Respiratory

Ventilation-perfusion physiology, obstructive vs restrictive disease, and pulmonary vascular pathology.

Exam weight 6–8% · 2 QBank items · 4 flashcards

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Respiratory physiology

A-a gradient widens in shunt, V/Q mismatch and diffusion limitation; it is normal in hypoventilation and high altitude.
Shunt does not correct with 100% oxygen; V/Q mismatch does.
The oxygen-hemoglobin curve right-shifts with acidosis, high CO₂, high temperature and high 2,3-BPG — 'CADET, face right'.
Hypoxic pulmonary vasoconstriction diverts blood away from poorly ventilated lung — the opposite of systemic vessels.

Obstructive: FEV1/FVC below 0.7, increased total lung capacity and residual volume.
Asthma reverses with bronchodilator; Curschmann spirals and Charcot-Leyden crystals on sputum.
Centriacinar emphysema is smoking-related and upper lobe; panacinar is α1-antitrypsin deficiency and lower lobe with liver disease (PAS-positive globules).
Bronchiectasis follows cystic fibrosis, ABPA and Kartagener syndrome — chronic purulent sputum and tram-track opacities.

Restrictive: FEV1/FVC normal or high with a reduced total lung capacity.
Idiopathic pulmonary fibrosis: honeycombing at bases, treat with pirfenidone or nintedanib.
Pneumoconioses: asbestos lower lobes with pleural plaques, silica and coal upper lobes; silicosis increases TB risk.
Sarcoidosis: noncaseating granulomas, bilateral hilar adenopathy, hypercalcemia and elevated ACE, common in Black patients.

Pulmonary embolism: sudden dyspnea with hypoxia and respiratory alkalosis; CT pulmonary angiography is the standard test.
ARDS: bilateral infiltrates within a week of an insult, PaO₂/FiO₂ ≤ 300, non-cardiogenic — treat with low tidal volume ventilation.
Neonatal respiratory distress syndrome: surfactant deficiency, lecithin:sphingomyelin ratio below 2, treat mother with betamethasone.
Obstructive sleep apnea causes secondary polycythemia, systemic and pulmonary hypertension; treat with CPAP and weight loss.