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Cor Pulmonale

Definition

• RV enlargement from left-sided heart failure does NOT qualify
• RV enlargement from congenital heart disease does NOT qualify

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Types

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Causes / Etiology

• COPD (most common cause overall)
• Interstitial lung disease / pulmonary fibrosis
• Sleep-disordered breathing (OSA, obesity-hypoventilation)
• High altitude exposure

• Chronic thromboembolic pulmonary hypertension (CTEPH)

• Idiopathic PAH, connective tissue disease-related PAH
• Various miscellaneous causes

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Pathophysiology

1. Airway obstruction / lung fibrosis → loss of pulmonary vascular surface area + impaired gas exchange
2. Hypoxemia (±hypercapnia) → potent stimulus for hypoxic pulmonary vasoconstriction and vascular remodeling
3. Polycythemia from hypoxia-driven erythropoiesis → increased blood viscosity → higher pulmonary vascular resistance (PVR)
4. Endothelial dysfunction → further vasoconstriction and structural remodeling of pulmonary vessels
5. Elevated PVR → sustained increase in pulmonary artery pressure
6. RV pressure overload → RV hypertrophy (compensated)
7. With progressive disease: RV dilation, tricuspid regurgitation, RV failure

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Morphology (Pathology)

• Acute cor pulmonale: RV shows only dilation; if death is sudden (e.g., massive PE), the heart may appear near-normal in size
• Chronic cor pulmonale: RV (and often RA) hypertrophy; in severe cases, RV wall thickness may equal or exceed that of the LV; when failure develops, both RV and RA dilate; pulmonary arteries may show abnormal intimal thickening from chronic PH - Robbins & Kumar Basic Pathology, p. 363

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Clinical Features

• Dyspnea (often from underlying lung disease)
• Signs of right heart failure: peripheral edema, raised JVP, hepatomegaly, ascites
• Note: Peripheral edema correlates poorly with resting right atrial pressure - it may reflect activation of the renin-angiotensin-aldosterone system rather than RV failure alone
• Cyanosis (central, from hypoxemia)
• Parasternal heave, loud P2, RV S3 gallop, tricuspid regurgitation murmur

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Investigations

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Management

1. Supplemental oxygen (continuous) - the most evidence-based intervention; corrects hypoxic vasoconstriction and reduces erythropoiesis; in patients sensitive to O2, Venturi masks are preferred over nasal cannula
2. Diuretics - to optimize volume status and reduce RV preload
3. Treat the underlying condition - bronchodilators for COPD, antifibrotics for ILD, anticoagulation + pulmonary endarterectomy for CTEPH
4. Vasodilators (calcium channel blockers, PDE-5 inhibitors, prostacyclins): may dilate the pulmonary circulation, but calcium channel blockers can worsen hypoxemia, and their benefit in cor pulmonale from COPD is not well established
5. Noninvasive ventilation (NIV/CPAP) - for hypoventilation syndromes and OSA overlap
6. Phlebotomy for severe polycythemia (though recent data suggest polycythemia is less common and has uncertain outcome impact)

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Prognosis

• Once cor pulmonale develops, survival is significantly reduced
• If mPAP exceeds 25 mmHg, average 5-year survival is reduced by ~50%
• Prognosis is largely tied to the severity of the underlying lung disease and the degree of RV dysfunction

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• Robbins & Kumar Basic Pathology, p. 363 (Elsevier, 2023)
• Fuster and Hurst's The Heart, 15th Ed., Chapter 59, pp. 1773-1778
• Fishman's Pulmonary Diseases and Disorders, p. 734

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Investigations for COPD

1. Spirometry (Gold Standard / Mandatory)

• Post-bronchodilator FEV1/FVC < 0.70 confirms fixed (irreversible) airflow obstruction

Note: A 2025 GOLD Science Committee guideline (PMID 39638416) recommends post-bronchodilator spirometry as the standard for COPD diagnosis, reinforcing the established threshold.

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2. Lung Volume Measurements

• Plethysmography, helium dilution, nitrogen washout, or single-breath methods
• Show hyperinflation (elevated Total Lung Capacity, TLC) and air trapping (elevated Residual Volume, RV)
• Useful to exclude restrictive lung diseases, which show reduced TLC

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3. Diffusing Capacity (DLCO)

• Carbon monoxide diffusing capacity (DLCO) is reduced in emphysema
• Acts as an independent predictor of mortality in COPD
• Helps distinguish COPD from asthma (asthma typically has normal DLCO)

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4. Arterial Blood Gas (ABG)

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5. Chest Radiograph (CXR)

• Hyperinflation: flattened, low-lying diaphragm; barrel chest
• Increased anteroposterior diameter (lateral view)
• Widened retrosternal airspace (lateral view)
• Reduced peripheral vascular markings (oligemia)
• Bullae (avascular transradiant areas)
• Narrow transverse cardiac silhouette
• Irregular diaphragm contour (insertions visible on ribs)

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6. High-Resolution CT (HRCT) Chest

• Confirming and characterizing emphysema (type and extent)
• Phenotyping: distinguishing emphysema-predominant vs. airway-predominant disease
• Detecting bullae, air trapping, and bronchiectasis
• Early detection of emphysema before spirometric changes are apparent
• Guiding surgical decisions (bullectomy, lung volume reduction)

• Centrilobular (most common, upper lobe, smoking-related): small round low-attenuation areas around centrilobular arteries
• Panlobular (lower lobe, alpha-1 antitrypsin deficiency): diffuse destruction of entire acinus
• Paraseptal (near pleura/septa): associated with spontaneous pneumothorax
• Vessels in emphysematous areas appear straightened and splayed with decreased branching

Quantitative CT analysis is a validated research tool for early emphysema detection, but is not yet routine in clinical practice. - Fishman's Pulmonary Diseases & Disorders, p. 726

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7. Pulse Oximetry / Overnight Oximetry

• Screening tool for resting hypoxemia (SpO2 < 88% at rest = indication for LTOT)
• Overnight oximetry can detect nocturnal desaturation and screen for OSA-COPD overlap syndrome (though it cannot differentiate the relative contribution of each)

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8. Alpha-1 Antitrypsin (AAT) Level

• Should be measured when features suggest AAT deficiency (see below)
• Some experts recommend testing all patients with emphysema or fixed airflow obstruction, as treatments exist for severe deficiency

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9. ECG and Echocardiogram

• ECG: look for P pulmonale, right axis deviation, RV hypertrophy (cor pulmonale), atrial arrhythmias (common in COPD due to hypoxemia and RAE)
• Echocardiogram: assess RV function, estimate pulmonary artery pressure, rule out left heart disease as a contributor

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10. Full Blood Count (FBC)

• Polycythemia (raised Hct/Hb): secondary to chronic hypoxemia
• Anaemia: a poor prognostic marker in COPD; also worsens dyspnea
• Eosinophilia: may identify patients likely to respond to inhaled corticosteroids

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11. Sputum Analysis

• Routine culture during exacerbations to identify bacterial pathogens (H. influenzae, S. pneumoniae, M. catarrhalis, P. aeruginosa in severe disease)
• Sputum eosinophilia: identifies a treatable trait

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12. Exercise Testing / 6-Minute Walk Test (6MWT)

• 6MWT is simple and widely used; distance <350 m indicates poor prognosis
• Formal cardiopulmonary exercise testing (CPET): measures VO2 max, useful pre-operatively and in complex cases
• Exercise desaturation identifies patients who may need ambulatory O2

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13. Sleep Study (Polysomnography / HSAT)

• Indicated when OSA-COPD overlap syndrome is suspected
• PSG with CO2 monitoring preferred in moderate-severe COPD or when hypercapnia is anticipated
• HSAT may be used in mild COPD without hypoxemia - Murray & Nadel's Textbook of Respiratory Medicine

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Prognostic Markers (Additional Assessments)

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• Fishman's Pulmonary Diseases and Disorders, 2-Volume Set, pp. 726-727
• Goldman-Cecil Medicine International Edition, p. 890
• Grainger & Allison's Diagnostic Radiology, pp. 165-167
• Murray & Nadel's Textbook of Respiratory Medicine
• GOLD 2025 Science Committee - pre/post-bronchodilator spirometry guideline (PMID 39638416, Eur Respir J 2025)

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Lung Volumes and Capacities

Key Terminology

• Volume: a primary, non-overlapping compartment of air in the lung (4 volumes)
• Capacity: a combination of two or more volumes (4 capacities)

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The Four Primary Lung Volumes

Important: RV cannot be measured by spirometry alone, because no air flows out of the spirometer once it is reached. It requires special techniques (see below).

1. Prevents complete airway collapse - reinflating collapsed airways requires disproportionately high pressure
2. Maintains continuous gas exchange between episodic breaths; prevents wild swings in blood PO2

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The Four Lung Capacities

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Spirogram

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Memory Aid (Volumes from bottom to top)

TLC ──────────────────────  ← Maximal inspiration
      ↑ IRV (~3000 mL)
End of normal inspiration ──
      ↑ TV (~500 mL)
End of normal expiration ─── ← FRC level (= ERV + RV)
      ↑ ERV (~1200 mL)
      ↑ RV (~1200 mL)
0 ────────────────────────  ← Cannot reach this

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How to Measure RV, FRC, and TLC

1. Helium Dilution Method

• Subject breathes from a spirometer containing a known amount of He (insoluble in blood)
• He equilibrates between spirometer and lungs
• Using mass conservation: [He]initial × V_spirometer = [He]final × (V_spirometer + V_lung)
• Solves for V_lung = FRC (if measured after normal expiration)
• Limitation: underestimates FRC in COPD - He doesn't penetrate poorly ventilated (trapped) areas

2. Nitrogen Washout

• Subject breathes 100% O2; N2 is gradually washed out of lungs
• Total N2 exhaled is collected; since N2 starts at ~80% in alveolar gas, FRC can be calculated
• Same limitation as He dilution in obstructed lungs

3. Body Plethysmography (most accurate)

• Subject sits in an airtight box and attempts to breathe against a closed mouthpiece
• Applies Boyle's Law (P × V = constant)
• When the subject tries to inspire, chest expands, compressing the box gas, allowing calculation of lung volume
• Advantage: measures ALL gas in the lungs, including trapped air - gives the highest (most accurate) FRC in COPD - Costanzo Physiology, p. 197

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Changes in Lung Volumes in Disease

• In obstructive disease: air trapping raises RV and FRC; TLC may be elevated (hyperinflation); FEV1/FVC falls
• In restrictive disease: all volumes shrink proportionally; FEV1/FVC ratio is preserved or even elevated
• Plethysmography gives higher FRC than helium dilution in COPD, because it captures trapped air

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Factors Affecting Lung Volumes

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Additional Derived Values

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• Medical Physiology (Boron & Boulpaep), pp. 880-882
• Costanzo Physiology 7th Edition, pp. 196-197
• Fishman's Pulmonary Diseases & Disorders - Glossary Table 31-1
• Harriet Lane Handbook 23rd Ed., p. 839