Spirometry can measure all except

Correct Answer: C

Rationale: Spirometry measures lung volumes and capacities but cannot directly measure functional residual capacity (FRC), making choice C correct. Inspiratory capacity (IC, choice A) is the sum of tidal volume (TV) and inspiratory reserve volume (IRV), both measurable via spirometry. Expiratory reserve volume (ERV, choice B) is the additional air exhaled after a normal exhalation, also directly measured. Vital capacity (choice D) is the total of IRV, TV, and ERV, calculated from spirometry data. Tidal volume (TV, choice E) is the normal breathing volume, easily measured. FRC, however, is the volume remaining in the lungs after a normal expiration (ERV + residual volume, RV), and RV cannot be expelled or measured by spirometry alone it requires techniques like helium dilution or body plethysmography. Thus, FRC's dependence on RV excludes it from direct spirometry measurement, confirming C as the exception.

Correct Answer: C

Rationale: decreased alveolar pCO₂ (e.g., hyperventilation) causes bronchodilation via chemoreceptor feedback, reducing airway resistance, not increasing it. Choice A is false; Poiseuille's law (R = 8ηL/πr⁴) applies to laminar flow, not turbulent. Choice B is wrong; medium-sized bronchi, not smallest bronchioles, contribute most resistance due to cumulative cross-sectional area changes. ' as lung volume drops, resistance rises bronchioles narrow without radial traction. Choice E (adrenergic contraction increasing resistance) is false; adrenergic stimulation relaxes bronchial muscle, lowering resistance. Low pCO₂ signals reduced CO₂ clearance need, relaxing airways to adjust ventilation, opposite to bronchoconstriction (e.g., high pCO₂). This physiological response makes C the true statement about resistance dynamics.

Correct Answer: C

Rationale: automatic breathing's reciprocal innervation (inspiration vs. expiration) relies on descending medullary pathways (e.g., dorsal/ventral respiratory groups), not just spinal reflexes. Choice A is false; voluntary control stems from the cortex, not pons/medulla (automatic centers). Choice B is wrong; automaticity uses reticulospinal tracts, not corticospinal (voluntary). ' external intercostals aid inspiration, not expiration. Choice E (no phrenic output in expiration) is true in quiet breathing but not absolute. The pre-Bötzinger complex drives rhythm, coordinating via descending signals to inhibit expiratory neurons during inspiration. This supraspinal control ensures smooth cycling, making C the accurate depiction of automatic respiratory neural integration.

Correct Answer: D

Rationale: Choice D is not true; inspiratory capacity (IC) in men is ≈3.3 L (TV + IRV, 0.5 + 2.8 L), not 4.8 L. ' FRC (≈2.4 L) equals ERV (≈1 L) + RV (≈1.4 L). Choice B is true; IRV is ≈3.3 L in men. Choice C is accurate; RV in women is ≈1.1 L. Choice E is correct; TLC is ≈6 L (men), 4.2 L (women). IC reflects maximal inspiratory volume from FRC; 4.8 L exceeds typical male values (closer to vital capacity). Standard lung volumes (e.g., 70 kg male) confirm D's overestimation, making it the false statement.

Correct Answer: D

Rationale: mixed venous PO₂ (PvO₂) is ≈50 mmHg on 100% O₂. With FiO₂ = 1.0, PaO₂ rises to ≈650 mmHg (PIO₂ = 760 - 47 ≈ 713 mmHg, minus A-a gradient). O₂ content increases (dissolved O₂ ≈ 2 ml/100 ml + Hb-bound), but tissues extract ≈5 ml/100 ml O₂, dropping PvO₂ to 50-55 mmHg (SaO₂ near 100%). Choice A (40 mmHg) is normal air breathing. Choice B (713 mmHg) is arterial, not venous. Choice C (650 mmHg) overestimates venous saturation. D reflects the balance of high arterial O₂ and tissue uptake.