Asymmetric otolith function and increased susceptibility to motion sickness during exposure to variations in gravitoinertial acceleration level.

Lackner JR, Graybiel A, Johnson WH, Money KE.

Von Baumgarten and his colleagues (23,24) have suggested that asymmetries in otolith function between the left and right labyrinths may result from differences in otoconial mass and could play a role in space motion sickness. Such asymmetries would be centrally compensated for under terrestrial conditions but on exposure to weightlessness the persisting central compensation would produce a central imbalance that could lead to motion sickness. We have used ocular counterrolling as a way of measuring the relative "efficiency" of the left and right otoliths and have compared the ocular counterrolling scores of individuals with their susceptibility to motion sickness during passive exposure to variations in Gz in parabolic flight maneuvers. The experimental findings indicate that large asymmetries in counterrolling for leftward and rightward body tilts are associated with greater susceptibility to motion sickness in parabolic flight.

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Treatment of severe motion sickness with antimotion sickness drug injections.

Graybiel A, Lackner JR.

This report concerns the use of intramuscular injections of scopolamine, promethazine, and dramamine to treat severely motion sick individuals participating in parabolic flight experiments. The findings indicate that a majority of individuals received benefit from 50-mg injections of promethazine or 0.5mg-injections of scopolamine. By contrast, 50-mg injections of dramamine and 25-mg injections of promethazine were nonbeneficial. The use of antimotion drug injections for treating space motion sickness is discussed.

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Prediction of the incidence of motion sickness from the magnitude, frequency, and duration of vertical oscillation.

Lawther A, Griffin MJ.

Institute of Sound and Vibration Research, The University, Southampton, United Kingdom.

A method is proposed by which the incidence of motion sickness may be predicted from measurement of the motion exposure. The method is based on data from both field and laboratory studies involving large numbers of people and is applicable to marine and other environments where vertical oscillation occurs at frequencies below 0.5 Hz. The dependence of motion sickness on the frequency of oscillation requires the use of a weighting function between 0.1 and 0.5 Hz. The dependence of sickness on the duration of exposure is incorporated by the use of a cumulative measure of motion dose based on the product of root-mean-square (rms) acceleration magnitude and the square root of stimulus duration. The influence of population variables such as sex, age, and motion experience is discussed. The method enables separate predictions to be made of vomiting incidence and of feelings of illness. The prediction procedure, while not seeking to explain the underlying mechanisms of motion sickness occurrence, provides a generally applicable method which is simple to use and has an accuracy consistent with the experimental data on which it is based.

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Buspirone blocks motion sickness and xylazine-induced emesis in the cat.

Lucot JB, Crampton GH.

Department of Pharmacology and Toxicology, Wright State University, Dayton, Ohio 45435.

Cats were tested for motion sickness following s.c. pretreatment with four doses of buspirone. Buspirone blocked motion sickness with an ED50 of 0.46 mg . kg-1 base. Buspirone pretreatment (4.0 mg . kg-1 base) also significantly blocked vomiting in cats later injected with 0.66 mg . kg-1 (base) s.c. of the emetic drug xylazine. The results are interpreted as showing that buspirone is acting at the vomiting center, the point of convergence for the separate mechanisms subserving chemically-induced emesis and motion sickness.

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Gastrointestinal motility in space motion sickness.

Thornton WE, Linder BJ, Moore TP, Pool SL.

Astronaut Office, NASA/Johnson Space Center, Houston, Texas 77058.

Gastrointestinal (Gl) symptoms in space motion sickness (SMS) are significantly different from those in ordinary motion sickness (MS). Vomiting is sudden, often unexpected, infrequent, never prolonged and usually without nausea. Inflight bowel sounds are absent in those with SMS but present after recovery and in those not affected. Recording and tabulation of sounds was the only technique that could be used as a measure of motility during spaceflight operations. There were 17 subjects, 6 unaffected by SMS, who made ambulatory recordings pre- and inflight. With one exception, all those affected had sharply reduced sounds while those unaffected had increases or moderate reductions. The mechanism of vomiting in SMS appears to be secondary to this ileus in contrast to vomiting in ordinary MS, where the emesis center is thought to be directly triggered by the vestibular system. This ileus appears to be the only consistent and reliable indicator for SMS to date.

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The vestibulo-ocular reflex and its possible roles in space motion sickness.

Watt DG.

Dept. of Physiology, McGill University, Montreal, Quebec, Canada.

Prolonged exposure to an inappropriate vestibulo-ocular reflex (VOR) will usually lead to motion sickness, and it has been predicted on theoretical grounds that VOR gain may be decreased in weightlessness. While experiments during parabolic flight in aircraft tend to confirm this prediction, experiments during orbital spaceflight have led to apparently contradictory results. It is suggested that VOR gain is reduced initially, but that rapid compensatory mechanisms restore it to normal within minutes of reaching weightlessness. However, even though this process may lead to the rapid return of functionally normal gaze stability, it may not protect against the development of motion sickness.

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Head movements in low and high gravitoinertial force environments elicit motion sickness: implications for space motion sickness.

Lackner JR, Graybiel A.

Ashton Graybiel Spatial Orientation Laboratory, Brandeis University, Waltham, Massachusetts 02254.

Astronauts report that head movements in flight tend to bring on symptoms of space motion sickness (SMS). We evaluated how head movements in pitch, yaw, and roll--made both with normal vision and eyes-occluded--affect susceptibility to motion sickness in the zero G phase of parabolic flight maneuvers. The findings are clearcut: pitch head movements are most provocative, yaw least provocative, and roll intermediate. Susceptibility is greater with normal vision than with eyes occluded. The same susceptibility pattern emerged for head movements in the 1.8-2.0 G phase of parabolic flight. These experiments suggest that SMS is not a unique nosological entity but, rather, is the consequence of exposure to nonterrestrial force levels. Head movements during departures in either direction from 1 G elicit symptoms. This implies that, rather than speaking of "space motion sickness," it would be more appropriate to think in terms of "nonterrestrial motion sickness."

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Effects of proposed preflight adaptation training on eye movements, self-motion perception, and motion sickness: a progress report.

Parker DE, Reschke MF, von Gierke HE, Lessard CS.

Space Biomedical Research Institute, Johnson Space Center, Houston, TX 77058.

A program has been initiated to develop apparatus and procedures to preadapt astronauts to the sensory rearrangement associated with weightlessness in spaceflight. If space motion sickness is a consequence of adaptation to that sensory rearrangement, preflight training could afford astronauts significant relief from the motion sickness. The preflight adaptation trainer (PAT) was designed to produce rearranged relationships between visual and otolith signals analogous to those experienced in space. Investigations have been undertaken with three prototype trainers. The results indicated that exposure to the PAT sensory rearrangement altered self-motion perception, induced motion sickness, and changed the amplitude and phase of the horizontal eye movements evoked by roll stimulation. However, the changes were inconsistent. Appropriate measures of adaptation and protocols for producing the adaptation efficiently remain to be determined.

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