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Flashcards in CPR Contractility & Cardiac Output Deck (31)
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1

What is cardiac output dependent on?

Heart rate
Contractility
Preload
Afterload

2

How do cardiac glycosides work?

used to treat heart failure by

inhibition of K+ binding on Na/K ATPase
increases Na+ conc
decreases Ca2+ efflux thru Ca2+/Na+ exhanger
increases intracell Ca2+
positive inotropic effect

3

How do you calculate cardiac output?

CO=HR x SV

(SV relates to myocardial contractility)

4

What is left ventricular end-diastolic volume?

amount of blood ready to be pumped

wall tension in LV just before contraction is initiated

5

What is the Frank-Starling relationship?

volume of blood ejected by ventricle depends on volume present in ventricle @ end of diastole

6

How do CO & venous return relate?

CO=venous rate (steady state)

7

What is afterload?

for LV, is related to aortic pressure

the force opposing contraction/pressure required to eject blood from LV

8

Preload v Afterload w/ in cardiac cycle

Preload=LV end-diastolic volume (fiber length from where muscle contracts)

Afterload=aortic pressure (what is needed to open aortic valve)

9

What is stroke volume?

volume of blood ejected by ventricle w/ each beat

SV=EDV - ESV
Usually about 70ml

10

What is ejection fraction?

fraction of EDV ejected in each stroke volume
(measure of efficiency and contractility)

EF = SV/EDV, approx 55%

11

What is cardiac output?

total volume of blood ejected by ventricle per min

CO (Q) = SV x HR

usually is 5 L/min

12

What happens to CO if preload increases?

increases CO & contractility in a healthy heart

13

What happens to CO if afterload increases?

decrease CO (must increase contractility or increase HR)

14

What is the effect of HR on contractility?

increased HR increases contractility (more Ca2+ enters cells & taken up into SR)

15

What is the effect of sympathetic stimulation on CO?

positive ionotropic effect

inhibits troponin I & stimulates phospholamban & sarcolemma Ca2+ channels

16

What is the effect of parasympathetic stimulation on CO?

negative ionotropic effect in ATRIA only (no influence on ventricular myocytes)

activation of muscarinic receptor decreases inward Ca+ current & increase K+ efflux

17

What does phase 1 to 2 on vent pressure-volume loop represent?

isovolumetric contraction

18

What does phase 2 to 3 on pressure volume loop represent?

ventricular ejection

19

What does phase 3 to 4 on pressure volume loop represent?

isovolumetric relaxation

20

What does phase 4 to 1 on pressure volume loop represent?

ventricular filling

21

What compensation occurs with increased preload?

more venous return, more blood volume

increased SV

22

What compensation occurs with increased afterload?

aortic stenosis, hypertension

greater pressure needed w/ reduced SV & EF%

23

What compensation occurs with increased contractility?

adrenergic stimulation

increased SV & EF%

less blood left in heart

24

What is pressure work?

aortic pressure

25

What is minute work?

CO x aortic pressure

26

What is stroke work?

performed by LV (area w/ in pressure-volume loop)

stroke volume x aortic pressure

27

What is the Fick Principle?

describes O2 consumption

O2 consumption= CO x (O2 in pulmonary vein - (CO)(O2 in pulmonary artery))

28

What does the cardiac function curve describe?

relationship between CO & venous return

as venous return increases, RA pressure increases & EDV & end-diastolic fiber length increases

29

What does equilibrium on cardiac function curve indicate?

CO = venous return (will vary depending on state of CV system)

30

What is a vascular function curve?

mean circulatory filling pressure

when there is no CO & depends entirely on vascular compliance & blood volume