A patient with a right to left shunt: Mixed venous oxygen content = 15 ml/100 ml, Pulmonary capillary Oâ‚‚ content = 20 ml/100 ml, Arterial Oâ‚‚ content = 18 ml/100 ml. What fraction of total cardiac output passes through the shunt?

Correct Answer: D

Rationale: shunt fraction (Qs/Qt) = 40%. Using Qs/Qt = (CcOâ‚‚ - CaOâ‚‚) / (CcOâ‚‚ - CvOâ‚‚), where CcOâ‚‚ = 20, CaOâ‚‚ = 18, CvOâ‚‚ = 15 ml/100 ml: Qs/Qt = (20 - 18) / (20 - 15) = 2 / 5 = 0.4 (40%). Choice A (10%), B (20%), C (30%) underestimate; E (50%) overestimates. Right-to-left shunt mixes venous blood (low Oâ‚‚) with pulmonary capillary blood (high Oâ‚‚), reducing arterial Oâ‚‚ content. The formula quantifies this bypass, showing 40% of cardiac output skips oxygenation, matching D.

Correct Answer: D

Rationale: pulmonary stretch receptors (airway smooth muscle) show sustained firing during lung inflation (Hering-Breuer reflex), inhibiting inspiration. Choice A (central) senses chemical changes, not volume. Choice B (carotid) and C (aortic) monitor blood gases. Slow-adapting stretch receptors signal via vagus, prolonging activity with sustained volume, unlike rapidly adapting receptors, making D the match.

Correct Answer: D

Rationale: Choice D is true; irritant receptors adapt rapidly to stimuli (e.g., smoke), triggering cough. Choice A is false; stretch receptors are in smooth muscle. Choice B is wrong; J receptors cause rapid, shallow breathing (e.g., edema). ' irritant impulses are myelinated (vagus). Rapid adaptation distinguishes irritant receptors, making D the accurate statement.

Correct Answer: B

Rationale: long-term 100% O₂ therapy damages Type II pneumocytes, reducing surfactant, not increasing it (O₂ toxicity). Choice A is true; surfactant is ≈90% phospholipids (e.g., DPPC). ' hydrophobic tails face the lumen, hydrophilic heads face the cell, reducing tension. Choice D is accurate; smoking impairs surfactant via oxidative stress. Choice E (edema from absence) is true. Surfactant lowers alveolar surface tension (P = 2T/R), stabilizing lungs, but hyperoxia disrupts production, contradicting B's claim of increase, making it the false statement.

Correct Answer: D

Rationale: inspiratory capacity (IC = TV + IRV) is ≈3300 mL (500 + 2800), but the question implies a mismatch standard male IC is ≈3600 mL (TV + IRV ≈ 3.1 L), suggesting 3300 is low. Choice A (500 mL) is true. Choice B (1200 mL) fits RV. Choice C (1000 mL) matches ERV. Choice E (VC = 4800 mL) is correct (ERV + TV + IRV). For a 70 kg male, IC aligns closer to 3.5-3.6 L, making D's 3300 mL the error.