82. Obstructive lung diseases (bronchial asthma) - etiology, pathogenesis, clinical manifestations.

Obstructive lung diseases (bronchial asthma) – etiology, pathogenesis, and clinical manifestations.

Asthma is a chronic inflammatory disease of the airways characterized by reversible bronchial obstruction, airway hyperresponsiveness, and episodic symptoms.

Etiology

1. 1 Extrinsic (allergic, atopic) asthma

• Most common type, often starting in childhood.
• Triggers:
• Inhaled allergens: dust mites, pollen, animal dander.
• Food allergens (less common).
• Associated with:
• Allergic rhinitis.
• Eczema.
• Positive family history (strong genetic predisposition).

1. 2 Intrinsic (non- allergic) asthma

• Usually adult onset.
• Triggers:
• Respiratory infections (especially viral).
• Cold air, exercise.
• Stress, strong odors.
• Medications (aspirin —aspirin- exacerbated respiratory disease).

1. 3 Occupational asthma

• Due to workplace sensitizers (chemicals, dusts).

1. 4 Drug- induced asthma

• Aspirin and NSAIDs (by shifting arachidonic acid metabolism toward leukotriene production).

Pathogenesis

1. 1 Initial sensitization phase (in allergic asthma)

• Allergen exposure → uptake by antigen-presenting cells → activation of Th2 cells → B cells produce IgE antibodies.
• IgE binds to mast cells → sensitization.

1. 2 Re- exposure (early- phase reaction)

• Allergen cross-links IgE on mast cells → degranulation → release of histamine, leukotrienes, prostaglandins → bronchoconstriction, mucus secretion, vasodilation.

1. 3 Late- phase reaction

• Recruitment of eosinophils, neutrophils, and Th2 cells → sustained inflammation, epithelial damage, and further hyperreactivity

1. 4 Airway remodeling (in chronic asthma)

• Smooth muscle hypertrophy.
• Subepithelial fibrosis.
• Goblet cell hyperplasia → increased mucus.

Clinical manifestations

Typical symptoms (episodic)

• Dyspnea.
• Wheezing (mainly during expiration).
• Cough, often worse at night or early morning.
• Chest tightness.

During attack

• Prolonged expiration.
• Use of accessory muscles.
• Hyperinflated chest.
• Tachypnea, tachycardia.
• In severe cases ("status asthmaticus"): silent chest, severe hypoxia, possible respiratory failure.

Between attacks

• Often asymptomatic, especially in early disease.