Lung diseases are conditions in which some function of the lung is adversely affected. In some cases, the problem is in the gas exchange process at the membrane between the alveoli and blood – impeding efficient uptake of oxygen and removal of carbon dioxide. In other cases, the problem is the inability of the bronchial system to effectively deliver air to the alveoli – possibly due to blockage of the branches of the bronchial tree or due to compromised ability of the chest muscles to expand and contract enough to move 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 (attacks) of airway obstruction. 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 cigarette smoke and other particles in the air, dust, mold, allergens, exercise, cold air, and other factors. The triggers for each person may be different. 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. According to the American Lung Association (ALA), asthma is the most common chronic disorder in childhood. It affects more than 7 million children in the United States and about 23 million adults.
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 between the air sacs, inflammation of the air sacs, and stiffening of the lungs. Causes of pulmonary fibrosis include:
- Occupational or environmental exposure to small particles; this includes 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 can cause hypersensitivity pneumonitis and eventually lead 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 systemic illness caused by a virus that includes respiratory symptoms.
- Tuberculosis and nontuberculous mycobacteria (NTM) are chronic infections most commonly seen in people with compromised immune systems (such as those with HIV/AIDS). The infections caused by mycobacteria develop slowly and can be systemic or confined to the lungs.
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 considered metastatic because the cancer cells do not come from lung tissue. 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 exacerbate 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 that 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 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.]