In exercise:

Correct Answer: C

Rationale: diffusing capacity (DₗO₂) increases ≈3-fold (25 to 65-75 ml/min/mmHg) in exercise via recruitment and perfusion. Choice A is false; VO₂ is ≈3-4 L/min in fit subjects, not 6 L/min (elite athletes). Choice B is wrong; RER rises above 1.0 (e.g., 1.2), not to 0.8. ' cardiac output rises less than ventilation (e.g., 4x vs. 20x), but not a sixth. Choice E is false; the curve shifts right. C reflects enhanced O₂ uptake capacity, critical for exercise, making it true.

Correct Answer: C

Rationale: surface tension is the force along a liquid surface (e.g., alveoli), reducing area. Choice A is false; deflation volume exceeds inflation (hysteresis) due to surfactant. Choice B is wrong; compliance is ΔV/ΔP, not area (that's work). ' alveolar pressure is 2T/R (one surface), not 4T/R (soap bubble). Choice E is false; surfactant is from Type II cells, not I. C defines surface tension's role in Laplace's law, critical for alveolar stability.

Correct Answer: D

Rationale: pulmonary stretch receptors initiate the Hering-Breuer reflex, inhibiting inspiration during lung inflation. Choice A (central) controls chemically. Choice B (carotid) and C (aortic) sense blood gases. Stretch receptors, in bronchial smooth muscle, signal via vagus, preventing overinflation (e.g., prolonged expiration at high volumes), making D the accurate initiator.

Correct Answer: C

Rationale: acclimatization shifts the Oâ‚‚ curve right (increased 2,3-DPG), not left. Choice A is true; Oâ‚‚ toxicity (e.g., >1 atm) causes seizures. ' hyperoxia damages infant retinas. Choice D is accurate; polycythemia boosts Oâ‚‚ capacity. Choice E (mountain sickness) fits hypoxemia/alkalosis. Right shift aids Oâ‚‚ unloading at altitude, making C the error.

Correct Answer: D

Rationale: compliance (ΔV/ΔP) is a static measure of lung/chest elasticity, not dynamic (dynamic compliance includes airflow). Choice A is true; FRC balances recoil forces. Choice B is false but not the focus (hysteresis is surfactant-related). Choice C is incorrect but plausible; expiration compliance may appear higher in hysteresis. ' emphysema increases compliance (loss of recoil). Compliance reflects distensibility at rest (e.g., 200 mL/cm H₂O), not breathing dynamics, making E's ‘dynamic' label the error.