Cardiac Output & Contractility

Question 1

Define preload.

Answer 1

amt. of blood ready to be pumped

L ventricle end-diastolic volume

Question 2

Define venous pressure

Answer 2

pressure in the vena cava

can be used to estimate atrial pressure

Question 3

Why is ventricular end-diastolic pressure the most accurate estimate of preload?

Answer 3

it takes into account the amt of blood AND the muscle fiber length at the end of diastole

Question 4

Define afterload.

Answer 4

-pressure against which the heart must work to eject blood during systole

Question 5

What happens to afterload if arterial pressure increases?

Answer 5

afterload increases

Question 6

What happens to cardiac output (in the immediate time) as preload increases and as preload decreases?

Answer 6

• cardiac output increases as preload increases

- cardiac output decreases as preload decreases

Question 7

What happens to cardiac output (in the immediate time) as afterload increases and as afterload decreases?

Answer 7

• cardiac output decreases as afterload increases

- cardiac output increases as afterload decreases

Question 8

What happens to cardiac output (in the immediate time) as contractility increases and as contractility decreases?

Answer 8

• cardiac output increases as contractility increases

- cardiac output decreases as contractility decreases

Question 9

What is the positive staircase effect?

Answer 9

• as heartbeats get closer together, less calcium is removed from the cell b/w beats
• thus, contractility increases d/t extra calcium being taken up in the sarcoplasmic reticulum

Question 10

What is the equation for stroke volume?

Answer 10

SV = EDV - ESV

end-diastolic volume minus end-systolic volume

Question 11

What is a normal approximate stroke volume in a healthy adult?

Answer 11

70mL

Question 12

What is the equation for cardiac output?

Answer 12

HR x SV

heart rate multiplied by stroke volume

Question 13

What is a normal approximate cardiac output in a healthy adult?

Answer 13

5 L/min

Question 14

What is the equation for ejection fraction?

Answer 14

EF = SV/EDV

stroke volume divided by end-diastolic volume

Question 15

What is a normal approximate ejection fraction in a healthy adult?

Answer 15

55%

Question 16

What does it mean it something has a positive inotropic effect?

Answer 16

contractility is increased

Question 17

What type of receptors affect cardiac contractility when receiving sympathetic input?

Answer 17

beta-1

Question 18

What is the sympathetic influence on calcium channels in the sarcoplasmic reticulum?

Answer 18

phosphorylated

activated to release calcium

Question 19

What is the sympathetic influence on troponin I?

Answer 19

phosphorylation

-reveals binding sites to allow for muscle ctx

Question 20

What type of receptor affects cardiac contractility when receiving parasympathetic input?

Answer 20

muscarinic

Question 21

True or False: the ventricles receive parasympathetic input

Answer 21

False

Question 22

During what phase of the action potential does parasympathetic input have the most influence?

Answer 22

phase 4

Question 23

What are the ionic effects of parasympathetic input?

Answer 23

• decreases calcium entering the cell during the phase 2 plateau
• increases K+ leaving the cell

Question 24

On a pressure-volume loop diagram, what does point 1 represent and what cardiac activity happens after reaching point 1?

Answer 24

end-diastolic volume

–isovolumetric ctx

Question 25

On a pressure-volume loop diagram, what does point 2 represent and what cardiac activity happens after reaching point 2?

Answer 25

aortic valve opens | --ventricular ejection

Question 26

At what part of the pressure-volume loop does the ventricular pressure reach its maximum?

Answer 26

b/w pts 2 and 3

Question 27

On a pressure-volume loop, what does point 3 represent and what cardiac activity happens after reaching point 3?

Answer 27

aortic valve closes | --isovolumetric relaxation

Question 28

On a pressure-volume loop, what does point 4 represent and what cardiac activity happens after reaching point 4?

Answer 28

tricuspid valve opens | --ventricular filling

Question 29

What is represented by the width of the pressure-volume loop?

Answer 29

stroke volume

Question 30

What is represented by the area within the pressure-volume loop?

Answer 30

stroke work

Question 31

How is the pressure-volume loop affected when afterload changes?

Answer 31

- afterload increase - -loop gets taller - afterload decrease - -loop gets shorter

Question 32

How is the pressure-volume loop affected when the preload changes?

Answer 32

- preload increase - -loop gets wider - preload decrease - -loop gets narrower

Question 33

How is the pressure-volume loop affected when the contractility changes?

Answer 33

- increased contractility - -gets taller and wider (on the left) - decreased contractility - -gets shorter and narrower on the left

Question 34

What is stroke work?

Answer 34

work done by the L ventricle to eject blood during one cardiac cycle

Question 35

What is the equation for cardiac output in regards to oxygen (Fick Principle)?

Answer 35

CO = O2 consumption / ([O2pv] - [O2pa])

Question 36

What is the effect on cardiac output of blood returning to the heart with an abnormally low level of oxygen?

Answer 36

it takes more oxygen to re-oxygenate the blood and thus decreases cardiac output according to the Fick principle

Question 37

What happens to cardiac output as right atrial pressure iincreases?

Answer 37

cardiac output increases up to a certain point and then reaches a plateau

Question 38

What happens to venous return as right atrial pressure increases?

Answer 38

venous return decreases

Question 39

With a positive inotropic effect, what happens (in the immediate time) to cardiac output and venous return?

Answer 39

cardiac output increases | venous return increases

Question 40

With a positive inotropic effect, what happens (in the immediate time) to right atrial pressure so that cardiac output and venous return stay in equilibrium?

Answer 40

right atrial pressure decreases

Question 41

With a negative inotropic effect, what happens (in the immediate time) to cardiac output and venous return?

Answer 41

cardiac output decreases | venous return decreases

Question 42

With a negative inotropic effect, what happens (in the immediate time) to right atrial pressure so that cardiac output and venous return stay in equilibrium?

Answer 42

right atrial pressure increases

Question 43

What happens to cardiac output and venous return when total peripheral resistance changes?

Answer 43

as TPR increases, CO and venous return decrease | as TPR decreases, CO and venous return increase

Question 44

What happens to cardiac output and venous return (in the immediate time) when blood volume increases?

Answer 44

cardiac output increases | venous return increases

Question 45

What happens to right atrial pressure when blood volume increases, so that equilibrium b/w cardiac output and venous return is maintained?

Answer 45

right atrial pressure decreases

Question 46

What happens to right atrial pressure when blood volume decreases, so that equilibrium is maintained b/w cardiac output and venous return?

Answer 46

right atrial pressure increases