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1. CH. 43
HIGH ALTITUDE, AVIATION &
SPACE PHYSIOLOGY
AUMAN, ELGIE A.
-----------------------------------------------------------------------------------------
Bachelor of Science in Biology
College of Science andTechnology
Adventist University of the Philippines| Puting kahoy, Silang, Cavite 4118 Philippines

2. SEA LEVEL (Zero Altitude)
Atmospheric or Barometric pressure (PB) at a sea level:
760mm Hg= 760 torr=1 atmospheric=14.7lb/in2=1kg/cm2
For practical purpose, dry air is assumed to consist 79% N
2
and 21 % O
2
COMPOSITION OF DRY AIR AT SEA LEVEL
N2 78.09% pN2= 593.5mm Hg
O2 20.95% pO2= 159.2mm Hg
Argon 0.93% pAr=7.1mm Hg
CO2 0.03% pCO2= 0.2mm Hg

3. ABOVE SEA LEVEL (High Altitude)
Atmospheric or Barometric pressure (PB) above sea level:
< 760mm Hg
Exposure of Human Body to High Altitude Environments:
1. Mountain Climbing
2. Riding an Aircraft/Airplane
3. Riding a Spacecraft/Spaceship
As distance above the Earth’s surface (altitude) increases, density and pressure of air decreases
in a roughly exponential manner.
Sea Level: 760mmHg
18,000 feet ASL: 380 mmHg (PB is reduced by half)
33,700 feet ASL: 190 mmHg (PB is ¼ that of sea level)

4. CLASSIFICATION OF ALTITUDE
Moderately high 5000-8000 ft (1525-2440)
High 8000-14,000 ft (2440-2470m)
Very High 14,000-18,000 ft (4270-5490)
Extremely High > 18,000 ft (>5490m)

5. RELATIONSHIP of High Altitude & Barometric Pressure (PB) and Atmospheric pO2
Note: The higher the altitude, the lower PB and atmospheric pO2

6. Physiologic Challenges to Human Body in
High Altitude Environments
1. Exposure of body to low atmospheric/ barometric pressure.
2. Exposure of body to mechanical stresses (extreme accelerations):
* Linear acceleration
* Centrifugal acceleration (G forces)
3. Exposure of body to physical Factors
- Extremes of Climates
i. Upper atmosphere: Temperature of -20 to -50 °C
ii. Space: Temperature as high as 3000 °C
- Exposure to UV Radiation

8. ABOVE SEA
LEVEL (ft)
Physiologic Effects of High Altitudes
(Hypoxia)
6,000 ft Sensitivity of eyes to light (1st Sign of O2 deficiency)
8,000 ft i. Arterial O2 saturation falls to approximately 93%
ii. Chemoreceptors (Carotid & aortic bodies) begin to respond significantly to hypoxia (HVR) by
hypoxia (HVR) by causing hyperventilation (immediate compensation to hypoxia)
hypoxia)
12,000 ft • Acute effects of Hypoxia begin.
 Alteration in psychic behavior
> Euphoria (well-being, happiness, relaxation)
> Lassitude (weariness, fatigue)
 Mental Fatigue:
> Mental proficiency
> Judgment
> Poor memory
 Drowsiness (Aviator even goes to sleep)
 Headache
 Nausea and Vomiting

9. Above Sea Level
(feet) S/S of Hypoxia
18,000-24,000 ft S/S become severe and control of aircraft is endangered.
20,000 ft Sign of Collapsed (weakness and mental haziness)
23,000 ft 50% of arterial blood is saturated with O2 (ceiling) when an unacclimatized aviator is breathing
aviator is breathing pure air or when inside unpressured plane.
30,000 ft Unacclimatized person lapses into coma in about 1 minute.
47,000 ft 50% of arterial blood is saturated with O2 (ceiling) when an unacclimatized aviator is breathing
aviator is breathing pure O2
50,000 ft 1% of arterial blood is saturated with O2
O2 stored in the tissues diffuses backward to the interstitium, blood and lungs.
50% Arterial O2 saturation (23,000 ft and 47, 000 ft):
• Lowest level of O2 saturation at which a non-acclimatized person can remain conscious for more than few hours before passing into coma.
before passing into coma.
• Determinant of the ceiling for Aviator (dangerous altitude)

11. PRECAUTIONS
Aviator must breath pure O2 when he descend to
dangerous altitude (ceiling) whether he feels need
for O2 or not.
Pressurization of Aircraft of Airplane (21% O2 &
79% N2 corresponding to altitude of 5,000- 8,000
ft ASL.
If Aircraft/Airplane is pressurized with pure O2
there is a danger of explosion.

12. EFFECT OF WATER VAPOR & CO2 ON
ALVEOLAR PO2
PB Alveolar pH2O +
Alveolar pCO2
Alveolar pO2 +
Alveolar pN2
Sea Level 760 mm Hg Alveolar pH2O: 47 mmHg
Alveolar pCO2: 40 mmHg
= 87mm Hg
673mm Hg
50,000 ft. 87 mm Hg Alveolar pH2 O: 47mm Hg
Alveolar pCO2: 24 mm Hg
=71 mm Hg
16 mm Hg
• H2O vapor and CO2 “dilute” the O2 that can occupy alveoli.
 Alveolar pressure of water vapor (pAH2O) does not change (47 mmHg) at all as long as the body temperature is normal.
 Alveolar pressure of CO2 (pACO2) does not change greatly.
• Solution: to increase pAO2, the aviator should breathe O2 instead of air, to make the space in the alveoli formerly
occupied by N2 becomes occupied by O2

13.  Mt. Everest: Highest point of land on the Earth’s surface.
SEA Level Mt. Everest
0 Altitude 8848 m ASL
PB 760 mmHg PB 225 mm Hg
Atmospheric pO2:
159 mm Hg
Atmospheric pO2, 53 mm
Hg
Alveolar pO2: 105
mm Hg
Alveolar pO2, 44mm Hg

14. Acclimatization of Sea-Level Inhabitant or Lowlander to High
Altitude
Compensatory mechanism for O2 deficiency or Hypoxia.
Slow, progressive adjustments (over a period of Weeks) occurring in
the body exposed to high altitudes.
Not of special importance in aviation, because the aviator rarely
remains aloft long enough for acclimatization to occur.
Far more important to a mountain climber, who must become slowly
acclimatized if he is to succeed in ascending to the top of the highest
mountains.

15. Acclimatization of Sea-Level Inhabitant or Lowlander to High
Altitude/low pO2
If sea-level inhabitant or lowlander remains at high altitude for days, weeks, months or years.
1. Hypoxic ventilatory response (HVR): pulmonary ventilation by 1.65X normal.
Immediate compensation to hypoxia (within seconds).
A peripheral arterial chemoreceptor mechanism(carotid and Aortic bodies)
Further ascent to dangerous altitude > Hypoxia of Neurons in respiratory center > respiratory
center depression > most common cause of death.
Produces respiratory alkalosis ( arterial pCO2) Tx: Acetazolamide

16. 2. RBC production by BM (polycythemia/erythrocytosis/hemoconcentration)
Requires several weeks od exposure to hypoxia (high altitudes)
Hypoxia is the principal stimulus to erythropoietin secretion > erythropoiesis.
3. Hemoglobin in the blood (Hemoconcentration)
4. 2,3- DPG Affinity of hemoglobin for O2 O2 –Hb dissociation curve >O2 (Release)
(Shift to the right)
5. Diffusing capacity of RM for O2 (3X as in exercise)
6. Capillarity/ Capillary density ( Number of Capillaries Tissue vascularity)

17. 7. Cellular acclimatization: no. to Mitochondria and Oxidative enzymes
synthesis.
 Ability of cells to use O2 despite the low pO2.
 Myoglobin synthesis O2 stores in muscles transfer of O2 to
muscles.

18. Natural Acclimatization of Highlander Natives to High
Altitudes

19. Work Capacity at High Altitudes
Acclimatization increases work capacity at high altitude.
Normally acclimatized native can achieve a daily work output at 17,000 ft. almost equal to that of normal person at sea level.

20. HIGH ALTITUDES DISEASES
1.Chronic Mountain Sickness (CMS) or Monge’s Diseases
2. Acute mountain Sickness (AMS): Acute cerebral edema
Acute Pulmonary Edema
3. High-Altitude Cerebral Edema (HACE)
4. High-Altitude Pulmonary Edema (HAPE)
5. High- Altitude Retinal Hemorrhage (HARH)
6. High-Altitude Flatus Expulsion (HAFE)

22. ACCELERATIONS
Aircraft/Airplanes move rapidly and change directions of motion so frequently subjecting the
body to severe physical stresses.
1. Linear Acceleration.
> Rapid changes in velocity of Motion.
> induces forces during normal flight of an airplane which are not sufficient to cause major physiologic
effects.
2. Centrifugal Acceleration
> Rapid changes in the direction of motion (which the airplane turns, dives, or loops)
> induces forces which are frequently sufficient to promote serious derangement of bodily functions.
2 Types:
i. Positive Centrifugal Acceleration (Positive G Forces)
ii. Negative Centrifugal Acceleration (Negative G Forces)

23. CENTRIFUGAL ACCELERATIONS
oAircraft Flying level: +1G
oAircraft goes into dives: Negative
G force
oAircraft pulls/ come out of the
dive: positive G force.

24.  +1 G force:
When airplane is flying level.
The downward force that pushed the aviator against his
seats is exactly equal to his weight.
Pull of gravity= persons weight

25. NEGATIVE CENTRIFUGAL ACCELERATIONS
o Induces negative Force
oObserved at the beginning of the dive ( airplane changes from level flight to downward direction.
oPilot/Aviator is thrown upward against his seat belt and body fluids centrifuged/ translocated in the
upper part of the body.
oPilot/Aviator is not exerting any force at all against hi seat.
> 1g: if the force with which the aviator is thrown upward against his seat belt is equal to his
body weight.
> 3g: pilot/aviator is held down by the seat belt with force equal to 3x his weight.

26. NEGATIVE CENTRIFUGAL ACCELERATIONS

27. POSITIVE CENTRIFUGAL ACCELERATIONS
o Induces Positive G Force
o Observed when the Airplane begins to pull out after going into a dive.
o Pilot/Aviator is pushed against his seat with a force much greater that=n his weight.
o4g force: a force that the person can withstand( only symptom: Dizziness)
o6g force: when the airplane is at the lowest point of the dive; force is 6x greater that caused by normal
gravitational pull; aviator is pushed/pressed against his seat by a force 6x greater than his weight.
oPull of gravity (6x) > person’s weight

28. EFFECTS OF POSITIVE CENTRIFUGAL ACCELERATIONS

29. EFFECTS OF +G on ABP
 Suddenly applying +3.3 G to a setting person, both
SBP and DBP in the upper body fall below 22 and
1o mm Hg for the first few seconds after
acceleration begins.
 But with in another 10-15 sec. baroreceptor
reflexes are activated and SBP returns to about 55
mmHg and DB{ to 20 mm Hg.

30. EFFECTS OF POSITIVE CENTRIFUGAL
ACCELERATIONS (+G)

31. POSITIVE CENTRIFUGAL ACCELERATIONS
Anti-black-out measures: (When coming out of the Dive)
1. “Anti- G” suit with airbags that can inflated so that pressure is applied outside of
the legs and lower abdomen that can prevent pooling of blood.
2. Tightening of the Abdominal muscle by leaving forward to compress the abdomen
and delay the onset of blackout.
3. Lying prone: body can withstand +15 force in the Horizontal position.

32. PROBLEMS WITH TEMPERATURE
• As one ascends to higher elevations the temperature get colder.
Solution:
• 1. Special clothing for Aviator/ Pilot
• 2. Special heating apparatus must be designed for flying at high altitudes
The upper atmosphere is cold temperature
0 Altitude sea Level 20°C
10,000 feet ASL 0°C
20,000 feet ASL -22°C
30,000 feet ASL -44°C
40,000 feet ASL -55°C

33. SPACE PHYSIOLOGY

34. OUTER SPACE OR SPACE
Name coined by Gene Rodenberry, creator of the popular Science fiction TV series
“Star Trek, the Final Frontier” to A place beyond the escape level”
“Escape Level”
Situated approximately 700km (435 miles) from the surface of the Earth.
A point about sea level where gravitation pull is no longer effective in preventing
molecules from escaping into true space.

35. SPECIAL PROBLEMS IN SPACE
1. Intense linear acceleratory forces
i. Linear acceleration at take off or liftoff.
ii. Linear deceleration when returning to earth (reentry to
atmosphere)
2. Weightlessness in space (microgravity or 0 gravity)
3, Limited Supply of O2, and other nutrients.
4. Special environment hazards (specially radiation)
5. Other problems in the space flight.

36. 1. INRTENSE LINEAR OF ACCELERATION
AT TAKE OFF/LIFTOFF

37. LINEAR ACCELATORY FORCES
A. Linear acceleration at take off/ liftoff:
i. Spacecraft /spaceship is put into orbit(enter space) within 5 minutes using high-
velocity rocket propulsion from 1 or more boosters.
First booster: linear acceleration is increase to +9G
Second booster: Linear acceleration is further increased to 8+G
* At the end of 5 minutes, spaceman enters the state of weightlessness.
* Standing and sitting position during take off > spaceman cannot withstand >+4G acceleration
* Semi-reclining position during take off (transverse to the axis of acceleration) > spaceman
can withstand +9G and +8G during take Off

38.  First-stage booster: linear
acceleration as high as +9G.
 Second-stage booster : linear
acceleration as high as +8G.
 Best position at take off or lift-
off: Semi-reclining position.
 That is why
astronauts/cosmonauts uses
reclining seats.

39. LINEAR ACCELATORY FORCES
B. Linear deceleration when returning to Earth or reentering Atmosphere:
• As the spaceship returns to the Earth/Reenters atmosphere, it must be slowed down at a certain
distance for safe deceleration.
> Spaceship traveling at speed of Mach 1 (speed of sound and speed of fast
Airplanes) requires for its safe deceleration a distance of 0.12 miles.
> Spaceship travelling at a speed of Mach 100 (speed 100x the velocity of sound in
interplanetary travel) requires safe deceleration in a distance of 10, 000 miles.
>10,000 miles or more rapid deceleration: creation of more G forces than the spaceman could
withstand.
* The greater the velocity of the spacecraft, the greater the total amount of energy that must be spelled
during deceleration, the greater would be required distance for its safe deceleration, the longer must be
the time it must be decelerated.

40. 2. WEIGHTLESSNESS IN SPACE
(Microgravity or Zero Gravity)
• With little significant effect on the body
• Not due to failure of gravity to pull on the body because gravity from nearby heavenly bodies are still active.
• Forces of gravity & other trajectory forces are acting on both the spacecraft and the spaceman at the same time, with
exactly the same acceleratory forces and in the same direction
• No force is pulling the spaceman in any direction toward any part of the spaceship(bottom, sides or top of the
spaceship
1. Spaceman simply floats inside its chambers.
Solution: Spaceman should be strapped in place.
2. Foods float off any plate & fluids float out of any glass.
Solution: Foods are squeezed in to the mouth
Fluids are sucked form the tube.
3. Excreta floats freely in the spaceship
Solution: Excreta should be forced into a container.

41. EFFECTS of Weightlessness
in the Body (Space)
• 1. Motion sickness (50%)
* Nausea & sometimes vomiting during the first 2-5 days of space travel.
* Due to microgravity that makes it difficult for the vestibular apparatus to distinguish “up
"and “down.”
Solution: Pre-flight training + scopolamine patches & Oral antihistamine + biofeedback mechanism
2. Translocation of fluids to upper part of the body (cephalad shift of the blood) because of the failure of the
microgravity to cause hydrostatic pressures > Puffy face.
3. Diminished physical activity because no strength of muscle contraction is required to oppose the forces of gravity
(muscle deconditioning)
4. CVS reaction: slight decrease in the blood volume due to relaxation of the smooth muscles of the blood vessels of
the lower body (vasodilation)

42. EFFECTS of Weightlessness
Upon return to the Earth
• Spaceman has difficulty readjusting to weightfull state (+1G)
• Spaceman tend to faint when he first stands to the ground after return to gravity because the circulatory system is
adjusted to weightless state(reduced blood volume, dilated blood vessels in the lower extremities and diminished
response of ABP control mechanisms)
• Gravity (+1G) > blood are pulled to the lower extremities and to dilated BV of LE > Venous return > CO> ABP>
blood flow to the brain > brain fainting Anoxia
• Spaceman remains to be “weightless” for 1-3 weeks
• Severe decrease work capacity, decreased exercise tolerance for the first few days after returning to the Earth
Solution: Re-adaptation to gravity
Anti-gravity suit + ingestion of Saline solution + exercise training.

43. 3. LIMITED SUPPLY OF O2 and
other NUTRIENTS in Space
• Big limiting factor in today’s space flights:
> Space travel:
• Travel for few days to few weeks
• O2 and other nutrients needed by the spaceman could simply be provided.
> Interplanetary Travel:
• Travel for several moths to years
• It is impractical and Physically impossible to carry Sufficient O2 & other nutrients within the confines allowable in the spaceship
• Solution: Recycling procedures to complete the life cycle for the spaceman.
1. Physical Process: distillation and electrolysis of water to release O2
2. Biological process using algae:
1. Algae with their large store of chlorophyll can use CO2 to produce foodstuffs (carbohydrates, fats, proteins) and O2 by photosynthesis.
2. Disadvaantages:
A. Far greater amount of algae is needed than the space limitation the spaceship will allow.
B. Foods developed are neither palatable nor life-sustaining.
3. Chemical and Electrochemical procedures:
* To separate O2 from CO2 and resynthesize certain types of foodstuffs

44. 4. Special Environmental Hazards in Space
• Humans are protected by the Earth’s atmosphere form radiation from space.
• Outside the Earth’s atmosphere (in space), human do not have this protection
Van Allen Radiation Belts:
> radiations presents in space: gamma rays, x-rays, cosmic rays, etc.
> 2 points in space extending in the equatorial plane of the Earth
1. First or inner belt: begins at an altitude of about 300 miles and extend to about 3,000 miles
2. Seconds or outer belt: begins at an altitude of about 6,00 miles and extend to about 20,000 miles

45. 4. Special Environmental Hazards in Space
•Precautions:
A. 300 miles Space travel around the Earth must be confined to altitudes.
B. Space travel must take place mainly from one of the 2 poles.
C. Adequate radiation shield must be provided to the spaceman.
D. Spaceship must go through these radiation belts very rapidly.

46. VAN ALLEN RADIATION BELTS
•1st Belts:
300-3,000 miles ASL
•2nd Belt:
6,000miles to 20,000 miles ASL

47. 5. Other Problems in Space
1. Exposure to UV radiation causing severe sunburn and blindness.
Solution: Spaceman must be provided with protective
clothing and filters for the eyes.
2.Exposure to extreme heat when in the direct pathways of sunrays 350 miles ASL (space):3,000 °C due to extreme KE
but molecules, atoms and ions are too few to impart significant amount of heat to the spacecraft.
Solution: Spaceship must be provide with intricate heat-control systems.
3. Exposure to extreme cold when on the opposite side of the moon form sunrays.
Solution: Spaceman must be provided with appropriate clothing.
4. Exposure to a very low barometric pressures in case of decompression of spaceship
Solution: Spaceman should wear pressurized space suits.

48. EFFECTS OF PROLONGED STAY IN SPACE
Same effects also observed in bed-ridden patients:
1. Decrease in red blood cells mass.
2. Decrease in blood volume
3. Decrease in maximum cardiac output
4. Decrease in muscle strength and Work capacity (muscles “deconditioning” esp. of anti-gravity muscles)
5. Loss of Ca2+ and PO4-3 from bones and loss of bones mass > pathologic fractures.
Solution: Extensive exercise programs to reduce the ill-effects of prolonged stay in space.

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51. THANKYOU 