Generating pressure gradients - The Cardiac Cycle Flashcards

1
Q

How do you calculate cardiac output?

A

CO = SV x HR

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2
Q

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

A

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

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3
Q

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

A
CO - cardiac output
ABP - arterial blood pressure
CVP - central venous pressure
TPR - total peripheral pressure
SV - stroke volume
HR - heart rate
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4
Q

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

A

ABP - CVP = CO x TPR

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5
Q

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

A

ABP - CVP = SV x HR x TPR

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6
Q

Why do we need to know about the cardiac cycle?

A

its role in exercise
cardiac catheter
echocardiography

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7
Q

What does the SAN do?

A

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

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8
Q

What does the AVN do?

A

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

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9
Q

what is the mean blood pressure?

A

approx. 90mmHg

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10
Q

What is an average resting heart rate?

A

70bpm

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11
Q

What is the average cardiac cycle time

A

850ms

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12
Q

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

A

Systole - 250ms

Diastole - 600ms

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13
Q

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

A
  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.
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14
Q

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

A

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

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15
Q

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

A
  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)
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16
Q

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

A
  1. Atrial contraction increases P(atrial)

2. Contributes ~5ml to ventricular filling

17
Q

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

A
  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

18
Q

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

A

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

19
Q

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

A
  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

20
Q

What is the path of the cardiac cycle?

A
Ventricular Diastole (isovolumetric relaxation)
Ventricular Diastole (rapid/passive filling)
Ventricular Diastole (atrial systole, ventricular filling)
Ventricular Systole (isovolumetric contraction)
Ventricular Systole (ejection)
21
Q

What is EDV and ESV and the relationship with SV

A

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

22
Q

what does isovolumetric contraction enable us to do?

A

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.

23
Q

What are some normal pressures in the heart?

A
Units - mmHg
AO - 120/80
LA - 8
LV - 120/8
RV - 25/4
RA - 4
PA - 25/10
24
Q

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

A

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.

25
Q

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

A
  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
26
Q

What does the isovolumetric contraction phase mean?

A

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

27
Q

What is the average aortic pressure range?

A

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

28
Q

What is the average ventricular pressure range?

A

0-120 mmHg

29
Q

What is th average atrial pressure range?

A

0-10mmHg