stroke volume, heart rate & cardiac output

Question 1

What is stroke volume?

Answer 1

Volume of blood pumped out by heart ventricles in each contraction

Question 2

What is the average resting stroke volume?

Answer 2

70ml per beat

Question 3

What three things does stroke volume depend on?

Answer 3

1) Venous Return
2) Elasticity of Cardiac Fibres
3)Contractility of Cardiac Tissue (Myocardium)

Question 4

What is venous return?

Answer 4

The volume of blood returning to the heart via veins
Increased venous return = increased stroke volume

Question 5

What is elasticity of cardiac fibres?

Answer 5

Concerned with the degree of stretch of cardiac tissue during diastole phase of cardiac cycle
More cardiac fibres can stretch = greater force of contraction

Question 6

What can a greater force of contraction do?

Answer 6

Increase ejection fraction - called Starling’s Law

Question 7

What is the diastole phase?

Answer 7

When the heart relaxes to fill up with blood

Question 8

What is ejection fraction?

Answer 8

Percentage of blood pumped out by the left ventricle per beat

Question 9

Describe Starling’s Law

Answer 9

Increased venous return = Greater diastolic filling of the heart = Cardiac muscle stretched = More force of contraction = Increased ejection fraction

Question 10

What is myocardium?

Answer 10

The greater the contractibility of cardiac tissue = greater force of contraction

Question 11

What does a greater force of contraction lead to?

Answer 11

An increase in stroke volume

Question 12

What is the average percentage of blood pumped out by the left ventricle per beat?

Answer 12

60%
Can increase to 85% during a period of training

Question 13

What is heart rate?

Answer 13

The number of times the heart beats per minute

Question 14

What is the average resting heart rate?

Answer 14

72 beats per minute

Question 15

What is cardiac output?

Answer 15

The volume of blood pumped out by the heart ventricles per minute

Question 16

What is the cardiac output equation?

Answer 16

Cardiac Output (Q) = Stroke Volume (SV) x Heart Rate (HR)
If heart rate or stroke volume increases then cardiac output will also increase

Question 17

How does heart rate increase in relation to exercise?

Answer 17

In direct proportion to exercise intensity
(Higher the intensity = higher heart rate)

Question 18

How to work out maximum heart rate?

Answer 18

220-Age
e.g. 220-18 = max 202 bpm

Question 19

Why do trained performers have greater heart rate ranges?

Answer 19

Their resting heart rate is lower and maximum heart rate increases
e.g. Sir Bradley Wiggins had a resting HR of 35 bpm

Question 20

How to gain cardiac muscle?

Answer 20

Regular aerobic training

Question 21

What is cardiac hypertrophy?

Answer 21

When the cardiac muscle becomes bigger and stronger

Question 22

What effect does cardiac hypertrophy have on SV, HR and Q?

Answer 22

Bigger and stronger heart will allow more blood to be pumped out per beat

Question 23

What is bradycardia?

Answer 23

A decrease in resting heart rate

Question 24

What happens when bradycardia occurs?

Answer 24

Oxygen delivery to the muscles improves as there is less oxygen needed for contractions of the heart

Question 25

Does cardiac output differ for trained and untrained performers?

Answer 25

No
It stays the same at resting
Maximum output changes

Question 26

Benefits for trained performers due to increased max cardiac output:

Answer 26

They will be able to transport more blood to working muscles and therefore more oxygen
When the body starts to exercise the distribution of blood flow changes = a higher proportion of blood flows passes to the working muscles and less passes to organs where it is not needed as much

Question 27

What happens to stroke volume as exercise intensity increases?

Answer 27

It also increases
(Only up to 40-60% of max effort)
Once a performer reaches this point, SV plateaus

Question 28

Why does SV plateau?

Answer 28

The increased HR near maximum effort results in a shorter diastolic phase
(Ventricles do not have as much time to fill with blood so they can’t pump as much)