Shortness of Breath (Dyspnoea): Causes and When to Go to A&E

What Is Shortness of Breath (Dyspnoea)?

Hello, I am Dr. Emre Gecer. Shortness of breath — known medically as dyspnoea — is the subjective experience of breathing becoming difficult, insufficient or uncomfortable. Unlike the normal increase in respiration that everyone feels during exercise, dyspnoea is pathological breathlessness that appears unexpectedly or with unexpected severity.

From a respiratory-physiology standpoint, dyspnoea arises from the interaction of several mechanisms:

• Chemoreceptors: Low blood oxygen (hypoxaemia) and high carbon dioxide (hypercapnia) stimulate chemoreceptors in the medulla and carotid bodies
• Mechanoreceptors: Receptors in the lung parenchyma, chest wall and respiratory muscles sense mechanical loading
• Neural signal mismatch: Discrepancy between the breathing effort expected by the cerebral cortex and the actual breathing produces the sensation of dyspnoea (neuro-ventilatory dissociation)
• Afferent input: Vagal afferents, juxtapulmonary (J) receptors and pulmonary C-fibre receptors are stimulated in interstitial oedema and pulmonary congestion

Acute versus Chronic Dyspnoea

Dyspnoea is classified by speed of onset as acute (minutes to hours) or chronic (weeks to months). This distinction is crucial for narrowing the differential diagnosis and judging urgency.

Causes of Acute Dyspnoea

Sudden-onset shortness of breath usually requires urgent medical attention:

• Pulmonary embolism (PE): A clot from deep vein thrombosis blocking the pulmonary arteries — sudden dyspnoea, pleuritic chest pain, tachycardia and sometimes haemoptysis. Risk factors include immobilisation, surgery, cancer, oral contraceptives and long-haul travel. Untreated mortality can reach 30%.
• Pneumothorax: Air collected in the pleural space — sudden dyspnoea and unilateral chest pain. Spontaneous pneumothorax is common in tall, slim young men. Tension pneumothorax is a life-threatening emergency — mediastinal shift, hypotension and shock develop.
• Acute heart failure (acute pulmonary oedema): Fluid accumulation in the lungs from left ventricular failure — orthopnoea, paroxysmal nocturnal dyspnoea, pink frothy sputum. An elevated BNP is important diagnostically.
• Myocardial infarction (heart attack): Chest pain radiating to the jaw and arm, sweating with dyspnoea. In women and the elderly, it may present with dyspnoea alone, without chest pain.
• Cardiac tamponade: Pericardial fluid compressing the heart — Beck's triad: hypotension, jugular venous distension and muffled heart sounds
• Acute asthma attack: Bronchospasm, mucus plugs and airway inflammation — wheezing, cough and dyspnoea
• COPD exacerbation: Acute worsening of existing COPD triggered by infection or air pollution
• Pneumonia: Fever, sputum, chest pain and dyspnoea — gas exchange is impaired in areas of consolidation
• Anaphylaxis: Severe allergic reaction — laryngeal oedema, bronchospasm, hypotension and widespread urticaria together with sudden dyspnoea
• Foreign-body aspiration: Especially in children — sudden-onset cough, stridor and dyspnoea

Causes of Chronic Dyspnoea

Dyspnoea that builds gradually over weeks to months:

• Chronic heart failure: Exertional dyspnoea, orthopnoea (worse when lying down) and lower-limb oedema — due to left ventricular systolic or diastolic dysfunction
• COPD (Chronic Obstructive Pulmonary Disease): The most common cause of chronic dyspnoea in smokers — progressive airflow limitation, emphysema and chronic bronchitis
• Asthma: Recurrent attacks of dyspnoea, wheezing and cough — triggered by allergens, exercise or cold air
• Interstitial lung diseases: Idiopathic pulmonary fibrosis foremost — progressive dyspnoea, dry cough and finger clubbing
• Pleural effusion: Fluid in the pleural space — dyspnoea, chest pain and reduced breath sounds on the affected side
• Pulmonary hypertension: Raised pulmonary artery pressure — exertional dyspnoea, syncope and signs of right heart failure

Non-Cardiac and Non-Pulmonary Causes of Dyspnoea

Dyspnoea does not always originate in the heart or the lungs:

• Anaemia: A low haemoglobin reduces oxygen-carrying capacity — exertional dyspnoea, palpitations and fatigue. With haemoglobin below 7 g/dL, dyspnoea at rest can appear.
• Anxiety and panic attacks: Hyperventilation, chest tightness, numbness and tingling — should be considered after organic causes have been excluded. Anxiety is a diagnosis of exclusion; do not reach it before ruling out organic disease.
• Metabolic acidosis: Diabetic ketoacidosis, lactic acidosis, kidney failure — compensated by Kussmaul breathing (deep and rapid)
• Neuromuscular disorders: Guillain–Barré syndrome, myasthenia gravis, ALS — weakness of the respiratory muscles
• Obesity: Restricted diaphragmatic movement and increased work of breathing — obesity hypoventilation syndrome
• Thyrotoxicosis: Increased metabolic rate raises oxygen consumption and cardiac output
• Pregnancy: Progesterone stimulates the respiratory centre and the growing uterus pushes on the diaphragm — physiological dyspnoea, but pathological causes such as PE and peripartum cardiomyopathy must also be excluded

The mMRC Dyspnoea Scale

The modified Medical Research Council (mMRC) scale is widely used to grade the severity of chronic dyspnoea:

• Grade 0: Breathless only with strenuous exercise
• Grade 1: Breathless when hurrying on level ground or walking up a slight hill
• Grade 2: Walks slower than people of the same age on level ground because of breathlessness, or has to stop for breath when walking at own pace
• Grade 3: Stops for breath after walking about 100 metres or after a few minutes on level ground
• Grade 4: Too breathless to leave the house, or breathless when dressing

An mMRC score of 2 or higher in COPD calls for consideration of more advanced treatment strategies (pulmonary rehabilitation, combination therapy).

Diagnostic Approach: Systematic Assessment

The work-up of dyspnoea integrates history, physical examination and targeted investigations:

Initial Assessment

• Pulse oximetry (SpO2): The first and quickest assessment — below 95% is abnormal; below 90% indicates severe hypoxaemia. A normal SpO2 does not rule out dyspnoea, however; it can be normal in anaemia, metabolic acidosis and anxiety.
• Arterial blood gas (ABG): pH, PaO2, PaCO2 and bicarbonate — reveals hypoxaemia, hypercapnia and acid-base disturbances. The gold standard for distinguishing type 1 (hypoxaemic) from type 2 (hypercapnic) respiratory failure.

Imaging

• Chest X-ray (PA film): First-line imaging — shows pneumonia, pleural effusion, pneumothorax, pulmonary oedema, cardiomegaly and mediastinal pathology
• CT pulmonary angiography: Gold standard when pulmonary embolism is suspected — clots in the pulmonary arteries are directly visualised with contrast
• High-resolution CT (HRCT): For assessing interstitial lung disease
• Echocardiography: Evaluates cardiac structure and function, ejection fraction, valve disease and pericardial effusion

Laboratory Tests

• BNP / NT-proBNP: A biochemical marker of heart failure. BNP < 100 pg/mL makes heart failure unlikely; BNP > 400 pg/mL makes it highly likely. Very valuable for distinguishing cardiac from pulmonary causes of dyspnoea.
• D-dimer: Has a high negative predictive value — a normal D-dimer largely rules out low- to intermediate-probability PE. However, infection, inflammation, pregnancy and cancer can give false positives.
• Full blood count: Anaemia assessment
• Troponin: When acute coronary syndrome is suspected
• Thyroid function tests: Thyrotoxicosis or hypothyroidism

Functional Tests

• Spirometry and pulmonary function tests: Distinguish obstructive (asthma, COPD) from restrictive (interstitial disease) patterns
• 6-minute walk test: Assesses functional capacity and exercise-induced desaturation
• Cardiopulmonary exercise testing (CPET): Gold standard for distinguishing cardiac from pulmonary causes in unexplained dyspnoea

Emergency Signs: When Should You Call 112?

Call emergency services immediately in any of the following situations:

• Severe dyspnoea even at rest: Unable to speak in full sentences
• Blue discoloration of lips and fingers (cyanosis): A sign of severe hypoxaemia
• Chest pain together with dyspnoea: Acute coronary syndrome or pulmonary embolism
• Confusion or altered consciousness: Inadequate oxygen reaching the brain
• Sudden-onset severe dyspnoea: Pneumothorax, PE, anaphylaxis
• Stridor (inspiratory wheeze): Upper-airway obstruction — foreign body, angio-oedema
• Severe tachycardia (>120/min) or hypotension: Haemodynamic instability
• Use of accessory respiratory muscles: Neck-muscle contraction and intercostal recession — signs of severe respiratory distress

Home Management of Chronic Dyspnoea

For patients living with chronic lung or heart disease, the following strategies can be used at home:

• Pursed-lip breathing: Breathe in slowly through the nose and out slowly through pursed lips for twice as long as you inhaled. This raises expiratory pressure, prevents the small airways from closing early and reduces air trapping.
• Diaphragmatic breathing: Place one hand on your chest and the other on your abdomen; let your abdomen rise as you inhale and fall as you exhale
• Positioning: Leaning forward in a tripod position can ease dyspnoea — it optimises diaphragmatic mechanics
• Pulmonary rehabilitation: Structured exercise programmes have proven efficacy in COPD and interstitial lung disease
• Oxygen therapy: In chronic hypoxaemia (PaO2 < 55 mmHg or SpO2 < 88%), long-term oxygen therapy improves survival
• Smoking cessation: The single most effective intervention for slowing COPD progression
• Avoid triggers: Allergens, air pollution, very cold or very hot air

Conclusion

Shortness of breath can be the shared symptom of a wide spectrum of conditions, from a simple anxiety reaction to life-threatening pulmonary embolism. Acute-onset dyspnoea should always be taken seriously and assessed urgently. For chronic dyspnoea, a systematic diagnostic approach and treatment of the underlying disease are the cornerstones of management. If breathlessness is accompanied by blue lips, inability to speak, chest pain or altered consciousness, do not hesitate to call 112 — early intervention saves lives.

Wishing you good health.
Dr. Emre Gecer

References

• Murray & Nadel's Textbook of Respiratory Medicine, 7th Edition — Chapter: Dyspnea
• Harrison's Principles of Internal Medicine, 22nd Edition — Chapter: Dyspnea
• Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 12th Edition — Chapter: Heart Failure