We had to struggle a little bit, but we showed the reason that manned spaceflight has been as successful as it has for a large number of years. A large team of people scattered across the entire planet were able all together to get a major advance in the space station assembly operations.
Chuck Shaw, lead flight mission director for the 100th shuttle mission commenting from Houston Mission Control on the successful attachment by the shuttle Discovery astronauts of the nine-ton Z1 structural truss to the International Space Station's Unity module, October 14, 2000
Perhaps the most ambitious goal of the National Aeronautics and Space Administration's (NASA's) space medicine program is to be able to provide optimal health care to the first (and subsequent) astronauts who will go on exploration-class missions to Mars. Because any such mission lies more than a decade in the future, the challenge to the Institute of Medicine (IOM) Committee on Creating a Vision for Space Medicine During Travel Beyond Earth Orbit was this: what can usefully be said, so far in advance, about providing day-to-day health care in space, while on the Martian surface, and during the return trip to Earth? What types of illnesses and injuries might reasonably be anticipated on long-duration space missions?
In this chapter, the committee tries to begin answering those questions by looking at the only evidence available: the morbidity and mortality experiences of U.S. astronauts and Russian cosmonauts, U.S. Navy submariners, and Australian scientists and explorers in the Antarctic. This look back includes findings from physical examinations conducted in space to see what is normal, or baseline, in microgravity. The committee also examines potential health problems in each of several medical practice areas—cardiology, neurology, surgery, and psychiatry, to name a few—in which critical risks have been identified (see Table 2–2).
The committee anticipates that long-duration missions beyond Earth orbit will be qualitatively different from short spaceflights. Medical and behavioral issues that have not been particularly problematic on short flights may loom large on exploration-class missions. It is not possible to accurately predict the treatment innovations, technological advances, and shifting standards of care that may occur over the next 20 years and prove relevant to medical practice in space.
GENERAL PRINCIPLES AND ISSUES
The focus of this chapter is the care of the individual patient in space. Premission evaluation should include assessments of both the astronaut's health status (including the status of specific organ systems at risk, such as the musculoskeletal system [see Chapter 2 for the risks involved]) and other risks. The general principles of care are the maintenance of normal health status in microgravity and, if illness or injury occurs, restoration of normal function as quickly and efficiently as possible during and upon the return from the space mission. As part of a responsible space crew, each crewmember should be expected to participate in routine surveillance to be able to measure the health status of other members of the crew at regular intervals. Resources should be available for the diagnosis and treatment of the most common minor and major illnesses and injuries that are anticipated to occur in the Earth environment, as well as to diagnose and treat conditions that are unique to microgravity and the particular space mission. The crew should be prepared to treat a wide variety of conditions of various degrees of severity during a space mission and, most of all, be prepared to treat the unexpected.
The major health and medical issues related to exploration-class missions have been of little risk or concern to NASA up to the present for short-duration space travel (e.g., space transportation system [STS] space shuttle missions) (Box 3–1). All of the major health and medical issues are projected, however, to be moderate to severe concerns that affect astronaut health on the International Space Station (ISS), and except for radiation protection and bone mineral density loss, the degree of severity of the other health and safety challenges have yet to be estimated for exploration-class missions. Many of these issues and challenges are directly related to or are completely tied to known human physiological adaptations to space travel. Separation of these issues from the discussions of physiological adaptations in Chapter 2 is in many cases artificial. Similar concerns, issues, and topics on medical, surgical, rehabilitative, and behavioral health in this chapter and in Chapters 4 and 5 must also be considered in the continuum of clinical research and health care for astronauts to begin building the infrastructure and health care system (Chapter 7) needed for human exploration of deep space. The committee has chosen to separate these topics into chapters to place the emphasis on clinical research (Chapters 2 to 5), health care (Chapters 3 to 5), and opportunities and ethical and infrastructure concerns (Chapters 6 and 7) that it believes is necessary to promote the needed attention to the safe passage and the health of astronauts during travel beyond Earth orbit and into deep space.
BOX 3–1
Major Health and Medical Issues During Spaceflight.
Abbreviations: GRD, ground; AIR, airflight; STS, space shuttle; ISS, International Space Station; EXP, exploration-class mission; G, green, little or no risk; Y, yellow, moderate risk; R, red, severe risk; TBD, to be determined; NA, not applicable.
Source: Williams, 2000.
Medical Events in Extreme Environments
Evidence Base from Previous Space Missions
A review of 79 U.S. space missions involving 219 person-flights lasting 2 to 17 days each (Putcha et al., 1999) reported that the most common conditions experienced were space motion sickness (SMS), nasal congestion, and sleep disorders. None of these medical conditions have required the mission to end, have been life threatening, or have required intensive medical treatment; they are bothersome but are not medical emergencies. Exploration-class missions, however, because of their lengths of as many as 3 years beyond Earth orbit, raise in NASA's current judgment the probability of a major medical event, a condition requiring intervention by a medical practitioner, during the mission (Billica, 2000).
A study of 175 astronauts from 1959 to 1991 reported 20 deaths (19 males and 1 female), mostly unrelated to spaceflight because of high rates of automobile and aircraft accidents and accidental deaths on the Apollo 1 and the Challenger spacecrafts. The small numbers of participants and the premature deaths from injuries may well mask the morbidity and mortality figures from other disorders related to spaceflight, such as cancer, if the participants live long enough (Peterson et al., 1993). Related disorders such as the development of cancer and cardiovascular, arthritic, and other conditions may increase in frequency as the duration of space travel and the ages of astronauts increase, just as they would had the same individuals remained on Earth.
The risks of medical events increase with the lengths of missions (Billica et al., 1996). A survey of the perception of risk from spaceflight was returned by 65 medical professionals and showed that medical events with the highest perceived likelihood of occurrence had the least effect on the mission or the crew, but those with the greatest impact on the mission or crew were least likely to occur (Billica et al., 1996). Skin disorders (irritation from fiberglass, contact dermatitis, rashes, and furuncles) were thought to be the most common, followed by respiratory and digestive disorders.
NASA reported that 1,867 medical events occurred from 1981 to 1998 on space shuttle flights STS-1 to STS-89 (Billica, 2000). Among the population of 508 individuals on those flights, 498 reported a medical event or symptom other than SMS. The events, derived from a histogram presented to the committee (Billica, 2000), were ill-defined symptoms (n=788), respiratory events (n=83), symptoms related to nervous system or sensory organs (n=318), digestive disorders (n=163), symptoms related to skin or subcutaneous tissue (n=151), symptoms related to the musculoskeletal system (n=132), and injuries (n=141). Approximately 5 percent (77 of 1,777) were injuries, and 10 deaths occurred, 7 during a catastrophic explosion in the early phase of the launch (Challenger in 1986) and 3 from a fire on the launchpad (Apollo 1 in 1967).
Rates of events have not been reported, and associations of illness or injury with extravehicular activity (EVA) also have not been reported. EVAs are associated with a high workload and are associated with a much higher risk of injury because of the momentum imparted to large masses during EVAs and the lengthy periods of work outside the spacecraft (Nicogossian et al., 1994). Even in the non-EVA microgravity environment, fractures are possible due to movement of cargo, which can easily “get away” once set in motion or if an individual pushes away from a wall too hard and experiences a bone-jarring hit on the opposite wall (Nicogossian et al., 1994). This is a good example of the importance of training to prevent medical injury.
The microgravity environments of long-duration space missions will also be associated with overexertion, strains, and sprains, because backaches and effects from the physical demands of EVAs have been reported during shorter missions and require pharmacological treatment (Putcha et al., 1999). Backaches are not specifically associated with EVAs but are a common complaint thought to be associated with elongation in vertebral column length and stress placed on intervertebral discs. This type of pain has been reported to be ameliorated by axial compression performed by crewmembers while in orbit (NASA, 2000b).
The medications administered as a single dose or taken by only one person during 219 space missions have included phenazopyridine, omeprazole, zolpidem, sucralfate, an antifungal (Vagisil), clotrimazole (Mycelex), docusate, an antacid (Gaviscon), cimeditine, diclofenac, meclizine, ofloxacin, gentamicin, lovastatin, flavoxate, ketoprofen, metaxalone, and cephalexin. This spectrum of medications that has been taken and the disorders that have been treated on short missions point to the need to plan for a broad-based and space medicine-focused pharmacopoeia to treat a wide variety of signs, symptoms, and diseases on longer missions. The existence of such a pharmacopoeia also necessitates procedures to avoid potential abuse.
It would have been helpful to the committee's assessment if the data on illness and injury with and without an association with EVA made available to the committee had been stratified and publicly reported to allow the committee and others to have a better understanding of the health-related risks of spaceflight. Moreover, a number of questions remain unanswered. In addition, facts needed to best appreciate any list of health-related risks of spaceflight (Tables 3–1, 3–2, 3–3, and 3–4) to plan for future space missions were not available. For instance, (1) how were the symptoms distributed among astronauts with different specialties (e.g., pilots versus payload specialists)? (2) did astronauts who flew more than one mission experience fewer symptoms on subsequent flights? and (3) what was the degree of severity of the reported symptoms?
TABLE 3–1
In-Flight Medical Events for U.S. Astronauts During the Space Shuttle Program (STS-1 through STS-89, April 1981 to January 1998).
TABLE 3–2
Medical Events Among Seven NASA Astronauts on Mir, March 14, 1995, through June 12, 1998.
TABLE 3–3
Medical Events and Recurrences Among Astronauts of All Nationalities on Mir, March 14, 1995, through June 12, 1998.
TABLE 3–4
Pharmacopoeia Usage During Mir Missions.
It is therefore important to look at the totality of the data from space missions and what has been learned from other extreme isolated environments on Earth (e.g., Antarctica and extended underwater submarine missions). These data relate to the type and incidence of medical-surgical and behavioral health events that occur in these environments and are needed to best gauge and plan for future needs during extended space travel before commencement of exploration-class space missions with astronaut crews.
Evidence Base from Extended-Duration Submarine Missions
Medical events during submarine missions are instructive as they occur in a confined, remote environment where there is limited diagnostic and therapeutic support. They occur in an atmosphere where potentially life-threatening or other severe medical illnesses can end a mission, in the sense that the submarine is required to interrupt or even abort its mission.
The U.S. Navy described the incidence of illnesses and injuries on 136 submarine patrols from January 1, 1997, through December 31, 1998. The numbers of acute encounters were related to the total number of person-days under way, with 2,044 acute encounters in 1.3 million person-days at sea, or 157 acute encounters per 100,000 person-days (Table 3–5). Stratified by illness and injury, illness accounted for 112.9 episodes per 100,000 person-days, with 70 percent able to maintain full duty; and accidents accounted for 37.2 episodes/100,000 person-days, with 55 percent able to maintain full duty (Thomas et al., 2000).
TABLE 3–5
Incidence of Health Disorders and Medical-Surgical Procedures During 136 Submarine Patrols.
A different perspective is obtained when the health disorders and medical-surgical procedures in Table 3–5 are compared with the reasons for medical evacuations from U.S. submarines (Table 3–6). A range of 1.9 to 2.3 medical evacuations per 1,000 person-months was reported for all submarines in the U.S. Atlantic Fleet from 1993 to 1996. A range of 1.8 to 2.6 evacuations per 1,000 person-months was reported for humane reasons (i.e., death or serious illness in the family) (Sack, 1998), suggesting that if these data are extrapolated to extended space travel or habitation, the psychosocial support needs may well be just as important as the medical needs in a long-duration space mission.
TABLE 3–6
Reasons for 332 Medical Evacuations from All Submarines, U.S. Atlantic Fleet, 1993 to 1996.
The medical reasons for submarine evacuations from 1993 to 1996 varied (Table 3–6). The largest number of conditions requiring medical evacuation are trauma and “other” (miscellaneous). It should be noted, however, that psychiatric reasons rank second in the specific categories. The “other” category most likely consists of large numbers of unrelated clinical conditions, further reinforcing the diversity of clinical conditions that can be expected to occur during a space mission. Factors such as astronaut age and medical prescreening would affect the incidence of medical emergencies among the members of the space crew, but since prescreening for most conditions cannot be done, it is possible that similar disorders and the proportions of those disorders that could occur among the members of a space crew would be similar to those that occur among individuals on submarine missions.
Tansey and colleagues (1979) reviewed health data from 885 Polaris submarine patrols from 1963 to 1973, for 4,410,000 person-days of submarine activity. They described 1,685 medical events that resulted in 6,460 duty days lost. Only events that resulted in the loss of at least 1 workday were reported. The events with the six highest rates of occurrence were, in descending order, trauma, gastrointestinal disease, respiratory infections, dermal disorders, infection, and genitourinary disorders. The spectrum of disorders was very broad and included cases of arrhythmia, paroxysmal superventricular tachycardia, infectious hepatitis, gastrointestinal hemorrhage, meningococcemia, paranoid schizophrenia, appendicitis, pilonidal abscess, perirectal abscess, ureteral calculi, testicular torsion, and crush injuries, further emphasizing that the scope of anticipated medical conditions on long-duration space missions will be very broad (Tansey et al., 1979).
The incidence of the types of illnesses observed during extended submarine missions is generally similar to the incidence encountered during spaceflights. NASA has used the incidence of medical events on submarines to estimate that there may be one major medical event requiring intervention of the type usually delivered by a medical practitioner during a future exploration-class mission of 3 years in length with five to seven astronauts (Billica, 2000; Flynn and Holland, 2000). Unfortunately, the nature of that event is unpredictable, so preparations must be prioritized and must still be made for a wide spectrum of problems.
Evidence Base from Antarctic Expeditions
The Australian National Antarctic Research Expeditions (ANARE) Health Register compiled 1,967 person-years of data from 1988 to 1997. It documents 5,103 illnesses and 3,910 injuries (Table 3–7). The distribution and variety are similar overall to those from spaceflight data.
TABLE 3–7
ANARE Health Register Illnesses in Antarctica from 1988 to 1997.
Seventeen Australians, moreover, have died in the Antarctic and subantarctic since 1947 (Taylor and Gormly, 1997; D.J.Lugg, ANARE, personal communication, August 24, 2000). Excluding those conditions peculiar to the Antarctic environment (drowning and exposure, n=5; outdoor injuries, n=5), seven nonpredictable deaths occurred in the Antarctic because of appendicitis (n=1), cerebral hemorrhage (n=1), acute myocardial infarction (n=2), carbon monoxide poisoning (n=1), perforated gastric ulcer (n =1), and burns (n=1). Each of these is a possible medical event on a spacecraft, indicating the wide variety of medical emergencies that can occur and that must be considered in planning for health care management in the extreme environment of extended-duration space travel or habitation beyond Earth.
Health Risk Assessment
Individuals differ in their susceptibilities to disease, vulnerabilities to environmental assaults, and abilities to recover from injury. Current potential methods of risk assessment and screening (Box 3–2) rely heavily on the identification of preclinical disease or conditions known to predispose an individual to illness. For example, certain abnormal lipid profiles are an identified risk factor for atherosclerosis, elevated blood pressure is an identified risk factor for stroke and heart disease, and osteoporosis is a risk factor for hip fracture.
BOX 3–2
Potential Methods of Risk Assessment and Screening. Physiological profiling. Physiological profiling consists of profiling of the central nervous system; cardiovascular system; pulmonary system; musculoskeletal system; eyes, ears, nose, and throat; gastrointestinal (more...)
As a result of the Human Genome Project, investigators are also identifying DNA sequences that correlate with an increased risk for a particular disease or syndrome, and the basis for this increased risk is being elucidated. The presence of DNA or RNA sequences indicative of a potential health risk as well as those indicative of a preferential pharmacodynamic or other response to treatment may be an integral part of the standard of care in the future. Breast cancer (Box 3–3) and colon cancer are two diseases for which there are well-established risk assessment and screening tools, as well as an increasing number of DNA sequences that indicate a propensity for an increased risk of development of the diseases. As such linkages become more prevalent for a wider variety of diseases, they will offer increased means for profiling and screening of individuals to decrease major medical and health risks (Box 3–1) and promote the health and safety of astronauts for long-duration space travel.
BOX 3–3
Breast Cancer as an Example of Risk Assessment in Space Medicine. The possibility that breast cancer can occur in a woman while on long-duration space travel exists. The development of breast cancer in a physician at a base in Antarctica in 1999 reinforces (more...)
While on a long-duration mission beyond Earth orbit the starting point for medical care will most often be a description of the chief complaint and a physical examination. The physical examination technique must be adapted to the microgravity environment, where the method of determination of internal organ location and other diagnostic methods differ widely from those used in terrestrial environments. The patient, examiner, and equipment must be stabilized for proper examination technique in microgravity. The examiner must learn adaptive movements to perform the abdominal examination properly. Auscultation of heart or bowel sounds in the noisy spacecraft environment is difficult, and stethoscopes need to be modified with this in mind by the cooperative work of engineers and clinicians. Harris and colleagues (1997) have reported a number of variations to physical examinations performed in a microgravity environment (Box 3–4).
BOX 3–4
“Normal” Findings on Physical Examination in Microgravity. Facial and periorbital edema Oily facial skin
The physical findings listed in Box 3–4 are for five males and two females during 8- and 10-day missions (Harris et al., 1997). Facial and periorbital edema are most evident during the first 3 days of flight but persist throughout the mission. Facial and periorbital edema, nasal congestion, and jugular venous distention occur because of fluid shifts to the head and torso because the loss of gravity eliminates hydrostatic pooling in the extremities. Thinning of the lower extremities is due to an approximately 40 percent reduction in interstitial fluid levels in the lower extremities (Baisch, 1993).
Auscultated bowel sounds diminish on the 2nd through 5th days of the flight. Investigators note that absent bowel sounds were strongly associated with the development of motion sickness. The diaphragm is elevated by two intercostal spaces and appears to remain elevated during spaceflight. Normal variations in the positions of thoracic and abdominal viscera also occur in microgravity. It is important to recognize these variations because they could affect the interpretation of physical findings and the performance of invasive or diagnostic procedures. For example, failure to recognize a “normal” elevation of a hemidiaphragm in microgravity could result in improper placement of a thoracostomy tube for the treatment of pneumothorax, or alterations of peritoneal signs in microgravity could change the signs and symptoms of appendicitis. Pelvic examination has not been reported in microgravity, but a pelvic examination in microgravity may lead to other variations in normal findings.
Health Care Opportunity 1. Expanding, validating, and standardizing a modified physical examination, the microgravity examination technique, and including a technique for pelvic examination for use in microgravity.
Nutrition
Food quality and variety affect crew attitudes and overall performance. Nutritional concerns include sufficient caloric intake, nutritional density, food palatability, varied menus, and cultural variations in preferred foods. It is critical that the food supply be adequate, safe, and reliable and that it remains so throughout the mission. Inadequate food and water supplies or contamination or loss of the supplies, particularly since much will have to be generated from recycled materials during the mission, will result in termination of the mission or the loss of life.
Additionally, one must consider methods that can be used to ensure the adequacy of caloric intakes to prevent the ongoing loss of body mass. On the basis of current experience (Lane and Schoeller, 2000), a degree of malnutrition is anticipated in nearly all astronauts during space travel without the use of countermeasures and is expected in even 61 to 94 percent of astronauts with the use of countermeasures. Just as the effects of zero gravity or microgravity on the pharmacodynamics and metabolism of pharmaceuticals are unknown (see below), absorption of nutrients may be problematic, leading to unexpected deficiencies that result in the need for supplementation. Nutritional requirements have been found to be similar for short-duration space missions and life in normal terrestrial environments, but energy intake is decreased during space travel, so most astronauts lose body mass, including 1 to 2 liters of body water. A monitored mandatory caloric intake may be considered, as may monitoring of nutritional status in more standard ways, for example, via measurement of arm circumference. One must consider that inadequate intakes of micronutrients or vitamins would adversely affect the entire crew, making identification of all required nutrients and their absorption or elimination pharmacodynamics a priority.
Pharmacodynamics and Pharmaco*kinetics
Pharmacodynamics deals with the interactions of drugs and living systems, whereas pharmaco*kinetics is the study of the absorption, distribution, and metabolism-utilization of pharmacologicals. The microgravity environment can be expected to affect the pharmacodynamics and pharmaco*kinetics of all drugs, yet little clinical research has been performed in these areas. Clinical research on the pharmaco*kinetics and pharmacodynamics of drugs in space is limited by the small numbers of participants, limited opportunities for clinical study (i.e., few space missions), and the lack of a reasonable terrestrial proxy for microgravity in which to conduct pharmacological studies.
Drugs administered in microgravity may not have the anticipated local, regional, or systemic effects and may manifest different adverse effect profiles in space compared with those observed on Earth. For example, a case series of 21 crewmembers given 25 to 50 mg of promethazine intramuscularly reported only a 5 percent sedation rate, whereas the sedation rate was 60 to 73 percent in studies conducted in standard Earth gravity (Bagian and Ward, 1994). This phenomenon needs to be closely studied for several reasons. The decreased effectiveness of a sedative could be due to SMS or the sheer excitement associated with the space mission. There is also some evidence that receptor interactions may be altered under conditions of hypovolemia (Derendorf, 1994). The bioavailabilities of oral drugs given in space can be affected by gastric emptying, gastric motility, and hepatic blood flow (Tietze and Putcha, 1994). Bed rest, which is sometimes used to partially simulate the effects of microgravity, is reported to delay the absorption of common oral medications, and drug distribution is affected by the redistribution of fluids from the lower body to the head and torso in space (Tietze and Putcha, 1994). The bioavailabilities of oral scopolamine and acetaminophen are altered in flight and may be affected by SMS and the particular day of the mission (Cintron et al., 1987; Tietze and Putcha, 1994). Drug binding by protein and tissue is presumably altered in microgravity because of muscle and tissue atrophy, the latter of which has been documented upon the return from a space mission (Edgerton et al., 1995).
The frequency of use of medications during spaceflight (Putcha et al., 1999) is such that targeted research into the pharmaco*kinetics of various routes of drug administration (oral, intranasal, transcutaneous, subcutaneous, intramuscular, intravenous) is required, with the goal of determining the predictability of the effect and efficacy. The resources for the medical crew on the spacecraft for a long-duration mission should include a compendium of the indications and adverse effects of the pharmaceuticals on board and their anticipated kinetic changes, such as bioavailabilities and half-lives, that are predicted for the microgravity environment.
Health Care Opportunity 2. Developing an easily accessible database for medications on the spacecraft, including dosage, indications, adverse effects, and anticipated changes in the pharmaco*kinetic profile in microgravity.
Environmental and Occupational Health
Environmental Hazards
The environmental and occupational health of astronauts will be important issues for long-duration space travel. Missions beyond Earth orbit will dictate a unique set of requirements to protect crewmembers from hazards such as chemical contamination, volatile organic compounds, particulate matter, and microorganisms. Crewmembers may confront the challenge of living in a noisy environment, where vibration is also a potential hazard to human health and to sensitive experiments (Koros, 1991a; Koros et al., 1993). Crewmembers will work in an environment of artificial light, which could adversely affect their performance (Czeisler et al., 1990; Barger and Czeisler, 2000). Missions may include scheduled and unscheduled EVAs, which will be physically challenging and conducted by humans who may be physiologically compromised. Finally, there is the question of the deleterious effects of exposure to primary and secondary radiation (Johnston and Dietlein, 1977; Nicogossian and Parker, 1982; SSB and NRC, 2000). Operational requirements for EVAs will present significant physical challenges for crews. For the ISS, an estimated total of 1,100 hours will be required to carry out planned construction and maintenance. At a high inclination of orbit of 51.6 degrees, such activity will expose the crew to high-altitude radiation as well as temperature extremes, micrometeors, and physical injuries.
Decompression Sickness
Decompression sickness (DCS) represents another significant potential threat to astronauts on long-duration missions. Should emergency EVAs or sudden unexpected decompression of the spacecraft occur, DCS might ensue. NASA is well aware of these problems and is actively pursuing solutions to these issues, particularly so that it can effectively and safely finish the construction of the ISS. The committee believes that NASA's efforts in these areas should continue by including investigations of the possible relationship between a patent foramen ovale and DCS. Careful integration of engineering issues and habitability should take place in planning for EVAs as well as emergency contingencies for EVAs. Finally, the committee is confident that advances in materials will allow the inclusion of a lightweight, low-volume recompression chamber in the manifest for missions beyond Earth orbit, if it is considered necessary (i.e., if a pressure suit with an internal pressure greater than that in present suits has not been developed).
Internal Environment
During long-duration space missions, the internal environment of the spacecraft will offer its own unique challenges, ranging from chemical and microbial contamination to noise and vibration. Like any confined habitat there will be chemical and physical toxic elements. On a spacecraft, however, the crew has few opportunities to replace or recondition a toxic environment.
Exposure to Toxic Chemicals Environmental hazards come from several sources. Propulsion propellant (Freon, hydrazines, nitrogen dioxide) leaks into the spacecraft interior can be toxic in small quantities (Tansey et al., 1979). The spacecraft crew can be further exposed if propulsion chemicals enter the spacecraft through the air lock or if they crystallize on EVA suits. Accidental chemical releases during space shuttle flights have also been reported. The dominant source appears to be heat degradation of electronic devices. Thermodegradation of spacecraft polymers with the production of formaldehyde and ammonia adds to the environmental hazard (Nicogossian et al., 1994). There were nine incidents from STS-35 to STS-55, with four resulting from burning electrical wiring. Subsequent analysis found benzene, acetaldehyde, dimethyl sulfides, and other compounds in the space shuttle crew compartment atmosphere (James et al., 1994; Pierson et al., 1999).
The experience on Mir provided a glimpse of the potential risks of contamination from the very systems designed to protect the health of the crew. The Freon in cooling loops presented a significant hazard to the crew when the Freon was released. Oxygen canisters in Mir presented a life-threatening problem for the crew when they caught fire (Burrough, 1998; Linenger, 2000). There was danger not only from fire but also from the smoke and particulate matter released from the canisters themselves.
Data collected during the Extended-Duration Orbiter Medical Project's evaluation of volatile organic compounds in the cabin atmosphere indicated that levels were below maximum allowable concentration (SMAC) limits in the spacecraft. It was noted that most pollutants reach a state of equilibrium within the first 3 to 4 days of a mission; however, the exceptions are hydrogen, methane, dichloromethane, and formaldehyde. Dichloromethane and formaldehyde are of concern because both have significant toxic properties. Missions of 2 weeks' duration measured dichloromethane levels of 0.79 milligrams per cubic meter (mg/m3; 30-day SMAC of 20 mg/m3) and formaldehyde levels as high as 0.08 mg/m3 (30-day SMAC of 0.05 mg/m3) (Pierson et al., 1999).
Exposure to hazardous materials during space travel could result in multiple casualties with serious injuries, burns, or smoke inhalation that would soon outstrip the finite resources available on the spacecraft. Planning to minimize exposure of the crew includes the identification of potential hazards, recognition that a hazardous material is responsible for acute signs and symptoms, identification of the agent(s) involved, retrieval and review of information regarding toxicity and secondary contamination, protection of unexposed personnel from primary and secondary contamination, methods for triage and decontamination of the exposed individual(s), and treatment of the injured and exposed individuals. Available resources should be modified as the technology advances and should be easily available to the crew (ATSDR, 1991; Sidell et al., 1991). Methods for continuous surveillance for toxic contaminants should be in place, using Earth analog models (ATSDR, 1997).
Health Care Opportunity 3. Developing an easily accessible hazardous materials manual for space travel to aid in the surveillance, detection, decontamination, and treatment of chemical exposures.
The concentrations of the particulate pollutants detected in the space shuttle ranged from 35 to 56 mg/m3, with the majority of them being greater than 100 micrometers in diameter. Most particles did not settle out of the atmosphere during the mission. Most were organic in nature and were most likely generated by crewmembers (Pierson et al., 1999).
Health Care Opportunity 4. Monitoring and quantifying particulates on a continuing basis.
Microbial Contamination The quantification of airborne bacteria and fungi indicates that the levels of bacteria increase moderately with the duration of the mission and that the levels of fungi decrease with the duration of the mission. The levels of bacteria range from a few hundred to 1,000 colony-forming units per cubic meter (CFU/m3) of air during longer missions. Fifteen species of bacteria were recovered from samples collected during space missions. Staphylococcus, Micrococcus, Enterobacter, and Bacillus species were found on 85 percent of the missions; and Staphylococcus aureus was recovered during 57 percent of the missions (Nicogossian and Parker, 1982).
Fungi tended to be present at a few hundred CFU/m3 early in the missions, but their quantities dropped to undetectable levels toward the ends of the missions. Nevertheless, low levels of Aspergillus and Penicillium species are found during greater than 60 percent of the missions (Nicogossian and Parker, 1982; Mehta et al., 1996).
The essential questions are as follows: How transmissible are these organisms? How much mixing of flora occurs between and among crewmembers? Is bacterial or fungal overgrowth an issue for long-duration space travel? Lastly, how does the radiation environment affect the growth of microorganisms and their toxicities to humans?
Health Care Opportunity 5. Examining the capability of microbial identification, control, and treatment during space travel.
Noise In both the U.S. and the Russian space programs, noise has been a major problem. Spacecraft noise levels disrupt sleep, increase stress and tension, and can result in temporary or even permanent hearing loss. The environmental control system, system avionics, and payload experiments generate most of the noise. The design limits of most work environments range from 63 to 68 decibels (dBA). The noise levels on a number of space missions has exceeded this baseline limit, exposing the crew to noise levels far greater than normal terrestrial noise levels. The maximum permissible continuous exposure level in a work environment is 90 dBA for an 8-hour period, according to the Occupational Safety and Health Administration. Early in the life of the ISS it was about 75 dBA. In a spacecraft, the environmental noise level is steady, and it continues for months. This will certainly have a deleterious affect on astronauts' hearing (Koros, 1991b; Koros et al., 1993), and it may affect astronauts' concentration and behavior as well.
Health Care Opportunity 6. Developing methods for noise cancellation or reduction.
Ergonomic Issues Because the human body has evolved on Earth in the presence of Earth's gravity astronauts are vulnerable to ergonomic problems in microgravity. During a space mission, crewmembers try to maintain a neutral body posture, wherein the shoulders, arms, hips, and legs are flexed and in a relaxed position. Working on an experiment such as one in a glove box, however, requires the crewmember to work against the natural tendency of the body to assume this posture. This increases fatigue, decreases performance, and predisposes crewmembers to injury (Mount and Foley, 1999).
Health Care Opportunity 7. Standardizing ergonomic practices on the basis of the human body's response to the microgravity environment.
External Environment
Radiation Much is known about the radiation environment of low Earth orbit; little, however, is known about the radiation environment of high Earth orbit and beyond. The ISS will be exposed to primary ionizing radiation and high-energy particle radiation from solar and galactic sources (SSB and NRC, 2000a). Exposure to secondary radiation—that is, radiation emitted from spacecraft metals and other materials following collision of their nuclei with high-energy solar or galactic particles penetrating the spacecraft shell—may also be a problem. In low Earth orbit, a band of atmospheric radiation, known as the Van Allen belts, is concentrated over the South Atlantic, hence the term South Atlantic Anomaly. An orbiting spacecraft will spend only 2 to 5 percent of its time in this region, but astronauts receive more than half of their total radiation doses during this period.
Most penetrating radiation from the Sun results from solar particle events (SPEs) and mostly consists of protons generated by solar storms. The Earth's geomagnetic field shields against solar particle events up to 6,370 kilometers above the Earth (Letaw et al., 1987, 1988). Recent reports note that construction of the ISS will take place during a period of maximum solar activity, when the probability of encountering SPEs and Earth-trapped radiation is high. During periods of intense solar activity, solar winds result in elevated intensities of energetic electrons. These are known as known as highly radioactive events. Galactic cosmic rays make up about a third of the radiation in space and produce a continuous low-level form of radiation. Protons of only 10 million electron volts (MeV) of energy can penetrate a space suit, and 25- to 30-MeV protons can penetrate the space shuttle (Lemaire et al., 1996). Beyond Earth orbit, the issue of radiation exposure presents a major challenge for NASA as the quantities of solar and galactic radiation and the potential for exposure increase.
Health Care Opportunity 8. Developing methods to measure human solar and cosmic radiation exposures and the means to prevent or mitigate their effects.
HEALTH CARE PRACTICE OPPORTUNITIES
Cardiovascular Care
Cardiovascular integrity is essential to the health and well-being of astronauts on long-duration space missions, but there is no experience with the delivery of cardiovascular care on such missions. Therefore, the information and recommendations presented here are derived from the few published data on cardiovascular complications incurred during the Mercury, Gemini, Apollo, and Skylab missions (SSB and NRC, 1998c; Charles et al., 1999) and from general principles of cardiovascular care on Earth (Braunwald, 1999).
Standards for the initial screening of astronauts, follow-up annual physical requirements, and causes of rejection are listed in NASA's Astronaut Medical Evaluation Requirements Document (NASA, 1998a). Although there are provisions for waivers, it is reasonable to assume that selected crewmembers are at low risk for the development of cardiac problems. This is important, because it will be extremely difficult to treat moderate to severe cardiovascular complications during a long-duration space mission. Space limitations will preclude an extensive pharmacy or medical procedure unit, and no individual with expertise in cardiovascular system-related procedures may be on board to handle cardiovascular complications.
Some of the cardiovascular symptoms and abnormalities that astronauts may present with during a long-duration space mission include high blood pressure with or without symptoms; atrial and ventricular premature beats; atrial arrhythmias, such as atrial fibrillation, atrial flutter, and supraventricular tachycardia; sustained and nonsustained ventricular fibrillation; chest pain, ischemic and nonischemic; shortness of breath, cardiac and noncardiac; orthostatic hypotension; syncope; vasovagal and other cardioneurogenic responses; and edema, cardiac and noncardiac. A strategy must be in place to deal with these on a risk-assessed priority basis and with the possible occurrence of myocardial infarction, whose incidence may increase with the generally increasing age of astronauts at the start of space missions and the extended lengths of missions beyond Earth orbit.
Physiological adaptation to planetary gravity after long-term exposure to microgravity may take several days to weeks, with considerable individual variability. Symptoms from adaptive conditions such as orthostatic hypotension, whether on the Moon or Mars or after the return to Earth, should be treated as needed, with the understanding that normal physiological regulatory mechanisms will take over, allowing physiological function to return to normal.
Health Care Opportunity 9. Providing a thorough cardiovascular evaluation similar to the premission evaluation at the cessation of space travel to provide useful data as part of the continuum of astronaut care and to aid in establishing an evidence base for cardiovascular disorders during space travel.
Dental Care
In 1978, Soviet cosmonaut Yuriy Romanenko experienced a toothache during a 96-day flight of Salyut 6. As his problem worsened, Romanenko gulped painkillers and crewmembers pleaded for help from the ground. The Soviet space program had no contingency plans for dental emergencies; the advice from controllers was “take a mouthwash and keep warm.” Romanenko, “his eyes literally rolling with pain” (Wheatcroft, 1989, p. 7), suffered for 2 weeks before Salyut 6 touched down on schedule. His ordeal was the subject of a televised interview in the Soviet Union, as well as published accounts in Russian and U.S. space and dental literature (Wheatcroft, 1989). It also focused attention, including that of NASA, on the need to address the possibility of debilitating dental emergencies in space.
In April 2000, the IOM Committee on Creating a Vision for Space Medicine During Travel Beyond Earth Orbit held a public workshop entitled Space Dentistry: Maintaining Astronauts' Oral Health on Long Missions (see Appendix A). Presentations from invited experts, as well as other data and information reviewed by the committee, suggest that dental problems need not be a major health care issue for astronauts on long-duration missions. This optimistic outlook assumes appropriate premission dental screening and excellent preventive care, as well as the ability to provide in-flight prophylaxis and restorative treatment as needed. A review of advances in preventive dentistry (Box 3–5) led one workshop presenter to predict that by 2020 NASA may be able to select the first Mars crew from a pool of cariesfree astronauts (Mandel, 2000).
BOX 3–5
Advances in Preventive Dentistry. A three-part preventive strategy, aggressively pursued by dental researchers and practitioners since 1971, may mean a caries-free pool of astronaut candidates for the first mission to Mars with humans. The strategy consisted (more...)
Still, good teeth and a history of preventive care cannot guarantee that no caries will develop in anyone over the course of a 3-year mission. Some factors that could contribute to the development of tooth and gum disease include changes in bacterial flora in the mouth, inattention to good dental hygiene, changes in food consistency because of the consumption of dehydrated space meals, and lack of foods with natural gingival cleansing properties. For these reasons, the crew should be prepared to use restorative techniques and materials in microgravity, and NASA should support the development of new restorative techniques and materials that can be used in microgravity.
The committee's workshop on oral health included a presentation on atraumatic restorative treatment (ART), which may represent one potentially useful approach to the management of dental lesions in space. It is a conservative approach to caries management, in which carious tooth tissue is removed with hand instruments instead of electric rotating handpieces. The cavity is restored (filled) with an adhesive restorative material such as glass-ionomer. The result is a sealed restoration (Estupiñán-Day, 2000).
The reported advantages of ART include little or no pain, reduced need for local anesthesia, minimal trauma to the tooth, conservation of healthy tissue, and simplified infection control. Moreover, ART can be performed by individuals who are not dentists. The technique was originally devised for use in developing countries and disadvantaged communities where access to high-quality, definitive dental care is problematic. The Pan American Health Organization is evaluating the longevity of glass-ionomer restorations under various conditions (Estupiñán-Day, 2000). How they might perform in microgravity is not known, however.
The committee has reviewed dental health data from long-term missions in analog environments. Such data may be of limited predictive value, however. ANARE reported on the dental health experiences of 64 men over a 42-month period. There were 73 reported dental events, which accounted for 8.80 percent of all medical events (Fletcher, 1983). All the men had been prescreened and found to be “dentally fit.” The preexpedition screening examinations lacked uniform criteria, however, precluding useful comparisons of that population with other populations. Moreover, the examining dentists did not have the advantage of today's tools for early detection of developing caries.
The committee has learned that NASA is developing new, prevention-oriented dental protocols for space shuttle missions and the ISS and that these are undergoing internal agency review (M.Hodapp, NASA, personal communication, April 10, 2000).
An important question remains unanswered: does exposure to microgravity result in the loss of bone mineral density in alveolar bone? To date, no human data bearing on this question have been reported. The question arises because of the well-documented loss of bone mineral density in the weight-bearing bones. Also, although no human data exist in the current database, microgravity-induced decreases in bone density might also contribute to tooth and gum disease.
Health Care Opportunity 10. Developing a program for instruction in basic dental prophylaxis, the treatment of common dental emergenciessuch as gingivitis, tooth fracture, dental trauma, caries, and dental abscesses; and tooth extractions.
Endocrine Function
Changes in endocrine function in microgravity have been reported, but the clinical significance and effects on adaptation or maladaptation need more research to determine if they have clinical importance during long-duration space missions. The number of subjects is small and the data are sometimes conflicting. The polar tri-iodothyronine (T3) syndrome has been described in persons living for extended periods in Antarctica. It is characterized by baseline elevations of thyroid-stimulating hormone (TSH) levels, exaggeration of increases in TSH levels in response to a challenge with thyroid-releasing hormone, and more rapid production and clearance of T3 and thyroxin but normal levels of both in serum (Reed et al., 1990).
Thyroid axis kinetics should be further studied during space missions (Lovejoy et al., 1999), since models of prolonged bed rest used as analogs for conditions in space have also demonstrated changes in T3 levels and the effects of T3 on nitrogen balance and catabolism. Little has been reported on adrenal function, but its association with sleep disturbances should be investigated, as circadian fluctuations in steroid levels have been well described on Earth (Birketvedt et al., 1999).
Testosterone levels fell in both humans and rats during space missions and on their return to Earth, and studies with rats did not show changes in spermatogenesis (Plakhuta-Plakutina, 1977). There have been no reports that astronauts have had difficulty with reproduction, but no effects from long-duration space mission have been studied (Tigranjan et al., 1982; Deaver et al., 1992).
The metabolic stress syndrome is of great importance to space medicine, and cortisol production via adrenocorticotropic hormone production by the pituitary gland has been used as a marker. Cortisol levels increase during the first 2 days of a space mission, as do the rates of protein turnover and acute-phase protein synthesis (Stein et al., 1996), documenting the stress of launch and entry into orbit. Caution must be exercised in interpreting data on endocrine function for humans in space because of the large variations in hormone levels among humans, the problems of collection and storage of samples, and the variabilities of assays.
Gastrointestinal Issues
Gastrointestinal problems account for 8 percent of the recorded medical events on space shuttle missions (Billica, 2000). The incidence is 0.52 per person per 14 days in the space environment. Experience in analog environments suggests that the incidence of gastrointestinal problems is much lower, being only 0.01 per person per year. These data suggest that the motility problems identified during space shuttle missions can be attributed to the effects of the microgravity environment. Many astronauts who develop symptoms of SMS also seem to develop a transient ileus, diagnosed by an absence of bowel sounds. Although motility may remain decreased throughout the space mission and the bacterial population may change, the etiologies are unclear and data from short-duration space missions do not suggest that these lead to significant medical problems.
Some spacecraft crewmembers have experienced constipation during missions. This may be related to physiological alterations in the bowel induced by the microgravity environment, but the etiology remains unclear. Adequate hydration throughout long-duration space missions should prevent constipation. Some crewmembers have experienced diarrhea during the later parts of missions. The etiology is also unknown, but it may simply be related to overmedication for constipation. Diarrhea in the space environment presents several problems, including constant use of the Waste Containment System and dehydration, which may exacerbate landing orthostasis. Over-the-counter medications (Imodium and Pepto Bismol) for oral ingestion are available in the Shuttle Orbiter Medical Systems (SOMS) kit. Vigorous hydration with oral or intravenous fluids is recommended. Episodes of diarrhea during long-duration space missions can be treated similarly.
Gastrointestinal problems are largely prevented through optimal premission screening, and most residual symptomatic problems can be treated in a manner similar to that used on the ground. However, three problems to which the gastrointestinal tract is particularly prone are infection, malignancy, and inflammation.
Obstruction of the gallbladder or appendix with calculi and subsequent infection can be lethal without operative intervention. Consideration must be given to prophylactic cholecystectomy and prophylactic appendectomy before long-duration space missions. Although the procedures can be performed today with a minimum of morbidity and a low likelihood of any late postoperative complications, it is not clear whether prophylactic removal is warranted. A careful risk-benefit calculation should be performed with future data. Population-based data to determine how rapidly gallstones can form in an ultrasound-negative patient may be one useful methodology for determination of the advisability of prophylactic cholecystectomy.
Malignancy of the gastrointestinal tract can be ruled out through endoscopy. On the basis of current practice it would appear prudent that astronauts (especially those over age 50) being sent on long-duration space missions have a recent colonoscopy (with or without a concomitant air-contrast barium enema). Consideration might also be given to the screening of candidates by esophagogastroduodenoscopy before long-duration space travel for esophageal, stomach, and duodenal problems.
Inflammation of the pancreas, pancreatitis, is a life-threatening disease even with the best medical care. The many etiologies of pancreatitis include gallstones and specific medications. The use of pharmacological agents that continue to be developed and that are recognized to be associated with the development of pancreatitis should be avoided.
Given the technology available today and in the foreseeable future, it is unlikely that surgical procedures on the gastrointestinal tract (except for percutaneous drainage of an abscess, etc.) will be performed on long-duration missions beyond Earth orbit. At this time development of specific countermeasures related to the gastrointestinal tract does not appear to be required before long-duration space travel.
Gynecological Health Issues
Although the likelihood may be small that a gynecological condition that requires surgical intervention will occur during space travel, the occurrence of such a condition would present special problems. Therefore, as with other medical conditions, attention must be directed toward prevention, conversion of surgical conditions to medically treatable conditions, and, where necessary, the ability to do surgery. For example, pregnancy and its inherent complications, including spontaneous abortion, ectopic pregnancy, and abnormal bleeding, can be prevented with appropriate contraception. Sexually transmitted diseases and their complications will be able to be prevented or treated. Oral contraceptives can help the abnormal bleeding associated with anovulation and the development of functional cysts of the ovary. Surgical conditions, such as uterine myoma, endometriosis, and dysfunctional uterine bleeding, can now be treated medically.
Regardless of these measures, there will be some conditions, such as ovarian neoplasm, adnexal torsion, or bleeding, which will require surgery. Although elective laparoscopic appendectomy before prolonged space missions has been given some consideration, surgical prevention of adnexal abnormalities is not a consideration except perhaps for postmenopausal astronauts, and the relative risk and treatment means and priority must continue to be evaluated.
Contraception and Hormone Replacement Therapy
Because of the absolute preclusion of pregnancy while in the space program, many female astronauts have chosen contraceptive methods that are known to be very effective. These include intrauterine devices, implants, and oral contraceptives made up of various combinations of hormones, all of which have been continued during space travel (Jennings and Baker, 2000). Although an intrauterine device is an effective contraceptive, for long-duration space missions, the added noncontraceptive benefits of hormonal contraceptive agents may make them preferable. For example, hormonal agents reduce the volume of menstrual flow. Although most women on oral contraceptives have a withdrawal cycle every 28 days, it is possible to extend the cycle from every 28 days to several months. With some hormonal agents, complete cessation of bleeding for the duration of the mission may be possible. Oral contraceptives frequently relieve the dysmenorrhea associated with menses. The ovaries of women on oral contraceptives are less likely to form cysts, which may undergo torsion or other complications. Not only are oral contraceptives an effective way to manage dysfunctional uterine bleeding or bleeding associated with anovulation, should that occur in space, oral contraceptives are also effective treatment for the estrogen deprivation associated with hypogonadotropic hypogonadism and prevention of the bone mineral density loss associated with this condition.
Hormone replacement therapy is known to be effective in preventing osteoporosis among women of certain ages on Earth. During space travel, hormone replacement therapy, as on Earth, will be of importance in preventing calcium loss in postmenopausal crewmembers.
Health Care Opportunity 11. Studying the bioavailability and pharmacological function of exogenous hormone therapy during space travel and, as new medical therapies for gynecological surgical conditions evolve, testing of these therapies for use during space travel.
Hematology, Immunology, and Microbiology
Decreased red blood cell mass during space missions has been recognized since 1977 (Johnson et al., 1977; Leach and Johnson, 1984), but there is no resulting impairment from this “anemia.” The documented fall in erythropoietin levels and the fall in the numbers of reticulocytes indicate that this results from diminished production, not increased cellular destruction (Alfrey et al., 1996). However, because of the diminution of the plasma volume early in the flight, the measured hematocrit levels and red blood cell counts did not fall during flight but were noted after the return to Earth because of the more rapid restoration of plasma volume than the level of red blood cell production. Erythropoietin levels returned to normal in 1 to 2 weeks after landing. In 1990, Koury and Bondurant (1990) hypothesized that erythropoietin prevents programmed cell death in erythropoid progenitor cells, thereby adding significantly to general medical knowledge through research conducted in space. Anemia could become a clinical problem during long-duration space travel, and erythropoietin administration is being evaluated as a countermeasure.
Altered cell-mediated immunity has been reported in a variety of analog environments, including the Antarctic (Tingate et al., 1997) and space (Kimzey et al., 1975, 1977). Escherichia coli and Staphylococcus aureus isolates have also been shown to become more resistant to selected antibiotics during space travel (Lapchine et al., 1986). Although the clinical significance of these alterations has not been determined, the effects on skin and wound infections and wound healing during long-duration space missions could become clinically important.
Preflight isolation techniques for spaceflight crewmembers are reported to have decreased the infection rate for the 3 weeks preflight from about 50 percent to only occasional events (Ferguson, 1977; Ferguson et al., 1977). Gingivitis and skin furuncles are now the primary preflight infections reported (Taylor and Gormly, 1997). Increased shedding of herpesvirus and expansion of Epstein-Barr virus-infected B cells have been reported in the Antarctic environment (Tingate et al., 1997; Lugg and Shepanek, 1999) and in astronauts (Payne et al., 1999). The bases for the divergent changes are not understood. They do, however, indicate the importance of immunology and microbiology to healthy human physiology during space travel and the need for further research in this area of space medicine.
Health Care Opportunity 12. Performing clinical studies on anemia, immunity, wound infection, and wound healing as part of every space mission.
Mental Health Issues
The transition to long-duration space missions will require greater emphasis on ways to prevent and successfully manage an array of challenges to the cognitive capacities and emotional stabilities of astronauts who will find themselves in an isolated, confined, and hazardous environment. They will be devoid of much of what supports their emotional well-being on Earth and will need to develop and maintain new coping strategies appropriate to the unique environment of space beyond Earth orbit.
Current data on the psychiatric sequelae of long stays in surly environments come primarily from studies of military personnel on submarine duty, Antarctic field scientists, and Biosphere inhabitants (Billica, 2000), as well as more limited experience on the Russian space station Mir. These data suggest that the incidence of discernible psychiatric symptomatologies, including depression, anxiety, substance abuse, and psychosis, ranges from 3 to 13 percent per person per year, depending on the setting (see Tables 3–2 to 3–7). Transposed to a six- or seven-member space crew on a 3-year mission, the likelihood that psychiatric problems will arise on such an expedition is not insignificant but is less than 54 percent—(3 percent/year)×(six astronauts/year)×(a 3-year mission)—per astronaut during a 3-year mission among a space crew when one extrapolates from the crude available data on behavioral disturbances in space.
Such problems can range from simple boredom and fatigue to acute stress reactions, profound depression, and overt psychosis. Some mental health problems may become more likely over time as the cumulative effects of environmental and interpersonal stressors are magnified by the extended duration of the mission.
The NASA Experience to Date
Almost all of NASA's behavioral medicine experience with space travelers thus far has been with flights of relatively short duration (i.e., 2 to 3 weeks), where emergent signs and symptoms have included evidence of stress, anxiety, diminished concentration, depressed mood, malaise, and fatigue. These problems have been identified in less than 2 percent of astronauts, and their effects on individual and crew performance have reportedly been negligible (Flynn and Holland, 2000). As a result, with the exception of the astronaut selection process, the level of clinical and research interest in mental health problems that may affect human performance during space missions has been relatively low. At the same time, there is growing awareness that such problems could prove to be major impediments to the successful conduct of longer-duration missions.
Mental Health Aspects of Extended-Duration Spaceflight
Little is known about the psychological capacity of humans to withstand the stresses of long-duration space travel, but what is known (e.g., from the experience on Mir) is ominous. Experience with extended-duration flights, defined as flights longer than 100 days (about 1/10 the anticipated duration of a mission to Mars), suggests that boredom, fatigue, and circadian rhythm and sleep disturbances, coupled with the exacting human performance requirements of such missions, constitute risk factors for the development of depressive syndromes of various severities, anxiety and irritability, and at times, dysfunctional interpersonal relationships, either within the spacecraft or between astronauts and ground personnel. On missions beyond Earth orbit, in which spacecraft crews will be isolated and confined to a relatively small living space and in which medical evacuation will not be an option, the development of these and other mental health problems may exert cumulative detrimental effects both on individual astronauts and on their fellow crewmembers sufficient to jeopardize the mission.
Meeting this challenge will require a reassessment of the mental health needs of astronauts in the context of NASA's overall health care program. Areas of renewed emphasis and support should include premission psychiatric evaluation; intramission psychiatric support and treatment, including the possibility that acute interventions may be required, such as in a major psychotic break, possibly with the use of forcible restraint and psychoactive drugs; and a program of postmission assessment, follow-up, and intervention where appropriate, as discussed in Chapter 5. For international efforts involving multinational crews, language and cultural differences, along with different approaches to diagnosis and treatment, will complicate these tasks. Accordingly, the United States and its partners in space must move toward the development of a health care system for astronauts (see Chapter 7) with a common language, common diagnostic criteria, and common standards of care. In so doing, some suggested areas of emphasis (see also Chapter 5) are as defined below.
Health Care Opportunity 13. Developing methods for the identification and management of mood disorders and suicidal or homicidal ideation and developing protocols for the management of violent behavior, including crisis intervention, pharmacological restraint, and physical restraint.
Premission Screening and Selection
The issue of crew selection needs to be rethought in the context of longduration space missions. As detailed in Chapter 5, valid and reliable psychiatric screening instruments should be further developed, tested, and refined. The process of astronaut selection into or out of the program must include efforts to predict crewmembers' responses to the anticipated stresses of long-duration space missions on the basis of data derived from studies carried out on the ISS as well as in analog environments. Assessment of interpersonal, leadership, and followership skills, problem-solving capabilities, and emotional stability under conditions of extended isolation are some of the areas appropriate for future research. In addition, personal and family history data coupled with laboratory testing may identify individuals at increased risk for mental disorders (e.g., depression) that may emerge over the course of long-duration space travel and may be included in the database on which crew selection and flight assignments are based.
The development of more sophisticated selection and deselection criteria is a first step, to be followed by specific individual and group training in behavioral self-assessment and the self-administration of countermeasures designed for a range of anticipated health problems. Training individuals to work successfully within a small group and to engage in productive and collaborative problem solving with ground crews should be part of this process. The relative value of such training and the efficiency of specific countermeasures should also be assessed in the context of a well-designed program of behavioral and psychosocial research. Such studies should be carried out in the course of extended stays in space and in appropriate simulated or analog environments. Finally, the selection and training of the members of ground crews who will support and direct long-duration missions should be parallel to and integrated with the selection and training of the astronauts.
Dealing with Intramission Mental Health Problems
As mental health problems arise, some will respond to countermeasures designed and tested during premission training, whereas others will require the intervention of crewmembers or ground personnel. In this context, there will need to be clearly defined duties and responsibilities for such personnel, as well as appropriate training. Evidence-based clinical protocols and treatment algorithms that are specifically adapted for the space environment will need to be developed and tested.
In addition to the availability of psychiatric expertise on the ground, the preventive approach to in-mission mental health care should include the prior development of supportive and therapeutic relationships between mental health clinicians, crewmembers, and crewmember families. In this context, finding ways of ameliorating the effects of prolonged communication delays between space and the ground should be a research priority. An onboard formulary that anticipates the range of psychiatric problems that may or will arise is also essential, as is research on the pharmaco*kinetics of current and future psychotropic medications in microgravity environments.
Technology offers promise for maintaining behavioral health when professional assistance is millions of miles away. One type of countermeasure is software designed to self-diagnose and relieve emotional symptoms before they become a psychiatric condition. The first of most famous of these was ELIZA (Weizenbaum, 1966, 1979). It mimicked a nondirective therapeutic dialogue. The second generation of algorithm-driven software packages is now available. One example is the Therapeutic Learning Program (Gould, 1989). Software-guided therapy, when coupled initially with individual training and clinical oversight, has produced relief of symptoms ranging from headaches to anxiety and depression. Although, for the most part, the gains are nowhere near those obtained from individual treatment, the benefits are far superior to no treatment at all. An excellent and balanced review of this subject is contained in Massachusetts Institute of Technology Professor Sherry Turkel's book, Life on the Screen: Identity in the Age of the Internet (Turkel, 1995). It is likely that later versions of these methods will be far more effective and could be adapted, with adequate training and clinical oversight, for use by astronauts on long-duration missions.
Postmission Mental Health Care
Although acute and chronic in-mission psychiatric problems may jeopardize mission success, severe, postmission mental health problems, if directly attributable to astronauts' participation in long-duration missions, could jeopardize the program itself. The NASA-sponsored longitudinal follow-up study of astronauts' health has not revealed any untoward psychiatric sequelae of participation in the space program, although the stress of reintegration and postflight adjustment has been noted. The unpredictable effects of mission-related physiological changes and potential exposure to radiation, coupled with the emotional stress of reintegration following a long-duration mission, make it imperative that a postmission program of psychiatric assessment and individual, peer, and family support as well as mechanisms for long-term peer and family follow-up support be developed.
Neurological Issues
Nervous system dysfunction and illness may occur as a result of physiological adaptive responses (both neural and systemic) to microgravity, as a consequence of problems that arise within the spacecraft, or as a result of external events or exposures. In considering the neurological illnesses or events that might occur during a mission to deep space, the timing, type, and severity of problems should be taken into account. A logical medical distinction is to consider neurological problems that affect either the central nervous system or the peripheral nervous system, or both. This somewhat arbitrary distinction has practical implications from a diagnostic and therapeutic perspective. Available data indicate that a fairly high incidence of minor neurological complaints may occur (Tables 3–2 and 3–3). Contingencies are also needed for catastrophic neurological events, including those that threaten astronauts' lives and the mission itself. NASA recognizes that the occurrence of certain severe life-threatening events can exceed the capacities of either the astronaut crew or ground control to intervene medically. This concept of acceptable risk may be different for a single one-time mission than for a multimission exploratory program.
Acute Central Nervous System Illnesses or Events
There are insufficient data on which to base sound estimates of either the incidence of various central nervous system problems or the extent to which various central nervous system problems might occur during a long-duration space mission. So far, no major neurological illnesses have been reported. However, reports from the U.S. and Russian manned space missions suggest that minor neurological problems are frequently encountered (Tables 3–2 and 3–3). These include headache and vestibular dysfunction, particularly upon the initial entry into microgravity. A serious problem upon the return to Earth is orthostasis, with its consequent effects on many bodily systems including the central nervous system.
Closed head injuries and spinal cord injuries are among the most serious neurological events that could occur during travel beyond Earth orbit. Management and treatment of individuals with severe closed head injuries would likely be beyond the capability of an astronaut crew unless dramatic new approaches to clinical management are developed. Thus, injuries that produce very low Glasgow coma scales by today's standards will probably result in death, as they frequently do under the best of circ*mstances in current state-of-the-art medical centers. However, consideration should be given to training in the management of individuals with less severe closed head injuries. Individuals with mild or moderate closed head injuries may survive but remain disabled because of residual neurological deficits. Management issues today include placement of burr holes for evacuation of subdural hematomas, feeding and airway control, spinal cord stabilization, and management of bowel and bladder functions and infections. Other events to consider include toxic exposures, decompression sickness (especially in connection with EVAs), cerebrovascular-like events, spinal injuries, exposure to radiation, and seizures.
The current neurological clinical research program at NASA, although extensive, does not appear to be well coordinated among the various research organizations and those that design and conduct flight operations. Detailed treatment contingencies based on the accumulated evidence base for the entire spectrum of neurological diseases should be developed. Such treatments should be continuously reviewed and updated to maintain state-of-the-art readiness.
Health Care Opportunity 14. Establishing a coordinated clinical research program that addresses the issues of neurological safety and care for astronauts during long-duration missions beyond Earth orbit.
Urinary Disorders
Genitourinary disease may present as an infection, obstruction, or malignancy. Many potential genitourinary problems will be identified through standard screening. Renal stone formation (expected in 0 to 5 percent of astronauts) secondary to bone calcium mobilization and excretion in the urine is a well-identified concern in microgravity environments. The genitourinary effects of microgravity also include changes in urodynamics (unknown incidence) and urinary hesitancy (reported seven times). Nephrolithiasis is a concern during extended stays in microgravity, as alterations in calcium metabolism and hydration status have previously been identified in this environment. Dehydration (incidence, 0.01 per 14 days on the space shuttle) is a recognized problem (Lane and Schoeller, 2000). Dehydration or significant changes in pH and increases in calcium and citrate levels increase the risk of renal stone formation. Preflight screening should include appropriate ultrasound evaluation for nephrolithiasis.
Urinary tract infections are common (and are more common in females) and are generally easy to treat with antibiotics. Prostatitis can be treated with antibiotics. Preflight screening for prostate cancer by determination of the prostate-specific antigen level in serum and other evaluations, according to today's standards, appears to be adequate, although future consideration may be given to preflight ultrasound or other developing noninvasive methods.
Countermeasures for genitourinary problems are primarily oriented toward the prevention of nephrolithiasis through adequate hydration. The recommended daily fluid intake is greater than 2.5 liters. A more than adequate water supply must be ensured so that crewmembers do not hesitate to drink adequate volumes of water to prevent the formation of renal calculi. As ultrasound devices become smaller, it is likely that an ultrasound device will be standard medical equipment for all long-duration space missions. This would make it possible and desirable to perform in-mission screening for nephrolithiasis (to identify those who require medication or increased levels of hydration to treat calculi). As countermeasures are developed for the problem of bone mineral density loss in microgravity, it must be ensured that the solutions do not result in increased rates of renal stone formation secondary to alterations in calcium metabolism.
Some of the health care opportunities that may be explored to increase the future effectiveness of managing risks to astronaut health during space travel have been described in this chapter and are listed in Box 3–6. This is a short list of current opportunities. It is neither a comprehensive list nor a list of priorities but is presented as a list of areas of research and development to be considered. New opportunities, including some that may take precedence, will develop in the future as the field of space medicine continues to evolve.
BOX 3–6
Health Care Opportunities in Space Medicine. Expanding, validating, and standardizing a modified physical examination, the microgravity examination technique, and including a technique for pelvic examination for use in microgravity. Developing an easily (more...)
