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BRS Bioregulatory Systems > Cardiac Cycle > Flashcards

Cardiac Cycle Flashcards

1
Q

What are two main phases of a heart beat

A

Diastole-ventricular relaxation,ventricles fill with blood. Lasts 2/3 of each beat

Systole-ventricular contraction ,ventricles generate pressure then eject into arteries. Lasts 1/3 of each beat

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2
Q
  • What is end-diastolic volume?
A

The maximum volume of blood in heart just before ventricles start to contract (at max relaxation of heart)

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3
Q

What is end systolic volume

A

Amount of blood in heart after contraction completed- residual blood left in heart

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4
Q

Stroke volume

A

Voume of blood expelled by the heart in any one cardiac cycle

End-diastolic volume - End-systolic volume = Stroke volume

typical stroke volume in a resting 70 Kg man is 70ml

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5
Q

What is ejection fraction?

A

The fraction of end diastolic volume that is ejected by heart- gives indication of heart function

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6
Q

How is ejection fraction calculated and what is it’s normal range?

A

Stroke volume/End-diastolic volume) x 100 = Ejection fraction

Normal: 52-72%

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7
Q

What would be the ejection fraction range in a patient with heart failure

A

30-35%

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8
Q

7 steps of cardiac cycle

A

Atrial systole
Isovolumetric contraction
Rapid ejection
Slow ejection
Isovolumetric relaxation
Rapid passive filling
Slow passive filling aka diastasis

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9
Q

Atrial systole

A
  • Ventricle already almost full from passive filling driven by pressure gradient
  • Atria contract to ‘top up’ volume of blood in the ventricle
    P wave
    S4 may be heard but abnormal due to forceful contraction of atria to overcome stiff or hypertrophic ventricle
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10
Q

Isovolumetric contraction

A
  • This is the interval where both the AV valves and semi-lunar valves are closed, with the SL valves about to open
  • Due to this, the contraction of ventricles with no volume change occurs
  • Ventricular pressure increases to aortic pressure
    QRS complex
    First lub sound S1 due to closure of atrioventricular valve
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11
Q

Rapid ejection

A
  • As ventricles contract, ventricular pressure exceeds pressure in aorta and pulmonary arteries → semilunar valves open, blood pumped out due to pressure gradient and ventricular volume decreases
  • Opening of aortic and pulmonary valves marks start of phase
    Aortic pressure increases
    No sound made
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12
Q

Slow ejection

A
  • This phase marks end of systole
  • Blood flow from ventricles decreases and ventricular volume decreases more slowly
  • Reduced pressure gradient from ventricles into arteries so semilunar valves begin to close
    T wave
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13
Q

Isovolumetric relaxation

A
  • Semilunar valves shut but AV valves remain closed until ventricular pressure drops below atrial pressure
  • Atrial pressure continues to rise
    Dichrotic notch caused by rebound pressure
    2nd heart sound dub S2 due to semilunar valve closing
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14
Q

What is the rate of pressure decline in the ventricles here determined by and what is this rate called?

A

The rate of relaxation of the muscle fibres

Relaxation regulated largely by the Ca2+ ATPases in the SR membrane

Lusitropy (rate of muscle relaxation)

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15
Q

Rapid passive filling

A

Once intraventricular pressure drops below atrial pressure, AV valves open and atrial blood flows rapidly into ventricles
Isoelectric (flat) on ecg
Abnormal S3 due to severe hypertension or. Mitral incompetent

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16
Q

Slow passive filling aka diastasis

A
  • Ventricular volume fills more slowly
  • Ventricles are able to fill considerably without atrial contraction
  • After this phase cardiac phase restarts with atrial contraction to top up filling of ventricle
17
Q

What are the similarities and differences in blood pressure and volume between left and right ventricles?

A
  • left ventricle pumps blood at a higher pressure than right ventricle
  • However, right ventricle ejects same volume of blood as left, just into a lower pressure circuit
  • Patterns of pressure change are identical in both
18
Q
  • What is the difference between the pulmonary and systemic circuit?
A

Pulmonary circulation moves blood between the heart and the lungs

Systemic circulation moves blood between the heart and the rest of the body

Typical systemic pressure is 120/80

Typical pulmonary pressure is 25/5

19
Q

What is the pulmonary capillary wedge pressure an indirect measure of?

A

Left atrial pressure

20
Q

Why would a pulmonary capillary wedge pressure be measured clinically?

A

Gives an idea of the severity of left ventricular failure and mitral valve stenosis

Both of which are caused by an increase in the left atrial pressure → this increase pulmonary oedema which can be life threatening

Pulmonary artery pressure shows clear diastolic and systolic pressures

21
Q

Explain the pressure volume loop

A
  • We start with A, end-diastolic volume
  • Isovolumetric contraction occurs, causing increase in pressure but not volume change since no valves opened
  • We then encounter aortic pressure, B, causing aortic valve to open
  • Blood goes from ventricle to aorta so ventricular volume will decrease
  • This leads to end-systolic volume, C after pressure goes up then drops slightly due to rapid then slow ejection
  • Then we get isovolumetric relaxation- no change in ventricle volume but drop in ventricle pressure, D
  • We then gradually fill heart again with blood to reach end-diastolic volume and cycle repeats
22
Q

Preload on pressure volume loop

A

Blood filling the ventricles during diastole is determines preload that stretches the resting ventricular muscle

Larger amount of blood returning to heart → increased preload → increased stretch of ventricular muscle → increased force produced

23
Q

What is afterload on the pressure volume loop?

A

The blood pressures in great vessels (aorta and pulmonary artery) represent the afterload

If afterload increases, there’s less shortening of muscle fibres → less able to expel blood from ventricles

24
Q
  • What is the End-systolic pressure volume relationship (ESPVR)? (i.e. what does it show?)
A

Maximum pressure that can be developed by ventricle at any given volume

25
Q

How does the stroke volume and the appearance of the pressure volume loop change (horizontally and vertically) when we increase preload?

A

Increases in preload result in increased stroke volume- this is Frank-Starling relationship

loop gets wider horizontally

26
Q

How does the stroke volume and the appearance of the pressure volume loop change when we increase afterload

A

decreased stroke volume because the amount of shortening of muscle fibres that occurs decreases

loop gets thinner horizontally and taller vertically

27
Q

What are untie for cardiac output

A

L/min

28
Q

Cardiac output formula

A

Cardiac output (L/min)= heart rate (bpm) x stroke volume (L)

29
Q
  • Which 3 factors influence stroke volume?
    -
A

Preload
Afterload
Contractility

30
Q

What is the definition of contractility?

A

Contractile capability (strength of contraction) of heart

  • What is it increased by?Sympathetic stimulation
  • What is the extrinsic mechanism?Changes Ca2+ delivery to myofilaments
31
Q

How does the steepness of the ESPVR line change with increases and decreases in contractility?

A

When more calcium delivered to myofilaments (more sympathetic activity) and so more contractility, we get a steeper ESPVR and vice versa

32
Q

How does the End-Diastolic Volume change during exercise,

A

Increases

Due to increased venous return and respiratory pumps

33
Q

How does the End-Systolic volume change during exercise and what causes this?

A

Decreases

Sympathetic activation of the myocytes increases ventricular contractility

34
Q

How does the increase in arterial pressure during exercise affect the afterload?

A

Increases it

35
Q

Why doesn’t the increase in afterload, reduce the End-Systolic Volume?

A

This effect is offset by the large increase in contractility

36
Q
  • How is the Stroke Volume affected during exercise?
A

Increased End-Diastolic Volume and decreased End-Systolic Volume which leads to an increased Stroke Volume

37
Q

heart rate increases to an extremely high rate, how is the End-Diastolic Volume affected?

A

Decreases because the diastolic filling time can be reduced

BRS Bioregulatory Systems (54 decks)

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