Central Venous Pressure in Space

To the Editor: When a person enters zero gravity, a large amount of fluid (1 to 2 liters) shifts toward the head. The response to this shift includes the principal cardiovascular effects of spaceflight – e.g., hypovolemia, dehydration, and postflight orthostatic intolerance¹. On earth, a similar headward shift of fluid increases central venous pressure²; in space, however, peripheral antecubital venous pressure does not increase³,⁴. It is not known whether such peripheral measurements reflect central venous pressure. Only direct, continuous measurements recorded during a change from earth's gravity (1 g) to zero gravity can resolve these controversies…