barotrauma is injury caused by pressure effects on gas spaces. this may occur during ascent or descent. the ears are the most commonly affected body part. the most serious injury is lung barotrauma, which can result in pneumothorax, pneumomediastinum, pneumopericardium, subcutaneous emphysema, and arterial gas embolism. all divers, commercial air travelers, people traveling overland between different altitudes, and people who work in pressurized environments have had to deal with some degree of barotrauma effect upon their ears, sinuses, and other air spaces. at the most extreme, barotrauma can cause ruptured eardrums, bleeding sinuses, exploding tooth cavities, and the lung injuries described above. this is the reason why divers follow a procedure of not holding their breath during ascent. by breathing continuously, they keep the airways open and avoid pressure differences between their lungs and ambient pressure.