Upon entering microgravity, astronauts’ legs become thinner and their faces can look puffy, because of a shift of body fluids toward the head. This headward fluid shift affects the volume and pressure within veins in the head. These pressure and volume changes may underlie microgravity-associated visual symptoms because changes in pressures within the head can also affect the eye.
But, not all astronauts experience changes to their vision in weightlessness. Differences in the anatomy, flow, and compliance of the veins in the head between individuals may explain this discrepancy. Our goal is to develop a numerical model of the cerebral venous circulation that can predict the effects of the fluid shifts. We will validate the model by using magnetic resonance imaging (MRI) of the head to measure changes in venous flow, venous volume, venous pressure, intracranial compliance, cerebrospinal fluid (CSF) volume and flow pulsatility during both fluid shifts and changes in body position. The likely anatomic differences that could alter the responses to a fluid shift will be identified. This model and supporting data will provide a way to develop hypotheses about how microgravity produces visual changes over time and may allow predictions about which subjects may be at risk for the visual deficits associated with microgravity.