Unilateral Loss Of Vestibular Function Research Articles

Technique for the assessment of vestibular compensation--clinical observation/quantitative neuro-otometry?

Reliable evaluation of vestibular compensation in indispensable to determine whether labyrinth surgery or vestibular neurectomy is indicated. It is also important for postoperative follow-up. Vestibular compensation can manifest itself differently in distinct frequency ranges. Twenty volunteers were examined in five distinct situations of daily vestibular stimulation. Measurement of angular and linear head acceleration was performed using accelerometers fixed on the volunteers' head. A 200 Hz AD fed data to a PC database. FFT was used for data analysis. Stimulus frequency of the vestibular system varies between 0.01 and 2 Hz. Most of the patients suffering from vestibular lesions showed a reduced vestibulo ocular reflex (VOR) below 0.1 Hz. In all cases of unilateral vestibular function loss, there was a correlation between the symptoms during movement and the corresponding frequency range of the distinct motion pattern. Rotatory vestibular pendular testing was used to document vestibular disorders in patients who had normal findings in routine vestibular testing. Clinical use of rotatory vestibular pendular testing results must be performed using broad stimulus frequency spectra (0.01-0.06 Hz). This method must be used in preoperative examination before labyrinth surgery as well as in estimating individual tolerance for vestibular stimulation in daily situations.

Unilateral Vestibulotoxicity Due to Systemic Gentamicin Therapy

Systemic gentamicin can cause acute bilateral, simultaneous, symmetrical loss of vestibular function manifested by symptoms and signs of chronic vestibular insufficiency (ataxia and oscillopsia). We report 6 patients presenting with ataxia and oscillopsia, but without a history of vertigo, who had severe unilateral loss of vestibular function on caloric testing. The absence of vertigo in these patients could be explained by two possible mechanisms: either, the unilateral loss of vestibular function was subacute, occurring over several days so that compensation could occur, or bilateral vestibular loss occurred which was then followed by asymmetrical recovery of vestibular function. The second hypothesis is supported by the observation that vestibular hair cells can regenerate after aminoglycoside damage.

The Subjective Visual Horizontal after Stapedotomy: Evidence for an Increased Resting Activity in Otolithic Afferents

The subjective visual horizontal (SVH) was measured by means of a small rotatable luminous line in darkness in the upright body position and at 10, 20 and 30° of body tilt to the right and left prior to, and during a follow-up period after, stapedotomy in 12 patients with otosclerosis. In the acute stage after surgery, SVH in the upright body position was significantly tilted away from the operated side. In addition, the perception of roll tilt towards the operated side (Kop) was significantly increased after stapedotomy, while the perception of roll tilt towards the healthy side (Khe) showed a slight but not significant reduction. After exclusion of two outliers, a statistically significant correlation was found between changes in Kop and in Khe. The slope of the regression line was 1.8 : 1, probably corresponding to a preference of the utricle for ipsilateral as opposed to contralateral head tilt. In four patients there was a weak (<1°/s) spontaneous nystagmus, not systematically related to the side of surgery, while in most cases there were no nystagmus or subjective vertigo symptoms. These specific changes in the subjective horizontal show that the otolithic effects on perception can be dissociated from canal effects. Further, the results are opposite to those for patients with unilateral loss of vestibular function. The tilt of SVH after stapedotomy indicates an increase in resting activity of utricular afferents. In addition, based on recent theories on otolith function, we suggest that an increased activity in saccular afferents is of major importance for the changes in roll-tilt perception because of its interaction with the utricle on the central nervous level.

頭部に対する振子様回転の視運動性眼振に及ぼす影響

The influence of pendular head rotation on optokinetic nystagmus was studied with the use of a pendular rotating chair and an optic cylinder operated independently. Healthy subjects and patients with unilateral loss of vestibular function were examined.The pendular rotation and optokinetic stimuli were applied in both horizontal and vertical directions. The optokinetic stimuli consisted of 12 stripes rotating with applied uniform velocity of 90°/sec. The pendular rotation was applied at a frequency of 0.1 Hz and a peak angular velocity of 30°/sec.In healthy subjects, horizontal optokinetic nystagmus was promoted when the head rotated to the direction opposite to the optic cylinder rotation. On the other hand, when the head and optic cylinder rotated in the same direction, optokinetic nystagmus was inhibited.In patients with unilateral loss of vestibular function, a difference in response to ampullopetal and amupullofugal stimulation of the remaining intact labyrinth was seen. However, this difference gradually disappeared with compensation.In healthy subjects, vertical pendular rotation promoted and inhibited vertical optokinetic nystagmus.In patients with unilateral loss of vestibular function, promotion by vertical pendular rotation of vertical optokinetic nystagmus was the same as that in healthy subjects.The influence of active pendular head rotation on optokinetic nystagmus was studied with an optic cylinder fixed to the head. Inhibition of nystagmus during active pendular head rotation was weaker than that during passive pendular head rotation, but the effect on promotion was almost the same.

Postural Stability on Moving Platform Oscillating at High Frequencies:Effect of Vestibular Lesion

The effect of linear perturbation at a frequency range of 8 to 24 Hz on postural stability was studied in 7 patients with unilateral vestibular function loss. Force platform technique was used with automatic analysis resulting in the sway velocity of the center point of force. In all patients the support surface movement produced increased sway velocity which was significantly greater than in the controls. Tests at lower frequencies (8 and 10 Hz) produced higher sway velocities than tests at higher frequencies (12, 14, 16 and 24 Hz). The results indicate that the vestibular system controls postural reflexes at a substantially higher frequency range than hitherto suggested.

Effects of unilateral loss of vestibular function on the vestibulo-ocular reflex and postural control.

Long-term recovery from surgically induced unilateral loss of vestibular function was studied in 14 patients. Seven patients underwent surgical extirpation or section of the vestibular nerve, and seven patients underwent labyrinthectomy without vestibular nerve section. The vestibulo-ocular reflex (VOR) and postural control were evaluated preoperatively and monitored for up to 4 years postoperatively with use of pseudorandom rotation (combined sinusoidal frequencies from 0.009 to 1.5 Hz) and moving platform posturography. Immediately following surgery all patients showed minimal reductions in the VOR gain constant, but marked reduction in the time constant, and marked increase in slow eye velocity bias. Bias returned to normal values within about 10 days, but time constants never returned to normal values. Results of standard Romberg tests in these patients were normal throughout the preoperative and postoperative periods. However, all patients showed marked postural control abnormalities in tests of the ability to maintain balance in unusual sensory environments in the immediate postoperative period. Seventy-five percent of the patients eventually recovered normal postural control. Postural control returned to near baseline performance with a time course similar to that of the VOR bias. However, postural control also continued to improve after the recovery of VOR bias was complete.

Reduction of the time constant in the VOR as a protective mechanism in acute vestibular lesions.

Fourteen patients with vestibular neuritis were examined at onset of symptoms and after one year. Postrotatory time constant and gain in the vestibulo-ocular reflex (VOR) were measured after rotation with a velocity step of 150 deg/s. There was no significant difference in gain towards the healthy side at onset of the disease compared to recordings after one year. The time constant towards the healthy side was significantly shorter at onset compared to measurements after one year. The results reflect the loss of unilateral vestibular function on the velocity storage mechanism, both in the acute situation and after compensation. The findings indicate that reduction of the time constant in the VOR is not only due to unilaterally vestibular impairment but it is also an effect of the generally reduced activity in the vestibular system after a lesion and may act as protective mechanism in acute vertigo.

The contribution of vestibulo-spinal mechanisms to the maintenance of human upright posture.

The maintenance of upright stance in humans requires the integrative evaluation of vestibular, visual, and proprioceptive information. Recent experiments prove the existence of fast vestibulo-spinal reactions in humans. Their physiological significance for the compensation of sudden external displacements of the body is minor. For low frequency stabilization of the body, however, vestibulo-spinal afferents as well as vision and proprioception are important. Unilateral loss of vestibular function initially causes a tendency to fall to the ipsilateral side as well as nystagmus and vertigo. After the first days of compensation, the remaining functional disturbance can only be detected by exposing the patient to conflicting sensory reafferents or by reducing proprioceptive and visual inputs simultaneously. The loss of vestibular function not only alters low frequency stabilization and to some extent also reflex-like fast motor patterns, but also interferes with the selection of preprogrammed motor synergies.

Galvanic testing in neuro-otological diagnostics.

From 1980 to 1986, a total of 436 patients were investigated by galvanic testing. Pathological findings resulted in 45 (out of 54) patients with a suspect tumour of the cerebellopontine angle (CPA), 7 (out of 7) patients with a Herpes zoster infection, 25 (out of 32) patients with an isolated, unilateral loss of vestibular function, 4 (out of 14) patients with head injuries. No pathological results of galvanic testing were found in patients with sudden deafness, Meniere's disease, vertebrobasilar or cerebrovascular insufficiency, etc.

Transcanal labyrinthectomy for intractable vertigo.

Labyrinthectomy may be the therapy of choice for intractable and disabling vertigo that is caused by unilateral disease of the vestibular labyrinth. The transcanal method through the oval window offers the most direct surgical approach for complete ablation of the vestibular sense organs. The technique includes visual identification and removal of the utricle; this is followed by blind probing of the ampullae. This method was used in 124 patients, including 90 patients with unilateral Meniere's disease. Three of four cases of moderately severe continuing postoperative vertigo were successfully managed by revision transcanal labyrinthectomy. Twenty-seven (22%) of the 124 patients had continuing mild transient unsteadiness associated with quick head movements; this condition is considered to be the physiologic consequence of unilateral loss of vestibular function rather than unremitted disease.

Sudden unilateral loss of vestibular function.

Sudden unilateral loss of vestibular function.

A phenomenon in vestibular compensation

The role of spinal afferentation from the lower half of the body in compensation of the sequelae of unilateral loss of vestibular function was studied in experiments on guinea pigs. Division of the spinal cord at the thoracic level under local anesthesia had no appreciable effect on the development of compensation after simultaneous or subsequent destruction of the labyrinth and did not disturb compensation in previously labyrinthectomized animals. Division of the spinal cord in labyrinthectomized animals under ether or chloroform anesthesia was accompanied by a sharp disturbance of compensation. These substances evoked a similar picture of decompensation in unilaterally labyrinthectomized animals with an intact spinal cord also. The results indicate that the disturbance of vestibular compensation discribed in the literature after division of the spinal cord under ether anesthesia is not the result of removal of spinal afferentation from the lower half of the body, but is due to the direct effect of inhalational anesthetics on compensation mechanisms.

Study of compensation after unilateral loss of vestibular function

The dynamics of compensation of the after-effects of unilateral destruction of the labyrinth was studied in rabbits. Destruction of the labyrinth was followed by nystagmus, an increase in the external respiration and heart rates, and EEG activation. The investigations revealed differences in the rate of extinction of these reactions with time. In the late stages after labyrinthectomy marked asymmetry of the nystagmic response of the eyes to angular accelerations of equal intensity but opposite direction was observed. Stimulation of the intact otolith apparatus was accompanied by the appearance of positional nystagmus. The results point to imperfection of the mechanisms of compensation after total unilateral loss of vestibular function.

LXVII. Unilateral Loss of Vestibular Function Probably Due to Embolus

LXVII. Unilateral Loss of Vestibular Function Probably Due to Embolus