Lung diseases are conditions in which some function of the lung is adversely affected. Problems with the tiny air sacs (alveoli) may hamper the efficient uptake of oxygen and removal of carbon dioxide. Blockages in branches of the bronchial tree or conditions that inhibit chest muscle expansion or contraction may interfere with the delivery of air through the bronchial tree to the alveoli. Sometimes the problem is the inability of the lung to remove or detoxify foreign substances, possibly because of an underlying deficiency or because the amount of these substances has overwhelmed the lungs' defense systems.
Common lung diseases include:
Asthma is a chronic lung disease characterized by inflammation of the bronchi and bronchioles and episodes of airway obstruction. During an attack, the lining of the airways swell and the muscles surrounding the bronchi contract, narrowing the airway. Mucus secretion can further inhibit the flow of air, making breathing difficult and causing the affected person to wheeze. Most episodes do not cause permanent lung damage but frequently require immediate medical attention since lack of oxygen and build-up of carbon dioxide can be life-threatening. People with asthma are sensitive to a variety of substances that do not cause the same reaction in other people. Episodes may be triggered by cold air, exercise, cigarette smoke, or other particles in the air such as dust, mold, or allergens. The triggers for each person may be different. According to the American Lung Association (ALA), asthma is the most common chronic disorder in childhood. The number of people with asthma continues to grow with about 25 million Americans being affected as of 2009. It is estimated that 1 in 10 children have asthma.
Chronic obstructive pulmonary disease (COPD) is a term used for both emphysema and chronic bronchitis. According to the ALA, COPD is the third leading cause of death in the United States. With chronic bronchitis, the bronchial tubes become inflamed and scarred. With emphysema, the air sacs in the lungs are slowly destroyed. With both disorders, those affected experience increasing difficulty exhaling and getting a sufficient oxygen supply. Smoking causes about 85-90% of the deaths associated with COPD. Other risk factors include repeated exposure to air pollution.
Pulmonary fibrosis is a lung disease characterized by damage and scarring to the tissues of the lungs, including those between and supporting the air sacs. In many cases, the cause of the inflammation and stiffening is unknown but may include:
- Occupational or environmental exposure to small particles, including repeated exposure to inorganic substances such as asbestos, coal, beryllium, and silica
- Repeated exposure to organic substances such as moldy hay, animal droppings, and grain dust that causes hypersensitivity pneumonitis, an allergic reaction, that eventually leads to pulmonary fibrosis
- Chemicals and drugs that are toxic to the lungs
- Previous radiation treatment
- Scleroderma and other autoimmune disorders
- Unknown (idiopathic)
Infections can occur primarily in the lungs, may affect the entire body, including the lungs, or may develop in the pleura, which are the membranes surrounding the lungs. They may be acute or chronic and be caused by bacteria, viruses, and more rarely, fungi.
- Pneumonia is an acute lung tissue inflammation caused by a variety of microorganisms.
- Influenza is an acute illness caused by a virus that includes respiratory symptoms.
- Tuberculosis and nontuberculous mycobacteria (NTM) are chronic infections most commonly seen in people with weakened immune systems (such as those with HIV/AIDS). The infections caused by mycobacteria develop slowly and can be confined to the lungs or affect the body as a whole (systemic).
Lung cancer is the uncontrolled growth of malignant cells that originate in the lungs. There are two main types, small cell and non-small cell lung cancers. Other cancers may spread to the lungs but are not considered lung cancer and are treated differently. The number of lung cancer deaths has been rising in women in recent years and falling in men. According to the ALA, lung cancer is currently the leading cause of cancer death for American women and men, killing more people than the next three most common cancers (colon, breast, and prostate) combined. Risks for lung cancer include smoking and exposure to radon.
Pulmonary hypertension is a lung disorder characterized by a narrowing of the blood vessels in the lungs, increasing their blood pressure and causing the heart to work harder to transport blood into the lungs. This condition may co-exist and worsen a variety of lung diseases and can lead to heart failure.
Pulmonary embolism is a blood clot that usually originates in the veins of the legs or pelvis and travels to the lungs, where it blocks a blood vessel, causing chest pain, acute shortness of breath, and coughing. This condition can be life-threatening and requires prompt medical attention.
Bronchopulmonary dysplasia (BPD) is a lung disease that develops primarily in premature infants who have undergone prolonged oxygen therapy and/or have been on mechanical ventilation for extended periods of time but may also be seen in those who have experienced oxygen toxicity or had pneumonia. With this disorder, airways are inflamed, do not develop normally, and may be damaged.
Respiratory distress syndrome (RDS) of the newborn is a life-threatening breathing problem that may develop in infants born earlier than 6 weeks before their due date. These premature babies' lungs are not able to produce an adequate amount of the protective liquid substance called surfactant. Without sufficient surfactant, the lungs are not able to expand or inflate properly and the babies have difficulty breathing in enough oxygen. It is a condition that may occur within a few hours after a premature birth.
Acute respiratory distress syndrome (ARDS) is the rapid onset of severe breathing difficulties due to extensive lung inflammation and the lungs filling with fluid. It is a sometimes fatal condition that can be brought on by many types of injury to the lungs, including serious viral or bacterial infection, sepsis, trauma, multiple blood transfusions, drug overdose, or inhalation of substances such as salt water or smoke.
Cystic fibrosis is an inherited disease that affects the lungs, pancreas, and other body systems. It is characterized by salty sweat, the production of thick mucus that can obstruct breathing, and a decreased ability to digest fats and proteins, leading to malabsorption and malnutrition. It is more common in Caucasians than other ethnic groups and is usually diagnosed in infancy. According to the ALA, about 1,000 new cases are diagnosed in the U.S. each year.
Alpha-1 antitrypsin deficiency is an inherited deficiency of a protein that provides protection to the lungs. Without this protection, the lungs become progressively damaged and the person is at a significantly increased risk of developing early-onset emphysema and liver disease. The ALA estimates that about 100,000 Americans have this deficiency, and about 20 million are genetic carriers of the disease.
Other disorders do not affect the lungs directly, but they impair a person's ability to breathe properly. These extrinsic disorders may affect the chest cavity, muscles, nerves, and heart. They include a variety of conditions, such as neuromuscular diseases like muscular dystrophy, polio, myasthenia gravis, Guillain-Barré syndrome, and amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease), and disorders that result in abnormal spine formation or rib cage movement, which can restrict lung expansion. [Specific testing and treatment for these extrinsic disorders are not covered in this article.]