Generating pressure gradients - The Cardiac Cycle

Question 1

How do you calculate cardiac output?

Answer 1

CO = SV x HR

Question 2

What is the relationship between cardiac output, blood pressure and resistance?

Answer 2

CO = blood pressure ( ABP - CVP) / resistance (TPR)

Question 3

What do CO, ABP, CVP, TPR, SV and HR stand for?

Answer 3

CO - cardiac output
ABP - arterial blood pressure
CVP - central venous pressure
TPR - total peripheral pressure
SV - stroke volume
HR - heart rate

Question 4

what is the relationship between CO, TPR, ABP, and CVP?

Answer 4

ABP - CVP = CO x TPR

Question 5

what is the relationship between SV, HR, TPR, ABP, and CVP?

Answer 5

ABP - CVP = SV x HR x TPR

Question 6

Why do we need to know about the cardiac cycle?

Answer 6

its role in exercise
cardiac catheter
echocardiography

Question 7

What does the SAN do?

Answer 7

acts as the pacemaker of the heart and is used to generate electrical activity to stimulate contractions of cardiac muscles.

Question 8

What does the AVN do?

Answer 8

Slows the activity of the electrical impulse at the crossing between atria and ventricular stimulation allowing the chambers to fill in an organised manner.

Question 9

what is the mean blood pressure?

Answer 9

approx. 90mmHg

Question 10

What is an average resting heart rate?

Answer 10

70bpm

Question 11

What is the average cardiac cycle time

Answer 11

850ms

Question 12

How long does systole and diastole roughly last during the cardiac cycle?

Answer 12

Systole - 250ms

Diastole - 600ms

Question 13

What principles should be considered to explain how the cardiac cycle works?

Answer 13

1. pressure will increase in a chamber when muscle around it contracts
2. valves will open when there is a pressure/energy gradient across them. The AV valve will open when the P (atrial) > P (ventricular).
3. blood will flow down a pressure/energy gradient from an area of high pressure to an area of low pressure.
4. when valves are open, pressures in neighbouring chambers change together.
5. when valves are close, pressures in neighbouring chambers can be different.

Question 14

Why is the resistance in the right side of the heart ( pulmonary circulation) lower than in the peripheral circulation

Answer 14

Due to the pulmonary circulation path being shorter and having large veins and arteries meaning that there is little resistance

Question 15

Explain in terms of pressure gradients the rapid filling of the left side of the heart during ventricular diastole

Answer 15

1. P(atrial) > P(ventricular) means the A-V valve opens
2. P(ventricular) < P(aortic) means the aortic valve is closed
3. P(pulm vein) > P(atrial) > P(ventricular)

Question 16

Explain how contraction causes blood to move between atria to ventricles during ventricular diastole

Answer 16

1. Atrial contraction increases P(atrial)

2. Contributes ~5ml to ventricular filling

Question 17

Explain how isovolumetric contraction causes blood to move between ventricles to arteries during ventricular systole

Answer 17

1. Ventricular contraction increases P(ventricular)
2. A-V valve closes since P(ventricular) > P(atrial)
3. Aortic valve closed due to P(ventricular) < P(aortic)

therefore there is a closed system

Question 18

What keeps the aortic valve open during ejection when P(aortic) > P(ventricular)

Answer 18

due to the shear energy of the blood quickly flowing past the valve this ensures that the valve remains open

Question 19

Explain how isovolumetric relaxation causes blood to move between veins to atria and ventricles during ventricular diastole

Answer 19

1. Ventricular relaxation decreases P(ventricular)
2. Aoritc valve closes as the energy of blood leaving the ventricle is reduced
3. A-V valve closed since P(ventricular) > P(atrial)
4. leads to a fall in blood pressure in the ventricles so P(ventricular) < P(atrial)

therefore there is a closed system

Question 20

What is the path of the cardiac cycle?

Answer 20

Ventricular Diastole (isovolumetric relaxation)
Ventricular Diastole (rapid/passive filling)
Ventricular Diastole (atrial systole, ventricular filling)
Ventricular Systole (isovolumetric contraction)
Ventricular Systole (ejection)

Question 21

What is EDV and ESV and the relationship with SV

Answer 21

EDV - end diastolic volume (volume of blood in the heart after diastole)
ESV - End systolic volume (volume of blood in the heart after systole)

SV is the different between EDV and ESV

Question 22

what does isovolumetric contraction enable us to do?

Answer 22

allows us to keep the same volume of blood in the chambers but contraction of the cardiac muscle can increase the pressure in the chambers without affecting volume.

Question 23

What are some normal pressures in the heart?

Answer 23

Units - mmHg
AO - 120/80
LA - 8
LV - 120/8
RV - 25/4
RA - 4
PA - 25/10

Question 24

Why does the right ventricular muscle not need to be as thick?

Answer 24

As PVR (pulmonary ventricular resistance) is low, a lower pressure is required to drive CO. The ventricular muscle does not need to be as thick as a result.

Question 25

Explain the stages/points in a P-V loop diagram

Answer 25

1. EDP/V which also accompanied with the closure of the mitral valve.
2. Aortic valve opening
3. ESP/V which also accompanied with the closure of the aortic valve
4. Mitral valve opening

Question 26

What does the isovolumetric contraction phase mean?

Answer 26

Where the volume of blood remains the same in the ventricles but then contraction of the ventricles increases the pressure very rapidly.

Question 27

What is the average aortic pressure range?

Answer 27

80-120 mmHg (120/80 = systolic / diastolic)

Question 28

What is the average ventricular pressure range?

Answer 28

0-120 mmHg

Question 29

What is th average atrial pressure range?

Answer 29

0-10mmHg