Space Medicine is the practice and science of medicine on astronauts in outer space and the health effects on the body of space flight. It is also concerned with equipping astronauts to deal with medical treatments and emergencies in space. Some of the changes to the body during space flight affect the foot and lower limb.
Health problems associated with space travel:
Heart rhythm disturbances (eg atrial fibrillation); proprioception deficits and poor coordination; wound healing is impaired; immune system suppression (T-cells do not reproduce properly in space); increased infection risk (experiments have shown some bacteria can become more virulent in zero gravity); osteoporosis (‘spaceflight osteopenia’; after several months in space it can take several years for bone mineral density to return to normal); loss of muscle mass (as muscles do longer need to work as hard in zero gravity); facial swelling; increase in height; hypotension; syncope; blurred vision; sleep disorders (common); fatigue (long period of time without rest and poor sleep); possible decreased fertility; decompression sickness (risk is high when returning from space walks in space suits due to pressure changes); may accelerate the onset of Alzheimer’s disease; increased radiation exposure; psychological issues (especially from the isolation).
Diagnostic ultrasound being used by astronauts. From the NASA Photo Library.
Medical Treatment During Space Flight:
Medical problems and emergencies will happen during space flight. Resources to deal with these will be limited and it will take time to return ill or injured astronauts to earth.
To date there have been a few emergencies such as arrhythmias, renal stone, venous thrombosis (see case report here), and infections that have been documented during space flights. Some common non-emergency problems include motion sickness; sinus congestion; constipation; headaches; low back pain (may affect 50% of astronauts); upper respiratory tract infection; minor cuts and bruises; musculoskeletal trauma; corneal irritation; insomnia.
NASA do have a number of publicly available documents on space crew health issues (eg this one) that specify the levels and standards of care as well as the risks. Medical training is provided to astronauts and missions are supported by medical staff in mission control.
Ultrasound is the main diagnostic imaging tool on International Space Station. X-ray and CT involve radiation so is too dangerous and MRI equipment is currently too heavy to make it practical.
The German Society of Aerospace Medicine and the European Society of Aerospace Medicine Space Medicine Group have produced these guidelines for performing CPR in microgravity.
Astronaut performing exercise to counter some of the effects of zero gravity.
Most Recent Textbooks in Space Medicine (advertisement):
Effect of Space Travel on the Foot and Lower Limb:
The feet and legs become somewhat redundant in space as there is no weightbearing, so there is substantial deconditioning with the bones and muscles deteriorating.
There is a redistribution of body fluids from the lower to upper body due to no gravitational loading. This manifests as the facial oedema and the reduced leg volume gives the so-called ‘chicken legs’ appearance.
Selected Relevant Research on the Effects of Space Travel on the Foot and Lower Limb:
Saveko et al used a 7 day dry immersion technique to simulate the zero gravity of space flight found a raising of the longitudinal arch and by flattening the transverse arch, which was accompanied by a decrease in the soft tissues stiffness of the foot and superficial muscles of the shin.
Cavanagh et al (2010) used in-shoe plantar pressure measuring in 4 astronauts having a 6 month stay on the International Space Station. The insoles collected data during the entire typical working days both on Earth and on-orbit. BMD estimates from the hip and spine regions were obtained from dual energy X-ray absorptiometry (DXA) pre- and post-flight. They found that in-shoe forces during treadmill walking and running on the ISS were reduced by 25% and 46% compared to similar activities on Earth. Bone mineral density decreased by 0.71% and 0.83% per month during their missions in the femoral neck and lumbar spine. They concluded that the ISS exercise durations and/or loading were insufficient to provide the loading stimulus required to prevent bone loss.
Genc et ak (2010) investigated foot loading during exercise on the ISS. Three exercise countermeasure devices were available on the International Space Station (ISS) were the treadmill with vibration isolation and stabilization (TVIS), the cycle ergometer with vibration isolation and stabilization (CEVIS), and the interim resistance exercise device (iRED). They compared in-shoe loads to those using that exercise equipment and comparable loads on Earth and concluded that, in general, that the three exercise devices studied were not able to elicit loads comparable to exercise on Earth.
Miller et al (2010) looked at toe clearance during gait immediately on return from space and reported a lower toe clearance which is considered a risk factor for falls and tripping.
Lowrey et al (2014) reported: “Skin sensory input from the foot soles is coupled with vestibular input to facilitate body orientation in a gravitational environment…..Overall an increase in vibration threshold at low frequencies was found, indicating a decreased sensitivity to slow-adapting receptor input. Increased sensitivity to high-frequency vibration (250 Hz) was found for 6 out of 11 subjects indicating an increased sensitivity to velocity and high-frequency information, reflecting increased weighting of FAII receptor input in these subjects.”
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Foot forces during typical days on the international space station (Podiatry Arena)
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