ATI LPN
NCLEX PN Questions Respiratory System Questions
Question 1 of 5
Which abolishes automatic respiration? Destruction of:
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.
Question 2 of 5
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.
Question 3 of 5
The amount of Oâ‚‚ in blood with a PaOâ‚‚ of 100 mmHg is:
Correct Answer: B
Rationale: dissolved O₂ at PaO₂ = 100 mmHg is ≈0.3 mL/100 mL (solubility = 0.003 mL/mmHg/100 mL · 100 = 0.3). Choice A (0.003) is a typo or misunit. Choice C (3 mL) includes Hb-bound O₂ (≈19 mL with Hb 15 g/dL, SaO₂ 97%), not just dissolved. Choice D (3 mL/mL) is absurdly high. Total O₂ content is ≈20 mL/100 mL, but dissolved fraction is minor; B specifies this accurately per Henry's law.
Question 4 of 5
Which show sustained activity with lung inflation?
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.
Question 5 of 5
Which of the following statements is TRUE?
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.