84. Restrictive lung diseases (neonatal respiratory distress syndrome, pulmonary edema, idiopathic pulmonary fibrosis) - etiology, pathogenesis, clinical manifestations.

Restrictive lung diseases (neonatal respiratory distress syndrome, pulmonary edema, and idiopathic pulmonary fibrosis) – etiology, pathogenesis, and clinical manifestations.

Restrictive lung diseases are characterized by reduced lung expansion, resulting in decreased total lung capacity (TLC) and reduced compliance, making it harder to inhale.

I. Neonatal respiratory distress syndrome (NRDS)

Etiology

• Primarily seen in preterm infants (especially <32 weeks).
• Caused by deficiency of surfactant production by type II pneumocytes.
• Risk factors:
• Prematurity.
• Maternal diabetes.
• Cesarean delivery without labor (lack of stress-induced cortisol surge).

Pathogenesis

1. Lack of surfactant → increased alveolar surface tension → alveolar collapse (atelectasis).
2. Reduced lung compliance → impaired gas exchange.
3. Hypoxemia and CO₂ retention → acidosis → further surfactant inhibition.
4. Hyaline membrane formation from fibrin-rich exudates lining collapsed alveoli → worsens gas exchange.

Clinical manifestations

• Rapid, shallow breathing (tachypnea).
• Grunting.
• Nasal flaring.
• Intercostal and subcostal retractions.
• Cyanosis.
• Ground-glass appearance on chest X-ray.

II. Pulmonary edema - Pulmonary edema is the abnormal accumulation of fluid in the alveolar spaces and interstitial tissue of the lungs, leading to impaired gas exchange and reduced lung compliance.

Etiology

Cardiogenic (most common)

• Left-sided heart failure → increased pulmonary venous pressure.

Non-cardiogenic (increased permeability)

• Acute respiratory distress syndrome (ARDS).
• Inhalation injury (toxic gases, smoke).
• Severe infections, sepsis.
• High-altitude pulmonary edema.

Pathogenesis

1. Increased hydrostatic pressure (cardiogenic) or increased permeability (non-cardiogenic).
2. Fluid leaks into interstitium → alveoli.
3. Alveolar flooding → impaired gas exchange → hypoxemia.
4. Reduced lung compliance → restrictive ventilatory defect.

Clinical manifestations

• Dyspnea (especially when lying flat — orthopnea).
• Cough with frothy, sometimes pink sputum.
• Crackles on auscultation.
• Cyanosis, severe hypoxia.

III. Idiopathic pulmonary fibrosis (IPF)

Etiology

• Unknown (idiopathic).
• Usually affects older adults (50–70 years).
• Possible risk factors:
• Smoking.
• Environmental exposures (dusts, metals).
• Genetic predisposition (telomerase mutations).

Pathogenesis

1. Repeated microscopic alveolar epithelial injury → abnormal wound healing.
2. Excessive fibroblast activation and collagen deposition → interstitial fibrosis.
3. Distorted lung architecture → stiff, non-compliant lungs.
4. Impaired gas exchange → progressive hypoxemia.

Clinical manifestation

• Progressive exertional dyspnea.
• Non-productive (dry) cough.
• Velcro-like inspiratory crackles (fine basilar crackles).
• Digital clubbing.
• Hypoxemia (initially with exertion, later at rest).
• Gradual progression to respiratory failure.