Back to the future-revisiting Skylab data on ocular counter-rolling and motion sickness.

In the early 1970s, nine astronauts participated in missions to the Skylab space station. During two preflight testing sessions at the Naval Aerospace Medical Research Laboratory in Pensacola, the amplitudes of their ocular counter-rolling (OCR) during body tilts were assessed to determine if their vestibular functions were within normal ranges. We recently re-evaluated this data to determine asymmetry of each astronaut's OCR response and their OCR slope from sigmoid fits during static leftward and rightward body tilts, which we then compared with their Coriolis sickness susceptibility index (CSSI) on the ground, their motion sickness symptom scores during 0 g maneuvers in parabolic flight, and the severity of the symptoms of space motion sickness (SMS) they reported during their spaceflights. We arranged the astronauts in rank order for SMS severity based on the SMS symptoms they reported during spaceflight and the amount of anti-motion sickness medication they used. As previously reported, the OCR amplitudes of these astronauts were within the normal range. We determined that the OCR amplitudes were not correlated with SMS severity ranking, CSSI, or motion sickness symptoms experienced during parabolic flight. Indices of asymmetry in the OCR reflex were generally small and poorly correlated with SMS scores; however, the only subject with a high index of asymmetry also ranked highly for SMS. Although OCR slope, CSSI, and motion sickness symptoms induced during parabolic flight were each only moderately correlated with SMS severity ranking (rho = 0.41-0.44), a combined index that included all three parameters with equal weighting was significantly correlated with SMS severity ranking (rho = 0.71, p = 0.015). These results demonstrate the challenge of predicting an individual's susceptibility to SMS by measuring a single test parameter in a terrestrial environment and from a limited sample size.

Virtual reality as a countermeasure for astronaut motion sickness during simulated post-flight water landings.

Entry motion sickness (EMS) affects crewmembers upon return to Earth following extended adaptation to microgravity. Anticholinergic pharmaceuticals (e.g., Meclizine) are often taken prior to landing; however, they have operationally adverse side effects (e.g., drowsiness). There is a need to develop non-pharmaceutical countermeasures to EMS. We assessed the efficacy of a technological countermeasure providing external visual cues following splashdown, where otherwise only nauseogenic internal cabin visual references are available. Our countermeasure provided motion-congruent visual cues of an Earth-fixed scene in virtual reality, which was compared to a control condition with a head-fixed fixation point in virtual reality in a between-subject design with 15 subjects in each group. We tested the countermeasure's effectiveness at mitigating motion sickness symptoms at the end of a ground-based reentry analog: approximately 1 h of 2Gx centrifugation followed by up to 1 h of wave-like motion. Secondarily, we explored differences in vestibular-mediated balance performance between the two conditions. While Motion Sickness Questionnaire outcomes did not differ detectably between groups, we found significantly better survival rates (with dropout dictated by reporting moderate nausea consecutively over 2 min) in the visual countermeasure group than the control group (79% survival vs. 33%, t(14) = 2.50, p = 0.027). Following the reentry analogs, subjects demonstrated significantly higher sway prior to recovery (p = 0.0004), which did not differ between control and countermeasure groups. These results imply that providing motion-congruent visual cues may be an effective mean for curbing the development of moderate nausea and increasing comfort following future space missions.

Pharmacological and non-pharmacological countermeasures to Space Motion Sickness: a systematic review.

Introduction: Space Motion Sickness (SMS) is a syndrome that affects around 70% of astronauts and includes symptoms of nausea, dizziness, fatigue, vertigo, headaches, vomiting, and cold sweating. Consequences range from discomfort to severe sensorimotor and cognitive incapacitation, which might cause potential problems for mission-critical tasks and astronauts and cosmonauts' well-being. Both pharmacological and non-pharmacological countermeasures have been proposed to mitigate SMS. However, their effectiveness has not been systematically evaluated. Here we present the first systematic review of published peer-reviewed research on the effectiveness of pharmacological and non-pharmacological countermeasures to SMS. Methods: We performed a double-blind title and abstract screening using the online Rayyan collaboration tool for systematic reviews, followed by a full-text screening. Eventually, only 23 peer-reviewed studies underwent data extraction. Results: Both pharmacological and non-pharmacological countermeasures can help mitigate SMS symptoms. Discussion: No definitive recommendation can be given regarding the superiority of any particular countermeasure approach. Importantly, there is considerable heterogeneity in the published research methods, lack of a standardized assessment approach, and small sample sizes. To allow for consistent comparisons between SMS countermeasures in the future, standardized testing protocols for spaceflight and ground-based analogs are needed. We believe that the data should be made openly available, given the uniqueness of the environment in which it is collected. Systematic review registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021244131.

Astronauts eye-head coordination dysfunction over the course of twenty space shuttle flights.

BACKGROUND: Coordination of motor activity is adapted to Earth's gravity (1 g). However, during space flight the gravity level changes from Earth gravity to hypergravity during launch, and to microgravity (0 g) in orbit. This transition between gravity levels may alter the coordination between eye and head movements in gaze performance. OBJECTIVE: We explored how weightlessness during space flight altered the astronauts' eye-head coordination (EHC) with respect to flight day and target eccentricity. METHODS: Thirty-four astronauts of 20 Space Shuttle missions had to acquire visual targets with angular offsets of 20°, 30°, and 49°. RESULTS: Measurements of eye, head, and gaze positions collected before and during flight days 1 to 15 indicated changes during target acquisition that varied as a function of flight days and target eccentricity. CONCLUSIONS: The in-flight alterations in EHC were presumably the result of a combination of several factors, including a transfer from allocentric to egocentric reference for spatial orientation in absence of a gravitational reference, the generation of slower head movements to attenuate motion sickness, and a decrease in smooth pursuit and vestibulo-ocular reflex performance. These results confirm that humans have several strategies for gaze behavior, between which they switch depending on the environmental conditions.

Influence of Inosine on Cerebral Hemodynamics in Space Motion Sickness in Experimental Animals.

BACKGROUND: Motion sickness occurs worldwide in healthy individuals regardless of age, ethnicity, or gender. It is an acute disorder; it can also present as a chronic disorder in some individuals. Motion sickness not only includes vomiting and nausea, but also includes other features such as pallor of varying degrees, cold sweating, headache, drowsiness, increased salivation, and cranial pain, which are severe. Some of the other assessment scales can interpret sickness on exposure to virtual or visual stimulation and while travelling in different types of transport. AIM: The aim of our research is to study the effect of the drug on the level of blood flow and vascular reactivity of cerebral vessels when simulating changes in the cerebral circulation in terrestrial conditions characteristic of hypogravity. METHODS: Chronic experiments were performed on non-anesthetized rabbits with large hemispheres, thalamus and hypothalamus were implanted with the needle-platinum electrodes 150 mm in diameter in the cortex, and local blood flow and vascular reactivity were recorded accordingly. Cerebrovascular disturbances were modeled using an MSAOP (motion sickness of animals in the anti-orthostatic position) with an inclined angle of 45° for 2 hours. Local blood flow (BF) was measured in ml/min/100g of tissue by the method of registration of hydrogen clearance. The vasodilator coefficient of reactivity (CrCO2) was calculated by the ratio of BF against the background of inhalation of a mixture of 7% CO2 with air to the initial BF; vasoconstrictor - in relation to BF on the background of inhalation of 100% O2 to the initial BF (CrO2). A series of experiments were carried out with different routes of drug administration: First, inosine was administered intravenously at a dose of 5 mg/kg immediately before the start of SMS modeling, same dose was administered 30 minutes before the start of exposure. As a control, we used the results of experimental animals under similar conditions without the administration of the drugs. RESULTS: Inosine has pronounced protective properties in cerebrovascular disorders on the background of space motion sickness (SMS) modeling, which is manifested by normalization of BF and restoration of compensatory reactions of cerebral vessels. In the mechanism of cerebroprotective action of inosine, it is able to correct the metabolic processes, which play an important role and help increase the compensatory capabilities and functional stability of the cerebrovascular system under gravitational influences. CONCLUSION: When using inosine orally, the effects are more pronounced than when administered intravenously, which should be taken into account when using it for the prevention of cerebrovascular disorders in extreme conditions.

The assessment of the impact of a training process on the habituation of the vestibular-vegetative system, using a special rotational test as a condition of maintaining flight safety.

OBJECTIVES: The authors formulated a hypothesis that, on completion of the training program by cadets, their vestibular habituation would increase, measured by the time of the duration of the test on the unlocked looping, in contrast to the initial values and the control group. MATERIAL AND METHODS: The research involved 35 male cadets, first-year students of the Polish Air Force Academy in Deblin. The examined persons were on average 20 years of age. They were divided into 2 groups. Group A (N = 25, tested) continued training on Special Aviation Gymnastic Instruments (SAGI). The cadets were a homogeneous group of participants in the jet pilot course, selected by the Military Aeromedical Board. Group B (N = 10, control) conducted the standard physical military education program. Groups A and B were tested on the unlocked looping before and after the training process. In the training process, the groups had heart rate (HR) monitored. RESULTS: The cadets in group A on the test in the unlocked looping, at the beginning of the training period, had an average score of 468.5±96.6 s, and on completion of the training period 575.6±47.9 s, which is a statistically significant difference at p < 0.000001. Similarly, the examined individuals in group B received an average score of 396.2±31.8 s, and at the end of the training period 473.4±72.0 s, which is a statistically significant difference at p < 0.01. In group A, a statistically significant decrease in the average HR value was observed. In group B, there was a statistically significant increase in the average HR value. CONCLUSIONS: The exercises on SAGI have a beneficial impact on improving the habituation of the vestibular organ in training cadets in examination II, as opposed to examination I and the control group. Int J Occup Med Environ Health. 2020;33(4):497-506.

Space motion sickness: A common neurovestibular dysfunction in microgravity.

This article presents a review of the current findings related to neurovestibular physiology, aetiology, and proposed theories on space motion sickness (SMS) during acute and sustained exposure to microgravity. The review discusses the available treatment options including medication and nonpharmacological countermeasure methods that help to prevent the development of SMS in weightlessness. Ground-based simulations using virtual reality, flight simulations, and Barany's chairs can be applied to study SMS and demonstrate its signs and symptoms to space crew members. Space motion sickness has been observed in approximately 70% of astronauts within the first 72 h in microgravity, having in general an instantaneous onset of signs and symptoms. Stomach discomfort, nausea, vomiting, pallor, cold sweating, salivation, tachypnoea, belching, fatigue, drowsiness, and stress hormone release have been documented. This can have detrimental effects on the well-being of astronauts in the initial phase of a space mission. Mental and physical performance may be affected, jeopardizing operational procedures and mission safety.

Restricted sedation and absence of cognitive impairments after administration of intranasal scopolamine.

INTRODUCTION: Space motion sickness in astronauts during spaceflight causes significant discomfort, which might impede their functionality. Pharmacological treatment has been mainly restricted to promethazine. Transdermal and oral scopolamine have also been used in space; however, their use was reduced due to unpredictable effectiveness and side effects. Recently, intranasal scopolamine administration has gained much interest, since this route ensures fast and reliable absorption with a decreased incidence of undesirable side effects. The aim of this study was to evaluate the effect of intranasal scopolamine on cognitive performance and to determine its side effects. METHODS: This double-blind, placebo controlled, repeated measures study evaluated vigilant attention, short-term memory, implicit memory and working memory. Side effects were reported on a 22-item questionnaire and sleepiness was assessed by the Karolinska, Stanford and Epworth Sleepiness Scales. RESULTS: Scopolamine had no effect on cognitive function. Only the Karolinska score was significantly increased for scopolamine compared to placebo. Participants reported a dry mouth and dizziness after receiving scopolamine. DISCUSSION: Results show that intranasal scopolamine did not impair cognitive performance. Intranasal scopolamine might be a good alternative to promethazine for the alleviation of space motion sickness, since the agent has minimal sedative effects and does not hamper cognitive performance.

Microgravity Simulated by the 6° Head-Down Tilt Bed Rest Test Increases Intestinal Motility but Fails to Induce Gastrointestinal Symptoms of Space Motion Sickness.

BACKGROUND: Space motion sickness (SMS) is the most relevant medical problem during the first days in microgravity. Studies addressing pathophysiology in space face severe technical challenges and microgravity is frequently simulated using the 6° head-down tilt bed rest test (HDT). AIM: We were aiming to test whether SMS could be simulated by HDT, identify related changes in gastrointestinal physiology and test for beneficial effects of exercise interventions. METHODS: HDT was performed in ten healthy individuals. Each individual was tested in three study campaigns varying by a 30-min daily exercise intervention of either standing, an upright exercise regimen, or no intervention. Gastrointestinal symptoms, stool characteristics, gastric emptying time, and small intestinal transit were assessed using standardized questionnaires, (13)C octanoate breath test, and H2 lactulose breath test, respectively, before and at day 2 and 5 of HDT. RESULTS: Individuals described no or minimal gastrointestinal symptoms during HDT. Gastric emptying remained unchanged relative to baseline data collection (BDC). At day 2 of HDT the H2 peak of the lactulose test appeared earlier (mean ± standard error for BDC-1, HDT2, HDT5: 198 ± 7, 139 ± 18, 183 ± 10 min; p: 0.040), indicating accelerated small intestinal transit. Furthermore, during HDT, stool was softer and stool mass increased (BDC: 47 ± 6, HDT: 91 ± 12, recovery: 53 ± 8 g/day; p: 0.014), indicating accelerated colonic transit. Exercise interventions had no effect. CONCLUSION: HDT did not induce symptoms of SMS. During HDT, gastric emptying remained unchanged, but small and large intestinal transit was accelerated.

Intranasal scopolamine affects the semicircular canals centrally and peripherally.

Space motion sickness (SMS), a condition caused by an intravestibular conflict, remains an important obstacle that astronauts encounter during the first days in space. Promethazine is currently the standard treatment of SMS, but scopolamine is used by some astronauts to prevent SMS. However, the oral and transdermal routes of administration of scopolamine are known to have substantial drawbacks. Intranasal administration of scopolamine ensures a fast absorption and rapid onset of therapeutic effect, which might prove to be suitable for use during spaceflights. The aim of this study was to evaluate the effects of intranasally administered scopolamine (0.4 mg) on the semicircular canals (SCCs) and the otoliths. This double-blind, placebo-controlled study was performed on 19 healthy male subjects. The function of the horizontal SCC and the vestibulo-ocular reflex, as well as the saccular function and utricular function, were evaluated. Scopolamine turned out to affect mainly the SCCs centrally and peripherally but also the utricles to a lesser extent. Centrally, the most probable site of action is the medial vestibular nucleus, where the highest density of muscarinic receptors has been demonstrated and afferent fibers from the SCCs and utricles synapse. Furthermore, our results suggest the presence of muscarinic receptors in the peripheral vestibular system on which scopolamine has a suppressive effect. Given the depressant actions on the SCCs, it is suggested that the pharmacodynamic effect of scopolamine may be attributed to the obliteration of intravestibular conflict that arises during (S)MS.

Quantitative orientation preference and susceptibility to space motion sickness simulated in a virtual reality environment.

Orientation preference should appear when variable weightings of spatial orientation cues are used between individuals. It is possible that astronauts' orientation preferences could be a potential predictor for susceptibility to space motion sickness (SMS). The present study was conducted to confirm this relationship on Earth by quantifying orientation preferences and simulating SMS in a virtual reality environment. Two tests were carried out. The first was to quantitatively determine one's orientation preference. Thirty-two participants' vision and body cue preferences were determined by measuring perceptual up (PU) orientations. The ratio of vision and body vector (ROVB) was used as the indicator of one's orientation preference. The second test was to visually induce motion sickness symptoms that represent similar sensory conflicts as SMS using a virtual reality environment. Relationships between ROVB values and motion sickness scores were analyzed, which revealed cubic functions by using optimal fits. According to ROVB level, participants were divided into three groups - body group, vision group, and confusion group - and the factor of gender was further considered as a covariate in the analysis. Consistent differences in motion sickness scores were observed between the three groups. Thus, orientation preference had a significant relationship with susceptibility to simulated SMS symptoms. This knowledge could assist with astronaut selection and might be a useful countermeasure when developing new preflight trainings.

Effects of location training and orientation training on the visual-motor coordination under up-down reversed vision / 医用生物力学

Objective To compare the effects of location and orientation training on the improvement of visual motor coordination under up down reversed vision, provide reference for the preventation of space motion sickness and the design of adaptation training for sensory conflict. Method Sixteen subjects were instructed to complete the maze task wearing the up down reversing prism spectacle before and after the location training and the orientation training. Both trainings lasted 30 minutes respectively. The error rate and the executing time during the maze test were analyzed and compared. Results Both trainings significantly decreased the error rate and the executing time. In addition, the results of different training methods had significant difference, and the effects of the orientation training was better than that of the location training under up-down reversed vision. Conclusions Under the sensory conflict environment arising from the visual change, the adaptation induced by some task training could also be of benefit to some other task training so as to improve the ability of visual-motor coordination and the adaption to the sensory conflict. However, different trainings could have various degrees of improvement.