Medicine – Causes of Breathlessness

Breathlessness, or dyspnoea, is the subjective sensation of uncomfortable or difficult breathing. It is a very common clinical symptom and may result from disorders of the respiratory system, cardiovascular system, or other systemic and functional conditions.

When assessing breathlessness, it is important to determine whether the onset is acute or chronic, whether symptoms occur at rest or on exertion, and whether associated features such as chest pain, cough, wheeze, fever, orthopnoea, haemoptysis, or palpitations are present.

1. Respiratory Causes

Respiratory disease is one of the major causes of breathlessness. Dyspnoea can result from airway obstruction, impaired gas exchange, reduced lung expansion, pulmonary vascular disease, pleural disease, or respiratory muscle dysfunction.

Asthma

Asthma causes episodic breathlessness because reversible bronchoconstriction and airway inflammation narrow the conducting airways.

Patients typically experience wheeze, cough, chest tightness, and variable breathlessness. Symptoms may be triggered by allergens, exercise, respiratory infections, smoke, or certain medications.

Chronic Obstructive Pulmonary Disease

COPD produces gradually progressive breathlessness because of persistent airflow obstruction.

Patients commonly have a history of significant smoking or other inhalational exposure and may experience chronic productive cough, wheeze, exertional dyspnoea, and recurrent exacerbations.

Emphysema additionally causes loss of alveolar surface area, hyperinflation, and impaired gas exchange.

Pneumonia

Pneumonia can cause acute breathlessness because infection produces inflammation and filling of the alveoli with inflammatory exudate.

This interferes with ventilation and gas exchange, producing V/Q mismatch and hypoxaemia.

Associated features commonly include fever, cough, sputum production, pleuritic chest pain, and systemic illness.

Pneumothorax

A pneumothorax occurs when air enters the pleural space and causes partial or complete collapse of the affected lung.

It classically presents with sudden-onset breathlessness and unilateral pleuritic chest pain.

A tension pneumothorax can cause severe respiratory and haemodynamic compromise and requires immediate treatment.

Pulmonary Embolism

Pulmonary embolism (PE) occurs when a thrombus, usually originating from the deep veins of the lower limbs or pelvis, travels to the pulmonary circulation.

It can produce sudden unexplained breathlessness, pleuritic chest pain, tachycardia, hypoxaemia, haemoptysis, or syncope.

Massive PE may cause acute right-heart strain and cardiovascular collapse.

Bronchiectasis

Bronchiectasis is characterised by permanent abnormal dilatation of the bronchi associated with impaired mucus clearance and recurrent infection.

Patients typically experience chronic productive cough, large amounts of purulent sputum, recurrent chest infections, haemoptysis, and varying degrees of breathlessness.

Pulmonary Fibrosis

Pulmonary fibrosis causes progressive scarring and stiffening of the lungs.

Reduced lung compliance increases the work required to breathe, while abnormalities of the alveolar–capillary interface impair oxygen transfer.

The typical presentation is progressive exertional breathlessness, persistent dry cough, and fine bibasal inspiratory crackles.

Lung Cancer

Lung cancer can cause breathlessness through several different mechanisms.

The tumour may obstruct a major bronchus, cause collapse of part of the lung, produce a pleural or pericardial effusion, cause lymphangitic spread, or coexist with underlying COPD.

Other concerning features include persistent cough, haemoptysis, chest pain, unexplained weight loss, and recurrent pneumonia.

Pleural Effusion

A pleural effusion is an abnormal accumulation of fluid within the pleural space.

A sufficiently large effusion compresses the underlying lung and restricts its expansion, producing breathlessness.

Examination may demonstrate reduced breath sounds, reduced chest expansion, and stony dullness to percussion over the affected area.

Pulmonary Hypertension

Pulmonary hypertension causes progressive exertional breathlessness because increased pulmonary vascular resistance impairs the ability of the right ventricle to increase pulmonary blood flow during exercise.

Patients may eventually develop fatigue, exertional chest discomfort, syncope, raised JVP, peripheral oedema, and right-sided heart failure.

Phrenic Nerve Palsy

The phrenic nerve supplies the diaphragm.

Phrenic nerve injury can therefore cause diaphragmatic weakness or paralysis. Unilateral paralysis may cause relatively mild symptoms, whereas bilateral involvement can cause substantial breathlessness and ventilatory impairment.

An elevated hemidiaphragm may be visible on chest imaging in unilateral disease.

2. Cardiac Causes

Cardiovascular disease is another major cause of breathlessness.

Dyspnoea can result from reduced cardiac output, elevated left-sided filling pressures, pulmonary venous congestion, pulmonary oedema, arrhythmias, or impaired ventricular filling.

Angina and Myocardial Ischaemia

Myocardial ischaemia usually causes chest discomfort, but some patients—particularly older adults and people with diabetes—may present predominantly with exertional breathlessness.

Dyspnoea can therefore occasionally represent an anginal equivalent.

Left Ventricular Failure

Left ventricular failure is an important cardiac cause of breathlessness.

Failure of the left ventricle increases left atrial and pulmonary venous pressures, causing pulmonary congestion and potentially pulmonary oedema.

Patients may develop exertional dyspnoea, orthopnoea, paroxysmal nocturnal dyspnoea, bibasal crackles, and reduced exercise tolerance.

Valvular Heart Disease

Significant valvular heart disease can cause breathlessness by reducing effective cardiac output or increasing pressures within the pulmonary circulation.

Important examples include aortic stenosis, aortic regurgitation, mitral stenosis, and mitral regurgitation.

The image appears to state “atrial stenosis” and “atrial regurgitation”; this should be corrected to aortic stenosis and aortic regurgitation.

Aortic Stenosis

Aortic stenosis obstructs blood flow from the left ventricle into the aorta.

Advanced disease may produce the classic combination of exertional breathlessness, angina, and syncope.

Aortic Regurgitation

Aortic regurgitation causes blood to flow backwards from the aorta into the left ventricle during diastole.

Chronic severe regurgitation eventually causes left ventricular dilatation and failure, producing exertional breathlessness and symptoms of heart failure.

Mitral Stenosis

Mitral stenosis obstructs blood flow from the left atrium into the left ventricle.

The resulting elevation of left atrial and pulmonary venous pressures produces exertional breathlessness, orthopnoea, and sometimes pulmonary oedema or haemoptysis.

Mitral Regurgitation

Mitral regurgitation allows blood to flow backwards from the left ventricle into the left atrium during systole.

Severe disease increases left atrial and pulmonary venous pressures and can eventually cause pulmonary congestion and breathlessness.

Arrhythmias

Both rapid and slow cardiac arrhythmias can cause breathlessness by reducing effective cardiac output.

Patients may also report palpitations, dizziness, chest discomfort, presyncope, or syncope.

Examples include atrial fibrillation, supraventricular tachycardia, ventricular arrhythmias, and severe bradyarrhythmias.

Pericardial Effusion

A pericardial effusion is an accumulation of fluid within the pericardial sac.

Large or rapidly developing effusions may interfere with cardiac filling and cause breathlessness.

If intrapericardial pressure becomes sufficiently high, cardiac tamponade can develop, producing hypotension, raised JVP, tachycardia, and circulatory compromise.

Cardiomyopathy

Cardiomyopathy can impair ventricular contraction, relaxation, or filling.

Reduced cardiac output and increased intracardiac pressures can cause exercise intolerance, fatigue, pulmonary congestion, and progressive breathlessness.

Depending on the underlying condition, cardiomyopathy may be dilated, hypertrophic, restrictive, or another recognised subtype.

3. Other Causes of Breathlessness

Not all breathlessness originates directly from the lungs or heart. Several systemic, mechanical, and functional disorders can produce a sensation of dyspnoea.

Psychogenic and Functional Breathlessness

Anxiety, panic attacks, and dysfunctional breathing patterns can produce significant breathlessness even when cardiopulmonary investigations are normal.

Hyperventilation may be accompanied by light-headedness, tingling around the mouth or fingers, chest tightness, and a sensation of being unable to obtain a satisfying breath.

However, breathlessness should not be attributed to anxiety until important organic causes have been appropriately considered.

Massive Ascites

Massive ascites increases intra-abdominal pressure and pushes the diaphragm upward.

This restricts diaphragmatic movement, reduces lung volumes, and can cause significant breathlessness, particularly when lying flat.

Treating the underlying cause and reducing severe ascites can improve respiratory symptoms.

4. Additional Important Causes

A broader differential diagnosis should also include several common systemic causes that were not shown in the original image.

Anaemia

Anaemia reduces the oxygen-carrying capacity of blood.

Patients may therefore develop exertional breathlessness, fatigue, palpitations, dizziness, and tachycardia, despite having structurally normal lungs.

Obesity and Deconditioning

Severe obesity increases the mechanical work of breathing and may restrict diaphragmatic movement.

Physical deconditioning can also produce disproportionate breathlessness during relatively minor exertion.

Metabolic Acidosis

Conditions causing severe metabolic acidosis, such as diabetic ketoacidosis, stimulate respiratory compensation.

Patients may develop rapid, deep breathing known as Kussmaul respiration, which may be perceived as breathlessness.

5. Causes of Breathlessness – Note Form

Respiratory Causes

Asthma: variable airflow obstruction with wheeze, cough, chest tightness, and episodic breathlessness.

COPD: persistent airflow obstruction causing progressive exertional dyspnoea, cough, sputum, and wheeze.

Pneumonia: alveolar infection and inflammation causing impaired gas exchange and acute breathlessness.

Pneumothorax: sudden breathlessness with pleuritic chest pain due to air within the pleural space.

Pulmonary embolism: often sudden unexplained dyspnoea ± pleuritic pain, tachycardia, haemoptysis, or syncope.

Bronchiectasis: chronic productive cough, recurrent infections, haemoptysis, and breathlessness.

Pulmonary fibrosis: progressive exertional dyspnoea with dry cough and fine inspiratory crackles.

Lung cancer: may cause dyspnoea through airway obstruction, lung collapse, effusion, or extensive pulmonary involvement.

Pleural effusion: pleural fluid compresses the lung and restricts expansion.

Pulmonary hypertension: progressive exertional dyspnoea due to increased pulmonary vascular resistance.

Phrenic nerve palsy: diaphragmatic weakness or paralysis causes impaired ventilation.

Cardiac Causes

Myocardial ischaemia/angina: exertional breathlessness may occasionally be an anginal equivalent.

Left ventricular failure: pulmonary venous congestion produces exertional dyspnoea, orthopnoea, and paroxysmal nocturnal dyspnoea.

Aortic stenosis: exertional dyspnoea, angina, and syncope in advanced disease.

Aortic regurgitation: chronic volume overload eventually causes left ventricular failure and dyspnoea.

Mitral stenosis: raised left atrial pressure produces pulmonary venous congestion and breathlessness.

Mitral regurgitation: severe regurgitation can cause pulmonary congestion and heart failure.

Arrhythmias: impaired cardiac output can cause breathlessness, palpitations, and dizziness.

Pericardial effusion: impaired ventricular filling can cause breathlessness and, when severe, cardiac tamponade.

Cardiomyopathy: impaired cardiac function produces reduced exercise tolerance and dyspnoea.

Other Causes

Psychogenic/functional: anxiety, panic attacks, and dysfunctional breathing may cause breathlessness and hyperventilation.

Massive ascites: upward displacement of the diaphragm restricts lung expansion.

Anaemia: reduced oxygen-carrying capacity causes exertional dyspnoea.

Obesity: increased respiratory workload and reduced lung volumes can cause breathlessness.

Deconditioning: reduced cardiovascular and muscular fitness causes early exertional dyspnoea.

Metabolic acidosis: compensatory hyperventilation can present as rapid, deep breathing.

Key Clinical Pattern

A useful way to approach breathlessness is to divide the differential into three major groups:

Respiratory → asthma, COPD, pneumonia, pneumothorax, PE, bronchiectasis, pulmonary fibrosis, lung cancer, pleural effusion, pulmonary hypertension, and diaphragmatic dysfunction.

Cardiac → myocardial ischaemia, left ventricular failure, valvular heart disease, arrhythmias, pericardial effusion, and cardiomyopathy.

Other → anxiety or dysfunctional breathing, massive ascites, anaemia, obesity, deconditioning, and metabolic disorders.

The time course is particularly useful diagnostically. Sudden breathlessness should raise concern for conditions such as PE, pneumothorax, acute pulmonary oedema, acute severe asthma, or an acute cardiac event, whereas gradually progressive breathlessness is more typical of conditions such as COPD, pulmonary fibrosis, chronic heart failure, pulmonary hypertension, anaemia, or malignancy.