Transcript Space Medicine - Mike Brotherton

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% Nitrogen
21% Oxygen
~ None
None
95% CO2
3% nitrogen
2% argon
Pressure
760 mmHg
~ None
None
~ 5 mmHg
Temperature
(Celsius)
21o
-178o to + 110o
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
~ same as LEO
-120o to +25o
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 lifesupport 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
Microgravity
Neurovestibular
• 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
Microgravity
Neurovestibular
• 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
Microgravity
Cardiovascular
• 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
Microgravity
Cardiovascular
• 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
Microgravity
Hematological
• 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
Microgravity
Hematological
• 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 Blymphocytes
• Eosinophils decrease by an average of 62%
of pre-flight values
Microgravity
Musculoskeletal
• 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
Microgravity
Musculoskeletal
• 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
Microgravity
Musculoskeletal
• 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
Microgravity
Musculoskeletal
• 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
Microgravity
Countermeasures 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
Microgravity
Countermeasures 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
Microgravity
Countermeasures 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