AsthmaWhile COPD typically refers to a combination of chronic bronchitis and emphysema, asthma is also sometimes included in the “classic triad” of COPD symptoms, though its inclusion is somewhat controversial, with many believing that it is more of a prelude to COPD than an actual consequence.
Asthma affects 5-10% of the population, which comes to roughly 23.4 million people worldwide, including 7 million children. Annually, it affects around 300 million people, according to a study conducted by the WHO, and around 250,000 deaths are reported globally on an annual basis. In children, it is mostly predominant in boys (with a male to female ratio of 2:1), but after hitting puberty, the number of women affected equals that of the men.
Asthma affects children mostly before the age of 18, and adult onset is seen mainly after 40 years of age. This may be due to lower levels of lung activity in childhood or in old age (both extreme cases). The symptoms of asthma normalize on progress towards adulthood.
Passive smoking, urbanization, and exposure to allergens are the main causes behind the development of asthma.
Pathophysiology for asthma is a complex phenomenon, and includes three main phases:
- Airway inflammation: Inflammation due to exposure to allergens and smoke lead to higher levels of T-lymphocyte, eosinophil, and macrophage infiltration along with epithelial and endothelial cells contributing to the chronic nature of the condition in extreme cases. An imbalance between Th1 cells (secreting cytokines responsible for cellular defense mechanisms) and Th2 cells (releasing cytokines responsible for mediating allergic inflammation) also leads to airway inflammation.
- Airflow obstruction: It begins from 6-24 hours of allergen exposure, IgE dependent inflammatory mediator release leading to mucus plug formation from serum proteins and cell debris, causing acute bronchoconstriction and airway edema in later stages. The net result is resistance to airflow, decreased expiratory rates and reduction in the ability to expel air, and hyperinflation of the lungs (thoracic cavity).
- Bronchial hyperresponsiveness: This is caused as a result of chronic inflammation, leading to bronchospasm, wheezing, shortness of breath, coughing among other discomforts. Hypoxia is caused as a result of a mismatch in the ventilation and perfusion rates (the amount of air reaching the alveoli and the amount of blood reaching the alveoli, respectively), which can alsio lead to bronchial hyperresponsiveness.