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Emphysema - Comprehensive MBBS Notes

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1. Definition

The key word is permanent - this distinguishes it from physiological overinflation. The absence of fibrosis distinguishes it from other parenchymal lung diseases.

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2. Types / Classification

A. Centriacinar (Centrilobular) Emphysema - MOST COMMON

• Central / proximal parts of the acinus (respiratory bronchioles) are involved; distal alveoli are spared
• Both emphysematous and normal air spaces coexist in the same acinus and lobule
• More common and severe in the upper lobes, especially apical segments
• Constitutes >95% of clinically significant cases
• Strongly associated with cigarette smoking and often coexists with chronic bronchitis
• In advanced cases, distal acinus also involved (hard to distinguish from panacinar)

B. Panacinar (Panlobular) Emphysema

• The entire acinus is uniformly enlarged - from respiratory bronchioles all the way to terminal blind alveoli
• More common in lower lung zones and anterior margins; worst at the bases
• Associated with α1-antitrypsin deficiency (exacerbated by smoking)
• Produces pale, voluminous lungs that can obscure the heart at autopsy

C. Distal Acinar (Paraseptal) Emphysema

• Proximal acinus is normal, distal part is primarily involved
• Found near the pleura, along lobular connective tissue septa, and adjacent to areas of fibrosis/scarring
• Usually more severe in the upper half of lungs
• Multiple enlarged air spaces (0.5 mm to >2 cm), sometimes forming bullae
• Cause is unknown; classically presents as spontaneous pneumothorax in young adults

D. Irregular (Paracicatricial) Emphysema

• Acinus is irregularly involved
• Almost invariably associated with scarring (post-inflammatory or fibrotic)
• Usually clinically insignificant

Only types A and B cause clinically significant airflow obstruction and are associated with COPD.

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3. Etiology / Risk Factors

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4. Pathogenesis

Key Mechanisms:

• Inhaled toxins recruit neutrophils and macrophages into lung parenchyma
• These cells release proteases (especially elastase) that degrade connective tissue (elastin, collagen)
• Normally, α1-antitrypsin (α1-AT) inhibits elastase
• In smokers: cigarette smoke oxidizes and inactivates α1-AT; smoking also directly stimulates more protease release
• In α1-AT deficiency: constitutively reduced antiprotease activity - panacinar emphysema develops at an earlier age (30s-40s) and is more severe
• Result: unimpeded elastin degradation → loss of alveolar wall elastic recoil → air-space enlargement

• Cigarette smoke contains reactive oxygen species (ROS)
• Inflammatory cells (macrophages, neutrophils) release additional ROS
• ROS cause direct tissue damage, endothelial dysfunction, and amplify inflammation
• ROS also inactivate antiproteases, compounding protease imbalance
• NRF2 (encoded by NFE2L2) is a key protective transcription factor against oxidant damage

• Noxious inhalants damage respiratory epithelium → chronic inflammation
• Inflammatory mediators: LTB4, IL-8, TNF-α attract more neutrophils/macrophages
• Accumulation of T and B lymphocytes in advanced disease

• Small airways are normally held open by elastic recoil of surrounding parenchyma
• Destruction of elastic tissue in alveolar walls → loss of radial traction on respiratory bronchioles
• Respiratory bronchioles collapse during expiration (dynamic airway collapse) → functional air trapping even without mechanical obstruction
• This is the mechanism of obstructive ventilatory defect

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5. Morphology

Gross Appearance:

• Panacinar: Pale, voluminous lungs; may obscure the heart when chest is opened at autopsy; uniformly enlarged air spaces
• Centriacinar: Lungs slightly deeper pink and less voluminous (until late stages); upper two-thirds more affected; focal emphysematous areas mixed with normal parenchyma
• Bullae: Large air-filled cysts >1 cm; seen especially in paraseptal emphysema; prone to rupture → pneumothorax

Histology:

• Destruction of alveolar walls without fibrosis
• Enlarged air spaces (fenestrations in walls)
• Loss of alveolar capillary bed → reduced diffusing capacity
• Fragmented elastic fibers (can be seen with elastic stains)
• Reduced number of alveolar walls per unit area

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6. Clinical Features

"Pink Puffer" (Emphysema type)

Contrast with "Blue Bloater" (Chronic Bronchitis):

Most real patients fall somewhere in between with mixed bronchitic and emphysematous features.

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7. Investigations

Pulmonary Function Tests (PFTs) - Most Important

• FEV1/FVC ratio < 0.7 - hallmark of obstructive ventilatory defect (GOLD criteria)
• FEV1 reduced (correlates with severity)
• TLC, RV, FRC all increased (air trapping, hyperinflation)
• DLCO (diffusing capacity) reduced - specific for emphysema (loss of alveolar surface area); helps distinguish emphysema from asthma
• Flow-volume loop: shows expiratory flow limitation, "scooped-out" appearance

Chest X-Ray

• Hyperinflated lungs - increased translucency
• Flattened diaphragm - most reliable sign (diaphragm level at or below 10th posterior rib)
• Increased AP diameter (barrel chest)
• Bullae - avascular hyperlucent areas
• Narrow mediastinum, elongated heart shadow
• Attenuated peripheral vascular markings ("pruning")

HRCT Chest

• Most sensitive method for diagnosing and quantifying emphysema
• Low-attenuation areas without visible walls
• Can differentiate centriacinar from panacinar patterns
• Centrilobular nodules in centriacinar type

Blood Gas Analysis (ABG)

• Maintained relatively normal until late stages in pure emphysema
• Eventually: hypoxemia (PaO2↓), hypercapnia (PaCO2↑)

Other Tests

• α1-antitrypsin serum levels (especially if age <45, non-smoker, panacinar pattern, family history)
• CBC: polycythemia secondary to chronic hypoxia (late)
• ECG: right axis deviation, P pulmonale (if cor pulmonale develops)

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8. Treatment / Management

Non-Pharmacological

1. Smoking cessation - single most effective intervention; slows FEV1 decline
2. Pulmonary rehabilitation - improves exercise tolerance and quality of life
3. Nutritional support - weight loss is common in emphysema
4. Vaccination - influenza and pneumococcal vaccines to prevent exacerbations

Pharmacological

Oxygen Therapy

• Long-term oxygen therapy (LTOT): indicated when PaO2 ≤55 mmHg (or ≤59 mmHg with cor pulmonale/polycythemia) at rest
• Recommended for ≥15-16 hours/day
• Reduces pulmonary hypertension and improves survival

Surgical Options

1. Bullectomy - removal of large bullae compressing adjacent normal lung
2. Lung Volume Reduction Surgery (LVRS) - resects severely emphysematous areas (upper lobe predominant); improves elastic recoil and diaphragm function
3. Bronchoscopic lung volume reduction - endobronchial valves (less invasive)
4. Lung transplantation - for end-stage disease in selected candidates

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9. Complications

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10. Key Concepts Summary

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