34.14 Entrapped Gases

34.14.2 Explain the causes of barotrauma.

Barotrauma is injury or pain caused by a difference in pressure between gas trapped within the body and the surrounding atmospheric pressure.

As altitude changes, atmospheric pressure changes. According to Boyle’s Law, as pressure decreases, the volume of a gas increases, and as pressure increases, the volume of a gas decreases.

Therefore:

• during a climb, atmospheric pressure decreases and trapped gas tends to expand; and

• during a descent, atmospheric pressure increases and trapped gas tends to contract.

If the pressure cannot equalise, a pressure difference develops across the surrounding tissue. This may cause discomfort, severe pain or tissue damage.

Areas of the body where gas may become trapped include:

• the middle ear;

• the sinuses;

• the stomach and intestines;

• the teeth; and

• in some circumstances, the lungs.

Conditions such as:

• a cold;

• sinus infection;

• hay fever; or

• allergies

may cause swelling that prevents the normal equalisation of pressure and increases the risk of barotrauma.

Middle Ear

The Eustachian tube connects the middle ear to the back of the throat and allows pressure on either side of the eardrum to equalise.