Table 2.

Countermeasures to minimize risks to astronauts before, during and after spaceflight

Physiologic effects; duration of flight	Before flight	During flight	After flight
Shift in body fluids (cardiovascular effects)
Long and short duration	None	Exercise Negative pressure suits for the lower body (to mechanically induce an earth-equivalent body fluid distribution while in space) On re-entry: isotonic fluid taken orally,2 use of a pressurized anti-gravity suit to minimize fluid pooling in the legs, use of a liquid cooling garment, recumbent position for astronauts on long-duration missions3	The use of midodrine (to counter postflight orthostatic intolerance) is being considered
Space motion sickness (neurovestibular effects)
Long and short duration	Neurovestibular conditioning (virtual reality, parabolic or aerobatic flights) Antinauseant medications	Antinauseant medications4 (promethazine, scopolamine5) often given with dextroamphetamine to counter sedation	Intravenous antinauseant and fluid administration for severe postlanding syndrome
Muscle atrophy
Long and short duration	Resistance exercise program Aerobic exercise program	Exercise (aerobic and strength) monitored and modified by on-ground medical support team6,7,8 Others measures under consideration: electrical muscle stimulation, dietary supplementation with amino acids, artificial gravity (e.g., rotating spaceship)6,7,8,9	Muscle conditioning and rehabilitation program, including a combination of adapted exercises, massages, icing and nonsteroidal anti-inflammatory agents
Bone demineralization
Long and short duration	3 DXA scans per year
Long duration	2 DXA scans within 6 months after flight	Resistance exercises10,11,12 Diet supplemented with calcium and vitamins D and K10,13 Others measures under consideration: bisphosphonates; potassium citrate; parathyroid hormone; low magnitude, high frequency vibrations10,11,14	4 DXA scans over 3 years Temporary restriction of some activities (e.g., flying high-performance jets)14,15
Psychosocial effects
Long and short duration	Specific criteria for recruitment16,17 and specific behavioural competencies for assignment to missions Didactic training, including teamwork in multicultural settings, and field-based training in leadership and followership skills	Individualized work schedules monitored by ground support crew, with 8 hours rest per day Short-acting hypnotics (to prevent sleep loss and cumulative sleep deficit) and modafanil (to enhance performance after periods of reduced sleep)
Long duration			Psychological debriefing sessions
Immune dysregulation
Long and short duration	Quarantine program Restricted contact with general public for 1 week before flight	Daily exposure to artificial gravity18 and nutritional supplementation with nucleotides19 are being considered	Collection of biological samples to assess immune function

Note: DXA = dual energy x-ray absorptiometry.