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Cardiovascular System > The Cardiac Cycle > Flashcards

The Cardiac Cycle Flashcards

1
Q

What is the cardiac cycle?

A

Sequence of mechanical events that occur during a single heart beat

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2
Q

When are all the chambers of the heart relaxed?

A

Towards the end of diastole

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3
Q

Why do the valves between the atria and ventricles open?

A

Because atrial pressure remains slightly greater than ventricular pressure until the ventricles are fully distended

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4
Q

Why are the pulmonary and aortic outflow valves closed?

A

As pulmonary artery and aortic pressures are greater than ventricular pressure

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5
Q

When does the cardiac cycle begin?

A

When sinoatrial node initiates the heartbeat

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6
Q

What happens in late diastole?

A

Both sets of chambers are relaxed and ventricles fill passively

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7
Q

What happens during atrial systole?

A

Atrial contraction forces a small amount of additional blood into the ventricles

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8
Q

What happens during isovolumic ventricular contraction?

A

First phase of ventricular contraction, pushes atrioventricular valves closed but does not create enough pressure to open the semilunar valves

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9
Q

What happens during ventricular ejection?

A

As ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected

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10
Q

What happens during isovolumic ventricular relaxation?

A

As ventricles relax, pressure in the ventricles falls, blood flows back into the cusps of the semilunar valves and snaps them closed

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11
Q

What completes ventricular filling?

A

Contraction of the atria

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12
Q

At rest, the atria contribute less than 20% of ventricular volume, how does this change with heart rate?

A

This proportion increases with heart rate as diastole shortens and there is less time for ventricular filling

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13
Q

Why does some blood regurgitate into the veins during atrial systole?

A

Because there are no valves between the veins and atria

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14
Q

What reflects atrial systole?

A

The a-wave of atrial and venous pressure traces

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15
Q

What is the name given to ventricular volume after filling? What is the normal volume for this?

A

End diastolic volume (EDV)

120-140mL

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16
Q

What is the value of end diastolic pressure (EDP)?

A

Less than 10mmHg

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17
Q

Where is end diastolic pressure higher?

A

Higher in the left ventricle than in the right due to the more muscular left ventricular wall

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18
Q

What is EDV an important determinant of?

A

The strength of the subsequent contraction

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19
Q

What does ventricular contraction cause?

A

Sharp rise in ventricular pressure

Atrioventricular valves close once this exceeds atrial pressure

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20
Q

What causes the first heart sounds?

A

Closure of atrioventricular valves

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21
Q

What does ventricular depolarisation correspond to on the ECG?

A

QRS complex

22
Q

Why do the outflow valves remain closed during the initial phase of ventricular contraction?

A

Pressure is less than that in the pulmonary artery and aorta so outflow valves remain closed

23
Q

What does increasing pressure during ventricular systole cause?

A

AV valves to bulge into the atria resulting in the small atrial pressure wave (c wave) followed by a fall

24
Q

When do outflow valves open?

A

When pressure in the ventricle exceeds that in its respective artery

25
Q

What is the difference between pulmonary artery pressure and the pressure in the aorta?

A

Pulmonary artery pressure is considerably less than that in the aorta - 15mmHg vs 80mmHg

26
Q

What is the change in flow into the arteries during ejection?

A

Flow into the arteries is initially very rapid but as contraction wanes, ejection is reduced

27
Q

What might rapid ejection be heard as?

A

A murmur

28
Q

When does active contraction cease?

A

During the second half of ejection

29
Q

Ventricular pressure during the reduced ejection phase is slightly less than in the artery, why does blood continue to flow out of the ventricle?

A

Due to momentum

30
Q

What causes the second heart sound?

A

Closure of the semilunar valves

31
Q

What causes closure of the outflow valve?

A

Brief reversal of flow during ejection

32
Q

What is the amount of blood ejected by the ventricle in one beat known as? What is the usual value for this?

A

Stroke volume

70mL

33
Q

What is the name given to the amount of blood left int he ventricles at the end of systole? What is the usual volume for this?

A

End systolic volume

About 50mL

34
Q

What is the name given to the proportion of end diastolic volume that is ejected?

A

Ejection fraction (SV/EDV)

35
Q

Why does atrial pressure rise during the last 2/3 of systole?

A

As a result of filling from the veins

36
Q

What happens to the ventricles following the closure of the outflow valves?

A

Ventricles are rapidly relaxing

37
Q

Why do AV valves remain closed during diastole?

A

As ventricular pressure is still greater than atrial pressure

38
Q

What happens when ventricular pressure falls below atrial pressure?

A

AV valves open and atrial pressure falls as the ventricles refill

39
Q

What is the the refilling of the ventricles assisted by?

A

Elastic recoil of the ventricular walls

40
Q

When might a third heart sound be heart?

A

In young people or when EDP is high

41
Q

What happens to refilling as the ventricles relax completely?

A

Refilling slows

42
Q

What happens to diastole during exercise and with increasing heart rate?

A

Diastole at rest is twice the length of systole, this decreases proportionally during exercise and as heart rate increases

43
Q

What generates the pressure-volume loop?

A

Ventricular pressure plotted against volume

44
Q

What is the shape of the pressure-volume loop affected by?

A

Contractility of the ventricles and factors that alter refilling or ejection

45
Q

What does the bottom dotted line of the pressure-volume loop show?

A

Passive elastic properties of the ventricle

46
Q

What would happen to the curve of the pressure-volume loop is compliance was decreased e.g. as a result of fibrotic damage following an infarct?

A

The curve would be steeper

47
Q

What is the area of the pressure-volume loop an indicator of?

A

Cardiac function

48
Q

What is a phonocardiogram?

A

Chart/record of the sounds made by the heart

49
Q

What causes the first heart sound?

A

Closure of the atrioventricular valves (mitral and tricuspid)

50
Q

What causes the second heart sound?

A

Closure of the semilunar valves (aortic and pulmonary)

51
Q

When does the third heart sound occur? What causes this?

A

Occurs early in diastole
Normal phenomenon in young people and athletes
In older adults it indicates the presence of congestive heart failure
Caused by a sudden deceleration of blood flow into the left ventricle from the left atrium

52
Q

When does the fourth heart sound occur? What causes this?

A

Extra heart sound occurring in late diastole
Due to atrial contraction inducing ventricular filling
Caused by a greatly thickened left ventricular wall e.g. due to hypertension or aortic stenosis, may be an indicator of coronary heart disease

Cardiovascular System (40 decks)

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