A Predictive Test for Space Motion Sickness

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. On the first he had no malaise but experienced a single ep isode of vomiting after dinner on the 1st day Each subject was described by a single mea of flight. Using the scale of Davis and col sure of torsional disconjugacy, the "mean ieagues (1): we considerec his SMS to be mile:. slope," this being obtained b~ ' averaging the ,L_s::-onau: ./;, - f., ~:'''' : h'1!ssi :m~ 2.nc he.: na t} - slopes from the 10 to 20 ;Jaraboias he haC: u:' dergone. '!'h~' :near: siop ~ SCOie> 0' ~ht "':;: ' . " \·U .. }:l ;; .. i !:: t ~ S !:: ·: n':', pe: ::-:;:- !7I ~ : r:!~ :t"::i~ .:- i:- ar e ~ contai:1inl; :he ::'iviS his i Cl:"ie ~ were l:1e" opell-::C:. ecp l ~ry ~ · 2. .s hi~nl ~j . ~~ : /he ~ 51i7lila- n1e2.SUre ~ oj It wa~ found that the t, asn oGauH having the w;:-siona; asymme:,y were performeci at ; G lowest scores had not experienced SMS. The 5 on the ground, there were no differences be with the highest scores had all had SMS. The tween subjects. See top of Figure 2. For fur mean scores of the two groups were signifi ther details, see Diamond and Markham 1991 cantly different (P =0.01, two-tailed Wilcoxon (11). Based on these results, we were encour rank sums test) (10). aged to think we might have identified a long Within the group who had SMS, the se sought predictive test of SMS. verity of SMS paralleled the magnitude of 2. The following year, we performed an torsional disconjugacy scores. For example, other series of parabolic flight experiments. 292 C. H. MarkhafTl 'ld S. G. Diamond J TORSIONAL ASYMMETRY IN GROUND-BASED 1G 0.5

0 ------

3.001 TORSIONAL ASYMMETRY IN HYPO- AND HY?E2GRAVITY t I .u il. 0 ~ './l 2.00 ~ Z

1.00

o -----I -----I -- I -- I ------I -- I -- I I I A-9 A-1 --A-3 --A-7 --A-8 --A-S A-4 A-2 A-6

Figure 2_ The top portion shows the 1 G dlsconjugate eye torsion scores of 9 astronauts. There were no differences between the subjects; all had low scores. The lower portion depicts the Inflight scores. The 4 astronauts with the lowest scores of torsional asymmetry in the hypogravlty and hypergravity on the KC-135 (shown with black bars) did not get sick in space. The 5 astronauts with the highest scores (gray bars) are those who had SMS during their space missions. Torsional asymmetry scores on the KC-135 differed signifi cantly (p = 0.01) in the two groups. Severity of SMS was correlated with torsional asymmetry scores.

We tested 8 astronauts, 4 of whom were new jects. This finding gives support to our previous to us. Each was examined for 20 parabolas. assertion that changes in ocular disconjugacy One of the questions we asked was whether the during parabolic flight are related to SMS. 4 new astronaut subjects would yield the same 3. In 1992 we retested 4 of the 5 astronauts suIts as the rior study. We were blinded to tested in 1991 who had previously had SMS. their prior histories of as escn above. As before, we ranked the torsional conjugacy in parabolic flight. The responses asymmetry scores from the least to greatest. thus appear to be stable. Those two astronauts who had the lower 4. We had hypothesized that in certain sub scores did not have SMS, and those who had jects the utricles might be angulated differently the higher scores both had SMS (see Figure 3). to each other, that a loss of compensation in A one-tailed t test found that the mean scores duced by parabolic flight causes ocular tor in these groups differed at P == 0.015. A one sional disconjugacy, and that increasing the tailed Wilcoxon rank sums test of the signifi gravity vector to 1.8 G when the head is tipped cance of the difference in scores in these very in certain head positions might results in a small groups resulted in P = 0.06, the lowest "nulling" or lessening or other alteration in I I':.,, P value this test can produce with only 4 sub- disconjugacy. We tested 8 astronauts upright I :P-r-edicting SMS 293

TORSIONAL ASYMMETRY IN GROUND-BASED 1G 0.5 FIVE POSITIONS -----____ IIIIL ______IIIIL ______o

3.00 TORSIONAL ASYMMETRY IN HYPO- AND HYPERGRAVITY FIVE POSITIONS

UJ 11. 9en 2.00 ~ UJ == mean = 0.30 (0.05) +-- p = 0.015 ---. mean = 0.85 (O.15)

1.00

o I I I I A-10 A-11 A-12 A-13

F!gure 3_ Four new former astronaut subjects are arranged in order of increasing scores of torsional discon jugacy In hypogravity and hypergravity of parabolic flight. The 2 with lowest scores, shown in black bars, did not have SMS In space; the 2 wIth the higher scores, shown In grey bars, did get sick on theIr Shuttle mIs sions. The top of the figure shows their torsional disconjugacy scores in 1 G; all had similar very low scores. for 4 parabolas, 4 parabolas with the chair a G with increasing number of parabolas in all tilted 5 a right ear down, 4 at 10° right ear subjects (0.001 :5 P:5 0.02), and far more in down, 4 more at 5 a left ear down, and then those who had had SMS. Repeated measures 4 at 100 left ear down. We found that in all ANOVA found the effect significant at P = tilted positions there was increased torsional 0.001 in the SMS group and at P = 0.02 in the discor:jug:acy. This is the same findinf we re non-SM~ group. The finding with repeated portee a: 1 G many years before (9). In the episodes of ~ . S G is no~ 2.S ciea. (see Figure 4). present s~udy. the increased disconjugacy re wr: concluded that 10 to 20 parabolas are latec ~:-: : h:' Iin,-=( neac 1~~~~i'Jr T""'2~ !c.'ve masked any other changes, and we couid not disconjugacy to predict SMS. confi::-:::: :.ha: tii:Inf the subjects had any effect The mas: likely substra:e h :' D'Jtn SIv.::S ane on equaiizing a utricular asymmetry. ocular tOisionai disconjuga':'-y, as ciesCiibed ir:. 5. Vv'e asked the question whether fewer this paper. is a structural or functional asym than 10 or 20 parabolas could serve as a pre metry of the otolith apparatus on the two sides dictive test for SMS. We were able to include of the head in certain individuals. Future test data from both the 1991 and 1992 studies ing of more astronauts and of prospective as using a total of 13 astronaut-subjects, group tronauts, and the more ready availability of ing the results in sets of 4 parabolas (see Fig data on SMS itself will lead to a better under ure 4). Torsional disconjugacy increased in standing of its cause and prevention. 294 C. H. Markham and S. G. Diamond

TORSIONAL DISCONJUGACY IN 0 G AND 1.8 G

1.60 SMS 0 G ,~,," ", '''' <,. ,,' "

SMS 1.8 G ""''X'''''=,'X''''"'''~'''",' 1.50 NO SMS 0 GIS'"' .. • .. , NOSMS 1.3G

1.30 --l I > (,) < " 1.20 :: ~ ~ o ~ 1.10 Q /l -J < ~ 1.00 en a: t( Q ~ .90 u. ~ o .~I/ft en w 'S> w /!' '" a: .80 4- m + '" Q .,. ~ Z "t < .70 4' W ~ ~

.60

.50 .... .40

.10

o~-----r------~------+------~------~------1·4 5-8 9·12 13-16 17·20 PARABOLAS

Figure 4. Torsional dlsconjugacy in 0 G increased significantly (0.0001 s P s 0.02) with increasing number, of parabolas in all subjects, more markedly in those who had SMS on their space mission. Dlsconjugacy In 1.8 G was less than in 0 G. Predicting 8M8 295

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