Space Adaptation Syndrome (SAS) is a significant medical problem adversely affecting approximately 50 percent of U.S. and Russian crewmembers. Although many of the symptoms are similar to those seen in motion sickness on Earth, SAS has not been positively correlated with susceptibility to ground-based motion sickness, and therapeutic responses to anti-motion sickness drugs in flight have not been uniformly successful. Acute Mountain Sickness (AMS) with symptoms of lassitude, headache, anorexia, nausea, and emesis common to SAS, may be a more accurate ground-based correlate.
Increased intracranial pressure and cerebral edema are thought to be contributing factors to the development of AMS. The well documented upward fluid shifts that occur in microgravity may induce increased intracranial pressure and mild cerebral edema in crewmembers, which may contribute to SAS. As gravity has been shown to be a major factor which influences brain hydration, the role of increased intracranial or mild cerebral edema as a contributing factor in SAS was investigated.
Color retinal transparencies obtained in microgravity using the Kowa RC2 portable fundus camera provided evidence of intracranial pressure changes. Images were analyzed by digital image analysis for mean retinal artery and vein diameter changes and compared with two preflight photographs. These images were also examined stereoscopically for subtle evidence of optic disc elevation. Results were correlated with susceptibility to SAS and time in orbit. Retinal images were obtained twice preflight during which training for the crew/photographer also occurred. Complete mydriasis (pupil dilation) is essential to obtain quality retinal images but only one eye needed to be dilated (1-2 drops of 0.5 percent tropicamide and 2.5 percent phenylephrine). Retinal photographs were also taken at least three times on orbit at 6-12 Mission Elapsed Time (MET), 48 MET, and prior to the final sleep period.
A full-face photograph was taken in flight in conjunction with the retinal photography sessions. During retinal photography, the operator looked for venous pulsations and recorded them on the subject identification card.
A numerical SAS severity index was generated from each crewmember's subjective reporting of symptoms to the flight surgeon. Data was recorded in flight (a written checklist) and postflight from crew debriefings: 1=mild, 2=moderate, 3=severe. In addition, a value between 0-3 was recorded based upon the severity of individual symptoms (headache, malaise, lethargy, anorexia, stomach awareness, nausea, sleep disturbance, emesis, or disequilibrium). Individual crewmembers were also asked to rate each other on a scale 0-3 for overall severity of SAS.
Note regarding STS-50: The power supply for DSO-474 failed to function right from the start of STS-50. No photographs were collected. The informal part was a live downlink of the retina using the funduscamera, adaptor, and Canon L-1 camcorder.
The data collected indicate a tendency for both retinal arteries and veins to dilate during the first day of space flight.