Operational Medicine

Abstract

Spaceflight, whether it be a suborbital joyride, a flight to an orbiting outpost, or an interplanetary flight beyond Earth orbit, is by several orders of magnitude far, far more hazardous than flying commercial. Why? Well, aside from the obvious risks posed by acceleration, radiation exposure and explosive decompression, there are the risks associated with pre-existing medical conditions, which may not only be aggravated by being subjected to stressors such as acceleration and microgravity but could potentially be fatal. So, it is helpful to have a rudimentary understanding of how the operational environment may affect commercial astronauts.

Fig. 6.1

Medical hazards of spaceflight. (Credit NASA)

Medical Concerns for Spaceflight Participants: Spaceflight participants will face myriad health risks beyond the obvious perils of the initial rocket launch. Medical data on the effects of spaceflight on the human body have largely been provided by professional astronauts. Little research exists into the medical consequences of spaceflight on the health of untrained participants. Health risks of spaceflight will vary based on a number of factors, including spaceflight profile, vehicle configuration, destination, and duration, as well as preexisting medical conditions in passengers. Orbital and suborbital flights will pose different risks, as will the duration of time a participant endures microgravity, high speeds, and increased gravitational forces.

CRS Report: The Future of Space Tourism August 28, 2020

Congressional Research Service https://crsreports.congress.gov R46500

Spaceflight, whether it be a suborbital joyride, a flight to an orbiting outpost, or an interplanetary flight beyond Earth orbit, is by several orders of magnitude far, far more hazardous than flying commercial. Even if that airline happens to be Southwest! Why? Well, aside from the obvious risks posed by acceleration, radiation exposure and explosive decompression (Fig. 6.1), there are the risks associated with pre-existing medical conditions, which may not only be aggravated by being subjected to stressors such as acceleration and microgravity but could potentially be fatal. So, it is helpful to have a rudimentary understanding of how the operational environment may affect commercial astronauts. And, on the topic of commercial orbital, and beyond Earth orbit passengers, it is also useful to have a basic appreciation of the types of medical interventions that may be available on orbit in extremis.

If we applied government astronaut medical certification standards to our commercial astronaut group, we would find ourselves with a very, very small group of candidates. Fortunately, for suborbital flight at least, we don’t have to do this because the stresses of suborbital flight are much less than those imposed by orbital flight which we’ll get to shortly. But what exactly are those stresses? Let’s consider a typical suborbital flight on board Virgin Galactic’s SpaceShipTwo. This vehicle carries two pilots and four to six spaceflight participants in a cabin pressurized to an altitude of 2440 meters. Flights begin with a rocket-powered boost after being dropped from underneath the WhiteKnightTwo carrier aircraft at an altitude of 15,000 meters. During the 70-second boost phase, passengers are subject to an acceleration load up to 3.8 G and speeds up to Mach 3, a speed that is attained about 30 seconds after the rocket fires. The suborbital coast phase lasts a little over three minutes and SpaceShipTwo typically reaches a maximum altitude of 85 to 88 kilometers. During the deceleration phase passengers are subjected to up to 6G. To increase stability and drag for re-entry, SpaceShipTwo’s wings rotate to a feather position. Then, at an altitude of 24,500 meters, the 25-minute glide phase begins with a return to an unpowered horizontal runway landing. Total flight duration is about one-and-a-half hours. The risks of such a flight? Well, a suborbital flight is not as risky as an orbital flight but there are still some to consider.

Launching a rocket—any rocket—is a noisy business, and vehicles being launched into suborbital or orbital space require powerful thrust that happens to be noisy. Very noisy. And this noise is transmitted through the whole vehicle and because the vehicle is an enclosed space, this noise is reflected multiple times off the walls, bulkheads, floors, and ceilings. Although the noise duration is short, the magnitude can be quite intense; so intense that passengers may suffer reduced visual acuity, vertigo, nausea, disorientation, and ear pain. Noise levels in the crew compartment during a Shuttle launch reached almost 120 dB (equivalent to the sound of an Iron Maiden—a band some of you older readers may remember—concert in front of the speakers). Because of this assault on your hearing, auditory protection may be required during a suborbital launch. As well as all that noise, the power being unleashed to launch a rocket generates an awful lot of vibration. How much? Think about the vibration you feel when an aircraft takes off and multiply that by several orders of magnitude and you’ll have some idea. While vibration won’t be more than a mild and temporary inconvenience for some passengers, for commercial astronauts tasked with flying payloads, it could be a problem. That’s because vibration can cause manual tracking errors and can interfere with ability to visually track displays, which may be an issue for an astronaut tasked with keeping an eye on an experiment.

If you have watched a SpaceShipTwo flight, you don’t need to be a rocket scientist to appreciate these flights will expose occupants to an environment that is much riskier than flying on a Boeing 767, although with all the problems Boeing encountered in 2022, 2023 and 2024 with doors and panels falling off their aircraft, perhaps not! For the general population there aren’t too many medical issues of concern because the stressors passengers are subjected to during suborbital flight are less serious than those encountered during an orbital flight. But there is still that acceleration problem, especially the rapid change from acceleration launch forces to zero G weightlessness followed quickly by re-entry deceleration. Even a relatively benign flight profile like SpaceShipTwo’s is provocative enough to make even the most ardent rollercoaster fan a little queasy. And, medically, these acceleration transitions could exacerbate cardiovascular conditions that may be of concern. You see, from the flight surgeon’s perspective, some of the most troubling events of a rocket’s flight profile are the launch acceleration and re-entry deceleration, especially when the acceleration exposure is in the head-to-foot (“eyeballs down” or + Gz) direction (Fig. 6.2). That’s because Gz acceleration can magnify certain vestibular, cardiovascular, and musculoskeletal problems. Exposure to Gz can also affect pulmonary function proportionally to its applied force magnitude—for example, at the lower end of the G^1. scale, say two to three G’s, most people will have trouble breathing, while at the other end of the G load spectrum, say five to six G’s, there is a risk of airway closure.

Fig. 6.2

G explained. (Credit NASA)

Obviously, it is in the interest of spaceflight operators to make your flight experience as safe as possible and one way to do this is to minimize launch and re-entry acceleration forces by ensuring as much acceleration is in the +Gx (eyeballs in) direction. This is because people are more tolerant to +Gx acceleration, and because the heart and brain are located at approximately the same level within the acceleration field there is less risk for gravity-induced loss of consciousness (G-LOC—see sidebar) or almost loss of consciousness (A-LOC). Acceleration stress is one of the issues that most worry flight surgeons because it is dysrhythmogenic, which means the heart’s rate, rhythm, and conduction can be upset. In fact, high G forces, and/or particularly long exposures to acceleration, could potentially increase the frequency of a heart problem known as a dysrhythmia, which is why spaceflight acceleration have been designed to be in the +Gx axis. One of the challenges of determining if someone is fit for spaceflight is the limited data on prolonged acceleration on the public. For example, we have very little data on the effects of acceleration on those people with aortic insufficiency, artificial heart valves or cardiac malformations. It is for this reason that some flight surgeons recommend a preflight centrifuge familiarization (a G Challenge Test for example), which could be tailored to permit a physiological evaluation of each prospective spaceflight participant.

(G: a primer). When a person is exposed to increased +Gz (head-to-toe acceleration), the pressure required to perfuse the eyes and brain increases and blood begins to pool in the large blood vessels of the lower extremities. As G levels increase, perfusion pressure requirements increase and the volume of blood returning to the heart decreases further. Exacerbating the situation, the eyes and brain receive a decreasing amount of oxygenated blood. And, if the duration of the exposure is long enough, the eyes, which require a certain amount of perfusion pressure to function, won’t receive enough blood and therefore insufficient oxygen. This lack of oxygen will result in symptoms such as a loss of peripheral vision, which can proceed to a total loss of vision if the acceleration is high enough and long enough. As acceleration and duration increases, the person will eventually lose consciousness—G-LOC—and only regain consciousness once the acceleration level is below that person’s perfusion pressure threshold.

In the early days of human spaceflight, the direction of acceleration was more important than it is today because of the sheer magnitude of the acceleration generated by the rockets used in the early days of the human spaceflight program. For example, during launch, Mercury astronauts were subjected to more than 11 G, and Gemini, and Apollo astronauts had to deal with G levels exceeding 6.5 + Gx for six minutes. Re-entry was a similar story, with G levels exceeding 6 G during re-entry. In those days, NASA was so concerned about the possible effects acceleration might have on the astronauts they required crews to spend 50 hours training in the centrifuge, to help astronauts adapt. When the Shuttle came along, astronauts had a reprieve from high G since the Shuttle exposed astronauts to just 3.2 + Gx during launch and to 1.2 + Gz (briefly 2.0 + Gz during turns) during re-entry.

How you perform in a centrifuge is partly down to physiological luck of the draw because individual tolerance to +Gz acceleration is linked to factors such as height and weight, smoking history, fitness level, hydration, the type of acceleration profile, previous and recent exposure to +Gz forces, and recent centrifuge training. For example, if you happen to be tall and thin then you may not fare well in a centrifuge because the blood must travel a greater vertical distance from the heart to the brain and the eyes. Smokers tend to do well because their arterial beds are less flexible which means it’s easier for blood to travel through them. So, if you’re a short, squat, chain-smoker, chances are you’ll do well in a centrifuge! The type of G exposure is important too because the maximum +Gz level, exposure duration and the rate of +Gz onset determine the impact on your heart and musculoskeletal system. The most problematic acceleration is rapid-onset rate (ROR), which is an increase greater than 0.33 G/sec. RORs can result in the dreaded G-LOC without any visual warning symptoms such as tunnel vision, gray-out or black-out. A helpful article about acceleration can be found in Appendix I. Also, for those interested in acceleration I can recommend the excellent ‘Pulling G’ book written by yours truly and published by Springer-Praxis.

Okay, enough about acceleration. Once you’ve survived the G’s you can look forward to some time in microgravity. The physiological changes resulting from exposure to microgravity vary from individual to individual. While suborbital microgravity exposure will only last for about three to four minutes, if you happen to be highly sensitive, you may experience some cardiovascular and/or vestibular symptoms. A common cardiovascular effect observed in Shuttle astronauts while they were lying down awaiting launch was a shift in fluids from their legs to their head. Part of the reason for this was due to the slightly head-down pre-launch position. In orbit, due to the absence of gravity, fluids shifted again, with body fluids rushing to the head, giving astronauts a sensation of head fullness. Fortunately, most of these effects won’t be a problem during a suborbital flight simply because these physiological changes take time to develop in microgravity. Vestibular effects on the other hand, may manifest as space motion sickness. Why? Well, your vestibular system (Fig. 6.3) provides information about motion, head position, and spatial orientation. The system comprises several structures that help you balance, maintain equilibrium, and maintain posture. The semicircular canals are arranged at right angles to one another and provide information about angular acceleration (pitch, roll and yaw) whereas the otolith organs provide information about linear acceleration. Another key element in the vestibular system is the hair cell (stereocilia), which are embedded in a gelatinous structure called the cupula. When you move your head, these hair cells move and information is carried from the hair cells to the brain (brainstem and cerebellum), which interprets the movement accordingly.

Fig. 6.3

Structure of the inner ear. (Credit FAA)

Disruption to the vestibular system, which may occur when exposed to microgravity, can cause symptoms such as nausea, vertigo, loss of balance and vomiting. The microgravity environment may not only be disruptive to the vestibular system but may also affect the visual system. Why? For years, we accumulate sensory information via our vestibular system and our visual system, and all this information is stored in a repository for sensory information. And when something conflicts with that database of information, motion sickness may be the result. In fact, 60 percent of first-time astronauts suffer from space motion sickness (SMS). Take look at Fig. 6.4. It shows Expedition 23, STS-131 and Russian crew members in the Kibo module. Imagine seeing this when you arrive on orbit!

Fig. 6.4

STS-131 and Expedition 23 crew members gather for a group portrait in the Kibo laboratory of the International Space Station. STS-131 crew members pictured (light blue shirts) are NASA astronauts Alan Poindexter, commander; James P. Dutton Jr., pilot; Clayton Anderson, Rick Mastracchio, Dorothy Metcalf-Lindenberger, Stephanie Wilson and Japan Aerospace Exploration Agency astronaut Naoko Yamazaki, all mission specialists. Expedition 23 crew members pictured are Russian cosmonauts Oleg Kotov, commander; Mikhail Kornienko and Alexander Skvortsov; Japan Aerospace Exploration Agency astronaut Soichi Noguchi, and NASA astronauts T.J. Creamer and Tracy Caldwell Dyson, all flight engineers. (Credit: NASA)

Countermeasures? Well, astronauts can take anti-motion sickness medication such as promethazine, although this doesn’t always help. Do you get motion sick? Well, not to worry, because there is little to no correlation between being sick on Earth and being sick in space. In fact, some people who are chronically motion sick on Earth are fine in space. Equally, those who have never experienced terrestrial motion sickness are sometimes sick as the proverbial dog when they reach orbit. No doubt about it, SMS is a problem. Unfortunately, there is just no way that will guarantee you won’t be sick. Parabolic flight adaptation and experience in high performance jet aircraft don’t work. Neither do rotating chairs or centrifuge training.

After surviving acceleration and dodging the SMS bullet there is the risk of hypoxia to deal with. Now life support systems on spacecraft nowadays, are very reliable, but it’s always best to be prepared, so you will need to know what to do in the event of a rapid decompression. We’ll cover the training for this in the training chapter, but since this chapter covers physiology, we’ll deal with the physiological consequences of an event that has already killed several spacefarers. You see, any vehicle that ventures beyond the Armstrong (nothing to do with Neil Armstrong incidentally; the Armstrong Line was named after USAF General Harry Armstrong) Line² will operate at such a high altitude that there is a risk for decompression, which may result in hypoxia and/or death due to hypoxia or ebullism. In case you’re wondering how bad such an event might be here is an extract from The USAF Flight Surgeon’s Guide.

Gastrointestinal Tract during Rapid Decompression.

One of the potential dangers during a rapid decompression is the expansion of gases within body cavities. The abdominal distress during rapid decompression is usually no more severe than that which might occur during slower decompression. Nevertheless, abdominal distension when it does occur, may have several important effects. The diaphragm is displaced upward by the expansion of trapped gas in the stomach, which can retard respiratory movements. Distension of these abdominal organs may also stimulate the abdominal branches of the vagus nerve, resulting in cardiovascular depression, and if severe enough, cause a reduction in blood pressure, unconsciousness, and shock.

Sounds painful, doesn’t it? Well, rapid decompression is more survivable than explosive decompression, an event that can cause your blood to boil. Here’s what Dr. Tamarack R. Czarnik, a specialist in aerospace medicine, has to say about the medical effects of an explosive decompression:

Damage to the lungs in rapid or explosive decompression occurs primarily due to pulmonary overpressure, the tremendous pressure differential inside versus outside the lungs. 80 mm Hg is enough to cause pulmonary tears and alveolar rupture; pulmonary hemorrhaging, ranging from petechiae to free blood is also seen. Emphysematous changes are seen especially in the upper lungs, while atelectasis and edema predominate in the lower lungs. When we get to the patient, the lungs will be a bloody, ruptured mess.

Though these are the most life-threatening changes seen in ebullism, subcutaneous swelling is also seen, due to creation of water vapor under the skin. This can rapidly distend the body to twice its normal volume. Our patient will look no better than he feels, though this means little in terms of survival.

Of course, the best way to avoid these nasty hypobaric events is to wear a pressure suit (Fig. 6.5). Until very recently, pressure suits were expensive and tended to weigh a lot. For example, the Shuttle pressure suit weighed over 20 kg fully loaded and cost more than US$300,000. Fortunately, for the new crop of commercial astronauts, pressure suits are less bulky and, for the operators, less expensive (around US$100,000). Nevertheless, even if you are wearing a pressure suit, it is useful to understand the consequences of one failing, which is why most operators include high altitude indoctrination (Fig. 6.6) to familiarize passengers with the hazards of hypoxia and depressurization.

Fig. 6.5

Here’s a picture of yours truly wearing a commercially available pressure suit designed by Final Frontier Design. (Credit: author)

Fig. 6.6

Astronauts and military aircrew prepare for high altitude indoctrination in a hypobaric chamber like this one. (Credit: USAF)

Next on the list of space risks is radiation (Fig. 6.7). In space, ionizing radiation, which consists of subatomic particles, can interact with biological tissues, and destroy DNA strands, causing genetic damage that can in turn lead to dangerous mutations. The two types of radiation in space are galactic cosmic radiation (GCR), which originate from outside the solar system, and solar particle events (SPEs), which originate inside the solar system. 99% of the radiation astronauts are exposed to is from SPEs and 1% from GCR, but 99% of the damage done by radiation is caused by just 1% (the heavy particles such as lithium and iron) of the GCR.

Fig. 6.7

Space radiation explained. (Credit: ESA)

So, how much radiation is too much? Well, here on earth you will be exposed to 3 milliSieverts (mSv) a year, whereas an astronaut completing a six month increment on the ISS will be exposed to around 75 mSv. Fortunately, radiation levels at suborbital flight altitudes won’t be anything close to these levels. In fact, if you fly a suborbital flight, you won’t be exposed to radiation much higher than a Concorde—remember those days? Perhaps not, but back in the old days we had something called supersonic flight before the industry turned the clock back and decided to tread water. During a typical transatlantic supersonic flight, a passenger might be exposed to less than 15 microSv/hr. It doesn’t sound a lot but if you happen to be a commercial suborbital astronaut, chances are you may fly several missions, so what might be the recommended occupational exposure limits for this astronaut category? Well, the International Commission on Radiological Protection (ICRP) states that for commercial aircrews the occupational limit is 20 mSv per year, averaged over 5 years, with a maximum in any one year of 50 mSv. So, what do these risks mean in terms of how healthy you need to be to be medically qualified for suborbital flight? Well, the Federal Aviation Administration (FAA) thought about this and appointed a team to evaluate the medical standards that would be appropriate for suborbital passengers, and this included guidelines for radiation which stated: ‘radiation dose will not exceed the yearly commercial airline passenger dose, defined as no more than 1 mSv/year’. Since the report, titled ‘Flight Crew Medical Standards and Spaceflight Participant Medical Acceptance Guidelines for Commercial Space Flight,’, lays out the suggested medical guidelines for commercial astronauts, it’s worth reviewing, so what follows is a synopsis.

The FAA-sponsored medical guidelines project was conducted in three phases, the first of which collected and reviewed documents addressing suborbital crew member and spaceflight participant (SFP) medical certification. In the second phase, a preliminary document incorporating the guidelines and recommendations as outlined in Phase I was prepared and a working group of experts was convened to consider the comments from Phase II. Then, in Phase III, a consolidated set of recommendations for the medical certification of crew members, medical acceptance guidelines for SFPs, and recommended training procedures was prepared, and the document was provided to the FAA.

The first part of this document outlined a reference mission, which set out several assumptions. The first of these was that a suborbital spacecraft will provide a shirt-sleeve cabin environment with an appropriate temperature, a cabin pressure of not more than 8,000 ft, and appropriate oxygen, and humidity levels. The second assumption was that the acceleration in a suborbital spacecraft should not exceed +6Gx, +1Gy, and +4Gz. If the acceleration profile exposed SFPs to greater than +4Gz, then the SFPs should be medically screened according to the guidelines outlined for orbital passengers. The third assumption dealt with flight rates and assumed that SFPs will only participate in one sub-orbital flight per day, whereas commercial astronauts or flight crew could make multiple flights per day. The document also noted that repeated flights to the acceleration limits listed, with 4 minutes of zero-g exposure between launch and entry, haven’t been performed before, so caution should be exercised until an experience base is acquired. Finally, the document assumed that radiation dose will not exceed the yearly commercial airline passenger dose, defined as no more than 1 mSv/year.

The next part of the document dealt with the guidelines for screening. The guidelines suggested that the content and extent of a medical questionnaire and physical exam should be related to each operator’s flight profile and that SFPs should complete a medical questionnaire (see Table 6.1) and a physical exam by a qualified physician with knowledge of the spaceflight environment.

If you’re planning to take a commercial spaceflight, chances are that you will need to indicate a history of any of the following conditions:

Table 6.1 Spaceflight participant questionnaire

In addition to completing the questionnaire, you will be required to inform the doctor if you have a medical condition that would impair your ability to safely perform a spaceflight without compromising the safety of other occupants and/or safely perform an emergency egress without assistance. And, given the novel flight environment, a post-flight medical debrief is recommended to collect post-flight medical data, and enquire about health effects of the flight. After completing the questionnaire, prospective commercial astronauts will be medically screened (expect this to take a long time if your destination is LEO). According to the project’s findings, the medical screen may determine that a potential commercial astronaut has a medical problem requiring additional consideration. While there are no hard and fast commercial astronaut medical standards for suborbital flight, for orbital flight it’s another story. For example, any condition that may result in an in-flight death or injury is obviously a red flag. Also, a person that has a condition with functional defects that could interfere with the use of personal protective equipment or interfere with an emergency egress shouldn’t be sold a ticket. Another medical issue is any problem that may be exacerbated by the operational environment or flight-related stress. So, what do you do if you don’t meet the recommended guidance criteria? One option is a mitigation strategy, although the operator and aerospace medicine physician must ensure that the condition and the mitigation process won’t impair the ability of the prospective astronaut to safely perform activities required for the flight including an emergency egress. Part of this mitigation strategy may involve training, which forms the subject of the following chapter.

So, we briefly discussed the radiation issue as it pertains suborbital and orbital flight but since this risk increases with time on orbit it is helpful to understand it better for those commercial astronauts venturing to LEO. Of all the medical challenges orbital astronauts must deal with, radiation is the most damaging. Part of the reason is that the body cannot adapt to radiation, so the longer an astronaut is in space the more radiation they will be exposed to. As discussed earlier, the most damaging type of radiation is GCR. This radiation keeps flight surgeons, mission planners and astronauts up at night for the simple reason it is nigh on impossible to shield against because GCR’s are highly energetic charged particles that bullet along at close to the speed of light, propelled through space by the force of exploding stars. This means these particles have tremendous energy and the mass of some particles, combined with their phenomenal speed, means they can slice through the spacecraft like the proverbial hot knife through butter. The next component of space radiation are SPEs, which comprise energetic electrons, protons, and alpha particles that are accelerated by shock waves that precede coronal mass ejections (CMEs), which occur near solar flare sites. The most energetic SPEs may arrive in LEO within 20 or 30 minutes of the event and may cause significant effects in the Earth’s atmosphere. Unfortunately, there is no way to reliably predict when a SPE may strike, so the best scientists and mission planners can do is to study the relationship between SPE intensity and the parameters of shock and plasma, to better understand the conditions when these events occur. So, if you happen to be a commercial astronaut visiting one of the commercial habitats in LEO, we know you can expect to be exposed to 75 mSv during a six-month increment, but if you decide to sign up for the Mars Messiah’s interplanetary colonization plan you can expect to be exposed to around 466 mSv just on the outbound trip to the Red Planet. What will happen to your body as it is bombarded by radiation? Well, out there in deep space, it will take only three to four days for every cell in your body to be hit by a high-energy proton. Now, for some cells, it isn’t much of a problem, but when these speeding radiation particles hit important cells such as DNA, then mutations may result. Another more serious effect of GCR is that it may accelerate the onset of symptoms like those exhibited by Alzheimer’s patients:

Galactic cosmic radiation poses a significant threat to future astronauts,” “The possibility that radiation exposure in space may give rise to health problems such as cancer has long been recognized. However, this study shows for the first time that exposure to radiation levels equivalent to a mission to Mars could produce cognitive problems and speed up changes in the brain that are associated with Alzheimer’s disease.

Professor M. Kerry O’Banion, M.D., Ph.D., University of Rochester Medical Center Department of Neurobiology and Anatomy.

O’Banion’s research focused on how GCR affects the central nervous system (CNS), and the news was less than rosy. O’Banion’s research examined the effect of GCR-equivalent radiation on cognitive function, which is a fancy way of describing how long it took mice to find their way through a maze. To do the study, mice were exposed to doses of radiation comparable to levels Mars-bound astronauts will be subjected to. The mice then performed recall tests and O’Banion and his fellow researchers found that mice exposed to radiation were more likely to fail the tests (in other words, they couldn’t find their way through the maze), a finding that indicated cognitive impairment. After examining the mice more closely, researchers found that the brains of the mice had a larger than normal amount of beta amyloid, which is a signature of Alzheimer’s (sidebar). But that is just one side-effect of exposure to space radiation on the CNS. Other studies have revealed neurogenesis.³ may be sensitive to radiation which may in turn result in cognitive deficits such as memory, and as if that wasn’t enough, we know that radiation causes something known as oxidative stress,⁴ and this type of stress is thought to be implicated in heart failure, and chronic fatigue syndrome. Since radiation has been shown to increase oxidative damage, oxidative stress represents yet another mechanism of radiation-induced cognitive injury.

Alzheimer’s disease. This is a neurodegenerative disease that causes dementia in most cases. Common symptoms include short-term memory loss, language problems, disorientation, lack of motivation, and behavioral problems. The disease, which is chronic, begins slowly and symptoms become worse with time. There are no treatments that can stop the disease or even slow its progression.

Another radiation-induced injury is bone remodeling, which is a subject we’ll discuss later. In zero gravity or reduced gravity, bone remodeling is disrupted, resulting in a loss of bone mineral density. Astronauts on board the ISS typically lose between 1.0 and 1.2 percent of their bone mineral density per month, which equates to an overall loss of about 7 percent during a typical six-month increment. For astronauts in LEO, this rate of this loss is steady, but beyond LEO, the radiation environment is harsher, and the rate of bone loss could increase due to a process known as osteoradionecrosis, which is radiation-induced bone loss. We have a good understanding of this process because radiation is used as a treatment for malignancies and has been a factor in reducing cancer mortality. One reason bone mineral density is reduced following irradiation is because the cells responsible for bone remodeling (the osteoblasts and osteoclasts) are damaged and when these bone cells are damaged, bone formation is impaired due to cell-cycle arrest. One of the processes by which the osteoclasts and osteoblasts are damaged is by oxidative stress caused by the radiation since it is this oxidative stress that damages osteoprogenitors. To begin with, irradiation causes an increase in osteoclast number which thereby causes osteoporosis. Shortly after exposure there is a decline in the number of osteoclasts and osteoblasts which results in suppression of bone remodeling and degradation of bone quality. This may result in osteitis, which is a condition in which the bone’s ability to withstand trauma is reduced. In this condition, non-healing bone may be susceptible to infection, and the ability of the bone to heal is further complicated by hypovascularization. So, as the body is subjected to increased radiation, the very small blood vessels inside the bone are destroyed. This is devastating because these blood vessels carry nutrients and oxygen to the bone. Without blood vessels to do this, the bone simply dies. On Earth, one treatment option for patients with osteoradionecrosis/osteitis is hyperbaric oxygen therapy, but this will not be an option on an interplanetary spaceship.

In addition to inflicting damage upon the CNS and skeletal system, radiation can break molecular bonds and cause biological damage such as single strand or double strand breaks in DNA. While the body is tremendously resilient in its capacity to repair radiation damage, some cells die in this onslaught of radiation. Worse, some cells may propagate the ionized-induced damage to progeny.

The skeletal system plays several important roles. It serves as a structure that supports the body, it stores calcium, and it produces blood. Bone is also very dynamic due to a process known as bone remodelling, which relies on the activity of two especially important bone cells. Osteoblasts that build up bone and osteoclasts that break down bone (bone resorption). On Earth your skeleton undergoes a tremendous amount of loading. Those of you who wear Fit Bits will know that you take between 8000 and 10,000 steps every day just performing daily activities. That loading is detected by your brain and signals those osteoblasts and osteoclasts to go to work. The result is a healthy skeleton that is remarkably fracture resistant. But in space? Well, all that loading is removed, and this causes problems because your brain detects that reduction in load and adapts accordingly by decreasing the action of the osteoblasts and increasing the action of the osteoclasts. The result? A reduction in bone mass density of one percent or more per month, which happens to be a rate ten times the rate at which osteoporosis patients lose bone. It is catastrophic (Fig. 6.8). The body not only alters the responses of the osteoblasts and osteoclasts, but it also alters the body’s calcium balance. Calcium is a key bone building material. But in microgravity it is not necessary to have strong bones, so the body gets rid of calcium by as much as 250 mg per day. Not only does calcium excretion result in weaker bones, but it also increases the risk of kidney stones because that calcium must be routed through the kidneys before being excreted. But worse is to come.

Fig. 6.8

Osteoporosis. (Credit: NASA)

Fig. 6.9

Nick Hague, Russian cosmonaut Alexey Ovchinin and United Arab Emirates astronaut Hazzaa Ali Almansoori relaxing after their ISS mission. (Credit: NASA)

Look at Fig. 6.9. That is a photo of NASA astronaut Nick Hague, Russian cosmonaut Alexey Ovchinin and United Arab Emirates astronaut Hazzaa Ali Almansoori. They have just returned from an ISS increment lasting several months. Notice anything particular in this image (apart from the fact they’re on their cellphones)? They are horizontal. Why? Because their bones (and muscles, which we’ll get to next) are so weak after having spent so long in space. And those people attending to the crew? Some are flight surgeons entrusted with the care of the crew. Shortly after landing, the crew are whisked away to their respective agencies and embark on a dedicated and personalized rehabilitation program to regain lost muscle and bone. After about 90 days, most astronauts have recovered their muscle. But bone? Well, that’s another story. There have been some astronauts who, ten years following their six-month increment stay in space, did not completely recover their bone loss. Ten years! You see, some astronauts recover their bone mass (relatively) quickly (three to four years) and other astronauts take longer. Another element of the bone loss story is bone mass density and architecture. Take another look at Fig. 6.8. You see those rod-shaped structures? Those form the architecture of the bone. The better the arrangement of the rods and plates the better the architecture and, theoretically, the stronger your bones. But another element that has a bearing on bone strength is bone density. You can have great bone architecture but if your bone density is low then your bones will be weak and vice versa. The ideal scenario is to have both good bone density and good bone architecture. In space, because of the absence of gravity the body remodels bone in response to the load demands on the bone. And, since those load demands are low, bone density is reduced, and those rods and plates are arranged to deal with the loads in microgravity which means weaker bone architecture. In LEO, the effect is manageable thanks to limited time on orbit and thanks to personalized rehab programs waiting for astronauts when they return to Earth. But a Mars mission? That will require astronauts to spend the best part of 12 months in deep space (for the return journey) plus a surface stay in reduced gravity. Imagine a crewmember suffering a femoral fracture. How would the crew cope? Could they cope? Now astronauts are a resourceful lot, and they could cope for a while, but sure as eggs are eggs, sooner rather than later, the demands of caring for a disabled astronaut would exceed the limits of crew health care resources. Think I’m exaggerating? Look at Fig. 6.10. The image depicted in Fig. 6.10 is one way of dealing with a broken bone. The technique is known as external fixation. Imagine all the challenges of dealing with this in a reduced gravity environment! Bleeding, infection, re-infection, sepsis, 24/7 care, etc. So, what can we do? Well, one strategy is to apply countermeasures and another, if the worst comes to the worst, is to treat the outcome surgically.

Fig. 6.10

External fixation. Imagine a crew having to deal with this situation on the surface of Mars. (Open source/Ashish j29)

Any commercial astronaut who spends more than a few days on orbit will need to spend at least a couple of hours a day exercising. To give you an idea of the range and type of exercise countermeasures available, it is worth looking at what is available in the United States Orbital Segment of the orbiting outpost. Here, astronauts have a choice between devices such as the Advanced Resistive Exercise Device (ARED), the Flywheel Exercise Device (FWED), and the Combined Operational Loadbearing External Resistance Treadmill (COLBERT). Typical workout guidelines (Table 6.2) can be found below:

Table 6.2 Characteristics of the ISS countermeasure program

Now you may be wondering how effective all this exercise is. Well, that’s difficult to say, and here’s why. While on board ISS, all long duration mission astronauts must abide by Flight Rules which state quite clearly that all crewmembers must perform exercise. No exceptions. This means it is impossible to compare the effects of inflight exercise with no exercise, but there is a wealth of data from long duration missions we can draw upon. For example, we know the rate of bone mass loss in ISS crew is less than measured in Mir crews. That said, there is a significant difference across crewmembers, with some astronauts losing up to 15% of their bone mass following a 6-month mission, which equates to a troubling 2.5% every month! Lately the trend is a gradual lowering of bone mass loss in astronauts thanks to careful manipulation of exercise schedules and judicious selection of effective exercise. Another application of countermeasures is in reducing muscle atrophy, but before we discuss this topic an introduction to the muscular system is helpful, so here goes. There are three types of muscle in the body. Smooth muscle, also categorized as involuntary muscle, is found in organs and organ structures, whereas cardiac muscle, which is also involuntary muscle, is found only in the heart. Skeletal muscle, which is also categorized as voluntary muscle, is used for movement. You have about more than 600 skeletal muscles in your body. Also known as striated muscle due to its appearance under the microscope, skeletal muscle (Fig. 6.11) helps support the body, assists in bone movement, and protects internal organs. It is divided into various subtypes. Type I, also known as slow twitch (red), is dense with capillaries, which means these muscles can carry a lot of oxygen and sustain lengthy periods of aerobic activity. Type II, also known as fast twitch, can sustain short bursts of activity.

Fig. 6.11

Skeletal Muscle structure. (Open source/www.scientificanimations.com)

Now some basic—very basic!—exercise physiology. Despite what you may hear in the gym, fat cannot be turned into fat and fat cannot be turned into muscle. Impossible! Second, the number of muscle fibers cannot be increased, no matter how hard you exercise. So, how do muscles get bigger? Simple: muscle cells get bigger in a process known as hypertrophy, which is the opposite of atrophy which is the term that describes the wasting away of muscles. In skeletal muscle, movement is achieved by contraction that is stimulated by nerve impulses at a site known as the neuromuscular junction. Energy for muscle movement is found in the form of glycogen, which is stored in the muscles and in the liver. When exercising, the muscles contract by actin and myosin filaments sliding over one another, a mechanism known as the sliding filament theory (Fig. 6.12). On Earth muscle tone is maintained by means of exercise. Even sedentary people will take 8000 to 10,000 steps every day, which is usually sufficient exercise to maintain some muscle tone. But in space, muscles don’t get used nearly as much as on Earth. The result is that muscles begin to atrophy at a rapid rate. In just 6 months astronauts will lose about 25 percent of their total muscle mass. But this loss is not evenly distributed. A larger proportion of muscle loss is in the load-bearing muscles (your big leg muscles) and the balance muscles (those muscle groups that support your spine for example). As astronauts spend increased time in space, their muscle cells shrink and become smaller and smaller. And as those muscles become smaller, they become weaker and weaker which means astronauts cannot exert as much force. Why is this important? Well, think operationally. Think of all those images and videos we’ve been bombarded with of astronauts going about their business bouncing around on the surface of Mars. Astronauts building outposts and exploring the surface during lengthy EVA’s. Do you really think they will be able to do that in such a deconditioned state? Don’t forget that these astronauts will have lost a quarter of their muscle mass, which includes their cardiac muscle mass. This means the heart is much less efficient, which means exercise capacity is significantly reduced. And as mission time increases, astronauts will become weaker and weaker and... well, you get the picture. So, what can be done? Well, countermeasures again.

Fig. 6.12

The sliding filament theory. (Credit: David Richfield)

Of course, countermeasures for bone loss and muscle atrophy will comprise only part of the suite of exercise equipment that will be available to commercial astronauts because having strong bones and muscles will only get you so far; astronauts also need to maintain their exercise capacity. One metric for measuring aerobic capacity is maximal oxygen uptake which measures the amount of oxygen utilized by each kilogram of bodyweight per minute of exercise. As a commercial astronaut you will undoubtedly perform preflight, inflight and postflight measures of oxygen uptake and, like all physical fitness metrics, you will undergo an observed decline in your ability to utilize oxygen. Why? Well, first there is the issue of muscle atrophy. Imagine losing 20–25% of your respiratory muscle mass (your intercostal and intracostal muscles). This will make breathing more difficult. And then of course there is the loss of working (skeletal and cardiac) muscle mass. If your muscles—and heart!—are smaller, it stands to reason you will find it more difficult to work out. How much more difficult? Well, compared with pre-flight data, maximal oxygen uptake declines by between 15% and 25%.

So, by now we know astronaut’s bodies suffer in microgravity. Without effective countermeasures, muscles atrophy, bones shed calcium, and astronauts get sick. But that’s not all. Eyesight may also be affected. We’ve known about vision impairment in astronauts for some time, but the problem has only been put under the spotlight recently after some astronauts experienced severe eyesight deficiencies. Thanks to anecdotal reports by astronauts and a comparison of pre- and post-flight ocular measures, microgravity-induced visual acuity impairments have now been recognized as a significant risk (you can read more about this in Springer’s Microgravity and Vision Impairments in Astronauts written by yours truly). And this problem doesn’t affect a minority of crewmembers: retrospective analysis of medical records revealed 29% of 300 Shuttle astronauts and 60% of space station astronauts have suffered some form of visual degradation. That’s a serious problem for an agency planning to send astronauts back to the Moon and eventually Mars. The problem has its own acronym—this is NASA after all—and is referred to as the visual impairment/ intracranial pressure (VIIP) syndrome. Even though VIIP has only recently been identified, there has been significant research performed, so scientists are beginning to better understand the syndrome. The data shows that astronauts who suffer VIIP related symptoms experience varying degrees of visual performance decrements. Some suffer cotton-wool spot formation while others may present with edema of the optic disc. Other astronauts may suffer flattening of the posterior globe while some may present with distension of the optic nerve sheath. In short, there is a profusion of signs and symptoms but the reason for the vision impairment still has researchers flummoxed. One theory suggests the changes in ocular structure and impairment to the optic nerve is caused by the cephalothoracic fluid shift astronauts experience while on board the ISS. It is theorized some astronauts are more sensitive to fluid shift due to genetic and anatomical factors. While conducting studies on the VIIP syndrome, researchers have focused on three systems—ocular, cardiovascular, and central nervous. These studies have revealed a variety of symptoms other than visual decrements, including increased intracranial pressure (ICP) and changes in cerebrospinal fluid (CSF) pressure. But, because preflight, inflight, and post-flight data are thin on the ground, it is very difficult to define why and how these symptoms occur. Inevitably, since the impact of VIIP is an operational concern, space agencies have increased preflight, inflight, and post-flight monitoring of the syndrome to better characterize the syndrome and the risks.

When considering the cardiovascular system and how it adapts to microgravity, this system, like so many physiological systems, remains poorly understood. That’s because the adaptive process is so complex and involves so many control mechanisms such as the autonomic nervous system, cardiac function, and peripheral vasculature. The primary cause of, and the trigger for these adaptive processes, is the headward fluid shift and redistribution of body fluids that occurs in every astronaut on arrival on orbit (Fig. 6.13). The body has about five liters of blood in addition to other body fluids such as interstitial fluid (found between the organs) and CSF, which is found in the spinal cord. When astronauts arrive on orbit, between 1.5 and 2.0 liters of this fluid moves from the lower extremities to the chest and head. Not surprisingly, this causes various signs and symptoms, including facial puffiness, ‘bird-leg’ syndrome, pounding headaches and those vision problems mentioned earlier.

Fig. 6.13

Fluid shift in microgravity. (Credit: NASA)

This fluid shift also triggers a series of adaptive processes in the body (remember: the body will always try to adapt to the environment). Inside your body you have all sorts of sensors and receptors that send the brain information about temperature, electrolyte balance, and pressure. The pressure receptors are termed baroreceptors and if fluid is maintained within certain thresholds, no action must be taken. But when up to two liters of fluid is translocated from the lower to the upper body, this causes a spike in pressures that exceed thresholds. So, the baroreceptors send this information to the brain and the brain decides that something must be done and that something is to reduce pressure. The way it does this is to get rid of the excess fluid by triggering suppression of the renin-angiotension-aldosterone system which releases atrial natriuretic peptide which results in diuresis which is a physiological term meaning you have to visit the washroom frequently to urinate. Unfortunately, all this urination has a side-effect of reducing plasma volume. About 55% of your blood is plasma and about 90 percent of your plasma is water. So, if you’re urinating frequently, you are losing body water and hence, blood volume. In fact, in the first 24 hours on orbit, astronauts lose 17% of their plasma volume which equates to an overall reduction of about 10% of total blood volume. The body does its best to adapt, which it does after about six weeks, although this adaptation is to microgravity, not one G. On return to Earth, guess what happens? All that fluid that was in the upper body rushes to the lower body which causes orthostatic intolerance (inability to stand upright)—25 percent of astronauts returning from space cannot stand upright for 10 minutes within hours of landing because of orthostatic intolerance.

Immune dysregulation was first observed in astronauts in the 1960s and 1970s, including the Apollo crews, half of whom suffered bacterial infections. While there is much data about astronauts’ immune system responses following spaceflight, less is known about what happens during a mission. Of the research conducted postflight, data has revealed several changes, including changes in leukocytes, cytokine production, reduced natural killer cell activity and altered immune responses. Many of these altered immune system changes are related to very high levels of physical and psychological stress that astronauts must endure during their missions. Isolation, confinement, changed circadian rhythms are all factors that are implicated in the altered immune responses observed in astronauts following long duration missions. Another major factor that has a profound negative impact on immune system function is the exposure to ionizing radiation, although the exact mechanisms that cause radiation-induced immune dysregulation have yet to be fully elucidated. In addition to radiation exposure, the effect of weightlessness causes significant immune system changes, since the absence of gravity alters signalling pathways that are key to T-cell activation.

Astronauts possess a wide-ranging repertoire of behavioural competencies that help them function effectively in a multi-cultural environment. This repertoire is critical because a spacecraft is an environment in which faults cannot be tolerated. To ensure all astronauts have these skill sets, space agencies apply very specific ‘select-out’ and ‘select-in’ criteria during selection (see below). And, once selected, astronauts complete extensive preflight training to develop ‘expeditionary behavior’ which comprise space-related psychosocial skills designed to ensure mission success. In addition to all this preparation, to ensure missions proceed smoothly, there is a ground-based complement of support staff who provide behavioral support via video conferences.

Single men, perfect health, considerable strength, perfect temperance, cheerfulness, ability to read and write English, prime seamen of course. Norwegians, Swedes and Danes preferred. Avoid English, Scotch and Irish. Refuse point-blank French, Italians and Spaniards. Pay to be Navy pay. Absolute and unhesitating obedience to every order, no matter what it may be.

Captain De Long’s crew requirements for the Jeanette Arctic Expedition, 1879–1881

The CSA is seeking outstanding scientists, engineers and/or medical doctors with a wide variety of backgrounds. Creativity, diversity, teamwork, and a probing mind are qualities required to join the CSA’s Astronaut Corps. To withstand the physical demands of training and space flight, candidates must also demonstrate a high level of fitness and a clean bill of health.

Canadian Space Agency’s Astronaut Recruitment Campaign announcement, 2008

Just like trying to predict whether a crewmember had the right stuff for a polar expedition, trying to guess whether an astronaut will be vulnerable to psychiatric or psychosocial problems during multi-month missions remains an inexact science at best. Current screening involves a standard battery of tests that are administered to collect psychological information, as well as successive two-hour interviews. The first interview is conducted by a psychiatrist and a psychologist and the second with a psychiatrist alone. Standard tests (which the Canadian Space Agency also employ to select their astronauts) include the Minnesota Multiphasic Personality Inventory and the Personality Characteristics Inventory, which are used to identify ‘right stuff’, ‘no stuff’ and ‘wrong stuff’ characteristics. What constitutes the “right stuff” for a long duration space odyssey includes a history of emotional stability and little sign of depression or neuroticism. These long duration crewmembers tend to be socially adept introverts who get along well with others but don’t need other people to be content. Another important characteristic is a high toleration for lack of achievement, which makes sense when you think about the sheer length of the mission. In common with Shackleton, Amundsen and Co., this group of astronauts need to be prepared for changes of plan, contingencies, and the possibility that goals won’t be achieved.

Another reason the doom and gloom merchants like to highlight the psychological aspect as being the weak link in human spaceflight is the fact that astronauts work in isolated, confined, and extreme (ICE) environments. Working in these environments, aforesaid doom and gloom merchants argue, will cause astronauts to lose their minds, turn on each other, and even come to blows. This is fantasy. Let’s look at a real-life ICE experience to prove my point. In 1893, Fridtjof Nansen sailed to the Arctic in the Fram, a purpose-built, round-hulled ship designed to drift north through the sea ice. Nansen’s theory was inspired by the voyage of the Jeannette which foundered northeast of the New Siberian Islands and was found on the southwest coast of Greenland after having drifted across the Polar Sea. Nansen reckoned the Polar current’s warm water was the reason for the movement of the ice. But, after more than a year in the ice it became apparent that Fram would not reach the North Pole. So, Nansen, accompanied by Hjalmar Johansen, continued north on foot when the Fram reached 84° 4´ North. It was a bold move, as it meant leaving the Fram not to return, and a return journey over drifting ice to the nearest known land 800 kilometres south of the point where they started. Nansen and Johansen started their journey on 14 March 1895 with three sledges, two kayaks and 28 dogs. On 8 April 1895, they reached 86° 14´ N, the highest latitude ever reached at that time. The men then turned around and started back but they didn’t find the land they expected. On 24 July 1895, after using their kayaks to cross open leads of water, they came across a series of islands where they built a hut (Fig. 6.14) of moss, stones, and walrus hides. Here they spent nine mostly dark months, spending up to 20 hours out of every 24 sleeping, waiting for the daylight of spring. They survived on walrus blubber and polar bear meat. In May 1896, Nansen and Johanssen decided to strike out for Spitsbergen. After travelling for a month, not knowing where they were, they were delivered from their endeavours through a chance meeting with Frederick George Jackson, who was leading the British Jackson-Harmsworth Expedition, which was wintering on the island. Jackson informed them that they were on Franz Josef Land. Finally, Nansen and Johansen made it back to Vardø in the north of Norway.

Fig. 6.14

The hut where Nansen and Johansen spent nine months. No Netflix, no streaming video, no North face sleeping bags, no cell phones. Neither had had the advantage of years of astronaut training or spending months in analogs. Neither had written a psychological evaluation questionnaire. Together they proved that the human spirit is resilient, and that the psychological aspect will be the least of mission planners worries when astronauts finally strike out for Mars. (Public domain) Credit: NASA

Another negative the doom and gloom merchants like to focus on is boredom. Personally, I’ve never heard of any astronaut complaining of being bored. In fact, in all the astronaut autobiographies written, the focus is mostly on the positive Psychologists even have a term for how astronauts spin the positive aspects of being in such an isolated and extreme environment: salutogenesis. It’s a term coined by Aaron Antonovsky, a professor of medical sociology, and it is intended to convey the idea that under certain conditions stress is beneficial and health-promoting, and not pathogenic or destructive to health. As you can imagine, polar explorers experienced all sorts of negative effects as they struggled to cope with isolation, deprivation, and extreme conditions. But, on the flip side, the elation of having coped with so much successfully brought positive benefits. So, explorers tended to enjoy the experience and enjoyed positive reactions to the challenges of the environment. Not only that, but this unique group of individuals thrived on the feeling of having successfully overcome these challenges. In their diaries they routinely refer to the beauty and grandeur of the land, ice, and sea, the camaraderie and mutual support of the team, and the thrill of facing and overcoming the challenges of the environment. Which is why so many signed up for repeat expeditions. But space agencies and space psychologists are still fixated with the deleterious effects of long duration missions and their countermeasures and scant attention has been paid to the beneficial effects of such an endeavour. Which is a shame, because polar exploration has shown that individuals who adapt positively to an inhospitable or extreme environment can derive benefit from their experiences. And this positive effect may include an initial improvement in mental health as a crewmember adapts to the environment.

Despite some researchers choosing to ignore the salutogenic effects of spaceflight, these effects have been observed during most missions. Astronauts report positively about friendship and the cohesiveness among the crew, satisfaction in jobs well done, pride in having been chosen to fly in space, and an appreciation of the beauty of Earth from space—this effect has been given the term the overview effect (I strongly recommend the following video that describes this phenomenon: https://www.youtube.com/watch?v=CHMIfOecrlo). In fact, the current trend in memoirs written by spacefarers is to refer to positive emotions three times as often as to negative ones, a good recent example being Chris Hadfield’s An Astronaut’s Guide to Life on Earth. Astronauts autobiographical accounts routinely mention trust in others, autonomy, initiative, industry, strong personal identity, and a conviction that their life makes sense and is worthwhile. These astronauts were confident about their emotional stability and coping abilities and viewed themselves as active agents in dealing with problems—just like Shackleton and his crew, or Nansen and Johansen. These autobiographical reports point to some inescapable conclusions. First, space agencies select resilient people who are good at solving problems and getting along with others (Table 6.3). Second, for most astronauts, spaceflight is their peak life experience. Third, among post-flight changes, astronauts consider themselves to be changed for the better. These findings in no way detract from the importance of anticipating problems and preparing countermeasures for the challenges of long duration missions—but equally, they underline the importance of also considering the unique benefits of this great adventure, to the astronauts themselves and to humankind.

Table 6.3 Astronauts characteristics for long duration missions

So, we’ve reviewed some of the physiological and psychological consequences of spending time on orbit and some of the countermeasures that may be employed, but what happens if, despite taking all the precautions, an accident occurs that requires the chief medical officer to break out the medical kit? Performing surgery in spaceflight presents all sorts of challenges due to the unique environment and conditions of space. We’ll discuss some of them here.

If you’re a surgeon faced with operating on a crewmember, one of the first tasks is to stabilize and restrain the patient because surgeons rely on a stable environment to perform precise surgical procedures. In microgravity, there is no natural way to keep a patient or surgical tools in place but there are some traditional methods of restraint used in Earth-based surgeries that can be adapted for restraining an injured astronaut during surgery in space, one of which is the use of tethering and straps. These specialized tethering systems and adjustable straps can be used to secure the injured astronaut to the surgical table or a stable surface. To ensure optimal body positioning, Velcro straps and soft restraints can be used to secure the patient’s limbs and body. If thus system doesn’t work, then a vacuum mattress or an inflatable air chamber could be used. A vacuum mattress is air-tight and molds to the shape of the patient’s body whereas an inflatable air chamber can be used to create gentle pressure around the patient’s body, stabilizing them without causing discomfort. Once the surgeon has the patient secured it is time to ensure positive control of the surgical instruments. One way to achieve this is by using magnetic anchoring.

Now, with the Mars Messiah’s plans to establish a human settlement on Mars sometime in the next half a century, the chances are this operation might be performed on a planetary surface, so one of the next considerations is dealing with the communication delay. During surgery on Mars, the communication delay will present a significant challenge due to the substantial time delay in transmitting signals between Earth and Mars. Depending on the positions of the planets in their respective orbits, communication delays can range from around 4 minutes (at their closest) to over 22 minutes (at their farthest). This delay could severely impact real-time decision-making and guidance during surgical procedures. So, to address this challenge, surgeons will need to adopt a combination of technologies, strategies, and protocols. For example, autonomous systems, such as surgical robots (Fig. 6.15) will need to be developed that can perform tasks with minimal to no human intervention. These systems will be pre-programmed with a range of surgical procedures and scenarios.

Fig. 6.15

A da Vinci Surgical System. (Credit: Public domain)

This new breed of robotic surgical systems will need to be equipped with high-definition cameras, 3D imaging capabilities, and other advanced sensors to provide real-time feedback. Surgeons on Earth could then remotely assess the situation using this data, even with the communication delay.

Virtual reality (VR) and augmented reality (AR) technologies will no doubt assume ever greater importance to create an immersive experience for remote surgeons. And to prepare for the surgery, simulation and training of these remote surgical teams will be crucial. One element of these simulations will be to help surgeons practice for the communication delay and understand how to respond in various situations. Another element will be preoperative planning and the establishment of clear communication protocols between the on-site and remote surgical teams. Helping the surgeons will be a real-time decision support based on AI-driven decision support systems that can analyze data from the surgical site and provide suggestions or alerts to the remote surgical team based on predefined criteria. This system will also be responsible for implementing redundant systems and fail-safe mechanisms to mitigate technical failures that could occur in the remote guidance equipment or the robotic surgical systems.

Now, to the surgery. Microgravity presents myriad problems for a surgeon since the absence of gravity in space changes the behavior of fluids, organs, and tissues, which makes it difficult to control bleeding and manage bodily fluids during surgery (Fig. 6.16). That said, there are strategies and techniques flight surgeons could employ to manage bleeding effectively. For example, hemostatic agents could be used. These agents are substances that promote blood clotting, and they can be applied directly to the bleeding site to control bleeding. Another strategy is using electrocautery and laser devices that could be used to seal blood vessels by creating controlled burns or coagulation. Clips and ligatures, which are small devices used to close off blood vessels and prevent bleeding, could be used to seal blood vessels during surgery, and to remove excess blood from the surgical field, the surgeon could use suction and irrigation, although because of the way blood behaves in microgravity, this technique would need to be adapted. Inflatable tourniquets could be used to temporarily block blood flow to a specific area of the body during surgery, reducing blood loss and surgical staplers could be used to securely close blood vessels and tissue layers. Another commonly used technique used on Earth that could be adapted to work in microgravity is the application of hemostatic sponges. And, once the wound is ready for closing, suturing would be required, but, again, this technique will require some modification.

Fig. 6.16

The Aqueous Immersive Surgical Solution AISS. The ability to provide surgical support on the surface of the Moon or Mars is a challenge since in these microgravity or partial gravity environments, containment of the surgical site is required to prevent cabin contamination, maintain acceptable visualization of the surgical field, avoid gaseous embolization in the patient, and control bleeding. One possible solution is the AISS. Developed by Dr. George Pantalos (University of Louisville) and his colleagues at Carnegie Mellon University, this container creates a hermetically sealed surgical field that controls and staunches bleeding during surgery by isolating the wound and creating an aqueous environment within the surgical field

When performing surgery, drugs are administered. But the problem with microgravity is that it affects pharmacokinetics and pharmacodynamics. These two processes, which refer to how drugs move through the body and how they exert their effects, are influenced by the unique conditions of microgravity. For example, the absorption and distribution of drugs in the body can be altered due to microgravity-induced fluid shifts within the body, affecting blood flow and potentially altering drug absorption and distribution. This could impact the rate at which drugs are delivered to target tissues. Then there is the problem of altered metabolism, which is due to changes in gravitational forces. This might affect the rates at which drugs are metabolized by the liver and other organs. Enzyme activities involved in drug metabolism could also be influenced. Microgravity also affects kidney function and fluid balance, which might affect drug excretion, which could lead to drugs staying in the body longer than expected. Another process affected is protein binding since changes in protein synthesis and distribution in microgravity might alter the binding of drugs to proteins in the blood, potentially affecting their pharmacokinetics. In addition to the pharmacokinetic changes, there are pharmacodynamic changes to consider, which include, among other changes, the clearance time of drugs from the body, and the sensitivity of drug receptors in cells, which could lead to altered responses to drugs, requiring adjustments in dosing. Added to these changes are the effects of cellular signaling, since cellular signaling pathways that drugs interact with could be affected by microgravity, which would lead to changes in how drugs exert their effects. And then there is the tissue response to consider, since microgravity-induced changes in tissue structure and function might impact how drugs interact with and affect target tissues. And the altered pharmacokinetics and pharmacodynamics in microgravity might lead to changes in drug-drug interactions, potentially impacting the safety and efficacy of drug combinations.

With all these changes affecting something as straightforward as administering drugs, you may be wondering how effective anesthesia in microgravity will be. After all, if you are the patient being operated on, it would be comforting to know that you will be properly sedated. Unfortunately, in common with many surgical procedures, administering anesthesia presents several unique challenges of its own. One challenge is fluid redistribution since microgravity causes fluid to shift towards the head, potentially affecting the distribution of intravenous medications and altering drug concentrations in the bloodstream. Then there is the challenge of airway management, which may be problematic because the absence of gravity does not assist in airway clearance or drainage of fluids. And, since anesthesia is a drug, the problems alluded to in the previous paragraph apply here, so the altered fluid dynamics in microgravity could impact the rate of drug infusion and distribution throughout the body. This could affect the timing and effectiveness of anesthesia induction and maintenance. Even if the anesthesia is effective, the surgeon may encounter difficulties monitoring vital signs due to the lack of a stable reference point. Another variable to consider is response variability, which pertains to the altered physiological responses to drugs in microgravity. The problem is every person has their own unique response to drugs. Some people only need one painkiller pill to do the job, whereas others need two or three pills. The same applies to individual astronauts responding differently to anesthesia agents, making it challenging to predict and manage dosing. And then there are cardiovascular changes, because, as we know by now, fluid shifts and changes in cardiovascular function in microgravity can affect blood pressure, heart rate, and cardiac output, which will require adjustments in anesthesia management. Obviously, addressing these challenges requires collaboration between anesthesiologists, surgeons, engineers, and space medicine experts, and one platform that can help with this and other medical procedures is simulation.

One such simulation platform is virtual reality (VR). This type of simulation can play a significant role in preparing surgeons for performing surgery in microgravity by providing a realistic and immersive training environment that simulates the challenges and conditions of space. Here’s how VR simulation can help. Firstly, VR simulations can replicate the microgravity environment, helping surgeons become familiar with the absence of gravity and its effects on movement, instrument handling, and fluid dynamics. Secondly, VR allows surgeons to practice surgical procedures in microgravity settings, allowing them to experience and adapt to the unique challenges they might encounter during space surgeries. Not only that, but VR simulations can feature virtual versions of the equipment used in space surgeries, allowing surgeons to practice with tools and instruments designed for use in microgravity. This allows surgeons to refine their motor skills and dexterity in a space-like environment, where precision and control will be crucial due to the lack of gravity. Another application of VR is team training, since VR simulations can facilitate multidisciplinary team training, where surgeons, anesthesiologists, and other medical personnel can practice coordinating their actions in a microgravity setting. Added to this is the utility of using VR to replicate emergency situations that might arise during space surgeries, helping surgeons develop strategies to handle unexpected complications, and these scenarios can obviously present varying scenarios to challenge surgeons’ decision-making abilities and adaptability to different microgravity-induced conditions. Given the utility of VR it isn’t surprising that VR simulations have been used on the International Space Station (ISS) to refresh astronaut skills, but while VR simulations can offer valuable training, it’s important to recognize that they provide a simulated experience and might not perfectly replicate the complexities of microgravity surgery. Integrating VR training with other forms of training, such as parabolic flights or physical mock-ups, can provide a more comprehensive preparation for surgeons. As technology advances, VR simulations can become increasingly sophisticated, offering an integral part of the training and preparation process for surgeons who will be performing surgeries in space environments.