31. ASTHMA

Introduction

Asthma is a long-term inflammatory disorder of the airways. It is associated with variable and usually reversible airflow obstruction and increased bronchial hyperresponsiveness to different triggers. In simple terms, the lungs of an asthma patient are extra sensitive, and exposure to certain allergens or irritants causes the airways to swell, tighten and fill with mucus, making breathing difficult.

Etiology (Causes)

Asthma develops due to a combination of genetic and environmental factors. The airways become overly sensitive and react strongly to various triggers.

Physiological Triggers

  • Viral upper respiratory infections
  • Heavy exercise
  • Untreated conditions like rhinitis, sinusitis or GERD
  • Medicines such as NSAIDs (aspirin, ibuprofen, naproxen, ketoprofen)
  • Statin drugs and other anti-inflammatory medicines
  • Stress and strong emotions
  • Hormonal changes during menstrual cycle

Indoor Environmental Triggers

  • Pet hair, dander, saliva and urine
  • House-dust mites
  • Cockroach waste and decomposed insects
  • Mold and mildew (from leaks or damp areas)
  • Tobacco smoke and wood smoke
  • Perfumes, hairsprays, scented lotions and colognes
  • Air fresheners, incense sticks, scented candles
  • Cleaning sprays, pesticides and paint fumes

Outdoor Environmental Triggers

  • Pollen from trees, grasses and weeds
  • Mold spores from wet leaves
  • Changes in humidity
  • Exposure to cold, hot or humid air
  • Industrial emissions, vehicle exhaust, coal dust
  • Ozone formed from sunlight reacting with fuel combustion gases

Food Allergy

Food allergies occur when the immune system overreacts to certain food proteins. Around 2–10% of people are affected, especially children. Reactions may appear within minutes or hours. Severe reactions can be fatal if untreated.

Types of Asthma (Based on Cause)

  • Intrinsic Asthma: Often develops after age 40; not linked to allergens.
  • Extrinsic Asthma: Common in children; triggered by definite allergens.

Classification (Based on Clinical Severity)

1. Mild Intermittent Asthma

  • Daytime symptoms ≤ 2 times/week
  • Night symptoms ≤ 2 times/month
  • Normal peak flow between attacks
  • Exacerbations brief
  • Need only quick-relief inhalers

2. Mild Persistent Asthma

  • Daytime symptoms > 2 times/week but not daily
  • Night symptoms > 2 times/month
  • Abnormal pulmonary function
  • Activity may be slightly limited

3. Moderate Persistent Asthma

  • Daily daytime symptoms
  • Night symptoms > 1 time/week
  • Exacerbations ≥ 2/week
  • Activity limitation
  • Need 1–2 long-term control medicines

4. Severe Persistent Asthma

  • Continuous daytime symptoms
  • Frequent nighttime symptoms
  • Severely limited physical activity
  • Frequent exacerbations
  • Need multiple long-term control medicines

Pathophysiology

The main allergens such as pollen, dust mites, food substances and drugs start the allergic reaction.

1. Role of IgE & Mast Cells

  • Initial exposure → IgE production
  • IgE binds to mast cells
  • Re-exposure → allergen binds IgE → mast cell degranulation
  • Release of inflammatory mediators: histamine, leukotrienes, prostaglandins

2. Inflammatory Cell Response

WBCs (especially eosinophils) migrate to airways and release toxic proteins → more inflammation and tissue damage.

3. Airway Changes During Attack

  • Increased thick, sticky mucus formation
  • Mucosal swelling due to vascular permeability
  • Bronchial smooth muscle contraction (bronchospasm)

These changes produce:

  • Hyperresponsiveness
  • Airflow obstruction
  • Air trapping → hyperinflation → increased breathing effort
  • Reduced alveolar perfusion → hypoxia

Late Asthma Response

Occurs 4–12 hours after allergen exposure. It is due to ongoing cellular activation and may be more severe.

Airway Remodeling

Chronic untreated inflammation can permanently thicken airway walls, causing irreversible airflow limitation.

Clinical Manifestations

Asthma symptoms vary from mild to severe:

  • Coughing (especially at night, during exercise or laughing)
  • Shortness of breath
  • Chest tightness
  • Wheezing (high-pitched sound while exhaling)

Severe symptoms can be life-threatening if untreated.

Diagnosis

Diagnosis requires early detection to prevent long-term complications like airway remodeling.

1. Medical History & Physical Exam

  • Wheezing
  • Runny nose or nasal swelling
  • Eczema or other allergic skin conditions

2. Lung Function Tests

Spirometry

Measures the amount and speed of air breathed in and out to assess airway obstruction. Very useful for determining severity and treatment needs.

Methacholine Challenge Test

Used when routine tests do not confirm asthma. Methacholine causes airway narrowing in asthma patients. Helps diagnose mild or occupational asthma.

3. Exhaled Nitric Oxide Test

Measures airway inflammation. High NO levels indicate asthma-related swelling.

4. Allergy Tests

Skin tests or blood tests help identify allergen triggers.

Detailed Notes:

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