Institut für Luft- und Raumfahrtmedizin Cerebral and ocular fluid balance as a function of hydrostatic pressure gradients and environmental factors: insights into the VIIP syndrome (enVIIP Study) Before you apply as a participant in the enVIIP study, we would like to provide you with more information about the purpose and content of the study. 1. Scientific Background For decades, there have been reports of vision changes in astronauts during spaceflight. This visual Impairment and Intracranial Pressure (VIIP) syndrome is fairly common, with about 50% of astronauts presenting with VIIP during and after long-duration space missions (~6 months). The cause of VIIP is currently unknown, however several hypotheses exist. First, it is hypothesized that an increase in intracranial pressure due to the upward shift of fluids in space causes structural changes in the eye, ultimately resulting in vision changes. In addition, the atmosphere on the international space station is very high in carbon dioxide (20x higher than the Earth’s atmosphere). It is hypothesized that this could have added effects on the increase in intracranial pressure as carbon dioxide is a potent vasodilator. Currently the VIIP syndrome and its causative mechanisms are unknown. This study will address potential mechanisms, obviously without causing the problem. This will help to understand what is causing the vision changes and how to deal with the problem (and prevent it in the future). Head Down Tilt (HDT) Head Down Tilt studies have been used for decades by space medicine researchers as an analogue of space conditions on Earth. When an astronaut goes into space, gravity no longer pulls blood to the feet, and fluids shift to your upper body. On Earth, lying in bed with at a -6° angle induces a similar shift of fluids from your legs to your upper body as happens in space. Head Down Tilt has been shown to stimulate many of the same physiological responses as in space, and it is a widely accepted model for simulated microgravity research. This study will also utilize Head Down Tilt as a model of spaceflight to study the effects of a headward fluid shift on ophthalmic structures and cerebral fluid balance. 2. Implementation of the Study In the enVIIP study, there will be 12 male subjects that participate in all parts of the experiment. All measurements will be taken at the Deutsches Zentrum für Luft- und Raumfahrt (DLR) in Köln. Overall, the enVIIP study will consist of 7 visits total to DLR (as shown in Figure 1). The first visit will include a medical check-up and baseline data collection. Then, if the subjects are deemed eligible for the study, they will participate in 5 acute head down tilt sessions (4-hours of head down tilt each). Various measurements and images of the eye will be taken, and also measurements of the brain. After completion of the experimental phase, the subjects will come back to DLR for final reference data collection. The subjects are required to participate in the entire study, which will occur between April and October, 2014 (exact dates and schedule will be provided if the subject is chosen to participate in the study). Figure 1: The enVIIP Study includes 7 visits total [HDT – Head Down Tilt; CO2 – Carbon Dioxide; LBNP – Lower Body Negative Pressure]. Several measurements will be taken before and during the experiment. This includes Intraocular Pressure (IOP) measurement, an Optical Coherence Tomography (OCT) image (a picture of the back of the eye), Magnetic Resonance Imaging (MRI) of the brain and eye, ultrasound of the eye and noninvasive intracranial pressure measurement. Additional cardiovascular factors will be monitored including heart rate, blood pressure, electrocardiogram (ECG) and fluid shifting (impedance).