Regarding lung compliance, all of the following are correct EXCEPT?

Correct Answer: C

Rationale: Lung compliance (C) is the change in lung volume per change in transpulmonary pressure (C = ΔV / ΔP), correctly defined. It's not maximal during quiet breathing (tidal volume ~500 ml); it's tested across a range, peaking at moderate volumes but decreasing at high volumes (e.g., near TLC) due to stiffness. In quiet breathing, compliance operates efficiently but isn't at its maximum. Crucially, compliance is inversely related to surface tension higher tension (e.g., no surfactant) stiffens alveoli, reducing compliance, as in RDS, not increasing it. This statement is incorrect, contradicting Laplace's law (P = 2T/r), where high tension raises collapse pressure, lowering compliance. Fibrosis decreases compliance by stiffening lungs with collagen, and emphysema increases it by destroying elastic fibers both correct. The surface tension error misrepresents surfactant's role, making it the exception among these statements, as compliance falls with rising tension.

Correct Answer: C

Rationale: Asthma, an obstructive disease, features reversible bronchoconstriction, inflammation, and mucus production during attacks. Narrowed airways increase resistance, especially on expiration, when dynamic compression worsens airflow, producing wheezing louder and more prolonged than on inspiration, making that statement false. Work of breathing rises as respiratory muscles (e.g., diaphragm) work harder against resistance and trapped air, a consistent expectation. Bronchodilators (e.g., albuterol) are standard treatment, relaxing bronchial smooth muscle, not contraindicated. FEV1 decreases (e.g., from 80% to 50% predicted) due to obstructed airflow, not increases. Increased work of breathing reflects the effort to overcome narrowed passages, elevating energy expenditure and often leading to accessory muscle use, aligning with asthma's acute physiology where resistance and air trapping dominate, distinguishing it from incorrect options misaligned with clinical presentation.

Correct Answer: A

Rationale: Air enters the lungs during inspiration per Boyle's law: thoracic expansion lowers intrapulmonary pressure below atmospheric (e.g., 760 to 758 mmHg), creating a pressure gradient driving airflow. Increasing this gradient via stronger diaphragm and intercostal contraction directly boosts inspired volume (e.g., from 500 ml to 600 ml), the primary factor. Increase in action potential' likely means neural impulses to respiratory muscles; more impulses enhance contraction, but this is secondary to the gradient they produce. Combining both overcomplicates pressure is the direct mechanism. Decreasing the gradient reduces flow, opposing the goal. The pressure gradient is the key driver, quantifiable (e.g., 1-2 mmHg for tidal breathing), linking muscle action to volume via physics, distinguishing it as the most impactful factor in ventilation mechanics.

Correct Answer: D

Rationale: Minute ventilation (VE) = tidal volume (VT) × respiratory rate (RR), fixed at 6 L/min (6000 ml/min). Alveolar ventilation (VA) = (VT - VD) × RR, with anatomic dead space (VD) = 150 ml. For 200 ml at 30/min: VE = 200 × 30 = 6000 ml/min, VA = (200 - 150) × 30 = 50 × 30 = 1500 ml/min. For 300 ml at 20/min: VA = (300 - 150) × 20 = 150 × 20 = 3000 ml/min. For 400 ml at 15/min: VA = (400 - 150) × 15 = 250 × 15 = 3750 ml/min. For 600 ml at 10/min: VA = (600 - 150) × 10 = 450 × 10 = 4500 ml/min. The 600 ml at 10/min maximizes VA (4.5 L/min), as larger VT exceeds VD more, despite lower RR. High RR with low VT wastes ventilation in dead space, reducing VA efficiency. This deeper, slower pattern optimizes gas exchange, making it the best choice.

Correct Answer: D

Rationale: Pneumothorax introduces air into the pleural space, negating intrapleural pressure (~-4 mmHg), collapsing the lung via elastic recoil and expanding the chest wall outward via its recoil increasing thoracic diameter, true. Venous return drops as positive pleural pressure (e.g., tension pneumothorax) compresses vena cava, reducing preload true. Vital capacity (VC) falls as collapsed lung limits exhalable volume (e.g., from 4-5 L) true. Lung compliance (C = ΔV / ΔP) doesn't increase collapsed lung tissue isn't more stretchable; compliance is a lung property unaffected by deflation, effectively zero in collapse, not raised. The false notion of increased compliance misrepresents pneumothorax, where pressure loss, not elasticity, drives effects, making it the untrue statement amid accurate mechanical outcomes.