Which of these statements is false regarding Pulmonary Resistance?

Correct Answer: C

Rationale: Choice C is false. Pulmonary resistance decreases as lung volume increases because extra-alveolar vessels (arteries and veins) are pulled open by radial traction, reducing resistance, not increasing it. Choice A is true; increased pulmonary arterial pressure recruits and distends vessels, lowering resistance. ' pulmonary resistance is about 1/10 of systemic due to shorter, wider vessels. Choice D is true; acetylcholine, via parasympathetic stimulation, relaxes bronchiolar smooth muscle, though its effect is less pronounced than adrenaline's. Choice E is also true; at large lung volumes, pulmonary capillaries are compressed, increasing resistance. The error in C stems from misunderstanding lung volume effects: as lungs expand, airway resistance drops (bronchioles widen), and extra-alveolar vessel resistance decreases due to mechanical stretching, not increases. This aligns with physiological principles of pulmonary circulation, making C the false statement.

Correct Answer: A

Rationale: Hypoventilation (choice A) doesn't occur at high altitudes; it's the exception. Low pOâ‚‚ triggers hyperventilation via peripheral chemoreceptors, increasing ventilation to raise PaOâ‚‚. Polycythemia (choice B) increases RBCs/Hb, boosting Oâ‚‚ capacity after days. Capillary density rises (choice C) in tissues, enhancing Oâ‚‚ delivery over weeks. The Oâ‚‚ dissociation curve shifts right (choice D) due to increased 2,3-DPG, aiding Oâ‚‚ unloading despite lower PaOâ‚‚. Pulmonary vasoconstriction (choice E) occurs acutely, shunting blood to better-ventilated areas. Hypoventilation would worsen hypoxemia, countering acclimatization's goal of optimizing Oâ‚‚ availability. Hyperventilation lowers PaCOâ‚‚, causing alkalosis (later compensated renally), making A the process that doesn't aid high-altitude adaptation.

Correct Answer: A

Rationale: carbon monoxide (CO) poisoning doesn't stimulate carotid bodies effectively, as they sense arterial pO₂, not O₂ content. CO binds hemoglobin (COHb), reducing O₂ delivery, but PaO₂ stays normal (≈100 mmHg), masking hypoxia. Choice B (cyanide) triggers them via metabolic acidosis/hypoxia signals. Choice C (hypoxia, low pO₂) directly activates them (<60 mmHg). Choice D (hypercapnia) stimulates via pCO₂ and pH changes. Choices E (H⁺) and F (nicotine) also activate them. Located at carotid bifurcations, these chemoreceptors drive ventilation in hypoxia or acidosis. CO's failure to lower PaO₂ distinguishes A as the non-stimulant, despite tissue hypoxia.

Correct Answer: C

Rationale: the Bohr effect shifts the O₂ dissociation curve right due to pCO₂ increasing H⁺, reducing Hb affinity. Choice A is false; left shift increases affinity. Choice B is wrong; decreased 2,3-DPG shifts left, not right. ' temperature shifts the curve (right with increase). Choice E is false; 2,3-DPG rises at altitude. The Bohr effect, driven by CO₂'s pH impact, aids O₂ unloading in tissues (P₅₀ rises), a key adaptation. C accurately describes this mechanism.

Correct Answer: D

Rationale: Choice D is correct (replacing E); helium (low density) reduces turbulence (lower Reynolds number, Re = ρvD/μ). Choice A is false; large airways (higher velocity) are more turbulent than small (laminar). Choice B is wrong; turbulent flow scales less than linearly with pressure (not doubled). ' turbulence depends on density, not viscosity (laminar does). Low-density gases decrease Re, easing flow in obstructive disease, making D true.