Chronic obstructive pulmonary disease (COPD) is a long-term lung condition that makes it progressively harder to breathe. It occurs when the airways and lung tissue become damaged, leading to reduced airflow and reduced efficiency of oxygen exchange in the lungs. COPD develops gradually over time, and while it cannot currently be cured, treatments and lifestyle changes can help control symptoms and slow disease progression. Early diagnosis and prompt treatment are recommended.
The condition includes two related lung problems: chronic bronchitis and emphysema. Chronic bronchitis involves ongoing inflammation of the airways, causing excess mucus production, coughing, and chest discomfort. Emphysema involves damage to the small air sacs in the lungs, which reduces the lungs' ability to transfer oxygen into the bloodstream. Many people with COPD experience shortness of breath, persistent cough, wheezing, and reduced exercise tolerance. Symptoms can become more severe during acute flare-ups, which can be triggered by viral and bacterial infections and exposure to irritants. People with COPD generally display a combination of these symptoms, and are likely to have additional health issues.
COPD can develop due to multiple factors, most often involving long-term exposure to lung irritants. The strongest risk factors are tobacco smoke, air pollution, and workplace dust and chemical fumes. Smoke from fuels used for cooking and heating is a primary risk factor in some places, particularly for women and young children. Factors affecting lung development in early life such as respiratory infections, poor nutrition, and physical inactivity, can increase risk of COPD in later life. Genetics can also play a role.
The diagnosis of COPD is usually confirmed using lung function tests that measure how well air moves in and out of the lungs. While COPD cannot currently be cured, treatment can significantly improve quality of life. Common treatments include inhaled medications that help open the airways, pulmonary rehabilitation programmes that improve fitness and breathing control, and oxygen therapy for people with advanced disease. Quitting smoking is strongly recommended, as is reducing exposure to other lung irritants.
As of 2021, COPD affected about 213 million people worldwide. COPD typically occurs in people over the age of 35–40, and risk increases with age. In 2021, COPD was the fourth-biggest cause of death, responsible for approximately 5% of total deaths. Almost 90% of COPD deaths in those under 70 years of age occur in low and middle income countries. The number of deaths is projected to increase further because of continued exposure to risk factors and an ageing population.
Signs and symptoms
The Global Initiative for Chronic Obstructive Lung Disease (GOLD) defines COPD as a lung condition with multiple underlying causes, characterized by long-lasting respiratory symptoms (shortness of breath, cough, and mucus) which can flare up intermittently. Symptoms are due to impairments of the airways (bronchitis, bronchiolitis) or small air sacs of the lungs (emphysema) that cause persistent, often progressive, airflow obstruction.
Shortness of breath A cardinal symptom of COPD is chronic and progressive shortness of breath. Breathlessness is often the most distressing symptom, causing anxiety and the level of disability that is experienced. Symptoms of wheezing and chest tightness associated with breathlessness can vary over the course of a day or between days and are not always present. Chest tightness often follows exertion.
People experiencing distress may naturally adopt a sitting posture, leaning forward with their hands on their knees, known as the tripod position. This can help to decrease breathlessness by stabilizing and lifting the shoulder girdle. People with more advanced COPD may also breathe through pursed lips, which can improve shortness of breath.
Shortness of breath often results in reduced physical activity, and low physical activity levels are associated with worse outcomes. People with COPD often have increased breathlessness and frequent colds before seeking treatment. In severe and very severe cases, there may be constant tiredness, weight loss, muscle loss, and anorexia.
Cough The first symptom of COPD to appear is usually a chronic cough, which may or may not bring up thick slippery fluid (referred to as sputum, mucus or phlegm). Coughing up mucus can be intermittent and may be difficult to evaluate. A productive cough that brings up mucus is seen in less than 30% of cases. Sometimes, limited airflow may develop without a cough. Symptoms are usually worse in the morning. Depending on social or cultural factors, mucus may be swallowed or spat out.
A chronic productive cough may result from the release of too much mucus within the airways. When it persists for more than three months each year for at least two years, it is called chronic bronchitis. Chronic bronchitis can occur before the restricted airflow diagnostic of COPD. People tend to under-report symptoms, and may assume that symptoms result from short-term irritation rather than underlying changes in lung function. In severe COPD, vigorous coughing may lead to rib fractures or to a brief loss of consciousness.
Exacerbations An acute exacerbation is a sudden flare-up or worsening of signs and symptoms that lasts from several days to two weeks. Worsening of symptoms can involve increased breathlessness, an increase in mucus volume, a change in mucus character, or a change in cough or wheeze. A commonly found sign is air trapping, difficulty in breathing out fully.
Flare-ups are often associated with inflammation resulting from viral or bacterial infection or environmental irritation of the airways. Viral infections such as the common cold account for 70% of flare-ups. Colds more often occur during the winter months, but can occur at any time. Bacterial respiratory infections are the second most frequent triggers, including Haemophilus influenzae, Pseudomonas aeruginosa and Streptococcus pneumoniae. Bacterial infections may occur in combination or be secondary to viral infections.
Environmental insults that can trigger acute flare-ups include exposure to smoking, use of solid fuels, and other sources of indoor or outdoor air pollution. Exposure to tobacco smoke can be either active or passive. Smoke from wildfires is an increasing risk in many parts of the world due to climate change. The United States Environmental Protection Agency recommends the use of well-fitting particulate masks, which give more effective protection than dust masks when dealing with the fine particles from wildfires. This same advice is offered by governments in Canada and Australia regarding forest fires.
The risk of developing a COPD flare-up is higher in women; in people with one or more flare-ups in the last year; in those with more severe COPD as measured by lung function tests; and in those with chronic bronchitis or related conditions such as gastroesophageal reflux, pulmonary hypertension or pulmonary embolism. People with two or more flare-ups a year are associated with worse disease progression and are classed as frequent exacerbators. More flare-ups are associated with more rapid decline in lung function, lower quality of life, and higher morbidity and mortality. Frailty in ageing is linked to more flare-ups and hospitalizations.
Other conditions COPD often occurs along with multiple other conditions (comorbidities) affecting the body's systems. This reflects both shared risk factors and the role of inflammation in illness. Compared to people of the same age without COPD, people with COPD have higher rates of cardiovascular disease, respiratory conditions (lung cancer, pneumonia and asthma), musculoskeletal conditions (osteoporosis), neuropsychiatric conditions (depression, dementia, anxiety), and metabolic disorders (diabetes mellitus, metabolic syndrome, chronic kidney disease, and skeletal muscle dysfunction). Cognitive impairment is common in those with COPD, as it is for other lung conditions that affect airflow. Cognitive impairment is associated with the declining ability to cope with the basic activities of daily living.
People with COPD have up to 83% higher risk of pneumonia, atrial fibrillation, and heart failure, and 78% higher risk of depression. Metabolic syndrome has been seen to affect up to 50% percent of those with COPD and significantly affects the outcomes. When metabolic syndrome occurs with COPD, there is more systemic inflammation. Metabolic syndrome on its own has a high rate of morbidity and mortality, and this rate is amplified when it occurs with COPD.
There is also an associated risk of developing pulmonary hypertension, which leads to worse outcomes, including the risk of death. The likelihood that pulmonary hypertension will complicate COPD has been reported as 39%. Of the people with COPD listed for lung transplantation, 82% were documented as having pulmonary hypertension.
Other complications include reduced quality of life and increased disability, cor pulmonale, chest infections, secondary polycythemia, respiratory failure, pneumothorax, and cachexia (muscle wasting). Tuberculosis is a risk factor for the development of COPD, and is also a potential comorbidity.
In cases of COVID-19, COPD patients were at higher risk for severe complications, including hospitalization, intensive care unit admission, and mortality. They were also likely to exhibit symptoms of long COVID involving persistent respiratory symptoms, fatigue, and cognitive dysfunction. Differentiating COVID-19 symptoms from an exacerbation is difficult; when symptoms include loss of taste or smell, COVID-19 should be suspected.
People with COPD have more health issues than those without COPD. Multimorbidity is associated with a worse COPD prognosis. People with COPD are more likely to die of respiratory or heart-related causes than those without COPD, and to die at younger ages. People with COPD often die as a result of comorbidities rather than from respiratory problems.
Categorization Categorizing COPD in terms of subtypes can support more targeted treatment approaches for patients. A phenotype refers to a collection of observable characteristics, including symptoms, frequency of episodes, and other details of patient history that are used in clinical practice. An endotype links such observable traits to underlying mechanisms. One phenotype may be related to multiple endotypes. A genotype is based on the presence or absence of a genetic factor and its effects on underlying mechanisms. An etiotype is a grouping based on contributory causes. Individuals can be affected by multiple causes. Specific causes may be related to particular phenotypes.
Emphysema and chronic bronchitis phenotypes Historically, phenotypic definitions of COPD have often focused on symptoms of emphysema and chronic bronchitis. Emphysema involves enlarged air sacs in the lungs (alveoli) whose walls break down resulting in permanent damage to the lung tissue. Emphysema can exist without airflow limitation, but it commonly involves it. Other structural abnormalities can also limit airflow. Chronic bronchitis is defined as a productive cough that is present for at least three months each year for two years. It does not always result in airflow limitation, although the risk of developing COPD is great.