A 22-year-old woman inhales as much air as possible and exhales as much air as she can, producing the spirogram shown in the figure. A residual volume of 1.0 liter was determined using the helium dilution technique. What is her FRC (in liters)?

Correct Answer: A

Rationale: Functional residual capacity (FRC) is the volume in the lungs after a normal expiration, equaling expiratory reserve volume (ERV) plus residual volume (RV). The spirogram shows maximal inhalation to total lung capacity (TLC) and exhalation to RV, with VC (vital capacity) as TLC - RV. RV is given as 1.0 L via helium dilution. FRC = ERV + RV, but without the figure, assume a typical female FRC (~2-3 L). If VC is ~4 L (normal for a young woman) and TLC ~5 L, then after maximal exhalation to RV (1 L), the difference from TLC to FRC includes ERV. Standard ERV is ~1-1.5 L; with RV = 1 L, FRC = 1 + 1 = 2.0 L fits option A, plausible for a smaller female frame. Higher values (2.5-3.5 L) align with larger individuals or males (~3 L). Without exact spirogram data, 2.0 L is reasonable, matching RV + minimal ERV, consistent with helium-derived RV and typical physiology.

Correct Answer: D

Rationale: Inspiration relies on Boyle's law: expanding the thorax lowers intrapulmonary pressure (e.g., 760 to 758 mmHg) below atmospheric, creating a pressure difference driving air in. Diaphragm and intercostal contraction generate this ~1-2 mmHg gradient for tidal breathing (~500 ml). Atmospheric pressure (760 mmHg) is static, not a force its difference with intrapulmonary pressure matters. Muscular spasm implies involuntary action, unlike controlled respiratory muscle contraction. Reduced surface tension (via surfactant) eases expansion but isn't the force pressure difference is. Muscle relaxation drives expiration, not inspiration. This gradient, directly linking mechanics to airflow, is the primary force, quantifiable and fundamental to ventilation, distinguishing it from secondary factors like surfactant or muscle state.

Correct Answer: D

Rationale: Restrictive lung disease (e.g., fibrosis) stiffens lungs, reducing expansion. Forced vital capacity (FVC) drops (e.g., from 4-5 L to 2-3 L) due to limited volume. FEV1 also falls (e.g., 3-4 L to 1.5-2 L) proportionally, but the FEV1/FVC ratio stays normal or high (≥80%), as both decrease similarly, unlike obstructive disease (<70%). Ventilation/perfusion (V/Q) ratio may rise in fibrosis (ventilation falls more than perfusion), not remaining normal. FEV1 and FVC individually are reduced, not normal. The FEV1/FVC ratio's preservation is a restrictive hallmark volume-limited, not airflow-obstructed making it the relatively normal value, key for spirometric diagnosis and distinguishing restrictive from obstructive patterns.

Correct Answer: A

Rationale: During mild exercise, gas exchange meets increased O2 demand and CO2 output. CO2 diffuses ~20 times faster than O2 across the alveolar-capillary membrane due to higher solubility (0.51 vs. 0.024 ml/mmHg/L), despite molecular weight (44 vs. 32), per Fick's law (D ∝ solubility / √MW) true. Diffusing capacity (DL) for O2 is less than CO2's; exercise boosts both via capillary recruitment, but solubility, not weight, drives CO2's edge false. Capillary equilibrium length may shorten with faster flow, but this is nuanced, not definitive false. Arterial blood gases (ABGs) stay normal (PaO2 ~100 mmHg, PaCO2 ~40 mmHg) in health during mild exercise false. CO2's easier diffusion, rooted in solubility, ensures rapid CO2 clearance, a key truth distinguishing gas exchange dynamics in exercise physiology.

Correct Answer: B

Rationale: Initial: VT = 1000 ml, VD = 200 ml, RR = 20/min. VE = VT × RR = 1000 × 20 = 20 L/min; VA = (VT - VD) × RR = (1000 - 200) × 20 = 16 L/min. T: VT = 2000 ml, RR = 10/min; VE = 2000 × 10 = 20 L/min (constant), VA = (2000 - 200) × 10 = 18 L/min (increases). V: VT = 500 ml, RR = 40/min; VE = 500 × 40 = 20 L/min (constant), VA = (500 - 200) × 40 = 12 L/min (decreases). T's higher VT boosts VA despite lower RR; V's lower VT cuts VA as dead space dominates. Option B (T: VE constant, VA increases; V: VE constant, VA decreases) fits, showing VT's impact on alveolar efficiency at fixed VE.