Electrical Vestibular Stimulation after Vestibular Deafferentation and in Vestibular Schwannoma

Background

Vestibular reflexes, evoked by human electrical (galvanic) vestibular stimulation (EVS), are utilized to assess vestibular function and investigate its pathways. Our study aimed to investigate the electrically-evoked vestibulo-ocular reflex (eVOR) output after bilateral and unilateral vestibular deafferentations to determine the characteristics for interpreting unilateral lesions such as vestibular schwannomas.

Methods

EVOR was recorded with dual-search coils as binocular three-dimensional eye movements evoked by bipolar 100 ms-step at EVS intensities of [0.9, 2.5, 5.0, 7.5, 10.0]mA and unipolar 100 ms-step at 5 mA EVS intensity. Five bilateral vestibular deafferented (BVD), 12 unilateral vestibular deafferented (UVD), four unilateral vestibular schwannoma (UVS) patients and 17 healthy subjects were tested with bipolar EVS, and five UVDs with unipolar EVS.

Results

After BVD, bipolar EVS elicited no eVOR. After UVD, bipolar EVS of one functioning ear elicited bidirectional, excitatory eVOR to cathodal EVS with 9 ms latency and inhibitory eVOR to anodal EVS, opposite in direction, at half the amplitude with 12 ms latency, exhibiting an excitatory-inhibitory asymmetry. The eVOR patterns from UVS were consistent with responses from UVD confirming the vestibular loss on the lesion side. Unexpectedly, unipolar EVS of the UVD ear, instead of absent response, evoked one-third the bipolar eVOR while unipolar EVS of the functioning ear evoked half the bipolar response.

Conclusions

The bidirectional eVOR evoked by bipolar EVS from UVD with an excitatory-inhibitory asymmetry and the 3 ms latency difference between normal and lesion side may be useful for detecting vestibular lesions such as UVS. We suggest that current spread could account for the small eVOR to 5 mA unipolar EVS of the UVD ear.     

Flight Performance and Dispersal Potential of Red Palm Weevil Estimated by Repeated Flights on Flight Mill

The red palm weevil (Rhynchophorus ferrugineus; Olivier, 1790) (Coleoptera: Curculionidae) has recently become the most severe palm pest in the Mediterranean basin. Its dispersal was initially supported mainly by the acquisition of infested trees, but was further facilitated by the weevils’ flight. Therefore, knowledge of weevils’ flight capacity is a key element in evaluating their dispersal capability and setting preventive actions in advance. We tested the weevils’ flight ability in repeated flights that were 7–10 days apart by computer-monitored flight mill with a seesaw design. Tested flight parameters were: flight distance, duration, and velocity, number of flights, and cumulative flight distance, of virgin and mated weevils of both sexes. Our tests found no differences in flight distance between virgin and mated individuals or between sexes. Weevils showed flight capability between the ages of 2 and 97 days, and covered up to 315 km of cumulative distance during this time. In addition, we tested the effect of age of flight initiation and found that old starters perform fewer flights than young starters, and are thus assumed to possess inferior dispersal capabilities.     

Development and Improvement of Countermeasures against Negative Effects of Weightlessness in Long-Term Space Flights on Board International Space Station

Human Physiology - The paper describes the history of development and improvement of the means of the Russian system of countermeasures against the negative effects of space flights over the past...     

The Effect of Long-term Space Flights on Human Urine Proteins Functionally Related to Endothelium

It is known that long-term space flights lead to dysregulation of the cardiovascular system, and the endothelium is the most important functional element of such dysregulation. In order to find the signs of endothelial dysfunction in cosmonauts who have been in long-term space flights, we collected urine samples from 21 cosmonauts before the flight and on the first and seventh days after landing. The urine samples were investigated by chromatography–mass spectrometry analysis. Proteins were identified using the MaxQuant software and the SwissProt database. The software package Perseus was used for semi-quantitative analysis. The reconstruction of associative molecular networks was performed using the ANDSystem software. We identified 200 different proteins in urine samples of 21 Russian cosmonauts. The ANDSystem software made it possible to determine seven processes related to endothelium functioning. These processes had direct relations to 17 urine proteins, which were functionally associated with the endothelium. At the same time, eight proteins (such as serotransferrin, prostate-specific antigen, fibrinogen gamma chain, UFO tyrosine kinase receptor, aminopeptidase N, vascular cell adhesion molecule 1, osteopontin, and syndecan-4) were significantly changed (p < 0.01) at different points of the recovery period (the first and seventh days). Thus, we performed the first study of the urine protein composition in cosmonauts for the evaluation of signs of endothelial dysfunction after space flight using proteomics methods.     

Visual Dependency and Dizziness after Vestibular Neuritis

Symptomatic recovery after acute vestibular neuritis (VN) is variable, with around 50% of patients reporting long term vestibular symptoms; hence, it is essential to identify factors related to poor clinical outcome. Here we investigated whether excessive reliance on visual input for spatial orientation (visual dependence) was associated with long term vestibular symptoms following acute VN. Twenty-eight patients with VN and 25 normal control subjects were included. Patients were enrolled at least 6 months after acute illness. Recovery status was not a criterion for study entry, allowing recruitment of patients with a full range of persistent symptoms. We measured visual dependence with a laptop-based Rod-and-Disk Test and severity of symptoms with the Dizziness Handicap Inventory (DHI). The third of patients showing the worst clinical outcomes (mean DHI score 36–80) had significantly greater visual dependence than normal subjects (6.35° error vs. 3.39° respectively, p = 0.03). Asymptomatic patients and those with minor residual symptoms did not differ from controls. Visual dependence was associated with high levels of persistent vestibular symptoms after acute VN. Over-reliance on visual information for spatial orientation is one characteristic of poorly recovered vestibular neuritis patients. The finding may be clinically useful given that visual dependence may be modified through rehabilitation desensitization techniques.     

Using Low Levels of Stochastic Vestibular Stimulation to Improve Balance Function

Low-level stochastic vestibular stimulation (SVS) has been associated with improved postural responses in the medio-lateral (ML) direction, but its effect in improving balance function in both the ML and anterior-posterior (AP) directions has not been studied. In this series of studies, the efficacy of applying low amplitude SVS in 0–30 Hz range between the mastoids in the ML direction on improving cross-planar balance function was investigated. Forty-five (45) subjects stood on a compliant surface with their eyes closed and were instructed to maintain a stable upright stance. Measures of stability of the head, trunk, and whole body were quantified in ML, AP and combined APML directions. Results show that binaural bipolar SVS given in the ML direction significantly improved balance performance with the peak of optimal stimulus amplitude predominantly in the range of 100–500 μA for all the three directions, exhibiting stochastic resonance (SR) phenomenon. Objective perceptual and body motion thresholds as estimates of internal noise while subjects sat on a chair with their eyes closed and were given 1 Hz bipolar binaural sinusoidal electrical stimuli were also measured. In general, there was no significant difference between estimates of perceptual and body motion thresholds. The average optimal SVS amplitude that improved balance performance (peak SVS amplitude normalized to perceptual threshold) was estimated to be 46% in ML, 53% in AP, and 50% in APML directions. A miniature patch-type SVS device may be useful to improve balance function in people with disabilities due to aging, Parkinson’s disease or in astronauts returning from long-duration space flight.     

Vergence and Standing Balance in Subjects with Idiopathic Bilateral Loss of Vestibular Function

There is a natural symbiosis between vergence and vestibular responses. Deficits in vergence can lead to vertigo, disequilibrium, and postural instability. This study examines both vergence eye movements in patients with idiopathic bilateral vestibular loss, and their standing balance in relation to vergence. Eleven patients participated in the study and 16 controls. Bilateral loss of vestibular function was objectified with many tests; only patients without significant response to caloric tests, to video head impulse tests and without vestibular evoked myogenic potentials were included in the study.

Vergence testing (from 8 patients and 15 controls)

A LED display with targets at 20, 40, and 100 cm along the median plane was used to elicit vergence eye movements, recorded with the IRIS device.

Standing balance (11 patients and 16 controls)

Four conditions were run, each lasting 1 min: fixation of a LED at 40 cm (convergence of 9°), at 150 cm (convergence of 2.3°); this last condition was repeated with eyes closed. Comparison of the eyes closed-eyes open conditions at 150 cm allowed evaluation of the Romberg Quotient. In the forth condition, two LEDS, at 20 and at 100 cm, were light on, one after the other for 1 sec, causing the eyes to converge then diverge. Standing balance was recorded with an accelerometer placed at the back near the center of mass (McRoberts, Dynaport).

Results

Vergence

Relative to controls, convergence eye movements in patients showed significantly lower accuracy, lower mean velocity, and saccade intrusions of significantly higher amplitude.

Balance

The normalized 90% area of body sway was significantly higher for patients than for controls for all conditions. Yet, similarly to controls, postural stability was better while fixating at near (sustained convergence) than at far, or while making active vergence movements. We argue that vestibular loss deteriorates convergence, but even deficient, convergence can be helpful for postural control.     

Turning Semicircular Canal Function on Its Head: Dinosaurs and a Novel Vestibular Analysis

Previous investigations have correlated vestibular function to locomotion in vertebrates by scaling semicircular duct radius of curvature to body mass. However, this method fails to discriminate bipedal from quadrupedal non-avian dinosaurs. Because they exhibit a broad range of relative head sizes, we use dinosaurs to test the hypothesis that semicircular ducts scale more closely with head size. Comparing the area enclosed by each semicircular canal to estimated body mass and to two different measures of head size, skull length and estimated head mass, reveals significant patterns that corroborate a connection between physical parameters of the head and semicircular canal morphology. Head mass more strongly correlates with anterior semicircular canal size than does body mass and statistically separates bipedal from quadrupedal taxa, with bipeds exhibiting relatively larger canals. This morphologic dichotomy likely reflects adaptations of the vestibular system to stability demands associated with terrestrial locomotion on two, versus four, feet. This new method has implications for reinterpreting previous studies and informing future studies on the connection between locomotion type and vestibular function.     

Vestibular and somatosensory interaction during recovery of balance instability after spaceflight

The aim of our contribution was to characterize vestibular and somatosensory influence on human balance recovery during readaptation to the earth conditions after spaceflight. We tested how post-spaceflight postural reactions to galvanic stimulus (related to vestibular input) and to vibration of the lower leg muscles (somatosensory input) were changed.     

Modern Tests of Vestibular Function,with Special Reference to their Value in Clinical Practice

The many vestibular tests now available provide the means of accurate localization of lesions at all levels of the vestibular pathways. The value of the test procedures described has been well established in the examination of very many patients over the past twenty years, and though other forms of tests are available only those have been included which have proved to give consistently useful information.Most of these tests can be undertaken by the clinician without the use of any costly equipment, and together with a careful history and examination the diagnosis can in most cases be arrived at. Recognition of the highly important role of optic fixation and ocular deviations on vestibular nystagmus, together with recent facilities to demonstrate this electronystagmographically, may provide additional valuable and more precise information.