Which of the following regarding Residual volume is correct?

Correct Answer: C

Rationale: Residual volume (RV) is the air left in the lungs after maximal expiration (~1-1.5 L), preventing collapse and measurable only indirectly (e.g., helium dilution). It's not just after tidal expiration that's FRC (~2.5-3 L), including RV plus ERV, making that false. In COPD, RV increases (e.g., to 2-3 L) due to air trapping from obstructed airways and lost elasticity, not decreases. In pulmonary fibrosis, a restrictive disease, RV decreases (e.g., to <1 L) as stiff lungs limit all volumes, including residual air, making this correct. RV doesn't stay constant lifelong aging and disease alter it but in health, it's relatively stable, though this isn't the strongest fit. Fibrosis's reduction reflects restricted lung expansion, contrasting with obstructive hyperinflation, making it the accurate statement amid options misaligned with RV's physiological behavior.

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.

Correct Answer: C

Rationale: A lower tracheostomy involves an incision below the thyroid isthmus, typically between the 2nd and 4th tracheal rings, to create an airway. The superior thyroid artery (A) arises from the external carotid and supplies the upper thyroid, far from this site. The inferior thyroid artery (B), from the thyrocervical trunk, supplies the lower thyroid and lies posterior, near the recurrent laryngeal nerve, but is less exposed. The inferior thyroid veins (C) drain the thyroid plexus into the brachiocephalic veins, running anteriorly across the trachea, making them highly vulnerable during midline incision. The internal jugular vein (D) lies lateral, near the carotid sheath, and is less at risk unless the incision deviates significantly. Anatomical variations (e.g., a thyroid ima artery) exist, but C is the most consistently endangered due to its anterior position and delicate nature.