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CVS > 3. Mechanical Properties of the Heart 2 > Flashcards

3. Mechanical Properties of the Heart 2 Flashcards

1
Q

What is diastole and systole?

A
  • Diastole: ventricular relaxation - ventricles fill with blood (4 sub-phases)
  • Systole: ventricular contraction - blood pumped into the arteries (2 sub-phases)
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2
Q

What happens during the diastole before excitation?

A
  • Late, slow filling
  • Atrial contraction
  • Allows the topping up of ventricular volume
  • End diastolic volume (EDV) - volume in ventricles just before contraction starts (maximum blood for cardiac cycle and determines how stretched the muscle fibres are before contraction)
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3
Q

What happens during systole?

A
  • Period of contraction but no change in volume - isovolumetric contraction
  • Pressure builds up in the ventricles but blood isn’t expelled until pressure gets to the point where it overcomes afterload
  • Period of ventricular ejection
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4
Q

What happens during diastole after excitation?

A
  • Isovolumetric ventricular relaxation - aortic valve closes and mitral valve opens
  • Ventricular muscle decreases its tension, without lengthening so volume remains unaltered
  • Rapid filling
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5
Q

What is the stroke volume and ejection fraction?

A
  • SV = EDV - ESV (blood expelled from the ventricle)
  • EF = SV/EDV (proportion of the end diastolic volume pumped out of the heart, normally about 65%, exercise 80%, heart failure 35%)
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6
Q

What 7 events can the cardiac cycle be split into?

A
  • Atrial systole
  • Isovolumetric contraction
  • Rapid ejection
  • Reduced ejection
  • Isovolumetric relaxation
  • Rapid ventricular filling
  • Reduced ventricular filling
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7
Q

What happens during atrial systole (physically and ECG)?

A
  • Just before, blood flows passively through open AV valves into ventricles
  • SA node => atria contract
  • Atrial systole pushes more blood into ventricles
  • Left side at higher pressure than right
  • Jugular pulse - small pulse in jugular vein due to atrial contraction pushing some blood back up the jugular vein
  • P wave - atrial depolarisation
  • S4 - abnormal heart sound caused by valve incompetency (leading to turbulent flow) happens at this time
  • S4 occurs with pulmonary embolism, congestive heart failure and tricuspid incompetence
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8
Q

What happens during isovolumetric contraction (physically and ECG)?

A
  • Between AV valves closing and semi-lunar valves opening
  • Ventricles sealed off
  • Ventricles start to contract against closed valves - no volume change = isovolumetirc
  • Rapid increase in pressure
  • First heart sound (S1) occurs - closing AV valves (lub)
  • Ventricular pressure > aortic pressure = afterload
  • Aortic valve opens - blood ejected from ventricles - end of isovolumetric contraction

• QRS complex - ventricular depolarisation

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9
Q

What happens during rapid ejection (physically and ECG)?

A
  • Aortic and pulmonary valves open
  • End of isolvolumetric contraction (afterload) marks the start of rapid ejection
  • Semi-lunar valves open - ventricular volume decreases
  • ‘c wave’ seen in atrial pressure = right ventricular contraction pushing the tricuspid valve into atrium - small wave into jugular vein
  • Aortic pressure increases in line with ventricular pressure
  • No closing valves - no sounds

• No wave on ECG

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10
Q

What happens during reduced ejection (physically and ECG)?

A
  • End of systole
  • Ventricular pressure falls as blood leaves
  • Aortic and pulmonary pressure > ventricular pressure
  • Valves will begin to close

• T wave - ventricular repolarisation

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11
Q

What happens during isovolumetric relaxation (physically and ECG)?

A
  • Beginning of diastole
  • Aortic and pulmonary valves shut
  • AV valve remains shut
  • No change in ventricular volume - pressure decreases - isovolumetric relaxation
  • ‘v wave’ in the atrial pressure caused by blood pushing the tricuspid valve and giving a second jugular pulse
  • Dichrotic notch - small, sharp increase in aortic pressure - rebound pressure against aortic valve as the distended aortic wall relaxes after being stretched while ventricles contracted
  • Second heart sound (S2) - aortic and pulmonary valves close - (dub)
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12
Q

What happens during rapid ventricular filling (physically and ECG)?

A
  • AV valve opens and blood flows rapidly from atria to ventricles
  • Ventricular volume increases
  • Atrial pressure decreases
  • Passive

• S3 - abnormal third heart sound

  • can signify turbulent ventricular filling
  • can be due to severe hypertension (leaking valve) or mitral incompetence (calcification of valve)
  • ventricular gallop
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13
Q

What is diastasis?

A
  • Slow filling of the ventricles
  • No changes in ECG and no heart sound
  • Information can be shown on Wiggers diagram
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14
Q

What is the difference in the volume of blood that the right and left ventricles eject?

A
  • Same volume

* Lower pressure on right

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15
Q

What are the normal systemic and pulmonary blood pressure values?

A
  • Systemic - 120/80mmHg

* Pulmonary - 25/5mmHg

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16
Q

What is pulmonary artery wedge pressure (PAWP) and how can you measure it?

A

• Preload on the left side of the heart

  • Insert catheter with pressure tip into a large vein => right atrium => right ventricle
  • Diastolic pressure rises in pulmonary artery as you have the valve closing
  • Balloon at the end prevents blood from passing
  • Pressure changes further up the pulmonary system => left atrium, measured distal to the balloon
17
Q

What might an elevated pulmonary artery wedge pressure (PAWP) indicate?

A
  • Problems with left side of heart
  • Particularly left atrium
  • Problems with mitral valve
18
Q

What does a pressure-volume loop show?

A
  • Ventricular (LV) pressure (y-axis) agasint ventricular volume (x-axis)
  • Point 1 (bottom right) - EDV, large ventricular volume, no pressure yet, preload
  • Point 2 - Isovolumetric contraction - increased pressure, no change in volume, afterload just after P2 when LV encounters aortic pressure
  • Point 2 to 3 (stroke volume) - ventricles expel blood, volume decreases, ventricular pressure rises then falls (curves back)
  • Point 3 - ESV
  • Point 4 - low pressure due to isovolumetric relaxation, same volume
  • Heart refills back to point 1
19
Q

How does the pressure-volume loop fit into the Frank-Starling relationship when increasing the amount of blood flowing back to the heart?

A
  • Point 1 and 2 move further right
  • Preload increases (Point 1, related to passive force, elastic recoil) - so EDV increases
  • Point 2 further from point 3 so stroke volume increases
  • End systolic PV line - active force curve of FSr up to point 3 (ESV)
20
Q

How does the pressure-volume loop fit into the Frank-Starling relationship when increasing the afterload?

A
  • Decreased shortening as working against increased afterload
  • Decreased stroke volume (P3 and 4 move right) so ESV (P3) is higher
  • Ventricular muscle has to work harder to eject blood against the higher pressure
  • When afterload is increased, more pressure is needed to open the aortic valve - Point 2 moves up (y direction)
  • Point 1 remains the same as EDV is the same
  • End systolic PV line from active curve is longer
21
Q

How can you change the stroke volume?

A
  • Changing the amount of blood returning to the heart
  • Changing the arterial pressure
  • i.e. preload and afterload
  • Altering contractility (force of contraction) e.g. adrenaline
22
Q

What is contractility, how can it be measured and increased?

A
  • Contractile capability of heart
  • Measured using ejection fraction
  • Increased by sympathetic stimulation
23
Q

How does a change in contractility change the ESV PV lines?

A
  • Increased - more blood pumped out, stroke volume increases, P3 moves left, ESV PV line is steeper
  • Decreased - less blood pumped out, stroke volume decreases, P3 moves right, ESV PV line is shallower
  • P1 and 2 don’t change
24
Q

What happens to contractility and the PV relationship during exercise?

A
  • Increased sympathetic activity => contractility
  • Changes in peripheral circulation (e.g. venoconstriction and muscle pump) - more blood returned to the heart - End diastolic volume increases (P1 and 2 are pushed right)
  • Increased contractility - P3 and 4 are pushed left
  • Therefore, increased stroke volume

CVS (21 decks)

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