What is asthma?

Definition of Asthma

Asthma is a chronic inflammatory disorder of the airways characterized by variable and recurring symptoms, airflow obstruction, bronchial hyperresponsiveness, and underlying inflammation that causes recurrent episodes of wheezing, breathlessness, chest tightness, and coughing, which are often reversible either spontaneously or with treatment. 1

Key Components of Asthma

Asthma involves four fundamental pathophysiological features:

• Chronic airway inflammation: Involves multiple cell types including mast cells, eosinophils, neutrophils, T lymphocytes, macrophages, and epithelial cells 1
• Bronchial hyperresponsiveness: Exaggerated bronchoconstrictor response to various stimuli 1
• Variable airflow obstruction: Caused by bronchoconstriction, airway edema, mucus hypersecretion, and airway remodeling 1
• Symptom variability: Symptoms that are intermittent, variable in intensity, worse at night, and triggered by specific exposures 1, 2

Clinical Manifestations

The primary symptoms of asthma include:

• Wheeze (typically diffuse, polyphonic, bilateral, and expiratory)
• Shortness of breath
• Chest tightness
• Cough (may be the predominant or only symptom in cough-variant asthma) 1

These symptoms are characteristically:

• Variable in intensity
• Intermittent rather than constant
• Often worse at night or early morning
• Provoked by specific triggers including exercise, allergens, cold air, and irritants 2

Pathophysiological Changes

Airflow limitation in asthma results from several mechanisms:

1. Bronchoconstriction: Bronchial smooth muscle contraction that narrows airways in response to various stimuli 1
2. Airway edema: Progressive inflammation leads to edema and mucus hypersecretion 1
3. Mucus plugging: Formation of inspissated mucus plugs further limiting airflow 1
4. Airway remodeling: Long-term structural changes including sub-basement fibrosis, smooth muscle hypertrophy, and angiogenesis that may lead to irreversible airflow limitation 1

Diagnostic Considerations

Diagnosis is primarily clinical but can be supported by:

• Documentation of variable airflow limitation through PEF or FEV1 measurements
• Demonstration of reversibility with bronchodilators
• Evidence of diurnal variability in lung function 1

Repeated normal lung function tests in the presence of symptoms should raise doubt about an asthma diagnosis 1.

Common Triggers

Asthma symptoms are often triggered by:

• Exercise
• Viral respiratory infections
• Allergen exposure (pollens, dust mites, animal dander)
• Environmental irritants and chemicals
• Tobacco smoke
• Aspirin/NSAIDs (in susceptible individuals)
• Beta-blockers 2, 3

Understanding asthma as a chronic inflammatory condition with variable airflow obstruction helps guide appropriate management strategies focused on controlling inflammation and preventing exacerbations to reduce morbidity and mortality.