Some astronauts are little affected, while others have severe symptoms.
Women are more often affected than men. The goal of this DSO is to discover the mechanisms responsible for these differences in order to customize countermeasure protocols. It has been well documented that spaceflight significantly alters cardiovascular function. One of the most important changes from a crew safety standpoint is postflight loss of orthostatic tolerance, which causes astronauts to have difficulty walking independently and induces lightheadedness or fainting. These effects may impair their ability to leave the orbiter after it lands.