1. Scientific Background

Institut für Luft- und
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
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).