A patient has a dead space of 150 milliliters, FRC of 3 liters, VT of 650 milliliters, ERV of 1.5 liters, TLC of 8 liters, and respiratory rate of 15 breaths/min. What is the alveolar ventilation (Va)?

Correct Answer: B

Rationale: Alveolar ventilation (VA) is the air reaching alveoli for gas exchange: VA = (VT - VD) × RR, where VT (tidal volume) = 650 ml, VD (dead space) = 150 ml, and RR (respiratory rate) = 15 breaths/min. Calculate: VT - VD = 650 - 150 = 500 ml per breath. VA = 500 ml × 15 = 7500 ml/min = 7.5 L/min. Verify: FRC (3 L) = ERV (1.5 L) + RV (1.5 L), and TLC (8 L) = FRC + IC (VT + IRV), consistent but not needed for VA. Total ventilation (VE) = VT × RR = 650 × 15 = 9750 ml/min = 9.75 L/min, with 2.25 L/min as dead space ventilation (150 × 15), leaving 7.5 L/min as VA. This matches option B, reflecting effective gas exchange volume, critical for oxygenation and CO2 removal, aligning with standard respiratory calculations.

Correct Answer: D

Rationale: Residual volume (RV) is the air remaining after maximal expiration (~1-1.5 L), preventing alveolar collapse and measurable via helium dilution or body plethysmography. Tidal volume (VT, ~500 ml) is normal breath size, not post-forceful exhalation. Expiratory reserve volume (ERV, ~1-1.5 L) is extra air exhaled beyond normal expiration, expelled during forced effort, leaving RV. Vital capacity (VC, ~4-5 L) is the maximum exhailable volume (IRV + VT + ERV), excluding RV. RV's persistence reflects lung elasticity and chest wall limits, ensuring some air stays, distinct from volumes tied to active breathing or maximal efforts, making it the correct term for this residual air critical for maintaining lung structure.

Correct Answer: A

Rationale: Physiological dead space (VDphys) includes anatomic dead space (~150 ml) and alveolar dead space (ventilated, non-perfused alveoli). Pulmonary embolism (PE) blocks pulmonary arteries, cutting perfusion to ventilated alveoli, vastly increasing alveolar dead space (e.g., from near 0 to 150+ ml), raising VDphys significantly. Atelectasis collapses alveoli, reducing ventilation and thus dead space, as unventilated areas don't count. Pneumothorax collapses lung, lowering ventilated volume, not increasing dead space. Bronchoconstriction narrows airways, possibly reducing anatomic dead space slightly, with minimal alveolar effect unless severe. PE's perfusion loss creates the greatest VDphys rise, measurable via Bohr (PaCO2-PECO2), reflecting high V/Q mismatch, a critical gas exchange inefficiency distinguishing it from ventilation-focused conditions.

Correct Answer: A

Rationale: Idiopathic pulmonary fibrosis (IPF) scars lung interstitium, reducing elasticity. Functional residual capacity (FRC, ~2.5-3 L) drops (e.g., to 2 L) as stiff lungs limit resting volume true, a restrictive feature. Tidal volume (VT, ~500 ml) decreases, not increases, as breathing shallows to compensate false. Pulmonary vascular resistance rises, not falls, as fibrosis narrows capillaries false. Total lung capacity (TLC, ~6 L) decreases (e.g., to 4 L), not rises, due to restricted expansion false. Lower FRC reflects IPF's mechanics stiff lungs shrink volumes, impair gas exchange, and raise breathing effort, aligning with restrictive pathophysiology and distinguishing it from options contradicting volume and resistance changes.

Correct Answer: D

Rationale: Fick's law: Diffusion rate = (A × D × ΔP) / d. Normal A ~70 m², d ~0.5 μm. A decreases 50% to 35 m², halving rate (0.5 × normal). Edema doubles d to 1 μm, halving rate again (0.5 × 0.5 = 0.25 × normal). Diffusion becomes 25% of normal, a 75% decrease (1 - 0.25 = 0.75). D and ΔP (e.g., 100-40 mmHg) are constant. This mirrors emphysema (area loss) plus edema (thickened barrier), slashing O2 transfer, causing hypoxemia. Increases (25%, 50%) defy physics; 25% decrease underestimates; 50% decrease (to half) fits the combined effect, aligning with Fick's proportional changes, critical for diffusion-limited states.