Cardiac cycle

Question 1

What is the sequence of events that leads to volume changes in the heart, starting with the initiation of an AP?

Answer 1

Electrical activity —> Mechanical activity —> Pressure changes —> Volume changes

Question 2

How long does one cardiac cycle last?

Answer 2

850ms

Question 3

What is the average HR?

Answer 3

70bpm

Question 4

Which part of the cycle allows for an increase in HR?

Answer 4

Diastole

Question 5

What happens to a chamber when the surrounding muscle contracts?

Answer 5

The pressure will increase proportionally to the mass of muscle

Question 6

When do valves open?

Answer 6

When a pressure gradient is present across the valve, due to different pressures in the chambers in separates.

Question 7

What is the pressure gradient dependent on?

Answer 7

Pressure and energy of the blood

Question 8

Which way does blood flow?

Answer 8

DOWN the pressure gradient

Question 9

What is the difference in the chambers when the valve is open versus when it is closed?

Answer 9

When the valve is open the pressure changes in the chambers are equal and occur together. When the valve is closed the pressures can be different and alter independently. The pattern of changes on L and R occur at the same time but to difference quantities.

Question 10

What are the stages of ventricular diastole?

Answer 10

Isovolumetric relaxation
Rapid filling of ventricles
Atrial systole and ventricular filling

Question 11

What pressure changes and flow occur during ‘rapid filling of the ventricles’ in ventricular diastole?

Answer 11

1) AV valve open allowing ventricles to fill as blood flows down the gradient from veins to ventricle = Pvein > Patrial > Pventricular
2) Aortic valve is closed to ensure blood doesn’t leave until ventricle is full = Paortic > Pventricular

Question 12

What changes occur during ‘artial systole’?

Answer 12

Atrial contraction increased Patrial to contribute 5ml into ventricular filling

Question 13

When is atrial systole important?

Answer 13

During high HRs

Question 14

What are the stages of ventricular systole?

Answer 14

Isovolumetric contraction

Ejection

Question 15

What events occur during isovolumetric contraction?

Answer 15

Ventricular contraction increases Pventricular so AV valve closes as Pvent > Patrial.
Aortic valve remains shut as Paortic > Pvent.
As the chamber is completely closed off the pressure in the chamber rises with contraction without any changes in volume.

Question 16

What events occur during ejection?

Answer 16

The aortic valve opens when Pvent exceeds Paortic.
Both the ventricular and aortic pressure now begin to rise at the same time as the chambers are continuous.
The atria begin to fill slowly.

Question 17

What events occur during isovolumetric relaxation?

Answer 17

1) Relaxation of the ventricles causes a rapid drop in Pvent. The momentum of blood slows and the pressure gradient is lost.
2) Aortic valve closes as Paortic > Pvent
3) AV valve closed as Pvent still > Patrial
4) As the Pvent continues to fall and the atrium fills, Patrial will eventually be > Pvent opening the AV again for rapid filling.

Question 18

What is the definition of SV?

Answer 18

SV is the volume of blood pumped out of the left ventricle per beat.
SV = EDV - ESV
SV = 70ml

Question 19

What is the EDV?

Answer 19

End diastolic volume is the volume in the ventricle after filling. L.EDV = 120ml

Question 20

What is ESV?

Answer 20

End systolic volume is the volume remaining in the ventricle after systole. L.ESV = 50ml

Question 21

What is important about ESV reserve?

Answer 21

The reserve after systole allow for an increase in SV if required.

Question 22

Why can HR increase without compromising ventricular filling?

Answer 22

As heart rate increases the cardiac cycle shortens, initiating the next P wave sooner. The P wave can move far to the left before compromising ventricular filling as most filling occurs at the BEGINNING OF DIASTOLE.

Question 23

When does most filling occur?

Answer 23

At the beginning of diastole

Question 24

What is diastolic pressure?

Answer 24

The pressure in the aorta immediately BEFORE the aortic valve opens = lowest pressure

Question 25

What creates S1 sound?

Answer 25

The first heart sound is produced as AV valve closes

Question 26

When does most ejection occur?

Answer 26

At the beginning of systole as ejection slows as the volume in the ventricles decreases.

Question 27

How does the blood continue to eject in systole if it slows as the volume decreases?

Answer 27

The momentum from the contraction keeps the blood moving whilst the energy gradient keeps the valve open.

Question 28

What produces the S2 sound?

Answer 28

The second sound is produced by closure of the aortic valve.

Question 29

Why does the R ventricle have less muscle mass than the L?

Answer 29

The pulmonary circulation is shorter and has wider vessels so the vascular resistance is lower. This means less pressure is needed to drive CO, so the muscle doesn’t need to be as thick.

Question 30

Why does the left ventricle require a higher muscle mass?

Answer 30

The systemic circulation is long and contains narrow vessels, so the TPR is high. This means a large pressure is required for CO, meaning the muscle needs to be thicker to create a greater force.

Question 31

As the pressures changes on each side of the heart are different, does this affect the volume ejected?

Answer 31

No, the volume changes on the L and R side are equal to prevent build up and HF.