The Cardiac Cycle

Question 1

What is the cardiac cycle?

Answer 1

Sequence of mechanical events that occur during a single heart beat

Question 2

When are all the chambers of the heart relaxed?

Answer 2

Towards the end of diastole

Question 3

Why do the valves between the atria and ventricles open?

Answer 3

Because atrial pressure remains slightly greater than ventricular pressure until the ventricles are fully distended

Question 4

Why are the pulmonary and aortic outflow valves closed?

Answer 4

As pulmonary artery and aortic pressures are greater than ventricular pressure

Question 5

When does the cardiac cycle begin?

Answer 5

When sinoatrial node initiates the heartbeat

Question 6

What happens in late diastole?

Answer 6

Both sets of chambers are relaxed and ventricles fill passively

Question 7

What happens during atrial systole?

Answer 7

Atrial contraction forces a small amount of additional blood into the ventricles

Question 8

What happens during isovolumic ventricular contraction?

Answer 8

First phase of ventricular contraction, pushes atrioventricular valves closed but does not create enough pressure to open the semilunar valves

Question 9

What happens during ventricular ejection?

Answer 9

As ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected

Question 10

What happens during isovolumic ventricular relaxation?

Answer 10

As ventricles relax, pressure in the ventricles falls, blood flows back into the cusps of the semilunar valves and snaps them closed

Question 11

What completes ventricular filling?

Answer 11

Contraction of the atria

Question 12

At rest, the atria contribute less than 20% of ventricular volume, how does this change with heart rate?

Answer 12

This proportion increases with heart rate as diastole shortens and there is less time for ventricular filling

Question 13

Why does some blood regurgitate into the veins during atrial systole?

Answer 13

Because there are no valves between the veins and atria

Question 14

What reflects atrial systole?

Answer 14

The a-wave of atrial and venous pressure traces

Question 15

What is the name given to ventricular volume after filling? What is the normal volume for this?

Answer 15

End diastolic volume (EDV)

120-140mL

Question 16

What is the value of end diastolic pressure (EDP)?

Answer 16

Less than 10mmHg

Question 17

Where is end diastolic pressure higher?

Answer 17

Higher in the left ventricle than in the right due to the more muscular left ventricular wall

Question 18

What is EDV an important determinant of?

Answer 18

The strength of the subsequent contraction

Question 19

What does ventricular contraction cause?

Answer 19

Sharp rise in ventricular pressure

Atrioventricular valves close once this exceeds atrial pressure

Question 20

What causes the first heart sounds?

Answer 20

Closure of atrioventricular valves

Question 21

What does ventricular depolarisation correspond to on the ECG?

Answer 21

QRS complex

Question 22

Why do the outflow valves remain closed during the initial phase of ventricular contraction?

Answer 22

Pressure is less than that in the pulmonary artery and aorta so outflow valves remain closed

Question 23

What does increasing pressure during ventricular systole cause?

Answer 23

AV valves to bulge into the atria resulting in the small atrial pressure wave (c wave) followed by a fall

Question 24

When do outflow valves open?

Answer 24

When pressure in the ventricle exceeds that in its respective artery

Question 25

What is the difference between pulmonary artery pressure and the pressure in the aorta?

Answer 25

Pulmonary artery pressure is considerably less than that in the aorta - 15mmHg vs 80mmHg

Question 26

What is the change in flow into the arteries during ejection?

Answer 26

Flow into the arteries is initially very rapid but as contraction wanes, ejection is reduced

Question 27

What might rapid ejection be heard as?

Answer 27

A murmur

Question 28

When does active contraction cease?

Answer 28

During the second half of ejection

Question 29

Ventricular pressure during the reduced ejection phase is slightly less than in the artery, why does blood continue to flow out of the ventricle?

Answer 29

Due to momentum

Question 30

What causes the second heart sound?

Answer 30

Closure of the semilunar valves

Question 31

What causes closure of the outflow valve?

Answer 31

Brief reversal of flow during ejection

Question 32

What is the amount of blood ejected by the ventricle in one beat known as? What is the usual value for this?

Answer 32

Stroke volume | 70mL

Question 33

What is the name given to the amount of blood left int he ventricles at the end of systole? What is the usual volume for this?

Answer 33

End systolic volume | About 50mL

Question 34

What is the name given to the proportion of end diastolic volume that is ejected?

Answer 34

Ejection fraction (SV/EDV)

Question 35

Why does atrial pressure rise during the last 2/3 of systole?

Answer 35

As a result of filling from the veins

Question 36

What happens to the ventricles following the closure of the outflow valves?

Answer 36

Ventricles are rapidly relaxing

Question 37

Why do AV valves remain closed during diastole?

Answer 37

As ventricular pressure is still greater than atrial pressure

Question 38

What happens when ventricular pressure falls below atrial pressure?

Answer 38

AV valves open and atrial pressure falls as the ventricles refill

Question 39

What is the the refilling of the ventricles assisted by?

Answer 39

Elastic recoil of the ventricular walls

Question 40

When might a third heart sound be heart?

Answer 40

In young people or when EDP is high

Question 41

What happens to refilling as the ventricles relax completely?

Answer 41

Refilling slows

Question 42

What happens to diastole during exercise and with increasing heart rate?

Answer 42

Diastole at rest is twice the length of systole, this decreases proportionally during exercise and as heart rate increases

Question 43

What generates the pressure-volume loop?

Answer 43

Ventricular pressure plotted against volume

Question 44

What is the shape of the pressure-volume loop affected by?

Answer 44

Contractility of the ventricles and factors that alter refilling or ejection

Question 45

What does the bottom dotted line of the pressure-volume loop show?

Answer 45

Passive elastic properties of the ventricle

Question 46

What would happen to the curve of the pressure-volume loop is compliance was decreased e.g. as a result of fibrotic damage following an infarct?

Answer 46

The curve would be steeper

Question 47

What is the area of the pressure-volume loop an indicator of?

Answer 47

Cardiac function

Question 48

What is a phonocardiogram?

Answer 48

Chart/record of the sounds made by the heart

Question 49

What causes the first heart sound?

Answer 49

Closure of the atrioventricular valves (mitral and tricuspid)

Question 50

What causes the second heart sound?

Answer 50

Closure of the semilunar valves (aortic and pulmonary)

Question 51

When does the third heart sound occur? What causes this?

Answer 51

Occurs early in diastole Normal phenomenon in young people and athletes In older adults it indicates the presence of congestive heart failure Caused by a sudden deceleration of blood flow into the left ventricle from the left atrium

Question 52

When does the fourth heart sound occur? What causes this?

Answer 52

Extra heart sound occurring in late diastole Due to atrial contraction inducing ventricular filling Caused by a greatly thickened left ventricular wall e.g. due to hypertension or aortic stenosis, may be an indicator of coronary heart disease