Page 7 of 32

PA25.3 | Obstructive Airway Disease & Bronchiectasis — SDL Guide (Part 3)

Bronchiectasis -- Definition, Causes, and the Obstruction-Infection Cycle

A multi-panel medical diagram explains bronchiectasis as permanent bronchial dilatation, showing airway wall destruction, morphological types, causes, and the obstruction-infection cycle. — **Panel A:** Normal bronchus, bronchiectatic bronchus, permanent abnormal dilatation, destroyed muscular and elastic components, mucus-pus in lumen, segmental/subsegmental bronchus involvement. **Panel B:** Cylindrical bronchiectasis, fusiform bronchiectasis, saccular/cystic bronchiectasis. **Panel C:** OI-CF-KA causes: obstruction, infection, cystic fibrosis, chronic foreign body, Kartagener syndrome/primary ciliary dyskinesia, ABPA. **Panel D:** Obstruction or impaired clearance, mucus stasis, persistent infection, neutrophilic inflammation, bronchial wall destruction, permanent dilatation, worsening mucociliary clearance.

Bronchiectasis is defined as permanent, abnormal dilatation of bronchi and bronchioles resulting from destruction of the muscular and elastic components of the bronchial wall.

Key word: permanent (unlike reversible dilatation in acute pneumonia). The bronchi involved are typically segmental and subsegmental; they may be cylindrical, fusiform, or saccular (cystic).

Causes -- a practical mnemonic (OI-CF-KA):

Category	Example
Obstruction	Tumour, foreign body, mucus plug (e.g., asthma, ABPA)
Infection	TB (most common in India), severe/recurrent pneumonia, pertussis, measles
Cystic fibrosis	CFTR mutation -> thick mucus -> chronic Pseudomonas infection
Foreign body (chronic)	Aspirated foreign body in children
Kartagener/ciliary dyskinesia	Primary ciliary dyskinesia -> impaired mucociliary clearance
ABPA	Allergic bronchopulmonary aspergillosis

The obstruction-infection cycle (pathogenesis):

Airway obstruction or impaired clearance -> secretion retention -> bacterial colonisation and infection -> wall inflammation and destruction -> permanent dilatation -> further impairment of clearance -> more infection -> progressive expansion.

This vicious cycle is the unifying mechanism regardless of the initial insult. Breaking the cycle (airway clearance, antibiotics, surgery) is the therapeutic principle.

Bronchiectasis -- Morphology and Complications

Diagram of bronchiectasis showing dilated pus-filled bronchi reaching the pleura, bronchial wall destruction on microscopy, comparison with a normal bronchus, and major complications. — **Panel A:** Lower-lobe lung segment cross-section showing pleural surface, dilated bronchi reaching pleura, thickened grey-green walls, mucopurulent secretions, peribronchial fibrosis, and adjacent organising pneumonia.. **Panel B:** Side-by-side normal and bronchiectatic bronchial cross-sections showing normal tapering bronchus with intact cartilage versus dilated irregular bronchus with wall destruction and purulent lumen.. **Panel C:** Microscopy-style bronchial wall detail showing ulcerated mucosa, loss of cartilage, smooth muscle and elastic tissue, dense neutrophil-lymphocyte-plasma cell infiltrate, and fibrous replacement.. **Panel D:** Complication flowchart showing haemoptysis, brain or metastatic abscess, cor pulmonale, secondary AA amyloidosis, and respiratory failure arising from chronic infected dilated bronchi..

Macroscopy:
- Dilated bronchi extending to the pleural surface (normal bronchi taper and don't reach the pleura -- diagnostic clue on imaging).
- Bronchi filled with mucopurulent or frankly purulent secretions.
- Walls thickened, grey or greenish.
- Lower lobes most commonly affected (gravity-dependent drainage failure); also right middle lobe, lingula.

Microscopy:
- Destruction of bronchial wall -- loss of cartilage, smooth muscle, elastic tissue.
- Dense chronic inflammatory infiltrate (neutrophils, lymphocytes, plasma cells).
- Ulceration and fibrous replacement of bronchial wall.
- Adjacent lung: fibrosis, organising pneumonia.

Complications:

Haemoptysis -- due to hypertrophied bronchial arteries; can be massive and life-threatening.
Brain abscess / metastatic abscess -- septic emboli from infected bronchi.
Cor pulmonale -- hypoxic pulmonary hypertension -> right ventricular hypertrophy and failure.
Secondary amyloidosis (AA) -- from chronic suppurative infection -> serum amyloid A deposition in kidney, liver, spleen.
Respiratory failure -- in advanced bilateral disease.

Diagram comparing bronchiectatic lung cross-section with dilated pus-filled thick-walled bronchi reaching the pleura, surrounding fibrosis, and a normal bronchus inset. — **Panel A:** Dilated bronchus, thickened bronchial wall, purulent lumen content, fibrotic bands, distorted alveoli, pleural surface, loss of bronchial tapering. **Panel B:** Normal bronchus, thin bronchial wall, patent clean lumen, ciliated mucosa, surrounding normal alveoli. **Panel C:** Defective ciliary clearance, recurrent infection, bronchial wall destruction, permanent bronchial dilatation, Kartagener syndrome, dynein arm defect, sinusitis, situs inversus.

SELF-CHECK

A 35-year-old man with recurrent sinusitis and infertility is found to have bilateral lower-lobe bronchiectasis. CT of the chest shows situs inversus. Which underlying defect is responsible?

A. CFTR gene mutation

B. alpha-1-Antitrypsin deficiency

C. Dynein arm defect (primary ciliary dyskinesia)

D. IgA deficiency

Reveal Answer

Answer: C. Dynein arm defect (primary ciliary dyskinesia)

The triad of bronchiectasis + sinusitis + situs inversus is Kartagener syndrome -- a subset of primary ciliary dyskinesia caused by defective dynein arms of cilia. Immotile cilia fail to clear secretions, causing recurrent sinopulmonary infections; defective nodal cilia cause situs inversus. CFTR mutation (cystic fibrosis) causes bronchiectasis but not situs inversus. IgA deficiency causes recurrent infections but not situs inversus.

COPD Complications and Evaluation

Multi-panel COPD diagram summarizing cor pulmonale, respiratory failure types, pneumothorax, polycythaemia, infections, and evaluation with spirometry, imaging, ABG, and alpha1-antitrypsin testing. — **Panel A:** COPD lungs, emphysematous hyperinflation, chronic bronchitis mucus retention, right ventricular hypertrophy, thickened pulmonary artery, ruptured paraseptal bulla, pneumothorax, secondary polycythaemia, recurrent respiratory infections.. **Panel B:** Chronic hypoxaemia, hypoxic pulmonary vasoconstriction, pulmonary hypertension, thickened pulmonary artery wall, right ventricular hypertrophy, right heart failure, cor pulmonale.. **Panel C:** Type I respiratory failure in emphysema: low PaO2 with normal/low PaCO2; Type II respiratory failure in chronic bronchitis: low PaO2 with raised PaCO2.. **Panel D:** Spirometry obstruction with FEV1/FVC <0.70, FEV1 % predicted GOLD I-IV severity ladder, chest X-ray hyperinflation, flattened diaphragm, widened intercostal spaces, bullae, increased peribronchial markings.. **Panel E:** HRCT low-attenuation emphysema areas, bronchial wall thickening, dilated bronchi, ABG hypoxaemia +/- hypercapnia, alpha1-antitrypsin level for early-onset emphysema in non-smokers..

Complications of COPD (emphysema + chronic bronchitis):

Cor pulmonale -- Hypoxia -> hypoxic pulmonary vasoconstriction -> pulmonary hypertension -> right ventricular hypertrophy -> right heart failure. More severe in chronic bronchitis (hypoxaemia more pronounced).
Respiratory failure -- Type I (low PaO2, normal/low PaCO2) in emphysema; Type II (low PaO2 + raised PaCO2) in chronic bronchitis.
Spontaneous pneumothorax -- Rupture of paraseptal bullae; classically in young, thin men or as a complication of emphysema.
Secondary polycythaemia -- Chronic hypoxaemia -> increased erythropoietin -> raised haematocrit (compensatory, but increases viscosity).
Recurrent respiratory infections -- Mucus retention (chronic bronchitis) impairs clearance.

Evaluation:

Spirometry: FEV1/FVC <0.70 confirms obstruction; FEV1 % predicted grades severity (GOLD stages I-IV: >80%, 50-79%, 30-49%, <30%).
Chest X-ray: Hyperinflation (>6 anterior ribs), flattened diaphragm, widened intercostal spaces, bullae in emphysema; peribronchial markings increased in chronic bronchitis.
HRCT: Low-attenuation areas in emphysema; bronchial wall thickening, dilated bronchi in bronchiectasis.
ABG: Hypoxaemia +/- hypercapnia.
alpha1-AT level: In non-smokers with early-onset emphysema.

SELF-CHECK

Post-mortem examination of a 65-year-old with known COPD shows marked right ventricular hypertrophy and dilation. Pulmonary artery walls are thickened. Which mechanism best explains this finding?

A. Systemic hypertension transmitted retrogradely

B. Left ventricular failure leading to pulmonary venous congestion

C. Hypoxic pulmonary vasoconstriction causing pulmonary hypertension

D. Pulmonary thromboembolism from deep vein thrombosis

Reveal Answer

Answer: C. Hypoxic pulmonary vasoconstriction causing pulmonary hypertension

Cor pulmonale -- right ventricular hypertrophy from pulmonary causes -- in COPD results from chronic hypoxia. Hypoxia triggers vasoconstriction of pulmonary arterioles (the Euler-Liljestrand reflex), raising pulmonary vascular resistance. Sustained vasoconstriction leads to medial hypertrophy of pulmonary arteries and pulmonary hypertension, which the right ventricle must pump against. Systemic hypertension affects the left ventricle; left ventricular failure causes left-sided congestion, not right ventricular hypertrophy in isolation.

CLINICAL PEARL

Remember the spirometry rule for long-answer questions: COPD severity is graded by post-bronchodilator FEV1 (GOLD stages), not FEV1/FVC ratio alone. The ratio just confirms obstruction; the FEV1 % predicted tells you severity. In asthma, obstruction is reversible -- FEV1/FVC improves by >=12% and >=200 mL after bronchodilator. This reversibility distinguishes asthma from fixed obstruction in COPD in clinical examination stations.