[Preparation and processing of clinical ERA-datas using a small laboratory computer: tentative experiences and results for the late, acoustically evoked potential N1 (author's transl)]

The efficacy of the Electric Response Audiometry (ERA) in the supraliminal range can be enlarged and improved by the use of laboratory computers. The acoustic system has to be described as objectively as possible from the lot of datas resulting especially from clinical examinations. An off-line-program sequence which may be routinely used, was elaborated for the laboratory computer PDP 12 in order to measure and evaluate the late, acoustically evoked potential N1. In addition to the organisation and documentation of the datas it is shown that for many cases the described and performed preparation and processing of the datas yield qualitatively and quantitatively better results.

[Registration of the early acoustically evoked potentials using monaural and binaural stimulation (author's transl)]

At seven normally hearing test persons the early acoustically evoked potentials were registered using monaural, binaural and contralateral click-stimulation with a repetition-rate of 10/sec at the intensities of 90 and 70 dB SPL. In comparison to the monaural stimulation the binaural stimulation yields in the mean no significant alteration of the potentials I, II and III at both intensities. The mean enlargement of potential IV by binaural stimulation amounts to about 40% and is highly significant, but this advantage does not apply always to everybody: the factor of magnification of potential IV covers the range from one to two. The average increase of 66% at potential V is weakly significant for the intensity of 90 dB SPL. As expected from the results of contralateral stimulation the registrations at patients suffering from unilateral hearing impairment show on both sides the potential's threshold of the better hearing ear when stimulating binaurally; therefore you cannot determine the better cochlea. In addition to this fact the binaural stimulation of patients suffering from an acoustic neuroma removes the diagnostically important tool to recognize differences between the two sides. These findings are demonstrated by examples. Since it is impossible to predict an increase of the amplitude in the individual case and since there are serious diagnostic disadvantages, we don't deem advisable a binaural stimulation.

[ERA-findings by "cortical hearing disorder" (author's transl)]

Since about the last 2 years the late potential's component N1 (90--110 ms) as well as the early acoustically evoked potentials, appearing in a latency range of 1--8 ms and consisting of the nerve action potential (Pot. I) and the brain-stem potentials (Pot. II-V), were registered at some hearing impaired patients. This procedure enabled us to diagnose a "cortical hearing defect" at five patients: a) three children at an age of 2--3 years; they all have a slight cerebral damage, a hearing impairment and no speech-development; b) a 15 year old girl with a hearing impairment which is on the right side more severe than on the left side, as consequence of an encephalitis; and c) a 50 year old man suffering on both sides from a loss of temporal brain's substance and from a total deafness after an insult of both arteriae meningeae mediae. At all these patients the ERA-findings result in an almost normal behaviour of the bioelectrical transfer of the acoustic stimuli in the region of the brain-stem, whereas the late potential's component N1 showed a pathologic distortion. The ERA-results together with the anammesis make a "cortical hearing disorder" probable at these five patients. The audiograms and the ERA-characteristic lines are shown and discussed.

Does promethazine (Atosil) influence the human's early acoustically evoked potentials in the same way as the late potential N1?

In a former investigation the effect of promethazine (Atosil) on the late acoustically evoked potential component N1 was examined. Now the cochlear and the brain-stem potentials were registered by the earlobe-vertex pick-up with i.m. application of 0.8 mg/kg (body weight) promethazine. There was no influence of promethazine either on the compound action potential (NAP) or on the brain-stem potentials (Pot. II-V), but sedation improves significantly the signal-to-noise ratio, therefore we sedate all patients when registering the five early acoustically evoked potentials.

[Topodiagnostic ERA results at a female patient with multiple sclerosis in the brainstem (author's transl)]

At a female patient suffering from multiple sclerosis with demyelinisation mainly in the pontine and mesencephalic tegmentum, the five early potentials consisting of the compound action potential of the acoustic nerve (Pot. I) and the four brainstem potentials (Pot. II-V) as well as the slow evoked vertex-potential were registered. The threshold behaviour, the characteristic curve and the latency curve of all potentials were obtained, and thereby damages of the central acoustic pathways found out. A topodiagnostic is tried by means of the alterations of the peripheral and central ERA, and by means of the informations described in the literature. A control registration, carried out four weeks later, demonstrated an improvement of the diagnosis.

Input-output function and adaptation behaviour of the five early potentials registered with the earlobe-vertex pick-up

At twenty-three 20-30-year-old normal-hearing subjects the characteristic curves of amplitudes and latencies of the five early potentials, appearing within the first 8 ms after stimulus onset, were obtained. The potentials were registered with the earlobe-vertex pick-up, as described by Sohmer and with click stumulus rates of 5/sec, 10/sec and 100/sec; It could be seen: All five potentials depend in amplitude and latency on intensity; all potentials show with increasing click rate an adaptation and a delayed latency, when increasing the click rate from 10/sec to 50/sec; the adaptation phenomenon of the 1st, 2nd, 3rd and 4th potential is the most prominent, the 4th potential shows the smallest adaptation effect; the characteristic curve at 10/sec of the 1st and 3rd potential demonstrates a break at 70 dB SPL; the latencies of the five potentials begin to increase at click rates higher than 10/sec; the 4th potential seems to be the most suitable one for measuring the acoustical threshold; only the fifth potential diminishes in amplitude and increases in latency after administration of an anaesthetic, but an additional relaxant does not alter it any more.

[Electrocochleographic potential pattern, recorded by different pick-ups (author's transl)]

At electrocochleography, the active electrode was placed on the earlobe, the mastoid, the nasopharynx, the hard palate and the external ear-canal respectively. It could be shown that the potential pattern, consisting of five components, during the first 8 msec after the click-onset could be obtained from all the above mentioned sites. In relation to the various electrode pick-ups we obtained different amplitude functions with nearly the same latency behaviour for all five potentials.