EDAIC Cardiovascular Physiology and Pharmacology 4 — Questions and Answers
Question 1: Which ion channel is primarily responsible for the plateau phase (phase 2) of the ventricular action potential?
- Fast sodium channels
- L-type calcium channels (Correct answer)
- Inward rectifier potassium channels
- Transient outward potassium channels
Correct answer: L-type calcium channels
L-type (long-lasting) calcium channels carry slow inward calcium current responsible for the prolonged plateau phase 2 of the ventricular action potential.
Question 2: In a patient with right heart failure, which hemodynamic finding is MOST characteristic?
- Elevated PCWP with low CVP
- Elevated CVP with relatively normal PCWP (Correct answer)
- Low CO with low CVP
- High SVR with low CVP
Correct answer: Elevated CVP with relatively normal PCWP
Right heart failure causes venous congestion (elevated CVP/JVP) but initially without pulmonary congestion, so PCWP may remain relatively normal.
Question 3: Which of the following describes the effect of increased afterload on the LV pressure-volume loop?
- Increased stroke volume with unchanged LVEDV
- Decreased stroke volume with increased end-systolic volume (Correct answer)
- Decreased LVEDP with unchanged stroke volume
- Increased loop width with decreased loop height
Correct answer: Decreased stroke volume with increased end-systolic volume
Increased afterload raises the pressure against which the ventricle must eject, resulting in decreased stroke volume and an elevated end-systolic volume.
Question 4: Nitroglycerin at low doses primarily reduces preload by:
- Arterial vasodilation reducing SVR
- Venodilation reducing venous return and LVEDP (Correct answer)
- Negative chronotropy reducing filling time
- Coronary artery dilation increasing supply
Correct answer: Venodilation reducing venous return and LVEDP
At low doses, nitroglycerin predominantly dilates veins, pooling blood in the venous capacitance system, reducing venous return and cardiac preload.
Question 5: The oxygen delivery (DO2) equation is best represented as:
- DO2 = CO × SaO2
- DO2 = CO × (Hb × 1.34 × SaO2 + 0.003 × PaO2) (Correct answer)
- DO2 = SvO2 × CO × Hb
- DO2 = VO2 / O2ER
Correct answer: DO2 = CO × (Hb × 1.34 × SaO2 + 0.003 × PaO2)
DO2 = CO × CaO2, where CaO2 = (Hb × 1.34 × SaO2) + (0.003 × PaO2), reflecting both hemoglobin-bound and dissolved oxygen contributions.
Question 6: Beta-blockers reduce myocardial oxygen demand primarily by:
- Reducing afterload via peripheral vasodilation
- Decreasing heart rate and contractility (Correct answer)
- Increasing coronary perfusion pressure
- Inhibiting platelet aggregation
Correct answer: Decreasing heart rate and contractility
Beta-blockers reduce heart rate and myocardial contractility by blocking beta-1 receptors, both of which are major determinants of myocardial oxygen consumption.
Question 7: Which finding on a pulmonary artery catheter tracing suggests mitral regurgitation?
- Elevated pulmonary artery diastolic pressure
- Large V waves on the PCWP tracing (Correct answer)
- Equalization of diastolic pressures
- Absent A waves on PCWP tracing
Correct answer: Large V waves on the PCWP tracing
Severe mitral regurgitation produces large V waves on the PCWP tracing due to regurgitant systolic volume entering the compliant left atrium.
EDAIC Cardiovascular Physiology and Pharmacology 4
Which ion channel is primarily responsible for the plateau phase (phase 2) of the ventricular action potential?