34.24 Gravitational Forces

The human body is most accustomed to the gravitational force experienced on Earth, which is approximately 1G.

During flight, particularly during manoeuvring, the body may experience acceleration forces greater or less than 1G.

These forces may be:

• positive G, where blood tends to move towards the feet; or

• negative G, where blood tends to move towards the head.

Because blood has mass, acceleration can cause it to move within the body. This can affect blood pressure and the supply of blood and oxygen to the eyes and brain.

Changes in G force can therefore affect:

• the circulatory system;

• vision; and

• consciousness.

34.24.2 Explain the effects of positive and negative accelerations on:

(a) the circulatory system

During positive G, such as when pulling out of a dive or during a steep turn, blood tends to be forced towards the feet and away from the head.

This can:

• reduce blood pressure in the head;

• reduce blood flow to the brain and eyes;

• cause blood to pool in the lower part of the body; and

• reduce the supply of oxygen to the brain.