L4: Cardiac Cycle

Question 1

What is the heart as a pump?

Answer 1

Two pumps acting in series.

Systemic and Pulmonary circulation.

Question 2

Which operates at a high pressure and which operates at a low pressure?

Answer 2

Systemic circulation is high pressure system.

Pulmonary circulation is low pressure system.

Question 3

Define systole and diastole?

Answer 3

Contraction and ejection of blood from ventricles.

Relaxation and filling of ventricles.

Question 4

What is the typical pressure of the aorta?

Answer 4

120 systole/ 80 diastole

Question 5

How much blood does each ventricle eject each beat? What is this also known as?

Answer 5

70ml of blood per beat

Stroke volume

Question 6

What type of muscle makes up the heart?

Answer 6

Cardiac muscle

Question 7

How is cardiac muscle specialised to carry out its function?

Answer 7

Made up of discrete cells that are interconnected electrically by gap junctions (intercalated discs) forming a functional syncytium.
Fibres arranged in a figure of 8 type pattern so that the ventricle contract from the base upwards.

Question 8

What causes the cells to contract?

Answer 8

An action potential causes an increase in the intracellular calcium. It is propagated by the spread of excitation from cell to cell.

Question 9

Name the heart valves? Where are they located?

Answer 9

Tricuspid valve- between the right atrium and the right ventricle
Pulmonary valve- located in the pulmonary trunk/artery, between the right ventricle and pulmonary artery
Mitral valve- between the left atrium and the left ventricle
Aortic valve- located in the aorta, between the left ventricle and aorta

Question 10

What is the structure of the valves?

Answer 10

Tricuspid valve- 3 cusps each is attached to chordae tendineae and papillary muscles.
Mitral valve- 2 cusps each attached to chordae tendineae and papillary muscles.
Pulmonary valve- 3 cusps
Aortic valve- 3 cusps

Question 11

What is the function of the valves?

Answer 11

Valve cusps are pushed together to prevent backflow of blood.

Question 12

Compare and contrast the valves in the heart?

Answer 12

Tricuspid valve is made up of 3 cusps that attach to chodae tendineae and papillary muscles and prevents backflow of blood from the right ventricle into the right atrium.
Mitrial valve is made up of 2 cusps also attached to chordae tendineae which prevents the back flow of blood from the left ventricle into the left atrium during contraction.
Pulmonary valve is made up of 3 cusps located in the pulmonary trunk/ artery.
Aortic valve is made up of 3 cusps located in the aorta.

Question 13

How is the heart designed to prevent prolapse of the valves?

Answer 13

Valves are connected to papillary muscles via chordae tendineae which contract as the ventricles contract to prevent inversion of the valve.

Question 14

Describe the conducting system of the heart?

Answer 14

Originates at the sinoatrial node (SAN)
SAN–> right atrium –>collection of specialised cardiac myocytes –>produce an action potential.
Electrical activity passes over the atria- contraction- atria systole
Reaches atrioventricular node (AVN)–> interatrial septum–> delayed for 120ms to allow the atria to contract.
From the AVN–> down the Bundle of His and along the purkinje fibres–> spread along the base of the heart allowing the heart
Contraction from base upwards–> pushing the blood up out the heart.
The impulse spreads from the inner (endocardial) surface to the outer (epicardial) surface.

Question 15

What are the 7 phases of the cardiac cycle? How long is the total cycle? How long is it in systole for and diastole for?

Answer 15

1) Atrial contraction
2) Isovolumetric contraction
3) Rapid ejection
4) Reduced ejection
5) Isovolumetric relaxation
6) Rapid filling
7) Reduced filling
Total time = 0.9s (HR= 67bpm)
Systole= 0.35s (steps 2, 3, 4)
Diastole= 0.55s

Question 16

What happens to the cardiac cycle when heart rate is increased?

Answer 16

The cycle goes faster however the systolic phase still take 0.35s but the diastolic phase goes quicker.

Question 17

What does Wiggers diagram show?

Answer 17

Wiggers diagram typically plotted for the left side of the heart shows hows the pressure and volume changes in the aorta, LV and LA during the cardiac cycle and how it relates to the ECG and heart sounds

Question 18

How does the function of the valves relate to the heart sounds?

Answer 18

The ‘lub’ sound (1st sound) in the cardiac cycle corresponds to the closing of the AV valves (tricuspid and mitral).
The ‘dub’ sound (2nd sound) in the cardiac cycle corresponds to the closing of the semilunar valves (pulmonary and aortic).

Question 19

Wiggers diagram is used to show?

Answer 19

The changes in pressure (in aorta, LV and LA) and volume (LV only) and the relationship to the ECG and sounds (phonocardiogram) in the left side of the heart, conventionally it starts with atrial contraction.

Question 20

Draw Wiggers diagram?

Answer 20

Slide

Question 21

Describes the changes in each stage of the cardiac cycle using Wiggers diagram to help?

Answer 21

1: Atrial systole
- P wave on ECG- atria contraction
- A wave- atrial pressure rises due to atrial systole
- Final 10% of ventricle filling-atrial kick
- Tricuspid and mitral valves are open
2: Isolvumetric contraction
- QRS on ECG- ventricle depolarisation
- Rapid increase in ventricular pressure
- C wave (atrial pressure curve)- mitral valve closes when ventricular pressure exceed atrial pressure causing atrial pressure to increase slightly
- Closing of valve results in 1st sound ‘lub’ sound
- Isometric volume as no change in volume as the valves are close
- All valves closed
3: Rapid ejection
- Just after QRS complex
- X descent - atria get pulled downwards decreasing the pressure
- Ejection begins when the pressure in the ventricles exceeds pressure in the aorta- aortic valve opens
- Rapid increase in the pressure in the aorta
- Pressure in ventricle still increases as the ventricle are contracting but the volume decreases as ejected into aorta
4: Reduced ejection
- T wave- ventricle repolarisation
- V- wave- atria pressure rises due to the continuous venous return
- Pressure in ventricles and aorta begins to decrease
- Rate of ejection begins to fall
- Pulmonary and aortic valve are open
5: Isovolumetric relaxation
- Dichrotic notch- aortic valve closes, pressure in aorta greater than the pressure in the ventricle brief backflow of blood (supplies coronary arteries)
- Closure of semilunar valves 2nd sound heard ‘dub’ sound
- Rapid decline in ventricular pressure but volume remains the same as all valves are closed
6: Rapid filling
- Y descent- pressure in atria decreases as the mitral valve opens
- volume in ventricle increases as the blood flows into ventricles
- 3rd sound of ventricles filling- normal in children could be a sign of pathology in adults.
- mitral and tricuspid valve is open
7: Reduced filling
- Just before P wave
- Rate of ventricle filling slows down as the ventricles reach diastasis–> relaxed volume
- Ventricles 90% full

Question 22

How can the function of valves go wrong?

Answer 22

• Valve may not open enough, reduced stroke volume, due to stenosis
• Valve doesn’t close all the way maybe leaky when valve should be closed leads to regurgitation.

Question 23

Where can stenosis occur?

Answer 23

Commonly occur on aortic valve and mitral valve.

Question 24

What are the causes of aortic valve stenosis? What are the problems associated?

Answer 24

Can be
- degenerative (senile calcification/ fibrosis)
- congenital (bicuspid form of valve (2 cusps instead of 3)
- Chronic rheumatic fever (autoimmune response to valve, causes inflammation and fusion)
Causes (less blood can get through)
- Left sided heart failure–> sycope (fainting) and angina
- Increased LV pressure –> LV hypertrophy as heart is having to work harder to eject the blood (more resistance)

Question 25

Mitral valve stenosis is caused by what? and leads to what?

Answer 25

-99.9% of cases caused by rheumatic fever –> inflammation due to autoimmune response
- results in fusion of the valves
Causes
- increase LA pressure
- LA dilation –> more blood in atrium –> atrial fibrillation (thrombus formation) OR oesophagus compression (dysphagia–> problems swallowing)
- OR pulmonary oedema, dyspnea and pulmonary hypertension –> RV hypertrophy (higher pressure so gets bigger)

Question 26

What cause aortic regurgitation? What does it result in?

Answer 26

Valve fails to closer properly due to aortic root dilation or valvular damage (rheumatic fever)
Results in:
-Blood flows back into left ventricle during diastole
-Increases stroke volume
-Systolic pressure increase
-Diastolic pressure decrease
-Bounding pulse (head bobbing, Quinke’s sign (nail beds flash red))
-LV hypertrophy as heart having to work harder to eject blood

Question 27

How does mitral valve regurgitation occur?

Answer 27

• Papillary muscles and chordae tendineae become weakened leading to prolapse.
• Due to myxomatous degeneration (CT degeneration), damage due to heart attack,
• left sided heart failure-> LV dilation which stretches heart valve,
• rheumatic fever –> leaflet fibrosis prevents closure
• Blood flows back into atria, increases preload, LV hypertrophy