Chronic obstructive pulmonary disease (COPD) is characterized by progressive degeneration of lung tissue and partially reversible airway obstruction. It encompasses chronic obstructive bronchitis and emphysema. Most people with COPD have both of these conditions. According to some classifications, chronic asthma is a third condition that can characterize chronic obstructive pulmonary disease.
Chronic obstructive bronchitis
Chronic bronchitis is characterized by the excessive production of mucus in the trachea and in the bronchi, causing a cough and sputum that is seen for at least 3 consecutive months over a period of two years. Chronic asthmatic bronchitis is a similar comorbidity, recognizable by its symptoms of coughing, wheezing, and partially reversible airway obstruction. It occurs mostly in people with asthma who are smokers.
Emphysema results from destruction of the lung parenchyma resulting in loss of elasticity, loss of radial traction and destruction of the alveolar septum. It can cause the airways to collapse. Its consequences are restricted airflow and even air retention, and hyperinflation of the lungs.
Incidence and prevalence worldwide
64 million people suffer from COPD worldwide;
It is estimated that by 2030, COPD will become the 3rd leading cause of death in the world;
Risk and protective factors
The risk factors for COPD are numerous and several are linked to irritation of the lungs by one or more external agents:
Smoking and exposure to second-hand smoke
Respiratory disorders in childhood
Occupational exposure to irritants and inhalation of chemicals
Certain socio-demographic conditions such as gender (the prevalence of COPD is higher in women, but mortality from the disease is equivalent in women and men), ethnicity (the incidence and mortality rate is higher among Caucasians) and socioeconomic status (incidence and mortality rate are higher among more disadvantaged groups in society);
Several factors are causing an increase in the incidence of COPD globally, including the increase in smoking in developing countries, the reduction in mortality from infectious diseases and the use of large-scale biomass fuels.
The main causes of lung inflammation are smoking, the greatest risk factor for COPD, and inhaling toxins (chemicals, dust, pollutants) from occupational exposure or from air pollution. Otherwise, an inherited α-1 antitrypsin deficiency can cause COPD in non-smokers. It is responsible for less than 1% of cases of emphysema. Although this deficiency is the only one that has been shown to cause the disease, several genetic variants are thought to be associated with COPD or with declining lung function in some populations. The α-1 antitrypsin deficiency usually manifests itself by involvement of the lower lung lobes.
Respiratory infections, especially those in childhood, can also lead to the development of COPD, especially if they are recurrent.
Chronic obstrusive lung disease
Airway obstruction, inflammation, infection, and complications unique to COPD are multifactorial:
Inhalation of toxins causes an inflammatory process in the airways and pulmonary alveoli which is expressed by an increase in the activity of proteases and a decrease in the activity of antiproteases. The balance between these two substances being broken, the result is a degradation of elastin and the connective tissues involved in the normal process of tissue repair. In the course of COPD, neutrophils and other inflammatory cells release proteases, while free radicals cause inhibition of antiproteases, disrupting the protease / antiprotease balance, leading to tissue destruction, hypersecretion of mucus, bronchoconstriction and edema in the mucous membranes. The more COPD progresses, the more severe the inflammation becomes.
People with COPD are more prone to respiratory infections due to the destruction of the pulmonary parenchyma which is expanding. Bacteria, especially haemophilus influenza, are found in the airways of about 30% of people with the disease. Lung colonization by bacteria such as pseudomonas aeruginosa sometimes occurs in people with more severe disease. Repeated infectious episodes can accelerate the progression of the disease, in particular due to the release of proteases by certain bacteria of the pulmonary flora.
The loss of lung elasticity and airway obstruction are the causes of the limitation in airflow that characterizes COPD. The various inflammatory processes are responsible for the obstruction. In emphysema, the enlarged alveolar spaces resulting from the destruction of the septa (bullae) limit gas exchange. Increased resistance in the airways and hyperinflation of the lungs make it harder to breathe, which can create hypoxia in the person.