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Abstract:
Space motion sickness (SMS) remains a persistent problem in human spaceflight since up to 60 of all astronauts suffer from SMS during the first 72 hours of spaceflight and during transitions from different gravitational environments. To date, there are no effective drug countermeasures that are able to combat SMS while preserving the full cognitive function of the astronaut.
It was first suggested by Von Baumgarten Thumler in 1979 that an asymmetry between the left and right otoliths might contribute to susceptibility to SMS in astronauts. To determine the level of asymmetry, a test that enables the unilateral evaluation of both utricles is needed. The unilateral centrifugation test allows such a side-by-side investigation. During this test, the subject is rotated about an earth-vertical axis at high rotation speeds (e.g. 400°/s) and translated along an interaural axis to consecutively align the axis of rotation with the left and the right utricle. The combined rotation and translation induces ocular counter rolling (OCR), which is measured using 3-D video-oculography. A recent refinement of the stimulation paradigm and an improved model to analyse the test results have enabled a more detailed extraction of the otolith characteristics such as otolith asymmetry, gain and bias. In addition, characteristics of the semicircular canals such as the cupular time constant and the velocity storage component can be determined. This detailed analysis allows us to evaluate the effects of drugs on the different characteristics of the vestibular system. Hereto, a double blind placebo controlled pharmacological ESA study investigating the effects of four different drugs (baclofen, meclizine, cinnarizine in combination with dimenhydrinate and promethazine in combination with dextro-amphetamine) on the different parts of the vestibular and cardiovascular system was performed in 20 healthy, male subjects. The effects of the different medications on the otolith-ocular reflex and the level of otolith asymmetry will be presented.
