Deoxygenated blood travels through the veins from the rest of the body into the heart, which pumps it through the pulmonary arteries into the lungs for reoxygenation. Blood coming to the heart from the veins may contain large particles, such as pieces of blood clots or tissue, fat globules, or air bubbles. A sufﬁciently large particle (embolus) can block an artery that leads to the lung’s network of capillaries (where gas exchange occurs). Pulmonary embolism refers to the sudden blockage of one or more of the pulmonary arteries.
Conditions that cause clots in the veins, such as deep vein thrombosis (see page 236), frequently lead to pulmonary embolism. Although they are a rare cause of pulmonary embolism, fat globules can form after bone fractures and lodge within the capillary network (rather than in the pulmonary arteries them- selves).
The onset of symptoms of pulmonary embolism is sudden. As the level of oxygen in the blood decreases, the brain increases the respiratory rate, leading to hyperventilation (abnormally deep or rapid breathing). Even if the clot breaks up, a pulmonary embolism can lead to pulmonary hypertension, a condition in which high blood pressure in the pulmonary artery puts strain on the right side of the heart, which may cause it to fail. Over time, the left side of the heart also begins to fail. Heart disease that results from any pulmonary disease is called cor pul- monale. If you already have heart or lung disease, a pulmonary embolism that a healthy person could easily tolerate may be life-threatening or fatal.
Diagnosing pulmonary embolism requires one of two imaging procedures: a pulmonary arteri- ogram or a high-resolution CT scan. In both procedures, contrast medium (dye) is injected into the veins, and X rays are taken to locate the block- age. However, because symptoms of pulmonary embolism also can indicate a heart attack, your doctor probably will perform a chest X-ray exam- ination, electrocardiography (an examination of the electrical activity of the heart), blood tests, and possibly radionuclide scans (in which a radioactive substance is injected into the bloodstream to produce images of the pulmonary arteries) to help conﬁrm the diagnosis.
In most cases the clot or embolus breaks up on its own and does not need to be removed surgically. Painkillers, oxygen, and blood thinners (to prevent further clots from forming and to help dissolve existing clots) are given while the artery is blocked. Treatment with thrombolytic (clot-dissolving) drugs also may be helpful. In rare cases, surgery to remove the clot may be required if it is very large.
The long-term goal of treatment for pulmonary embolism is to prevent the development of blood clots in the legs and other parts of the body. Usually this involves long-term use of anticoagulant (blood-thinning) drugs such as heparin or warfarin. This is especially important after hip surgery, elective neurosurgery, or a major injury. In cases of chronic, persistent clots, a ﬁlter may be installed in a major vein (location of the ﬁlter depends on the source of the clots) to prevent clots from traveling through the veins into the pulmonary artery.
Warning Signs of Pulmonary Embolism
Pulmonary embolism occurs suddenly. If you have a condition that puts you at
risk for pulmonary embolism—such as immobility, cancer, a leg injury, or heart failure—seek immediate medical care if you have any of the following warning signs:
• shortness of breath
• sharp chest pain
• rapid pulse
• coughing up bloody mucus
Infectious Lung Disorders
Your lungs have built-in mechanisms for ﬁltering out foreign substances that are inhaled with each breath. Despite these mechanisms, however, with repeated exposure to infectious agents such as viruses and bacteria, or with a change in your immune system, your risk of contracting a respiratory infection increases. This is especially true if your lungs have been damaged by smoking or exposure to environmental pollutants or if you have a chronic disease or take medications that decrease the effectiveness of your immune system. Some infectious microorganisms that enter the body through the lungs can affect many different organ systems. Others remain in the lungs, causing infection and inﬂammation.