Shortness of Breath (Dyspnea)

What Is Dyspnea?

Major Causes of Dyspnea

Disease-by-Disease Breakdown

1. 🫁 Asthma

Pathophysiology

• Inhaled allergens trigger IgE-mediated mast cell degranulation → release of histamine, leukotrienes (C, D, E), bradykinin, prostaglandins, and eosinophil chemotactic factors
• Parasympathetic overactivity contributes: vagal afferents in bronchi are sensitive to cold air, irritants, and histamine → reflex bronchoconstriction via ↑ intracellular cGMP
• Bronchoconstriction + mucosal edema → ↑ airway resistance at all levels → air trapping → ↑ TLC, RV, FRC
• V/Q mismatch → hypoxemia; tachypnea → hypocapnia initially
• In severe attacks: normal or ↑ PaCO₂ = impending respiratory failure

Symptoms

• Episodic wheezing, cough (especially nocturnal), chest tightness
• Shortness of breath with exertion or allergen exposure
• Symptoms reversible (spontaneously or with treatment)

Diagnosis

• Spirometry: ↓ FEV₁/FVC ratio; reversibility with bronchodilator (≥12% improvement)
• Peak expiratory flow (PEF): variability >20%
• Methacholine challenge for borderline cases
• CXR: hyperinflation during acute attack

Treatment

2. 🌬️ COPD (Chronic Obstructive Pulmonary Disease)

Pathophysiology

• Cigarette smoke → chronic airway inflammation → neutrophil/macrophage infiltration → protease-antiprotease imbalance → alveolar destruction (emphysema)
• Loss of elastic recoil → dynamic airway collapse on expiration → air trapping
• Mucus hypersecretion (chronic bronchitis) → ↑ airway resistance
• Pulmonary hypertension can develop due to hypoxic vasoconstriction → right heart failure (cor pulmonale)

Symptoms

• Chronic progressive dyspnea (cardinal symptom)
• Chronic productive cough, sputum
• Wheezing; barrel chest in advanced disease
• Exercise intolerance, cyanosis, weight loss

Diagnosis

• Spirometry (post-bronchodilator): FEV₁/FVC < 0.70 (obstructive pattern, not fully reversible)
• GOLD classification (Grade I–IV) by FEV₁ % predicted
• CXR: hyperinflation, flattened diaphragm, increased AP diameter
• CT chest: emphysematous bullae
• ABG: hypoxemia ± hypercapnia

Treatment

3. 🦠 Pneumonia

Pathophysiology

• Microorganisms (bacteria, viruses, fungi) reach the alveoli via aspiration, inhalation, or hematogenous spread
• Inflammatory exudate fills alveoli → consolidation → ↓ alveolar ventilation → V/Q mismatch → hypoxemia
• Cytokine release → systemic effects (fever, sepsis)

Symptoms

• Dyspnea, cough (productive with purulent sputum), fever, chills
• Pleuritic chest pain (if pleura involved)
• Tachypnea, tachycardia; crackles/bronchial breath sounds on auscultation
• Confusion in the elderly (atypical presentation)

Diagnosis

• CXR or CT chest: lobar/segmental consolidation (key finding)
• Sputum culture & Gram stain
• Blood cultures (if severe)
• CBC: leukocytosis
• Urine antigen: Legionella, Streptococcus pneumoniae
• Severity: CURB-65 score (Confusion, Urea, Respiratory rate, BP, Age ≥65)

Treatment

4. ❤️ Heart Failure (Cardiac Dyspnea)

Pathophysiology

• Left ventricular failure → ↑ pulmonary venous pressure → pulmonary edema → stiff, fluid-filled lungs → ↑ work of breathing
• Key forms of dyspnea:
  • Exertional dyspnea (earliest symptom)
  • Orthopnea: dyspnea when supine → ↑ venous return → ↑ pulmonary congestion
  • Paroxysmal nocturnal dyspnea (PND): awakens patient from sleep, relieved by sitting upright
• In acute heart failure: pulmonary edema → crackles, frothy sputum, severe hypoxemia

Symptoms

• Progressive exertional dyspnea → dyspnea at rest
• Orthopnea, PND, leg edema, fatigue
• "Air hunger" sensation (typical descriptor)
• Wheezing ("cardiac asthma") in pulmonary edema

Diagnosis

• BNP/NT-proBNP: elevated (best initial test for cardiac dyspnea)
• CXR: cardiomegaly, pulmonary vascular congestion, Kerley B lines, pleural effusions
• Echocardiography: ↓ EF (systolic HF) or ↓ diastolic function
• ECG: LVH, arrhythmias, ischemia

Treatment

5. 🩸 Pulmonary Embolism (PE)

Pathophysiology

• DVT (most often femoral/popliteal) → embolus lodges in pulmonary arteries → ↑ pulmonary vascular resistance → right ventricular pressure overload
• Dead-space ventilation ↑ (perfusion lost, ventilation maintained)
• Hypoxemia from V/Q mismatch + right heart failure → ↓ cardiac output
• Massive PE → hemodynamic collapse, syncope, death

Symptoms

• Sudden onset dyspnea (most common)
• Pleuritic chest pain, hemoptysis (infarction)
• Tachycardia, tachypnea, hypoxia
• Syncope, hypotension (massive PE)
• Signs of DVT: unilateral leg swelling, erythema, tenderness

Diagnosis

• D-dimer (high sensitivity; normal D-dimer + low pre-test probability = PE excluded)
• CT Pulmonary Angiography (CTPA): gold standard imaging
• V/Q scan: when CT is contraindicated
• Wells score / Geneva score: pre-test probability assessment
• ECG: sinus tachycardia; S1Q3T3 pattern (classic but not sensitive)
• ABG: hypoxemia, hypocapnia, ↑ A-a gradient

Treatment

6. 😰 Other Important Causes

Diagnostic Approach to Dyspnea

Dyspnea
│
├── ACUTE onset
│    ├── Chest pain? → ACS, PE, pneumothorax, aortic dissection
│    ├── Fever + cough? → Pneumonia
│    ├── Wheezing? → Asthma/COPD exacerbation
│    └── Orthopnea/edema? → Acute heart failure / pulmonary edema
│
└── CHRONIC/PROGRESSIVE
     ├── BNP elevated → Heart failure
     ├── FEV₁/FVC <0.7 → COPD/Asthma
     ├── Low Hgb → Anemia
     └── CXR + CTPA → PE, ILD, malignancy

• Pulse oximetry (SpO₂): quick hypoxia screen
• CXR
• ECG
• ABG: assess oxygenation, ventilation, acid-base
• CBC, BNP, D-dimer, troponin
• Spirometry / PFTs
• Echocardiography (if cardiac cause suspected)
• CT chest / CTPA (as indicated)

Summary Table