COPD and Restrictive Lung Disease

The Fundamental Difference: Obstructive vs. Restrictive

• Normal: FEV1 = 3.3 L, FVC = 4.0 L, FEV1/FVC = 83%
• Obstructive: FEV1 = 1.0 L, FVC = 2.0 L, FEV1/FVC = 50% - slow steady slope, air trapping
• Restrictive: FEV1 = 1.8 L, FVC = 2.0 L, FEV1/FVC = 90% - fast initial flow, quickly plateaus

PART 1: COPD

Definition

Risk Factors

• Cigarette smoking - the dominant risk factor (present in ~85% of cases)
• Occupational dusts and chemicals
• Alpha-1 antitrypsin (AAT) deficiency - a genetic risk factor
• Air pollution, childhood respiratory infections
• Note: COPD develops in only 15-30% of habitual smokers by traditional measures, though radiographic evidence shows important progressive changes in bronchial wall thickness and lung tissue even in smokers with normal spirometry

Pathogenesis

Emphysema

1. Cigarette smoke activates macrophages and recruits neutrophils
2. Inflammatory cells release proteases (elastase, MMP)
3. These destroy elastin in alveolar walls
4. Normally, alpha-1 antitrypsin (AAT) inhibits this - but smoking also inactivates AAT
5. Result: permanent enlargement of air spaces, loss of elastic recoil, air trapping

• Centriacinar (centrilobular) - most common; involves the central/proximal acinus; strongly smoking-related; worse in upper lobes
• Panacinar (panlobular) - involves the entire acinus uniformly; seen in AAT deficiency; worse in lower lobes

Chronic Bronchitis

• Hyperplasia of tracheal/large airway mucous glands (Reid index >0.5)
• Goblet cell metaplasia in small airways
• Small airway inflammation (chronic bronchiolitis) - the main driver of obstruction
• Bronchiolar wall fibrosis

V/Q Mismatch in COPD

COPD vs. Asthma Comparison

GOLD Classification (Severity by Spirometry)

Clinical Features

• Progressive exertional dyspnea
• Chronic cough ± sputum production
• Barrel chest (increased AP diameter from air trapping)
• Hyperresonance on percussion
• Decreased breath sounds, prolonged expiration, wheeze
• In advanced disease: cyanosis, use of accessory muscles
• Cor pulmonale (right heart failure from chronic hypoxic pulmonary vasoconstriction) in severe/late COPD

Treatment

Bronchodilators (mainstay)

• Short-acting β2 agonists (SABA) - e.g., albuterol (salbutamol): for acute symptom relief
• Short-acting anticholinergics - e.g., ipratropium: for acute relief; can combine with SABA
• Long-acting β2 agonists (LABA) - e.g., salmeterol, formoterol: for persistent symptoms
• Long-acting muscarinic antagonists (LAMA) - e.g., tiotropium: often first choice in stable COPD
• Dual LABA + LAMA: superior to monotherapy for most patients

Inhaled Corticosteroids (ICS)

• Severe airflow obstruction (FEV1 < 50%)
• Frequent exacerbations
• High blood eosinophil count (suggests steroid responsiveness)
• Clear concurrent asthma
• Risk: increased bacterial pneumonia

Anti-inflammatory / Other

• Roflumilast (PDE4 inhibitor): reduces exacerbations in severe COPD with chronic bronchitis phenotype
• Theophylline: older agent; recent placebo-controlled trials failed to show exacerbation benefit
• Azithromycin (long-term): reduces exacerbation frequency in select patients

COPD Exacerbations

• Short-acting bronchodilators (increased dose/frequency)
• Systemic corticosteroids (e.g., prednisolone 40 mg x 5 days)
• Antibiotics - routinely used (unlike asthma), as bacterial infection is frequently involved; common agents: beta-lactams, macrolides, fluoroquinolones
• Controlled oxygen (target SpO2 88-92% in hypercapnic patients)
• Non-invasive ventilation (NIV/BiPAP) for hypercapnic respiratory failure

Non-pharmacological

• Smoking cessation - the single most important intervention to slow disease progression
• Pulmonary rehabilitation
• Long-term oxygen therapy (LTOT): if PaO2 ≤ 55 mmHg (or ≤ 60 mmHg with cor pulmonale/polycythemia) - proven mortality benefit
• Lung volume reduction surgery (LVRS): for upper-lobe predominant emphysema with poor exercise tolerance
• Lung transplantation: for very severe end-stage disease

AAT Deficiency

Prognosis

PART 2: Restrictive Lung Disease

Definition

Classification by Etiology

Intrinsic (Parenchymal / Intrapulmonary)

• Idiopathic Pulmonary Fibrosis (IPF) = Usual Interstitial Pneumonia (UIP) pattern
  • Most common and most severe IIP
  • Patchy interstitial fibrosis, fibroblastic foci, honeycomb cysts on HRCT
  • Associated with germline mutations in telomerase; genetic variants in mucin (MUC5B) and surfactant genes
  • Affects adults >50 years; ~132,000 Americans currently affected
  • Median survival ~3-5 years without treatment
  • Mechanism: repeated alveolar epithelial injury → ER stress, apoptosis, epithelial-mesenchymal transition → fibroblast activation → irreversible fibrosis
  • Robbins & Kumar Basic Pathology; Ganong's Review

• Pathogenesis: inhaled particles phagocytosed by alveolar macrophages → inflammasome activation → fibrogenic cytokine release
• Coal workers' pneumoconiosis: ranges from simple (anthracosis) to Progressive Massive Fibrosis (PMF)
• Silicosis: most common pneumoconiosis worldwide; crystalline silica (quartz); risk of TB and lung cancer
• Asbestosis: interstitial fibrosis; also linked to pleural plaques, pleural effusions, lung cancer (synergistic with smoking), and malignant mesothelioma

• Sarcoidosis: multisystem disease of unknown etiology; non-necrotizing (non-caseating) granulomas; CD4+ Th1 driven
  • Lung involvement in ~90% of cases
  • Other features: bilateral hilar lymphadenopathy, erythema nodosum, uveitis, hypercalcemia
  • Can progress from granulomatous to diffuse interstitial fibrosis
• Hypersensitivity Pneumonitis (HP): immune-mediated response to organic antigens (farmer's lung, bird fancier's lung)

• Connective tissue diseases: RA, SLE, systemic sclerosis (most common CTD-ILD), Sjogren's, polymyositis/dermatomyositis
• Drug-induced: amiodarone, bleomycin, methotrexate, nitrofurantoin

Extrinsic (Extra-pulmonary)

Pathophysiology

• Decreased lung compliance - stiff lungs resist inflation; more work to breathe
• All lung volumes reduced: TLC ↓, FRC ↓, RV ↓
• FEV1 and FVC both fall proportionally, preserving the ratio
• Diffusion impairment (reduced DLCO) develops as alveolar surface area is destroyed
• Hypoxemia via V/Q mismatch and diffusion limitation
• In advanced disease: pulmonary hypertension and cor pulmonale (as in COPD)
• Decreased compliance vs. increased resistance: restrictive = stiff lungs (compliance problem); obstructive = airway narrowing (resistance problem)

Clinical Features

• Progressive exertional dyspnea (hallmark)
• Dry, non-productive cough (in ILD)
• Fine, "velcro" (bibasilar) crackles on auscultation (IPF)
• Clubbing of fingers (especially IPF)
• Cyanosis and right heart failure in advanced stages
• Symptoms/signs of underlying cause (e.g., skin rash in dermatomyositis, arthritis in RA)

Investigations

Pulmonary Function Tests

• FVC ↓, FEV1 ↓, FEV1/FVC normal or ↑, TLC ↓ (confirmatory of restriction), DLCO ↓
• A low FVC with a normal FEV1/FVC should prompt TLC measurement to confirm restriction vs. a non-specific pattern

Imaging

• CXR: basilar reticular pattern (IPF), bilateral hilar lymphadenopathy (sarcoidosis), upper lobe opacities (silicosis)
• HRCT (standard of care for ILD evaluation):
  • IPF: basal, peripheral honeycombing ± traction bronchiectasis (UIP pattern)
  • HRCT can be diagnostic for IPF in the right clinical context, avoiding the need for lung biopsy

Bronchoscopy (BAL + biopsy)

• BAL: eosinophilia >25% suggests chronic eosinophilic pneumonia; lymphocytosis suggests HP or sarcoidosis
• Transbronchial biopsy: good for sarcoidosis (granulomas); limited for most IIPs
• Cryobiopsy: emerging technique with larger yield

Surgical Lung Biopsy (VATS)

• Gold standard for IIP diagnosis when HRCT is non-diagnostic
• Short-term mortality risk ~5%; higher in IPF patients
• Should ideally be obtained before starting treatment

Treatment

IPF (Intrinsic/Fibrotic ILD)

• Antifibrotic agents (slow progression, do not reverse fibrosis):
  • Pirfenidone: anti-fibrotic, anti-inflammatory, antioxidant
  • Nintedanib: tyrosine kinase inhibitor; targets PDGFR, VEGFR, FGFR pathways
• Lung transplantation: definitive for eligible patients; 5-year survival ~50%
• Supplemental oxygen, pulmonary rehabilitation, smoking cessation

Sarcoidosis

• Many cases spontaneously remit; treatment for symptomatic/progressive disease
• Oral corticosteroids remain the mainstay
• Steroid-sparing agents: methotrexate, azathioprine

Pneumoconioses

• No curative treatment; remove from exposure
• Supportive management; treat complications (TB in silicosis)

Extrinsic Restriction

• Treat the underlying cause (weight loss, orthotic devices, respiratory support in NMD)

Summary Comparison Table

• Robbins & Kumar Basic Pathology - COPD and ILD pathology, emphysema subtypes, sarcoidosis, pneumoconioses
• Ganong's Review of Medical Physiology, 26th ed. - PFT spirometry diagram, airflow mechanics, IPF
• Katzung's Basic and Clinical Pharmacology, 16th ed. - COPD pharmacotherapy, exacerbation management
• Fishman's Pulmonary Diseases and Disorders - GOLD classification, BODE index, AAT deficiency
• Harrison's Principles of Internal Medicine, 22e (2025) - Restrictive PFT interpretation, HRCT, biopsy
• Costanzo Physiology, 7th ed. - COPD physiology case, V/Q mismatch, A-a gradient