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Release date: 07/01

Effects of Microgravity on the Peripheral Subcutaneous Veno-arteriolor Reflex in Humans (Xenon1)

Missions: Expedition Three, ISS Mission 7A.1, STS-105 Space Shuttle Flight

Principal Investigator: Dr. Anders Gabrielson, National University Hospital, Copenhagen, Denmark.

Project Manager: Suzanne McCollum, Johnson Space Center, Houston


When a person stands, there is a pooling of blood in the lower part of the body and legs. If blood circulation is impeded, this leads to a reduced filling of the heart, which in turn results in a decrease in blood pressure and possibly fainting or swooning. An important mechanism which is activated to protect the circulation is a reflex in muscle and skin called local veno-arteriolar reflex. Activation of these local reflexes results in constriction of the small blood vessels in skin and muscle tissue, which increases the resistance to blood flow and assists in maintaining blood pressure during upright posture.

After space flight, the ability of a person's body to regulate blood pressure while upright is reduced. This is called orthostatic intolerance, which can severely inhibit the functional capacity of crewmembers during re-entry and landing. At present there is no effective treatment to prevent orthostatic intolerance that is induced by space flight. This study will investigate the mechanism of this syndrome -- specifically the extent to which the blood vessels are active in maintaining normal blood pressure, and will lay an important foundation for the development of treatments for orthostatic intolerance.

Experiment Operations

This experiment requires no in-flight activity by crewmembers. Prior to, and following Expedition Three, Space Station crewmembers will be placed on a gurney as a small amount of a radioactive isotope, 133Xenon, dissolved in sterile saline solution, is injected into the subcutaneous tissue of the lower leg. Arterial blood pressure will be recorded continuously with a Continuous Blood Pressure Device (CBPD) on the crewmember's index finger. This measurement is used to calculate how blood vessels help regulate arterial blood pressure and prevent orthostatic hypotension, or dizziness when standing.

A double-sided self-adhesive tape will be fastened onto the Xenon Detector Unit. The unit will be circled slowly over the injection area to measure the presence of the Xenon. The area showing the most Xenon will be marked with a pen, and the unit will be secured in place over the marked position. Thirty minutes after injection, the subcutaneous blood flow in the lower leg will be measured in what is called the 133Xenon washout technique. The crewmember will be placed in a relaxed, supine position for seven minutes, then one leg will be lowered 16 inches (40 centimeters) relative to the heart for seven minutes, and then be returned to the relaxed supine position for an additional seven minutes.

After the procedure, data from the Xenon Detector Unit's memory box will be downloaded to a computer and the local vascular resistance will be calculated.


Understanding how local veno-arteriolar reflex is active, attenuated reduced, or absent following exposure to microgravity -- the unique low-gravity environment inside the International Space Station and other spacecraft - could lead to future treatments to ensure normal blood circulation for Space Station crewmembers returning to Earth, thus enhancing mission effectiveness and crewmembers' safety.

More Information

For more information and photos on the Human Research Facility and Expedition Three science experiments, visit:

Steve Roy
Public Affairs Office
(256) 544-0034

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