Chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by chronic respiratory symptoms and airflow limitation.^[9] GOLD defines COPD as a heterogeneous lung condition characterized by chronic respiratory symptoms (shortness of breath, cough, sputum production or exacerbations) due to abnormalities of the airways (bronchitis, bronchiolitis) or alveoli (emphysema) that cause persistent, often progressive, airflow obstruction.^[10]

The main symptoms of COPD include shortness of breath and a cough, which may or may not produce mucus.^[4] COPD progressively worsens, with everyday activities such as walking or dressing becoming difficult.^[3] While COPD is incurable, it is preventable and treatable. The two most common types of COPD are emphysema and chronic bronchitis, and have been the two classic COPD phenotypes. However, this basic dogma has been challenged as varying degrees of co-existing emphysema, chronic bronchitis, and potentially significant vascular diseases have all been acknowledged in those with COPD, giving rise to the classification of other phenotypes or subtypes.^[11]

Emphysema is defined as enlarged airspaces (alveoli) whose walls have broken down, resulting in permanent damage to the lung tissue. Chronic bronchitis is defined as a productive cough that is present for at least three months each year for two years. Both of these conditions can exist without airflow limitations when they are not classed as COPD. Emphysema is just one of the structural abnormalities that can limit airflow and can exist without airflow limitation in a significant number of people.^[12][13] Chronic bronchitis does not always result in airflow limitation. However, in young adults with chronic bronchitis who smoke, the risk of developing COPD is high.^[14] Many definitions of COPD in the past included emphysema and chronic bronchitis, but these have never been included in GOLD report definitions.^[9] Emphysema and chronic bronchitis remain the predominant phenotypes of COPD, but there is often overlap between them, and several other phenotypes have also been described.^[11][15] COPD and asthma may coexist and converge in some individuals.^[16] COPD is associated with low-grade systemic inflammation.^[17]

The most common cause of COPD is tobacco smoking.^[18] Other risk factors include indoor and outdoor air pollution including dust, exposure to occupational irritants such as dust from grains, cadmium dust or fumes, and genetics, such as alpha-1 antitrypsin deficiency.^[14][19] In developing countries, common sources of household air pollution are the use of coal and biomass such as wood and dry dung as fuel for cooking and heating.^[20][14] The diagnosis is based on poor airflow as measured by spirometry.^[4]

Most cases of COPD can be prevented by reducing exposure to risk factors such as smoking and indoor and outdoor pollutants.^[21] While treatment can slow worsening, there is no conclusive evidence that any medications can change the long-term decline in lung function.^[6] COPD treatments include smoking cessation, vaccinations, pulmonary rehabilitation, inhaled bronchodilators and corticosteroids.^[6] Some people may benefit from long-term oxygen therapy, lung volume reduction and lung transplantation.^[22] In those who have periods of acute worsening, increased use of medications, antibiotics, corticosteroids and hospitalization may be needed.^[23]

As of 2021, COPD affected about 213 million people (2.7% of the global population).^[7] It typically occurs in males and females over the age of 35–40.^[1][3] In 2021, COPD caused 3.65 million deaths.^[8] Almost 90% of COPD deaths in those under 70 years of age occur in low and middle income countries.^[3] In 2021, it was the fourth biggest cause of death, responsible for approximately 5% of total deaths.^[3] The number of deaths is projected to increase further because of continued exposure to risk factors and an aging population.^[9] In the United States, costs of the disease were estimated in 2010 at $50 billion, most of which is due to exacerbation.^[9]