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Cardiovascular > EXAM #1: CARDIAC OUTPUT > Flashcards

EXAM #1: CARDIAC OUTPUT Flashcards

1
Q

What is the definition of CO?

A

Volume of blood ejected from the heart per minute

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2
Q

What is the Stroke Volume?

A

Volume of blood ejected from the heart per beat

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3
Q

What is the equation for CO?

A

CO= HR x SV

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4
Q

What is the normal CO?

A

5 L/min

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5
Q

What is the Cardiac Index?

A

CO x SV x m2

m2= unit of body surface area

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6
Q

What is the normal Cardiac Index?

A

3 L/min/m2

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7
Q

What are the major contributions to the EDV?

A

1) Atrial kick (20%)

2) Ventricular filling (80%)

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8
Q

How does a-fib affect CO?

A

Loss of atrial kick lowers CO

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9
Q

What is the preload?

A

End diastolic volume

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10
Q

What are the three major determinants of SV?

A

1) EDV
2) Ventricular contractility
3) Afterload

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11
Q

What is preload?

A

Tension exerted on the cardiac ventricular muscle when it begins to contract

Directly related to EDV

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12
Q

Draw and label the ventricular pressure volume loop.

A

N/A

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13
Q

What is afterload?

A

Pressure the ventricle has to expel blood against

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14
Q

Draw the ventricular pressure volume loop with an increase in afterload.

A

N/A

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15
Q

What is the End Systolic Volume (ESV)?

A

Volume of blood left in the ventricle after systole

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16
Q

What are the three major determinants of ESV?

A

1) Preload (determines contractility)
2) Ventricular contractility
3) Afterload

17
Q

What is the effect of increased preload on stroke volume?

A

Increased preload will INCREASE stroke volume TO A POINT

18
Q

What is the Frank-Starling Law of the Heart?

A

Ventricular contractility is determined by EDV

  • Increased EDV= increased contractility
  • Decreased EDV= decreased contractility
19
Q

What is the mechanism of the Frank-Starling Law of the heart?

A

Myocardial sarcomere length determines the sensitivity to Ca++

  • Increased length= earlier contraction
  • Decreased length= later contraction
20
Q

What happens with inadequate preload?

A

Decreased CO and hypotension

21
Q

What can happen with excessive preload?

A

Decompensation and decreased CO

Remember, the contractility only increased with increased EDV TO A POINT

22
Q

What happens to SV with increased afterload?

A

SV DECREASES with increased afterload

23
Q

What is the ANREP effect?

A

Aortic pressure elevates abruptly and leads to a POSITIVE INOTROPIC effect within 1-2 minutes

Think the hand grip maneuver

24
Q

What is the mechanism of the ANREP effect?

A
  • Increased LV wall tension
  • Increases Na+
  • Increases Ca++ sensitivity
  • Increased myocardial contraction
25
Q

What happens to SV with increased contractility?

A

Increased SV

26
Q

What does a sympathetically activated state i.e. excersicse do to the Frank-Starling Curve?

A

Shifts up and left

Less stretch/volume is needed for the same CO

27
Q

How is the Frank-Starling curve shifted in HF?

A

Down and to the right

More stretching/ volume is needed compared to normal to produce the same increase in CO

28
Q

How does hypoxia/ hypercapnia alter myocardial contractility?

A

Reduces contractility

29
Q

What is the force-frequency relationship or the heart called?

A

1) “Bowditch Phenomenon”
2) Treppe Phenomenon

Increased HR= increased contractility

30
Q

What factor opposes the Bowditch Phenomenon?

A

Decreased ventricular filling

Note that up to 180 bpm CO will be normal despite decreased ventricular filling

31
Q

How is CO measured in practice?

A

Pulmonary Artery Catheterization (PAC) thermodilution with cold fluid bolus

32
Q

How is PAC with thermodiluation performed?

A
  • Catheter into the PA
  • Cold saline injected and exits a hole in catheter in RA
  • Temp sensor in PA

Time it takes for temp. to return to normal is how the CO is determined

33
Q

Is a small curve or a large curve with the PCA thermodiluation indicative of a larger CO?

A

Small curve= larger CO

Cardiovascular (38 decks)

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