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Cardiology > The Cardiac Cycle > Flashcards

The Cardiac Cycle Flashcards

1
Q

What is preload?

A

Degree of stretch the ventricular wall undergoes when blood fills the ventricle

The greater the preload, the greater the resting length of the ventricualr sarcomeres

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2
Q

What is the Frank Starling Law?

Why does it occur

A

Frank Starling Law: Stroke volume increases in response to an increase in the volume of blood in the ventricles (i.e. increased preload)

WHY:

Increase in preload → increased stretch of sarcomeres → increased overlap of thin and thick filament → increases the amount of cross-bridges that can form → increasing contractility → increased SV

Remember: there is a limit to the benefits

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3
Q

Describe Frank-Starling’s Law in congestive heart failure

A

CHF patients have a right shifted and flattened curve

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4
Q

What is afterload?

A

the resistance that the ventricles must overcome to eject blood

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5
Q

What does afterload depend on?

A
  1. Arterial pressure
  2. Ease of blood flow through the pulmonary and aortic valves

Thus dueing high BP or semilunar valve stenosis there is an increased afterload

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6
Q

What is the End Systolic Volume (ESV)

A

Residual blood remaining in ventricle after it pumps

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7
Q

What is stroke volume?

A

how much blood was pumped out of the ventricle successfully during systole

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8
Q

What is HR

A

BPM

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9
Q

What are the 5 stages of the cardiac cycle?

A
  1. Late Diastole
  2. Atrial systole
  3. Isovolumetric contraction
  4. Ventricular Ejection
  5. Isovolumetric relaxation
  • 1,2,5 are part of ventricular diastole
  • 3,4 are part of ventricular systole
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10
Q

Describe the relative pressures (e.g. atria, ventricle, arteries) and movement of blood in Late diastole

A
  • P(atria) > P(ventricle)
    • Thus passive filling of ventricle
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11
Q

Describe the relative pressures (e.g. atria, ventricle, arteries) and movement of blood in atrial systole

A
  • Atria contract
  • Additional 15% of blood is pumped into the ventricle
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12
Q

Describe the relative pressures (e.g. atria, ventricle, arteries) and movement of blood in Isovolumetric contraction

A
  • Ventricle contract
  • Blood fills sinus of AV valves
    • AV valves close
  • P(ventricle) < P(arteries)
    • Thus semilunar valves stay closed
  • No movement of blood
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13
Q

Describe the relative pressures (e.g. atria, ventricle, arteries) and movement of blood in ventricular ejection

A
  • P(ventricles) finally > P(arteries)
    • blood ejected
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14
Q

Describe the relative pressures (e.g. atria, ventricle, arteries) and movement of blood in isovolumetric relaxation

A
  • Ventricles relax but P(ventricles) > P(atria)
    • Thus AV valves stay closed
  • No movement of blood
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15
Q

Identify what step in the cardiac cycle occurs at the the various deflections on an ECG

A
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16
Q

Describe the events that occur at A

A
  • Aortic valve opens
  • Sudden spike in pressure as blood is initially pumped into aorta
17
Q

Describe the events at B

A
  • Dicrotic notch
  • P(ventricle) < P(aorta)
  • blood in aorta flows backwards towards heart
  • This fills sinuses of aortic valves and closes them
  • Pressure of blood pushing back against the valve causes the spike
18
Q

Describe the events at C

A
  • Ventricular systole
  • P(ventricle) spikes
19
Q

Describe the events at D

A
  • P(ventricle) < P(atria)
  • blood starts to flow passivle form atria to ventricle
  • this slowly increases the pressure in the ventricles
20
Q

What causes heart sound 1

A

Closing of the mitral and tricuspid valves (the atrioventricular valves)

At this point ventricular pressure is higher than atrial pressure

21
Q

What causes heart sound 2

A

Closure of thepulmonic and aortic valves

At this point aortic/pulmonary artery pressure is higher than ventricular pressure

22
Q

How is CO calculated?

A

CO = SV x HR

23
Q

How is SV calculated?

A

EDV - ESV

24
Q

How is the EDV increased (2)

A
  1. Increasing venous return
  2. Decreasing heart rate
    • Increases filling time
25
Q

How is ESV increased (2)

A
  1. Improving contractility
    • Increased sympathetic input
    • Increased circulating adrenaline
    • Increase calcium within myocyte
    • Ionotropic drugs
    • Increase preload
  2. Decreasing the afterload
    • Decreasing arterial blood pressure
    • Repairing stenotic (narrowed) aortic or pulmonary valves (making it easier for the heart to pump blood)
26
Q

How is HR modulated (2)

A
  1. Increased sympathetic tone
  2. Decreased parasymathetic tone
27
Q

What reflex responds to a high BP?

A

Baroreceptor reflex

28
Q

What happens when BP inceases?

A
  1. Stretching of baroreceptorsat theaortic arch and carotid sinus
  2. Opens the Na+ ion channels → increases the rate of AP’s it shoots off → does a number of things:
    1. Causes activation of the cardioinhibitory centre of the parasympathetic nervous system → CO decreased → BP decreased
    2. Inhibits the cardioaccelatory centre of the sympathetic nervous system → CO is decreased → BP decreased
    3. Inhibits the vasomotor centre of the sympathetic nervous system → causing vasodilation of the blood vessels → BP decreased
  3. Homeostasis restored

If blood pressure falls below normal, the opposite of the above happens (1. stimulation of sympathetic nervous system, 2. inhibition of the parasympathetic nervous system, and 3. vasoconstriction)

29
Q

What reflex responds to a low BP?

Why does this work at low BP

A

Chemoreceptors

At a low BP (< 60mmHg) we are going to have an issues with increased levels of carbon dioxide in the systemic circulation as the blood is not going to flow fast enough to remove all the CO2 produced by the tissues

30
Q

Where are the chemoreceptors located?

A
  • Aortic bodies
  • Carotid bodies
31
Q

What do the chemoreceptors sense

A

decrease in O2, increase in CO2, decrease in pH

32
Q

What is the chemoreceptors response when stimulated?

A
  1. Activates respiratory centre
  2. Inhibits the cardioinhibatory centre
  3. Activates the cardioaccelatory centre
  4. Activates the vasomotor centre

Increases O2, decreases CO2, increases pH

Cardiology (6 decks)

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