Dror Tal

Mal de Debarquement and Posture: Reduced Reliance on Vestibular and Visual Cues

Objective The neural mismatch theory assumes that the intersensory conflicts leading to motion sickness are resolved by changes in the relative weighting of the various senses that contribute to orientation. If this sensory rearrangement persists after disembarkment, it might result in mal de debarquement (MD): ataxia and a rocking sensation sometimes felt after landing. The objective of the present study was to examine possible changes in sensory organization in naval crew members with differing susceptibility to MD with computerized dynamic posturography (CDP).

Otoacoustic Emissions in Early Noise-induced Hearing Loss

Objectives: To follow changes in transient evoked and distortion product otoacoustic emissions (TEOAEs, DPOAEs) as they relate to pure-tone audiometry (PTaud) thresholds during the first 2 years of occupational noise exposure. Design: Prospective controlled. Methods: Pure-tone audiometry thresholds, TEOAE and DPOAE amplitudes, and contralateral medial olivocochlear reflex strength were repeatedly evaluated during 2 years and compared between and within a cohort of 135 ship engine room recruits and a control group of 100 subjects with no noise exposure. Results: Pure-tone audiometry thresholds for 2,000, 3,000 and 4,000 Hz in both ears were significantly elevated in the study group after 2 years of noise exposure. Significantly lower TEOAE amplitudes were found at 2,000 Hz in the right ear and 2,000 and 4,000 Hz in the left ear. Longitudinal intrasubject analysis of the study group revealed significant reductions of TEOAE amplitudes at 2,000 to 4,000 Hz in both ears and reduced DPOAE amplitudes for 5,957 Hz in the right ear and 3,809, 4,736, and 5,957 Hz in the left ear in the second follow-up evaluation. Baseline medial olivocochlear reflex strength showed no correlation to PTaud thresholds after 2 years of noise exposure. Poor to moderate negative linear correlations (r = −0.07 to −0.37) were found between the DPOAE-averaged amplitudes at 2,979 to 5,957 Hz and PTaud threshold means at 3,000 to 6,000 Hz. Abnormal TEOAE parameters after the first year of noise exposure had high sensitivity (86-88%) and low specificity (33-35%) for the prediction of noise-induced hearing loss (NIHL) after 2 years. Conclusion: The DP-gram is not significantly correlated with PTaud and cannot be used as an objective measure of pure-tone thresholds in early NIHL. Medial olivocochlear reflex strength before the beginning of chronic exposure to occupational noise has no relation to individual vulnerability to NIHL. Although TEOAEs changes after 1 year showed high sensitivity in predicting NIHL after 2 years of exposure, they cannot be recommended as an efficient screening tool due to high false-positive rates.

Frequency tuning of input-output relation in a rat cortical neuron in-vitro

The input-output relation of a single neuron stands at the basis of every biologically oriented description of the brain. This report shows that the input-output relation of cultured cortical neurons is non-linearly tuned by the input frequency. Increasing the rate of stimulation results in the appearance of ordered temporal firing patterns, which are qualitatively different for different input frequencies. The experimental results of this study lead to the conclusion that frequency tuning of neuronal input-output relation arises from activity-dependent rates at the molecular level underlying the mechanism of excitability itself.

Performance of Infusion Pumps during Hyperbaric Conditions

Background Many hyperbaric facilities use infusion pumps inside the chamber. It is therefore important to ensure that this equipment will perform accurately during hyperbaric conditions. The authors tested the function and accuracy of the Imed 965 and Infutec 520 volumetric infusion pumps, the Easy-pump MZ-257 peristaltic infusion pump, and the Graseby 3100 syringe pump. Methods The authors calculated the deviations of infused volumes at low and high rates (12–18 and 60–100 ml/h) on three different hyperbaric protocols (up to 2.5, 2.8, and 6 atmospheres absolute [ATA]), resembling a standard hyperbaric oxygen treatment and US Navy treatment tables used for decompression illness and for arterial gas embolism. Two examples of each pump model were examined in every experiment. Results The Easy-pump MZ-257 failed to function completely beyond a chamber pressure of 1.4 ATA, making it unsuitable for use inside the hyperbaric chamber. The Graseby 3100 failed to respond to all keyboard functions at 2.5–2.8 ATA, making it unsuitable for use in most hyperbaric treatments. The Imed 965 performed within an acceptable volume deviation (≤10%) during most hyperbaric conditions. During the compression phase of the profiles used, and for the low infusion rates only, exceptional volume deviations of 20–40% were monitored. The Infutec 520 demonstrated an acceptable deviation (within 10%) throughout all the hyperbaric profiles used, unaffected by changes in ambient pressure or infusion rate. Conclusions Commercially available infusion pumps operating during hyperbaric conditions demonstrate substantial variations in performance and accuracy. It is therefore important that the hyperbaric facility staff make a careful examination of such instruments to anticipate possible deviations in the accuracy of the equipment during use.

Prolonged optokinetic stimulation generates podokinetic after rotation.

Previous studies showed that after prolonged stepping in place on the center of a rotating platform blindfolded subjects could no longer step in place on a firm floor. Instead, they invariably rotated themselves relative to space without perceiving their rotation, a phenomenon termed podokinetic after‐rotation (PKAR). We speculated that prolonged optokinetic stimulation (OK) alone may generate similar PKAR. The purpose of this study was to evaluate the effects of prolonged OK on podokinetic (PK) responses. Ten healthy subjects participated in the study. After a control stepping test, they were seated in a circular closed cage and randomly (right or left) exposed to an OK (45°/s) covering the whole visual field for 30 min. After this procedure, blindfolded subjects attempted to step in place on the stationary floor for 30 min. When trying to do so, all subjects turned relative to space without any perception of rotation. The direction of this optokinetically after‐rotation (oPKAR) was opposite of that of the direction of OK. Mean peak velocity of oPKAR was 7.8 ± 4.1°/s, and it was reached after approximately 6 min of stepping. After that, there was a progressive velocity decay, which exhibited a discharging time constant on the order of 42 min toward a final positive asymptote of 3.1°/s. We conclude that OK alone causes oPKAR. Long‐term OK probably charges a storage element for podomotor activity with a relatively prolonged time constant. This novel form of neural interaction and adaptive plasticity may have significant implications for the treatment of vestibular and parietal lobe disorders.

Mal de debarquement, motion sickness and the effect of an artificial horizon

BACKGROUND Exposure to unfamiliar motion patterns commonly results in motion sickness and a false perception of motion, termed mal de debarquement, on the return to stable conditions. OBJECTIVE To investigate whether motion sickness severity is correlated with the duration and severity of mal de debarquement; to study the possible preventive effect of projecting earth-referenced scenes (an artificial horizon) during exposure to motion on the development of mal de debarquement. METHODS Thirty subjects were exposed to the recorded motion profile of a boat in a 3-degrees-of-freedom ship motion simulator. During the simulated voyage, the study participants were repeatedly put through a performance test battery and completed a motion sickness susceptibility questionnaire, while self-referenced and earth-referenced scenes were projected inside the simulator cabin. Six hours post disembarkation, subjects completed a questionnaire on mal de debarquement duration and severity. RESULTS Mal de debarquement, mostly of mild severity, was reported following 59% of the exposures to the provocative motion profile, and in 79% of cases lasted less than 6 hours. The incidence of mal de debarquement, its duration, and the severity of symptoms did not differ between the various artificial horizon projection modes. Significant correlations were found between motion sickness severity and the duration and severity of the mal de debarquement that followed. CONCLUSIONS The significant correlations found between motion sickness severity and mal de debarquement duration and severity imply that both syndromes might stem from a failure to adapt to new motion conditions. There is a disparity between the previously reported reduction in motion sickness symptoms by an artificial horizon, and its failure to influence the duration and symptoms of mal de debarquement. This might be explained by the different response in the two syndromes, physical versus cognitive.

Artificial Horizon Effects on Motion Sickness and Performance

Hypothesis To investigate whether the projection of Earth-referenced scenes during provocative motion can alleviate motion sickness severity and prevent motion sickness-induced degradation of performance. Background Exposure to unfamiliar motion patterns commonly results in motion sickness and decreased performance. Methods Thirty subjects with moderate-to-severe motion sickness susceptibility were exposed to the recorded motion profile of a missile boat under moderate sea conditions in a 3-degrees-of-freedom ship motion simulator. During a 120-minute simulated voyage, the study participants were repeatedly put through a performance test battery and completed a motion sickness susceptibility questionnaire, while self-referenced and Earth-referenced visual scenes were projected inside the closed simulator cabin. Results A significant decrease was found in the maximal motion sickness severity score, from 9.83 ± 9.77 (mean ± standard deviation) to 7.23 ± 7.14 (p < 0.03), when the visual display better approximated the full scale of the roll, pitch, and heave movements of the simulator. Although there was a significant decrease in sickness severity, substantial symptoms still persisted. Decision making, vision, concentration, memory, simple reasoning, and psychomotor skills all deteriorated under the motion conditions. However, no significant differences between the projection conditions could be found in the scores of any of the performance tests. Conclusion Visual information regarding the vessel’s movement provided by an artificial horizon device might decrease motion sickness symptoms. However, although this device might be suitable for passive transportation, the continued deterioration in performance measures indicates that it provides no significant advantage for personnel engaged in the active operation of modern vessels.

Safety of double-dose transdermal scopolamine.

Study Objective. To evaluate the safety of double‐dose transdermal scopolamine patch therapy.

A comparison of cinnarizine and transdermal scopolamine for the prevention of seasickness in naval crew: a double-blind, randomized, crossover study.

ObjectivesThe objective of the study was to compare the efficacy of transdermal scopolamine and cinnarizine in the prevention of seasickness and their adverse reactions. MethodsSeventy-six naval crew members participated in a double-blind, randomized, crossover study. On 2 voyages, they were administered either a transdermal scopolamine patch containing 1.5 mg scopolamine and placebo tablets or 25-mg cinnarizine tablets and a placebo patch. Subjects completed questionnaires for each voyage, reporting on the efficacy of the drugs, the severity of their adverse reactions, and the preferred treatment. ResultsSubjects reported the scopolamine patch to be significantly more effective than the cinnarizine tablet (P = 0.029). A moderate to high degree of drowsiness was attributed more frequently to cinnarizine than to the scopolamine patch (34% and 17%, respectively; P < 0.02). Any adverse reaction, to at least a moderate degree, was more frequent with cinnarizine (38%) than with the scopolamine patch (22%), although the significance of this association was borderline. A significantly greater percentage of subjects preferred transdermal scopolamine to cinnarizine (41 vs 12%, P < 0.001). ConclusionsHigher efficacy, a lower rate of adverse reactions, and convenience all led the participants of this study to prefer the scopolamine patch to cinnarizine. Considering the 2 therapeutic options assessed in this study, and in light of the findings of previous studies, it is recommended that the scopolamine patch be used as the drug of choice for the treatment of seasickness among naval crew in particular and probably also among all other sea travelers.

Ondansetron for the prevention of seasickness in susceptible sailors: an evaluation at sea.

BACKGROUND Seasickness is a common problem, causing a significant decrement in performance among naval crew. In about 20-60% of crewmembers, symptoms appear with varying intensity depending on the sea state and the duration of the voyage. Recent studies have suggested antiemetic 5HT3 blockers as a possible treatment for motion sickness, emphasizing their minor clinical and cognitive side effects. The purpose of the present study was to evaluate the 5HT3 blocker ondansetron in the prevention of seasickness. METHODS There were 16 volunteers with a normal otoneurologic examination and no previous medical history of inner ear disease or vertigo who took part in a double blind, randomized, crossover study. During an initial learning phase, the participants practiced on a battery of computerized performance tests until their results stabilized. Ondansetron 8 mg or placebo was administered 2 h before sailing aboard a 500-ton naval vessel in mild sea conditions. Participants did the performance tests and completed a questionnaire evaluating their seasickness symptoms 4 h into the voyage. RESULTS No statistically significant reduction of seasickness symptoms was demonstrated between ondansetron treatment and placebo (a Wiker score of 2.69 +/- 1.78 and 2.81 +/- 1.97, respectively). There was no statistically significant difference in side effects or the results of the performance tests. CONCLUSION In this study, ondansetron was not found to be beneficial in the treatment of seasickness. It could be speculated that the mechanism of nausea in seasickness is different from that of toxin-induced nausea.