The purpose of this study is to determine and better understand the pathophysiology of vision changes in astronauts during and after long-duration spaceflight using a ground-based analog. For this purpose we use head down tilt to simulate a similar head-ward fluid shift as experienced in space. Fluid dynamics in the brain are then analyzed along with various cardiovascular and ocular measurements.
To investigate the effects of head down tilt, the test subjects lie for few hours in the lying position (0 degrees) and then for 5 hours at different degrees of head down tilt (-6, -12 and -18 degrees). In an additional experiment, the subjects lie in -12 degree head down tilt while breathing a 1% carbon dioxide mixture. This will help us to better understand the effect of increased carbon dioxide exposure, a hypothesized contributor to the Visual Impairment and Intracranial Pressure (VIIP) Syndrome in astronauts. In the last experiment, a countermeasure to prevent the fluid shift is evaluated. It is called "Lower Body Negative Pressure" (LBNP), and it is a chamber that encloses the legs and pulls the fluids back down to the lower body.
The entire experiment takes place in the DLR's new research facility, :envihab, and the test subjects participate in all 5 experimental conditions to evaluate their individual responses to the different angles, the increased carbon dioxide atmosphere, and the lower body negative pressure. Measurements include various MR imaging (with a 3-tesla MRI in the :envihab) of the eyes, brain, and fluid spaces around the brain, a non-invasive intracranial pressure measurement, intraocular pressure, imaging of the retina and choroid layers of the eye (via optical coherence tomography), and several cardiovascular measurements.