3. Determinants fo Cardiac Output Flashcards Preview

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Flashcards in 3. Determinants fo Cardiac Output Deck (31):
1

List the determinants of cardiac output.

  • VENOUS RETURN
  • Preload
  • Afterload
  • Contractility
  • HR

2

Energetically, are HR and SV equivalent to increase cardiac output? Explain.

No. SV primarily drives cardiac output b/t it's linked to venous return

3

Equation for work done by heart

Work = force x distance

  • force = directly proportional to pressurization of blood
  • distance = ejection distance (how far fluid is squeezed)

4

Define external work.

Movement of blood from the ventricles to the great vessels (stroke work)

5

Equation for stroke work

Stroke work = arterial pressure x SV

6

Define internal work.

-Work done against structural elements in the heart

-Mostly dissipated as heat

7

What happens to internal and external work when you increase SV? Explain.

Increase SV --> filling more or empying more completely --> maximizes external work (based on stroke work equation) and minimizes internal work

8

For a given SV, which is more energetically costly: an increase in volume or pressure? Why?

PRESSURE.

High BP --> heart has to keep squeezing during isovolumetric contraction --> additional work done on blood that pressurizes it to vessel-damaging pressures --> heart can't contract as far --> lost stroke volume

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9

What happens to the external and internal work when you increase volume load?

External work increases more than internal work

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10

Define preload.

  • Ventricular filling
  • Central venous pressure

11

Define afterload.

Increased aortic pressure

12

What is the effect of preload on SV?

Increased SV

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13

What is the effect of afterload on SV?

Decreased SV

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14

List the 2 venous compartments.

  • Central venous compartment
  • Peripheral venous compartment

15

Central vs. Peripheral venous compartment

CENTRAL:

  • provides preload for ventricular filling
  • always less than 1L

PERIPHERAL:

  • 3.5-4L sitting in peripheral veins
  • 4x as large as central venous compartment at rest

 

16

What is the significance of veins' high compliance?

Can have large changes in volume w/ little change in pressure

17

Where is the majority of the blood volume located? What % of blood volume is this?

60% of blood volume is peripheralized in venous compartment

18

Equation for flow of venous return.

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19

What pressure gradient b/t the venous compartments favors venous return?

  • High peripheral venous pressure 
  • Low central venous pressure

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20

How does muscular contraction enhance venous return?

Contract a muscle —> presses on veins —> no backflow distally b/c of closed valves —> only direction of flow is back to the heart

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21

How does the venous muscle pump affect the volume and pressure of blood it pumps?

  • Amount of blood that gets pumped is proportional to how much muscle you activated
  • Pressure at which it’s pumped out is proportional to how hard you contract that muscle

22

What is the relation b/t ventricular volume and tension?

Pre-loaded resting cardiac muscle length affects the magnitude of developed tension

23

At steady state, venous return equals __?

Cardiac output

24

How does central venous pressure affect venous return? Cardiac output?

  • Decrease venous return
  • Increase cardiac output

25

What does the equilibrium values of central venous pressure tell us?

  • CVP sufficient to stretch the heart for cardiac output
  • CVP low enough against driving pressure of venules to get same amount of drainage from venules

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26

How does afterload affect blood flow?

Increases amount of time isovolumetric contraction lasts --> impedes forward flow --> decreases SV

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27

How does preload affect blood flow?

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28

Define contractility.

How much force of contraction generated for a given unit of preload

29

How does increased contractility affect the heart and blood flow?

For same length and ventricular filling:

  • greater peak tension
  • greater shortening
  • greater SV

30

What are the short and long term ways to increase contractility?

  • Short term: catecholamine (norepinephrine) stimulation

  • Long term: cardiac hypertrophy (increase myofibrils per myocyte)

31

What changes w/ contractile state?

 End Systolic Pressure Volume Relation (ESPVR)

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