Pathophysiology of Asthma: Understanding the Mechanisms

An asthma attack unfolds in three overlapping layers, usually within minutes of a trigger. (1) Bronchoconstriction: smooth muscle wrapped around the airway walls contracts suddenly — the airway tube narrows dramatically, like squeezing a garden hose. This is the fastest component (seconds to minutes) and is what a rescue inhaler (salbutamol/albuterol — a short-acting beta-2 agonist) reverses by relaxing smooth muscle. (2) Airway inflammation: the lining swells from inflammatory cells pouring in — eosinophils, mast cells, neutrophils. The airway wall thickens from the inside, further reducing the internal diameter. This takes hours to days to develop and is what inhaled corticosteroids (ICS) treat. (3) Mucus plugging: goblet cells secrete thick, viscous mucus in excess. During a bad attack, mucus can physically plug smaller airways, creating areas of complete blockage. This explains why chest tightness persists even after smooth muscle relaxes — the plug is still there. Physical sensation: patients often describe it as breathing through a wet blanket, or trying to exhale through a straw. The characteristic wheeze is the sound of air pushing through narrowed, mucus-coated airways.

Nocturnal worsening is extremely common — around 70% of asthma deaths occur at night or in the early hours of the morning. Multiple mechanisms converge at night: (1) Circadian dip in cortisol (natural anti-inflammatory hormone) — peaks in early morning, hits its nadir around 2–4 am; airway inflammation is least suppressed in this window. (2) Supine position — lying flat increases vagal tone, promotes mucus pooling in central airways, and reduces functional residual capacity (lung volume), making the airways more prone to closure. (3) GERD micro-aspiration — stomach acid is more likely to reflux in a supine position; even small amounts reaching the back of the throat can reflexively trigger bronchospasm via the vagal nerve. (4) Allergen exposure in bed — dust mites live in pillows and mattresses and peak allergen load is during sleep. If you're consistently waking between 2–4 am with wheeze, discuss with your pulmonologist: this pattern often indicates that daytime ICS alone isn't sufficient and may need a long-acting bronchodilator (LABA) or leukotriene modifier added. It's not inhaler failure — it's a specific pathophysiological pattern that often requires a step-up in the preventer regimen.

Diagnosis combines history, examination, and objective lung function testing. History: the classic pattern is episodic wheeze, cough (worse at night), chest tightness, and breathlessness triggered by identifiable factors — important because asthma's variability is itself a diagnostic clue. A single normal examination in clinic doesn't rule out asthma (airways may be fine between attacks). Spirometry: the key test. It measures FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity). Asthma shows obstructive pattern (FEV1/FVC <0.7) that is reversible — FEV1 improves ≥12% and ≥200 mL after inhaling a bronchodilator (salbutamol 400 mcg via spacer). This reversibility differentiates asthma from COPD (fixed obstruction). Peak flow monitoring: daily home peak flow readings over 2 weeks — variability >20% between morning and evening supports asthma. Allergy testing: skin-prick test or specific IgE blood test identifies allergen triggers. Bronchial provocation test (methacholine challenge): used when spirometry is normal but clinical suspicion is high — confirms airway hyperresponsiveness. In India, spirometry is available at all medical college pulmonology departments (₹200–500), most private respiratory clinics, and major diagnostic centres (Dr Lal Path Labs, Metropolis, SRL).

Two completely different types of medication serving two different purposes. Reliever (rescue) inhaler: contains a short-acting beta-2 agonist (SABA) — salbutamol (Ventolin, Asthalin) most commonly in India. Works within 5–15 minutes by relaxing smooth muscle. This is your emergency tool — use it when you have symptoms. It doesn't treat the underlying inflammation. Using it more than twice a week means your asthma is not well-controlled. Preventer inhaler: contains an inhaled corticosteroid (ICS) — budesonide (Foracort, Budecort), fluticasone (Flixotide), beclomethasone. Reduces airway inflammation over time; must be used daily even when feeling well. Takes 2–4 weeks to reach full effect. Many patients make the mistake of stopping the preventer when they feel better — this allows inflammation to build back up, leading to the next attack. Some inhalers are combination devices (ICS + LABA in one inhaler — e.g., salmeterol/fluticasone = Seretide/Foracort). These are preventer + controller in one, but you still need a separate salbutamol rescue inhaler for acute symptoms. The GINA 2023 guidelines recommend against using reliever-only therapy for anyone with persistent asthma — even mild persistent asthma needs a daily ICS preventer to reduce exacerbation risk.