Lecture 8: Cardiac cycle and metabolism

Question 1

Describe the shape of a typical pressure-volume loop of the left ventricle (with numbers!!)

Answer 1

starts at 50mL, ~10mmHg, then volume increases to 70mL on slight downward slope (ventricle expanding while filling), then increases up to 120mL at approximately same pressure, slight bump due to atria contracting. Then goes straight up to 80mmHg (isovolumetric contraction) then curves to 120mmHg and 80mL (rapid ejection phase), then bigger curve down to 100mmHg and 50mL (slow ejection phase) and then straight down to 10mmHg (isovolumetric relaxation).

Question 2

What is the ejection fraction?

Answer 2

SV/EDV = distance between 2 sides of PV loop/EDV

Question 3

Describe how the PV loop changes with increased preload

Answer 3

increased EDV, higher peak blood pressure. due to increased venous return or slower heart rate.

Question 4

How does the PV loop change with increased afterload?

Answer 4

must go to higher pressure before aortic valve opens (longer isovolumetric contraction), higher peak pressure, aortic valve closes at higher pressure and higher ESV (decreased SV). Due to increased arterial pressure

Question 5

How does the PV loop change with increased contractility

Answer 5

higher peak pressure, lower ESV therefore higher SV, due to increased force of contraction

Question 6

How does the heart use fatty acids for energy?

Answer 6

crosses into myocyte via fatty acid binding protein, activated by carnitene acyl transferase into acetyl co-A then sent through TCA and beta-oxidation and e-transport chain.

Question 7

How does the heart use glucose for energy?

Answer 7

comes via GLUT4, then goes through glycolysis then through TCA and e-transport chain.

Question 8

How does the heart use lactate for energy?

Answer 8

lactate converted to pyruvate through lactate dehydrogenase then through TCA and e-transport chain.