Scuba Diving: Barotrauma and Decompression Sickness
Barotrauma/Decompression Sickness Overview
Barotrauma refers to medical problems that arise from the pressure differences between areas of
the body and the environment and is a particular concern for scuba divers.
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 when scuba diving, pressure increases and this volume change in gas-filled spaces and organs within your body accounts for the distortion and damage to surrounding tissues.
- 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
descends than when ascending to the surface. However, if a diver ascends 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 or a very rapid descent. 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 where pressure cannot equalize during descent causing 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 through your nose into the dive 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.
- Tooth squeeze:
This occurs during an ascent while scuba diving and air becomes trapped in a
filling or cavity.
- Gastric squeeze (aerogastralgia):
This occurs when gas swallowed during diving expands during ascent. This happens more often with novice divers and causes temporary pain but rarely significant damage.
- Barotrauma can occur during ascent also. A reverse squeeze occurs in the 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. During "bounce diving" the eustachian tube may become inflamed and lead to a middle ear squeeze.
- Pulmonary barotrauma (pulmonary overpressurization syndrome, POPS, or burst lung) can occur if
the diver fails to expel air from the lungs during ascent. As the diver rises, the volume of the gas in
the 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 scuba diving, gas bubbles can enter the circulatory system through small ruptured veins in
- These bubbles expand during ascent, following Boyle's Law, and can pass
through the heart to obstruct blood flow in the arteries of the 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.
- The brain is affected more than other organs because gas rises, and most divers are in a vertical position while ascending.
- Decompression sickness (DCS, "the bends") involves gases diffusing into
the 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, the diver absorbs nitrogen into the tissues until
they reach a pressure balance.
- When the diver ascends at the right rate, the gas diffuses from the tissues. However, if
the diver ascends too rapidly to allow diffusion, the nitrogen bubbles will expand in
the tissues as pressure decreases.
- Different body parts can be affected, depending on where the bubbles are located.
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