Muscle Physics & Heart as a Pump (complete) Flashcards

1
Q

Define cardiac output

A

Volume of blood pumped per minute by left ventricle

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2
Q

What is the equation used for cardiac output?

A

CO = HR x SV

HR: heart rate
SV: stroke volume

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3
Q

Describe the changes in pressure through the cardiac cycle as a function of time

A
  • After diastole & passive filling of LA, atrial contraction => increased atrial pressure => increased ventricular pressure (while mitral valve is open)
  • When mitral valve closes, ventricular contraction starts => ventricular pressure ^ rapidly until it exceeds that in aorta => aortic valve opens
  • Results in slow decrease in ventricular pressure => then faster drop in pressure once it’s below aortic pressure
  • Ventricle continues to relax with both valves closed => pressure falls rapidly
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4
Q

Describe the changes in volume through the cardiac cycle as a function of time

A
  • Ventricle passively fills => Atrium contract towards the end of diastole
  • During isovolumetric contraction phase no ∆ in volume b/c aortic and mitral valves are closed
  • aortic valve opens and blood leaves ventricle => volume decreases
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5
Q

What are the four phase of the cardiac cycle?

A

1) Filling phase
2) Isovolumetric contraction phase
3) Ejection phase
4) Isovolumetric relaxation phase

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6
Q

Describe the filling phase

A
  • At end of diastole, LA has filled w/ blood from pulm vein
  • Contraction triggered by electrical signal originating from SA node
  • As LA starts to contract, atrial pressure ^ => no ∆ in volume
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7
Q

Describe the isovolumetric contraction phase

A
  • As wave of depolarization reaches ventricle, it contracts and ventricular pressure ^
  • This pushes mitral valve closed b/c pressure exceeds that in atrium
  • Ventricular pressure increases rapidly b/c ventricle contracts but blood has no place to go
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8
Q

Describe the ejection phase

A
  • As the ventricle contracts, ventricular pressure exceeds that in aorta => aortic valve opens, blood flow begins
  • Decreased ventricular volume
  • Increased and then decreases in ventricular pressure
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9
Q

Describe the isovolumetric relaxation phase

A
  • As ventricle relaxes, pressure falls
  • when ventricular pressure goes below aortic pressure => aortic valve closes
  • Ventricles continues to relax => both valves closed, pressure falls rapidly (slowly at first)
  • as ventricle relaxes, pressure eventually falls below that of atrium => mitral valve opens
  • cycle begins again
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10
Q

Describe the Frank-Starling Law of the Heart

A
  • Instrinsic mechanism by which the heart adapts to changes in preload
  • Heart response to ^ EDV by increasing force of contraction
  • Heart always functions on ascending limb ventricular function curve
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11
Q

Describe the PV loop diagram

A

Just go look at the ppt

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12
Q

Define stroke volume

A

SV = EDV - ESV

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13
Q

Define ejection fraction

A

Fraction of EDV ejected during systole

EF = SV/EDV = (EDV - ESV)/EDV

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14
Q

Define stroke work

A
  • energy per beat (Joules)
  • corresponds to area inside PV loop diagram

NOT the same for left and right sides of the heart

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15
Q

Define pulse pressure

A

End diastolic pressure - peak systolic pressure

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16
Q

Where are SV, EF, SW, and PP in the PV loop diagram?

A

GO LOOK AT THE PPT

17
Q

Define preload

A

Pressure stretching the ventricle prior to contraction

18
Q

Define afterload

A

resistance the LV must overcome to circulate blood

LV afterload: aortic pressure

19
Q

Define contractility

A
  • Inotropy
  • Force of contraction that’s independent of fiber length
  • describes systolic function of heart
  • sympathetic tone is biggest factor affecting inotropy
  • changes => new ventricular function

Reflects the strength of contraction at any given preload and afterload

20
Q

Describe how altering preload, afterload, or contractility changes ventricular function

A

Increase in preload:

  • results in ^ SV for next beat
  • same ESV, EF ^

Increase in afterload:

  • decrease in SV
  • ventricle has to work harder against the increased aortic pressure => less blood ejected
  • EDV unchanged, EF decreased, ESV increased

∆ in contractility:

  • new starling curves
  • corresponds to greater systolic pressure development
  • Associated with ^ stroke risk
  • ^ SV
21
Q

Describe generally the systolic/diastolic pressure-volume relations and ventricular functions curves

A
  • Pressure and volume changes in LV bound by 2 curves

1) systole pressure-volume relationship
2) end-diastolic pressure-volume relationship

22
Q

Describe the end-diastolic pressure volume relationship

A
  • Pressure-volume relationship during filling of heart BEFORE contraction
  • Corresponds to passive elastic properties of ventricle
  • Slope of EDPVR is shallow in normal physiological range
  • represents PRELOAD on LV
23
Q

Describe the systolic pressure volume relationship

A
  • Curve at peak of isometric contraction
  • Maximum pressure that can be developed for a given set of circumstances
  • Steeper than EDPVR — pressure ^ a lot for small changes in volume
  • Includes active plus passive properties