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Biomedical subjects

K Terkildsen

Publications and source records attributed to K Terkildsen.

At least 19 recordsLinked to original sources
PubMed1985

The effect of sleep on the auditory brainstem response (ABR) and the middle latency response (MLR).

The ABR and the MLR were measured without interruption in 4 subjects during a whole night of natural sleep and compared with the awake responses. The conventional EEG activity was monitored during the whole procedure, which permitted a precise rating of the sleep stage during each recording period. Only minor changes were found in the latencies for the ABR during sleep. The MLR responses showed quite dramatic changes in morphology and latencies. Our results appear to indicate that the 40/sec stimulus presentation mode of the MLR will not be very effective during sleep due to the pronounced latency shifts of the different peaks in the MLR. The 40/sec response is based on an inter-peak latency of 25 msec. If this presumption is not fulfilled the different waves in the 40/sec response will not be superimposed and consequently enhanced in the averaging procedure.

Acoustic Stimulation↗
PubMed1983

Acoustic neuromas. Progression of hearing impairment and function of the eighth cranial nerve.

The results obtained by conventional otologic evaluation are reported for fifty-nine patients with acoustic neuromas, sixty-one patients primarily suspected of an acoustic neuroma but in whom Pantopaque cisternography had invalidated the diagnosis, and in seventy-one patients with Meniere's disease. The audiologic tests were confined to the following: pure-tone audiometry, speech audiometry, recruitment examination by ABLB and Metz recruitment tests, and examination for reflex decay a.m. Anderson. Nineteen patients had an audiogram taken at their initial visit with the otologist, and already at this examination--4.2 years before the diagnosis was made--a high-tone hearing impairment was present. Fourteen patients had anacusis in the tumor ear and one patient had an impairment of 90 dB. The audiologic evaluations are based only on patients with hearing equal to or better than 80 dB. There was no connection between preoperative hearing impairment and the age at operation, and anacusis was found in all age groups. Four patients had recruitment by the ABLB test and six patients by the Metz recruitment test. When these two tests were combined, two patients had recruitment by both tests. Twenty percent had pathologic stapedial reflex decay. Only one patient had a normal differential caloric test. It is concluded that the typical patient with an acoustic neuroma has a gradually increasing unilateral hearing impairment of eight years' duration. A pronounced high-tone impairment with PTA of 55 dB and a poor discrimination score are to be expected. The patient is uncertain at pure-tone threshold determination and displays a lack of recruitment at both ABLB and Metz recruitment tests. The patient has a decreased or nonexistent differential caloric reaction in the ear in question. A normal differential caloric test does in all probability exclude an acoustic neuroma; however, all possible audiometric and anamnestic configurations may be encountered, and deviation from the "typical" picture should not lure the investigator into excluding the presence of a neuroma.

Adult↗
PubMed1980

The normal middle ear reflex thresholds towards white noise and acoustic clicks in young adults.

The acoustic middle ear muscle reflex thresholds towards white noise and fast sequences of clicks were determined in 46 normal-hearing young adults using electronic averaging. For white noise the thresholds were normally distributed around an average value of 72.7 dB SPL. With sequences of clicks the threshold depended above all on the click repetition rate within each stimulus sequence. When the repetition was 128/sec the threshold distribution was almost normal around an average value of 73.9 dB SPL. For the individual test subject there was good correlation between the white noise and the click reflex thresholds. It was our impression that the click generated reflexes had a more well defined threshold than with white noise stimuli, but this impression needs further validation.

Acoustic Impedance Tests↗
PubMed1978

Auditory brain stem responses in patients with acoustic neuromas.

In the continuing search for methods to diagnose acoustic neuromas at an early stage, we have applied the auditory brain stem response examination to 27 patients with surgically verified acoustic neuromas. It is confirmed that the main indicator of retrocochlear versus cochlear disease is the interaural latency difference of the Jewett5 wave, the IT5. Women exhibit significantly lower latency values to J5 than men, approximately 0.25 msec. Age also has some influence, so that the J5 latency tends to increase with age, but in this investigation the trend did not reach statistical significance. We were unable to find a correlation between tumour size and IT5. Even if the audiogram shows a considerable hearing impairment at 2 kHz this technique can be used without any correction factors, when the stimulus is a 2 kHz filtered tone-pip. In the presence of an acoustic neuroma there will often be adaptation of the response and it is preferable to arrange the mode of stimulus presentation so that this phenomenon eventually becomes prominent. One patient came out with a false-negative result. We believe this to have been due to our lack of experience at that time and that today we would have recognized the presence of a tumour. If this correction is accepted, the series contains no false-negatives. Regardless of this it can be concluded that for the time being, out of the functional audiological tests, the auditory brain stem response examination is the most reliable indicator for the presence of retrocochlear lesions.

Adolescent↗
PubMed1977

Inner ear malformations with oto-liquorrhea. Tomographic findings in three cases with a mixed hearing impairment.

The paper deals with three boys suffering from a mixed hearing loss. They were all referred to tomography of the temporal bones in order to find some middle ear malformation amenable to surgery. The tomograms revealed identical malformations of the inner ear; the lumen of the labyrinth are found irregularly dilated and the internal acoustic meatus is widened. Its course in the lateral end is abnormal with a downwards turn towards the basal coil of the cochlea. Explorative tympanotomy in one of the patients revealed a severe otoliquorrhea during an attempt to perform a stapedectomy, and this may serve as a warning against operation in patients presenting the mentioned tomographic changes which, once seen, are easily recognized.

Adolescent↗
PubMed1977

Frequency following auditory brain stem responses in man.

The most interesting electrode positions for recording the FFR are the Vertex and the mastoid. The response is greatest at the Vertex. At the mastoid it comes earlier and probably in a different phase. As a combined result of these relations the responses are in opposite phase with a 500 Hz stimulus, and at 400 Hz they are in-phase. The Vertex-derived response is contaminated by the Jewett waves and at the mastoid there is in addition a CM-like activity. In order to simplify the interpretation we recommend use of the Vertex only as active electrode position, with reference electrodes on the neck, which is largely neutral. A very effective stimulus is a 500 Hz tone-burst with rise-fall times of 2 msec and a plateau of 6 msec. Shorter stimuli yield a smaller response, and with longer stimulus duration, adaption becomes a problem. The Jewett wave contamination can be eliminated by means of recording the response twice with opposite stimulus polarity and subtracting the two from each other.

Acoustic Stimulation↗
PubMed1977

The frequency selectivity of the 500 HZ frequency following response.

In order to evaluate the frequency selectivity of the 500 Hz FFR we applied narrow-band masking at closely spaced center frequencies in the range 0.25 to 4 kHZ. The results show clearly that it is the apical part of the cochlea that generates the 500 Hz FFR, but the area of the basilar membrane that contributes is rather broad. It was evident that some of the masking effect that was observed in the Vertex-derived response stemmed from as yet obsure brain stem mechanisms. Examination of 3 patients with selected types of hearing impairment confirmed the masking results. When there is a low frequency loss there will still be a 500 Hz FFR and the same is true when the loss is in the medium to high frequencies. It is possible that precise determination of the latency to single waves in the response may allow a more exact prediction with regard to which location on the basilar membrane generates the response in the individual patient.

Acoustic Stimulation↗
PubMed1977

Auditory brain stem responses in the diagnosis of cerebellopontine angle tumours.

There is a constant search for more reliable methods of diagnosing cerebellopontine angle tumours at an early stage. The auditory brain stem responses promise to be of use as such a method. In two patients with extracanalicular neurinomas we found a definitely abnormal brain stem response even though conventional tests produced a cochlear type of test pattern. In a third patient with a meningeoma we obtained a similar type of response. Here the conventional tests clearly pointed to the presence of retrocochlear disease. Characteristic findings are a broadening of the whole nerve action potential and a delay in the appearance of the Jewettv-FFP7 complex.

Adult↗
PubMed1977

A quasi-free-field transducer system for high-frequency audiometry.

Previous attempts to measure human hearing capacity in the high frequencies (8 to 20 kHz) have only been met with rather limited success. Based on the results of Shaw and co-workers we have developed a free-field transducer system where the stimuli are delivered from a point source and meet the ear as plane progressive waves at a carefully chosen angle of incidence. The system can be calibrated in a precise manner by means of a specially designed coupler. Preliminary results indicate that the procedure is easily applicable also in a group of inexperienced test subjects and the test-retest variability was within such limits that are acceptable for subjective audiometric testing. These results require validation in a large group of subjects and we hope it will be possible to establish normative values for various age groups.

Audiometry↗