Biomedical subjects

D Hydén

Publications and source records attributed to D Hydén.

41 records · Page 3Linked to original sources

PubMedDate not supplied

Quantification and localization of vestibular loss in unilaterally labyrinthectomized patients using a precise rotatory test.

Unilateral vestibular loss was characterized using a high torque rotatory test and spectral analysis. The vestibulo-ocular reflex (VOR) of unilaterally labyrinthectomized patients was measured during passive body rotation using sinusoidal (0.5-3 Hz) and pseudo-random (0.5-5 Hz) stimulation 1) while the patient fixated an earth-fixed target and 2) during fixation of a moving target. Asymmetrical responses towards the labyrinthectomized side (as postulated by Ewald's second law) were exhibited by all patients at and above approximately 2 Hz sinusoidal stimulation and during random stimulation under illuminated conditions. The most pronounced gain loss and minimal response variability between subjects was observed during VOR suppression (moving target fixation) and random stimulation. Therefore, clinical quantification as well as the side detection of peripheral vestibular loss is best based on a fixation suppression task under fully lit conditions with a random stimulus.

Adult↗

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

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

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↗