Physiological effects Effect of spaceflight on the human body

1 physiological effects

1.1 research
1.2 ascent , reentry
1.3 space environments

1.3.1 vacuum
1.3.2 temperature
1.3.3 radiation


1.4 weightlessness

1.4.1 motion sickness
1.4.2 bone , muscle deterioration
1.4.3 fluid redistribution
1.4.4 disruption of senses

1.4.4.1 vision
1.4.4.2 taste


1.4.5 additional physiological effects

physiological effects

many of environmental conditions experienced humans during spaceflight different in humans evolved; however, technology able shield people harshest conditions, such offered spaceship or spacesuit. immediate needs breathable air , drinkable water addressed life support system, group of devices allow human beings survive in outer space. life support system supplies air, water , food. must maintain temperature , pressure within acceptable limits , deal body s waste products. shielding against harmful external influences such radiation , micro-meteorites necessary.

of course, not possible remove hazards; important factor affecting human physical well-being in space weightlessness, more accurately defined micro-g environment. living in type of environment impacts body in 3 important ways: loss of proprioception, changes in fluid distribution, , deterioration of musculoskeletal system.

on 2 november 2017, scientists reported significant changes in position , structure of brain have been found in astronauts have taken trips in space, based on mri studies. astronauts took longer space trips associated greater brain changes.

research

space medicine developing medical practice studies health of astronauts living in outer space. main purpose of academic pursuit discover how , how long people can survive extreme conditions in space, , how fast can re-adapt earth s environment after returning space. space medicine seeks develop preventative , palliative measures ease suffering caused living in environment humans not adapted.

ascent , reentry

during takeoff , reentry space travelers can experience several times normal gravity. untrained person can withstand 3g, can blackout @ 4 6g. g-force in vertical direction more difficult tolerate force perpendicular spine because blood flows away brain , eyes. first person experiences temporary loss of vision , @ higher g-forces loses consciousness. g-force training , g-suit constricts body keep more blood in head can mitigate effects. spacecraft designed keep g-forces within comfortable limits.

space environments

the environment of space lethal without appropriate protection: greatest threat in vacuum of space derives lack of oxygen , pressure, although temperature , radiation pose risks.

vacuum

this painting, experiment on bird in air pump depicts experiment performed robert boyle in 1660 test effect of vacuum on living system.

human physiology adapted living within atmosphere of earth, , amount of oxygen required in air breathe. minimum concentration, or partial pressure, of oxygen can tolerated 16 kpa (0.16 bar). below this, astronaut @ risk of becoming unconscious , dying hypoxia. in vacuum of space, gas exchange in lungs continues normal results in removal of gases, including oxygen, bloodstream. after 9 12 seconds, deoxygenated blood reaches brain, , results in loss of consciousness. death gradually follow after 2 minutes of exposure—though absolute limits uncertain.

humans , other animals exposed vacuum lose consciousness after few seconds , die of hypoxia within minutes. blood , other body fluids boil when pressure drops below 6.3 kpa (47 torr), vapor pressure of water @ body temperature. condition called ebullism. steam may bloat body twice normal size , slow circulation, tissues elastic , porous enough prevent rupture. ebullism slowed pressure containment of blood vessels, blood remains liquid. swelling , ebullism can reduced containment in flight suit. space shuttle astronauts wore fitted elastic garment called crew altitude protection suit (caps) prevented ebullism @ pressures low 2 kpa (15 torr). spacesuits necessary prevent ebullism above 19 km. spacesuits use 20 kpa (150 torr) of pure oxygen, enough sustain full consciousness. pressure high enough prevent ebullism, simple evaporation of blood, or of gases dissolved in blood, can still cause decompression sickness (the bends) , gas embolisms if not managed.

a short-term exposure vacuum of 30 seconds unlikely cause permanent physical damage. animal experiments show rapid , complete recovery normal exposures shorter 90 seconds, while longer full-body exposures fatal , resuscitation has never been successful. there limited amount of data available human accidents, consistent animal data. limbs may exposed longer if breathing not impaired. rapid decompression can more dangerous vacuum exposure itself. if victim not hold breath, venting through windpipe may slow prevent fatal rupture of delicate alveoli of lungs. eardrums , sinuses may ruptured rapid decompression, soft tissues may bruise , seep blood, , stress of shock accelerates oxygen consumption, leading hypoxia. injuries caused rapid decompression called barotrauma, , known scuba diving accidents. pressure drop small 100 torr (13 kpa), produces no symptoms if gradual, may fatal if occurs suddenly.

most of information known way human body reacts due accidental decompression, during experimental spaceflight projects. 1 such case discussed in nasa technical report: rapid (explosive) decompression emergencies in pressure-suited subjects:

@ nasa s manned spacecraft center (now renamed johnson space center) had test subject accidentally exposed near vacuum (less 1 psi) [7 kpa] in incident involving leaking space suit in vacuum chamber in 65. remained conscious 14 seconds, time takes o2 deprived blood go lungs brain. suit did not reach hard vacuum, , began repressurizing chamber within 15 seconds. subject regained consciousness @ around 15,000 feet [4600 m] equivalent altitude. subject later reported feel , hear air leaking out, , last conscious memory of water on tongue beginning boil.

there has been 1 recorded incident of death decompression in spaceflight, soyuz 11 decompression accident in 1971, resulted in death of 3 cosmonauts on board.

temperature

in vacuum, there no medium removing heat body conduction or convection. loss of heat radiation 310 k temperature of person 3 k of outer space. slow process, in clothed person, there no danger of freezing. rapid evaporative cooling of skin moisture in vacuum may create frost, particularly in mouth, not significant hazard.

exposure intense radiation of direct, unfiltered sunlight lead local heating, though distributed body s conductivity , blood circulation. other solar radiation, particularly ultraviolet rays, however, may cause severe sunburn.

radiation


comparison of radiation doses – includes amount detected on trip earth mars rad on msl (2011–2013).

without protection of earth s atmosphere , magnetosphere astronauts exposed high levels of radiation. year in low earth orbit results in dose of radiation 10 times of annual dose on earth. high levels of radiation damage lymphocytes, cells heavily involved in maintaining immune system; damage contributes lowered immunity experienced astronauts. radiation has been linked higher incidence of cataracts in astronauts. outside protection of low earth orbit, galactic cosmic rays present further challenges human spaceflight, health threat cosmic rays increases chances of cancer on decade or more of exposure. nasa-supported study reported radiation may harm brain of astronauts , accelerate onset of alzheimer s disease. solar flare events (though rare) can give fatal radiation dose in minutes. thought protective shielding , protective drugs may lower risks acceptable level.

crew living on international space station (iss) partially protected space environment earth s magnetic field, magnetosphere deflects solar wind around earth , iss. nevertheless, solar flares powerful enough warp , penetrate magnetic defences, , still hazard crew. crew of expedition 10 took shelter precaution in 2005 in more heavily shielded part of station designed purpose. however, beyond limited protection of earth s magnetosphere, interplanetary manned missions more vulnerable. lawrence townsend of university of tennessee , others have studied powerful solar flare ever recorded. radiation doses astronauts receive flare of magnitude cause acute radiation sickness , possibly death.

a video made crew of international space station showing aurora australis, caused high-energy particles in space environment.

there scientific concern extended spaceflight might slow down body s ability protect against diseases. radiation can penetrate living tissue , cause both short , long-term damage bone marrow stem cells create blood , immune systems. in particular, causes chromosomal aberrations in lymphocytes. these cells central immune system, damage weakens immune system, means in addition increased vulnerability new exposures, viruses present in body—which suppressed—become active. in space, t-cells (a form of lymphocyte) less able reproduce properly, , t-cells reproduce less able fight off infection. on time immunodeficiency results in rapid spread of infection among crew members, in confined areas of space flight systems.

on 31 may 2013, nasa scientists reported possible manned mission mars may involve great radiation risk based on amount of energetic particle radiation detected rad on mars science laboratory while traveling earth mars in 2011–2012.

in september 2017, nasa reported radiation levels on surface of planet mars temporarily doubled, , associated aurora 25-times brighter observed earlier, due massive, , unexpected, solar storm in middle of month.

weightlessness

astronauts on iss in weightless conditions. michael foale can seen exercising in foreground.

following advent of space stations can inhabited long periods of time, exposure weightlessness has been demonstrated have deleterious effects on human health. humans well-adapted physical conditions @ surface of earth, , in response weightlessness, various physiological systems begin change, , in cases, atrophy. though these changes temporary, have long-term impact on human health.

short-term exposure microgravity causes space adaptation syndrome, self-limiting nausea caused derangement of vestibular system. long-term exposure causes multiple health problems, 1 of significant being loss of bone , muscle mass. on time these deconditioning effects can impair astronauts performance, increase risk of injury, reduce aerobic capacity, , slow down cardiovascular system. human body consists of fluids, gravity tends force them lower half of body, , our bodies have many systems balance situation. when released pull of gravity, these systems continue work, causing general redistribution of fluids upper half of body. cause of round-faced puffiness seen in astronauts. redistributing fluids around body causes balance disorders, distorted vision, , loss of taste , smell.

a 2006 space shuttle experiment found salmonella typhimurium, bacterium can cause food poisoning, became more virulent when cultivated in space. on april 29, 2013, scientists in rensselaer polytechnic institute, funded nasa, reported that, during spaceflight on international space station, microbes seem adapt space environment in ways not observed on earth , in ways can lead increases in growth , virulence . more recently, in 2017, bacteria found more resistant antibiotics , thrive in near-weightlessness of space. microorganisms have been observed survive vacuum of outer space.

motion sickness


bruce mccandless floating free in orbit space suit , manned maneuvering unit.

the common problem experienced humans in initial hours of weightlessness known space adaptation syndrome or sas, commonly referred space sickness. related motion sickness, , arises vestibular system adapts weightlessness. symptoms of sas include nausea , vomiting, vertigo, headaches, lethargy, , overall malaise. first case of sas reported cosmonaut gherman titov in 1961. since then, 45% of people have flown in space have suffered condition. duration of space sickness varies, has lasted more 72 hours, after body adjusts new environment.

on earth, our bodies react automatically gravity, maintaining both posture , locomotion in downward pulling world. in microgravity environments, these constant signals absent: otolith organs in inner ear sensitive linear acceleration , no longer perceive downwards bias; muscles no longer required contract maintain posture, , pressure receptors in feet , ankles no longer signal direction of down . these changes can result in visual-orientation illusions astronaut feels has flipped 180 degrees. on half of astronauts experience symptoms of motion sickness first 3 days of travel due conflict between body expects , body perceives. on time brain adapts , although these illusions can still occur, astronauts begin see down feet are. people returning earth after extended weightless periods have readjust force of gravity , may have problems standing up, focusing gaze, walking , turning. initial problem, recover these abilities quickly.

nasa jokingly measures sas using garn scale , named united states senator jake garn, sickness during sts-51-d worst on record. accordingly, 1 garn equivalent severe possible case of space sickness. studying how changes can affect balance in human body—involving senses, brain, inner ear, , blood pressure—nasa hopes develop treatments can used on earth , in space correct balance disorders. until then, astronauts rely on medication, such midodrine , dimenhydrinate anti-nausea patches, required (such when space suits worn, because vomiting space suit fatal).

bone , muscle deterioration


aboard international space station, astronaut frank de winne attached colbert bungee cords

a major effect of long-term weightlessness involves loss of bone , muscle mass. without effects of gravity, skeletal muscle no longer required maintain posture , muscle groups used in moving around in weightless environment differ required in terrestrial locomotion. in weightless environment, astronauts put no weight on muscles or leg muscles used standing up. muscles start weaken , smaller. consequently, muscles atrophy rapidly, , without regular exercise astronauts can lose 20% of muscle mass in 5 11 days types of muscle fibre prominent in muscles change. slow twitch endurance fibres used maintain posture replaced fast twitch rapidly contracting fibres insufficient heavy labour. advances in research on exercise, hormone supplements , medication may maintain muscle , body mass.

bone metabolism changes. normally, bone laid down in direction of mechanical stress. however, in microgravity environment there little mechanical stress. results in loss of bone tissue approximately 1.5% per month lower vertebrae, hip , femur. due microgravity , decreased load on bones, there rapid increase in bone loss, 3% cortical bone loss per decade 1% every month body exposed microgravity, otherwise healthy adult. rapid change in bone density dramatic, making bones frail , resulting in symptoms resemble of osteoporosis. on earth, bones being shed , regenerated through well-balanced system involves signaling of osteoblasts , osteoclasts. these systems coupled, whenever bone broken down, newly formed layers take place—neither should happen without other, in healthy adult. in space, however, there increase in osteoclast activity due microgravity. problem, because osteoclasts break down bones minerals reabsorbed body. osteoblasts not consecutively active osteoclasts, causing bone diminished no recovery. increase in osteoclasts activity has been seen particularly in pelvic region, because region carries biggest load gravity present. study demonstrated in healthy mice, osteoclasts appearance increased 197%, accompanied down-regulation of osteoblasts , growth factors known formation of new bone, after sixteen days of exposure microgravity. elevated blood calcium levels lost bone result in dangerous calcification of soft tissues , potential kidney stone formation. still unknown whether bone recovers completely. unlike people osteoporosis, astronauts regain bone density. after 3–4 month trip space, takes 2–3 years regain lost bone density. new techniques being developed astronauts recover faster. research on diet, exercise , medication may hold potential aid process of growing new bone.

to prevent of these adverse physiological effects, iss equipped 2 treadmills (including colbert), , ared (advanced resistive exercise device), enable various weight-lifting exercises add muscle nothing bone density, , stationary bicycle; each astronaut spends @ least 2 hours per day exercising on equipment. astronauts use bungee cords strap treadmill. astronauts subject long periods of weightlessness wear pants elastic bands attached between waistband , cuffs compress leg bones , reduce osteopenia.

currently, nasa using advanced computational tools understand how best counteract bone , muscle atrophy experienced astronauts in microgravity environments prolonged periods of time. human research program s human health countermeasures element chartered digital astronaut project investigate targeted questions exercise countermeasure regimes. nasa focusing on integrating model of advanced resistive exercise device (ared) on board international space station opensim musculoskeletal models of humans exercising device. goal of work use inverse dynamics estimate joint torques , muscle forces resulting using ared, , more accurately prescribe exercise regimens astronauts. these joint torques , muscle forces used in conjunction more fundamental computational simulations of bone remodeling , muscle adaptation in order more model end effects of such countermeasures, , determine whether proposed exercise regime sufficient sustain astronaut musculoskeletal health.

fluid redistribution

the effects of microgravity on fluid distribution around body (greatly exaggerated).



astronaut clayton anderson observes water bubble floats in front of him on discovery. water cohesion plays bigger role in microgravity on earth

the second effect of weightlessness takes place in human fluids. body made of 60% water, of intra-vascular , inter-cellular. within few moments of entering microgravity environment, fluid re-distributed upper body resulting in bulging neck veins, puffy face , sinus , nasal congestion can last throughout duration of trip , symptoms of common cold. in space autonomic reactions of body maintain blood pressure not required , fluid distributed more around whole body. results in decrease in plasma volume of around 20%. these fluid shifts initiate cascade of adaptive systemic effects can dangerous upon return earth. orthostatic intolerance results in astronauts returning earth after extended space missions being unable stand unassisted more 10 minutes @ time without fainting. due in part changes in autonomic regulation of blood pressure , loss of plasma volume. although effect becomes worse longer time spent in space, yet individuals have returned normal within @ few weeks of landing.

in space, astronauts lose fluid volume—including 22% of blood volume. because has less blood pump, heart atrophy. weakened heart results in low blood pressure , can produce problem orthostatic tolerance , or body s ability send enough oxygen brain without astronaut s fainting or becoming dizzy. under effects of earth s gravity, blood , other body fluids pulled towards lower body. when gravity taken away or reduced during space exploration, blood tends collect in upper body instead, resulting in facial edema , other unwelcome side effects. upon return earth, blood begins pool in lower extremities again, resulting in orthostatic hypotension.

disruption of senses
vision

in 2013 nasa published study found changes eyes , eyesight of monkeys spaceflights longer 6 months. noted changes included flattening of eyeball , changes retina. space traveler s eye-sight can become blurry after time in space. effect known cosmic ray visual phenomena

...[a] nasa survey of 300 male , female astronauts, 23 percent of short-flight , 49 percent of long-flight astronauts said had experienced problems both near , distance vision during missions. again, people vision problems persisted years afterward.

intracranial pressure

because weightlessness increases amount of fluid in upper part of body, astronauts experience increased intracranial pressure. appears increase pressure on backs of eyeballs, affecting shape , crushing optic nerve. effect noticed in 2012 in study using mri scans of astronauts had returned earth following @ least 1 month in space. such eyesight problems major concern future deep space flight missions, including manned mission planet mars.

if indeed elevated intracranial pressure cause, artificial gravity might present 1 solution, many human health risks in space. however, such artificial gravitational systems have yet proven. more, sophisticated artificial gravity, state of relative microgravity may remain, risks of remain unknown.

taste

one effect of weightlessness on humans astronauts report change in sense of taste when in space. astronauts find food bland, others find favorite foods no longer taste (one enjoyed coffee disliked taste on mission stopped drinking after returning earth); astronauts enjoy eating foods not eat, , experience no change whatsoever. multiple tests have not identified cause, , several theories have been suggested, including food degradation, , psychological changes such boredom. astronauts choose strong-tasting food combat loss of taste.

additional physiological effects

after 2 months, calluses on bottoms of feet molt , fall off lack of use, leaving soft new skin. tops of feet become, contrast, raw , painfully sensitive. tears cannot shed while crying, stick ball. in microgravity odors permeate environment, , nasa found in test smell of cream sherry triggered gag reflex. various other physical discomforts such , abdominal pain common because of readjustment gravity, in space there no gravity , these muscles freely stretch. these may part of asthenization syndrome reported cosmonauts living in space on extended period of time, regarded anecdotal astronauts. fatigue, listlessness, , psychosomatic worries part of syndrome. data inconclusive; however, syndrome appear exist manifestation of internal , external stress crews in space must face.

astronauts may not able return earth or receive medical supplies, equipment or personnel if medical emergency occurs. astronauts may have rely long periods on limited existing resources , medical advice ground.