Biomedical subjects

B Larsby

Publications and source records attributed to B Larsby.

47 records · Page 3Linked to original sources

PubMedDate not supplied

Electronystagmographic findings in rats exposed to styrene or toluene.

A previously described experimental model for studying the effect of industrial solvents in the vestibular system of rabbits has been applied to rats. To achieve a constant concentration, the solvent was infused intravenously, dissolved in a lipid emulsion. Arterial blood levels were estimated by gas chromatography. The vestibulo-oculomotor behaviour of rats during repeated rotatory acceleration was investigated by electronystagmography. The effect of two solvents-toluene and styrene-on the rotatory induced nystagmus was examined. Both solvents caused an exaggerated reaction at arterial blood levels above 75 ppm. The investigation indicated that the rat will be suitable species for further electronystagmographic investigation of the influence of organic solvents on the vestibular system, for example in screening studies of the toxicity of these solvents.

Animals↗

PubMedDate not supplied

Quantification of slow compensatory eye movements in patients with bilateral vestibular loss. A study with a broad frequency-band rotatory test.

Seven patients with bilateral vestibular dysfunction were investigated with a new broad frequency oscillatory test. The vestibular stimulation was of two types: a pseudo-random oscillation in the frequency range 0.5-4 Hz and a sinusoidal frequency sweep from 0.5 to 3.5 Hz. Compensatory eye movements were recorded by EOG. Gain and phase values between eye and head movements were extracted using power spectral analysis technique. Two different visual conditions were used: 1) fixating a stationary target and /) fixating a moving target (visual suppression test). At high frequencies all patients showed a reduced VOR gain compared to normal subjects. At low frequencies gain values were close to normal when using a predictable (sinusoidal) stimulation. With a non-predictable (pseudo-random) stimulation gain values were significantly reduced even at low frequencies. The patients with the most severe loss showed a phase lag at higher frequencies (condition 1). The results in the oscillatory test were compared to subjective symptoms and caloric responses. The new test appears to be better suited to assess the vestibular function in patients with suspected bilateral vestibular loss than the caloric test or other traditional procedures.

Adult↗

PubMedDate not supplied

Gain and phase characteristics of compensatory eye movements in light and darkness. A study with a broad frequency-band rotatory test.

Thirteen normal subjects were investigated with a broad frequency-band (up to 4.5 Hz) rotatory test. The vestibular stimulation consisted of either a pseudo-random or a sinusoidal frequency sweep oscillation. Eye movements were recorded by EOG. Head movements were recorded either by a potentiometer attached to the chairs axis of rotation or by an angular rate sensor attached to a biteboard . Gain and phase values between eye and head movements were calculated. Measurements were performed in light and darkness during the execution of various fixation tasks. In the higher frequency range there was a in gain and phase between potentiometer and rate sensor measurements due to movement of the head relative to the headholder . Visual suppression, in agreement with earlier studies, was more effective during a sinusoidal stimulation than during a pseudo-random stimulation at low frequencies, using the more precise rate sensor measurement technique. Different instructions in the dark could alter the gain values at lower frequencies (up to 2 Hz) during sinusoidal stimulation. During pseudo-random stimulation no such differences could be elicited. Under all test conditions with the rate sensor, the gain values approached unity at about 3 Hz.

Adolescent↗

PubMedDate not supplied

The effect of toluene on the vestibulo- and opto-oculomotor system in rats. A computerized nystagmographic study.

The short-term effect of exposure to toluene on the vestibulo- and opto-oculomotor system in rats was investigated. Stimulation of the vestibulo- and opto-oculomotor system was either a constant rotatory acceleration, a sinusoidal oscillation, a randomized oscillation or an optokinetic stimulation. Eye movements in response to the different stimulations were recorded by EOG and fed into a computer for analysis. Due to toluene exposure the slow phase velocity gain during constant acceleration increased and the post-acceleratory nystagmus response was prolonged. The optokinetic gain at stimulation velocities above 10 deg/sec decreased during toluene exposure. Toluene also prolonged the duration of optokinetic after- and after-afternystagmus. The findings in this study strongly suggest an effect of toluene on the cerebellum.

Acceleration↗

PubMedDate not supplied

Effects of trichloroethylene on the human vestibulo-oculomotor system.

Ten healthy volunteers were subjected to a vestibulo-oculomotor test battery before, during and 1 hour after trichloroethylene exposure. The concentration of trichloroethylene in inspiratory air was 32-78 ppm (176-429 mg/m3). The concentration of trichloroethylene in venous blood was followed throughout the experiment. The mean pulmonary uptake was estimated. Each test person was also subjected to a control experiment, breathing air free of trichloroethylene. A decreased ability to visually suppress the vestibulo-oculomotor reflex during sinusoidal stimulation was noticed during trichloroethylene exposure. One hour after exposure the test subjects showed a decreased maximum velocity of the voluntary saccade and a decreased ability to follow a sinusoidally moving target.

Adult↗

PubMedDate not supplied

The effect of stimulus predictability and age on human tracking eye movements.

Human tracking eye movements were recorded in healthy volunteers of varying age. The target motion was either predictable (pure sinusoids or sinusoidal frequency sweep) or unpredictable (pseudorandomized). Gain and phase values for the tracking and the smooth pursuit eye movement signal were calculated as a function of target frequency from 0.2 to 2 Hz. Max. target velocity was 20 or 40 deg/sec. In the low frequency area the smooth pursuit gain for predictable stimulation was higher than the gain elicited by the pseudorandomized stimulation. In the high-frequency area, gain values did not differ significantly. For the predictable stimulation, the phase of the smooth component was always a lag, increasing with increasing frequency. At low frequencies of the pseudorandomized signal a phase lead was observed. At higher frequencies the lead turned into a lag that was greater than for the predictable stimulation. The young and old groups showed reduced smooth pursuit gain values, compared with the main group specially when the target waveform was pseudorandomized. The reduced smooth pursuit ability was mostly compensated for by an increased amount of saccades.

Adult↗

PubMedDate not supplied

Effects on the vestibulo- and opto-oculomotor system in rats by lesions of the commissural vestibular fibres.

Eye movements were recorded from rats with a magnetic search coil system before and after sectioning of the midline commissural pathways in the brain stem at the level of the vestibular nuclei. After lesion, the findings were as follows: 1) During sinusoidal vestibular stimulation the eyes moved in a sinusoidal way similar to the head movement without any regular saccades. There was a reduced gain and a phase lead. 2) During optokinetic stimulation the eyes moved in the stimulus direction to an excentric position and stayed there until stimulation ceased. 3) During acceleratory/deceleratory rotation in the light there was a drift of the eyes in the direction of the expected slow phase movement to an excentric position. In some animals there was a directional asymmetry. The findings may be explained by a failure of the central neural integrator for horizontal eye movements. The results support the hypothesis that vestibular commissural fibres are of crucial importance for the function of this integrator system.

Acceleration↗

PubMedDate not supplied

Otoneurological findings in psycho-organic syndrome caused by industrial solvent exposure.

Nine subjects with long-term (8-30 years) occupational exposure to industrial solvents and a confirmed diagnosis of psycho-organic syndrome (POS) have been studied with audiological and otoneurological test batteries. The results were compared to a matched control group of nine industrial workers not exposed to solvents and to normal data from healthy volunteers. In the clinical examination, the Romberg test identified 5/9 workers as pathologic and concurrently the stabilometry showed significantly larger sway areas in the POS-group. In the audiological test battery, the significantly pathologic tests were discrimination of interrupted speech and evoked cortical responses to frequency glides (CRA-delta-f). The saccade test disclosed abnormal findings in 5/9 workers. In the smooth pursuit test, abnormality was found at some test frequencies using pseudorandomized stimulus. The VOR-suppression test was significantly abnormal at all test frequencies. The test battery used strongly indicates CNS lesions due to industrial solvents.

Adult↗

PubMedDate not supplied

Speech recognition and just-follow-conversation tasks for normal-hearing and hearing-impaired listeners with different maskers.

Speech recognition (SRT) and just-follow-conversation (JFC) tasks were performed by normal-hearing and hearing-impaired listeners matched for age and sex using three masking backgrounds: speech spectrum random noise, continuous forward speech and reversed speech. In the SRT task, the signal-to-noise (S/N) ratio for 50% correctly repeated words of short, 5-word, low-redundancy sentences was determined. In the JFC task, the listener adjusted the speech level until he felt he could just understand what was being said. The listeners needed a higher S/N ratio for the JFC task than for the SRT task. The speech maskers gave less masking than the random noise. No difference between forward and reversed speech was observed. The hearing-impaired listeners needed a higher S/N ratio than the normal-hearing subjects. Correlations between results obtained with the SRT and the JFC techniques were significant with speech but not with random noise as masker. The highest correlations between pure-tone hearing thresholds at different frequencies and results in the SRT and JFC tests were seen at 0.5 and 1 kHz.

Adult↗

PubMedDate not supplied

Evaluation of a cognitive test battery in young and elderly normal-hearing and hearing-impaired persons.

A cognitive test battery sensitive to processes important for speech understanding was developed and investigated. Test stimuli are presented as text or in an auditory or audiovisual modality. The tests investigate phonologic processing and verbal information processing. Four subject groups, young/elderly with normal-hearing and young/elderly with hearing impairment, each including 12 subjects, participated in the study. The only significant effect in the text modality was an age effect in the speed of performance, seen also in the auditory and audiovisual modalities. In the auditory and audiovisual modalities, the effects of hearing status and modality were seen in accuracy parameters. Interactions between hearing status and modality, both in accuracy and in reaction times, show that hearing-impaired subjects have difficulties without visual cues. Performing the test battery in noise made the tasks more difficult, especially in the auditory modality and for the elderly, affecting both accuracy and speed. Test-retest measurements showed learning effects and a modality-dependent variability. The test battery has proven useful in assessing the relative contribution of different input signals and the effects of age, hearing impairment, and visual contribution on functions important for speech processing.

Adult↗

PubMedDate not supplied

The influence of visual and somatosensory input on the vestibulo-oculomotor reflex of pigmented rats.

Eye movements were recorded in the pigmented rat during vestibular, optokinetic and combined visual-vestibular stimulation. The dominant time constant in pigmented rats, tested during angular vestibular stimulation in darkness, is about two times longer than the cupular time constant. The gain and the duration of nystagmus, achieved by angular vestibular stimulation, can be enhanced by visual impulses. This is most evident during an optokinetic temporonasal stimulation, but is also seen with a nasotemporal stimulation. A mere optokinetic monocular stimulation without a synchronous vestibular excitation causes nystagmus only when the stimuli has a temporonasal direction. The duration of nystagmus, achieved by angular vestibular stimulation, is prolonged by disturbances of the neck proprioceptive system. This is more evident during a simultaneous visual input than in darkness. The ability to cancel nystagmus during conflicting vestibular and optokinetic impulses is well developed in the pigmented rat.

Animals↗