Physiology - Cardiac Cycle

Question 1

What are the 5 main events during the cardiac cycle?

Answer 1

1. Passive filling
2. Atrial contraction
3. Isovolumetric ventricular contraction
4. Ventricular ejection
5. Isovolumetric ventricular relaxation. Slide 7

Question 2

What does the P wave on an ECG signify?

Answer 2

Atrial depolarisation, meaning the atria contracts just enough to get the last part of blood into the ventricles. Slide 10

Question 3

What happens during isovolumetric ventricular contraction and when does it start?

Answer 3

Occurs just after the QRS complex.
The ventricular pressure increases until it exceeds atrial pressure and the AV valves shut.
The aortic valve is also shut meaning no blood enters or leaves and tension rises, ‘isovolumetric contraction’. Slide 11

Question 4

When does ventricular ejection occur, what happens and what signifies it on an ECG?

Answer 4

When the ventricular pressure exceeds aortic pressure then the aortic valve opens.
The T wave signals ventricular repolarisation and the blood is pushed out of the ventricles.
When the pressure falls the ventricles relax an dthen the valves shut. Slide 12+13

Question 5

What signifies the 1st and 2nd sounf of the heart beat? (lub-dub)

Answer 5

Lub - AV valves shutting e.g. mitral/tricuspid

Dub - Aortic/pulmonary valves shutting. Slide 11+13

Question 6

What does isovolumetric ventricular relaxation mean?

Answer 6

The ventricle is once sealed off with all valves closed. The tension decreases around a closed volume and once the pressure falls below atrial pressure the AV valves open starting the cycle again. slide 14

Question 7

Why does arterial pressure not fall to 0 during diastole?

Answer 7

Due to the arteries having elastic properties so they recoil. Slide 18

Question 8

If there are ever any changes in the right atrium, where clinically could you see this?

Answer 8

Any problems would be reflected in the JVP. Slide 19