Any lung disease is an absolute contraindication to diving, despite the fact that the afflicted person may be capable of ordinary, or even extraordinary, physical activities.There are many asthmatics who are quite fit, and there are asthmatics who hold Olympic and World records for a number of sports, including swimming. Doctors even recommend swimming to asthmatics seeking to increase their fitness. But these abilities and the individual's obvious determination do nothing to mitigate the physics of pressure-change while diving. Asthma, also known as reactive airway disease, is a contraindication to diving for several reasons. During attacks, asthmatics cannot adequately ventilate because small airways close, trapping inhaled air. However unintentionally, asthmatics with an attack on ascent, or who have an attack and accidentally ascend, are holding their breath. The same is true of emphysemics who experience similar inability to exhale fully, and who may have air trapped in lungs that have become less pliant due to the disease. Stretched past its limit, about a two psi (0.14 kg/cm2) pressure change, lung tissue tears. Air is released into the body cavity and the circulatory system underwater behaves according to Boyle's Law, expanding on ascent. Healthy lungs, let alone diseased ones, can rupture from a breathhold ascent on compressed air in as little as four feet of seawater. The results of lung overpressure injury are easily fatal. Unfortunately, persons with lung disease face factors which can aggravate their conditions and lead to attacks on most dives. Among these are dehydration, cold (compressed air cools when expanded through a regulator), stress and the exertion of diving. In addition, most scuba compressor's air filtration systems cannot totally eliminate ambient air mold spores and micro particulate matter that can trigger allergic reactions to which such persons are sensitive. Though many asthmatics and emphysemics use medication successfully to avoid these problems at the surface, many of these medications can also cause problems when diving. Another example of a lung problem that prevents people from participating in diving is recurring spontaneous pneumothorax. Some very athletic people, generally those with tall, lean physiques such as basketball players, have this problem, though otherwise are quite fit. In these persons, the collapse can occur at rest or during stressful activity, such as diving. On a ball court or at home, people can receive immediate treatment without the complication of a breathing difficulty under water, and the dangerous possibility of compressed air migrating into the body cavity or circulatory system at depth.