Cardiac PV Loops

Question 1

cardiac output

Answer 1

CO

total volume of blood pumping into the aorta and pulmonary artery in 1 minute

Question 2

equation for CO

Answer 2

CO = SV x HR

Question 3

is cardiac output in the RV >< or = LV

Answer 3

equal

Question 4

stroke volume

Answer 4

amount of blood ejected with each beat

Question 5

cardiac index

Answer 5

cardiac output indexed to body size

Question 6

what are measures of cardiac performance

Answer 6

volume
pressure
flow (echocardiogram)

Question 7

right vs left heart pressure

Answer 7

right: lower pressure system b/c PA is lower pressure than aorta

left: higher pressure system b/c aorta is higher pressure than PA

Question 8

pressure volume loops

Answer 8

shows the relationship between pressure and volume during 1 cardiac cycle

Question 9

PV Loop: marker A

Answer 9

end-systolic volume; volume remaining after contraction

AV: open (begins filling)
SL: closed

Question 10

PV Loop: marker B

Answer 10

end-diastolic volume; volume in ventricles after filling

AV: close (allows pressure to rise)
SL: closed

Question 11

PV Loop: marker C

Answer 11

pressure generated in ventricle prior to contraction

AV: closed
SL: opens –> ejection of blood

Question 12

PV Loop: marker D

Answer 12

pressure remaining after emptying ventricle

AV: closed
SL: close –> prevent regurg

Question 13

diastole on PV loop

Answer 13

ventricular relaxation and filling

A (early) –> B (late)

volume INCREASES
pressure NO CHANGE

low pressure phase allows for passive filling (atrial > ventricular contraction)

Question 14

what is compliance

Answer 14

stretch of the ventricle walls that allows for minimal change in pressure during filling

Question 15

isovolumetric contraction on PV loop

Answer 15

closing of AV valves

B (EDV) –> C

volume NO CHANGE
pressure INCREASES

moderate pressure phase - ventricular pressure rises until it exceeds aortic pressure

Question 16

systole on PV loop

Answer 16

ventricular contraction nad ejection

C –> D

volume DECREASES
pressure INCREASES

high pressure phase (ventricular > aortic to allow for blood flow out of ventricles, then ventricular decreases until < aortic)

Question 17

isovolumetric relaxation on PV loop

Answer 17

closing of SL valves

D (ESV) –> A

volume NO CHANGE
pressure DECREASES

Question 18

does the ventricle completely empty after systole

Answer 18

NO - always some blood remaining in ventricle (end systolic volume)

Question 19

equation for stroke volume

Answer 19

SV = EDV - ESV

Question 20

ejection fraction

Answer 20

fraction of blood in the ventricles that gets ejected with every beat

Question 21

equation for ejection fraction

Answer 21

EF = stroke volume / EDV

EF = (EDV - ESV) / EDV

Question 22

what are the two determinants of cardiac output

Answer 22

1. heart rate
2. stroke volume

Question 23

how does HR affect SV

Answer 23

increase HR = increase CO BUT only up to a point

once HR gets too high –> reduced time to fill during diastole –> less blood available to eject –> decreased CO

also effected by contractility

Question 24

what 4 components of stroke volume affect CO

Answer 24

1. preload
2. afterload
3. contractility (inotropy)
4. relaxation (lusitropy)

Question 25

preload

Answer 25

diastolic wall stress - the stress put on the ventricular walls by blood entering during diastole

Question 26

how does preload affect cardiac output

Answer 26

increase preload = increase CO heart wants to return to the same ESV --> must get rid of more blood if preload increases --> increases CO

Question 27

what is the main determinant of preload

Answer 27

blood volume/venous return

Question 28

afterload

Answer 28

systolic wall stress - the pressure required to generate a strong enough contraction to push blood out against aortic pressure "impedance to ejection"

Question 29

how does afterload affect cardiac output

Answer 29

increase afterload = decrease CO too much pressure in aorta --> heart can't push out as much blood --> decrease CO

Question 30

what is the main determinant of afterload

Answer 30

systemic vascular resistance/blood pressure (hypertension --> high pressure in aorta --> high afterload --> low CO)

Question 31

Laplace's law

Answer 31

measures the amount of wall stress wall stress = (pressure x radius) / (2 x wall thickness)

Question 32

what does Laplace's law show

Answer 32

the heart can accommodate to increased wall stress by increasing wall thickness to lower wall stress back to baseline proven by L ventricle wall being thicker than R ventricle

Question 33

contractility (inotropy)

Answer 33

degree that muscle fibers shorten

Question 34

how does contractility affect cardiac output

Answer 34

increase inotropy = increase CO stronger contraction results in more blood being ejected per beat

Question 35

how does inotropy affect the PV loop

Answer 35

increases the slope of the ESPVR curve results in a lower ESV (because more blood ejected) does NOT affect load

Question 36

does inotropy depend on load

Answer 36

NO - regulated by ANS to alter Ca influx and sensitivity

Question 37

relaxation (lusitropy)

Answer 37

ventricular compliance and diastolic function

Question 38

how does lusitropy affect cardiac output

Answer 38

increase lusitropy = increase cardiac output increased compliance allows for greater filling (increase EDV) --> increased CO

Question 39

how does diastolic dysfunction affect CO

Answer 39

decreases relaxation --> decreased compliance --> decreased CO

Question 40

equation for ventricular compliance

Answer 40

deltaV / deltaP

Question 41

equation for ventricular stiffness

Answer 41

deltaP / deltaV

Question 42

myocardial oxygen demand

Answer 42

MVO2; the amount of oxygen required by the myocardium to function

Question 43

what is MVO2 dependent on

Answer 43

1. heart rate (inc HR = inc MVO2) 2. wall stress/pressure (inc pressure = inc MVO2) 3. contractility (inc inotropy = inc MVO2)

Question 44

when do the coronary arteries delivery oxygenated blood to the heart

Answer 44

during diastole