Regarding pulmonary vascular resistance, which one of the following is true?

Correct Answer: B

Rationale: Pulmonary vascular resistance (PVR) dips at low lung volumes (B) near FRC (~2.5 L), where capillaries stretch optimally . At high volumes (A), extra-alveolar vessels compress, raising PVR; at very low volumes, collapse hikes it too FRC's the sweet spot (~0.1 mmHg/L/min). Increased PVR (C) strains the right heart (e.g., fibrosis, Q10), but it's true, not the query's focus. PVR isn't routine in spirometry (D, false). B's low-volume minimum reflects physiology's balance unlike A's high-volume rise or D's testing mismatch per vascular dynamics.

Correct Answer: D

Rationale: Vital capacity (VC) is IRV + Vt + ERV (~4.8 L). All volumes (A) include RV, making TLC (~6 L). Vt + RV (B) is ~1.7 L, not VC. IRV + ERV (C) omits Vt (~3.8 L). D's sum IRV (~3 L), Vt (~0.5 L), ERV (~1.3 L) is max exhale, measurable by spirometry, unlike A's total or B's partial, per lung volume definitions (Q14).

Correct Answer: C

Rationale: At FRC, intra-alveolar pressure equals atmospheric . FRC (~2.5 L) is lung resting volume (A, true) and thorax's (B, true), but query seeks one. Alveolar pressure is 0 mmHg (760 mmHg) at rest (C), with intrapleural at -5 cm H2O (D, false). Compliance isn't lowest (E, false maximal, Q37). C's equilibrium unlike D's pressure error defines FRC's no-flow state, per physiology (Q2).

Correct Answer: A

Rationale: Later airway generations don't increase total resistance (A, false). Resistance (R ∝ 1/r^4) peaks in medium airways (bronchi), not terminal bronchioles total cross-sectional area (~70 m^2) cuts R in alveoli (Q16). Large airways dominate normally (B, true). High R lowers FEV1/FVC (C, true, Q8). Elasticity loss and constriction (D, true) raise R (e.g., COPD, asthma). A's error unlike B's norm misreads airflow dynamics, per physiology.

Correct Answer: D

Rationale: Bloody pleural effusion occurs in pulmonary infarction (A) and post-myocardial infarction (C) thus D (A & C). Infarction from embolism lyses RBCs into pleura; post-MI (e.g., Dressler's syndrome) involves inflammation, bleeding into pleural space. Cholesterol effusion (B) is chronic, crystalline, not bloody. Meig's syndrome (D) ovarian tumor-related causes transudative effusion, rarely hemorrhagic. A and C reflect acute vascular or inflammatory damage, yielding high RBC counts (>10,000/mm³), key in thoracentesis analysis to differentiate malignancy or trauma, guiding chest management.