Space Medicine Biological Hazards and Medical Care in Space H.G. Stratmann, M.D.

Space Medicine

Biological Hazards and Medical Care in Space

H.G. Stratmann, M.D.

Vostok Launch

Mercury-Atlas 3 Liftoff

Gemini 12 Liftoff

Apollo 11 Launch

Astronaut on Moon

Skylab

Apollo-Soyuz Apollo capsule

Apollo-Soyuz Soyuz capsule

Mir

Earth from Moon

Terrestrial versus Extraterrestrial Environment

Earth LEO Moon Mars

Atmosphere 78% Nitrogen21% Oxygen

~ None None 95% CO2

3% nitrogen2% argon

Pressure 760 mmHg ~ None None ~ 5 mmHg

Temperature(Celsius)

21o -178o to + 110o ~ same as LEO -120o to +25o

Gravity (g) 1.0 ~ None 0.16 0.38

Radiation(rems/year)

0.1 to 0.2 ~ 14.0-21.0 ~ 20.0 ~ 15.0

Major Biological Risks of Space Travel

• Loss of atmosphere• Exposure to toxins• Mechanical trauma• Acceleration and deceleration• Extreme temperatures• Meteoroids and space debris• Circadian rhythms and sleep• Psychological• Adverse biological effects of microgravity• Radiation

Loss of Atmosphere• Barotrauma

– Expansion of gas temporarily trapped in a body cavity (e.g. ear or sinus)

– Pressure differences causing pain or injury• Decompression sickness

– Ambient atmosphere pressure < partial pressure of inert gases (e.g. nitrogen)

– Nitrogen forms bubbles in bloodstream• “Bends” (pains in joints and muscles)• “Chokes” (gas emboli)• Neurological symptoms (weakness,

convulsions, syncope)

Loss of Atmosphere

• Explosive decompression– Rate of decompression is so great that transient

overpressure occurs in lungs and other air-filled cavities

– Pressure difference in the lungs ≥ 80 mm Hg causes rupture and possible air embolism

– Ebullism - “boiling” of body fluids (e.g. blood)• At body core temperature of 37o C, ebullism

occurs at an ambient pressure of 47 mm Hg (Armstrong limit, roughly an altitude of 19 kilometers)

Loss of Atmosphere

• Ambient pressure/atmosphere in Space Shuttle is similar to sea level on Earth (14.7 psi, 78% nitrogen, 21% oxygen)

• Extravehicular activity (EVA) requires space suit pressure of 4.3 psi

• To prepare for EVA, cabin pressure is slowly lowered (maximum 0.1 psi/sec) to 10.2 psi for 24 hours

• Astronauts don space suits and prebreathe 100% oxygen to purge nitrogen from the blood, then undergo final decompression to 4.3 psi

Toxins

• Ammonia– Used in Shuttle environmental control and life-

support systems– Causes irritation of eyes and mucous membranes– More severe exposure causes dyspnea, vomiting,

and pulmonary edema• Freon

– Used in the heat exchange system– Can produce lightheadedness, dyspnea, liver

damage, and arrhythmias

Toxins

• Hydrazine and monomethyl hydrazine– Use in Shuttle auxillary power unit– Cause severe burns, liver and kidney damage,

and seizures in liquid and gaseous forms• Nitrogen tetroxide

– Used as oxidant in Orbital Maneuvering System– Causes burns and blindness in liquid form and

pneumonitis and pulmonary edema when inhaled (Apollo-Soyuz, 1975)

Trauma and Mechanical Failure

• Astronauts are vulnerable to conventional injuries– Burns– Abrasions– Lacerations– Electrical shock– Fractures– Deliberately inflicted injuries

Space Fatalities

• Soyuz 1 (1967)—1 fatality when parachute system failed during reentry

• Soyuz 11 (1971)—3 fatalities due to sudden depressurization during reentry

• STS-51L (1986)—7 fatalities due to failure in booster rockets

• STS-107 (2003)—7 fatalities during reentry due to damage to left wing

Challenger Explosion

Columbia Launch

Acceleration and Deceleration

• Excessive g (an acceleration of 9.8 m/s2) can cause lightheadedness or syncope

• Upper limit of 4 g for sustained long-term acceleration and (briefly) 18 g for control of movement

• Mercury program—up to 8 g briefly during launch and up to 11 g during reentry– “The Right Stuff”

• Shuttle—3 g during launch, 1.2 to 1.4 g during reentry

Temperature Control

• Heat exchange in space is based solely on radiation, either from the Sun or to space itself—not by conduction or convection

• Effective temperature-control systems are available for both space suits and spacecraft

Meteoroids and Space Debris

• Represent a risk of collision with spacecraft or astronauts during EVA

• Meteoroids consist of stone and iron, with a total of 200 kg within 200 km of Earth’s surface at any given time

• Average velocity of meteoroids is about 16 km/sec

• Most are ≤ 0.1 mm in diameter, but can be ≥ 1 cm

Meteoroids and Space Debris

• Over 3 million kg of man-made debris (old rocket boosters, destroyed satellites, flecks of pain or particles of rocket fuel) are within 2000 km of Earth’s surface

• Over 7000 objects > 20 cm in size are tracked by NORAD

• Collision velocity with an orbiting spacecraft would be about 10 to 13 km/sec

• Range in size from < 0.1 mm to meters

Circadian Rhythms and Sleep

• Body rhythms that occur over a period of about 24 hours

• Sleep/activity cycle, body temperature, heart rate and blood pressure, secretion of growth hormone, cortisol, melatonin, etc.

• Entrained on cyclical environmental stimuli, especially the light-dark cycle based on Earth’s 24-hour rotation

Circadian Rhythms and Sleep

• Rapid travel through different time zones on the Earth’s surface disrupts the synchronization between endogenous biological “clocks” and external cues like light/darkness

• The resulting desynchronosis (“jet lag”) is associated with insomnia, loss of appetite, and fatigue

• Light-dark cycles in space vary widely• Light-dark cycle in low Earth orbit is between 80 to

140 minutes, 30-40% of which is darkness

Circadian Rhythms and Sleep

• Sleep disturbances are common in astronauts– Insomnia– Intermittent, poor quality, or even

prolonged (up to 12 hours) sleep– Sleep disturbances can degrade work

performance and alertness during routine or emergency situations

– Half of Shuttle astronauts use sleeping medications

Psychosocial Stressors of Space Flight

• Isolation, loss of social contacts, reduced sensory stimulation, anxiety, boredom, loss of privacy, dealing with emergencies, overly busy work schedules

• Decreasing motivation, emotional hypersensitivity and lability, and irritability or hostility toward Earth-bound control personnel and crewmates occur during extended missions (e.g. Skylab, Mir, ISS)

Radiation

• Serious hazard for acute and long-term injury during prolonged space missions

• Sun produces electromagnetic (gamma rays and X-rays) and particulate (electrons and protons) radiation

Radiation

• Solar radiation is produced continuously (solar wind) and increases dramatically during solar particle events (high energy protons of 10 to 500 MeV)

• Cosmic radiation is a constant source of radiation, consisting of very high energy protons (up to 2 GeV), alpha particles, and heavier ions originating outside the Solar System (possibly from old supernovas)

Radiation

• Surface of Earth is protected by:– Atmosphere (e.g. ultraviolet light, X-rays,

and gamma rays)– Van Allen Belts

• Two ring-shaped regions at average altitudes of 1000 to 10,000 km and 13,000 to 20,000 km where extraterrestrial electrons and protons are trapped by Earth’s magnetic field

• Lower belt descends to about 500 km at the “South Atlantic anomaly,” where the most radiation exposure in low Earth orbit occurs

Radiation

• Average annual radiation exposure at sea level is 0.1 to 0.2 rem

• Average annual radiation exposure in low Earth orbit (366-day Mir mission) was up to 14 to 21 rem

• EVA and solar events (particularly solar particle events associated with coronal mass ejections) increase radiation exposure– Could expose an astronaut to potential level dose of

hundreds of rem• Proper shielding of spacecraft and use of underground

habitats on lunar and Martian missions would dramatically decrease radiation exposure

Risks of Radiation Exposure

• Acute effects of whole-body exposure– Prodromal syndrome (50 to 150 rem)– Hematopoietic syndrome (150 to 400 rem)– Hematopoietic-gastrointestinal syndrome (400 to

800 rem)– Gastrointestinal syndrome (800 to 2000 rem)– CNS syndrome (>2000 rem)

• LD50 is about 400 rem

Risks of Radiation Exposure

• Long-term effects– Cataracts– Infertility– Defects in offspring– Malignancy

• Breast• Thyroid• Leukemia• Lung

Biological Effects of Micro and Low gravity

• Neurovestibular

• Cardiovascular

• Hematological

• Musculoskeletal

MicrogravityNeurovestibular

• Space Adaptation Syndrome– Occurs in 2/3 of astronauts (males > females)– Headache, nausea, vomiting, dizziness, malaise– Made worse by head and body movements– Develops shortly after entering orbit, peaks after 1

to 2 days, and usually resolves after 4 to 7 days– Responds fairly well to dimenhydrinate,

promethazine, and other motion sickness medications

MicrogravityNeurovestibular

• Sensory illusions (e.g. “inversion illusion”)• Postflight problems

– Feeling “levitated” over bed when trying to sleep at night

– Ataxic gait and walking straight when trying to turn a corner

– Feeling extraordinarily heavy or that one is being pushed to one side while only standing

– May take weeks or months to resolve

MicrogravityCardiovascular

• Shift of 1.5 to 2.0 L of fluid from lower to upper body within minutes of entry into microgravity from loss of gravity-induced hydrostatic pressure– Jugular venous distention– Facial puffiness, nasal congestion, headaches,

nasal voice– Reduction of calf diameters by 30% (“bird legs”)– Enlargement of liver and other visceral organs

MicrogravityCardiovascular

• Decreased sympathetic tone– Can cause orthostatic hypotension and syncope

on return to Earth, particularly when coupled with redistribution of at least 1 L of reduced total body fluid volume to lower extremities

– Heart size and mass decrease slightly– Variable, relatively mild changes in heart rate,

blood pressure, and left ventricular systolic function

– Minor arrhythmias

MicrogravityHematological

• Red blood cell counts decrease by 10 to 20% of preflight values within 2 to 3 weeks in space, then slowly recover after about 60 days– May represent increased destruction and

decreased production of RBCs

• Spherocytes and echinocytes increase

MicrogravityHematological

• Neutrophil counts increase an average of 32%– May be due to stress-induced release of

epinephrine and glucocorticoids

• Killer T-lymphocytes show diminished number and activity

• Little change in helper T-lymphocytes or B-lymphocytes

• Eosinophils decrease by an average of 62% of pre-flight values

MicrogravityMusculoskeletal

• Relaxed astronauts in microgravity assume a fetal position, with loss of normal curve of the thoracolumbar spine

• Increase in height of 3 to 6 cm from decompression of intervertebral disks, with possible associated pressure on nerve roots and back pain

MicrogravityMusculoskeletal

• Decrease in muscle mass (primarily in weight-bearing muscles of legs and back)– Vigorous exercise programs (up to 3 hours per

day) using isotonic and isometric exercises help stabilize muscle mass at 80 to 85% of preflight value

– Muscle weakness and soreness postflight, with gradual return of preflight muscle mass after weeks to months of exercise

MicrogravityMusculoskeletal

• Microgravity causes demineralization of bone, decreased total bone mass, and increased urinary and fecal calcium loss (greater risk of urolithiasis)

• Mechanism for bone loss is not established– Activity of osteoclasts unchanged– Activity of osteoblasts decreased

MicrogravityMusculoskeletal

• With exercise programs, total bone mass loss is similar to muscle loss (about 15 to 20% of preflight values)– Percentage of bone loss is greater in

weight-bearing bones (e.g. calcaneus)– Bone mass may not return to preflight

value even years later

MicrogravityCountermeasures to microgravity

• Vigorous exercise programs– Treadmill– Rowing machine– Ergometer– Isometric exercise is more effective than isotonic

(aerobic) exercise for reducing bone and (probably) muscle loss

– Effectiveness of supplemental calcium or medications (calcitonin or clodronate) for controlling calcium loss hasn’t been established

– “Penguin” suit

MicrogravityCountermeasures to microgravity

• Postflight orthostatic hypotension– Ingestion of salt tablets and 1 L of water

shortly before reentry– Lower-body negative-pressure devices

• Chibas suit

– G-suit

MicrogravityCountermeasures to microgravity

• Artificial gravity– Rotation of spacecraft or habitat– Tethered system– Centrifuge for intermittent use

• Adverse effects of reduced gravity should be milder on Mars (0.38g) and the Moon (0.16g)

Medical Care of Astronauts

• Preflight screening• Medical requirements for Shuttle crews

vary– Pilot (Class I)– Mission Specialist (Class II)– Payload Specialist (Class III)– Space Flight Participant (Class IV)

Medical Care of Astronauts

• Requirements are most stringent for Class I (pilot)– Near vision better than 20/20 in each eye

(uncorrected) and either far vision 20/100 or better uncorrected, or correctable to 20/20 each eye

– BP no greater than 140/90 mmHg– Height between 64 inches and 76 inches

Medical Care of Astronauts

• Requirements for Class II (mission specialist)– Distance visual acuity: 20/200 or better

uncorrected, correctable to 20/20 each eye– Blood pressure no greater than 140/90

mmHg measured in a sitting position– Height between 58.5 and 76 inches.

Medical Care of Astronauts

• Class III and IV have no limit on near vision and BP must be no greater than 150/90 mmHg

Medical Evaluation of Astronaut Candidates

• Medical history and physical examination• Cardiopulmonary tests

– Pulmonary function tests– Exercise treadmill test– Echocardiogram– EKG and 24-hour Holter monitor

• Eye and ear examination– Audiometry, visual acuity, color perception,

tonometry

Medical Evaluation of Astronaut Candidates

• Dental examination• Neurological examination (including EEG)• Psychiatric interview and psychological tests• Tests

– X-rays of chest, sinuses, and teeth– Abdominal ultrasound– Mammogram in women

Medical Evaluation of Astronaut Candidates

• Laboratory tests– Chemistries, blood counts, screens for STDs– Urinalysis– 24-hour excretion of calcium– Stool for ova and parasites– Drug screen– PPD– Pregnancy test (premenopausal women)

Medical Care of Astronauts

• Medical examinations are done 10 days, 2 days, and immediately before a Shuttle launch

• Crew members live in restricted quarters for a week prior to launch to minimize exposure to infectious diseases

Medical Care of Astronauts

• Two members of every Shuttle crew are assigned as medical officers– Non-physicians receive paramedic-level training– Advice during flight is available from ground-based

Crew Surgeon and Deputy Crew Surgeon

• All crew members receive 16 hours of lectures on the physiological effects of space flight and are trained in CPR and first aid

Injuries and illnesses during space flight

• Space Adaptation Syndrome• Nasal/sinus congestion• Headache• Backache• Skin irritation/dryness/dermatitis• Boils• Urinary tract infection• Renal colic• Prostatitis

Injuries and illnesses during space flight

• Upper respiratory infection (“cold”)• Pneumonitis• Minor abrasions/lacerations• Constipation• Arrhythmias• Decompression sickness• Corneal abrasion/foreign body• Musculoskeletal strain/sprain• Minor trauma/contusions

Medical Supplies on Shuttle Missions and the ISS

• Medications– Analgesic and NSAIDs– Antiemetics

– Antihistamines and H1 blockers

– CNS stimulants– Cardiovascular agents

Medical Supplies on Shuttle Missions and the ISS

• Medications– Antibiotics– Sedative-hypnotics– Antidepressants– Gastrointestinal agents– Dermatological agents– Ophthalmic and otic agents

Medical Supplies on Shuttle Missions

• Diagnostic equipment and supplies– Blood pressure cuff and sphygmomanometer– Stethoscope– Disposable thermometers– Otoscope– Ophthalmoscope– Fluorescein strips

Medical Supplies on Shuttle Missions

• Therapeutic items and other supplies– Needles– Syringes and tourniquet– IV tubing and normal saline– Suture equipment and supplies– Scalpels and scissors– Alcohol and betadine wipes, bandaids, gauze,

bandages, sponges– Surgical masks and gloves– Oral airway and cricothyroidotomy set

Medical Supplies on Shuttle Missions

• A defibrillator is not carried on most Shuttle flights

• A ventilator and X-ray equipment are not carried on Shuttle flights

• A defibrillator and an ultrasound system are carried on the International Space Station

Nutritional Factors

• Food intake of at least 2500 to 3000 calories/day– Negative nitrogen balance

• Fluid intake up to 4200 ml/day (e.g. from fuel cells)• Changes in sensitivity to taste and odors• Food on Shuttle includes thermostabilized,

rehydratable, intermediate-moisture, and natural-form items– Prepackaged for each crew member and stored in dry form

when possible– Forced-air convection oven for heating foods

Infection Control

• Personal hygiene is difficult in microgravity• Contamination by microorganisms from food, water

(especially if recycled), wastes, experimental animals, and payload items

• Microorganisms continuously shed from skin, mucous membranes, and GI and respiratory tracts– Released as aerosols by sneezing, coughing, and talking– Droplets do not settle but remain suspended until striking a

surface or coming into contact with a crewmember (e.g. inhalation)

– Increased bacterial resistance to antibiotics and reduced immune function

Problems with Medical Care in Space

• Limited equipment and supplies

• Limited expertise and medications

• Adverse effects of microgravity

Problems with Medical Care in Microgravity

• Direct effects on the body– Relative anemia– Increased susceptibility to and delayed healing of

fractures

• Difficulties with diagnostic and therapeutic procedures– No rising of air or layering of fluid on X-rays– No air-fluid levels in bowel obstruction– Placing patient in Trendelenburg position (e.g.

hypovolemia) or reverse Trendelenburg (e.g. congestive heart failure) are ineffective

Problems with Medical and Surgical Care in Microgravity

• Space pharmacology– Timing of dosing and changes in

absorption and metabolism of medications are not established

– Limited types and supplies of medications

Problems with Medical and Surgical Care in Microgravity

• Surgery– All individuals involved (physician, nurse, patient)

must be restrained– Difficulty maintaining a sterile field

• Drapes must be secured• Special techniques for putting on surgical gowns and

gloves• Airborne particles don’t settle• Special equipment required for washing and disinfecting

surgical equipment

Problems with Medical and Surgical Care in Microgravity

• Surgery– Use of inhaled agents for general anesthesia is

dangerous in confined area of a spacecraft– Effectiveness of spinal anesthesia is at least partly

gravity-dependent– Spurting arteries produce blood droplets suspended

in air, and venous blood forms hemispheric domes– Abdominal viscera float out of the abdomen– IV fluids require a pressure pump– Collected urine and blood don’t settle to bottom of a

measuring container

ISS

Mars

Spirit Rover