Activities The Great Outdoors Pulmonary Barotrauma and Scuba Diving Share PINTEREST Email Print mychadre77 / Getty Images The Great Outdoors Scuba Diving & Snorkeling Safety Gear Skills Hiking Climbing Skiing Snowboarding Surfing Paddling Fishing Sailing Learn More By Natalie Gibb Natalie Gibb owns a dive shop in Mexico and is a PADI-certified open water scuba instructor and TDI-certified full cave diving instructor. our editorial process Natalie Gibb Updated March 11, 2019 One of the most important rules in scuba diving is to breathe continuously and never hold your breath. In basic scuba training, you are taught that you must avoid holding your breath underwater and trapping air in your lungs. If you ascend while holding your breath, your lungs could expand ("explode") as the air expands. This is known as a pulmonary barotrauma. Just explaining this is often enough to frighten students into following the rule, but the details of what happens to a diver's lungs when they over-expand are usually glossed over. For example, did you know that other conditions and actions besides holding your breath can cause lung over-expansion? Definition Barotrauma refers to a pressure-related injury. The word pulmonary refers to your lungs. A pulmonary barotrauma may also be called: lung over-expansion, burst lungs, or exploded lungs. May Occur on a Small Scale The term "exploded lungs" makes a pulmonary barotrauma sound like a very dramatic injury, but it isn't very likely your lungs are actually going to explode. The alternate names for pulmonary barotraumas make the condition seem catastrophic, but pulmonary barotraumas more often occur on a nearly microscopic level. At depth, air is caught in the tiny air sacs (called alveoli) where gas exchange takes place in a diver's lungs. These air sacs are made of extremely thin and fragile tissue. If air is trapped in the sacs as a diver ascends, it will expand from the change in pressure and burst the sacs like many tiny balloons. This air escapes from the lungs and causes various types of damage depending upon where it travels. Pressure Change Very small changes in pressure can cause a pulmonary barotrauma. Because the lungs' air sacs are so tiny and thin, even the pressure that occurs over a few feet can cause injury if air is trapped in the lungs. Divers should remember that the greatest pressure change underwater is near the surface, so all divers, regardless of depth, are at risk. Pulmonary barotraumas have even been documented in swimming pools. Who Is at Risk All divers are at risk. Pulmonary barotraumas are caused by expanding air trapped in the lungs and are not related to depth, dive time, or the amount of nitrogen a diver has absorbed underwater. Actions and Conditions That Cause a Pulmonary Barotrauma There are three main causes of pulmonary barotrauma: 1. Breath Holding If a diver holds his breath and ascends as little as 3-5 feet, he is at risk for a pulmonary barotrauma. While most divers know they the shouldn't hold their breath underwater, panic, out-of-air situations, sneezing, and even coughing can cause a diver to inadvertently hold his breath underwater. Remember that underwater, the simple act of holding your breath will frequently cause you to become positively buoyant and ascend, so it is best to avoid breath-holding while scuba diving. 2. Rapid Ascents The faster a diver ascends, the more rapidly the air in his lungs will expand. At a certain point, the air will expand rapidly enough that it can not efficiently exit a diver's lungs, and some of the expanding air will become trapped in his lungs. 3. Pre-Existing Lung Conditions Any condition that can block and trap air in the lungs can lead to pulmonary barotrauma. Even conditions such as asthma, which only partially obstructs air from exiting the lungs can prevent expanding air from exiting the lungs efficiently on ascent. This includes temporary conditions, such as bronchitis or a cold, and permanent conditions such as scars, fibrosis, and tuberculosis. Aspiring divers with a history of lung problems should undergo a full medical exam by a doctor knowledgeable in diving medicine before undertaking scuba diving. Scroll down for a more complete list of medical conditions that predispose divers to pulmonary barotrauma. Main Types Pulmonary barotrauma can manifest in several different ways. 1. Arterial Gas Embolism (AGE) If the thin wall of the lungs' air sacs rupture, air can escape into the small blood vessels in the lungs' tissues. From there, the tiny air bubble travels to the heart, where it is pumped to any of several places, such as the arteries of the heart and brain. As the diver continues to ascend, the tiny bubble of air will continue to expand until it becomes too big to fit through an artery and is trapped. An air bubble trapped in an artery blocks blood flow, cutting off the oxygen supply to organs and tissues. In extreme cases, an air bubble in the heart's arteries can cause cardiac arrest, and an air bubble in the brain's arteries can mimic the symptoms of a stroke. 2. Emphysema A burst air sac can also force expanding air into the tissues surrounding the lungs. There are two main kinds of emphysema caused by pulmonary barotrauma: Mediastinal emphysema - Air is forced into the tissues surrounding the heart and trachea. Characterized by pain under the sternum, in the chest, and shortness of breath.Subcutaneous emphysema - Air is forced into the space under the skin around the neck and collarbone. There is a characterized "crunchiness" under the skin around the neck and collarbone. 3. Pneumothorax Pneumothorax is perhaps the most dramatic of all the manifestations of pulmonary barotrauma. In pneumothorax, air from the burst lung expands into the pleural cavity, or the area between the lungs and chest walls. As the expanding air pushes against the lungs' thin tissues, it exerts pressure which collapses the ruptured lung. X-rays of pneumothorax show the area once occupied by the lung almost completely filled with air, with the deflated lung compressed to a fraction of its original size. In extreme cases, expanding air on one side of the lung cavity can exert pressure on the heart, trachea, and other lung, causing a tension pneumothorax. This pressure can be so extreme that it visibly distorts the trachea, stops the heart, or collapses the second lung. Medical Conditions That Predispose a Diver Both temporary and permanent conditions can predispose divers to pulmonary barotrauma by completely or partially obstructing expanding air from exiting the lungs. Here are some examples of conditions that can cause barotrauma. Temporary conditions - Bronchitis, respiratory tract infections, congestion from allergies, active asthmaPermanent conditions - Scarred lung tissue, fibrosis, sarcoidosis, tuberculosis, lung abscesses, damage from severe pneumonia, chronic bronchitis, persistent asthma, tumors, calcified glands, mucous obstructions from heavy smokingBLEBS - Research indicates that BLEBs, balloon-like extensions of the lungs air sacs, BLEBs are believed to reduce the lungs' elasticity. They release air more slowly during exhalation than the lungs' air sacs. As a diver with BLEBs ascends, expanding air may not be able to exit the BLEBs rapidly enough, and some expanding air may become trapped in the BLEB, causing it to burst. BLEBs are normally found in chronic smokers but have been observed in non-smokers as well. Divers may be tested for BLEBs using breathing tests, x-rays, and CT scans. Can Be Distinguished From Other Decompression Illness While many symptoms of pulmonary barotrauma are similar to those of decompression sickness, pulmonary barotrauma can be distinguished from other dive-related injuries because its effects are immediate, which is not the case with the majority of decompression sickness incidents. According to scuba-doc.com, "Out of 24 cases of pulmonary barotrauma in United States Navy divers, symptoms of pulmonary barotrauma appeared in 9 cases while the diver was still ascending underwater, in 11 cases within one minute of the diver reaching the surface, and in 4 cases within 3-10 minutes of the diver reaching the surface." This seems to indicate that if a diver surfaces with chest pain, stroke-like symptoms, immediately falls unconscious, or manifests other symptoms within a minute or two of surfacing, pulmonary barotrauma should be suspected. Prevention Never hold your breath underwater. Ascend slowly. Most training organizations recommend an ascent rate of less than 30 feet per minute. Don't dive with pre-existing medical conditions that are known to cause pulmonary barotrauma. If you are unsure whether you are fit to dive, get a diving fitness exam from a qualified physician. Don't dive if you are likely to panic underwater. This frequently leads to inadvertent breath holding and rapid ascents. Follow good diving practices such as monitoring your air supply to avoid out-of-air and low-on-air situations; practice good buoyancy and properly weight yourself to avoid uncontrolled ascents; use well-maintained gear; and dive with a good buddy who can assist you in case of an equipment failure or other emergency. Watch Now: What Is the Respiratory System?