EXAM #1: CARDIAC OUTPUT

Question 1

What is the definition of CO?

Answer 1

Volume of blood ejected from the heart per minute

Question 2

What is the Stroke Volume?

Answer 2

Volume of blood ejected from the heart per beat

Question 3

What is the equation for CO?

Answer 3

CO= HR x SV

Question 4

What is the normal CO?

Answer 4

5 L/min

Question 5

What is the Cardiac Index?

Answer 5

CO x SV x m2

m2= unit of body surface area

Question 6

What is the normal Cardiac Index?

Answer 6

3 L/min/m2

Question 7

What are the major contributions to the EDV?

Answer 7

1) Atrial kick (20%)

2) Ventricular filling (80%)

Question 8

How does a-fib affect CO?

Answer 8

Loss of atrial kick lowers CO

Question 9

What is the preload?

Answer 9

End diastolic volume

Question 10

What are the three major determinants of SV?

Answer 10

1) EDV
2) Ventricular contractility
3) Afterload

Question 11

What is preload?

Answer 11

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

Directly related to EDV

Question 12

Draw and label the ventricular pressure volume loop.

Answer 12

N/A

Question 13

What is afterload?

Answer 13

Pressure the ventricle has to expel blood against

Question 14

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

Answer 14

N/A

Question 15

What is the End Systolic Volume (ESV)?

Answer 15

Volume of blood left in the ventricle after systole

Question 16

What are the three major determinants of ESV?

Answer 16

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

Question 17

What is the effect of increased preload on stroke volume?

Answer 17

Increased preload will INCREASE stroke volume TO A POINT

Question 18

What is the Frank-Starling Law of the Heart?

Answer 18

Ventricular contractility is determined by EDV

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

Question 19

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

Answer 19

Myocardial sarcomere length determines the sensitivity to Ca++

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

Question 20

What happens with inadequate preload?

Answer 20

Decreased CO and hypotension

Question 21

What can happen with excessive preload?

Answer 21

Decompensation and decreased CO

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

Question 22

What happens to SV with increased afterload?

Answer 22

SV DECREASES with increased afterload

Question 23

What is the ANREP effect?

Answer 23

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

Think the hand grip maneuver

Question 24

What is the mechanism of the ANREP effect?

Answer 24

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

Question 25

What happens to SV with increased contractility?

Answer 25

Increased SV

Question 26

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

Answer 26

Shifts up and left *Less stretch/volume is needed for the same CO*

Question 27

How is the Frank-Starling curve shifted in HF?

Answer 27

Down and to the right *More stretching/ volume is needed compared to normal to produce the same increase in CO*

Question 28

How does hypoxia/ hypercapnia alter myocardial contractility?

Answer 28

Reduces contractility

Question 29

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

Answer 29

1) "Bowditch Phenomenon" 2) Treppe Phenomenon *Increased HR= increased contractility*

Question 30

What factor opposes the Bowditch Phenomenon?

Answer 30

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

Question 31

How is CO measured in practice?

Answer 31

Pulmonary Artery Catheterization (PAC) thermodilution with cold fluid bolus

Question 32

How is PAC with thermodiluation performed?

Answer 32

- 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*

Question 33

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

Answer 33

Small curve= larger CO