1991

[The bioequivalence of doxycycline in two preparations in capsule form].

In a randomized cross-over study the bioavailability of doxycycline (CAS 17086-28-1) in two preparations was examined by determining AUC and Cmax. The bioavailability of Doxycyclin-Kapseln (T = test preparation) relatively to a reference preparation (R) in 20 healthy subjects. Statistical analysis of plasma concentration curve and maximum concentration showed no differences between the pharmaceutical preparations tested. Both preparations proved to be bioequivalent.

Adult↗
PubMed1986

[Neurophysiologic correlates in rhythm perception: early auditory evoked potential responses as indicators of a rhythm detection system].

The results of this experimental study on human subjects indicate that the "far-field recorded auditory evoked wave VI potential" is correlated with auditory information processing of "rhythms" ("rhythm recognition", "rhythm experience"). Topography and functional mechanisms of a "neuronal system for rhythm detection" which is a prerequisite of "rhythmic experience" are discussed. The results cannot be interpreted as motor or attention effects.

Acoustic Stimulation↗
PubMed1979

Cochleo-vestibular correlations in Meniere's disease.

The cochlear and vestibular functions were investigated in a sample of 36 patients with unilateral Meniere's disease. Caloric reactions and hearing thresholds were compared separately at several frequencies. A topodiagnostic relationship between the cochlear and vestibular function was discovered. Using four qualitative categories, a significantly high correlation was obtained between the basal hearing loss (4000 Hz) and unilateral weakness, whereas no correlation was obtained when evaluating the more apical hearing loss (lower frequencies 250-1 000 Hz). A normal caloric reaction can be reasonably expected in cases of unilateral Meniere's disease if the hearing loss is less than approx. 40 dB HL at 4 000 Hz.

Adolescent↗
PubMed1979

[The semiautomatic speech audiometry (author's transl)].

In co-operation with the Viennatone Company we developed an apparatus to perform a "semiautomatic speech audiometry (SAS)". The patient is instructed to repeat the understood words into a cassette recorder when a signal lamp is on. The sequence of the test including the attenuation of intensities and a programmed change of the ear to be tested is automatically controlled. The evaluation of the patient's answers can be carried out by the assistent at any time that is suitable. The advantages of the SAS are a gain in time and the fact that during the test performance the assistent is free to pursue other activities. With the means of the SAS the possibility is now available to perform speech audiometry in very well frequented surgeries of specialists. In a surgery the apparatus was tested in 700 patients with success.

Audiometry↗
PubMed1979

[Critical review of the SISI-test (author's transl)].

For the last twenty years since the first publication the SISI-test (Jerger et al. 1959) is used as a standard test in audiometry, although the clinical utility has been doubted by many audiologists. The aim of this study is to show essential test-theoretical mistakes which exist--apart from the bad clinical results--in the SISI-test. The most important fault is, that the diagnosis of clinical groups is established by means of the comparison of different test-stimuli (different main intensities).

Diagnosis, Differential↗
PubMed1978

[The objectivation of auditory and optical imaginations in the electroencephalogramm (author's transl)].

This study describes two new DC-potentials, which are related to auditory or optical imagination. The "auditory imagination potential" (AIP) is a negative DC-shift on the vertex lasting during the whole period of an auditory imagination. During an optical imagination there is a similar negative DC-shift in the ocipital region only. These "imagination potentials" can be already recognized in the "raw-EEG" by means of a special experimental technique. The magnitude of amplitudes correlates with the degree of concentration of the subject. In the case of intense imaginations potentials with amplitudes up to 20 muV and a duration of some seconds are recorded. The comparison between the vertex and the occipital lead permits the examination of the alternate occurence of auditory and optical conscious processes. The "imagination potentials" (AIP and OIP) are not related to any external stimulation or motor reaction and represent modality-specific EEG-correlates of cognitive, conscious processes (memory and imagination). Their significance for the "objective audiometry" is discussed.

Acoustics↗
PubMed1978

[New methods in the objective audiometry for the proof of simulation and for the determination of the differential thresholds for frequency and intensity (author's transl)].

The "late acoustically evoked potentials" (50 to 300 msec) can be recorded in different stages of vigilance and awareness; therefore their significance as a correlate of conscious central perception is doubtful. The "very late DC-potentials" (300 msec and more) reflect conscious central perception because of their cognitively determinated features and can be used for the proof of simulation. Their application in ERA comprises the determination of the hearing threshold, the "objective speech audiometry" and the determination of the differential thresholds. The "objective frequency decrement test" gives additional informations about the degree and the specifity of a hearing loss. The objective proof of the differential threshold for intensity demonstrates the insufficient significance of the SISI test.

Audiometry↗
PubMed1977

[The importance of the "contingent negative variation" (CNV) for audiometry (author's transl)].

Previous proofs of "central processes" in hearing were based on the determination of the late "auditory evoked potentials" (AEP's: 50--300 ms) in EEG. The appearance of AEP's in different sleep stages raises the question, if the AEP actually conscious hearing. Since the discovery of the "Contingent Negative Variation" (CNV), as a potential depending on conscious and cognitive factors, an appropriate "instrument" is available to solve this problem. Using the CNV-technique three proofs of central auditory perception are described and discussed: a) "The objective proof of the perception of pure-tones", useful for threshold determination, test in the case of simulation and central hearing disorders. b) "The objective proof of the perception of stimulus-changes", useful for exact determination of differential thresholds for frequencies or intensities. c) "The objective speech audiometry", proof of speech comprehension, useful in case of aphasia and simulation.

Auditory Perception↗
PubMed1975

[Basis and clinical application of the "contingent negative variation" in "evoked response audiometry" (author's transl)].

After repeated stimulation with an indicative stimulus and a second imperative stimulus, a slow negative potential shife, the "Contingent Negative Variation" (CNV), can be recorded in the EEG before the second stimulus. On account of the main features of CNV two qualitative tests can be used in audiometry. "Tone-CNV" is an objective test of perception of a pure-tone. The indicative pure-tone is followed regularly by a second imperative stimulus, a flash of light or a slide. The appearance of CNV is the positive sign of perception, even if the "acoustically evoked potential" (AEP) is difficult to define. Adults and children (5 to 12 years) with normal hearing or suffering from several forms of hearing loss developed a CNV, except those patients with severe brain damage. The advantage of this method is the short testing time and accentuation of AEPs. The test can be also done under sedation. In "Objective Speech Audiometry", a proof of concept discrimination, only words of one concept are combined with a second imperative stimulus. The other group of words of the second concept remains "unreinforced". After correct discrimination all normal subjects developed a CNV before the second stimulus and after the "unreinforced" concept a "Discriminative Positive Variation" (DPV). Thus, this method can be used for clinical purposes. Loss of discrimination, perseveration phenomena and hemispheric differences were observed in aphasic patients.

Acoustic Stimulation↗
PubMed1975

[The objective frequency decrement test (OFDT): a new objective EEG-test for determination of the difference limen for frequencies (author's transl)].

Subjective methods measuring the difference limen for frequencies (DLF) take a lot of time and are not reliable. You can find this fact not only while testing normal subjects, but also while testing patients with hearing loss combined with tinnitus. Therefore this new objective DLF-test has been developed. Apart from the testing function for clinical purpose, the different results of other studies can also be controlled. After 1080 msec a pure tone is changed to a lower frequency for a period of 670 msec. Immediately after the tone is finished a picture is presented. As a control pure tones of unvarying pitch are offered. This stimulus sequence is repeated for several times. The expectancies to the change of pitch and to the picture produce a negative slow potential shift (Walter's CNV) in the EEG. The perception of frequency change yields to a late evoked potential and to a DC-shift; as a result of the optimum conditions of the expectancy-situation and the appropriate recording-technique only 5-10 sweeps must be summed up to obtain a potential, sometimes it even can be seen in the "raw-EEG". The test makes a differentiation between a just believed and a real perception possible. A sample of subjects with normal hearing and a subgroup (musicians) were selected for the standardization. Because of objectivity, reliability and economy the test can be used for clinical application.

Electroencephalography↗