Which statement is false about anatomical dead space?

Correct Answer: C

Rationale: Choice C, stating anatomical dead space is significantly large in shallow breathing, is false. Anatomical dead space is the volume of air in conducting airways (about 150 ml in a 75 kg adult) that doesn't participate in gas exchange. Choice A is true; it varies with age due to changes in airway size. ' Fowler's method uses nitrogen washout to estimate it. Choice D is wrong as a description it's Fowler's method, not Bohr's, that plots N₂ concentration (Bohr's uses CO₂ to calculate dead space), but it's still a true statement about measurement options. Choice E is accurate; 150 ml is a standard estimate. In shallow breathing, tidal volume decreases, making dead space a larger fraction of each breath, but the absolute anatomical dead space volume doesn't increase it remains fixed. Thus, ‘significantly large' misrepresents this, making C false.

Correct Answer: D

Rationale: peripheral chemoreceptors (carotid and aortic bodies) respond to decreased arterial pOâ‚‚, driving ventilation in hypoxia. Choice A is false; the apneustic centre is in the lower pons, not medulla (medulla houses DRG/VRG). Choice B is wrong; central chemoreceptors (medulla) detect CSF pH changes from COâ‚‚, not Oâ‚‚. Choice C is true; aortic body chemoreceptors sense pH drops (acidosis), stimulating breathing. Choice E is false; pOâ‚‚, not COâ‚‚, is the primary arterial driver under normal conditions COâ‚‚ via central chemoreceptors dominates. Peripheral chemoreceptors' sensitivity to low pOâ‚‚ (e.g., <60 mmHg) complements COâ‚‚/pH control, critical in hypoxemia (altitude, disease). This specificity and location make D the accurate statement in ventilatory control.

Correct Answer: A

Rationale: destroying pre-Bötzinger complexes abolishes automatic respiration, as they generate the inspiratory rhythm in the medulla. Choice B (ventral group) modulates inspiration/expiration; damage impairs but doesn't stop rhythm. Choice C (dorsal group) drives inspiration; loss disrupts but doesn't abolish automaticity. Choice D (pons section) alters patterns (e.g., apneusis) via pneumotaxic/apneustic loss, not cessation. Choice E (rostral transection) preserves medullary function. The pre-Bötzinger complex, a pacemaker cluster, initiates breathing via spontaneous firing, driving phrenic and intercostal activity. Lesion studies confirm its destruction halts rhythm, unlike accessory regions. Thus, A is the critical site for automatic respiration's abolition.

Correct Answer: B

Rationale: glottal abductors (posterior cricoarytenoids) contract early in inspiration to widen the glottis. Choice A is false; adductor paralysis (e.g., vocal cord) causes weak voice, not stridor (abductor issue). Choice C is true; abductor paralysis narrows the glottis, risking aspiration. Choice D is wrong; both adductors and abductors are vagus-innervated (recurrent laryngeal), not hypoglossal. Choice E is partially true but not absolute. Abductors, vagus-driven, open the glottis pre-inspiration, ensuring airflow. This timing, critical for ventilation, makes B the accurate statement.

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.