12 & 16: Regulation of Cardiac Function

Question 1

What are four important determinants of ventricular performance?

Answer 1

• Inotropy (contractility)
• Lusitropy (ability to relax)
• Chronotropy (heart rate)
• Dromotropy (AV node conduction)

Question 2

What is the major determinant of mechanical function of the ventricles?

Answer 2

Calcium homeostasis

Question 3

Explain how intracellular Ca is regulated

Answer 3

• L type Ca channels open post depolarisation in T tubules
• Ca enters and binds to RyR causing Ca release from the SR
• Ca binds to TnC - exposing actin sites, x bridge cycling
• SERCA reuptakes Ca from cytoplasm to the SR
• NCX removes Ca from the cell passively

Question 4

What are two ways to modulate inotropy?

Answer 4

• Magnitude and rate of Ca release (and reuptake)

- Affinity of TnC for Ca

Question 5

Where do the pre-ganglionic fibres of the SNS originate?

Answer 5

Upper thoracic segment of SC

Question 6

Why does the SNS have a slow but long term effect on heart rate and inotropy?

Answer 6

• Exerts effect via cAMP

- Termination slow due to re-uptake at nerve terminals

Question 7

What is the consequence of abnormal Ca homeostasis on mechanical function?

Answer 7

Impaired ventricular filling (inc. intracellular Ca during diastole)

Question 8

Describe the cellular architecture of the heart

Answer 8

• LV is a truncated, thick wall ellipsoid to which the RV is attached
• Myocytes organised within an extensive extracellular CT network
• Orientation of myocytes varies across the wall

Question 9

How does the ventricular wall change shape during systole?

Answer 9

• Radial thickening
• Torsional deformation
• Transmural shear

Question 10

Changes in cardiac ___ and myocyte ____ in structural heart disease impairs mechanical function

Answer 10

Cardiac geometry

Myocyte arrangement

Question 11

How does systemic hypertension change cardiac structure?

Answer 11

• LV muscular hypertrophy (wall thickening, inc. collagen density)
• Inc. LV stiffness and cavity volume
• Reduction in EF

Question 12

What are the two determinants of myocardial oxygen supply?

Answer 12

Perfusion pressure and impedance

Question 13

What are the four determinants of myocardial oxygen demand?

Answer 13

• Basla metabolism
• Inotropic state
• Mural force development
• Heart rate

Question 14

Define coronary reserve

Answer 14

The amount by which it is possible to increase coronary flow