From the Guidelines
Asthma is a complex disorder characterized by variable and recurring symptoms, airflow obstruction, bronchial hyperresponsiveness, and an underlying inflammation, as defined by the expert panel report 3 (EPR-3) guidelines 1. The pathophysiology of asthma begins with exposure to triggers like allergens, irritants, or infections that activate inflammatory cells including mast cells, eosinophils, and T-lymphocytes in genetically susceptible individuals.
- These cells release inflammatory mediators such as histamine, leukotrienes, and cytokines, causing bronchial smooth muscle contraction, increased mucus production, and airway edema.
- The airway inflammation leads to airway narrowing and the classic symptoms of wheezing, coughing, chest tightness, and shortness of breath.
- The inflammatory process also causes airway remodeling over time, with thickening of the airway wall, increased smooth muscle mass, and subepithelial fibrosis, which can lead to fixed airflow obstruction in some patients. Key features of asthma pathophysiology include:
- Bronchoconstriction—bronchial smooth muscle contraction that quickly narrows the airways in response to exposure to a variety of stimuli, including allergens or irritants.
- Airway hyperresponsiveness—an exaggerated bronchoconstrictor response to stimuli.
- Airway edema—as the disease becomes more persistent and inflammation becomes more progressive, edema, mucus hypersecretion, and formation of inspissated mucus plugs further limit airflow. Recent studies provide insights on different phenotypes of asthma that exist, with varying patterns of inflammation and therapeutic response 1. Understanding this complex inflammatory cascade has led to targeted therapies including bronchodilators, anti-inflammatory medications, and newer biologics that target specific inflammatory pathways.
From the Research
Pathophysiology of Asthma
The pathophysiology of asthma is characterized by:
- Chronic inflammation of the lower respiratory tract 2
- Variable airway obstruction and bronchial hyperresponsiveness 2, 3
- Airway inflammation, smooth-muscle contraction, epithelial sloughing, mucous hypersecretion, bronchial hyperresponsiveness, and mucosal edema contributing to the underlying pathophysiology of asthma 3
- Recurrent episodes of wheezing, coughing, chest tightness, and shortness of breath 2, 3
Key Features
Key features of asthma include:
- Chronic inflammatory disorder of the airways 3
- Hyperreactivity and variable expiratory airflow limitation 3, 4
- Variable expiratory airflow limitation on spirometry confirms the diagnosis 4
- Forced expiratory volume in 1 second to forced vital capacity ratio less than the level predicted for the patient's age is suggestive of airflow limitation 4
Classification and Management
Asthma can be classified into:
- Intermittent or persistent, and the latter is either mild, moderate, or severe 3
- Allergic (immunoglobulin E mediated), nonallergic, occupational, aspirin-exacerbated respiratory disease, potentially fatal, exercise-induced, and cough variant asthma 3 Management of asthma involves:
- Control-based management administered in a stepwise manner, with goals of achieving symptom control and minimizing the risks of exacerbations, future fixed airway limitation, and adverse effects of therapy 4
- Use of short-acting bronchodilators as needed for symptom relief, with the addition of an inhaled corticosteroid early as maintenance therapy if symptoms are not well controlled 4