The lungs, gastrointestinal tract, part of the face covered by a face mask, eyes, ears, or sinuses can be affected.
Risk of barotrauma is greatest from the surface to 33 feet (10 meters).
Measures that can help prevent barotrauma include ascending slowly and breathing during ascent (pulmonary barotrauma), blowing out air from the nose into the face mask (mask barotrauma), and yawning or swallowing with the nostrils pinched and taking a nasal decongestant before diving (sinus and ear barotrauma).
(See also Overview of Diving Injuries.)
Increased pressure outside the body is transmitted equally throughout the blood and body tissues, which do not compress because they are composed mainly of liquid. Thus, the legs, for example, do not feel squeezed as water pressure increases. However, gases (such as the air inside the lungs, sinuses, or middle ears or inside a face mask or goggles) compress or expand as outside pressure increases or decreases. This compression and expansion can cause pain and damage to tissue.
Barotrauma most often affects the ears. However, barotrauma affecting the lungs (pulmonary barotrauma) is the most serious. Risk of barotrauma is increased by conditions that can keep air from freely flowing between spaces, such as sinus congestion or blockage of an eustachian tube (a small passageway that connects the middle ear with the back of the nose).
Because air under high pressure is compressed, each breath taken at depth contains many more molecules than a breath taken at the surface. At 33 feet (2 atmospheres absolute), for example, each breath contains twice as many molecules as a breath taken at the surface (and therefore depletes an air tank twice as rapidly). As pressure decreases, air expands—its volume increases. So, when divers fill their lungs with compressed air at 33 feet and ascend without freely exhaling, the volume of air doubles, causing the lungs to overinflate.
Overinflation of the lungs can rupture small air sacs, allowing air to leak out. Air that leaks out of the lungs can be trapped in the space between the lungs and the chest wall and expand, causing the lungs to collapse (pneumothorax). Alternatively, air may be forced out of the lungs into the tissues surrounding the heart (pneumomediastinum), under the skin of the neck and upper chest (subcutaneous emphysema), or into the blood vessels (air embolism—see Unusual Types of Emboli). Air in the arteries typically travels to other parts of the body (arterial gas embolism), where it may block blood flow.
The most common cause of pulmonary barotrauma is breath-holding during an ascent from a scuba dive, typically resulting from running out of air at depth. In panic, divers may forget to exhale freely as air in the lungs expands during the ascent. Air embolism can occur in as little as 4 feet (about 1 meter) of water when people breathing pressurized air hold their breath while ascending rapidly. Pulmonary barotrauma can even happen in a pool when air is breathed in at the bottom of the pool (such as from an inverted bucket) and not exhaled during ascent. Pulmonary barotrauma can also occur due to gas expansion in abnormal areas of the lung due to disease.
Symptoms of barotrauma usually begin near the surface during descent or ascent. Symptoms depend on which organ is affected. Divers often use the term squeeze for injuries other than those to the lungs caused by differences in pressure.
Pneumothorax and pneumomediastinum cause chest pain and shortness of breath. Some people cough up blood or develop bloody froth at the mouth when lung tissue is injured. Air in the tissues (subcutaneous emphysema) of the neck can compress the nerves to the vocal cords, causing the voice to sound different or hoarse. Subcutaneous emphysema causes crackling when the affected area of skin is touched.
When divers do not properly equalize pressure in the face mask with the water pressure during descent, the relatively lower pressure inside the mask causes it to act like a suction cup applied to the eyes and face. The difference in pressure inside and outside the mask causes blood vessels near the surface of the eyes (or on the face) to dilate, leak fluid, and finally burst and bleed. Although the eyes appear red and bloodshot, vision is not usually affected. Rarely, bleeding behind the eyes can occur, causing loss of vision. Bleeding of blood vessels in the face causes usually a bruised appearance.
If pressure in the middle ear becomes lower than the water pressure during descent, the resulting stress causes a painful inward bulge of the eardrum. When the pressure difference becomes high enough, the eardrum ruptures, resulting in a rush of cold water into the middle ear, causing vertigo (severe dizziness with a spinning sensation), disorientation, nausea, and sometimes vomiting. These symptoms are hallmarks of ear barotrauma and may place divers at risk of drowning. The vertigo diminishes as the water in the ear reaches body temperature. A ruptured eardrum impairs hearing and may lead to a middle ear infection hours or days later, causing pain and producing discharge from the ear. The inner ear can be injured as well, causing a sudden loss of hearing, buzzing in the ear (tinnitus), and vertigo.
Breathing improperly from a regulator or using ear and sinus pressure-equalization techniques may cause divers to swallow small amounts of air during a dive. This air expands during ascent, causing abdominal fullness, cramps, pain, belching, and flatulence. These symptoms usually resolve on their own. Rarely, the stomach or intestine bursts, causing severe abdominal pain and severe illness.
Doctors recognize barotrauma mainly by the nature of the symptoms and their onset in relation to diving. Depending on the symptoms, imaging tests may be done. For example, people with pulmonary barotrauma usually require chest x-rays. People with ear or eye barotrauma may need to have their hearing or vision tested.
Pressure in the lungs and airways is automatically equalized with outside pressure when a supply of pressurized air is available at depth, as from a diving helmet or air tank. This pressurized air also equalizes pressure in the sinuses, as long as the openings to the sinuses are not narrowed, for example, by inflammation due to allergies or an upper respiratory tract infection.
Pressure in a face mask is equalized by blowing out air from the nose into the mask. Divers equalize pressure differences in the middle ear by yawning or swallowing with the nostrils pinched, which opens the tube connecting the middle ear and the back of the throat (eustachian tube).
Wearing earplugs or a tight-fitting wet suit hood creates a closed space between the earplug and the eardrum in which pressure cannot be equalized. The pressure inside eye goggles cannot be equalized either. Therefore, neither earplugs nor eye goggles should be worn during diving. Tight-fitting wet suit hoods should be properly vented so that they do not block the external ear.
A decongestant (such as pseudoephedrine taken by mouth or a nasal spray such as oxymetazoline) is taken before diving by people with nasal congestion that could block nasal passages. Relief of congestion can facilitate equalization of pressures between the ears and sinuses, helping prevent sinus and ear barotrauma.
To prevent pulmonary barotrauma, people must freely exhale any air inhaled at depth—even the depth of a swimming pool—during ascent. People with lung disease such as asthma should be assessed before engaging in diving for fitness to dive.
Some people with pneumothorax require treatments such as inserting a plastic tube into the chest cavity to allow air to drain and the lung to re-expand. Treatment of pneumomediastinum and subcutaneous emphysema usually is bed rest and supplemental oxygen.
Ear and sinus barotrauma are treated with nasal decongestants (such as oxymetazoline nasal spray) or oral decongestants. Occasionally, when recovery is slow, corticosteroids may be given as a nasal spray or pills.
A ruptured eardrum usually heals by itself, although a middle ear infection requires antibiotics given by mouth or as eardrops. A rupture between the middle and inner ear may require prompt surgical repair to prevent permanent damage.
A rupture of the stomach or intestine requires surgical repair.