Seasickness susceptibility and the vestibular time constant: a prospective study.

Human passive motion during boat, car or airplane travel may trigger motion sickness. Seasickness is the most provoking manifestation of motion sickness. It imposes major constraints on quality of life and human performance. Based on seasickness susceptibility the population is usually categorized into susceptible (S) and non-susceptible (NS). During repeated exposure some susceptible individuals undergo habituation and obtain symptoms relief, reflecting a third group of habituating (H) individuals. Recently, accumulative evidence suggests that the vestibular time constant (Tc) is associated with motion sickness susceptibility and attenuation of symptoms. These studies demonstrated that repeated passive motion stimuli lead to temporary short-term (days) changes in Tc, whereas sea sickness habituation process lasts 3 to 6 months. Therefore, the goal of the present study was to examine the behavior of Tc during the entire span of the seasickness habituation process between the H, S and NS groups to find an objective test for seasickness severity prediction. Tc of 30 subjects was prospectively evaluated pre, 3 and 6 months post exposure to sea environment using a computerized rotatory chair system protocol. Seasickness severity was evaluated by Wiker questionnaire. Significantly shorter Tc was found in the S group compared with the NS and H groups. Further analysis revealed lower maximal Slow Phase Velocity (mSPV) and nystagmus frequency (total number of beats/second) in the S group. Our results suggest that Tc, mSPV and nystagmus frequency might serve as a prediction for seasickness severity. This study was retrospectively registered on December 7th 2022 and assigned the identifier number NCT05640258.

The Vestibular Time Constant and Clinical Response to Antimotion Sickness Medication.

OBJECTIVE: The therapeutic effects of antimotion sickness medications involve suppression of several components along the vestibular system. Scopolamine-based medications have proved to be the most effective anti-seasickness agents. However, there is high variability in individual responses. The vestibular nuclei, in which the vestibular time constant is modulated, contain acetylcholine receptors which are affected by scopolamine. The hypothesis of the study was that successful seasickness prevention by scopolamine requires vestibular suppression to be reflected by the shortening of the vestibular time constant. DESIGN: Subjects were 30 naval crew members suffering from severe seasickness and were treated with oral scopolamine. The study participants were defined as responsive or non-responsive to the anti-seasickness medication according to the clinical outcome: successful response to scopolamine was defined as a reduction of seasickness severity from the highest score of 7 according to the Wiker scale to 4 or less. Scopolamine and placebo were assigned to each subject in a crossover, double-blind design. The horizontal semicircular canal time constant was evaluated by a computerized rotatory chair before, 1 and 2 hours after drug or placebo administration. RESULTS: The vestibular time constant was significantly shortened from 16.01 ± 3.43 seconds to 12.55 ± 2.40 seconds ( p < 0.001) in the scopolamine-responsive group but not in the nonresponsive group. In contrast, vestibular time constant values were 13.73 ± 4.08 and 12.89 ± 4.48 for baseline and 2 hours measurements, respectively. This change was not statistically significant. CONCLUSIONS: Reduction in the vestibular time constant after scopolamine administration can be used to predict whether motion sickness alleviation will occur. This will enable the administration of appropriate pharmaceutical treatment without the need for prior exposure to sea conditions.

Galvanic vestibular stimulation as a novel treatment for seasickness.

Motion sickness is the cause of major physical discomfort and impaired performance in many susceptible individuals. Some habituate to sea conditions, whereas others remain chronically susceptible, requiring lifelong pharmaceutical treatment. The present study sets out to investigate whether galvanic vestibular stimulation (GVS) coupled with rotatory chair stimulation could mimic sea conditions and alleviate motion sickness symptoms in individuals deemed chronically susceptible. Thirty seasickness susceptible subjects, after at least six months of regular sailing, were enrolled in a prospective, single-blind, randomised controlled study. The treatment group underwent GVS coupled with inverse phase rotatory chair impulse in sinusoidal harmonic acceleration protocol. The control group underwent a sham procedure. All subjects performed repeated velocity step tests to determine the vestibular time constant (Tc) and completed a seasickness questionnaire. The GVS rotatory chair procedure decreased the prevalence of severe seasickness. The number of motion sickness clinic visits and anti-motion sickness drug consumption were reduced in the treatment group three-month post intervention as compared to control. In addition, there was significant reduction of Tc in the treatment group. GVS coupled with rotatory chair impulse could decrease motion sickness severity, induce neurophysiological learning processes and promote habituation to seasickness in chronic susceptible subjects. This is a novel and promising non-pharmacological method to treat motion sickness susceptible individuals. Furthermore, the investigation demonstrated that adaptation to sea conditions may take place even after years of susceptibility to seasickness. This study was retrospectively registered on August 10th 2021 and assigned the identifier number NCT05004818.

Scopolamine Treatment and Adaptation to Airsickness.

BACKGROUND: Airsickness is a clinical syndrome manifesting in a variety of symptoms, particularly nausea and vomiting during flight. Studies of habituation to motion sickness in humans treated by scopolamine have produced conflicting results. The drug accelerated habituation, but a rebound effect on symptom severity was observed after its withdrawal. The purpose of the present study was to investigate whether scopolamine affects the adaptation process. We also evaluated the relationship between initial symptom severity and adaptation to airsickness.METHODS: Aviator cadets in the first two stages of their training were divided into two groups, treated and not treated by scopolamine. Airsickness severity was evaluated using both simulator sickness and motion sickness questionnaires, and drug administration was recorded.RESULTS: A statistically significant higher rate of adaptation was observed among the scopolamine-treated group compared with the nontreated group. On the simulator sickness questionnaire, rate of adaptation for the two groups was -0.21 ± 0.53 and -0.1 ± 0.17, respectively, and for the motion sickness questionnaire -2.34 ± 1.54 and -0.91 ± 1.41, respectively. Examination of a possible connection between initial symptom severity and adaptation rate failed to reveal a significant relationship.CONCLUSIONS: We recommend the use of oral scopolamine to accelerate habituation and find it a relatively safe short-term treatment for airsickness. Our results support the notion that scopolamine accelerates the natural adaptation process.Doron O, Samuel O, Karfunkel-Doron D, Tal D. Scopolamine treatment and adaptation to airsickness. Aerosp Med Hum Perform. 2020; 91(4):313-317.

Long-term scopolamine treatment and dental caries.

OBJECTIVES: To investigate whether scopolamine, an anticholinergic agent which induces hyposalivation, represents a risk factor for the occurrence of dental caries. MATERIALS AND METHODS: A retrospective cohort study was carried out among sailors treated with scopolamine for seasickness. The study population included 370 young healthy male adults (18-30 years old) who served in the Israel Navy between 2012 and 2016. Of these, 66 subjects who were chronically treated with intermittent administration of scopolamine, either by the oral or transdermal route, were assigned to the study group. Documented subject characteristics included age, socioeconomic status, level of education, body mass index, smoking history, and dental hygiene. Follow-up lasted 1 to 3.5 years. RESULTS: Two- to 3.5-year follow-up revealed a higher risk of dental caries in 15 of 16 subjects (93.8%) treated with an average of 50.9 mg scopolamine, in contrast to only 71 of 108 control subjects (65.7%) (RR = 1.43, p = 0.02 [95% CI = 1.18-1.72]). Follow-up for 1-1.5 years revealed a lower occurrence of dental caries in both the study group (11/22, 50.0%) and the control group (46/104, 44.2%). Follow-up of 1.5-2 years also revealed less dental caries, in 16/28 subjects (57.1%) in the study group and 51/92 subjects (55.4%) in the control group. The differences were not statistically significant. CONCLUSIONS: In healthy young adults, prolonged intermittent use of scopolamine was found to be a risk factor for the development of dental caries. CLINICAL SIGNIFICANCE: Dental care and hygiene should be intensified when administering hyposalivatory anticholinergic agents.

Vestibular Derangement and Motion Intolerance in VATER Association.

VATER association is a nonrandom occurrence of congenital malformations: vertebral defects, anal atresia, tracheoesophageal fistula, renal defects, and radial bone anomalies. We report the case of a 19-year-old man with a childhood diagnosis of VATER association, who presented to the motion sickness clinic with severe seasickness. We discuss the clinical and laboratory diagnosis of vestibular pathophysiology, which was confirmed by MRI of lateral semicircular canal and vestibule dysplasia. We suggest the possibility of vestibular involvement as part of the developmental field defect associated with VATER syndrome, which hitherto has rarely been reported.

Vestibular evoked myogenic potentials and motion sickness medications.

OBJECTIVE: Seasickness is a widespread problem among naval crew, and has a major impact on their performance at sea. The three pharmacological agents most commonly employed in the treatment of seasickness are dimenhydrinate, cinnarizine, and scopolamine. At present, the effectiveness of anti-seasickness drugs is tested by a process of "trial and error", while sailing and exposed to sea conditions. A physiological test to evaluate the action of a drug might save crew members long periods of suffering, as well as simplifying the procedure of selecting the appropriate treatment for each individual. The cervical vestibular evoked myogenic potentials (cVEMP) test has come to be recognized as a reliable procedure for the objective evaluation of saccular function. It was the hypothesis of the present study that cVEMP otolith responses may be affected by anti-motion sickness drugs, which might thus make cVEMP a useful clinical neurophysiological tool for the assessment of drug absorption and efficacy. METHODS: Thirty male sailors who regularly took medication for the treatment of seasickness participated in the study. Participants underwent the cVEMP test pre- and 1h post-drug administration. RESULTS: A statistically significant decrease in p13 latency was found after administration of scopolamine compared with baseline (14.46ms vs. 15.09ms, p=0.0049), with significant prolongation of the binaural average inter-latency in this group. No differences were found in the dimenhydrinate and cinnarizine study groups. CONCLUSIONS: This study demonstrated that scopolamine absorption can be verified by changes in cVEMP latencies. SIGNIFICANCE: The potential of the cVEMP test for predicting action of scopolamine on the vestibular system.

Airsickness: Etiology, Treatment, and Clinical Importance-A Review.

Airsickness is one of the forms of motion sickness, and is of significance in both commercial and military flight. Whereas commercial airline passengers may simply feel poorly, the effect of airsickness on military aircrew may lead to a decrement in performance and adversely affect the mission. This is of major importance in the case of flight safety, when a pilot who is incapacitated may endanger the aircraft. The problem is particularly evident in pilot training, because of the high incidence of airsickness at this stage in the pilot's career. The majority of aircrew undergo habituation to airsickness during their service, with a reduction in symptoms and improved function. Although airsickness is a wellknown problem in aviation, we were unable to locate a review of this topic in the literature. This review focuses on the characteristics, clinical evaluation, and treatment of airsickness. It also presents the experience of the Israeli flight academy, and our solution for Navy pilots who have to contend with the risk of seasickness before taking to the air.

Evidence for the initiation of decompression sickness by exposure to intense underwater sound.

Mass stranding of cetaceans (whales and dolphins), in close association with the activity of naval sonar systems, has been reported on numerous occasions. Necropsy showed bubble-associated lesions similar to those described in human decompression sickness (DCS). We examined the hypothesis that exposure to underwater sound may potentiate DCS. Rats were subjected to immersion and simulated dives with and without simultaneous acoustic transmissions at pressure levels and frequencies of 204 dB/8 kHz and 183.3 dB/15 kHz. DCS severity was assessed using the rotating wheel method. Recording of somatosensory evoked potentials (SSEPs) was employed under general anesthesia as an electrophysiological measure of neurologic insult. A significantly higher rate of decompression sickness was found among animals exposed to the 204-dB/8-kHz sound field. Significantly higher pathological SSEPs scores were noted for both underwater sound protocols. Pathological SSEPs scores in animals immersed during the acoustic transmissions, but without changes in ambient pressure, were comparable to those observed in animals exposed to the dive profile. The results demonstrate induction of neurological damage by intense underwater sound during immersion, with a further deleterious effect when this was combined with decompression stress. The study outcome has potential implications for human diving safety and may provide an explanation for the mass stranding of cetaceans purportedly associated with sonar activity.

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.

Vestibular evoked myogenic potentials and habituation to seasickness.

OBJECTIVE: Seasickness may impose severe limitations on the performance of ships' crew. Cervical vestibular evoked myogenic potentials (cVEMP) assess the function of the saccule, the organ responsible for monitoring vertical linear acceleration, which has been found to be the most provocative motion stimulus in the evolution of motion sickness. We used the cVEMP test in a prospective evaluation of susceptibility and habituation to seasickness. METHODS: Forty-six naval recruits underwent the cVEMP test before exposure to sea conditions. After 6 months' sailing experience, participants completed a questionnaire evaluating their initial and current seasickness severity. Based on their most recent experience, subjects were divided into three groups: non-vomiting non-habituating (NV-NH), vomiting (V), and non-vomiting habituating (NV-H). RESULTS: Statistically significant lower thresholds for cVEMP were found in subjects who habituated to sea conditions (NV-H), compared with those remaining severely susceptible (V) (77.0 dB HL vs. 84.9 dB HL; p<0.01). CONCLUSIONS: The ability to produce the cVEMP at lower thresholds represents a broader dynamic range, in which the reflex can respond to a wider array of stimuli amplitudes. SIGNIFICANCE: The present study demonstrates the potential of the cVEMP test for predicting future habituation to seasickness.

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.

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

OBJECTIVES: The objective of the study was to compare the efficacy of transdermal scopolamine and cinnarizine in the prevention of seasickness and their adverse reactions. METHODS: Seventy-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. RESULTS: Subjects 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). CONCLUSIONS: Higher 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.

Medical waiver for flying after microvascular decompression for hemifacial spasm.

BACKGROUND: Microvascular decompression has become the treatment of choice for hemifacial spasm. Post-surgical symptoms of vestibular dysfunction may appear, but are mostly transient. The unique occupational demands of military aviators necessitate complete otoneurological evaluation after vestibular insults to allow safe return to flying duties. CASE REPORT: We present a case of a military jet-fighter pilot who developed transient vertigo and disequilibrium after microvascular decompression for hemifacial spasm. Resolution of symptoms and complete recovery as documented by vestibular bedside and laboratory tests allowed us to grant the pilot full solo flying privileges.

Postural dynamics and habituation to seasickness.

The computerized dynamic posturography (CDP) test examines the response pattern to simultaneous, multimodal sensory stimulation. The purpose of this prospective, controlled study was to investigate whether postural dynamics evaluated by CDP are related to seasickness severity and the process of habituation to sea conditions. Subjects included 74 naval personnel assigned to service aboard ship and 29 controls designated for shore-based positions. Study participants performed a baseline CDP test, and subsequent follow-up examinations 6 and 12 months after completion of their training. On those occasions they also completed a seasickness severity questionnaire. Longitudinal changes in postural parameters were examined, as well as a possible correlation between baseline CDP results and final seasickness severity scores. The results indicated longitudinal habituation to seasickness. Reduced scores were found for sensory organization sub-tests 3 and 5 in the first follow-up examination, reflecting increased weighting of visual and somatosensory input in the maintenance of balance. Scores in the second follow-up examination were above baseline values, indicating increased reliance on vestibular cues. These significant bimodal changes were found only in study subjects having the highest degree of habituation to seasickness. A significant decrease in motor response strength was found in parallel with increased habituation to seasickness. Baseline CDP results and postural control dynamics were not correlated with subjects' final seasickness severity score. These results suggest a potential role for CDP in monitoring the process of habituation to unusual motion conditions.

Monothermal caloric testing in the screening of vestibular function.

INTRODUCTION: The alternate binaural bithermal caloric test (ABBT) is the standard test for evaluation of the dizzy patient. Monothermal caloric testing (MT) has the potential benefits of reducing the administration time and patient discomfort. The goal of the present study was to investigate the role of MT screening in the prediction of ABBT results. METHODS: ABBT results of 218 patients having normal otoneurological examination, normal hearing, and normal electronystagmography (ENG) were retrospectively analyzed to generate norms for all subtests. These norms were then employed to calculate the sensitivity and specificity of MT for predicting normal ABBT in a group of 197 consecutive dizzy patients who were referred for vestibular testing. RESULTS: The best predictions of ABBT by MT results were achieved when ENG testing showed oculomotor integrity and no spontaneous, positional, or positioning nystagmus. Under these conditions, warm MT lateralization < 32% had 90% sensitivity and 92% specificity for the prediction of normal ABBT. DISCUSSION: When no pathology is detected in the other parts of the ENG, warm MT lateralization < 32% can indicate normal ABBT with a 10% probability for a false-negative result. This false negative rate precludes the routine use of warm MT in the clinical realm and its application as a screening tool for possible vestibular deficits in a generally healthy population like aviation or diving candidates. Higher sensitivity may be achieved by lowering the cut-off point of the response asymmetry required for the diagnosis of MT screening failure and the omission of directional preponderance diagnosis from the goals of the screening.

Vestibular evoked myogenic potentials and saccular plasticity in divers.

INTRODUCTION: Otolith function, which is dependent on linear velocity and acceleration, may be expected to change in underwater divers, who are submerged in a medium that is denser than air. The purpose of the present study was to examine possible changes in the sacculocollic reflex of professional divers and to investigate whether there might be diving-induced adaptation of the saccular response. METHODS: We used the vestibular evoked myogenic potential (VEMP) response to evaluate saccular function in 12 professional divers shortly after a dive and after an interval of at least 24 h. The control group consisted of 12 matched non-divers. Wave latencies and amplitudes, asymmetry ratio, and the response threshold were compared between the groups. RESULTS: Statistically significant shortening of N23-wave latency was found in the divers compared with the control group. The mean +/- SE were 22 +/- 0.1 and 22.1 +/- 0.7 ms early and late after a dive in the divers group vs. 24.5 +/- 0.5 ms in the control group. No significant differences were found in any of theVEMP parameters between the early and late post-dive recordings. DISCUSSION: We suggest that the reduction in N23 latency reflects long-term adaptation of the sacculocollic reflex to underwater conditions. Increased sensitivity of the reflex is required to compensate for the decrease in linear velocity and acceleration, resulting in reduced stimulation of the otolith organ.

Safety of double-dose transdermal scopolamine.

STUDY OBJECTIVE: To evaluate the safety of double-dose transdermal scopolamine patch therapy. DESIGN: Randomized, crossover, double-blind study. SETTING: Motion sickness clinic in Haifa, Israel. PARTICIPANTS: Twenty male sailors aged 18-21 years whose seasickness symptoms improved only slightly or not at all with a single transdermal scopolamine patch. INTERVENTION: Subjects received either two transdermal scopolamine patches or one scopolamine patch plus a placebo patch for 24 hours (first session). After at least 1 week from the end of the first session, they received the other treatment for 24 hours (second session). MEASUREMENTS AND MAIN RESULTS: Plasma scopolamine concentrations, physiologic (heart rate and blood pressure), visual, and cognitive function parameters, and adverse effects were assessed before the first session (baseline) and after each 24-hour session. Visual function was tested again 24 hours after patch removal. Subjects also completed an adverse-effects questionnaire immediately after and 24 hours after patch removal for both treatment sessions. A significant difference was found in mean plasma scopolamine concentrations between the single-dose and double-dose treatments (81 vs 127 pg/ml [therapeutic level 100 pg/ml], p<0.01). No significant differences were found in heart rate, blood pressure, cognitive function, or visual function measurements. Mild blurred vision was the only adverse effect for which there was a significant difference between the single-dose and double-dose treatments; however, this adverse effect was judged to be not clinically significant. CONCLUSION: Double-dose transdermal scopolamine may improve treatment in patients who fail to respond to a single patch by increasing the plasma scopolamine concentration, without aggravating systemic, visual, or cognitive adverse effects. Thus we recommend that a double dose can be administered safely to these patients.

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.

Seasickness pathogenesis and the otolithic organs: vestibular evoked myogenic potentials study--preliminary results.

BACKGROUND: Seasickness is thought to result from conflicting inputs from the vestibular, visual and somatosensory systems. The otolithic organs, which are responsible for the sensation of linear acceleration and tilt, are important in the pathogenesis of seasickness. The vestibular evoked myogenic potentials test is an objective evaluation of saccular function. OBJECTIVE: To examine whether saccular function is related to the pathogenesis of seasickness. METHODS: VEMP was performed in 10 subjects susceptible to seasickness and in 14 non-susceptible subjects. RESULTS: Bilateral VEMP responses were obtained in 7 (50%) of the non-susceptible subjects and 1 (10%) of the susceptible subjects. No differences were found between the groups in P13 and N23 wave latencies, amplitudes, N13-P23 inter-peak latencies, and peak-to-peak asymmetry ratios. More subjects in the susceptible group had asymmetry ratios > 35%. CONCLUSIONS: The attenuated saccular response might be explained in the context of the neural-mismatch theory and/or the subjective vertical theory, as reflecting an adaptation effort to sea conditions. A larger study is necessary to determine whether a statistically significant difference in VEMP responses exists between seasickness-susceptible and non-susceptible subjects.