5.2 Decompression Sickness & Ear/Sinus Pain

Source: Sections 5.4 - 5.5

Decompression Sickness (The Bends)

At ground level, the body tissues are saturated with nitrogen. When the atmospheric pressure diminishes, bubbles of nitrogen form in the tissues.

Symptoms

These bubbles may track into joint spaces causing a dull, sickening pain called the bends. More critically, these bubbles can be released into the lungs or the brain, giving rise to chest pain or collapse.

Altitude Risks

Atmospheric pressure diminishes with altitude and, at 18,000 ft ASL, is half the pressure at sea level. Although susceptibility varies (age, obesity, fitness, temperature, rate of climb), most pilots flying above 25,000 ft ASL in an unpressurized aircraft will be subject to the bends.

Transport Canada specifies that flights above 20,000 ft ASL should not be attempted unless a pilot has completed specialized high-altitude indoctrination (HAI) training.

Scuba Diving Danger

Although decompression sickness does not usually occur below 20,000 ft ASL, pilots who fly after scuba diving may develop symptoms at much lower altitudes. Pressure underwater increases by 1 atmosphere for every 33 ft. Divers who breathe air underwater supersaturate their tissues with nitrogen, greatly facilitating bubble formation when flying later. For these pilots, the bends can occur as low as 8,000 ft ASL.

Wait Times After Scuba Diving

• After non-decompression dives: a pilot should not fly for 12 hours.
• After dives requiring decompression stops: the interval should be 24 hours.
• For flights above 8,000 ft: the interval should be 24 hours regardless of the type of dive.

Relief

The remedy for decompression sickness is to re-expose the pilot to a greater pressure. When flying, this means descending to a safer altitude.

Middle Ear and Sinus Discomfort or Pain

The middle ear is similar to a box: closed at one end by a flexible cover (the ear drum) and drained at the other end by a thin, straight tube (the Eustachian tube).

During Climb

Air in the body cavities expands as barometric pressure decreases. Normally, air will escape from the middle ear/sinuses and pilots will only notice their ears “popping”.

During Descent

The outlet of the Eustachian tube is narrow. If the pilot has a head cold or throat infection, local swelling may narrow it further. On descent, particularly at high rates, the outlet may close like a flap, preventing air from re-entering the middle-ear cavity. The increasing ambient air pressure forces the eardrum inward, leading to severe pain and decreased hearing.

Barotrauma

Sometimes, the pressure in the middle ear on descent is so low relative to the external pressure that the eardrum can bleed and even rupture. This is known as barotrauma.

Relief and Equalizing

Pressure in the ears can be equalized by opening and closing the mouth, swallowing, yawning, chewing gum, or by holding the nostrils shut while gently blowing the nose.

If pressure cannot be relieved by these manoeuvres, it is best to climb if possible. The ears should then be cleared and a gradual descent made, clearing the ears frequently on the way down.