Oral Session 5: Motion Sickness and Pharmacology

Spaceflight is known to induce vestibular and cardiovascular deconditioning. Consequently, astronauts suffer from orthostatic intolerance and spatial disorientation upon return to a gravitational environment. The aim of the current ESA SPIN-D study was to identify the most appropriate pharmacological countermeasure against the aforementioned symptoms. This double blind placebo controlled study was conducted on 20 healthy, male volunteers. Tested medications were: baclofen (10 mg), meclizine (50 mg), dimenhydrinate (40 mg) in combination with cinnarizine (20 mg), promethazine (25 mg) combined with dextroamphetamine (5 mg). The effects of the drugs were investigated by a series of specific vestibular tests: elektronystagmography, cervical vestibular evoked myogenic potentials and unilateral centrifugation for canal, saccular and utricular function evaluation respectively. A head up tilt-test (HUT) was conducted in order to evaluate the cardiovascular response of the subjects during orthostatic stress. Baclofen significantly increased the phase of the vestibulo-ocular reflex (VOR). This observation confirms the known inhibitory effect of baclofen on the velocity storage mechanism. Promethazine and dextroamphetamine caused a significant increase of the diastolic blood pressure (DBP) only during the supine part of the HUT, suggesting an influence of the combination on the activation of the vestibulo-sympathetic reflex when standing up. Based on the preliminary analysis of our data, we can conclude that the different medications seem to be acting on different, specific parts of the vestibular system.