If dead space is one third of the tidal volume and arterial PCO2 is 45 mmHg, what is the mixed expired pCO2?

Correct Answer: B

Rationale: Mixed expired PCO2 (PECO2) reflects exhaled CO2 diluted by dead space. If dead space (VD) is one-third tidal volume (VT), VD/VT = 1/3. Per Bohr's equation: VD/VT = (PaCO2 - PECO2) / PaCO2, with PaCO2 = 45 mmHg. Then: 1/3 = (45 - PECO2) / 45, so 45 / 3 = 45 - PECO2, 15 = 45 - PECO2, PECO2 = 30 mmHg. Assuming physiological dead space equals anatomic here (no alveolar dead space specified), one-third of each breath (~0 mmHg CO2 from inspired air) dilutes the alveolar CO2 (~45 mmHg) to two-thirds strength (30 mmHg). A 45 mmHg PECO2 implies no dead space, while 20 mmHg over-dilutes. The 30 mmHg fits the ratio and respiratory mechanics, showing how dead space lowers expired CO2 relative to arterial levels, a key ventilatory efficiency measure.

Correct Answer: B

Rationale: Alveolar ventilation (VA) = (VT - VD) × RR, where VT (tidal volume) = 650 ml, VD (dead space) = 150 ml, RR = 15/min. VA = (650 - 150) × 15 = 500 × 15 = 7500 ml/min = 7.5 L/min. Verify: FRC = ERV (1.5 L) + RV (1.5 L) = 3 L; TLC = FRC + IC (VT + IRV) = 8 L, consistent. Total ventilation (VE) = 650 × 15 = 9750 ml/min = 9.75 L/min, with dead space ventilation = 150 × 15 = 2250 ml/min, leaving VA = 9.75 - 2.25 = 7.5 L/min. The 7.5 L/min reflects air reaching alveoli, key for gas exchange, aligning with respiratory calculations and matching option B.

Correct Answer: B

Rationale: Wind stress on the ocean surface is the primary driver of global ocean currents, transferring momentum from atmospheric winds (e.g., trade winds, westerlies) to surface waters, initiating gyres and flows like the Gulf Stream (~100 Sv). Density differences (temperature, salinity) drive thermohaline circulation (e.g., AMOC, ~20 Sv), significant but secondary to wind-driven surface currents (~80% of kinetic energy, per oceanography, e.g., Stewart). Tides from Moon/Sun cause local flows, not global patterns false. Earth's magnetic field affects charged particles, not currents false. Wind's dominance, via Ekman transport and Coriolis, shapes major current systems, making it the key global driver.

Correct Answer: D

Rationale: Foreign bodies aspirated into the respiratory tract favor the right lung due to its wider, more vertical bronchus. The right main bronchus splits into upper, middle, and lower lobe bronchi. The lower lobe's posterior basal (apicobasal, D) segment is most common for gravity-dependent lodging in an upright position, unlike upper (A) or middle (C) lobes. The left lung (A, B) is less likely due to its oblique bronchus. D aligns with anatomical and clinical patterns.

Correct Answer: C

Rationale: Recurrent laryngeal nerve injury paralyzes all intrinsic muscles except cricothyroid, but posterior cricoarytenoid (C) abducts cords its loss leaves cords adducted, closing rima. C is correct.