Available data regarding overall incidence to date of SMS in the U.S. and Soviet manned space programs indicates that the frequency of occurrence of this syndrome has been approximately equal in both countries. An important feature of these data is that with the advent of larger spacecraft in the U.S. program (i.e., Apollo, Skylab and Shuttle) that permit greater mobility of crewmembers, the incidence of SMS has increased. In an effort to resolve the SMS or at least minimize the operational impact of the syndrome, NASA has significantly expanded its research efforts in this area. As part of this expanded effort, a systematic program of operationally oriented motion sickness data collection was implemented on most individuals assigned to Shuttle flights from April 1981 to April 1985. The primary objective of this program was to collect preflight, inflight and postflight data on the crewmembers in an effort to begin validating ground based tests which may be predictive of susceptibility to the syndrome. The development of reliable predictors is operationally important because they would permit the a priori identification of individual crewmembers for whom special preventative measures should be taken. A secondary objective of the program was to acquire data which could be used to validate countermeasures for the syndrome.
For the first nine Shuttle missions, which involved 29 different crewmembers, a standard Coriolis Sickness Susceptibility Index test (CSSI), originally developed by Miller and Graybiel was used. This procedure, which stimulates primarily the semi-circular canals, requires the performance of head movements while rotating. Prior to the start of the test the crewmember was instructed on how to report his or her symptoms of motion sickness to an observer who was skilled in the recognition of signs and symptoms of motion sickness. The signs and symptoms were recorded and scored according to diagnostic categorization. The test was terminated when the blindfolded crewmember reached the Malaise III level of motion sickness or performed 150 head movements, whichever occurred first. The higher the score, the longer the subject continued the test, indicating a greater resistance to motion sickness. A majority of the crewmembers on the first nine Shuttle missions were tested at least one additional time with the CSSI procedure in order to evaluate the efficacy of an anti-motion sickness medication. The medication most frequently evaluated was oral scopolamine (.4 rag) plus dexedrine (5 mg).
The second motion sickness susceptibility procedure used was a modified version of an off-vertical rotation or OVR test originally developed by Graybiel and Miller. The OVR produces a rotating linear acceleration and is essentially an otolith stimulus. During this procedure crewmembers were blindfolded and restrained in the rotating chair with lap, shoulder and leg straps. The head was also restrained. While in the vertical position the chair was accelerated to a velocity of 20 rpm and rotated for 5 minutes. Following stabilization of 0 degrees tilt the angle of tilt of the chair was increased in 5 degree increments at 5 minute intervals until the crewmember reached the Malaise III maintained at 30 degree tilt for 5 minutes. The OVR test was performed on 29 individual astronauts most of whom flew subsequent to the ninth Shuttle flight.
The third procedure used was a modified version of an eyes open sudden-stop test developed by Graybiel and Lackner. This test assessed susceptibility to a vestibulo-visual interaction stimulus. Visual stimulation was provided by a stationary optokinetic field which surrounded the chair in which the crewmember was restrained. The chair was accelerated to a velocity of 50 rpm and held at that velocity for 30 seconds. The chair was then decelerated at 150 deg/sec to a complete stop and maintained at zero velocity for 30 seconds, after which the sequence was repeated for a total of 20 clockwise and 20 counterclockwise stops or until the Malaise III level of symptoms was reached, whichever occurred first. Data were collected on only six crewmembers with this procedure.
Inflight data collection was limited to the use of a microcassette tape recorder and a motion sickness symptom checklist. The checklist was similar in content to the diagnostic scale and allowed comparisons between the pattern of symptoms that occurred during the preflight pro vocative tests and those that occurred inflight. The checklist also required crewmembers to report on preventative measures used such as anti-motion sickness drugs and voluntary restriction of head and body movements. Each crewmember was required to use the recorder and checklist each mission day to report any symptoms or sensations that had been experienced during that day. Operational definitions for SMS were categorized as:
Questions pertaining to SMS, vestibular sensations, and performance were also asked of each crewmember on the day of landing and during postflight medical debriefings. Both the inflight and postflight crew debriefing data were used to categorize crewmembers as susceptible or non-susceptible to SMS. Those who were defined as being susceptible were further classified into mild, moderate and severe subgroups for subsequent data analysis.
Results include preflight and inflight symptomatology data, antimotion sickness drug data and preflight versus inflight motion sickness susceptibility data. There was a striking difference in the pattern of symptomatology generated inflight versus during the ground-based tests. Subjective warmth, sweating, and pallor, which were dominant ground-based test symptoms, were almost nonexistent inflight. In contrast, vomiting, anorexia, headache, malaise and lethargy were dominant inflight symptoms. The vomiting episodes often occurred abruptly with little or no prodromal nausea, although a sensation of stomach fullness or discomfort was often present prior to vomiting. In most cases, vomiting resulted in relief from the uncomfortable stomach sensations, although for some crewmembers the discomfort would gradually return.
The specific nature and time course of inflight symptomatology tends to be highly variable. Some crewmembers reported that symptoms appeared within the first one to two hours of the mission. Others did not become aware of symptoms until the second day of flight. In general, however, symptoms began during the first day of flight, plateaued between 24-48 hours and gradually diminished between approximately 48-96 hours. During this time the symptoms usually waxed and waned in severity. Unquestionably, head and body movements exacerbated the symptomatology. Accelerometric data obtained by Oman during the Spacelab 1 mission (STS-9), and subsequently confirmed by verbal reports from a number of crewmembers, indicate that in microgravity head movements in the pitch and roll planes are the most provocative. Anti-motion sickness and/or anti-emetic medication was used by 40 of the 65 crewmembers included in this study. The oral scopolamine plus dexedrine combination was the most frequently used with 25 crewmembers taking one or more doses during the first few days of flight. Oral metoclopramide was used by 18 crewmembers in an effort to restore gastric motility and alleviate nausea and vomiting. Of the 31 crewmembers who experienced symptoms, 29 used medication during the course of their symptomatology.
Results related to a comparison of preflight motion sickness data with SMS are by no means unequivocal. The motion experience questionnaire indicated that all of the crewmembers had a minimal history of susceptibility to terrestrial forms of motion sickness. The questionnaire revealed that a few had experienced some motion sickness during past exposures to aerobatic flight, parabolic flight, and heavy sea conditions. The questionnaire results, however, did not correlate with the actual incidence of SMS reported.
The subgroups of astronauts who experienced SMS were slightly more susceptible to the preflight motion sickness tests than were the non-SMS susceptible astronauts. However, the test score ranges for all subgroups are large and the difference between the means of the subgroups for each test are not statistically significant. In a further attempt to establish a relationship between the ground-based tests and SMS, correlation coefficients between the ground-based test scores and the scores assigned for the inflight level of severity of SMS symptoms were computed. The correlation coefficients were non-significant for all three ground-based tests.
As an alternative approach to determining whether or not the preflight susceptibility tests might have some predictive value for SMS, the astronaut data for each test was compared to a frequency distribution of non-astronaut normative data. The normative data were collected over the past several years by the Johnson Space Center Neurophysiology Laboratory. Figure 2 summarizes the CSSl test data. The hatched bars are the normative data and the closed circles are the astronaut data. The "star" symbol indicates astronauts who reported SMS. The astronaut mean CSSI score is 28.7 while the normative population mean CSSI score is 14.0. Of potentially greater significance is the finding that 67% of the astronauts whose CSSI score was below the population mean experienced SMS, while only 40% whose scores were above the population mean experienced SMS.
Data from the OVR test show virtually no difference between the astronaut and normative population data. The mean OVR test scores are almost identical and there were as many crewmembers above the normative population mean who reported SMS as there were below the mean. For the sudden-stop test data, the number of astronaut data points were too few to permit drawing any meaningful conclusions. However, it is of interest to note that two astronauts who were very susceptible to the preflight sudden stop test experienced SMS.
All of the data summarized thus far in this report have compared SMS susceptibility to a single preflight test. The weighted score is the algebraic sum of the differences between the astronaut's test scores and the normative population means for each test. It would be predicted that a positive weighted score (i.e., greater than average resistance to experimentally induced motion sickness) should relate to a lack of SMS and a negative weighted score should be related to the presence of SMS. A correct match was obtained in 64% of the cases.
In conclusion, on the basis of data collected during this study, it can be generally concluded that the prediction of SMS susceptibility on an individual crewmember basis remains a difficult and challenging task. Certainly the use of a single ground-based parameter or test procedure is inadequate. The use of a composite index or weighted score which takes into account several response parameters appears to have greater predictive potential. A larger sample size of composite scores based on the collection of preflight CSSI, OVR and sudden-stop data on Shuttle crewmembers would be desirable. The data needed to derive these composite scores do not exist, nor do plans currently exist to collect these data.
Despite inability to identify preflight, ground-based predictors of SMS susceptibility, there does appear to be one reasonably accurate predictor and that is space flight itself. Out of 16 individuals who have flown two or more space missions only 3 changed their response pattern from one flight to the next. Out of the remaining 13, 7 individuals were symptom free on all of their flights, while the other 6 experienced symptoms on each of their flights. Obviously, the routine use of space flight as the method of identifying SMS susceptible individuals is impractical. Thus the need to identify and validate ground-based methods remains an important issue. It is important to emphasize that efforts in this area have not been abandoned. The collection of inflight and postflight symptom reporting data is continuing as a standard operating procedure. Improved methods for characterizing the exact nature and time course of SMS are being evaluated. Also, various pre-, in- and postflight measurements of vestibular function are being conducted, the data from which may be useful in our attempts to develop predictors of SMS susceptibility.
|Mission||Launch/Start Date||Landing/End Date||Duration|