Physiology

1. Effects of acceleratory forces on
body in aviation & space
physiology
Dr Asma Shariq

2. LEARNING OBJECTIVES
• Discuss the effect of acceleratory forces on the body
• Explain the concept of weightlessness in space
• Discuss the effects of linear acceleration on the body

3. EFFECTS OF ACCELERATORY FORCES ON
THE BODY
• Because of rapid changes in velocity and direction of motion in
airplanes or spacecraft, several types of acceleratory forces affect the
body during flight.
• At the beginning of flight, simple linear acceleration occurs;
• At the end of flight, deceleration;
• Every time the vehicle turns, centrifugal acceleration.

4. 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 (in 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)

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

6. • +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

7. NEGATIVE CENTRIFUGAL ACCELERATIONS
• Induces negative Force
• Observed at the beginning of the dive ( airplane changes from level
flight to downward direction.
• Pilot/Aviator is thrown upward against his seat belt and body fluids
centrifuged/ translocated in the upper part of the body.
• Pilot/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.

8. NEGATIVE CENTRIFUGAL ACCELERATIONS

9. POSITIVE CENTRIFUGAL ACCELERATIONS
• Induces Positive G Force
• Observed when the Airplane begins to pull out after going into a dive.
• Pilot/Aviator is pushed against his seat with a force much greater
that=n his weight.
• 4g force: a force that the person can withstand( only symptom:
Dizziness)
• 6g 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.
• Pull of gravity 6 x the person’s weight

10. EFFECTS OF POSITIVE CENTRIFUGAL
ACCELERATIONS

11. EFFECTS OF +VE G ON ARTERIAL BLOOD
PRESSURE
• Suddenly applying +3.3 G to a sitting
person, both Systolic and Diastolic
blood pressures in the upper body fall
below 22 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.

12. EFFECTS OF POSITIVE CENTRIFUGAL
ACCELERATIONS (+G)

13. 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

14. SPACE PHYSIOLOGY

15. OUTER SPACE OR SPACE
• A point about sea level where gravitation pull is no longer effective in
preventing molecules from escaping into true space.
• Situated approximately 700km (435 miles) from the surface of the
Earth.

16. 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. Effects of prolonged stay in space

17. INTENSE LINEAR ACCELERATION
AT TAKE OFF/LIFTOFF

18. LINEAR ACCELATORY FORCES
Linear acceleration at take off/ liftoff:
• 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 increased 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

19. LINEAR ACCELATORY FORCES
• First-stage booster: linear
acceleration as high as +9G.
• Second-stage booster : linear
acceleration as high as +8G.
• Best position at take off or
liftoff: Semi-reclining position.
• That is why
astronauts/cosmonauts uses
reclining seats.

20. LINEAR ACCELATORY FORCES
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.
• The principal reason for this difference is that the total amount of energy
that must be dispelled during deceleration is proportional to the square of
the velocity, which alone increases the required distance for decelerations
between Mach 1 versus Mach 100 by about 10,000-fold. Therefore,
deceleration must be accomplished much more slowly from a high velocity
than from a lower velocity.

21. 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.

22. 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)

23. EFFECTS of Weightlessness
Upon return to the Earth
• Spaceman has difficulty readjusting to weight full 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
Blood vessels of lower extremities > Venous return > CO> ABP> blood flow to
the brain > brain fainting Anoxia
• 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.

24. 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: Algae with their large store of chlorophyll can use CO2 to produce foodstuffs (carbohydrates,
fats, proteins) and O2 by photosynthesis.
Disadvantages:
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

25. 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