The Expedition Four crew wrapped up its orbital construction duties this week with a science experiment to measure how well the crew's lungs function following exposure to the low pressure environment of their spacesuits as well as exposure to the confined atmosphere of the Space Station.

Following his spacewalk on Monday, Jan. 14, Flight Engineer Carl Walz performed a post-EVA session Tuesday with the Pulmonary Function in Flight (PuFF) experiment. Flight Engineer Dan Bursch also volunteered to perform the test, and the science team was enthusiastic to get the additional data. Following an EVA on Jan. 25 involving Bursch, he and Walz are scheduled to perform another PuFF session on Jan. 26, which will serve as Bursch's post-EVA test and Walz' monthly test.

PuFF, developed by the University of California, San Diego and managed by NASA's Johnson Space Center, focuses on lung function both following EVA and inside the station during long-term exposure to microgravity, laying the groundwork for future experiments key to understanding and maintaining crew health.

Spacewalkers can suffer decompression sickness just as scuba divers do when they come to the surface too quickly. Decompression sickness results from exposure to low barometric pressures that cause inert gases -- mainly nitrogen -- that are normally dissolved in body fluids and tissues to form bubbles. Symptoms can include headaches, memory loss and blurred vision. EVAs pose a risk of nitrogen bubble formation because spacesuits operate at 4.3 pounds of pressure instead of the 14.7 pounds found on Earth and inside the Space Station.

Each PuFF session includes five lung function tests, which involve breathing only cabin air. The focus is on measuring the evenness of gas exchange in the lungs and detecting changes in respiratory muscle strength, which may result from long periods in the absence of gravity.

In addition to benefiting future space explorers, PuFF may contribute to clinical medicine on Earth because gravity affects the way the lungs operate and may even exaggerate some lung disorders, such as emphysema and tuberculosis.

The Active Rack Isolation System ground team on Monday downlinked data and sent up various file management commands, important steps in completing ARIS' performance analysis and freeing up space on the computer hard drives. Ground commanded isolation tests of the experimental vibration dampening device continued this week. The first hammer tests by the Expedition Four crew are planned for next week. A crew member uses a small hammer to tap on and around the rack to see if ARIS can quiet the vibrations to EXPRESS Rack 2, where it is housed.

The Experiment on Physics of Colloids successfully completed a 120-hour run last week, the longest test to date by that experiment. Monday's 24-hour colloids test was the last prior to initiating the first fractal gel tests, which will last about five weeks. The Monday test was run to do some final measurements on the AB6 and glass samples prior to being unable to examine any sample other than the fractal gels. Colloids, fine particles suspended in a fluid, are commonly used in many products and manufacturing processes on Earth. Space experiments may contribute to development of new materials and other uses for colloids.

Sites uplinked to the Station for the Crew Earth Observations photography research program this week included wake clouds and von Karmen vortices in the Canary Islands, fires in the African Sahel, coral reefs and atolls in the Tuamotu Archipelago, tropical glaciers and ice fields in New Guinea, air pollutants off the Eastern United States shores, Patagonian glaciers, damage from Hurricane Juliette in the Cabo San Lucas area of Baja, California, and manmade lakes westward from the Nile River into the Egyptian desert.

The crew this week is continuing to participate in the Crew Interactions experiment on their station laptop computer, and they continue to perform normal maintenance and status checks on the station's various automated science experiments controlled from the ground.

Overall, of the 25 experiments planned for Expedition Four, three are complete, 15 are in progress now and seven are planned for later in the Expedition, including four, which will arrive on the upcoming 8A Space Shuttle mission.

Editor's Note: The Payload Operations Center at NASA's Marshall Space Flight Center in Huntsville, Ala., manages all science research experiment operations aboard the International Space Station. The center is also home for coordination of the mission-planning work of a variety of international sources, all science payload deliveries and retrieval, and payload training and payload safety programs for the Station crew and all ground personnel.