Space Medicine: Health in Extreme Environments

On the 12th of April 1961, Yuri Gagarin became the first human to participate in a manned space flight (United Nations, n.d.). Today, what was once viewed as a once-in-a-lifetime mission is now being reimagined as a leisurely activity existing in the form of space tourism (Davidian, 2020). Yet, no matter what the future holds for space exploration, there is no point in denying that space is an extremely harsh environment. For this reason, the health of space explorers must be prioritised before, during and after space flight.

Space medicine is a speciality of medicine that has been approved by the Royal College of Physicians in the UK. Entry into space has significant impacts on human health due to the austerity of the environment. An individual’s health before space flight comes under intense evaluation and is monitored throughout to avoid fatalities. Hence, the practice of space medicine encompasses a range of duties that ultimately prevent space-associated illnesses, and aid in the recovery of the space traveller’s normal physiology once they have returned to Earth (Hodkinson et al., 2017). Now, there is a relatively low demand for space medics, and this is reflected by the limited number of graduates with this speciality. However, a questionnaire distributed to 1,244 students across 60 higher-education institutions in the US demonstrated that most students express an eager interest in space medicine and research. The study also showed that students who were given opportunities to explore this subject in further detail were more likely to be willing to gain a career in space medicine (Semran Thamer et al., 2023). Hence, if space exploration is to become more habitual, it is of great importance that more specialist physicians become available who could ensure the safety and quality of life of passengers and pilots entering space. In addition, it is beneficial to integrate the education of space medicine for all medical students and clinical researchers, because discoveries made using patients with space-associated illnesses can prove to be equally relevant for terrestrial medicine (Mian & Aamir Mian, 2022).

Figure 1: Yuri Gagarin on his first mission to space (Rincon, 2011).

What Does a Space Medic Do?

Space medicine as a speciality requires an extensive understanding of space engineering and the specific health risks that can occur in extreme environments. Clinicians trained in space medicine are qualified to be aviation doctors (National Aeronautics and Space Administration [NASA], 2009). Although often referred to as ‘flight surgeons’, space medics play a large role before the actual space mission. Pre-flight screening, developing protective equipment, and educating passengers of the space mission about safety protocols constitute the preventative measures taken by space doctors. The aim is to have fit crew members who are at an inherently lower risk of suffering from acute fatal episodes, like heart attacks or strokes, and who can sustain themselves in short-duration flights with virtual assistance from a space medic.

For long space missions (which would involve Mars exploration missions), the advice is to have a flight surgeon on board. This is because transmission delays from Earth will impede effective communication between doctors on Earth and passengers in space (Hodkinson et al., 2017). The likelihood of an acute emergency occurring, which would need specialist intervention, also rises as the duration of space flight increases. In cases when a doctor is on board a space flight, they will be trained in how to administer treatments, anaesthesia, and surgery in a manner that would be appropriate for the space vehicle and in conditions of microgravity (Pantalone, 2023). Upon return, a space medic will need to ensure the rapid and effective rehabilitation of the space travellers. This would involve physical training, psychological therapy and the identification of any space-associated effects that need to be further researched (Hodkinson et al., 2017).

Figure 2: Flight surgeon performing an ultrasound (Wright, 2015).

What Happens to the Body in Space?

The environment in space poses unique risks to the human body. Exposure to radiation in space is heightened as there is no magnetic field that can act as a barrier, like the one that exists around the Earth (Patel, 2020). Space radiation comes in the form of galactic cosmic rays and solar particle events, travelling at high speeds as high-energy protons and particles that can easily penetrate surfaces. While cosmic rays are most often encountered by space travellers, solar particle events are less predictable and can have more severe health effects. Space radiation is ionising, meaning the energy that is formed comes from the removal of electrons in an atom (NASA, 2009). Radiation bypassing the skin and being absorbed inside the body is deleterious for human health as it results in the destruction of DNA and its consequent erroneous repair. Repetition of this process leads to carcinogenesis, which is the accumulation of mutations that cause normal cells to become cancerous.

Although humans can be exposed to radiation on earth, in the form of X-rays and UV radiation, a person faces significantly higher concentrations of radiation in space. Therefore, space explorers are at an increased risk of developing cancer, especially if they are travelling on exploration missions (which can last for months) (Patel, 2020). This is one of the principal reasons why the itineraries for space expeditions are limited; space weather is variable, with events with high radiation output being difficult to forecast, and there is no availability of protective equipment that provides complete shielding against radiation (Hodkinson et al., 2017). Further research is also needed to comprehend if individuals with certain genetic signatures, which are associated with specific cancer types, are at an even greater risk of developing cancer when entering space (Krittanawong et al., 2022).

Figure 3: Effects of space flight on the human body (Hodkinson et al., 2017).

Entry into space also necessitates the human body to adapt to microgravity. On Earth, gravitational forces pull objects and people towards the centre of the Earth. Contrastingly, in space, the effects of gravity are near zero. The experience of microgravity is synonymous with a feeling of ‘weightlessness’, which impedes normal human physiology. In the acute phase, individuals entering space may experience Space Motion Sickness (SMS), which is characterised by vestibular symptoms like headaches, dizziness and vomiting (Khalid et al., 2023). The drastically reduced gravitational force also lowers the load that is generally applied to bones and skeletal muscles. As a result, prolonged periods in microgravity environments can cause the deterioration of bone density and muscle mass, weakening and making an individual more susceptible to injuries (Hodkinson et al., 2017. Muscle atrophy in space can be problematic as within one month in space, an individual may not have the capabilities to engage in required tasks due to a 30% reduction in muscle strength. Studies performed on mice exposed to microgravity showed that effects can be identified at a cellular level, with stem cells (which are cells that have the freedom to mature into a range of different cell types) showing less preference for becoming bone cells (Juhl et al., 2021).

As well as posing challenges during space flight, the effects on the musculoskeletal system that were endured in space are not immediately reversed upon the return to Earth. Researchers have shown that crew members who had shown drastic decreases in bone mass when returning from space had little to no recovery of the bone structure and bone strength one year after their mission, despite the bone mass regenerating (Wittry, 2007). This suggests that more research is required into the effects of space travel on the human musculoskeletal system to ensure the health and safety of individuals travelling to space.

Figure 4: Flight engineer exercising in microgravity (NASA, 2015).

Entry into space is an unnatural and challenging experience for many space travellers. Apart from the hazardous nature of the environment that can negatively impact physical health, long missions in space can also pose a serious threat to a person’s mental health (Arone et al., 2021). It has been acknowledged, through research on individuals who have spent a year in Antarctica, that extreme environments can reduce positive thoughts and increase the likelihood of depression (Sandal et al., 2018). Sleep is a significant aspect of human health. In space, a person’s circadian rhythm is disrupted, meaning that the physiological cycle that dictates when a person should be awake or asleep during the 24 hours of the day does not operate properly. This occurs because there is no noticeable shift between light and dark, as there would be on Earth when there is day and night. This, in addition to being in an unfamiliar place, causes an individual to experience sleep deprivation (May, 2016). Researcher Jones and colleagues elucidated that astronauts who had less than an average of six hours of sleep during their six-month mission were more stressed and experienced more neurobehavioural symptoms than those who had longer durations of sleep (Jones et al., 2022).

Furthermore, people travelling to space must endure long periods of confinement and isolation, experiencing separation from their loved ones and being allowed to socialise with only a small cohort. This, in turn, negatively impacts their mental wellbeing. Due to the unpredictability of space flight, astronauts have also reported feelings of anxiety. Space radiation can further harm an individual’s cognitive state (Arone et al., 2021). Evidence suggests that cosmic rays can have detrimental effects on the central nervous system, resulting in cognitive decline (Cucinotta et al., 2014). Overall, space is a harsh environment that can be traumatic for a person’s mental state, especially during long space flights. Therefore, the study of space medicine should not disregard the psychological effects that can be endured by a passenger during space travel.

Figure 5: Astronaut in a space simulator (Kelly, 2020).

Space Medicine and Terrestrial Medicine

Studying the effects of space flight on the human body can elucidate pressing questions about the pathophysiology of certain diseases and allow certain drug targets to be determined. Some advances in terrestrial medicine have already been made with the aid of discoveries made in relation to space travel (Shirah et al., 2023). For example, countries of low socio-economic status face high rates of maternal fatalities due to post-partum haemorrhage. The utilisation of a compression suit, which has been designed to alter haemodynamics and prevent astronauts from fainting upon take off into space, has proven itself effective in terminating severe bleeding during childbirth (UNICEF, n.d.).

Additionally, when exploring how to counteract the effects of microgravity on the musculoskeletal system, researchers devised a rehabilitation chair that could send vibrations to skeletal muscles that would deceive the body into thinking that it was performing strengthening physical activity. This tool has the potential to facilitate post-surgery recovery and prevent muscle atrophy in those who are immobile (Shirah et al., 2023). Experiments performed on mice that were exposed to microgravity gave further insights into how the effects of space travel on the musculoskeletal system can be combatted; inhibition of a myostatin and activin A signalling pathway depicted a recovery of bone and muscle mass (Lee et al., 2020). These findings indicate that physiological signalling pathways can be targeted pharmacologically, opening up new possibilities to treat terrestrial conditions, like osteoporosis, that pose similar threats to the musculoskeletal system as space travel.

Figure 6: Compression suit being used to stop heavy bleeding during child-birth (UNICEF, n.d.).

The health issues faced by crewmates in space are replicable to the conditions experienced by people during the COVID-19 pandemic. As well as going through isolation in a confined space, access to health support was also limited during the pandemic. This is similar to what crewmates experience during space travel (Cinelli & Russomano, 2021). Therefore, exploration of the practices used by astronauts to improve their mental and physical health can improve the global approach to future pandemics. This includes the use of telemedicine, which allows space travellers to be in contact with medical professionals at all times, and the education of crew members, prior to their travels, about techniques they can use to improve their mental well-being and sleep schedule (Shirah et al., 2023). All this, and more, can be applied to terrestrial medicine to ameliorate global health.

Conclusion

Space medicine is a fascinating speciality of medicine that explores and finds ways to counteract the health problems that can arise due to the adversity of the environment in space. Multiple organ systems and a person’s mental health can fall target to the effects of space radiation, microgravity, and long-term confinement to the space vehicle. Promoting the education of space medicine to medical students is hence a necessity that will ensure the safety of astronauts who aim to complete long-duration space missions. Extensive research into this speciality is also required to make space tourism a reality that is safe. Although space medicine is viewed as a highly specific area of medicine, the knowledge that is gained from exploring this field can be interchangeable with terrestrial medicine, promoting global health.

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