The thorax is the bony cage consisting of the ribs, the spine, and the breastbone or sternum. The floor of the thorax is formed by the diaphragm.
Within the thorax lie the two lungs and the heart, the organs whose function it is to oxygenate and pump blood. The lungs are large, relatively cone-shaped, spongy organs that lie with their narrow ends at the top and the broad ends at the bottom of the thorax. Between the paired lungs in an area called the mediastinum lies the heart. The inside of the chest cavity is lined with a sheet of elastic tissue, the pleura, which also covers each lung. The pleura on each side of the chest is independent from the other side; that is, the lining on the right covers the right lung and the right half of the thorax. A fluid called the pleural fluid fills the area between the two layers of pleura so that the membrane slides easily as the lungs work.
A constant negative pressure or vacuum is maintained in the chest to keep the lungs inflated. The diaphragm controls respiration. In its relaxed state it is dome shaped and projects into the chest. When it is tensed the diaphragm flattens and pulls air into the lungs. Carbon dioxide and oxygen are exchanged in the blood circulating through the lungs, the diaphragm relaxes and forces the air out of the thorax, and the oxygenated blood is returned to the heart for circulation.
Thoracic surgery may be needed as a result of a heart or lung disease, or to correct an abnormality of one of the large blood vessels. The heart may have a faulty valve that needs replacing, or a partially occluded coronary artery for which a bypass graft is needed. A hole in the wall separating the right and left sides of the heart may require patching. A lung tumor or a foreign object may need to be removed. A more serious procedure such as a heart transplant or heart-lung transplant may be needed. Any lung surgery will disrupt the negative pressure in the chest and render the lungs inoperable.
Thoracic surgery did not advance as rapidly as did surgery on other areas of the body because the means could not be found to maintain lung function during surgery and restore it after the surgery is completed. Not until early in the twentieth century did Samuel Meltzer and John Auer describe successful lung surgery carried out under positive-pressure air forced into the lungs. With this method the lungs remained inflated and the surgery could be completed without the lungs collapsing. Ironically, Andreas Vesalius (1514-1564) had described this methodology centuries earlier.
Heart surgery is carried out by placing the patient's heart and lung functions on a heart-lung machine, or cardiopulmonary bypass machine. First, the thorax is opened by cutting through the superficial tissue and using a saw to cut the sternum. A device called a retractor spreads the cut sternum to allow the surgeon to have full view of the heart.
The patient is connected to the bypass machine by tubes, or cannulas, attached to the large veins returning blood to the right side of the heart, the superior and inferior vena cavae. The cannula to return blood to the patient is implanted in the aorta, the large blood vessel leading from the heart to the body, or to a major artery such as the femoral artery in the thigh. When the machine is turned on blood is drawn from the vena cavae into the machine where it is cooled, oxygenated, and filtered to remove any unwanted particles and bubbles. The newly oxygenated blood is returned to the aorta which takes it to the body. Cooling the blood in turn cools the body temperature of the patient which reduces the amount of oxygen the tissues need. A third tube gathers blood at the point of surgery and shunts it into the machine to reduce blood loss.
With the patient safely on the heart-lung machine, the surgeon can stop the heart and lungs and carry out whatever procedure is needed. Attempting surgery on the beating heart or surgery while the lungs inflate and deflate would be difficult. Stopping the heart by cooling it and stopping lung action by giving a muscle relaxant that quiets the diaphragm provides an immobile field for the procedure. A vein taken from the leg, usually, can be grafted in place to bypass one or more blocked areas in the coronary arteries. A diseased heart valve can be removed from the heart and an artificial valve made from plastic and steel, pig valve, or monkey valve can be implanted. The entire heart or the heart and both lungs can be removed, emptying the chest cavity, and replaced with donor organs.
At the conclusion of the operation the chest is closed, the heart-lung machine warms the blood to restore normal body temperature, and the cannulae are removed from the vena cavae and aorta.
See also Heart diseases.
Larson, David E., ed. Mayo Clinic Family Health Book. New York: William Morrow, 1996.
Sezai, Y. "Coronary Artery Surgery Results 2000." Annals of Thoracic And Cardiovascular Surgery 8, no. 4 (2002): 241-247.