LUNG INFARCTION

death of one or more sections of lung tissue due to deprivation of an adequate blood supply. The section of dead tissue is called an infarct. The cessation or lessening of blood flow results ordinarily from an obstruction in a blood vessel that serves the lung. The obstruction may be a blood clot that has formed in a diseased heart and has travelled in the bloodstream to the lungs, or air bubbles in the bloodstream (both of these are instances of embolism), or the blockage may be by a clot that has formed in the blood vessel itself and has remained at the point where it was formed (such a clot is called a thrombus). Ordinarily, when the lungs are healthy, such blockages fail to cause death of tissue because the blood finds its way by alternative routes. If the lung is congested, infected, or inadequately supplied with air, however, lung infarctions can follow blockage of a blood vessel. Because neither the lung tissue nor the pleural sac surrounding the lungs has sensory endings, infarcts that occur deep inside the lungs produce no pain; those extending to the outer surface cause fluids and blood to seep into the space between the lungs and the pleural sac. The sac distends with the excess fluid and there may be difficulty in inflating the lungs. When pain is present it indicates pleural involvement. The pain may be localized around the rib cage, shoulders, and neck, or it may be lower, near the muscular diaphragm that separates the chest cavity from the abdomen. One explanation for the pain is that it is from tension on the sensitive nerve endings in the membrane lining the chest. Pain is most severe on inhalation. The symptoms of infarcts are generally spitting up of blood, coughing, fever, moderate difficulty in breathing, increased heartbeat, pleural rubbing, diminished breath sounds, and a dull sound heard when the chest is tapped. The blood shows an increase in number of white blood cells and sedimentation rate (clumping of red blood cells). Infarcts that do not heal within two or three days generally take two to three weeks to heal. The dead tissue is replaced by scar tissue.