One of the followings is expected in idiopathic pulmonary fibrosis.

Correct Answer: A

Rationale: Idiopathic pulmonary fibrosis (IPF) scars lung interstitium, reducing elasticity and volumes. Functional residual capacity (FRC), the resting volume (~2.5-3 L normally), decreases in IPF (e.g., to 2 L) as stiff lungs limit expansion, a hallmark of restrictive disease. Tidal volume (VT, ~500 ml) typically decreases, not increases, as breathing becomes shallow due to restricted capacity, often requiring faster rates to maintain ventilation. Pulmonary vascular resistance rises, not falls, as fibrosis compresses capillaries, increasing resistance and risking right heart strain. Total lung capacity (TLC, ~6 L) also drops (e.g., to 4 L), reflecting reduced maximum volume, not higher. Lower FRC aligns with IPF's mechanics stiff lungs reduce resting and total volumes, impair gas exchange, and elevate work of breathing, distinguishing it from options contradicting restrictive physiology.

Correct Answer: D

Rationale: In a severe asthma attack, bronchoconstriction obstructs airways, reducing airflow, especially on expiration, causing wheezing. FEV1/FVC decreases (<80%) as FEV1 drops more than FVC due to obstruction, not increases. The ventilation/perfusion (V/Q) ratio in affected areas falls, as ventilation is blocked while perfusion persists, causing hypoxemia (PaO2 60 mmHg vs. 75-100 mmHg normal). Arterial PCO2 (30 mmHg vs. 35-45 mmHg) is lower, not higher, because hypoxemia stimulates hyperventilation via peripheral chemoreceptors, expelling CO2 faster than it builds up, a compensatory response in acute asthma. Inadequate gas exchange lowers PaO2, not PCO2, here. Option D correctly ties low PCO2 to hyperventilation driven by hypoxia, aligning with asthma's physiology where obstruction impairs oxygen uptake but CO2 clearance accelerates with increased respiratory effort.

Correct Answer: D

Rationale: Vital capacity (VC) is the maximum air exhaled after maximal inhalation, measured as inspiratory reserve volume (IRV, ~2-3 L), tidal volume (VT, ~0.5 L), and expiratory reserve volume (ERV, ~1-1.5 L), totaling ~4-5 L via spirometry. Sum of all lung volumes' is total lung capacity (TLC, ~6 L), including RV (~1-1.5 L), not VC. VT plus RV' (~2 L) omits IRV and ERV, far below VC. IRV plus ERV' (~3-4 L) excludes VT, underestimating VC. VC (IRV + VT + ERV) captures the full expirable volume, a key respiratory health metric, distinct from TLC or partial sums, reflecting the lung's functional capacity for deep breathing, widely used in clinical assessment.

Correct Answer: C

Rationale: Lung compliance (C = ΔV / ΔP) measures volume change per pressure unit, correctly defined. It's not maximal during quiet breathing (VT ~500 ml) compliance peaks at moderate volumes, declining near TLC due to stiffness, making that false but not the exception here. The statement more surface tension, more compliance' is incorrect high tension (e.g., no surfactant) reduces compliance by stiffening alveoli, per Laplace's law (P = 2T/r), as in RDS, while low tension increases it. Fibrosis decreases compliance via collagen stiffening true. Emphysema (not listed) raises compliance by elasticity loss. The surface tension error contradicts physiology compliance falls with rising tension, making it the exception, as surfactant's role is to enhance compliance by reducing tension, critical for understanding lung mechanics.

Correct Answer: D

Rationale: Pulmonary function tests (PFTs) differ by disease. Obstructive (e.g., COPD) reduces airflow, lowering FEV1 (<80% predicted) from airway narrowing, with increased residual volume (RV) and total lung capacity (TLC). Restrictive (e.g., fibrosis) limits expansion, also reducing FEV1 due to less volume, with decreased RV and TLC. Decreased FEV1 fits both obstructive from obstruction, restrictive from capacity loss. Decreased RV is restrictive-only (obstructive increases RV). Normal or above TLC fits obstructive (restrictive lowers it). Vascular resistance (not a PFT) rises in fibrosis, not decreases. Decreased FEV1's commonality reflects exhalation impairment across types, making it the shared value, critical for broad PFT interpretation.