EDAIC Cardiovascular Physiology and Pharmacology 5 β Questions and Answers
Question 1: Which of the following best describes Poiseuille's law as applied to vascular resistance?
- Resistance is proportional to vessel radius
- Resistance is inversely proportional to the fourth power of radius (Correct answer)
- Resistance is proportional to vessel length and inversely to viscosity
- Resistance increases linearly with blood velocity
Correct answer: Resistance is inversely proportional to the fourth power of radius
Poiseuille's law states resistance = 8Ξ·L/Οrβ΄, meaning resistance is inversely proportional to the fourth power of radiusβa small change in radius causes a large change in resistance.
Question 2: In a patient receiving norepinephrine infusion, which hemodynamic change is expected?
- Increased CO, decreased SVR
- Increased SVR, reflex bradycardia, variable CO (Correct answer)
- Decreased SVR, increased heart rate
- Decreased MAP with increased stroke volume
Correct answer: Increased SVR, reflex bradycardia, variable CO
Norepinephrine predominantly activates alpha-1 receptors, increasing SVR and MAP; reflex vagal bradycardia may occur, and CO may decrease, stay unchanged, or increase depending on baseline status.
Question 3: The plateau of the oxygen-hemoglobin dissociation curve has clinical significance because it means:
- Small drops in PaO2 from 100 to 70 mmHg cause large drops in SaO2
- SaO2 remains high over a wide range of PaO2 values above 60 mmHg (Correct answer)
- Oxygen delivery is maximized at PaO2 of 40 mmHg
- Hemoglobin releases oxygen more readily at high pH
Correct answer: SaO2 remains high over a wide range of PaO2 values above 60 mmHg
The flat upper portion of the oxyhemoglobin dissociation curve means SaO2 remains above 90% across a wide PaO2 range (60-100 mmHg), providing a safety margin.
Question 4: Adenosine terminates paroxysmal supraventricular tachycardia by:
- Blocking L-type calcium channels in ventricular myocytes
- Transiently blocking AV nodal conduction via A1 receptor activation (Correct answer)
- Increasing SA node automaticity
- Prolonging ventricular refractory period
Correct answer: Transiently blocking AV nodal conduction via A1 receptor activation
Adenosine activates A1 receptors in the AV node, activating GIRK channels and hyperpolarizing the node, causing transient AV block that interrupts re-entrant circuits.
Question 5: Which statement about the Windkessel effect of the aorta is correct?
- It increases pulse pressure in young patients
- Aortic compliance buffers systolic pressure and maintains diastolic flow (Correct answer)
- It is enhanced in patients with arteriosclerosis
- It refers to aortic valve competence during diastole
Correct answer: Aortic compliance buffers systolic pressure and maintains diastolic flow
The Windkessel effect describes how aortic compliance stores energy during systole and releases it in diastole, maintaining forward flow and reducing pulse pressure.
Question 6: Which of the following is a direct effect of acute hyperkalemia on cardiac electrophysiology?
- Prolonged phase 0 upstroke velocity
- Decreased resting membrane potential (less negative) causing partial depolarization (Correct answer)
- Increased automaticity of Purkinje fibers
- Shortened PR interval
Correct answer: Decreased resting membrane potential (less negative) causing partial depolarization
Hyperkalemia reduces the electrochemical gradient for potassium, making the resting membrane potential less negative, partially inactivating fast sodium channels and slowing conduction.
Question 7: In a patient with distributive shock, which hemodynamic profile is expected?
- Low CO, high SVR, high PCWP
- High CO, low SVR, low to normal PCWP (Correct answer)
- Low CO, low SVR, high CVP
- High CO, high SVR, low PCWP
Correct answer: High CO, low SVR, low to normal PCWP
Distributive shock (e.g., septic shock) is characterized by high cardiac output, low systemic vascular resistance, and inappropriately low tissue perfusion despite high flow.
EDAIC Cardiovascular Physiology and Pharmacology 5
Which of the following best describes Poiseuille's law as applied to vascular resistance?