Causes of breathlessness
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Causes of Breathlessness (Dyspnea)
Dyspnea is defined as a subjective sensation of difficulty breathing or an uncomfortable awareness of breathing. It arises when a mismatch develops between the central respiratory drive and the ventilation actually achieved, signaling that the body is under physiological stress. The causes span multiple organ systems.
Pathophysiological Mechanisms
Three overlapping sensations are recognized:
- Air hunger - driven by hypercapnia, hypoxia, or increased chemoreceptor drive
- Increased work/effort of breathing - from airway obstruction, chest wall stiffness, or muscle weakness
- Chest tightness - typically from bronchoconstriction
(Fishman's Pulmonary Diseases and Disorders)
A. Pulmonary Causes
1. Airway Disease
| Condition | Notes |
|---|---|
| Asthma | Episodic, reversible bronchoconstriction; "tightness in the chest" |
| COPD | Often underreported by patients who limit activity |
| Upper airway obstruction | Laryngeal edema, foreign body, epiglottitis, laryngeal stenosis |
| Suprathoracic airway narrowing | Tumors, stenosis of laryngotracheal complex |
2. Alveolar/Parenchymal Disease
| Condition | Notes |
|---|---|
| Pulmonary edema | From heart failure or ARDS |
| Pneumonia | Bacterial, viral, fungal |
| Pneumocystis jirovecii pneumonia | In immunocompromised patients |
| Pulmonary hemorrhage | Alveoli filling with blood |
3. Interstitial Lung Disease
- Organic exposures: hay, cotton, grain (hypersensitivity pneumonitis)
- Mineral exposures: asbestos (asbestosis), silica (silicosis), coal dust
- Idiopathic/inflammatory: sarcoidosis, scleroderma, SLE, granulomatosis with polyangiitis
- Malignancy infiltrating the interstitium
4. Pleural Disease
| Condition | Notes |
|---|---|
| Pneumothorax | Sudden-onset dyspnea; tension pneumothorax is life-threatening |
| Pleural effusion - transudative | Heart failure, cirrhosis, nephrotic syndrome |
| Pleural effusion - exudative | TB, cancer, parapneumonic, connective tissue disease, hemothorax |
| Malignant pleural effusion | Breathlessness often multifactorial |
5. Pulmonary Vascular Disease
| Condition | Notes |
|---|---|
| Pulmonary embolism (PE) | Acute; a "must not miss" diagnosis |
| Pulmonary arterial hypertension | Progressive; primary or secondary |
| Arteriovenous malformations | Rare; causes platypnea (dyspnea in upright position) |
B. Cardiac Causes
| Condition | Notes |
|---|---|
| Heart failure with reduced EF (HFrEF) | From CAD, hypertension, alcohol; "air hunger" quality |
| Heart failure with preserved EF (HFpEF) | From hypertension, aortic stenosis, HCM |
| Acute coronary syndrome / ischemia | May present with dyspnea as angina equivalent |
| Valvular heart disease | Aortic stenosis, aortic regurgitation, mitral stenosis, mitral regurgitation |
| Arrhythmias | Bradycardia (sick sinus syndrome, AV block), tachycardia (AF, SVT, VT) |
| Pericardial disease | Cardiac tamponade, constrictive pericarditis |
| Orthopnea / PND | Exacerbation in recumbent position; suggests left ventricular failure |
(Goldman-Cecil Medicine; Symptom to Diagnosis)
Paroxysmal nocturnal dyspnea (PND) - dyspnea that wakes the patient from sleep and forces them to sit upright - classically denotes left ventricular failure. (Murray & Nadel's)
C. Chest Wall & Neuromuscular Causes
| Condition | Notes |
|---|---|
| Kyphoscoliosis | Restricts chest wall expansion |
| Obesity | Increased work of breathing; reduced lung volumes |
| Respiratory muscle weakness | Myopathy, Guillain-Barre syndrome, motor neuron disease |
| Bilateral diaphragm paralysis | Cannot assume supine position (instant orthopnea) |
D. Hematological Causes
| Condition | Notes |
|---|---|
| Anemia | Reduced O2-carrying capacity; drives compensatory increase in respiratory rate |
E. Metabolic Causes
| Condition | Notes |
|---|---|
| Metabolic acidosis | e.g., diabetic ketoacidosis - stimulates chemoreceptors causing Kussmaul breathing |
| Hyperthyroidism | Increased metabolic demand; increased respiratory drive |
| Deconditioning | "Heavy breathing, feeling of rapid breathing" |
| Salicylate overdose | Direct stimulation of respiratory centers |
F. Psychogenic / Functional Causes
- Anxiety and panic disorder - hyperventilation syndrome
- Functional dyspnea - after ruling out organic causes
Life-Threatening Causes - Act Immediately
The mnemonic CATASPN covers the acutely dangerous diagnoses requiring urgent management:
| Mnemonic | Condition |
|---|---|
| C | Coronary syndrome (acute) |
| A | Arrhythmia |
| T | Tamponade (cardiac) |
| A | Airway obstruction |
| S | Stenosis (aortic) |
| P | Pneumothorax |
| N | Anaphylaxis |
(Symptom to Diagnosis, 4th Ed.)
The Four Most Common Causes Overall
- Heart failure
- Pneumonia
- Obstructive lung disease (COPD / asthma)
- Pulmonary embolism
(Symptom to Diagnosis, 4th Ed.)
Clinical Approach
Multiple causes frequently coexist in a single patient. A patient with COPD, for example, is at increased risk for pneumonia, pneumothorax, PE, and lung cancer - so a new or worsening dyspnea in a known COPD patient should trigger evaluation for complications, not merely be attributed to disease progression.
Initial workup for most patients with new or worsening dyspnea should include:
- Chest X-ray
- ECG
- Hematocrit / CBC
- Pulse oximetry, BNP/NT-proBNP (if HF suspected), D-dimer or CT-PA (if PE suspected)
(Symptom to Diagnosis, 4th Ed.; Goldman-Cecil Medicine)
Sources: Symptom to Diagnosis (4th Ed.) | Goldman-Cecil Medicine | Murray & Nadel's Textbook of Respiratory Medicine | Fishman's Pulmonary Diseases and Disorders | Frameworks for Internal Medicine
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