Search PubMed⌕ Search

Biomedical subjects

R V Harrison

Publications and source records attributed to R V Harrison.

At least 91 records · Page 5Linked to original sources
PubMed1986

The use of a temporary extracochlear electrode in preoperative testing of permanent implant candidates.

This paper describes hearing and speech perception in 9 post-lingually deaf adults fitted with a temporary single electrode, surgically positioned close to the round window niche. After baseline testing, unaided and aided binaurally with the high-power Phonic Ear PE 845, each subject was admitted to hospital for a period of 7 days. During each test session, stimuli were presented directly to the electrode lead by means of an isolation unit. Current thresholds, upper tolerable limits and gap detection were measured for various acoustical waveforms and stimulus frequencies. A laryngograph was used to test the discrimination of prelinguistic and suprasegmental speech features. The results indicated that the prosthesis could provide acoustic sensations of loudness, pitch and duration that changed with stimulus waveform, level of current and frequency, and a gap threshold less than 50 msec. Lipreading appeared to be a necessary adjunct for consonant discrimination.

Adult↗
PubMed1986

Cochlear echoes, spontaneous emissions, and some other recent advances in auditory science.

This is the second of two tutorials designed as an update on recent advances in auditory science for audiologists, otolaryngologists, and others studying or working in the area of hearing and deafness. This article spans diverse areas from psychophysical measures of audiogram fine structure to physical measurements of the motion of the basilar membrane and to so-called cochlear echoes and acoustic emissions. The review is not comprehensive but it gives an overview of salient points of interest as well as an indication of the current state of knowledge in these areas.

Acoustic Stimulation↗
PubMed1985

Effects of glycerol on cochlear frequency selectivity in patients with Menière's disease.

During transtympanic electrocochleography, action potential (AP) tuning curves were derived as a measure of cochlear frequency selectivity. In 18 out of 21 patients with symptoms of Menière's disease, a poor frequency selectivity was observed. In 12 subjects the effects on frequency selectivity of oral glycerol were measured, and in 5 patients AP tuning curves indicated an improvement in sharpness of tuning by a factor of 1.5-2.5. These changes started approximately 30 min after oral glycerol administration. In 2 subjects there was a deterioration in AP tuning. In 5 patients no significant changes were observed.

Action Potentials↗
PubMed1985

Suppression by tones of the click evoked compound action potential in the normal and pathological guinea-pig cochlea and in man.

The compound action potential (AP) to a broad-hand click stimulus, recorded from the round window in guinea-pigs and from the promotory in humans, was suppressed by a tonal stimulus. The degree of suppression depended upon the relative levels of the click and masking tones and upon the tone frequency. Using a fixed 50% suppression criterion, the tone-on-click masking revealed that for near threshold click levels a relatively narrow population of nerve fibres contributed to the AP. Both for threshold and suprathreshold clicks the population of neurones contributing to the AP was centred at the minimum of the AP audiogram with no shift toward higher frequency as the click level was raised. The shape of the response area revealed by tone-on-click masking is similar to that shown by tone-on-tone masking. Application of the tone-on-click masking technique to Kanamycin poisoned guinea-pigs and to humans with cochlear lesions indicated that useful information about residual hearing could be obtained even at very low frequencies.

Acoustic Stimulation↗
PubMed1985

The physiology of the normal and pathological cochlear neurones--some recent advances.

This is the first of two auditory science tutorials designed for otolaryngologists, audiologists, and others dealing with deafness and its consequences. This tutorial is intended as an update on recent advances in the understanding of cochlear function both in the normal person and in patients with hearing loss of cochlear origin. It draws largely on studies involving electrophysiological recordings from cochlear nerve fibres in "animal models" of cochlear hearing loss. These data allow considerable insight into the underlying causes, for example, loudness recruitment, tinnitus, and poor speech intelligibility. Areas of scientific ignorance are also mentioned. This is not an exhaustive review of the literature but rather a general overview. The style of the tutorial is not starchily scientific, contains minimum jargon, and is intended to make easy reading.

Animals↗
PubMed1984

Some otological differences between pigmented and albino-type guinea pigs.

Cochlear action potential thresholds across frequency (AP audiograms) and AP tuning curves were compared in albino (Dunkin-Hartley) guinea pigs and normal pigmented animals. AP audiograms were very similar; on average the albinos had AP thresholds 2-3 dB lower at 2 kHz and below compared with the pigmented guinea pig. AP tuning curves at 16 kHz were, on average, significantly less sharply tuned in the albino, but similar at 8, 4, and 2 kHz. Although we find only small differences in these measures of normal cochlear function, other evidence in the literature suggests that in auditory research the use of "albino" guinea pigs is best avoided.

Animals↗
PubMed1984

Single cochlear fibre responses in guinea pigs with long-term endolymphatic hydrops.

Some cochlear fibre response properties have been measured in two GPs approximately one year after induction of endolymphatic hydrops (by surgical obliteration of the endolymphatic sac and duct). These animals are considered as models of the effects of hydrops in Menière's disease, and the purpose of the study was to examine any modifications of fibre response properties which may underly auditory symptoms of the disease in man. Neurones towards more apical cochlear regions (with low characteristic frequencies) showed the greatest deterioration in tuning properties; on average, in the 1-6 kHz range, Q10dB values were reduced by a factor of two compared with normal animals. Discharge rate versus intensity functions of such units were abnormally steep, with dynamic ranges reduced by 10-20 dB. Towards higher frequency regions neurone response properties showed less deterioration (contrasting with many other types of cochlear pathology where, in general, the high frequency basal region exhibits greatest vulnerability). We have also observed in a few units an abnormal bursting in both spontaneous and driven discharge. Interspike intervals during burst are less than 1 ms (within relative refractory period). These findings are related to the auditory symptoms of Menière's disease, in particular, poor frequency selectivity, loudness recruitment and tinnitus.

Action Potentials↗
PubMed1984

Electrophysiological measures of cochlear function in guinea pigs with long-term endolymphatic hydrops.

Experimental endolymphatic hydrops was induced in guinea pigs by obliteration of the endolymphatic sac and duct. From 3 to 24 months after this operation, cochlear action potential (AP) audiograms and AP tuning curves were measured. The purpose of this study was to establish parallels, if any, between this supposed animal model of Menière's disease and the auditory symptoms of the disease in man. In some animals, low and middle frequency AP threshold elevations were observed whilst higher frequency regions maintained normal sensitivity. Other animals developed flat or very gradually sloping AP audiograms. These patterns are qualitatively similar to those found clinically in Menière's disease. AP tuning curves measured in frequency regions of threshold elevation indicated a deterioration of cochlear frequency selectivity; psychophysical and electrocochleographic studies demonstrate related changes in Menière's patients. One animal exhibited modifications in AP thresholds and tuning as a result of glycerol administration. These observations improve our confidence in the validity of this animal model for further studies of the pathophysiology of Menière's disease.

Action Potentials↗
PubMed1984

Neurone response latency in the inferior colliculus in relation to the auditory brainstem responses (ABR) in the guinea pig.

In order to determine the possible source of the later vertex positive waves of the guinea pig auditory brainstem response (ABR), we have measured field potentials on the surface and at depths through inferior colliculus whilst making concurrent recordings of single unit responses (using identical broadband click stimuli). We find neurones, restricted to the antero-ventral inferior colliculus, with characteristic frequencies in excess of 12 kHz which have well synchronized onset responses short enough (c. 5 ms) to contribute to the P5 wave of the ABR.

Animals↗
PubMed1983

The effects of burn severity and institutional differences on the costs of care.

Burn care treatment is among the costliest yet least studied forms of care. This paper presents estimates of the magnitude and components of burn care costs. It analyzes the extent to which burn care cost is determined by severity of burns or by characteristics of the institution in which the patient is treated, based on patient-specific data from eight hospitals representing different levels of technical sophistication in the delivery of burn care. Costs of care are higher in specialized facilities. Many patients with small burns are treated in specialized facilities, at much higher costs than patients treated in general care facilities. Among specialized facilities, patient severity accounts for a portion of the variance in costs, but significant cost differences remain after adjusting for severity. These results suggest that cost-control efforts should concentrate on specifying criteria for admission to specialized burn facilities, regional coordination of facilities and institutions, and improved facilities design and management.

Burn Units↗
PubMed1982

Loudness recruitment: contributing mechanisms as revealed by cochlear AP measures in man.

A measure of the (average) rate of discharge versus intensity function of cochlear fibers can be obtained from cochlear-evoked compound action potentials using a tone-on-tone forward masking technique. The rationale for the method is presented. This technique was used to investigate, indirectly, cochlear fiber responses in human subjects, both with normal hearing and with deafness of cochlear origin and showing signs of loudness recruitment. In animals with pathologic cochleas, and change in rate of fiber discharge with intensity is more rapid than in normal animals. The present study confirms that this also is the case in human cochlear pathology and suggests that this abnormal steepening of rate versus intensity functions contributes to the phenomenon of loudness recruitment.

Audiometry↗
PubMed1982

A comparison of compound action potential and cochlear microphonic two-tone suppression in the guinea pig.

Cochlear microphonics (CM) and compound action potentials (AP) were recorded simultaneously with differential electrodes in the basal turn of the guinea pig cochlea. When CM two-tone suppression (2TS) curves were compared to AP simultaneous masking curves, good correspondence was observed between CM and AP suppression effects. The relationship between the 10 dB bandwidths of CM and AP 2TS curves remained constant for each animal despite differences between animals resulting from natural variations. Under pathological conditions (acute cochlear hypoxia) both CM and AP two-tone suppression effects were greatly reduced or disappeared. These results can be taken as evidence that CM suppression and AP suppression are the products of a common underlying mechanism.

Action Potentials↗
PubMed1982

Reverse correlation study of cochlear filtering in normal and pathological guinea pig ears.

The filtering properties of single cochlear fibres have been determined in normal and kanamycin-treated guinea pigs using the reverse correlation technique. This method allows investigation of filtering over a wide dynamic range. For normal guinea pig fibres, the near threshold filter functions obtained with this method correspond to the tone derived frequency threshold curves ((FTCs). The 10 dB bandwidth of the filter functions increased monotonically with increasing noise levels above threshold. Thus with noise levels at approximately 50 dB above threshold, the 10 dB bandwidth had increased by a factor of 1.3--3. The changes in 3 dB bandwidth with increasing levels were, for some fibres, different from those of the 10 dB bandwidths. For the pathological fibres, the derived filter functions corresponded to their tone determined FTCs, and were therefore comparatively broadly tuned. Their tuning (Q10dB) approximated to those of normal fibres when the latter were measured 60 dB or more above threshold (i.e., at similar levels of stimulus), and did not increase further with increase in level. The findings in the normal guinea pig are consistent with those obtained by others in rodents, but are not consistent with those from the cat, where normal filtering is more robust to high levels of stimulus noise.

Acoustic Stimulation↗