The Effects of EVA and Long-Term Exposure to Microgravity on Pulmonary Function (PuFF) - 07.29.14
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Various breathing tests were performed before, during, and after flight to see if pulmonary function is affected by long-term exposure to microgravity or extravehicular activity (spacewalks). Changes due to long stays on-orbit, either from removal of gravity itself or from exposure to contaminants in the closed spacecraft environment, could adversely affect crew health. Changes associated with spacewalks could indicate an increased risk of decompression sickness, commonly known as the bends.
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It was previously thought that the lungs were highly sensitive to gravity. So researchers who measured lung function of crew members before, during, and after long ISS flights were surprised to find an almost complete absence of change in their lung function. In fact, the magnitude of observed changes was so small that researchers concluded microgravity has no lasting effect on lung function. This finding is significant and encouraging, since it means that lung function may not be a concern inside the ISS or for extravehicular activity on future missions.
Johnson Space Center, Human Research Program, Houston, TX, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
August 2001 - May 2003
Previous ISS Missions
Other pulmonary function experiments were conducted on STS-40, STS-55, STS-58, STS-78 and STS -90.
- This experiment examined, using non-invasive techniques, the effect of long-term exposure to microgravity and the effects of extravehicular activity (EVA) on pulmonary (respiratory) function by studying crewmembers before and after flight, monthly during flight, and before and after performing EVAs.
- It also measured aspects of pulmonary function that may be affected by long-term exposure to noxious gases or particulate matter that may accumulate in the atmosphere of the ISS. These measurements form a precursor set of studies that can be followed up in more detail when more complete hardware is available on the ISS.
This experiment examined the effect of long-term exposure to microgravity and EVA on pulmonary function by studying crewmembers before and after they performed EVAs. It examined whether pulmonary function was affected by long-term exposure to noxious gases or to particulate matter that may accumulate in the atmosphere of ISS.
There is a large difference in pressure between the inside of ISS and in the spacesuit used for EVAs. The effects of this difference in pressure pose a significant risk of decompression sickness (DCS)--known in the diving world as "the bends"--for spacewalkers, including bubble formation within the blood. Even if the symptoms of DCS do not occur, venous gas microbubbles can alter pulmonary function, increasing the risk of forming a venous embolism.
Each Pulmonary Function in Flight (PuFF) session consisted of five noninvasive tests with the crew breathing only cabin air. The tests measured the pulmonary system's ability to exchange gases, the amount of air inspired and expired as a function of time, and the maximum pressure of the air inhaled and exhaled. The analysis looked for markers that indicate that the lungs have been weakened from exposure to microgravity, or that the body's ability to exchange and distribute gases has been disrupted.
PuFF hardware, including a manual breathing valve and flow meter, was attached to the HRF gas analyzer system for metabolic analysis physiology (GASMAP) hardware, physiological signal conditioners, and the HRF computer. GASMAP measured the volume of gases inspired and expired, frequency of respiration, and ambient barometric pressure.
There is a large difference in pressure between the inside of the Station and in the spacesuit used for EVA (extra vehicular activity). The effects of that difference in pressure pose a significant risk of decompression sickness for spacewalking astronauts (similar to a scuba diver getting the bends), including bubble formation within the blood. Even if symptoms of decompression sickness do not occur, venous gas microbubbles can alter pulmonary function. Noninvasive tests of pulmonary function that are altered by changes in the pulmonary blood vessels are an ideal way to follow a subject over the course of multiple EVAs, especially since many EVAs are required for ISS construction and maintenance. This study also helped assess the effects on pulmonary function of the buildup of particulates or other contaminating gases that can occur in the closed spacecraft environment. Results from this experiment may help develop countermeasures for pulmonary problems that occur aboard the ISS, further safeguarding crew health.
On Earth, many people experience decompression sickness or "the bends" while diving. This is a result from the gasses (oxygen, nitrogen and small amounts of other gasses) that are breathed in while diving. The gasses are under pressure, causing not all the oxygen to be absorbed but the nitrogen will be producing bubbles in the blood stream. The results from Puff may help develop an improved SCUBA systems that will provide maximize that about of oxygen absorbed by the body while diving.
Two to three Station crew members participated in the PuFF experiment each increment. The first data collection occurred approximately two weeks into the mission and sessions were repeated monthly thereafter. Crewmembers assigned to conduct EVAs performed a PuFF session within one week prior to the EVA and again after the EVA (preferably on the same day, but in practice on the day following the EVA). An abbreviated session of only two breathing tests could be implemented on the day of EVA, if dictated by time constraints, or if multiple EVAs were conducted close together.
On the day of a PuFF session, the crew set up and calibrated the equipment. All participating crewmembers then took turns perfoming a predetermined sequence of breathing tests (either the full five-test session or the abbreviated session). After testing with all crewmembers was complete, the crew conducted a final calibration, saved the data on the computer, and disassembled the equipment for stowage. The data was downlinked to the ground at the next opportunity.
In addition to the in-flight sessions, crewmembers were tested four times preflight and four times post-flight. These sessions included both the in-flight protocol plus additional tests that could not performed on-orbit due to hardware limitations.
To determine if long-term exposure to microgravity on board the ISS had any, detrimental effects on lung function preflight and postflight measurements of lung function were performed on ten crew members who lived for 130 - 196 days on board the ISS. The same crewmembers also performed lung function measurements while in microgravity. Lung volumes, maximum inspiratory and expiratory flows, respiratory muscle strength, resting gas exchange, and numerous indices of the uniformity of lung function were measured on several occasions before flight, and again on several occasions following return to Earth gravity. Results show that, unlike many other organ systems in the human body, lung function returns to normal almost immediately after long-duration exposure to microgravity. The most important, and somewhat surprising, aspect is the almost complete absence of a change in lung function before and after spending 4 - 6 months in low Earth orbit, despite the fact that the lung is highly sensitive to gravity, as evidence by previous inflight studies. The magnitude of the observed changes in the ten subjects were so small that the conclusions, of no lasting effect of microgravity on lung function, would hold even if the study had included a greater sampling group. Investigators uphold that the very tiny and subtle changes in lung function that persist soon after landing are possibly due to a reduction in circulating blood volume, and alterations in lung fluid balance, and while statistically observable, are of little, if any, physiological consequence. This finding is significant and encouraging since it proposes that lung function is not a concern under the normal oxygen and pressure environment such as that inside the ISS (Prisk 2005, 2006, 2008).
Prisk GK, Fine JM, Cooper TK, West JB. Pulmonary gas exchange is not impaired 24 h after extravehicular activity. Journal of Applied Physiology. 2005; 99(6): 2233-2238.
Prisk GK, Fine JM, Cooper TK, West JB. Lung Function is unchanged in the 1 G environment following 6-months exposure to microgravity. European Journal of Applied Physiology. 2008; 103: 617-623. DOI: 10.1007/s00421-0080754-2.
Prisk GK, Fine JM, Cooper TK, West JB. Vital Capacity, Respiratory Muscle Strength and Pulmonary Gas Exchange during Long-Duration Exposure to Microgravity. Journal of Applied Physiology. 2006; 101: 439-447. DOI: 10.1152/japplphysiol.01419.2005.
Cowell SA, Stocks JM, Evans DG, Simonson SR, Greenleaf JE. The exercise and environmental physiology of extravehicular activity. Aviation, Space, and Environmental Medicine. 2002; 73(1): 54-67.
Ground Based Results Publications
Balldin UI, Pilmanis AA, Webb JT. The effect of simulated weightlessness on hypobaric decompression sickness. Aviation, Space, and Environmental Medicine. 2002; 73(8): 773-778.
Dervay JP, Powell MR, Butler BD, Fife CE. The effect of exercise and rest duration on the generation of venous gas bubbles at altitude. Aviation, Space, and Environmental Medicine. 2002; 73(1): 22-27.
Pilmanis AA, Webb JT, Kannan N, Balldin UI. The effect of repeated altitude exposures on the incidence of decompression sickness. Aviation, Space, and Environmental Medicine. 2002; 73(6): 525-31.
Prisk GK, Guy HJ, Elliott AR, West JB. Cardiopulmonary adaptation to weightlessness. Journal of Gravitational Physiology. 1994; 1(1): 118-121.
Prisk GK. Microgravity and the respiratory system. European Respiratory Journal. 2014 March 6; epub: 13 pp. DOI: 10.1183/09031936.00001414.
Prisk GK. The Lung in Space. Clinics in Chest Medicine. 2005; 26: 415-438.
Prisk GK, Fine JM, Elliott AR, West JB. Effect of 6 degrees head-down tilt on cardiopulmonary function: comparison with microgravity. Aviation, Space, and Environmental Medicine. 2002; 73(1): 8-16.
UCSD Physiology / NASA Lab
NASA Fact Sheet
International Space Station Medical Project (ISSMP)
Astronaut Peggy Whitson trains to perform a test of lung function as part of the PuFF experiment. Image courtesy of University of California.
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Astronaut Don Thomas participates in ground training for the PuFF experiment. Crew members participated in tests of lung function following the decompression they experience after an EVA. Image courtesy of University of California.
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NASA Image: ISS006E07133 - Astronaut Donald R. Pettit, Expedition Six NASA ISS Science Officer, works to set up Pulmonary Function in Flight (PuFF) hardware in preparation for a Human Research Facility (HRF) experiment in the Destiny laboratory on the International Space Station (ISS). Expedition Six is the fourth and final expedition crew to perform the HRF/PuFF Experiment on the ISS.
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NASA Image: ISS006348005 - Astronaut Donald R. Pettit, Expedition 6 NASA ISS science officer, uses a camera during a session of extravehicular activity (EVA) on 15 January 2003.
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NASA Image: ISS026E027009 - European Space Agency (ESA) astronaut Paolo Nespoli, Expedition 26 flight engineer, performs periodic maintenance on the Pulmonary Function in Flight (PuFF) experiment by re-greasing the PuFF calibration syringe in the Columbus laboratory of the International Space Station.
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