Exercise and Coronary Flow Flashcards
Right coronary artery
– Walls of RA and RV
– SA and AV node
– Posterior part of interventricular septum (proximal portion of AV bundle of His)
– Small areas of LA and LV (in some people)
Left coronary artery
– Walls of LA and LV
– Most of the interventricular septum
including AV bundle
Great and small cardiac veins
– Via coronary sinus into right atrium
Issues with coronary blood flow
• 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
Control of coronary blood flow
- Primary controller is local metabolism
– In proportion to need of cardiac musculature for O2
– Stimulates release of vasodilators (e.g. adenosine)
Control of coronary blood flow Sympathetic stimulation
– Indirectly
• Via ↑ heart rate and ↑ contrac1lity which ↑ metabolism
– Directly
• High degree of sympathetic innervation
• Role unclear, but may contribute to pathophysiologies
Noradrenaline Sympathetic stimulation of skeletal muscle arteries
Noradrenaline causes vasoconstriction of skeletal muscle arterioles vs α1 receptors
Adrenaline Sympathetic stimulation of skeletal muscle arteries
Adrenaline causes vasodilation of skeletal muscle arterioles via β2 receptors
Static exercise
During static exercise, the same changes in ANS input to the heart occur as in dynamic exercise – therfore cardiac output increases.
However, the contraction of muscles for a prolonged period both (a) increases venous return to the heart and (b) occludes arteries and prevents tissue perfusion – therfore total peripheral resistance increases considerably.
The net effect is a huge increase in mean arterial pressure.
Cardiac output can only be increased to high
levels if venous return is ↑ to the same degree:
↑ skeletal muscle pump activity
↑ frequency and depth of inspiration
↑ venous tone via sympathetic innervation
Ease of flow from arteries to veins through dilated skeletal muscle arterioles
Effect of moderate exercise
on arterial pressure
Mean arterial pressure may only increase a small amount (if at all) during moderate exercise
Effect of moderate exercise
on arterial pressure, Pulse pressure ↑↑
– Systolic pressure increases
– Due to ↑ stroke volume
– And ↑ speed of ejection
Effect of moderate exercise
on arterial pressure ↑↑↑ Cardiac output
– ↑↑↑ Heart rate • ↓Parasymp SAnode • ↑Symp SA node – ↑ Stroke volume • ↑↑↑ contractility • ↑Frank-Starling
Effect of exercise on cardiac output
During exercise cardiac output increases from 5L/min
– ~15L/min
• moderate intensity
– ~30L/min
• highly trained athlete, at
maximum intensity
