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"Emphysema is the abnormal accumulation of air inside an organ or tissue. In dogs, it usually refers to the build-up of air in some part of the respiratory tract. Air enters the lungs normally when the dog breathes in, but it gets diverted and becomes trapped in places where it doesn&amp;rsquo;t belong. Why this happens is not really well. However, inflammation, physical pressure and other forces somehow disrupt lung tissue, trapping inhaled air. Trauma to the lungs, windpipe, esophagus or chest wall can trigger emphysema. Inflammatory lung disease, such as chronic obstructive pulmonary disease (COPD) and bronchitis, can also cause the condition, as can cancer and lung parasites. Emphysema is seen mostly in middle-aged dogs. Symptoms can come on suddenly or slowly; some dogs never act sick. More commonly, affected animals cough, develop breathing difficulties and become weak, lethargic and depressed. The symptoms can become severe, requiring emergency hospitalization."^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.petwave.com/Dogs/Health/Emphysema.aspx>