AVIATION & SPACE

Physiology

Acceleration in Aviation

Rapid changes in velocity and direction of

motion in airplanes or spacecraft results in

several types of acceleratory forces

affecting 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.

Measurement of

acceleratory force – ‘G’

G - force :Considered as force or pull of

gravity upon the body responsible for

body wt. on earth.

Force of ‘G’ increases in angular or centrifugal

acceleration.

The g-force acting on a stationary object

resting on the Earth's surface is 1 G (upwards)

Types of ‘G’ forces

Three types of G-forces acts on the body :

Gx – Transverse G (chest to back)

Gy - Lateral G (side to side)

Gz – Vertical G (head to foot)

**Gz is the most dangerous

Gx—is described as force acting on the body from chest to back (+Gx) or from back to chest (–Gx).

E.g.. During take off and landing

Gy—occur due to acceleration from side to side. from right to left: +Gy, from left to right: -Gy.

E.g. during rolling movement

Gz - is a gravitational force that is applied to the vertical axis of the body.

+Gz (positive) - it is experienced from head to foot. This happens when a pilot pulls into an inside loop. pulls out of a dive or

–Gz (negative) - it is experienced from foot to head, and it is experienced when a pilot pushes over into a dive.

Effect of ‘G’ force on body

Positive ‘G’

Effects on the Circulatory System:

blood is centrifuged toward the lowermost

part of the body.

Thus, if the centrifugal acceleratory force is +5

G and the person is in an immobilized

standing position, the pressure in the veins of

the feet becomes greatly increased (to about

450 mm Hg).

In the sitting position, the pressure becomes

nearly 300 mm Hg

+ G

Blood in the vascular system is translocated to the

lower part of the body, towards the feet

Great increased in the pressure and subsequent

distension of the veins of abdomen and legs

Veins store far more blood than usual and there is

decreased (↓) venous return

Decreased (↓) cardiac output

Decreased arterial blood pressure (systolic & diastolic)

decreased (↓) blood flow to brain

Grey out, Black out, loss of consciousness & death

GREY-OUT, where the loss of color

vision.

BLACK-OUT, a loss of vision while consciousness is maintained.

G-LOC a loss of consciousness ("LOC"

stands for "Loss Of Consciousness").

Death, if G-forces are not quickly

reduced, death can occur

Effects on the Vertebrae:

Extremely high acceleratory forces for even a

fraction of a second can fracture the

vertebrae.

The degree of positive acceleration that the

average person can withstand in the sitting

position before vertebral fracture occurs is

about 20 G.

Negative ‘G’

The human body is even less well equipped to handle –Gz, which is described as a foot-to-head force.

An aviator can withstand negative acceleratory forces of -4 to -5 G without any permanent harm.

centrifugation of the blood into the head is so great that the cerebral blood pressure reaches 300 to 400 mm Hg, sometimes causing small vessels on the surface of the head and in the brain to rupture.

- G

Blood in the vascular system is centrifuged to the

upper part of the body, towards the head

Great increase (↓) in the cerebral pressure

Brain edema and intense hyperemia of the face

Mental impairment , psychotic disturbances and

visual Red out

When “Red Out” happen, pilot vision turns red.

This is probably because capillaries in the eyes burst under the increased blood pressure.

“Red Out” are potentially dangerous and can cause retinal damage.

Protection of body against

the ‘G’ force Specific procedures and apparatus have been

developed to protect aviators against the

circulatory collapse that might occur during

positive G.

Use of Abdominal belts to prevent pooling of

blood.

Tightening the abdominal muscles and leaning

forward postpones black out.

Using Anti G suit. Exerts compressive ve pressure on lower limbs and abdomen and prevents pooling of

blood in lower part of body

A well-rested, hydrated, and fit aviator will

physically be able to withstand higher G forces.

When an aviator is well hydrated, there is more

circulating volume in the blood stream, and it is

easier for the heart to keep the brain with oxygen

blood.

G tolerance is degraded as a result of alcohol,

fatigue, and dehydration, which can make the aviator experience severe symptoms of G

exposure at much less than the customary level

In the standing position, the human body

cannot withstand acceleration force of 9G

that happens on space craft take-off , but in a

semi-reclining position transverse to the axis

of acceleration, this amount of acceleration can be withstood with ease.

Therefore, we see the reason for the reclining

seats used by astronauts.

Weightlessness in space

(micro gravity)

A person in an orbiting satellite or a spacecraft

experiences weightlessness, or a state of near-

zero G force, which is microgravity.

The person is not drawn toward the bottom, sides,

or top of the spacecraft but simply floats inside

its chambers.

The cause of this weightlessness is not failure of

gravity to pull on the body because gravity

from any nearby heavenly body is still active.

However, the gravity acts on both the

spacecraft and the person at the same time

so that both are pulled with exactly the same

acceleratory forces and in the same direction

Physiological Challenges of

Weightlessness (Microgravity).

1. motion sickness during the first few days of travel,

2. translocation of fluids within the body because of

failure of gravity to cause normal hydrostatic

pressures,

3. decrease in blood volume,

4. decrease in red blood cell mass,

5. decrease in muscle strength and work capacity,

6. decrease in maximum cardiac output,

7. loss of calcium and phosphate from the bones, as

well as loss of bone mass

8. impaired baroreceptor reflexes

Motion sickness In microgravity there is no

natural “up” and “down”

determined by our senses

You don’t know the

orientation of parts of your

body, especially your arms

and legs, because they

have no weight for you to

feel in space

Astronauts on the International

Space Station posing upside-

down (or is it right side up?)

Space motion sickness is caused by conflicting information that your brain receives from your eyes and the vestibular organs in your inner ear

Your eyes can see which way is up and down inside the space shuttle

However the sensors in your vestibular system rely on the pull of gravity to tell you up versus down

Your brain gets confused and produces nausea and disorientation which may lead to vomiting and loss of appetite

Translocation of fluids

In microgravity the blood shifts from legs chest

and head causing legs to shrink in size

This is called a “fluid shift”

Body senses an overabundance of fluids in

the chest and head area and sends a

message to the kidneys to eliminate the

excess fluid by producing more urine

Thirst is decreased and fluid intake reduced

The result is up to a 22% loss of blood volume

Decrease in RBC count

As kidneys eliminate excess fluid, they also

decrease their secretion of erythropoietin, a hormone that stimulates red blood cell production

by bone marrow cells

Anemia, the decrease of red blood cells in the

blood, is observed within 4 days of spaceflight

The number of red blood cells will decrease by

about 15% after a 3-month stay

Decrease in cardiac output &

heart size

The change in blood volume

affects heart.

Because of less blood volume the

heart doesn’t need to pump as

hard

It also takes less energy to move

around the spacecraft

Because it no longer has to work

as hard, the heart shrink in size

Predicted change in heart

shape Earth (green) and in

microgravity (red).(Image: © Dr. Chris May)

Muscle atrophy

In microgravity your muscles atrophy quickly because your body perceives it does not need

them

The muscles used to fight gravity and maintain

posture can vanish at the rate of 5% a week

The longer you stay in space, the less muscle mass

you will have

After only 11 days in space microgravity can shrink

muscle fibers as much as 30%

Bone loss

In microgravity, bones do not need

to support body

Weakening of the bones due to a

progressive loss of bone mass is a potentially serious side-effect of

extended space travel

It is reported that 3.2% of bone loss

occurs after 10 days of microgravity

The bones most commonly effected

are the lumbar vertebrae and the leg

bones

The best way to

minimize loss of muscle

and bone in space is to

exercise frequently, mainly with the

treadmill, rowing

machine, and bicycle

This prevents muscles

from deteriorating and

places stress on bones

to produce a sensation

similar to weight

Exercising in microgravity

(photos courtesy of NASA)

Radiation hazard

On Earth the atmosphere and

magnetic field provides a

shield for humans to prevent

space radiation from

penetrating

The absence of this shield in

space exposes astronauts to

greater amounts of radiation

Radiation ionizes molecules in

the body and can cause

damage to DNA

What happens when the

astronaut returns to Earth?

The heart is smaller and

weaker

The vestibular, or

balance, system has

become used to a new

set of signals

Body fluids are diminished

Muscles have atrophied

Bones have weakened

For a 4 to 6 month space flight it may require 5 to 6

years to regain lost bone and muscle and that too is

never 100%