Chronic Bronchitis

Definition

• Robbins & Kumar Basic Pathology, p. 449
• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 637

Pathogenesis

1. Mucus hypersecretion - The earliest and hallmark feature. Irritants stimulate hypertrophy of mucous glands in the trachea and bronchi, and an increase in goblet cells in bronchioles. Inflammatory mediators (IL-13, histamine) drive this process.
2. Acquired CFTR dysfunction - Cigarette smoking causes acquired CFTR dysfunction, leading to abnormal, dehydrated mucus that worsens obstruction.
3. Inflammation - Inhalants cause cellular damage, recruiting neutrophils, lymphocytes, and macrophages (notably, eosinophils are absent, unlike in asthma).
4. Infection - Does not initiate chronic bronchitis but sustains it and triggers acute exacerbations. Cigarette smoke impairs mucociliary clearance, increasing infection risk.
5. Small airway disease - Airflow obstruction results from chronic bronchiolitis: mucus plugging, bronchiolar wall inflammation, and fibrosis.

• Robbins, Cotran & Kumar Pathologic Basis of Disease, pp. 637-638

Morphology (Histopathology)

• Enlargement of mucus-secreting submucosal glands - the diagnostic hallmark
• Reid index (ratio of mucous gland thickness to bronchial wall thickness between epithelium and cartilage): normally ≤0.4; increased in chronic bronchitis, proportional to severity and duration
• Goblet cell hyperplasia in small airways
• Chronic inflammatory infiltrate (lymphocytes and macrophages)
• Smooth muscle hypertrophy and peribronchial fibrosis
• In severe cases: bronchiolitis obliterans (complete obliteration of bronchiolar lumen by fibrosis)

Fig. 11.8 - Chronic bronchitis. The lumen of the bronchus is above. Note the marked thickening of the mucous gland layer (approximately twice normal) and squamous metaplasia (arrow). (Robbins & Kumar Basic Pathology)

• Robbins & Kumar Basic Pathology, p. 449-450

Clinical Features

Early Stage

• Productive cough - the cardinal symptom; typically worse in the morning and during winter months
• Mucoid sputum, slight at first, increasing over time
• No significant airflow obstruction initially

Progressive Disease

The "Blue Bloater" Syndrome

• Persistent productive cough with copious sputum
• Hypercapnia (PaCO2 often >40 mm Hg) and hypoxemia
• Mild cyanosis due to V/Q mismatch and intrapulmonary shunting
• Elevated hematocrit (secondary polycythemia from chronic hypoxemia)
• Pulmonary hypertension and cor pulmonale (right ventricular failure) - develops early relative to emphysema
• Edema and ascites when right heart failure supervenes
• Patients are often overweight or obese, which can further impair ventilation, especially during sleep
• Respiratory drive becomes less sensitive to CO2; oxygen therapy can depress ventilation (hypoxic drive dependency)

Complications

• Recurrent pulmonary infections (viral and bacterial), often with bronchospasm ("asthmatic bronchitis")
• Acute exacerbations triggered by upper respiratory infections, viral/bacterial pathogens, or environmental pollutant exposure
• Progressive COPD with irreversible airflow obstruction
• Pulmonary hypertension and cor pulmonale
• Respiratory failure
• Increased risk of lung cancer (especially in smokers: change in cough character or hemoptysis mandates investigation)
• Obstructive sleep apnea (10-30% of patients)
• Robbins & Kumar Basic Pathology, p. 450; Morgan and Mikhail's Clinical Anesthesiology 7e, pp. 994-995

Investigations

1. Spirometry (Lung Function Tests) - Most Important

• Diagnostic test of choice for confirming airflow obstruction
• Shows FEV1/FVC ratio < 0.7 (post-bronchodilator) - confirms obstructive pattern
• FEV1 reduced with normal or near-normal FVC
• As disease progresses, the percentage predicted FEV1 is the best measure of severity
• Residual Volume (RV) is increased; Total Lung Capacity (TLC) is often normal (contrast with emphysema where TLC is markedly elevated)

2. Chest X-Ray

• May be normal in early disease - chronic bronchitis is not radiographically apparent unless bronchiectasis is present
• When abnormal: increased bronchovascular (lung) markings, prominent pulmonary vasculature
• Large heart size (right ventricular enlargement from cor pulmonale)
• No significant hyperinflation (contrast with emphysema)
• A chest X-ray is mandatory when there is a change in cough character (e.g., hemoptysis) to exclude lung cancer

3. CT Chest (High-Resolution CT)

• Not routinely needed for diagnosis but useful when CXR is equivocal
• Shows bronchial wall thickening, mucus plugging, and small airway disease
• Distinguishes bronchiectasis (which can look like chronic bronchitis clinically)
• Best method to confirm coexisting emphysema

4. Arterial Blood Gas (ABG) Analysis

• Typically shows type 2 respiratory failure in advanced disease: hypoxemia (low PaO2) + hypercapnia (elevated PaCO2)
• PaO2 < 55 mmHg and/or SaO2 < 88% at rest indicates need for long-term oxygen therapy
• ABG also guides assessment of ventilatory drive

5. Sputum Examination

• Macroscopy: Mucoid (early) to mucopurulent (during exacerbations)
• Microscopy: Neutrophils predominate (eosinophils absent, distinguishing it from asthma)
• Culture and sensitivity: To identify bacterial pathogens in acute exacerbations (common organisms: Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis)

6. Complete Blood Count (CBC)

• Polycythemia (elevated hematocrit/red cell mass) - secondary to chronic hypoxemia
• May show leukocytosis during infective exacerbations

7. ECG and Echocardiography

• ECG: May show right ventricular hypertrophy, right axis deviation, P pulmonale (peaked P waves in inferior leads); also detects dysrhythmias
• Echo: Evaluates pulmonary hypertension and right ventricular function (cor pulmonale)

8. B-type Natriuretic Peptide (BNP)

• Useful to differentiate COPD/chronic bronchitis exacerbation from acute left heart failure
• BNP < 100 pg/mL supports COPD as the cause
• BNP > 500 pg/mL suggests acute heart failure

9. Alpha-1 Antitrypsin Level

• Indicated in younger patients (<45 years), non-smokers, or with family history
• Low levels suggest hereditary deficiency (more associated with emphysema, but relevant in the COPD workup)

10. Pulse Oximetry

• Non-invasive continuous monitoring of oxygen saturation
• Useful for identifying hypoxemia and guiding oxygen supplementation
• SaO2 during 6-minute walk test can evaluate exercise-induced desaturation

Summary

• Robbins & Kumar Basic Pathology (Robbins Pathology), pp. 449-450
• Robbins, Cotran & Kumar Pathologic Basis of Disease, pp. 637-639
• Morgan and Mikhail's Clinical Anesthesiology, 7e, pp. 994-996
• Murray & Nadel's Textbook of Respiratory Medicine, Chapter on Chronic Bronchitis/COPD
• Tintinalli's Emergency Medicine: A Comprehensive Study, pp. 508-509

• Harrison's Principles of Internal Medicine, 22nd Edition (2025) - the gold standard international medicine reference
• Goldman-Cecil Medicine, International Edition (2 volumes) - another major comprehensive medicine text
• Frameworks for Internal Medicine

• Robbins & Kumar Basic Pathology
• Robbins, Cotran & Kumar Pathologic Basis of Disease
• Murray & Nadel's Textbook of Respiratory Medicine

Chronic Bronchitis - Harrison's Principles of Internal Medicine, 22nd Edition (2025)

Definition

"COPD includes emphysema, an anatomically defined condition characterized by destruction of the lung alveoli with air space enlargement; chronic bronchitis, a clinically defined condition with chronic cough and phlegm; and/or small airway disease."

• Harrison's, Chapter 303

Pathogenesis and Pathology (Harrison's)

Large Airway Disease (the basis of chronic bronchitis)

• Mucus gland enlargement and goblet cell hyperplasia in large airways - leading to the cough and mucus production that define chronic bronchitis
• Goblet cells increase in number and extend further down the bronchial tree
• Squamous metaplasia of bronchial epithelium - predisposes to carcinogenesis and disrupts mucociliary clearance
• Bronchial hyperreactivity in some patients (though less prominent than in asthma)
• Neutrophil elastase - one of the most potent secretagogues identified; associated with purulent sputum during respiratory tract infections
• Mucus plugs are frequently observed on chest CT scans of COPD patients and have been recently associated with increased mortality risk

Inflammation and Disease Mechanisms

• Cigarette smoke activates alveolar macrophages to release IL-8 and TNF-α, recruiting neutrophils
• CD8+ T cells release IP-10 (CXCL-7), driving macrophage production of MMP-12 (macrophage elastase)
• Matrix metalloproteinases and serine proteinases (notably neutrophil elastase) degrade each other's inhibitors - a destructive positive feedback loop
• Autoimmune mechanisms may promote progression: lymphoid follicles (B + T cells) around airways, IgG autoantibodies against pulmonary epithelium
• Long after smoking cessation, chronic inflammation persists in end-stage disease - suggesting cigarette smoke both initiates and establishes a self-sustaining process

Clinical Presentation (Harrison's)

History - Symptoms

1. Cough - often the first symptom; patients usually have symptoms for months or years before seeking medical attention
2. Sputum production - mucoid initially, becoming mucopurulent with infections
3. Exertional dyspnea - insidious in onset; described as increased effort to breathe, heaviness, air hunger, or gasping

• Many patients date onset to an acute illness/exacerbation, but a careful history reveals prior chronic respiratory symptoms
• Activities involving arm work at or above shoulder level are particularly difficult
• Activities allowing the patient to brace the arms (e.g., pushing a shopping cart, walking on a treadmill) are better tolerated - use of accessory muscles
• As disease advances: dyspnea on exertion progresses to breathlessness at rest and during basic activities of daily living
• Common comorbidities to screen for: cardiovascular disease, GERD, osteoporosis, frailty, depression, and anxiety
• Validated questionnaires used: COPD Assessment Test (CAT) and Modified Medical Research Council (mMRC) Dyspnea Scale

Physical Examination

• Prolonged expiratory phase - hallmark auscultatory finding
• Expiratory wheezing
• Signs of hyperinflation: barrel chest, enlarged lung volumes, poor diaphragmatic excursion on percussion
• Use of accessory muscles - sternocleidomastoid, scalene, intercostal muscles; characteristic "tripod" position
• Cyanosis - visible in lips and nail beds (the "blue bloater" phenotype)
• Cachexia - significant weight loss and diffuse loss of subcutaneous adipose tissue; associated with elevated inflammatory cytokines (TNF-α); an independent poor prognostic factor
• Signs of cor pulmonale (right heart failure): lower limb edema - relatively infrequent now with supplemental oxygen therapy, but pulmonary hypertension should be considered with persistent exertion limitations or leg edema

Important: Clubbing of the digits is NOT a sign of COPD. Its presence should prompt investigation for other causes - in a COPD patient, newly developed clubbing most likely indicates lung cancer.

Investigations / Laboratory Findings (Harrison's)

1. Spirometry (Pulmonary Function Tests) - The Hallmark Investigation

• FEV1/FVC < 0.7 (post-bronchodilator) confirms airflow obstruction - the classic COPD diagnostic criterion
• FEV1 reduction indicates severity
• With worsening disease: increased TLC, FRC, and RV (hyperinflation)
• In emphysema-predominant disease: reduced diffusing capacity (DLCO) reflecting alveolar destruction
• Degree of airflow obstruction is an important prognostic factor

• Body mass index
• Obstruction (FEV1)
• Dyspnea (mMRC scale)
• Exercise capacity (6-minute walk distance)

2. Arterial Blood Gas (ABG) Analysis

• May show resting or exertional hypoxemia
• Provides information on alveolar ventilation, acid-base status (PaCO2 and pH)
• Hypercapnia (elevated PaCO2) indicates ventilatory failure in advanced disease
• Guides need for long-term oxygen therapy

3. Chest X-Ray

• Chronic bronchitis is not radiographically apparent unless bronchiectasis is present
• May show increased bronchovascular markings, prominent pulmonary vasculature
• In COPD with emphysema: hyperinflation, flat diaphragms, increased lung lucency

4. CT Chest

• Mucus plugs are frequently observed on chest CT and are associated with increased mortality
• Identifies airway wall thickening, airway disease, and extent of emphysema
• Better characterization than plain X-ray for assessing coexisting emphysema or bronchiectasis

5. Pulse Oximetry and Oxygen Assessment

• Non-invasive assessment of resting and exertional hypoxemia
• 6-minute walk test with oximetry quantifies exercise capacity and exercise-induced desaturation
• Guides supplemental oxygen therapy decisions

6. Alpha-1 Antitrypsin (α1-AT) Level

• Indicated especially in patients presenting at younger age, non-smokers, or with family history
• Serum α1-AT level < 11 μM (~55 mg/dL) qualifies for augmentation therapy (relevant primarily in emphysema-predominant disease)

Natural History (Harrison's)

• Most individuals track on quantiles of pulmonary function based on genetics and environment
• COPD can result from:
  • Reduced pulmonary function growth during childhood/adolescence followed by normal rate of decline
  • Early initiation of decline after normal growth
  • Accelerated decline after normal growth (classic pattern)
• Pre-COPD: Substantial CT changes (emphysema, airway wall thickening) can be present with normal FEV1/FVC - these patients are at high risk of progression
• The rate of FEV1 decline is modified by smoking cessation - earlier cessation is more beneficial
• Risk of mortality closely associated with reduced FEV1 and presence of emphysema