FROM THE HISTORY OF IERASG
(report from the 1. ERA Symposium, translated from Danish, with kind permission
from the author, H.J. Krogh, Odense, Denmark)
First International Symposium of the ERA Club
ORL-Clinic Freiburg/Breisgau, West-Germany , 1-4 April 1970
The Symposium Chairman was Professor Dr. F. Zöllner with Dr. G. Stange as moderator. A welcome ceremony in the evening of Wednesday April 1 introduced the opening of the professional part on Thursday morning. Altogether 16 papers had been prepared by 15 authors where 5 had been invited by the ERA Club. Time was scheduled for questions and short presentations for discussion. The Symposium has been possible through economical support from different companies.
The Symposium gathered more than 80 participants, mostly from Europe but also USA and Japan were represented.
ERA Club - Origin and Organization
This Symposium represents the beginning of a second phase for ERA Club and its activities. At a meeting in connection with the International Society of Audiology congress in London in October 1968, the ERA Club was founded. Since then has the Club existed on an informal basis with a more visible activity in the form of the 'ERA Newsletter'. The increase of members from the starting three (Burian, Gestring & Davis) up to the present 150 subscribers to 'ERA Newsletter' has shown the increasing interest for ERA in the otological and audiological laboratories and clinics. It was therefore found necessary to create a more formal organization, and at this Symposium in Freiburg in April 1970 a change of name of the organization was made from ERA Club to 'International Electric Response Audiometry Study Group' (IERASG). This should underline the serious scientific and clinical objects of the Group. An international council was also founded to direct the Study Group. The members of the Council are also representing the following geographical areas:
Burian (Austria), Beagley (England), Mounier-Kuhn (France), Keidel (West-Germany), Salomon (Scandinavia), Davis (USA).
It was also decided to have a new meeting in 1971 in Vienna and thereafter every second year. For 1973 there is an invitation from Bordeaux.
Headlines of the Symposium
1. What quantitative precision can be expected by objective audiometry?
2. The clinical significance and results of objective audiometry
H. Davis (USA) introduced with the subject 'Is ERA ready for use in the clinical routines?',
a paper which was highly interesting for the many clinical participants. Davis answered the question positively but
underlined certain restrictions before taking the method into clinical use. The instrumental equipment is expensive,
the method is not easy and it requires a collaboration between two well trained operators. He further said that the best conditions
for investigating children, having been sedated or staying awake was keeping the time for measurement below 45 min.
Within this time limit one has to compromise between accuracy and the number of frequencies being tested.
The total number of measurements where ERA should be used is probably small, and the great value of performing
this measurement in cases where it is the only alternative, is balanced by the high cost. Dr. Davis concluded
pointing to the fact that one has to differentiate between the development of clinical routine procedures and
the training of operators for these routines, and the more complicated instruments and procedures that would be
necessary in the research laboratories. He also asked for more data and experience concerning measurements on children under sedation.
W.D. Keidel (West-Germany) presented basic neurophysiology for the single responses.
The origin of the responses and the distribution along the cortical projection area was discussed.
The description of the averaged complex response evoked by acoustic stimulation was also part of his presentation.
J.A. Ganglberger (Austria), a neurosurgeon and collaborator with Dr. Gestring,
Groll-Knapp and Haider described certain important anatomical and neurophysiological relations.
They concentrated on the late evoked potentials in relation to the patients' condition (state of arousal and determination).
The evoked responses were recorded from motor, premotor and somatosensory cortex.
Cortical and subcortical potentials were also discussed.
M. Spreng (West-Germany) looked at the possibilities of using 'small' computers, the socalled minicomputers.
They may undertake more advanced signal analyses than the simple signal averaging procedures normally used for ERA.
It was argued for a great advantage both for research and also for clinical work. In the case of recruitment in both ears,
the adaptaion to a hearing aid should be improved by a differential knowledge of the nervous activity in the auditory pathways.
Through a better knowlegde to intensity- and latencyfunctions, the possibility increases in the differentiation between
a peripheral and a central hearing loss.
K. Burian (Austria) was convinced that the poor correlation between objective (ERA)
and subjective threshold measurements was mainly due to muscle movements and unsuitable sedation.
The following demands were listed: 1) Careful dose of sedation drugs, 2) Fast effect, 3)
Limited and not prolonged effect, 4) Minimal influence on the evoked responses. Different sedation
drugs had been tested, and Valium delivered intravenously was practical applicable. The dosage to children was 0.5 mg/kg
body weight with around 1.5 h sedation effect and without any reactions.
G. Stange (West-Germany) had through the use of ERA found a clear difference between pure tone audiograms and
speech audiograms for a relatively large group of subjects with hearing loss. The two types of audiograms merged after
a medical therapy of the inner ear. Differences were also found in the evoked response before and after the medical treatment.
T. Soda (Japan) presented data on conventional averaging technique with filtering of the running EEG. The filter band width was 3-7 Hz. Stimulation was auditive and visual and also alternating. By comparing the responses from these three stumulation paradigms, the condition of the patient could be determined. The importance of standardization in the measurement procedures was evident from this presentation.
H. Davis (USA) described the mutual influence on the vertex potential when both vibrotactile and electrical stimuli are employed. If two stimuli are given with a short interval, the amplitude of the last evoked response is suppressed. This effect is largest when the two stimuli are of the same type. The variation is great between patients.
J.M. Mendel & R. Goldsteins (USA). Their paper about the influence of sleep on the responses earlier than 50 ms was read by H. Davis. They have shown that the late vertex potential is influenced to a large degree under sleep, and sometimes the responses cannot be detected. A pilot study has shown that the early responses can be identified during the complete period of sleep. Another study on corneoretinal potentials during sleep of different depths was also reported, and as a conclusion, the knowledge of the stability of the early component during sleep was claimed to have a great significance not alone in the clinic but also in the understanding of the functioning of the hearing mechanism.
H.A. Beagley (England) had tested children with receptive aphasia and found agreement with results from classical audiometry. A comparison of responses from children with receptive aphasia and normal controls showed no difference and did not support the hypothesis of delayed latency for children with speech diseases.
G.A.W. Sharrad (England) presented a pilot study with ERA investigating speech diseases in children. The CNV was recorded and the stimulus was speech replayed through a tape recorder in forward and reverse mode. A more refined version of this method may perhaps in the future give a better understanding of speech diseases.
A.B. Barnet (USA) presented a paper (read by Mrs. Gestring) on 241 children aged below 3 years where 141 were normals and 100 with hearing and neurological abnormalities. The pathology group was sedated in most cases. The normal hearing children presented responses down to 35 dBHL in 30% of the cases. Easier readable results near threshold were obtained in children less than 6 months. Threshold found during sleep was somewhat higher than the true threshold. The referred results were quite comprehensive, and in conclusion ERA was claimed to be suitable in a paediatric-medical center and less suitable for pure screening.
J.-M. Aran (France) was interested in an electrode application as close as possible to the cochlea. A needle electrode was placed through the tympanic membrane into the middle ear close to the cochlea, and different click stimuli gave responses which could give answers about the working mechanisms of respectively a pathological and a normal cochlea. Early responses were presented with this method.
This paper presented the most exciting and newest results. Early responses from the cochlea are interesting form various reasons. The transfer function may be studied for the peripheral system, and this may have important implements for hearing aid fittings. A more precise loudness determination may be found and a better description of the functioning of the ear under normal and pathological conditions is also possible since the early responses will represent a mid-station between the peripheral system and the central pathways.
G.F. Gestring (Austria) had a last presentation in the Symposium presenting ideas about ERA nomenclature and clinical procedures. A round table discussion followed where several recommendations were given. The following recommendations are referred:
- ERA now means 'Electric Response Audiometry'.
- Electrode placement is vertex and reference at the earlobe or at the processus mastoideus. The EEG 'ten-twenty' system should be used.
- Vertex negative is displayed upwards in the recording. Of special interest in awake subjects are the peaks N100 and P200.
- A limited bandwidth of 1-15 Hz would be practical to minimize muscle artefacts.
In general, the Symposium in Freiburg has not presented any significant new ideas. However, on an international level ERA has now been shown to represent a usable method for clinical measurements and we may also expect further research in the area.