Exercise and Coronary Blood Flow Flashcards
Learning outcomes
- 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.
Where do the coronary arteries start? When is the window for coronary flow?
- The coronary arteries are found on the coronary sinuses (aka aortic sinuses) of the right and left cusps of the aortic valve
- The window for coronary flow is during diastole, as this is when blood is able to flow through the coronary arteries
What are 3 ways we can decrease the window for coronary flow?
1) Heart rate increase
* Increasing the heart rate will cause the periods of systole and diastole to be shorter
* This will result in less amount of time for coronary flow, which will decrease the size of the window of coronary flow
2) Ventricular pressure increase
* An increase in ventricular pressure from incomplete emptying, resulting in a decrease in the size of the window of coronary flow
3) Aortic pressure decrease
* This is the pressure that pushes blood into the coronary arteries
* If aortic pressure drops, this will decrease the size of the window of coronary flow
What are 2 issues with coronary blood flow?
Why are these issues?
- Issues with coronary blood flow:
1) The myocardium cannot function anaerobically
* Anaerobic glycolysis causes an increase in lactic acid production
2) Arterioles of coronary arteries close mechanically during systole
* This results in a decrease in diastolic filling period during exercise, even though oxygen demand and metabolic demand increase during exercise
How much does work output of the heart increase during strenuous exercise?
How much of coronary artery blood flow O2 is used at rest?
What must an increase in demand be met by?
- Work output of the heart increased 6-9x during strenuous exercise
- 70-80% of coronary blood flow O2 is used at rest
- An increase in demand must be met by increase blood flow
What is the primary controller of coronary blood flow?
What is it in proportion with?
What does it stimulate the release of?
- The primary controller of coronary blood flow is the local metabolism, which controls coronary artery radius
- Local metabolism is in proportion to the need of the cardiac musculature for O2 e.g more local metabolism leads to greater cardiac musculature need for O2
- Local metabolism leads to the release of vasodilators (e.g adenosine - present through breakdown of ATP), which increase blood flow.
How does sympathetic stimulation indirectly and directly affect the coronary flow of the heart?
- Indirect Sympathetic stimulation of coronary blood flow:
- Sympathetic stimulation indirectly affects coronary flow by increasing heart rate and contractility, which increases metabolism and metabolic demands (O2)
- This will lead to an increase in coronary blood flow
- Direct sympathetic stimulation of coronary blood flow:
- The heart has a high degree of sympathetic innervation
- The role of this is unclear, but may contribute to pathophysiologies
- There is no reason we would want sympathetics to cause vasoconstriction of the coronary vessels, so it doesn’t make a lot of sense
Where is noradrenaline released from?
What effect does noradrenaline have on skeletal muscles?
What receptors does it act on?
- Noradrenaline is released predominantly from the ends of sympathetic nerve fibres
- Noradrenaline causes vasoconstriction of skeletal muscle arterioles by acting on alpha1 receptors (α1 receptors)
What is adrenaline (epinephrine)? What is it released by?
What is adrenaline part of?
What is it released in response to?
- Adrenaline (epinephrine) is a hormone and a neurotransmitter that is released by the adrenal medulla
- Adrenaline is part of the sympathetic nervous system and is released in response to fight or flight
What 2 things does adrenaline act on?
- Adrenaline can act on:
1) Alpha 1 (α1) receptors, which causes vasoconstriction of skeletal muscle arterioles
2) Beta 2 (β2) receptors, which causes vasodilation of skeletal muscle arterioles
How does vasodilation affect skeletal muscles?
How is vasodilation of skeletal muscle arterioles favoured during fight or flight responses?
- How vasodilation of skeletal muscle arterioles is favoured during fight or flight responses:
- Prolonged periods of fight or flight responses are mediated by circulating adrenaline
- Adrenaline has a higher affinity for Beta 2 receptors, which will favour vasodilation of skeletal muscle arterioles during the fight or flight
How does moderate and intense exercise affect cardiac output?
How does exercise change the distribution of the cardiac output?
How and why is this done?
- During exercise the cardiac output increases from 5L/min at rest to 15L/min at moderate intensity and 30L/min at maximum intensity for highly trained athletes
- Exercise changes the distribution of the cardiac output to:
1) The heart and muscle
* Done through active hyperaemia
* Blood is shunted from the digestive viscera and skin to the heart, brain, and skeletal muscles
* This is due to the types of receptors found on each tissues type
* e.g more beta 2 receptors present in the brain, so adrenaline will cause vasodilation to the brain during fight or flight
* e.g more alpha 1 receptors in the skin, so adrenaline will cause vasodilation to the skin during fight or flight
* Blood is directed towards
2) Skin
* The core temperature increases
* Detected by the hypothalamus
* Decreased sympathetic innervation to the skin
What is pulse pressure?
- Pulse pressure is the difference between systolic and diastolic pressure
how does moderate excursize effect pulse pressure?
1) Pulse pressure (increase)
* Moderate exercise increases pulse pressure
* This is due to an increase in systolic pressure, which is caused by an increase in stroke volume and speed of ejection
how does moderate exercise effect cardiac output?
2) Cardiac output (increase)
* Big Increase in HR due to decreased parasympathetic innervation to SA node and increase sympathetic innervation to the SA node
What needs to happen for Cardiac output to increase during exercise?
- Cardiac output can only be increased to high levels if venous return is increased to the same degree
How does dynamic exercise affect the kidneys?
decreased distribution of blood to the kidneys = decreased urine output.
- feedforward release of ADH = further enhances fluid retention
- this is because of increased losses of fluids occur through sweating and increased respiration.
How does dynamic exercise affect MABP?
- mean arterial blood pressure may increase slightly but is generally not elevated greatly due to the changes in cardiac output and total peripheral resistance balancing out.
- Pulse-pressure may increase, due to increased systolic pressure
Name the changes in these factors due to dynamic exercise:
* Skeletal muscle blood flow
* Total peripheral resistance
* Stroke volume
* Heart rate
* Cardiac output
* MABP
* Systolic arterial pressure
* Diastolic arterial pressure
* Renal blood flow
* Renin release
* Vasopressin release
* Urine production
Name the changes in these factors due to dynamic exercise:
* Skeletal muscle blood flow
* Total peripheral resistance
* Stroke volume
* Heart rate
* Cardiac output
* MABP
* Systolic arterial pressure
* Diastolic arterial pressure
* Renal blood flow
* Renin release
* Vasopressin release
* Urine production
