3-Cardiac Output

Question 1

cardiac output =

Answer 1

stroke volume x heart rate

vol of blood ejected by heart per min (L/min) FLOW

Question 2

regulation of stroke vol

Answer 2

1. myocyte contractility
2. afterload
3. preload

Question 3

regulation of heart rate

Answer 3

1. speed of diastolic depolarization
   -parasymp and symp nervous sys

Question 4

length-tension relationship

Answer 4

inc length of muscle fiber changes overlap of thick/thin filaments (resting tension) for contraction (active tension)
-aka inc length/stretch inc tension

titin important for this

Question 5

preload affect on length-tension

Answer 5

preload/filling of vents = stretch on ventricle prior to contraction

volume of ventricle

Question 6

pressure-volume loop

Answer 6

1. isovol contraction, pressure builds
2. aortic valve opens, pressure peaks as muscle contracts and systolic ejection, vol dec
3. aortic valve closes, pressure high volume low
4. isovol relaxation, vol stays same pressure dec until mitral valve opens
5. diastolic filling to phase 0 (LV end-diastolic pressure) then restart

width of loop = stroke volume

just look at power point chart

Question 7

increasing HR = ? CO

cardiac output

Answer 7

generally will inc CO up to a point then dec bc stroke volume is down, lose ventricle filling

Question 8

end diastolic volume

Answer 8

amount of blood in heart at end of filling

Question 9

end systolic volume

Answer 9

amount blood leftover in heart at end of ejection

Question 10

determinants of stroke vol

Answer 10

1. preload- vent filling, stretch of myocytes
2. afterload- tension needed to oepn aortic valve (after contraction), systemic resistance, aortic valve resist
3. contractility- inotropic agents

Question 11

inc afterload = ? stroke vol

Answer 11

stroke vol dec with inc afterload

Question 12

inc contractility = ? stroke vol

Answer 12

increases at any given point with pre and afterload bc calcium cycling

Question 13

inc preload = ? stroke volume

Answer 13

increases up to maximal stroke vol then dec

frank-starling law of heart- if more comes in then more goes out

Question 14

preload changes from

Answer 14

venous return into vena cava
-venous pressure needs to be higher than atrial (central) for blood to enter RA so if inc CVP then dec venous return

Question 15

mean systemic filling pressure changes

Answer 15

1. inc blood vol = inc preload, higher venous return
2. dec blood vol = dec venous return, from bleeding out or dehydration

Question 16

arteriolar tone on venous return

Answer 16

inc tone aka vasoconstriction = venous return slowed, blood vol stays the same just takes longer to return to heart

dec tone aka vasodilation = venous return inc bc returns quicker

Question 17

why afterload dec stroke vol

Answer 17

inc afterload = more effort to eject blood/harder bc inc tension required to open aortic valve = less blood gets ejected
-work harder to open the valve than eject blood

Question 18

positive inotropes = ? stroke vol

Answer 18

inc peak tension during contraction + inc amount blood ejected so lower end systolic vol = inc SV

norepinephrine

Question 19

disease states on contraction

Answer 19

reduce ability of heart muscle to contract + less tension produced = dec stroke vol

i.e. heart failure, MI, arrhythmias (change how electric signal moves thru tissue)

Question 20

regulation cardiac output

Answer 20

balance b/t stroke volume and HR so change CO by those two
-changes based on tissue demand

Question 21

venous pressure and CO

Answer 21

must be equal/matched
inflow = outflow

if not then congestion and volume acc somewhere not supposed to

Question 22

sympathetic stim = ? CO

Answer 22

cardiac output inc with symp stimulatin
-pos inotropy (contract) + pos chronotropy (HR)

Question 23

moderate heart failure and CO

Answer 23

1. reduced contractility
2. fluid retention > shift venous return bc inc volume to compensate for heart failure

CO stays at same level as normal bc of compensation

short term

Question 24

severe heart failure and CO

Answer 24

continued deterioration of contractility = inc venous pressure + dec CO
-decompensated

Question 25

how to assess CO

mainly

Answer 25

1. fick method
2. indicator dilution technique

both rely on conservation of mass

Question 26

fick method

Answer 26

relies on oxygen into lungs
-oxy leaving lungs = oxy entering for steady state so

oxy consumption / (arterial-venous oxygen difference) = cardiac output

Question 27

indicator dilution method

Answer 27

indicator injected upstream then measured downstream until gone

thermal dilution uses cold saline