A healthy 10-year-old boy Mohammad Emyan breathes quietly under resting conditions. His tidal volume is 400 milliliters and his ventilation frequency is 12/min. Which of the following best describes the ventilation of the upper, middle, and lower lung zones in this boy?

Correct Answer: D

Rationale: In a healthy upright individual, regional ventilation varies due to gravity and pleural pressure gradients. At rest, intrapleural pressure (IPP) is more negative at the apex (~-10 cm H2O) than the base (~-2.5 cm H2O) due to lung weight, making apices less compliant (stiffer) and bases more compliant (easier to expand). During quiet breathing (VT = 400 ml, RR = 12/min), the diaphragm's downward pull preferentially ventilates the lower zones, where compliance is higher and initial volume lower, allowing greater volume change (ΔV). Studies (e.g., West) show lower lobes receive ~4 times more ventilation per unit volume than apices. Thus, ventilation is greatest in the lower zones, followed by middle, then upper (Lower > Middle > Upper). Equal ventilation ignores gravity's effect, and Upper > Middle > Lower reverses the gradient. For this boy, VA = (400 - ~120 ml VD) × 12 = ~3.36 L/min, distributed predominantly to the base, making this the best description.

Correct Answer: D

Rationale: Intrapleural pressure (IPP) is the pressure in the pleural space, negative relative to atmospheric (760 mmHg) due to lung (inward) and chest wall (outward) recoil. At FRC, IPP is ~756 mmHg (-4 mmHg); inspiration drops it to ~-6 mmHg, and expiration raises it slightly, but it stays negative in health. It's always less than atmospheric pressure, maintaining lung expansion unless breached (e.g., pneumothorax). It's not just low during inspiration it's consistently subatmospheric. Respiratory muscles adjust IPP but don't equalize it to atmospheric pressure (that's pathological). IPP isn't the alveolar-pleural difference (transpulmonary pressure); it's the pleural cavity's absolute pressure. This constant negativity is vital for lung mechanics, making it the true statement reflecting pleural dynamics.

Correct Answer: D

Rationale: Physiological dead space (VDphys) comprises anatomic dead space (VDanat, ~150 ml, airways) and alveolar dead space (VDalv, non-perfused alveoli). Normally, VDphys ≈ VDanat, but in disease, it's ≥ VDanat due to added VDalv true. Lung diseases (e.g., PE) increase VDphys via VDalv true. High V/Q (ventilation > perfusion, e.g., PE) raises VDphys, as ventilated alveoli lack blood flow true. However, VDphys isn't just alveolar dead space; it's VDanat + VDalv, so equating it to VDalv alone is wrong, omitting the anatomic component always present. This misdefinition skews VDphys's scope, critical for assessing total ventilatory waste, not just alveolar inefficiency, making it the false statement amid accurate descriptions.

Correct Answer: A

Rationale: Bronchial asthma features reversible airway obstruction from inflammation and bronchoconstriction. Airway resistance rises due to narrowed bronchi true. During attacks, FEV1/FVC falls below 80% (e.g., 50-60%) as FEV1 drops more true. Bronchodilators (e.g., albuterol) relieve constriction true. Allergies (not listed) often trigger attacks true. However, cough suppressants aren't indicated asthma's productive cough clears mucus; suppressing it risks obstruction and infection false. Treatment prioritizes bronchodilation and inflammation control (e.g., steroids), not cough suppression, which could worsen symptoms. This exception contradicts asthma management, distinguishing it from true statements reflecting pathophysiology and therapy.

Correct Answer: B

Rationale: Solar radiation is the primary energy source for Earth's climate system, delivering ~1361 W/m² at the top of the atmosphere (solar constant), driving weather, ocean currents, and the hydrologic cycle. Geothermal heat (~0.087 W/m²) from Earth's core is minor, mainly affecting tectonics, not climate. Tidal forces from the Moon influence oceans but provide negligible energy for climate. Cosmic background radiation (~2.7 K, microwaves) is far too weak. Solar energy's dominance is evident ~99.97% of climate energy comes from the Sun, absorbed and redistributed via atmosphere and surface processes (e.g., albedo, greenhouse effect), making it the fundamental driver, per climate science (e.g., IPCC), distinguishing it from trivial contributors.