Lecture 4- Cardiac Cycle

Question 1

What is the cardiac cycle?

Answer 1

Sequence of pressure flow changes and valve operations that occur with each heartbeat

Question 2

Give a brief description of what happens in the cardiac cycle.

Answer 2

During diastole atrial pressure begins to exceed ventricular pressure. This causes the bicuspid and tricuspid valves to open and blood flows into the ventricles and fills them. At the point where intra ventricular pressure matches that in the atria blood stops flowing into the ventricles. Atrial systole now occurs which forces a small amount more blood into the ventricles.

Now systole occurs where the ventricles contract and force blood into the atria which causes turbulence and the closing of the atrio ventricular valves. Ventricles then contract isovolumetrically as all valves are closed. Th pressure generated exceeds the diastolic pressure in the arteries and so the aortic and pulmonary valves are forced open. Towards the end of systole intra ventricular pressure falls and the pulmonary and aortic valves close. The atria then fill up again and the process starts over

Question 3

What are the heart sounds?

Answer 3

s1 happens upon the closing of the atrio ventricular valves and s2 occurs on the closing of the pulmonary and aortic valves.

Systole happens between s1 and s2

Question 4

Why are resistance vessels important?

Answer 4

Create blood pressure which allows blood to perfuse areas of the body that are typically hard to perfuse

Question 5

What is systole?

Answer 5

Contraction and ejection of blood from ventricles

Question 6

What is diastole?

Answer 6

Relaxation and filling of ventricles

Question 7

What is typical stroke volume?

Answer 7

70ml per beat

Question 8

What is standard heart rate

Answer 8

70 bpm

Question 9

What is average cardiac output?

Answer 9

70ml by 70bpm= 4.9 litres

Question 10

How long is a cardiac action potential?

Answer 10

280ms (duration of a single contraction)

Question 11

What way to the mitral and tricuspid valves point and why is this relevant to prolapse?

Answer 11

Point down into ventricles and during prolapse ventricular contraction and subsequent force of blood forces them up into the atria

Question 12

What prevents inversion (prolapse) of the atrio ventricular valves during systole?

Answer 12

Papillary muscles which are attached to the valves through chordae tendineae

Question 13

Easy way of remembering valve direction?

Answer 13

They follow the flow of blood like the valves in veins

Question 14

How do pacemaker cells in SA node initiate action potential?

Answer 14

Have ion channels that depolarise automatically

Question 15

Why is there a delay of 120ms when action potential reaches AV node?

Answer 15

Allows the atria to contract before the ventricles

Question 16

Atrial vs ventricular fibrillation?

Answer 16

Atrial fibrillation means blood isn’t sent to ventricles properly and not life threatening while ventricular fibrillation is life threatening.

Atrial contraction only accounts for 10-20% of ventricular volume anyway

Question 17

How long do systole and diastole last?

Answer 17

Diastole= 0.55 seconds

Systole= 0.35 seconds

During exercise diastole is reduced while systole doesn’t change

Question 18

What are the 7 phases of the cardiac cycle?

Answer 18

Atrial contraction

Isovolumetric contraction

Rapid ejection

Reduced ejection

Isovolumetric relaxation

Rapid filling

Reduced filling

Question 19

What is a wiggers diagram?

Answer 19

Diagram of time against aortic pressure, left ventricular pressure, left ventricular volume, an electrocardiograph and a phonocardiogram

Question 20

Is a wiggers diagram for the left or right side of the heart?

Answer 20

Typically the left, right would be similar but with lower pressures

Question 21

How much is end diastolic volume?

Answer 21

Around 120ml

Question 22

What happens in atrial contraction phase 1?

Answer 22

Atrial pressure rises known as the A wave

P wave in ECG signifies onset of atrial depolarisation

Volume of left ventricle increases by around 10%

Question 23

What happens in phase 2 isovolumetric contraction?

Answer 23

Mitral valve closes which increases atrial pressure known as C wave.

Volume of left ventricle remains the same as all valves are closed

QRS complex in ECG signifies onset of ventricular depolarisation

Closing of mitral and tricuspid valves cause s1 sound

Mitral valve closes due to ventricular pressure exceeding atrial pressure

Pressure in left ventricle rises rapidly

Question 24

What happens in phase three rapid ejection?

Answer 24

Ejection begins when ventricular pressure exceeds aortic pressure.

During contraction atria are pulled down which initially lowers pressure known as the X descent

Rapid decrease in ventricular blood volume

Question 25

What happens in phase 4 reduced ejection?

Answer 25

Ventricle is depolarised, pressure is reduced and rate of ejection falls Atrial pressure rises as they are filled known as V wave Ventricular depolarisation known as T wave on ECG

Question 26

What happens in phase 5 isovolumetric relaxation?

Answer 26

Brief backflow of blood when ventricular pressure falls below aortic pressure causes aortic valve too close This valve closure results in a dicrotic notch in aortic pressure Ventricular pressure falls but volume remains the same due to all valves being closed End systolic volume is reached and gives a stroke volume of around 70ml Closure of aortic valve gives s2 heart sound

Question 27

What happens in phase 6 rapid filling?

Answer 27

Fall in atrial pressure known as Y descent When intraventricular pressure falls below atrial pressure the mitral valve opens and rapid ventricular filling begins This is normally silent but s3 sound sometimes heard in children and is normal but is a sign of pathology in adults

Question 28

What happens in reduced filling stage 7?

Answer 28

Ventricular pressure is close to reaching atrial pressure and so filling slows. Atrial contraction will be responsible for final volume

Question 29

What are the two main abnormal valve functions?

Answer 29

Stenosis where the valve doesnt open enough and blood flow is obstructed Regurgitation where valve doesnt close all the way so there is leakage

Question 30

What causes aortic valve stenosis?

Answer 30

Degenerative (senile calcification or fibrosis) Congenital (bicuspid valve) Chronic rheumatic fever leading to inflammation

Question 31

What are the problems associated with aortic valve stenosis?

Answer 31

Blood struggles to get through valve which means heart must pump harder eating to hypertrophy. It can also lead to left sided heart failure if sever enough which can result in angina as the cardiac muscle lacks blood supply through coronary arteries and syncope (fainting) as brain lacks oxygen It can also lead to anaemia if the space is small enough as RBC’s het sheared (microangiopathic haemolytic anaemia)

Question 32

What causes aortic valve regurgitation?

Answer 32

Aortic root dilation (leaflets pulled apart) Valvular damage (endocarditis rheumatic fever)

Question 33

What happens in aortic valve regurgitation?

Answer 33

During diastole blood flows into ventricle which increases the stroke volume and increases systolic pressure while decreasing diastolic pressure. Results in a Bounding pulse, head bobbing and quinkes sign where nail beds go flush and pale in time with pulse Causes left ventricular hypertrophy

Question 34

What happens in mitral valve regurgitation?

Answer 34

Prolapse can occur due to myxomatous degeneration, damage to papillary muscle after heart attack, left side heart failure dilation of LV and stretching of valve and rheumatic fever. Blood leaks back into atria which causes greater subsequent preload in ventricle and results in LV hypertrophy

Question 35

Mitral valve stenosis?

Answer 35

Almost all cases caused by rheumatic fever. Valve leaflets fuse and inhibit flow from LA to LV. Increased LA pressure leads to pulmonary oedema, dyspnea (shortness of breath) and pulmonary hypertension and RV hypertrophy as it struggles to pump blood to lungs. Can also lead to LA dilation which can cause atrial fibrillation and thrombus formation and oesophagus compression and dysphagia