Chronic obstructive pulmonary disease (COPD) refers to two related, progressive diseases of the respiratory system, chronic bronchitis and emphysema.
Chronic bronchitis is ongoing inflammation that eventually results in narrowing of the airways. Emphysema is the enlargement and destruction of the air sacs (alveoli) of the lungs. These are gradually progressive and permanent disease conditions in which a person has persistent difficulty in expelling (exhaling) air from the lungs, resulting in loss of lung function. Smoking is the major cause of both diseases. In most cases of COPD, chronic bronchitis and emphysema often occur together in the same individual.
The lungs are the site where oxygen enters the blood and carbon dioxide is removed from the blood. Healthy lungs perform this process, known as gas exchange, efficiently. When air is inhaled through the nose or mouth, it moves through the windpipe (trachea) to large bronchial tubes (bronchi) then through smaller tubes (bronchioles). At the ends of the bronchioles are small air sacs (alveoli). In healthy lungs, the alveoli and the bronchi are springy and elastic. Much like a balloon, the alveoli can fill with inhaled air and deflate when air is exhaled. In people with COPD, the alveoli have lost their elasticity and shape so that a smaller volume of air moves in and out with each breath. COPD develops slowly over many years. Once it develops, COPD is irreversible (permanent); the damage done to the lungs, airways, and walls of the airways cannot be repaired by the body.
Emphysema is a lung disease that affects a person's ability to breathe. Easier, deeper breathing steadily weakens over time as lung tissue is destroyed. Cigarette smoke causes an overproduction of the enzyme elastase, one of the immune system's infection-fighting biochemicals. This effect results in irreversible destruction of a protein in the lung called elastin. Elastin is essential in maintaining the structure of the walls of the alveoli. As the walls of the alveoli rupture, the number of alveoli is reduced, and many of those remaining are enlarged. This deterioration reduces the surface area for gas exchange and makes the lungs of the patient with emphysema less elastic and overinflated. Higher pressure inside the chest must be developed to force air out of the less-elastic lungs, so the bronchioles tend to collapse during exhalation, blocking air flow. Stale air gets trapped in the air sacs and less fresh air can be inhaled. Eventually, the person has to breathe more frequently or breathe harder to get enough oxygen and get rid of carbon dioxide. Airway cells also secrete more mucus than usual, which clogs airways and makes breathing even more difficult.
Cigarette smoking is the greatest risk factor for developing COPD. Cigar and pipe smoking also can cause COPD. Exposure to airborne pollutants, such as chemicals and industrial dust in the work place, also increases risk. Coal mining, cotton textile manufacturing, and gold mining are among the occupations in which risk is increased, but the effects of these occupational exposures are lower than the effects of cigarette smoke. There is some debate about the role of exposure to air pollution in the development of COPD, but it is agreed to be less important as a risk factor than cigarette smoking. It is well established, however, that air pollution can cause flare-ups and more severe effects in people who have COPD. Particulates in outdoor air pollution and exposure to indoor smoke from biomass fuels or secondhand tobacco smoke increase irritation to the lungs and decline in lung function. Around the world, COPD is a significant public health issue because of smoking as a risk behavior and exposure to air pollution. Some people have a genetic risk for COPD, and if someone has the genetic abnormality and smokes, the lung decline is speeded up considerably.
Almost all people with COPD are over age 40, and the highest rate of the disease is among those age 65 and older. More men than women have COPD, but at least in the United States the difference in rates between genders is narrowing.
The exact prevalence of COPD in the United States is unknown, although more than 9.3 million adults were diagnosed with COPD in the United States in 2016. According to the United States Centers for Disease Control and Prevention (CDC), COPD was the third leading cause of death in the United States in 2014. Internationally, COPD was the fourth leading cause of death in 2015. At least 80% of the people who died from COPD had been tobacco smokers; however, industrial pollutants also are to blame in up to 19% of cases. The disease occurs most frequently in South Africa, and Germany is among those countries with the lowest incidence. Chronic bronchitis is about four times more common than emphysema.
Cigarette smoking, along with the smoking of pipes and cigars, is a primary cause of COPD. Secondary (passive) exposure to cigarette smoke is also a contributing factor to COPD. Occupational chemicals, dusts, and airborne particulates in the workplace also have been documented to be factors that can lead to the disease, as have air pollutants in the home. Outdoor air pollution has not been documented to be a significant factor to COPD, although such pollution is never good for anyone's lungs, especially those at risk for developing COPD.
Genetic and hereditary factors also play a role in the development of COPD. One form of emphysema is known to recur in families. People with this type of emphysema have a hereditary deficiency of a blood component, an enzyme inhibitor called alpha-1-antitrypsin (AAT). This type of emphysema is sometimes called early-onset emphysema because it can appear when a person is as young as 30–40 years of age. This type of emphysema is estimated to account for only 1%–3% of all cases of emphysema. The risk of developing emphysema for an AAT-deficient individual who also smokes is much greater than for others.
The symptoms of COPD develop gradually, usually over years. The most common symptoms of chronic bronchitis are cough, production of sputum, and shortness of breath, especially with exercise. People with COPD also may experience wheezing and tightness in the chest. In emphysema, shortness of breath on exertion is the most common early symptom. Coughing is usually minor, and there is little sputum. As emphysema progresses, shortness of breath occurs with less exertion and eventually may be present even when the individual is at rest. At this point, a sputum-producing cough may also occur. Either chronic bronchitis or emphysema can lead to respiratory failure, a condition in which there is a dangerously low level of oxygen or a serious excess of carbon dioxide in the blood. Emphysema is not contagious, but people who have the disease are more vulnerable to infections such as pneumonia.
In addition to shortness of breath, coughing, and wheezing, people with emphysema often develop the following symptoms:
A history of heavy smoking is not enough to diagnose COPD. The first step in making a diagnosis is a good medical evaluation, including a medical history and a physical examination of the chest using a stethoscope. This examination may be followed by a variety of tests to evaluate lung function. A physician will combine information on symptoms, medical history, physical examination, lung function tests, and chest x-ray results to make a diagnosis.
Lung function tests help diagnose emphysema by measuring how much air a person can breathe in and out. A spirometer is used to measure a person's ability to breathe air in and how quickly the air can be blown out. Using a spirometer, an instrument that measures the air taken into and exhaled from the lungs, the doctor will determine two important values: (1) vital capacity (VC), the largest amount of air expelled after the deepest inhalation, and (2) forced expiratory volume (FEV1), the maximum amount of air expired in one second. The pulmonary function test can be performed in the doctor's office.
There is no cure for COPD. Treatment focuses on slowing the disease's progression and easing the patient's symptoms. Treatment for patients who smoke begins with helping them quit smoking. Although quitting does not reverse the effects of COPD, it can slow the worsening of lung function. Smoking cessation programs may be effective. Those who work in occupations that expose them to lung irritants must take steps to avoid the irritants. In addition to relieving symptoms, treatment emphasizes preventing complications and improving a patients' overall health. The treatment varies depending on each patient's symptoms and stage of COPD. Treatment also may change over time and if a patient experiences complications or sudden onset of more severe symptoms.
Supplemental oxygen is the only therapy that has been demonstrated to reduce the number of deaths in patients with COPD. The treatment usually is reserved for patients who are unable to get adequate oxygen on their own. The oxygen may be delivered by a portable tank that allows the patient to be mobile outside the home, through a concentrator unit placed in the home or through some combination. Some patients receive oxygen some of the time, such as when short of breath. Others may receive it only at night. Using extra oxygen more than 15 hours a day helps people perform activities with less shortness of breath and remain more alert during the day; it also protects the heart and other organs from damage.
Medications frequently prescribed for COPD patients include:
People with COPD also might be referred to pulmonary rehabilitation programs. The structured programs help them learn techniques and exercises to improve breathing, nutrition, and overall health to lessen the symptoms of COPD.
Surgery can be an option for some people with COPD, although its use is rare. Lung volume reduction surgery removes small portions of damaged lung tissue, and in rare cases, a patient might receive a lung transplant. This is an option only when other treatments have failed, when a matching donor lung is available, and typically for younger patients.
The public health role in preventing COPD is a global issue. The World Health Organization has made tobacco control and second-hand smoke a major initiative, with programs such as All World No Tobacco Days. An example of a U.S. initiative is Healthy People 2020, a program with specific public health goals, including reduction of respiratory infections caused by tobacco smoke. The CDC National Institute for Occupational Safety and Health helps prevent spread of flu and other viruses in the workplace and offers safety guidelines on fumes, dusts, and other irritants in the workplace.
COPD is a disease that can be treated and controlled, but not cured. Survival of patients with COPD is clearly related to the degree of their lung function when they are diagnosed and the rate at which they lose this function. Overall, the median survival is about 10 years for patients with COPD who have lost approximately two-thirds of their lung function at diagnosis. Prognosis for emphysema often is related to how heavily one smoked and for how many years. People with COPD need frequent hospitalizations as the disease progresses to care for flare-ups and infections. Complications related to the heart, or cardiovascular disease, also can lead to death. More women than men die of emphysema.
The most effective way to prevent COPD is to never smoke. Lifestyle modifications that can help prevent COPD or improve function in COPD patients include: quitting smoking, avoiding respiratory irritants and infections, avoiding allergens, maintaining good nutrition, drinking lots of fluids, avoiding excessively low or high temperatures and very high altitudes, maintaining proper weight, and exercising to increase muscle tone. COPD related to genetic factors cannot always be prevented, but its development can be postponed in people who inherited the defective gene by avoiding smoking and other lung irritants.
See also Bronchitis ; Smoking .
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Teresa G. Odle