The lower body negative pressure test places a stress on the cardiovascular
system very similar to the one experienced when standing in Earth's gravity.
The crew member is placed in the lower body negative pressure device. The
tube covers the astronaut from the feet to the waist and an airtight seal
is made around the waist. A pump then sucks air from the tube which
creates a negative pressure inside the tube and hence around the legs of
the subject. This in effect pulls blood from the upper part of the
body to the legs. The pressure is lowered for about 50 minutes during
which measurements are made.
The lower body negative pressure device is a cylinder that encloses
the lower abdomen and lower extremities to maintain a controlled pressure
differential below ambient during periods of extended weightlessness.