 Figure 1. The lack of gravity, which allows a shift of body fluids toward the head. |
 Figure 2. The stress of a high acceleration rate at launch. |
 Figure 3. Stress due to cramped quarters and lack of privacy on the shuttle. |
 Figure 4. The effects of higher radiation exposure away from the Earth. |
 Figure 5. Stress of reentry and landing. |
 Figure 6. Lack of exercise and weightlessness of objects, causing loss of muscle mass during flight. |
The truth is all the different aspects of space flight shown in Figures. 1 - 6 may have an effect on the functioning of the cardiovascular system. Scientists do not yet have enough data from space to tell exactly what causes the cardiovascular system to change during space flight, but there is plenty of evidence to tell that it does change the way it operates, even on a short journey into space. All the information we have suggests that these changes are "normal"; in other words, the operation of the cardiovascular system changes from an "Earth normal" condition to a "space normal" condition as it adapts to the new environment of space.
In this chapter, we will be examining an actual space flight investigation that was designed by Dr. Gunnar Blomqvist, the principal investigator, and his colleagues at the University of Texas Southwestern Medical Center in Dallas, Texas. This experiment, which flew on both the SLS-1 mission and the SLS-2 mission, was designed to examine the cardiovascular consequences of the fluid shift that occurs during space flight in order to determine how the operation of the cardiovascular system is changed in space when astronauts are at rest and when they are exercising. The results of this study have provided us with important information about what happens to the human heart and the cardiovascular system during space flight, how it adapts to the space environment, and how long it takes to adapt. This study also examined the problems caused by this adaptation process when space travelers return to Earth.
Before we begin to examine what we have learned from Dr. Blomqvist's study about how the heart, lungs, and blood vessels work together in space, it is important to understand how these important components of the body normally function on Earth. We will look at how the heart and blood vessels act as a superhighway to transport the blood and nutrients to every cell in the body and to carry away the carbon dioxide and other waste products of the cells. We will also examine how the lungs operate to supply the blood with the most important element that it will carry to the cells: oxygen.