Exercise and coronary blood flow

Question 1

Describe the coronary blood supply

Answer 1

Right coronary artery
– WallsofRAandRV
– SAandAVnode
– Posterior part of interventricular septum (proximal portion of AV bundle of His)
– Small areas of LA and LV (in some people)

Left coronary artery
– WallsofLAandLV
– Most of the interventricular septum
including AV bundle

Great and small cardiac veins
– Via coronary sinus into right atrium

Question 2

What are the issues with coronary blood flow?

Answer 2

• Myocardium cannot function anaerobically
– Anaerobic glycolysis ↑↑ lactic acid production
• Arterioles close mechanically during systole
• ↓diastolic filling period during exercise
• ↑oxygen demand and↑ metabolic demand during exercise

Work output of heart ↑ 6-9x during strenuous exercise
– Uses 70-80% of coronary blood flow O2 at rest
• ↑demand must be met by ↑flow

Question 3

Discuss control of coronary blood flow

Answer 3

rimary controller is local metabolism
– In proportion to need of cardiac musculature for O2
– Stimulates release of vasodilators (e.g. adenosine)
Sympathetic stimulation
– Indirectly
• Via ↑ heart rate and ↑ contractility which ↑ metabolism
– Directly
• High degree of sympathetic innervation
• Role unclear, but may contribute to pathophysiologies

Question 4

Discuss sympathetic stimulation of skeletal muscle arteries

Answer 4

Noradrenaline causes vasoconstriction of skeletal muscle arterioles vs α1 receptors
Adrenaline causes vasodilation of skeletal muscle arterioles via β2 receptors
β2 would dominate!

Question 5

Learning outcomes

Answer 5

To explain the limits of cardiac perfusion and the difficulties in matching the body’s demand for cardiac output versus cardiac tissue demand.
To predict and explain the changes in cardiovascular parameters in response to dynamic and static exercise.
To relate the major systems and effectors of blood pressure together and explain their dependencies.