The impact of physical activity and sport on SV; HR; Cardiac output

Question 1

What is the definition of SV?

Answer 1

-This is the volume of blood pumped out of the heart per beat

Question 2

What 3 things does SV depend on?

Answer 2

• increase in Venous Return
• Elasticity of cardiac fibres
• Contractility of cardiac tissue

Question 3

Why is the elasticity of cardiac fibres important for stroke volume?

Answer 3

• If the cardiac fibres can stretch more then they can produce a greater force of contraction.

Question 4

Why is the contractility of cardiac tissue important for stroke volume?

Answer 4

• The more that they can contract, the greater force of contraction can occur in the cardiac tissue.
• This leads to secondary increase in pre-load (amount of ventricular stretch at the end of diastole (relaxation of heart)).

Question 5

What other things can contractility of cardiac tissue lead to?

Answer 5

• Increase in SV

- Increase of Ejection fraction

Question 6

How does pre-load affect Cardiac Output?

Answer 6

• A decrease in preload diminishes the force of ventricular contraction and therefore decreases stroke volume. This may lead to a decrease in Cardiac Output.

Question 7

What is Starling’s Law of the heart?

Answer 7

• SV increases in response to an increase in blood volume filling the heart.
• This stretches the ventricular wall, causing the cardiac muscle to contract more forcefully.
• SV may also increase due to stronger contractions in the cardiac muscles during exercise.

Question 8

How does Starling’s Law effect SV?

Answer 8

-stroke volume of the left ventricle will increase as the left ventricular volume increases

Question 9

How does SV respond to exercise?

Answer 9

• Increase in exercise intensity leads to an increase in stroke volume
• This is only the case for 40-60% of maximum effort due to the increase in HR

Question 10

Why does stroke volume depend on venous return?

Answer 10

• Increased venous return leads to increased filling (preload) of the left ventricle, which increases left ventricular stroke volume by the processes in Starling’s Law

Question 11

Why does SV plateau during exercise?

Answer 11

• the ventricles do not have as much time to fill up with blood
• this means that they cannot pump out as much blood

Question 12

How does Starling’s Law affect an elite performer during exercise?

Answer 12

• The reduced heart rate of a trained athlete allows for greater filling during diastole
• so the stretch of the cardiac muscle is greater.
• This in turn increases the SV.