NBME Physiology 2 — Questions and Answers
Question 1: A patient has a cardiac output of 6 L/min and a heart rate of 75 bpm. What is the stroke volume?
- 50 mL
- 80 mL (Correct answer)
- 100 mL
- 120 mL
Correct answer: 80 mL
Stroke volume = cardiac output ÷ heart rate = 6000 mL/min ÷ 75 bpm = 80 mL.
Question 2: During isovolumetric contraction, which valves are open?
- Aortic valve only
- Mitral valve only
- Both aortic and mitral valves
- Neither aortic nor mitral valves (Correct answer)
Correct answer: Neither aortic nor mitral valves
During isovolumetric contraction, all four cardiac valves are closed as ventricular pressure rises before the aortic valve opens.
Question 3: Which condition causes a leftward shift of the oxygen-hemoglobin dissociation curve?
- Increased temperature
- Increased 2,3-DPG
- Alkalosis (Correct answer)
- Increased PaCO2
Correct answer: Alkalosis
Alkalosis raises pH, decreasing H+ concentration and increasing hemoglobin's oxygen affinity, shifting the curve leftward.
Question 4: Hypoxic pulmonary vasoconstriction primarily serves to:
- Increase overall pulmonary blood flow
- Redirect blood to better-ventilated lung segments (Correct answer)
- Decrease mean pulmonary arterial pressure
- Increase alveolar dead space
Correct answer: Redirect blood to better-ventilated lung segments
Hypoxic pulmonary vasoconstriction diverts blood from poorly oxygenated alveoli to better-ventilated regions, optimizing V/Q matching.
Question 5: In the West lung zones, which pressure relationship defines Zone 1?
- Alveolar > arterial > venous (Correct answer)
- Arterial > alveolar > venous
- Arterial > venous > alveolar
- Venous > arterial > alveolar
Correct answer: Alveolar > arterial > venous
Zone 1 (lung apex) has alveolar pressure exceeding arterial pressure, collapsing capillaries and creating dead space with no gas exchange.
Question 6: A patient develops acute hypoventilation. Which blood gas change occurs FIRST?
- Decreased PaO2
- Increased PaCO2 (Correct answer)
- Metabolic alkalosis
- Increased pH
Correct answer: Increased PaCO2
Hypoventilation leads to CO2 retention (increased PaCO2) as a primary event because CO2 production is continuous and its elimination depends entirely on ventilation.
Question 7: Which vessel type is the primary determinant of systemic vascular resistance?
- Large elastic arteries
- Arterioles (Correct answer)
- Venules
- Capillaries
Correct answer: Arterioles
Arterioles are the primary resistance vessels; resistance varies inversely with the fourth power of radius (Poiseuille's law), so small arteriolar changes dramatically alter SVR.
NBME Physiology 2
A patient has a cardiac output of 6 L/min and a heart rate of 75 bpm.
What is the stroke volume?