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Biomedical subjects

E Borg

Publications and source records attributed to E Borg.

At least 109 records · Page 6Linked to original sources
PubMed1982

Time course of acoustic intra-aural muscle reflex in non-anesthetized rabbits, normative data.

The dynamic properties of the intra-aural reflex in response to tones of 2 000 Hz in non-anesthetized rabbits is described. Rise time (time from start of stimulus to response has reached half of its steady-state amplitude) decreased from about 300 msec at threshold to 54 msec at high level for the ipsilateral and 60 msec for the contralateral reflex. Offset time (time from end of stimulus to relaxation to 50% of steady-state amplitude) increased from 100-150 msec at threshold to 250-300 msec at high level, being longer for the crossed than for the ipsilateral reflex. Impulse response (response to 16 msec burst of pure tone) reach its peak after about 60 msec, a value independent of sound level. The ipsilateral reflex had a 5-8 msec shorter time lag than the contralateral reflex, after correction for difference in response amplitude. This difference is compatible with additional synapses and a longer neural pathway for the crossed reflex. It has been pointed out that the intensity dependence of rise time has to be carefully considered when evaluating 'normal ranges' of temporal parameters for reflex responses. The rise time is suggested as a suitable parameter for quantification of suprathreshold stapedius responses.

Acoustic Stimulation↗
PubMed1982

Auditory brainstem response (ABR) to rarefaction and condensation clicks in normal and abnormal ears.

The shift in latency of wave V in ABR upon the reversal of stimulus phase was investigated in a normal-hearing reference material (65 ears) and in 20 ears of conductive hearing loss, 29 ears of steep high-frequency hearing loss and 17 ears of acoustic neurinoma or cerebellopontine angle tumor. In addition, reproducibility was studied in the reference material. The stimulus was a 2.0-kHz haversine wave at 75 or 35 dB nHL delivered at the rate of 20 Hz. 2000 responses were averaged for each stimulus phase. Electrodes were placed on the vertex and on ipsilateral mastoid. Stimulus wave form was determined in a 6-cc coupler and in a few cases with a miniature electrete microphone in the ear canal. In the reference material, a significant difference of the wave V latency between the condensation (C) and rarefaction (R) stimulus was observed. When taking the absolute difference, the mean value was 0.15 ms at 75 dB nHL. This time difference corresponds to a frequency of 3-4 kHz. In high frequency cochlear loss, the C-R difference increased in proportion to the downward shift in frequency of the high frequency slope of the audiogram. In conductive hearing loss, the C-R difference was similar to that of the reference material. In retrocochlear cases, the C-R difference was unpredictable, but was remarkably often small compared with the V latency. It was concluded that the difference in wave V latency between C and R clicks provides information about the excitation pattern in the inner ear but it is not reliable enough to give more than a rough estimate of the individual frequency of generation of ABR. The results are arguments against the use of the alternating stimulus phase as a routine procedure.

Audiometry↗
PubMed1982

Time course of the human acoustic stapedius reflex. A comparison of eight different measures in normal-hearing subjects.

Different measures of the dynamic properties of the contralateral stapedius reflex were compared in normal-hearing subjects. The stapedius reflex was measured as change of the acoustic impedance at 800 Hz. The stimulus was a 1-s burst of pure tone at 500 or 2000 Hz with a rise time of 10 ms; a 25-ms burst of pure tone at 500 Hz, rise time 2 ms; an amplitude modulated 500 Hz pure tone (30% modulation depth); a continuous pure tone in which a 1-s pause was introduced after at least 5 s. Onset was measured as rise time to 50% of maximum response and offset as time from end of stimulus until 50% of response amplitude was reached. The impulse response was quantified by time from start of stimulus to peak of response. The frequency transfer function was characterized by the 6 dB (half amplitude) cut-off point and decay was measured in percentage during a 5-s period. Recovery was quantified as the relative regain of amplitude after a 1-s pause. It was found that impulse response correlated to rise time for response to tone burst. Onset and offset were not correlated. Amplitude modulation was a mixture of onset and offset properties and not correlated to either measure. The decay and recovery were (nearly significantly) correlated and are probably different measures of the same process. A simplified test procedure for different aspects of time course was suggested but it remains to be shown if the pattern in pathological cases follows the pattern found in the present group of normal subjects.

Adaptation, Physiological↗
PubMed1982

Correlation between auditory brainstem response (ABR) and speech discrimination scores in patients with acoustic neurinoma and in patients with cochlear hearing loss.

In a pilot study of patients with cochlear hearing loss and hearing loss due to acoustic neurinoma (AN), the correlation between ABR wave V-features and speech discrimination was investigated. In cochlear hearing loss no correlation of ABR features to speech discrimination was found. In 12 patients with AN the correlation between ABR wave V amplitude to speech discrimination was significant. These results suggest that the decline of speech discrimination in AN patients is due to a deterioration in temporal accuracy of eighth nerve activity.

Brain Stem↗
PubMed1982

A lower audiometric limit for auditory brainstem response (ABR).

A lower audiometric frequency limit for reproducible ABR in response to 75 dB and 85 dB nHL 2.0 kHz haversine wave stimuli was defined by testing subjects with steep high-tone loss of varying cut-off frequencies. The limit between audiograms with and without reproducible ABR passed roughly through 40-50 dB HL at 500 Hz and 80-90 dB HL at 1000 Hz. Lack of ABR was not equivalent to lack of potentially useful hearing.

Audiometry, Evoked Response↗
PubMed1981

Life span and organ pathology in rats after life-long noise exposure.

The role of ambient sound level in longevity, cause of death, and incidence of disease was investigated in rats. Two hundred twenty-seven rats (154 Sprague-Dawley (N), 73 spontaneously hypertensive Wistar (SH)), were housed in three sound isolated boxes and subjected to controlled acoustic milieus from approximately three months of age until their natural death. Thirty-nine of the N rats were kept as external controls in a regular animal room. In one of the boxes, no noise was introduced (control). In the other two, the rats were exposed, respectively, to a frequency-modulated, chopped noise with an equivalent level of 80 dB Leq and 100 dB Leq, ten hours daily. It was found that the SH animals had a shorter life span and a higher incidence of cardiovascular disease than the N rats but a lower rate of malignant tumors. No measurable effects on life span or total incidence of disease were seen. Minor differences in incidence of various disease entities were observed but were not consistent across groups. The results do not support the hypothesis that physical sound environment represents a significant cause of somatic disease.

Animals↗
PubMed1981

Lesions to cochlear inner hair cells induced by noise.

A total of 28 un-anesthetized rabbits of the small chinchilla strain were unilaterally exposed to noise (2-7 kHz, 135 dB SPL in the ear canal). After a follow-up time ranging from 15 minutes to 10 months, the ears were perfused with glutaraldehyde and prepared for analysis by secondary emission electron microscopy and transmission electron microscopy. The typical finding was a fusion and clumping of inner hair cell (IHC) sensory hairs. In two of the animals, no loss of outer hair cells (OHC) was observed; in several of the others, only a small local loss of OHC was observed in the 2 and 4 kHz regions in spite of extensive IHC abnormality. A frequency map of the rabbit cochlea was obtained by pure tone lesions to OHC. The extent of IHC abnormalities corresponds to the 1-16 kHz region. The findings may provide a basis for the study of the functional relationship between the IHC and OHC.

Animals↗
PubMed1981

Basic contraction properties of the avian stapedius muscle.

The basic contraction properties of the solitary avian middle ear muscle, the M. stapedius, was investigated in chicken, Gallus gallus, by a sensitive tension transducer. Previous experimental studies on the in situ muscle preparation revealed both fast and slow components in the muscle's physiological responses. In the present study, brief electrical stimulus pulses delivered to the "isolated" M. stapedius elicited rapid twitch contractions with average tension levels of 46 mN for maximal stimulation. The contraction time was 15 ms, the half relaxation time was 15 ms and the total twitch time was 54 ms. Repetitive stimulation (2.5-200 Hz) revealed maximum summation of responses at 10-20 Hz and apparent complete fusion at 160 Hz. Peak tension at 160 Hz ranged from 150 mN to 200 mN. The twitch tetanus ratio was found to be 0.25. In earlier experiments with an in situ preparation, a slow component was observed in the physiological responses. However, this slow component was not seen in the single twitch responses or the responses or the response to repetitive stimulation in the present study. The M. stapedius of Gallus gallus was found to be a "fast" muscle by conventional terminology. Its contraction time is slightly shorter than the contraction times of the M. stapedius in mammals such as the cat (21 ms) and the rabbit (22 ms). These findings are consistent with earlier morphological studies which show the M. stapedius of Gallus gallus to have the features of a fast twitch muscle.

Animals↗
PubMed1981

Automatic analysis of electro-oculographic (EOG) recordings. Application to audio-vestibular diagnosis.

An automatic, computerized system for analysis of the ocular movements in nystagmus, slow pursuit and saccades is presented. The performance of the system has been tested in healthy subjects, as well as in patients with peripheral or brainstem audio-vestibular disorders. The automatized procedure enables an extended application of opto-motor tests in the clinical examination of patients with suspected retrocochlear and brainstem involvement.

Computers↗
PubMed1981

Physiological mechanisms in auditory brainstem-evoked response.

A critical review is presented of the physiological background for the interpretation of ABR auditory brainstem response). The importance of the transformation of the monophasic click stimulus to a dampled oscillation on the basilar membrane, the travelling wave velocity and the synchronization of high frequency units in the auditory nerve are emphasized. The ABR is an expression of the wave front of the leading volley of synchronized action potentials generated in nerve cell bodies in the relay stations of ascending auditory pathway. It is concluded that the physiological evidence for IC as sole, or main generator of wave V is very incomplete. The possibility of multiple generators in the SOC-complex is emphasized.

Acoustic Stimulation↗
PubMed1981

Brainstem response (ABR) in conductive hearing loss.

Results from an ongoing study were presented. The latency-intensity function for ABR was determined in subjects with unilateral pure conductive hearing loss, on the normal and the affected side. The shift of the latency-intensity function was found to correlate well (r = 0.84) to the air-bone gap at 3.0 kHz. A nomogram was constructed which allows a direct calculation of correlation factor (in ms) in pure conductive loss.

Brain Stem↗
PubMed1981

Brainstem response (ABR) to rarefaction and condensation clicks in normal hearing and steep high-frequency hearing loss.

ABR in response to 2.0 kHz haversine waves was obtained in normal-hearing subjects and in 27 ears with steep high frequency hearing loss. Rarefanction (R) clicks had a significantly shorter latency to wave V than condensation (C) clicks (mean = 0.13 ms SD = 0.16 ms, p less than 0.001). This value corresponds to a frequency of generation of ABR of 3-4 kHz. The latency difference between R and C clicks increased in reversed proportion to the cut-off frequency of the pure tone audiogram in the ears with steep high-frequency hearing loss. It was concluded that R-C latency difference can be used as an approximate indication of frequency of generation of ABR.

Acoustic Stimulation↗
PubMed1980

Processing of intensity-correlated information in an acoustic-autonomic reflex system.

The extraction and utilization of sound level changes in acoustic-autonomic reflex systems were studied on a vasoconstriction response in the tail of nonanesthetized rats. The vasoconstriction was found to depend on sound level and changes of level in the following ways. (a) It increased as a linear function of sound level (in dB) of short noise bursts. (b) It habituated during stimulation with a constant sound. (c) It was re-elicited by changes in the level of ongoing sound. (d) Its size, in response to a 10 dB increase in an on-going sound, was determined by the total level reached, and not by the size of the change. (e) Its size, in response to an increase varying from 5 to 50 dB, was equal if the total level reached was the same. (f) It gradually decreased if the stimulus steps were of less than 5 dB. The results are interpreted to show the existence of sound level specific information channels and level-specific habituation phenomena.

Acoustic Stimulation↗
PubMed1980

Role of heating in non-invasive blood pressure measurements in rats.

The "tail-cuff" technique for indirect blood pressure measurements was standardized, with respect to heating, in experiments on 47 adult Sprague-Dawley rats. The direct, intra-arterial, and the indirect blood pressures were simultaneously obtained. Pulse volume was recorded from the tail by a non-invasive technique, and was controlled by gradual application of heat. It was found that pulse volume and body temperature were poorly related. A stable relation existed, however, between the error in the indirect blood pressure recordings and the pulse volume. The error was minimized, provided that the heating was adjusted to induce a pulse volume of at least 25% of the maximum obtainable value. It was suggested that the validity of the indirect blood pressure recording could be improved, if heat application was regulated on the basis of observations of pulse volume in the tail instead of ambient temperature or body temperature. Errors due to excessive vasoconstriction, or discomfort due to overheating could thereby be minimized.

Animals↗
PubMed1980

Recovery of the human intra-aural muscle reflex after "pauses" of various depth.

Decay and recovery of the ipsilateral and contralateral stapedius reflex were studied in eight normal hearing subjects. The activity of the intra-aural muscle was recorded as a change of the ear's acoustic impedance in response to prolonged stimulation at 2 000 Hz. A one-second long attenuation of the stimulus tone by 2 to 40 dB was introduced when the response had decayed to a certain level. The recovery following the "pause" was observed. The results show that a "pause" with a depth as small as 2 dB produced approximately 40% of total recovery. A 20 dB attenuation resulted in a recovery equal to that seen after an interruption of the tone. No difference was seen between the ipsilateral and the contralateral reflex. The possibility of using stapedius reflex recovery for diagnosis of otoneurological disorders was discussed.

Acoustic Impedance Tests↗