Space medicine

Space medicine was a critical factor in the United States human space program, starting with Project Mercury.[8]

Heart rhythm disturbances have been seen among astronauts.[12] Most of these have been related to cardiovascular disease, but it is not clear whether this was due to pre-existing conditions or effects of space flight. It is hoped that advanced screening for coronary disease has greatly mitigated this risk. Other heart rhythm problems, such as atrial fibrillation, can develop over time, necessitating periodic screening of crewmembers’ heart rhythms. Beyond these terrestrial heart risks, some concern exists that prolonged exposure to microgravity may lead to heart rhythm disturbances. Although this has not been observed to date, further surveillance is warranted.

In space, astronauts use a space suit, essentially a self-contained individual spacecraft, to do spacewalks, or extra-vehicular activities (EVAs). Spacesuits are generally inflated with 100% oxygen at a total pressure that is less than a third of normal atmospheric pressure. Eliminating inert atmospheric components such as nitrogen allows the astronaut to breathe comfortably, but also have the mobility to use their hands, arms, and legs to complete required work, which would be more difficult in a higher pressure suit.

After the astronaut dons the spacesuit, air is replaced by 100% oxygen in a process called a "nitrogen purge". In order to reduce the risk of decompression sickness, the astronaut must spend several hours "pre-breathing" at an intermediate nitrogen partial pressure, in order to let their body tissues outgas nitrogen slowly enough that bubbles are not formed. When the astronaut returns to the "shirt sleeve" environment of the spacecraft after an EVA, pressure is restored to whatever the operating pressure of that spacecraft may be, generally normal atmospheric pressure. Decompression illness in spaceflight consists of decompression sickness (DCS) and other injuries due to uncompensated changes in pressure, or barotrauma.

Decompression sickness is the injury to the tissues of the body resulting from the presence of nitrogen bubbles in the tissues and blood. This occurs due to a rapid reduction in ambient pressure causing the dissolved nitrogen to come out of solution as gas bubbles within the body.[13] In space the risk of DCS is significantly reduced by using a technique to wash out the nitrogen in the body's tissues. This is achieved by breathing 100% oxygen for a specified period of time before donning the spacesuit, and is continued after a nitrogen purge.[14][15] DCS may result from inadequate or interrupted pre-oxygenation time, or other factors including the astronaut's level of hydration, physical conditioning, prior injuries and age. Other risks of DCS include inadequate nitrogen purge in the EMU, a strenuous or excessively prolonged EVA, or a loss of suit pressure. Non-EVA crewmembers may also be at risk for DCS if there is a loss of spacecraft cabin pressure.

Symptoms of DCS in space may include chest pain, shortness of breath, cough or pain with a deep breath, unusual fatigue, lightheadedness, dizziness, headache, unexplained musculoskeletal pain, tingling or numbness, extremities weakness, or visual abnormalities.[16]

Primary treatment principles consist of in-suit repressurization to re-dissolve nitrogen bubbles,[17] 100% oxygen to re-oxygenate tissues,[18] and hydration to improve the circulation to injured tissues.[19]

Barotrauma is the injury to the tissues of air filled spaces in the body as a result of differences in pressure between the body spaces and the ambient atmospheric pressure. Air filled spaces include the middle ears, paranasal sinuses, lungs and gastrointestinal tract.[20][21] One would be predisposed by a pre-existing upper respiratory infection, nasal allergies, recurrent changing pressures, dehydration, or a poor equalizing technique.

Positive pressure in the air filled spaces results from reduced barometric pressure during the depressurization phase of an EVA.[22][23] It can cause abdominal distension, ear or sinus pain, decreased hearing, and dental or jaw pain.[21][24] Abdominal distension can be treated with extending the abdomen, gentle massage and encourage passing flatus. Ear and sinus pressure can be relieved with passive release of positive pressure.[25] Pretreatment for susceptible individuals can include oral and nasal decongestants, or oral and nasal steroids.[26]

Negative pressure in air fill spaces results from increased barometric pressure during repressurization after an EVA or following a planned restoration of a reduced cabin pressure. Common symptoms include ear or sinus pain, decreased hearing, and tooth or jaw pain.[27]

Treatment may include active positive pressure equalization of ears and sinuses,[28][25] oral and nasal decongestants, or oral and nasal steroids, and appropriate pain medication if needed.[26]

Astronauts in space have weakened immune systems, which means that in addition to increased vulnerability to new exposures, viruses already present in the body—which would normally be suppressed—become active.[29] In space, T-cells do not reproduce properly, and the cells that do exist are less able to fight off infection.[30] NASA research is measuring the change in the immune systems of its astronauts as well as performing experiments with T-cells in space.

On April 29, 2013, scientists in Rensselaer Polytechnic Institute, funded by NASA, reported that, during spaceflight on the International Space Station, microbes seem to adapt to the space environment in ways "not observed on Earth" and in ways that "can lead to increases in growth and virulence".[31]

In March 2019, NASA reported that latent viruses in humans may be activated during space missions, adding possibly more risk to astronauts in future deep-space missions.[32]

A 2006 Space Shuttle experiment found that Salmonella typhimurium, a bacterium that can cause food poisoning, became more virulent when cultivated in space.[33] On April 29, 2013, scientists in Rensselaer Polytechnic Institute, funded by NASA, reported that, during spaceflight on the International Space Station, microbes seem to adapt to the space environment in ways "not observed on Earth" and in ways that "can lead to increases in growth and virulence".[31] More recently, in 2017, bacteria were found to be more resistant to antibiotics and to thrive in the near-weightlessness of space.[34] Microorganisms have been observed to survive the vacuum of outer space.[35][36] Researchers in 2018 reported, after detecting the presence on the International Space Station (ISS) of five Enterobacter bugandensis bacterial strains, none pathogenic to humans, that microorganisms on ISS should be carefully monitored to continue assuring a medically healthy environment for astronauts.[37][38]

Human spaceflight often requires astronaut crews to endure long periods without rest. Studies have shown that lack of sleep can cause fatigue that leads to errors while performing critical tasks.[39][40][41] Also, individuals who are fatigued often cannot determine the degree of their impairment.[42] Astronauts and ground crews frequently suffer from the effects of sleep deprivation and circadian rhythm disruption. Fatigue due to sleep loss, sleep shifting and work overload could cause performance errors that put space flight participants at risk of compromising mission objectives as well as the health and safety of those on board.

Leaving and returning to Earth's gravity causes “space sickness,” dizziness, and loss of balance in astronauts. By studying how changes can affect balance in the human body—involving the senses, the brain, the inner ear, and blood pressure—NASA hopes to develop treatments that can be used on Earth and in space to correct balance disorders. Until then, NASA's astronauts must rely on a medication called Midodrine (an “anti-dizzy” pill that temporarily increases blood pressure), and/or promethazine to help carry out the tasks they need to do to return home safely.[43]

Spaceflight osteopenia is the bone loss associated with human spaceflight.[3] After a 3–4 month trip into space, it takes about 2–3 years to regain lost bone density.[44][45] New techniques are being developed to help astronauts recover faster. Research in the following areas holds the potential to aid the process of growing new bone:

• Diet and Exercise changes may reduce osteoporosis.
• Vibration Therapy may stimulate bone growth.[46]
• Medication could trigger the body to produce more of the protein responsible for bone growth and formation.

In space, muscles in the legs, back, spine, and heart weaken and waste away because they no longer are needed to overcome gravity, just as people lose muscle when they age due to reduced physical activity.[3] Astronauts rely on research in the following areas to build muscle and maintain body mass:

• Exercise may build muscle if at least two hours a day is spent doing resistance training routines.
• Hormone supplements (hGH) may be a way to tap into the body's natural growth signals.
• Medication may trigger the body into producing muscle growth proteins.

After long space flight missions, astronauts may experience severe eyesight problems.[2][3][47][48][49][50][51][52] Such eyesight problems may be a major concern for future deep space flight missions, including a human mission to Mars.[47][48][49][50][53]

On December 31, 2012, a NASA-supported study reported that human spaceflight may harm the brain of astronauts and accelerate the onset of Alzheimer's disease.[54][55][56]

On 2 November 2017, scientists reported that significant changes in the position and structure of the brain have been found in astronauts who have taken trips in space, based on MRI studies. Astronauts who took longer space trips were associated with greater brain changes.[57][58]

The Beckman cardiovascular reflex conditioning system inflated and deflated cuffs in Gemini and Apollo flight suits to stimulate blood flow to lower limbs.[59]

"Under the effects of the earth's gravity, blood and other body fluids are pulled towards the lower body. When gravity is taken away or reduced during space exploration, the blood tends to collect in the upper body instead, resulting in facial edema and other unwelcome side effects. Upon return to earth, the blood begins to pool in the lower extremities again, resulting in orthostatic hypotension."[60]

In space, astronauts lose fluid volume—including up to 22% of their blood volume. Because it has less blood to pump, the heart will atrophy. A weakened heart results in low blood pressure and can produce a problem with “orthostatic tolerance,” or the body's ability to send enough oxygen to the brain without fainting or becoming dizzy.[60]

Comparison of Radiation Doses – includes the amount detected on the trip from Earth to Mars by the RAD on the MSL (2011–2013).[61][62][63][64]

Soviet cosmonaut Valentin Lebedev, who spent 211 days in orbit during 1982 (an absolute record for stay in Earth's orbit), lost his eyesight to progressive cataract. Lebedev stated: “I suffered from a lot of radiation in space. It was all concealed back then, during the Soviet years, but now I can say that I caused damage to my health because of that flight.”[3][65] On 31 May 2013, NASA scientists reported that a possible human mission to Mars may involve a great radiation risk based on the amount of energetic particle radiation detected by the RAD on the Mars Science Laboratory while traveling from the Earth to Mars in 2011–2012.[53][61][62][63][64]

Fifty percent of space shuttle astronauts take sleeping pills and still get two hours or less of sleep. NASA is researching two areas which may provide the keys to a better night's sleep, as improved sleep decreases fatigue and increases daytime productivity. A variety of methods for combating this phenomenon are constantly under discussion. A partial list of remedies would include:

• Go to sleep at the same time each night. With practice, you will (almost) always be tired and ready for sleep.
• Melatonin, once thought to be an anti-aging wonder drug (this was due to the well-documented observation that as people age they gradually produce less and less of the hormone naturally). The amount of melatonin the body produces decreases linearly over a lifetime. Although the melatonin anti-aging fad was thoroughly debunked following a large number of randomized trials, it was soon in the spotlight once more due to the observation that a healthy person's normal melatonin levels varies widely throughout each day: usually, levels rise in the evening and fall in the morning. Ever since the discovery that melatonin levels are highest at bedtime, melatonin has been purported by some to be an effective sleep-aid – it is especially popular for jet-lag. Melatonin's efficacy in treating insomnia is hotly debated and therefore in the US it is sold as a dietary supplement. "These statements have not been evaluated by the FDA" is printed on the packaging even though melatonin has been studied very extensively.
• Ramelteon, a melatonin receptor agonist, is a relatively new drug designed by using the melatonin molecule and the shapes of melatonin receptors as starting points. Ramelteon binds to the same M1 and M2 receptors in the suprachiasmatic nucleus (the "biological clock" in the brain) as melatonin (M1 and M2 get their names from melatonin). It also may derive some of its properties from its three-times greater elimination half-life. Ramelteon is not without detractors who claim that it is no more effective than melatonin, and melatonin is less expensive by orders of magnitude. It is unclear whether Ramelteon causes its receptors to behave differently than they do when bound to melatonin, and Ramelteon may have a significantly greater affinity for these receptors. Better information on Ramelteon's effectiveness should be available soon, and despite questions of its efficacy, the general lack of side effects makes Ramelteon one of the very few sleep medications that could potentially be safely used by astronauts.
• Barbiturates and Benzodiazepines are both very strong sedatives. While they certainly would work (at least short term) in helping astronauts sleep, they have side effects that could affect the astronaut's ability to perform his/her job, especially in the "morning." This side effect renders barbiturates and benzodiazepines likely unfit as treatments for space insomnia. Narcotics and most tranquilizers also fall into this category.
• Zolpidem and Zopiclone are sedative-hypnotics, better known by their trade names "Ambien" and "Lunesta". These are extremely popular sleep-aids, due in large part to their effectiveness and significantly reduced side-effect profiles vis-a-vis benzodiazepines and barbiturates. Although other drugs may be more effective in inducing sleep Zolpidem and Zopiclone essentially lack the sorts of side effects that disqualify other insomnia drugs for astronauts, for whom being able to wake up easily and quickly can be of paramount importance; astronauts who are not thinking clearly, are groggy, and are disoriented when a sudden emergency wakes them could end up trading their grogginess for the indifference of death in seconds. Zolpidem, Zopiclone, and the like – in most people – are significantly less likely to cause drug-related daytime sleepiness, nor excessive drowsiness if woken abruptly.
• Practice good sleep hygiene. In other words, the bed is for sleeping only; get out of bed within a few moments of waking up. Do not sit in bed watching TV or using a laptop. When one is acclimated to spending many hours awake in bed, it can disrupt the body's natural set of daily cycles, called the circadian rhythm. While this is less of an issue for astronauts who have very limited entertainment options in their sleeping areas, another aspect of sleep hygiene is adhering to a specific pre-sleep routine (shower, brush teeth, fold up clothing, spend 20 minutes with a trashy novel, for example); observing this sort of routine regularly can significantly improve one's sleep quality. Of course, sleep hygiene studies have all been conducted at 1G, but it seems possible (if not likely) that observing sleep hygiene would retain at least some efficacy in micro-gravity.
• Modafinil is a drug that is prescribed for narcolepsy and other disorders that involve excessive daytime exhaustion. It has been approved in various military situations and for astronauts thanks to its ability to stave off fatigue. It is unclear whether astronauts sometimes use the drug because they are sleep-deprived – it might only be used on spacewalks and in other high-risk situations.
• Dexedrine is an amphetamine which used to be the gold-standard for fighter pilots flying long and multiple sorties in a row, and therefore may have at some point been available if astronauts were in need of a strong stimulant. Today, Modafinil has largely – if not entirely – replaced Dexedrine; reaction time and reasoning among pilots who are sleep-deprived and on Dexedrine suffer, and get worse the longer the pilot stays awake. In one study, helicopter pilots that were given two-hundred milligrams of Modafinil every three hours were able to significantly improve their flight-simulator performance. The study reported, however, that modafinil was not as efficacious as dexamphetamine in increasing performance without producing side effects. [66]

• Aeromedical certification
• Aerospace medicine
• Aerospace studies
• Occupational and preventive medicine
• Global Health
• Public Health
• Disaster medicine
• Prehospital medicine
• Wilderness and extreme medicine

Space nursing is the nursing speciality that studies how space travel impacts human response patterns. Similar to space medicine, the speciality also contributes to knowledge about nursing care of earthbound patients.[67][68]

Ultrasound is the main diagnostic imaging tool on ISS and for the foreseeable future missions. X-rays and CT scans involve radiation which is unacceptable in the space environment. Though MRI uses magnetics to create images, it is too large at present to consider as a viable option. Ultrasound, which uses sound waves to create images and comes in laptop size packages, provides imaging of a wide variety of tissues and organs. It is currently being used to look at the eyeball and the optic nerve to help determine the cause(s) of changes that NASA has noted mostly in long duration astronauts. NASA is also pushing the limits of ultrasound use regarding musculoskeletal problems as these are some of the most common and most likely problems to occur. Significant challenges to using ultrasounds on space missions is training the astronaut to use the equipment (ultrasound technicians spend years in training and developing the skills necessary to be "good" at their job) as well as interpreting the images that are captured. Much of ultrasound interpretation is done real-time but it is impractical to train astronauts to actually read/interpret ultrasounds. Thus, the data is currently being sent back to mission control and forwarded to medical personnel to read and interpret. Future exploration class missions will need to be autonomous due to transmission times taking too long for urgent/emergent medical conditions. The ability to be autonomous, or to use other equipment such as MRIs, is currently being researched.

With the additional lifting capability presented by the Space Shuttle program, NASA designers were able to create a more comprehensive medical readiness kit. The SOMS consists of two separate packages: the Medications and Bandage Kit (MBK) and the Emergency Medical Kit (EMK). While the MBK contained capsulate medications (tablets, capsules, and suppositories), bandage materials, and topical medication, the EMK had medications to be administered by injection, items for performing minor surgeries, diagnostic/therapeutic items, and a microbiological test kit.[69]

John Glenn, the first American astronaut to orbit the Earth, returned with much fanfare to space once again on STS-95 at 77 years of age to confront the physiological challenges preventing long-term space travel for astronauts—loss of bone density, loss of muscle mass, balance disorders, sleep disturbances, cardiovascular changes, and immune system depression—all of which are problems confronting aging people as well as astronauts.[70]

In the interest of creating the possibility of longer duration space flight, NASA has invested in the research and application of preventative space medicine, not only for medically preventable pathologies, but trauma as well. Although trauma constitutes more of a life-threatening situation, medically preventable pathologies pose more of a threat to astronauts. "The involved crewmember is endangered because of mission stress and the lack of complete treatment capabilities on board the spacecraft, which could result in the manifestation of more severe symptoms than those usually associated with the same disease in the terrestrial environment. Also, the situation is potentially hazardous for the other crewmembers because the small, closed, ecological system of the spacecraft is conducive to disease transmission. Even if the disease is not transmitted, the safety of the other crewmembers may be jeopardized by the loss of the capabilities of the crewmember who is ill. Such an occurrence will be more serious and potentially hazardous as the durations of crewed missions increase and as operational procedures become more complex. Not only do the health and safety of the crewmembers become critical, but the probability of mission success is lessened if the illness occurs during flight. Aborting a mission to return an ill crewmember before mission goals are completed is costly and potentially dangerous."[71]

• Radiation therapy for the treatment of cancer: In conjunction with the Cleveland Clinic, the cyclotron at Glenn Research Center in Cleveland, Ohio was used in the first clinical trials for the treatment and evaluation of neutron therapy for cancer patients.[72]
• Foldable walkers: Made from a lightweight metal material developed by NASA for aircraft and spacecraft, foldable walkers are portable and easy to manage.
• Personal alert systems: These are emergency alert devices that can be worn by individuals who may require emergency medical or safety assistance. When a button is pushed, the device sends a signal to a remote location for help. To send the signal, the device relies on telemetry technology developed at NASA.
• CAT and MRI scans: These devices are used by hospitals to see inside the human body. Their development would not have been possible without the technology provided by NASA after it found a way to take better pictures of the Earth's moon.[73]
• Muscle stimulator device: This device is used for ½ hour per day to prevent muscle atrophy in paralyzed individuals. It provides electrical stimulation to muscles which is equal to jogging three miles per week. Christopher Reeve used these in his therapy.
• Orthopedic evaluation tools: Equipment to evaluate posture, gait and balance disturbances was developed at NASA, along with a radiation-free way to measure bone flexibility using vibration.
• Diabetic foot mapping: This technique was developed at NASA's center in Cleveland, Ohio to help monitor the effects of diabetes in feet.
• Foam cushioning: Special foam used for cushioning astronauts during liftoff is used in pillows and mattresses at many nursing homes and hospitals to help prevent ulcers, relieve pressure, and provide a better night's sleep.
• Kidney dialysis machines: These machines rely on technology developed by NASA in order to process and remove toxic waste from used dialysis fluid.
• Talking wheelchairs: Paralyzed individuals who have difficulty speaking may use a talking feature on their wheelchairs which was developed by NASA to create synthesized speech for aircraft.
• Collapsible, lightweight wheelchairs: These wheelchairs are designed for portability and can be folded and put into trunks of cars. They rely on synthetic materials that NASA developed for its air and space craft
• Surgically implantable heart pacemaker: These devices depend on technologies developed by NASA for use with satellites. They communicate information about the activity of the pacemaker, such as how much time remains before the batteries need to be replaced.
• Implantable heart defibrillator: This tool continuously monitors heart activity and can deliver an electric shock to restore heartbeat regularity.
• EMS communications: Technology used to communicate telemetry between Earth and space was developed by NASA to monitor the health of astronauts in space from the ground. Ambulances use this same technology to send information—like EKG readings—from patients in transport to hospitals. This allows faster and better treatment.
• Weightlessness therapy: The weightlessness of space can allow some individuals with limited mobility on Earth—even those normally confined to wheelchairs—the freedom to move about with ease. Physicist Stephen Hawking took advantage of weightlessness in NASA's Vomit Comet aircraft in 2007.[74] This idea also led to the development of the Anti-Gravity Treadmill from NASA technology.

The Advanced Diagnostic Ultrasound in Microgravity Study is funded by the National Space Biomedical Research Institute and involves the use of ultrasound among Astronauts including former ISS Commanders Leroy Chiao and Gennady Padalka who are guided by remote experts to diagnose and potentially treat hundreds of medical conditions in space. This study has a widespread impact and has been extended to cover professional and Olympic sports injuries as well as medical students. It is anticipated that remote guided ultrasound will have application on Earth in emergency and rural care situations. Findings from this study were submitted for publication to the journal Radiology aboard the International Space Station; the first article submitted in space.[75][76][77]