Cardiac Cycle (Flipped)

Question 1

Define cardiac cycle.

Answer 1

The movement of blood through the heart due to pressure changes generated by mechanical activity, which itself is generated by electrical activity.

Question 2

How are pressure and volume changes of the heart measured?

Answer 2

By inserting cardiac catheters into the heart.

Question 3

What is the equation for arterial blood pressure?

Answer 3

stroke volume * heart rate * total peripheral resistance.

or

cardiac output * total peripheral resistance.

Question 4

What proportion of the cardiac cycle is taken by diastole at resting heart rate?

Answer 4

2/3.

Question 5

Why is left ventricular pressure greater than right ventricular pressure?

Answer 5

Because the left ventricular wall muscle is thicker.

Question 6

If the pressure between two heart chambers is the same, what can be said about the valve that separates them?

Answer 6

The valve is open.

Question 7

Why is blood flow able to flow passively into the left ventricle without atrial contraction?

Answer 7

Because the pressure in the pulmonary vein is greater than both the atrial and ventricular pressure.

Question 8

At rest, what contribution does left atrial contraction make to left ventricular filling?

Answer 8

5ml.

Question 9

Why must the atria must contract with a greater force when heart rate is increased?

Answer 9

In order to offset the loss of passive ventricular filling that arises from a decreased length of diastole.

Question 10

What is the pressure difference between the ventricular and atrial pressures when the AV / mitral valve closes?

Answer 10

As soon as ventricular pressure and atrial pressure > 0.

Question 11

Define isovolumetric contraction.

Answer 11

The phase of the cardiac cycle where the ventricles contract whilst both the AV valve and aortic / pulmonary valves are closed.

Question 12

Is left ventricular pressure higher or lower than aortic pressure before isovolumetric contraction?

What about after isovolumetric contraction?

Answer 12

Left ventricular pressure is lower than aortic pressure before isovolumetric contraction but is higher than aortic pressure after isovolumetric contraction.

Question 13

How does aortic pressure change during ejection of blood through the aorta?

How does this affect the position of the aortic valve during ejection?

Answer 13

• Aortic pressure becomes greater than ventricular pressure halfway through ejection.
• The aortic valve does not close during ejection as the momentum of blood keeps the aortic valve open (energy of blood from the ventricle is still greater than the energy in the aorta).

Question 14

During ventricular diastole, is the pressure in the ventricle higher or lower than that in the atrium?

How does this affect the position of the AV valve during ventricular diastole?

Answer 14

• Ventricular pressure is still higher than atrial pressure during ventricular diastole.
• This means that the AV valve remains closed during ventricular diastole.

Question 15

Define isovolumetric relaxation.

Answer 15

The phase of the cardiac cycle where the ventricles relax whilst both the AV valve and aortic / pulmonary valves are closed.

Question 16

List the phases of ventricular systole and diastole.

Answer 16

Ventricular systole:

1 - Isovolumetric contraction.

2 - Ejection.

Ventricular diastole:

1 - Isovolumetric relaxation.

2 - Rapid / passive filling.

Question 17

Which events cause the ‘lub-dub’ sound of a heart beat?

Answer 17

• ‘Lub’ is caused by the AV valves closing.

- ‘Dub’ is caused by the semilunar valves closing.

Question 18

What is the average range of aortic pressure between systole and diastole?

Answer 18

• 120mmHg for systole.

- 80mmHg for diastole.

Question 19

What is the average range of left ventricular pressure between systole and diastole?

Answer 19

• 120mmHg for systole.

- 4mmHg for diastole.

Question 20

What is the average range of left atrial pressure between systole and diastole?

Answer 20

• 10mmHg for systole.

- 0mmHg for diastole.

Question 21

What is the average range of left ventricular volume between systole and diastole?

Answer 21

• 120ml for diastole.

- 50ml for systole.

Question 22

Define stroke volume.

Answer 22

End diastolic volume - end systolic volume.

Question 23

Why is it important for there to be residual volume left over at the end of ventricular diastole?

Answer 23

To allow for an increase in stroke volume if necessary.

Question 24

Why does atrial pressure increase slightly during ventricular systole?

Answer 24

Because the AV valve bulges back from the contracting ventricle into the atrium.

Question 25

Why does left atrial pressure increase at a slow and constant rate during ventricular ejection?

Answer 25

Because blood is passively filling the atrium from the pulmonary vein, but the AV valve is closed.

Question 26

How does aortic valve closure affect pressure in the aorta?

Answer 26

Aortic valve closure causes a slight bump in aortic pressure.

Question 27

What proportion of ventricular systole is taken by isovolumetric contraction?

Answer 27

50/250ms.

Question 28

What proportion of ventricular diastole is taken by isovolumetric relaxation?

Answer 28

80/600ms.

Question 29

At which heart rate is ventricular filling significantly compromised?

Answer 29

180bpm.

Question 30

What is the average range of right atrial pressure between systole and diastole?

Answer 30

• 4mmHg for systole.

- 0mmHg for diastole.

Question 31

What is the average range of right ventricular pressure between systole and diastole?

Answer 31

• 25mmHg for systole.

- 4mmHg for diastole.

Question 32

What is the average range of pulmonary artery pressure between systole and diastole?

Answer 32

• 25mmHg for systole.

- 10mmHg for diastole.