Fluid Loading Countermeasures

The purpose of Fluid Loading Countermeasures is to determine how the volume of blood and of plasma (liquid part of blood) change during a normal day, how these are affected by drinking an additional amount of fluid either as water and salt tablets (as astronauts do) or an electrolyte beverage (similar to but tastes saltier than Gatorade®), and how altering the timing at which the additional fluid is consumed affects blood and plasma volume. This study observes how blood volume changes over \~9 hours of the day during 4 separate visits in healthy participants. During 1 visit participants will drink a small amount of water throughout the visit. During the other 3 study visits participants will drink the small amount of water plus either more water with salt tablets or an electrolyte solution. Consuming the additional fluids is called "fluid loading". This study is meant to simulate the food and fluid consumption of astronauts on landing day. The goal of this study is to determine the magnitude of plasma volume change that occurs with each condition of the protocol. (ICF 1.1, 3.1)