Journal of Vestibular Research, Vol. 3, pp. 289-295, 1993 0957-4271/93 $6.00 + .00 Printed in the USA. All rights reserved. Copyright © 1993 Pergamon Press Ltd. A PREDICTIVE TEST FOR SPACE MOTION SICKNESS Charles H. Markham and Shirley G. Diamond Department of Neurology, UCLA School of Medicine, Los Angeles, California Reprint address: Charles H. Markham, MD, UCLA School of Medicine, Department of Neurology, Los Angeles, CA 90024-1769 o Abstract - Eye torsion was examined in 13 astro­ astronauts have had severe SMS, have per­ naut subjects, tested during repeated episodes of formed their missions successfully, and have OG and 1.8 G in parabolic flight aboard NASA's flown again. Secrecy regarding SMS contin­ KC-135. Four findings are included. 1) A strong re­ ues, has infected at least some astronaut-sci­ lationship between previous history of SMS and oc­ entists, and has inhibited research into its ular torsional disconjugacy in nove! gravitational cause and solution. (We should hasten to add states. 2) Responses were unchanged in 4 subjects that we have found the astronauts, payload retested a year later. 3) Ocular torsional disconju­ gacy scores increased as exposure to 0 and 1.8 G specialists, and mission specialists with whom increased. This was particularly evident in subjects we have worked to be very cooperative and who had had SMS. 4) Torsional studies during 10 frank.) to 20 parabolas are required to accurately predict What do we know about SMS? It appears SMS. The hypothesis of otolith asymmetry, com­ to be a unique form of motion sickness. That pensated in 1 G but becoming unmasked in novel is, there is no correlation between susceptibil­ gravitational states, is proposed to explain the tor­ ity to SMS and susceptibility to any form of sional disconjugacy and ensuing SMS. earth-based motion sickness, whether on land, sea, or air, including in parabolic flight. In o Keywords - space motion sickness; ocular space the susceptible individuals find that SMS counterrolling; otolith asymmetry; eye torsion is triggered by head movements producing an­ disconjugacy. gular acceleration stimuli acting on the semi­ circular canals. SMS is also triggered by Humans have been subject to space motion unusual visual scenes such as seeing a fellow sickness (SMS) since the beginning of space astronaut "upside down" or looking out of the fligh:. Initially, when space vehicles were smal1 por~ and seeing the earth with the southern anc" the :::osmonauts and astronams nad iim­ hemisDhere' "up." We ime, pre: the!.t :-indings itea mObilit: . it was not. a majo;' piobi em. As w mear: tila: SMS has an e~iojogy o~ne:- ~han the space vehicles have increasec ir size and simoJe stimu\atior of the' semici rcuiar canal~ has affected from one-haif to rwo-third~ of a~ promorer5. space f1yer :- (: ). SIv;~ le!,j;; tc begin 2.+1~" s:,vera~ hours 0 :­ The exact number!., duratior., severity, ami achieving mlcrogravity, but occasionally may symptoms are estimates. A systematic analy­ start within minutes. It usually lasts from 1 to sis of SMS has not been done, in spite of 4 days, but sometimes continues for the du­ NASA's frequently expressed interest in the ration of most NASA flights, namely 1 to 2 subject. The secrecy surrounding SMS may weeks. Symptoms may return on the first day stem from the astronauts' concern that a phys­ or two after landing. One astronaut told us ical complaint during space flight might result that several days postflight he became slightly in the possibility of not being able to partici­ nauseated on seeing small waves as he was din­ pate in future flights. This concern is not dif­ ing at a restaurant overlooking Clear Lake ficult to understand, despite the fact that some near Johnson Space Center. Scientist-astro- 289 290 C. H. Markham and S. G. Diamond nauts Ockels and colleagues (2) experienced a random movements becomes progressively full range of motion sickness symptoms after greater as the head is rotated about the naso­ lying supine for several hours in a hyper-G en­ occipital axis at progressively greater angles vironment and noted the similarity of these with respect to the gravity vector (9). sensations to their own previous SMS. They also stated that prior to and during shuttle launch, the astronauts and cosmonauts are po­ Methods sitioned on their backs for several hours. Microgravity is the underlying element in :'3 ~'1 I S, ar: t2 lie otolith .:;ystem is [he m:lin bio­ Se'/eral studies lre ~lescribed below: :og!cal uerecror or' sravity and other :or:ns or' : . 1<) test [he lypc tnesis of disturbec oto­ :i::'car :lcceierar' nn (' hC:. Il ~h ~O[ ~ ~ e only : f't~c- ~ it h "1mcti on 1 S 1. ::·,c;ro r in SMS. we ~ ~: ::m: i ned , - . : : . - 'e'.; ~ . : ~ .. :":': ~_ .. : .:::C _ :. ... ... E.:.e:- . L. \. I _ ; ~ c ::. ::-,:;ec i.:S :c:.::~,: ' ~: ~ Ji o n during ;Jar ~L) c tic Therefore, we look to alteration in otolith airplane night :n :lstronauts. All had had their {'.:::.ct: c n .lS !: he major SUDstr:ue :;I Si'viS . The .3 pac~ ilights .2 :0 5 ~ r :TIere years ~a :ier. ;v[ost :) [() lith .lsymmetry hypothesis of SMS, clS :'irst were :10 ;cnger active :n the astronaut pro­ propounded by von Baumgarten and Thiim­ gram. The testing was done in a blind fashion ler (4) proposes that some individuals have as foHows. Before the experiment the subjects otolith systems that are asymmetric on the two filled out a questionnaire regarding their prior sides of the head, that compensation for this SMS histories and then sealed it in an enve­ has taken place in a lifetime at 1 G on earth, lope. The envelope was not opened until the but that in exposure to novel G states, there experiment and the data analysis were com­ is a loss of this compensation and motion sick­ pleted. At that time, the written histories were ness is one result. Asymmetry could be due to converted to a widely used motion sickness differences in the mass of distribution of oto­ rating system by Davis and colleagues (1). conia; in hair cell sensitivity, distribution or During the experiment, the subjects were, numbers; in the neural relationships between seated in a special chair, fixed to the floor and the first order afferents and the receptors; or over the wings of NASA's KC-135 aircraft, in the brainstem connections of the first or­ and facing aft. Each subject's body was re­ der afferents. There are still other possible ex­ strained with velcro straps and the head held planations. The essence of the hypothesis is firmly by means of a preformed dental bite that there is a structural or physiological asym­ bar. A 35-mm motor-driven single lens reflex metry that is compensated on earth, and this camera was rigidly mounted on the chair compensation is lost in novel G states. about 11 inches in front of the subject's face. Ocular torsion is under reflex control of the Both eyes were included in each image. Three semicircular canals and of the otolith appara­ to five photos were taken at each episode of tus (5,6). The otolith contribution can be ob­ o G and of 1.8 G. The first 9 astronauts were served in isolation if the stimulus either does tested for 10 to 20 parabolas. At a later date, not include angular acceleration or if such ac­ 8 astronaut subjects were tested, 4 having celeration is below canal threshold. This can served as subjects on the previous flight. be achieved by observing ocular counterroll­ Data analysis took place at UCLA some ing with the head in the center of the axis of weeks after flight. A photographic superim­ rotation and rotating the subject about the position technique was used, in which ocular naso-occipital axis (7,8) with accelerations no torsion was measured in all frames of one eye. 2 greater than 0.2°/5 . Spontaneous ocular tor­ When this eye was completed, the other eye sion is also under otolith control. There are was similarly measured. We calculated the dif­ small random torsional eye movements, ap­ ference in ocular torsion between the two eyes proximately ± 0.75°, these being either con­ at each episode of 0 G and 1.8 G (see Figure 1 jugate or disconjugate. The amplitude of these for the steps in the data analysis). ';Predicting SMS 291 TORSIONAL ASYMMETRY ( mean right eye amplitude minus mean left eye amplitude) Astronaut A -7, Parabola 1 right eye amplitude left eye amplitude S 1.8 G 2.50 0 f' " 1.9 ~ f'"~ mean 2.20 mean 1.60 ri ght minus left 1.0 2.20 - 1. 60 = .60 .8 .6 / S { 0.7" slope =.4 0 0 .4 OG f 1.5" 0.6 1.JE ~ 1.8 G OG mean 1.60 mean 0.60 right minus left 1.60 - 0.60 = 1.00 FIgure 1. Steps· In data analysis of torsional asymmetry. Ocular torsion was measured by an Iris super­ imposition technique, using 3 to 5 Images (3 each In present example) at each episode of 0 G and 1.8 G. In the first parabola of Astronaut A-7, the mean torsion of the left eye at 1.8 G was subtracted from the mean of the right eye. The same was done for the values obtained at 0 G. These differences were then plotted and a slope obtained (rIght side of figure). The same was done for each parabola (not shown), and a "mean slope" was calculated for the subject. Results astronaut A-5 flew on 2 missions.