Asthma

Asthma is a chronic inflammatory disease of the airways in which the bronchial tubes become hyper-responsive, swollen, and narrowed — producing recurrent, reversible episodes of wheeze, breathlessness, chest tightness, and cough. What makes asthma both fascinating and clinically important is its variability: the same patient can be completely well on Monday and gasping in an emergency department on Thursday. Understanding why the airways behave this way — and how to control the underlying inflammation rather than just chasing symptoms — is one of the most useful pieces of respiratory medicine you can master.

Asthma affects roughly 260 million people worldwide and remains a common cause of preventable death, largely because the disease is under-treated or mismanaged. The good news is that with correct diagnosis and modern inhaled therapy, the overwhelming majority of patients can live entirely normal lives. This page teaches the mechanism, the diagnostic reasoning, and the management logic so the whole subject hangs together instead of being a list of drugs to memorise.

Learning Objectives

• Explain the two core pathophysiological processes: airway inflammation and bronchoconstriction, and how they interact.
• Describe common asthma triggers and the concept of airway hyper-responsiveness.
• Interpret spirometry, bronchodilator reversibility, and peak flow variability to diagnose asthma.
• Apply a stepwise management approach centred on inhaled corticosteroids (ICS).
• Recognise and initiate emergency management of an acute severe asthma attack.
• Distinguish asthma from COPD and other causes of wheeze.

Quick Answer

Asthma is a chronic, reversible obstructive airway disease driven by underlying inflammation that makes the airways twitchy (hyper-responsive). Triggers — allergens, viral infections, exercise, cold air, smoke — provoke bronchoconstriction, mucosal oedema, and mucus, causing wheeze, cough, chest tightness, and breathlessness that vary over time and are often worse at night or early morning. Diagnosis rests on a compatible history plus objective evidence of variable airflow obstruction: spirometry showing an obstructive pattern (reduced FEV1/FVC) that improves after a bronchodilator, or peak-flow variability. Management targets the inflammation with inhaled corticosteroids as the foundation, adds long-acting bronchodilators when needed, and uses a reliever for symptoms. Modern guidelines favour ICS-containing inhalers for everyone — reliever-only treatment is no longer recommended.

Where It Came From

The word "asthma" comes from the Greek ásthma, meaning "panting" or "short-drawn breath," and descriptions of episodic breathlessness appear in some of the oldest surviving medical texts. The Ebers Papyrus of ancient Egypt (around 1550 BCE) recorded remedies for wheezing, and Hippocratic writers in the 5th century BCE used the term, though loosely for any laboured breathing. The Roman physician Aretaeus of Cappadocia (2nd century CE) gave a strikingly accurate account of the paroxysmal attack, and Galen recognised airway obstruction. In the 12th century, the physician-philosopher Maimonides wrote an entire Treatise on Asthma for a patient, noting the role of climate, diet, and emotion — remarkably modern in spirit.

For centuries the driving question was simply: why do the airways suddenly close? Early theories blamed spasm of the airway muscle alone, and treatment for a long time meant relaxing that muscle — from strong coffee and belladonna to, by the 20th century, adrenaline injections and later inhaled beta-agonists. This "bronchospasm" model explained the acute attack but not the disease. The pivotal shift came in the late 20th century. Post-mortem studies of patients who died of asthma revealed airways plugged with mucus, thickened walls, and dense infiltration by inflammatory cells — even in people who had seemed only mildly affected. This forced the field to recognise that asthma is fundamentally an inflammatory disease, and that bronchoconstriction is the visible symptom of an inflamed, hyper-reactive airway underneath.

That paradigm shift — from "bronchospasm to be relaxed" to "inflammation to be suppressed" — is the single most important idea in modern asthma care. It explains why inhaled corticosteroids, which do nothing acutely for an attack but powerfully reduce inflammation over days to weeks, transformed outcomes from the 1970s onward and why over-reliance on quick-relief bronchodilators alone is dangerous.

Airway Inflammation: The Underlying Engine

In most asthma, the airway wall is chronically inflamed even between attacks. In the common allergic (type 2 / eosinophilic) phenotype, inhaled allergens are processed and presented to T-helper cells that adopt a Th2 pattern, releasing cytokines such as IL-4, IL-5, and IL-13. These orchestrate a cascade: IgE production by B cells, recruitment and survival of eosinophils, and priming of mast cells. When the trigger arrives, mast cells degranulate, releasing histamine, leukotrienes, and prostaglandins that cause immediate bronchoconstriction (the early phase), followed hours later by a late phase in which eosinophils infiltrate and sustain the inflammation.

Over time this inflammation produces airway remodelling — thickening of the basement membrane, hypertrophy of smooth muscle, increased mucus glands, and new blood vessels. Remodelling can make airflow obstruction partly fixed and less reversible, which is why leaving asthma untreated for years has consequences. Crucially, inflammation is the root cause of airway hyper-responsiveness (AHR): the exaggerated tendency of asthmatic airways to constrict in response to stimuli that would barely affect a normal airway. AHR is why an asthmatic coughs in cold air or laughs into a wheeze while others feel nothing.

Bronchoconstriction and the Anatomy of an Attack

Three things narrow the airway during an attack, and understanding all three explains treatment:

1. Smooth muscle contraction (bronchospasm) — the fast, reversible component relieved within minutes by a beta-2 agonist.
2. Mucosal oedema and inflammation — swelling of the airway wall, relieved over days by corticosteroids.
3. Mucus plugging — thick secretions that block small airways, the main cause of death in fatal asthma.

Because airway resistance rises steeply as the radius falls (resistance is inversely proportional to the fourth power of the radius), even modest narrowing produces dramatic increases in the work of breathing. Air is trapped behind narrowed airways, the lungs hyperinflate, and the patient breathes at a high, inefficient lung volume — hence the sensation of "not being able to get air out." Wheeze is the sound of turbulent airflow through narrowed tubes; ominously, a silent chest in a distressed patient means airflow is now too low to make any sound at all — a sign of life-threatening asthma.

Triggers

Triggers do not cause asthma but provoke symptoms in an already-sensitised airway. Common ones include:

• Allergens: house dust mite, pollen, animal dander, mould.
• Viral respiratory infections: the commonest cause of exacerbations, especially rhinovirus.
• Exercise: particularly in cold, dry air (exercise-induced bronchoconstriction).
• Cold air and weather change.
• Irritants: tobacco smoke, air pollution, perfumes, cleaning chemicals.
• Occupational exposures: flour, isocyanates, wood dust — occupational asthma may resolve if exposure stops early.
• Drugs: aspirin/NSAIDs (in aspirin-exacerbated respiratory disease), and beta-blockers.
• Emotion, stress, and laughter; and gastro-oesophageal reflux.

Identifying and reducing a patient's specific triggers is a cheap and powerful part of management that is easy to neglect.

Diagnosis: Proving Variable Airflow Obstruction

Asthma is a clinical diagnosis supported by objective tests. The history is suggestive when symptoms are episodic, variable, worse at night/early morning, triggered by the exposures above, and reversible. But history alone over-diagnoses asthma, so guidelines insist on objective confirmation wherever possible.

Spirometry is the key first-line test. It measures FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity).

• An obstructive pattern is FEV1/FVC below the lower limit of normal (traditionally less than 0.7).
• Bronchodilator reversibility: give a short-acting beta-agonist (e.g. salbutamol) and repeat spirometry. An increase in FEV1 of 12% or more and at least 200 mL supports asthma. Reversibility is the hallmark that distinguishes asthma from fixed obstruction.

Because asthma is variable, spirometry can be normal when the patient is well — a normal test does not exclude asthma. Additional tools:

• Peak expiratory flow (PEF) monitoring: diurnal variability greater than about 10–20% over two weeks supports asthma.
• FeNO (fractional exhaled nitric oxide): a marker of eosinophilic airway inflammation; a raised level supports type 2 asthma and predicts steroid responsiveness.
• Bronchial challenge testing (e.g. methacholine): measures airway hyper-responsiveness when other tests are equivocal.

Worked example

A 22-year-old has a nocturnal cough and wheeze after playing football. Spirometry: FEV1 2.4 L, FVC 4.0 L, ratio 0.60 (obstructive). After salbutamol, FEV1 rises to 2.9 L — an increase of 500 mL and about 21%. This is significant reversibility, and combined with the history confirms asthma. Contrast with a 65-year-old smoker whose ratio is 0.55 and rises only 3% after salbutamol — that fixed obstruction points to COPD.

Management: Treat the Inflammation

Modern management follows a stepwise approach: start at the step appropriate to severity, then step up or down to find the lowest treatment that maintains control. The foundational principle is that inhaled corticosteroids (ICS) are the cornerstone — they treat the underlying inflammation. A landmark change in guidance (GINA, from 2019) was to abandon short-acting beta-agonist (SABA)-only treatment, because relying on relievers alone leaves inflammation untreated and is linked to exacerbations and death.

A typical stepwise ladder:

Step	Typical approach
Mild, intermittent	As-needed low-dose ICS-formoterol (combined anti-inflammatory reliever)
Persistent, mild	Low-dose maintenance ICS plus as-needed reliever
Moderate	Low-dose ICS plus a long-acting beta-agonist (LABA) — never LABA alone
Uncontrolled	Medium/high-dose ICS-LABA; consider adding LAMA (tiotropium) or a leukotriene receptor antagonist
Severe	Refer to specialist; consider biologics (anti-IgE omalizumab, anti-IL5 mepolizumab, anti-IL4/13 dupilumab) targeting specific pathways

Key drug classes:

• ICS (beclometasone, budesonide, fluticasone): reduce inflammation; benefit builds over days to weeks. Rinse mouth to prevent oral thrush and hoarseness.
• SABA (salbutamol): rapid relief of bronchospasm; increasing use signals poor control.
• LABA (formoterol, salmeterol): long-acting bronchodilation — only ever combined with ICS.
• LAMA (tiotropium): add-on bronchodilator in more severe disease.
• Leukotriene receptor antagonists (montelukast): oral, useful in allergic and exercise-induced asthma.
• Biologics: for severe eosinophilic or allergic asthma.

Inhaler technique and adherence are as important as the drug choice — most "uncontrolled" asthma is really poor technique, poor adherence, or an unaddressed trigger. Always check these before escalating.

Acute severe asthma

An exacerbation is an emergency. Assess severity by ability to speak, respiratory rate, heart rate, PEF (% of best/predicted), and oxygen saturation. Treatment: high-flow oxygen to target saturations 94–98%, repeated/nebulised salbutamol, ipratropium for severe attacks, and systemic corticosteroids (oral prednisolone or IV hydrocortisone) early. Consider IV magnesium sulphate in severe cases. Warning signs of life-threatening asthma: silent chest, exhaustion, cyanosis, a "normal" or rising CO2 (a fatigued patient can no longer hyperventilate), altered consciousness. These need critical care.

Real-World Applications

In everyday clinical practice, recognising asthma turns a frightened, breathless patient into a manageable chronic-disease case: a written personal asthma action plan telling patients what to do when symptoms worsen measurably reduces hospital admissions. In primary care, an annual review checking symptom control, inhaler technique, SABA overuse, and trigger exposure prevents most crises. For patients, understanding that the "brown/purple preventer" must be taken daily even when well — while the "blue reliever" is for symptoms — is genuinely life-changing knowledge. In occupational health, spotting work-related asthma early (symptoms better on holidays) can prevent permanent lung damage.

Common Mistakes

1. "My blue inhaler works, so I don't need the steroid one." Why it's wrong: the reliever masks worsening inflammation while doing nothing to treat it. Correction: the preventer ICS is the treatment; heavy reliever use is a red flag for poorly controlled, higher-risk asthma.

2. Diagnosing asthma from history alone and skipping spirometry. Why it's wrong: wheeze and cough have many causes, and both over- and under-diagnosis are common. Correction: confirm variable airflow obstruction objectively whenever possible before committing a patient to long-term therapy.

3. Assuming normal spirometry excludes asthma. Why it's wrong: asthma is variable and lung function can be normal between episodes. Correction: if suspicion is high, use PEF variability, FeNO, or bronchial challenge, and reassess when symptomatic.

4. Prescribing a LABA without an ICS. Why it's wrong: LABA monotherapy improves symptoms while leaving inflammation untreated and is associated with increased asthma deaths. Correction: always pair a LABA with an ICS, ideally in a single combination inhaler.

Comparison and Connections

The most common confusion is asthma versus COPD. Both cause airflow obstruction and wheeze, but the underlying disease, reversibility, and treatment differ.

Feature	Asthma	COPD
Typical onset	Childhood/young adult	Usually after 40, smokers
Main mechanism	Eosinophilic airway inflammation	Neutrophilic inflammation, alveolar destruction
Reversibility	Significant with bronchodilator	Largely fixed
Variability	Marked, day-to-day and diurnal	Slowly progressive
Response to ICS	Very good	Limited (used selectively)
Atopy/allergy link	Common	Not typical

Some patients have features of both — termed asthma-COPD overlap. Other wheeze mimics to keep in mind include heart failure ("cardiac asthma"), inducible laryngeal obstruction, bronchiectasis, and foreign body in children.

Practice Questions

Recall

Q: Name the three components that narrow the airway in an asthma attack. A: Smooth muscle contraction (bronchospasm), mucosal oedema/inflammation, and mucus plugging.

Understanding

Q: Why do inhaled corticosteroids not relieve an acute attack, yet remain the cornerstone of treatment? A: ICS act by suppressing airway inflammation, a process that takes days to weeks to reduce swelling and hyper-responsiveness. They do not directly relax airway smooth muscle, so they do not give immediate relief. But by treating the root cause, they reduce the frequency and severity of attacks and the underlying twitchiness of the airways — which is why they are foundational while a SABA handles acute symptoms.

Application

Q: A 30-year-old with suspected asthma has FEV1 of 2.0 L rising to 2.35 L after salbutamol (FVC 3.5 L). Does this support asthma? A: Baseline ratio is 2.0/3.5 = 0.57, obstructive. FEV1 rose by 350 mL and 17.5%, exceeding the 200 mL and 12% thresholds. This significant reversibility, with a compatible history, supports asthma.

Analysis

Q: A distressed asthmatic arrives with a silent chest and a blood gas showing a "normal" CO2. Why is this alarming rather than reassuring? A: A patient in a severe attack should be hyperventilating and blowing off CO2, giving a low CO2. A normal or rising CO2 means the patient is tiring and can no longer maintain the ventilation needed — a sign of impending respiratory failure and life-threatening asthma requiring critical care.

FAQ

Is asthma curable? No, but it is highly controllable. Most people with correctly treated asthma have no daily limitation. Childhood asthma sometimes remits in adolescence, though it can return later.

Can I exercise with asthma? Yes, and you should. Well-controlled asthma should not limit exercise; many elite athletes have asthma. If exercise triggers symptoms, using a reliever beforehand and optimising preventer therapy usually solves it.

Are steroid inhalers dangerous long-term? Inhaled steroids deliver tiny doses directly to the airways, so systemic side effects are much smaller than with oral steroids. Local effects (thrush, hoarse voice) are minimised by rinsing the mouth. The risks of untreated asthma far outweigh those of ICS.

Why does my asthma get worse at night? Natural circadian dips in cortisol and airway calibre, plus allergen exposure in bedding and reflux when lying flat, make airways narrower overnight. Nocturnal symptoms are an important marker of poor control.

What is the difference between a preventer and a reliever inhaler? The preventer (usually an ICS, taken daily) treats the underlying inflammation. The reliever (a bronchodilator, taken when symptomatic) opens the airways quickly. Increasing reliever use means the disease is not controlled and preventer therapy needs review.

Quick Revision

• Asthma = chronic airway inflammation causing hyper-responsiveness and reversible bronchoconstriction.
• Symptoms: wheeze, cough, chest tightness, breathlessness — variable, worse at night, trigger-provoked.
• Attack narrows airways three ways: bronchospasm, oedema, mucus.
• Diagnose with spirometry showing obstruction (FEV1/FVC reduced) with reversibility (FEV1 up 12% and 200 mL); support with PEF variability and FeNO.
• Normal spirometry does not exclude asthma.
• ICS is the cornerstone; never use LABA alone; SABA-only treatment is obsolete.
• Life-threatening signs: silent chest, exhaustion, normal/high CO2, cyanosis — give oxygen, nebulised salbutamol, systemic steroids urgently.

Related Topics

Prerequisites

• Pulmonology overview
• Respiratory physiology and lung volumes — see Physiology

Related Topics

• Chronic obstructive pulmonary disease (COPD) — contrast fixed vs reversible obstruction
• Immunology — type 2/IgE-mediated hypersensitivity underlying allergic asthma
• Pharmacology — corticosteroids and beta-agonists

Next Topics

• Acute severe asthma and status asthmaticus in Emergency Medicine
• Allergic rhinitis and the unified airway concept