3: The cardiac cycle

Question 1

When do cardiac valves produce a sound?

Answer 1

When they shut (not when they open!)

Question 2

Give a simple definition of the cardiac cycle.

Answer 2

All the events occuring from the beginning of one heart beat to the beginning of the next

Question 3

Give a technical definition of the cardiac cycle.

Answer 3

The orderly depolarisations / repolarisations causing atrial / ventricular contractions and relaxations.

Question 4

Put simply, what happens during diastole?

Answer 4

The heart chambers relax and are filled with blood

Question 5

Put simply, what happens during systole?

Answer 5

The heart ventricles contact and pump blood into:

a) the aorta
b) the pulmonary artery

Question 6

How long is diastole compared to systole?

Answer 6

Diastole is about twice as long as systole

Question 7

Name the five events which take place during the cardiac cycle.

Answer 7

1. Passive Filling
2. Atrial Contraction
3. Isovolumetric Ventricular Contraction
4. Ventricular Ejection
5. Isovolumetric Ventricular Relaxation

Question 8

During the passive filling phase, what is the pressure in the atria and ventricles?

Answer 8

Nearly zero

Question 9

During passive filling, which valves open and what flows into the ventricles?

Answer 9

1) The AV valves (RA tricuspid valve, LA mitral valve)
2) Venous return from the systemic and pulmonary circulations flows into the ventricles

Question 10

During passive filling, the aortic and pulmonary valves are…

Answer 10

closed.

Question 11

How full do the ventricles become simply through passive filling?

Answer 11

Around 80% full

Question 12

Which wave on an ECG signals atrial depolarisation?

Answer 12

P wave

Question 13

Which interval on an ECG represents the whole of atrial contraction?

Answer 13

PR interval

Question 14

Which wave(s) on an ECG signal ventricular depolarisation?

Answer 14

QRS complex

Question 15

When does ventricular contraction start on an ECG?

Answer 15

After the QRS complex

Question 16

During isovolumetric ventricular contraction, what pressure change occurs in the ventricles?

Answer 16

Ventricular pressure rises

Question 17

When do the AV valves shut?

Answer 17

When ventricular pressure EXCEEDS atrial pressure

Question 18

In which phase of the cardiac cycle do the AV valves first shut - why?

Answer 18

Isovolumetric ventricular contraction

Ventricular pressure exceeds atrial pressure - valves shut to prevent backflow of blood into the atria

Question 19

When is the first heart sound heard in the cardiac cycle - why?

Answer 19

Isovolumetric ventricular contraction - because the AV valves shut

Question 20

In the isovolumetric ventricular contraction phase, the AV valves shut - what sound does this produce?

Answer 20

First heart sound - LUB

Question 21

During the isovolumetric ventricular contraction phase, the aortic valve is…

Answer 21

shut.

Question 22

Why is the ventricular contraction phase “isovolumetric”?

Answer 22

Tension (pressure) increases in a closed volume (the ventricle itself)

Question 23

In which phase of the cardiac cycle do the aortic / pulmonary valves open?

Answer 23

Ventricular ejection

Question 24

Is a sound produced when the aortic and pulmonary valves open?

Answer 24

No - silent event

Question 25

Which volume is ejected by the ventricles during the 4th phase of the cardiac cycle?

Answer 25

Stroke volume

Question 26

Which volume remains after the stroke volume has been ejected in the 4th phase of the cardiac cycle?

Answer 26

End systolic volume (ESV)

Question 27

Write an equation for stroke volume.

Answer 27

Stroke volume = end diastolic volume - end systolic volume

Question 28

What occurs after the ejection of the stroke volume?

Answer 28

Aortic pressure rises

Question 29

Which wave on an ECG signals ventricular repolarisation?

Answer 29

T wave

Question 30

After the ejection of blood from the ventricles, when ventricular pressure falls, what happens?

Answer 30

The aortic and pulmonary valves SHUT

Question 31

Why is the second heart sound produced?

Answer 31

Ventricular pressure falls below aortic pressure and the valves shut

Question 32

What is the second heart sound and when does it occur?

Answer 32

DUB - at the end of ventricular ejection

Question 33

When does isovolumetric ventricular relaxation start?

Answer 33

When the aortic/pulmonary valves close

Question 34

Why is ventricular relaxation “isovolumetric”?

Answer 34

Tension (pressure) falls in a closed volume (the ventricle)

Question 35

What happens when ventricular pressure falls below atrial pressure during the 5th phase of the cardiac cycle?

Answer 35

AV valves open

Question 36

When the AV valves open in the 5th phase of the cardiac cycle, is any sound produced?

Answer 36

No - opening of valves is silent

Question 37

The first heart sound occurs when the AV valves ___ and signals the beginning of ___.

Answer 37

shut , systole

Question 38

The second heart sound occurs when the aortic / pulmonary valves ___ and signals the beginning of ___.

Answer 38

close , diastole

Question 39

Where would you place your stethoscope to auscultate the aortic valve?

Answer 39

Right sternal edge, 2nd intercostal space

Question 40

Where would you place your stethoscope to auscultate the pulmonary valve?

Answer 40

Left sternal edge, 2nd intercostal space

Question 41

Where would you place your stethoscope to auscultate the mitral valve?

Answer 41

Mid-clavicular line, 5th intercostal space

or wherever the apex beat is in reality

Question 42

What happens after isovolumetric ventricular contraction?

Answer 42

Passive filling (the heart begins a new cardiac cycle)

Question 43

What prevents arterial pressure from falling to zero during diastole?

Answer 43

Elastic recoil