If human space exploration missions to the Moon and then Mars are to be successful, space life scientists need a good understanding of the effects of long-duration spaceflight on the human body and of how the body adapts to the microgravity environment. Failure to prevent or minimize harmful changes caused by spaceflight can lead to illness or even loss of life. Physiology is the branch of biology that deals with the functions of the human body (in this case, organs such as the brain, heart, muscle, skeletal system tissues, and cells that reside in the blood system) and with the physical and chemical events involved. Although many changes occur in the human body during spaceflight, this NASA project focuses mainly on 6 discipline groups or processes: cardiovascular, immunological, skeletal (bone), muscle, nutritional and pharmacological, and neurovestibular (sensory-motor) physiology. The Non-exercise Physiological Countermeasures (NxPCM) Project exists to deal with the physiological changes in body systems to make sure astronauts are healthy, safe, and able to perform the assigned transit and exploration tasks during space missions. Countermeasures are therapies, devices, or procedures that counteract harmful effects of spaceflight.

Cardiovascular Changes

Cardiovascular changes seem to increase with the amount of time spent in space. Soon after launch, body fluid including blood moves from the legs to the head and upper body. Additional cardiovascular changes include a decrease in the total amount of blood in the body and total cardiac output. When an astronaut returns to One Earth Normal (OEN) gravity, the cardiovascular changes that occurred during spaceflight result in low blood pressure and reduced cardiac output. Astronauts that have been in prolonged spaceflight (> 30 days) are often unable to stand up soon after landing. This greatly increases the risk that they would be unable to rapidly get out of the vehicle upon return to Earth in an emergency, and also greatly increases the health risks of performing surface operations when crew members land on Mars. When astronauts return to Earth, landing and rehabilitation personnel are ready to assist them, but these trained personnel will not be available to crew members arriving on Mars. To compensate for these cardiovascular changes, countermeasures for use before landing and self-sustaining rehabilitation regimens will need to be developed.

Immunological Changes

Changes in the immune system also occur and place crew members at risk. To understand the mechanisms involved and to determine the specific risks to crew members, we need to fully characterize these changes for flight durations longer than our current experience on the International Space Station (ISS). Reducing these risks will require NASA to develop procedures to boost the immune system, countermeasures to prevent conditions favoring infection by opportunistic microbes, and countermeasures to restore health to any crewmember that becomes ill.

Skeletal (Bone) Changes

Exposure to long-term reduced gravity causes reduction in bone density and change in bone composition. Currently, astronauts primarily use exercise during long-duration missions onboard ISS to mitigate these alterations, and upon return to Earth they enter a regimen of physical therapy that promotes recovery of lost bone density. Such support will not be readily available during long-duration missions on the Moon or to Mars, so astronauts may not be able to perform surface or emergency egress procedures necessary for mission success. Countermeasures other than exercise are being studied to provide additional protection against debilitating bone loss.

Muscle Changes

Exposure to long-term reduced gravity causes reduction in muscle mass and strength, especially in the lower extremities (legs), because of lack of use for normal locomotion (walking). Upper body strength does not typically decrease in microgravity since astronauts often "pull" themselves around with their arms. Currently, astronauts primarily use exercise during long-duration missions onboard ISS to mitigate these alterations, and upon return to Earth they enter a regimen of physical therapy that promotes recovery of lost muscle strength. Such support will not be readily available during long-duration missions to the Moon or Mars, so astronauts may not be able to perform surface or emergency egress procedures necessary to mission success. Countermeasures, other than exercise, are being studied to provide additional protection against debilitating loss of muscle strength.

Nutritional & Pharmacological Changes

Nutrition is the study of food and nourishment. Nutrition efforts are required to make sure the nutritional status of astronauts remains adequate throughout long-duration missions. When tested after missions, astronauts have shown high systemic levels of some nutrients and low levels of others. It can be hypothesized that either the body absorbs and processes foods differently in microgravity than on Earth, or that the foods themselves change in useful nutrient content during missions--NxPCM needs to determine which of these options is true.

Nutrition plays a critical role in all body systems and also may serve as a countermeasure itself. Optimal nutrition will enable other countermeasure systems such as exercise to be effective, while inadequate nutrition may cause planned countermeasures to fail. The potential for other countermeasures to have an adverse impact on nutrition also is significant. The possible consequences of having too much or too little of an important nutrient include performance losses, illness, and in many cases, if an imbalance is left uncorrected, even death.

Pharmacotherapeutics is the study of therapeutic uses and effects of drugs. Specifically, pharmacotherapeutics efforts are necessary to provide safe and effective medical care for astronauts. Microgravity can lower the efficacy of drugs, requiring additional dosing before getting the needed effect. It is likely that these drugs are not metabolized the same in space as on Earth, and these changes need to be quantified.

Some of the areas included in pharmacotherapeutics are pharmacokinetics and pharmacodynamics. Pharmacokinetics is the study of the process whereby a drug is absorbed, distributed, metabolized, and eliminated from the body. Pharmacodynamics is the study of the action or effects of drugs on living organisms. Current knowledge of the pharmacokinetics and pharmacodynamics of medications in space is lacking in detail. The number of effective, stable pharmaceuticals available for treatment in space is limited; this is an important part of the risk to astronaut health and limits the ability to treat illness or injury.

NASA's planned exploration missions, which feature long periods of travel to the Moon or Mars, will require unprecedented periods of being far away from Earth and from easy restocking of food stores and medicines. Astronauts will require a complete stock of everything they will need on their journey, and their cargo must be stable enough to perform as needed throughout the entire duration of the journey.

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