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CVS * > S2 Cardiac Cycle > Flashcards

S2 Cardiac Cycle Flashcards

1
Q

Is systemic or pulmonary circulation high pressure?

A

Systemic circulation is high pressure (pulmonary circulation is low pressure)

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2
Q

What is systole?

A

Contraction and ejection of blood from ventricles

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3
Q

What is diastole?

A

Relaxation and filling of ventricles

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4
Q

What is normal stroke volume at rest?

A

About 70ml blood per beat

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5
Q

When measuring blood pressure, what part of the heart is measured?

A

Aorta (normal BP is 120 systole/80 diastole)

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6
Q

Which side of the heart has the higher blood pressure?

A

The left side

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7
Q

At a heart rate of 70bpm, how many litres of blood are pumped per minute?

A

About 4.9L (average human body has 5L blood)

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8
Q

How long is a cardiac action potential?

A

Longer than skeletal muscle and neuronal action potentials - about 280ms

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9
Q

Describe cardiac muscle…

A
  • interconnected electrically by intercalated discs
  • cells contract in response to an action potential (AP)
  • AP causes a rise in intracellular Ca2+
  • slower AP
  • striated muscle
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10
Q

What are the four valves in the heart?

A
  1. Tricuspid valve (R)
  2. Mitral valve (L)
  3. Pulmonary valve (R)
  4. Aortic valve (L)
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11
Q

When do the heart valves open/close?

A

Open/close dependent on differential blood pressure (BP) on each side

E.g. mitral valve opens if higher BP in L atrium and close when higher BP in L ventricle

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12
Q

What prevents prolapse/inversion of the mitral and tricuspid valves?

A

Papillary muscles (attached to the heart wall) via chordae tendineae (‘strings’ connecting the papillary muscles to the valve)

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13
Q

Why do you want to prevent prolapse of valves in the heart?

A

To prevent regurgitation of blood (blood going backwards)

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14
Q

How is does a conduction signal cause contraction in the heart?

A
  1. Pacemaker cells in the SAN generate an action potential (AP)
  2. Activity spreads over the atria (atrial systole)
  3. The AP reaches the AVN and is delayed (for about 120ms)
  4. The the AVN, excitation spreads down the septum between ventricles
  5. Then spreads through ventricular myocardium (heart muscle) from inner to outer (endocardial to epicardial)
  6. The ventricle contracts from the apex up which forces blood through the outflow valves (aortic/pulmonary valves)
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15
Q

What are the 7 phases of the cardiac cycle?

A
  1. Atrial contraction
  2. Isovolumetric contraction
  3. Rapid ejection
  4. Reduced ejection
  5. Isovolumetric relaxation
  6. Rapid filling
  7. Reduced filling
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16
Q

Which side of the heart is a Wiggers diagram usually plotted from?

A

The left (if using the right, the pattern would be the same but at a lower pressure)

17
Q

What happens in atrial contraction (Phase 1)?

A
  • the atrial pressure rises due to atrial systole (contraction and ejection) - A wave in L atrial pressure curve
  • atrial contraction accounts for last 10% of ventricular filling, the rest fills passively (down pressure gradient)
  • onset of atrial depolarisation - P wave in ECG

AP

18
Q

What happens in isovolumetric contraction (phase 2)?

A
  • mitral valve closes as intraventricular pressure exceeds atrial pressure - C wave in L atrial pressure curve and closing of valve causes the first heart sound, S1
  • there’s a rapid rise in ventricular pressure as ventricle contracts
  • no change in ventricular volume (all valves are closed)
  • onset of ventricle depolarisation - QRS complex in ECG

C
QRS
S1

19
Q

What does isovolumetric mean?

A

No change in volume

20
Q

What happens in rapid ejection (phase 3)?

A
  • ejection begins when intraventricular pressure is higher than aortic pressure, which causes the aortic valve to open
  • atrial pressure initially decreases as the atrial base is pulled downward as the ventricle contracts - X descent in L atrial pressure
  • rapid decrease in ventricular volume as blood is ejected into the aorta

*blood continues to flow into the atria from the venous inputs

X

21
Q

What happens in reduced ejection (phase 4)?

A
  • ventricle repolarises and so tension decreases and the rate of ejection starts to fall - T wave in ECG
  • atrial pressure starts to rise due to continued blood supply from venous input - V wave in L atrial pressure

TV

22
Q

What happens in isovolumetric relaxation (phase 5)?

A
  • intraventricular pressure drops below aortic pressure, small backflow of blood causes aortic valve to close - dicrotic notch in aortic pressure, closure of aortic and pulmonary valves produces heart sound, S2
  • rapid decline in ventricular pressure, volume remains constant as all valves are closed
23
Q

How do you calculate stroke volume?

What is the norm?

A

End Diastolic Volume (EDV) - End Systolic Volume (ESV)

About 70-80ml

24
Q

When do you get the EDV and ESV?

A

EDV - atrial contraction (L ventricular volume in phase 1)

ESV - in isovolumetric relaxation (L ventricular volume in phase 5)

25
Q

What happens in rapid filling (phase 6)?

A
  • intraventricular pressure falls below atrial pressure, the mitral valve opens and rapid ventricular filling begins and atrial pressure decreases - Y descent in L atrial pressure
26
Q

Ventricular filling is normal silent, when is it not silent?

A

In young children there can sometimes be a third heart sound, S3, or in adults with cardiac pathology

27
Q

What happens in reduced filling (phase 7)?

A
  • rate of filling slows down as ventricle reaches relaxed volume
  • any further filling is driven by venous pressure
  • at rest ventricles are about 90% full by the end of phase 7
28
Q

What another name for when the rate of ventricle filling slows down?

A

Diastasis

29
Q

What happens if a heart valve doesn’t open enough?

A

Leads to an obstruction to blood flow and leads to stenosis

30
Q

What happens if a heart valve doesn’t close properly?

A

Lead to back leakage and leads to regurgitation

31
Q

What are two other names for regurgitation?

A

Incompetence and insufficieny

32
Q

What can 3 things can cause aortic valve stenosis?

A
  1. Can be degenerative due to senile calcification/fibrosis
  2. Congenital - bicuspid instead of tricuspid
  3. Chronic rheumatic fever - autoimmune response
33
Q

What 4 things can aortic stenosis cause?

A
  1. Left ventricular hypertrophy - increased pressure, has to pump harder
  2. Syncope - fainting due to rapidly reduced BP
  3. Angina - chest pain when blood supply to heart muscles is restricted
  4. Microangiopathic haemolytic anaemia - reduced blood vessel diameter, RBC forced through and destroyed due to stress
34
Q

What two things can cause aortic valve regurgitation?

A
  1. Aortic root dilation - leaflets pulled apart

2. Valvular (valve) damage - caused by rheumatic fever

35
Q

What happens in aortic valve regurgitation?

A
  • blood flows back in the left ventricle during diastole
  • increases the stroke volume
  • increases the systolic pressure
  • decreased the diastolic pressure
  • causes a bounding pulse and left ventricular hypertrophy
36
Q

What causes mitral valve regurgitation?

A

Normally chordae tendineae and papillary muscles prevent prolapse in systole but…

  • problems with collagen structure in the valve (myxomatous degeneration) weakens the tissue and leads to prolapse
  • damage to papillary muscle after a heart attack
  • left sided heart failure leads to left ventricle dilation which can stretch the the valve
  • rheumatic fever leading to leaflet fibrosis (disrupts seal formation)
37
Q

What does mitral valve regurgitation cause?

A

Blood leaks back into the left atrium which increases the preload - more blood enters left ventricle in subsequent cycles casing left ventricular hypertrophy

38
Q

What is the main cause of mitral valve stenosis?

What can mitral valve stenosis cause?

A

Rheumatic fever - commissural fusion of valve leaflets - harder for blood to flow from the left atrium to the left ventricle

Right ventricular hypertrophy, thrombus formation, dysphagia (swallowing difficulties)

39
Q

How does mitral valve stenosis cause right ventricular hypertrophy?

A

Reduced left atrial emptying increases the left atrial and pulmonary venous pressure - causes pulmonary hypertension.

Pulmonary hypertension results in right ventricular hypertrophy

CVS * (17 decks)

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