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BS - Cardiovascular System > Cardiac Cycle > Flashcards

Cardiac Cycle Flashcards

1
Q

What is the cardiac cycle?

A

It is all the events associated with the flow of blood through the heart during one heart beat

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2
Q

What are diastole and systole in the cardiac cycle?

A

Diastole - where the heart fills with blood

Systole - where the myocardium contracts and the blood is ejected

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3
Q

How long does one cardiac cycle last?

What is normal resting heart rate?

A

One cardiac cycle lasts 0.8 seconds

A normal resting heart rate is 55 - 60 beats per minute

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4
Q

What are the three phases of the cardiac cycle?

A
  1. diastole
  2. isovolumetric contraction
  3. systole
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5
Q

What are the stages involved in diastole?

A

It is the phase where the ventricles fill with blood:

  1. isovolumic relaxation
  2. rapid inflow
  3. slow inflow (diastasis)
  4. atrial systole
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6
Q

What is the role of the valves in diastole?

A

They prevent backflow of blood and ensure that blood goes to the correct place

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7
Q

What are the 4 heart valves?

A
  1. pulmonary valve
  2. aortic valve
  3. tricuspid valve
  4. mitral (bicuspid) valve
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8
Q

What is involved in diastole?

A

The filling of both the left and right ventricles with blood

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9
Q

How does blood flow into the ventricles change as diastole progresses?

A
  1. passive filling as blood from the atria enters the ventricles
  2. atrial systole involves contraction of the atria to ensure all blood enters the ventricles
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10
Q

What is heart sound 1 of the heart beat?

When does it occur?

A

Closing of the mitral/tricuspid valve

It occurs at the beginning of ventricular systole

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11
Q

What is heart sound 2 of the heart beat?

When does it occur?

A

Closing of the aortic and pulmonary valves

It occurs at the beginning of diastole

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12
Q

When does a split heart sound occur?

A

When there is increased venous return into the right atrium and ventricle

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13
Q

What is a split heart sound and why does it occur?

A

During systole, it takes longer for all of the blood to move from the RV into the pulmonary artery

The pulmonary valve shuts slightly later than the aortic valve

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14
Q

What structures prevent the heart valves from inverting?

A

The papillary muscles in the ventricles attach to the cusps of the valves via chordae tendineae

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15
Q

What is the consequence to the heart valves when damage to the myocardium causes tissue loss?

A

The papillary muscle may be damaged or the chordae tendineae may be ruptured

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16
Q

How is the movement of the tendinous cords influenced in atrial systole?

A

Blood flows down a pressure gradient from the atria into the ventricles

The tendinous cords are relaxed as the pressure is low

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17
Q

What happens to the tendinous cords as the ventricles contract and why?

A

As ventricles contract, valves are pushed upwards to prevent blood flowing back into the atria

The increase in blood pressure in the ventricles pulls the tendinous cords taut

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18
Q

What cardiovascular condition usually leads to damage to the chordae tendineae?

A

myocardial infarction

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19
Q

When does mitral regurgitation occur and what does it allow for?

A

It occurs when blood leaks backwards through the mitral valve each time the LV contracts

This allows blood to flow in 2 directions during contraction

20
Q

In an ECG, what does ST elevation and ST depression show?

A

ST elevation is typical of a myocardial infarction

ST depression shows myocardial ischaemia

21
Q

What is the frequency of fibrillation of the atria and ventricles?

Why are they different?

A

Atria can fibrillate up to 300 beats per minute

The ventricles can fibrillate up to 110-120 beats per minute due to the delay in the AV node

22
Q

What happens in a pressure-volume loop during the P wave?

A

P wave shows atrial depolarisation as the atria contract

Atrial pressure increases

Blood flows from the atria into the ventricle, leading to a quick increase in ventricular volume

23
Q

What happens in a pressure-volume loop during the QRS complex?

A

QRS complex shows ventricular depolarisation as the ventricles contract

There is an increase in ventricular pressure and decrease in ventricular volume

This is due to blood being ejected out of the ventricles

24
Q

When does an isovolumetric contraction occur?

A

When the pressure increases but the volume stays the same

25
Q

What are the different stages shown on a pressure-volume loop?

A
  1. isovolumic contraction
  2. ejection
  3. isovolumic relaxation
  4. rapid inflow
  5. diastasis
  6. atrial systole
26
Q

What happens during the isovolumic contraction stage of the pressure-volume loop?

A

For a brief period of time, all of the valves are shut

When all the valves are shut, the pressure is increasing but the volume stays the same

27
Q

What value does ventricular pressure build up to in the isovolumic contraction phase?

What is significant about this value?

A

80 mmHg

This is the point at which ventricular pressure rises above aortic pressure

28
Q

What happens once ventricular pressure rises above the pressure in the aorta?

A

The aortic valve opens and the ejection phase begins

29
Q

What occurs during isovolumetric relaxation?

A

All of the valves are shut

The pressure is decreasing but the volume stays the same

30
Q

What does the T wave show on an ECG?

A

Ventricle repolarisation as the ventricles start to fill with blood again

31
Q

What stage is shown during the T-wave on the pressure-volume loop?

A

The rapid inflow stage

This is where ventricular pressure decreases and ventricular volume increases

32
Q

What happens during diastasis and when does it occur?

A

It occurs mid-diastole

The initial passive filling of the ventricles has slowed down, but the atria have not yet contracted to complete active filling

33
Q

What is stroke volume?

A

The volume of blood ejected from the left ventricle with each cardiac cycle

34
Q

At rest, what is average stroke volume?

A

around 70 ml

35
Q

What is cardiac output?

A

The volume of blood ejected from the left ventricle each minute

36
Q

What is normal cardiac output at rest?

A

Around 5 L/min

37
Q

What is the equation for cardiac output?

A

cardiac output = heart rate x stroke volume

38
Q

What is blood pressure?

A

the pressure of the blood in the circulatory system

39
Q

Why is blood pressure often measured for diagnosis?

A

It is closely related to the force and rate of the heart beat

It is also related to the diameter and elasticity of the arterial walls

40
Q

What is the equation for blood pressure?

A

Blood pressure =

heart rate x stroke volume x TPR

This is the same as

cardiac output x TPR

41
Q

What is total peripheral resistance?

A

The resistance offered by the systemic circulation

This is the resistance of the arteries to the flow of blood

42
Q

What is the resistance offered by the pulmonary circulation?

A

pulmonary vascular resistance (PVR)

43
Q

How long does the PR interval last for?

A

from 0.12 to 0.20 seconds

44
Q

How long does the QRS complex last for?

A

from 0.08 to 0.12 seconds

45
Q

How long does the QT interval last for?

A

0.35 to 0.43 seconds

BS - Cardiovascular System (20 decks)

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