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Barotrauma/Decompression Sickness
Barotrauma/Decompression Sickness Overview
Barotrauma refers to medical problems that arise from the effects of water pressure when a scuba diver is beneath the surface. Water is heavier than air, so when you dive, small changes in depth cause large changes in pressure underwater.
Certain laws of physics apply to this topic. Boyle's law states that the product of the multiplication of pressure and volume remains a constant. As the pressure increases, the volume decreases and vice versa. As you dive deeper, this volume change in gas-filled spaces and organs within your body accounts for the distortion and damage to surrounding tissues.
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Decompression sickness, or "the bends," is related more to Henry's Law, which states that more gas will be dissolved in a liquid when the gas is pressurized. Because of the water pressure, body tissue absorbs nitrogen gas faster as a diver goes down than coming back to the surface. If a diver rises too quickly, nitrogen gas bubbles will form in body tissue rather than being exhaled. The nitrogen bubbles cause severe pain.
- External ear squeeze occurs when your ear canal is blocked by something such as earplugs or earwax. As the water pressure increases while you descend, the air pocket between the obstruction and the tympanic membrane (eardrum) shrinks. This can damage the tissue in the ear canal, usually your eardrum.
- Middle ear squeeze occurs when you cannot equalize the pressure in your middle ear. The eustachian tube is a small canal that connects the middle ear to the back part of the nasal cavities and allows pressure to equalize. When there is a problem with the tube, the middle ear volume decreases and pulls the eardrum inward, creating damage and pain. You can try certain maneuvers, called Valsalva maneuvers, such as yawning or trying to blow with your nose and mouth closed, to open the tube and equalize the pressure.
- Inner ear barotrauma occurs from the sudden development of pressure differences between the middle and inner ear. This can result from an overly forceful Valsalva maneuver. The result is usually ringing in the ear, dizziness, and deafness. This injury is less common than a middle ear squeeze.
- Less common types of barotrauma include the following. All involve air
trapped in an enclosed area that cannot equalize during descent and causes a
vacuum effect where it occurs.
- Sinus squeeze: When air becomes trapped in the sinuses because of
congestion or cold symptoms, a sinus squeeze can occur.
- Face mask squeeze: This occurs if you do not exhale into the diver mask
while descending.
- Suit squeeze: A dry diving suit tightly encloses an area of skin.
- Lung squeeze: This occurs when you are free-diving, but very few divers can hold their breath to depths that cause this injury to occur.
- Sinus squeeze: When air becomes trapped in the sinuses because of
congestion or cold symptoms, a sinus squeeze can occur.
- Barotrauma can occur during ascent also. A reverse squeeze occurs to your middle ear or sinus when a diver has an upper respiratory infection (cold) and has used nasal spray to open the breathing passages. As the spray wears off during diving, tissues swell and cause obstruction, resulting in a pressure difference and damage.
- Aerogastralgia occurs when gas that you swallowed during diving expands during ascent. This happens more often with novice divers and causes temporary pain but rarely significant damage.
- Pulmonary barotrauma (pulmonary overpressurization syndrome, POPS, or burst lung) can occur if you fail to expel air from your lungs during ascent. As you rise, the volume of the gas in your lung expands and can cause damage if the excess is not exhaled.
- Air embolism is the most serious and most feared consequence of
diving.
- While you are diving, gas bubbles can enter your circulatory system through
small ruptured veins in your lungs.
- These bubbles expand during ascent, following Boyle's Law, and can pass
through your heart to obstruct blood flow in the arteries of your brain or
heart.
- This most commonly occurs when a diver ascends rapidly because of air
shortage or panic.
- The diver then passes out, experiences a stroke,
or has other nervous system complaints within minutes of surfacing.
- Your brain is affected more than other organs because gas rises and most divers are vertical while ascending.
- This most commonly occurs when a diver ascends rapidly because of air
shortage or panic.
- While you are diving, gas bubbles can enter your circulatory system through
small ruptured veins in your lungs.
-
Decompression sickness (DCS, "the bends") involves gases diffusing
into your tissues and getting trapped there. The diver now has gas bubbles in
places where there should be none. Nitrogen is the usual culprit.
- During descent and while on the bottom, you absorb nitrogen into your
tissues until you reach a pressure balance.
- When you ascend at the right rate, the gas diffuses from your tissues.
However, if you ascend too rapidly to allow diffusion, the nitrogen bubbles
will expand in your tissues as pressure decreases.
- Different body parts can be affected, depending on where the bubbles are located.
- During descent and while on the bottom, you absorb nitrogen into your
tissues until you reach a pressure balance.
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