Cardiac Pressure Volume Loop

Question 1

equivalents for ventricle-specific values from isolated muscle values:

• force/tension
• length change
• work = force * length change
• power
• isometric and isotonic contractions

Answer 1

for ventricle:

• pressure (afterload)
• volume change (preload)
• work = pressure * volume change = preload * afterload
• power is the same; dW/dt
• isovolumic and isotonic contractions

Question 2

steps of cardiac cycle in terms of valves opening and closing

Answer 2

1. mitral valve open to mitral valve close (diastole to preload; isotonic relaxation)
2. mitral valve close to aortic valve open (isovolumic contraction)
3. aortic valve open to aortic valve close (systole to afterload; isotonic contraction)
4. aortic valve close to mitral valve open (isovolumic relaxation)

Question 3

mitral valve open to mitral valve close

Answer 3

ventricular filling (isotonic relaxation)

• increase in pressure due to increase in passive tension as ventricle muscle stretches
• -increase in passive tension = preload
• ventricle fills until it reaches end diastolic volume (EDV) and mitral valve closes in preparation for contraction

Question 4

mitral valve close to aortic valve open

Answer 4

isovolumic contraction of ventricle, isometric contraction of muscle fibers
-since both MV and AV are closed, there’s no way for blood to get out, so the pressure increases

Question 5

aortic valve open to aortic valve close

Answer 5

ventricular emptying (isotonic contraction)

• intraventricular pressure is sufficient to open AV, and ejection begins as ventricle muscle fibers shorten
• ventricular pressure increases during ejection, then decreases until AV closes
• AV closes at intersection point with volume pressure curve, as the end systolic volume

Question 6

aortic valve close to mitral valve open

Answer 6

isovolumic relaxation of ventricle

-cardiac twitch ends and tension (and pressure) decrease w/o any change in ventricular volume

Question 7

ESPVR

-what is it and what does it imply in regards to the pressure-volume loop?

Answer 7

end systolic pressure volume relationship

• curve that describes maximal pressure that can be developed by the ventricle at any given LV volume
• implies that the PV loop cannot cross the line defining ESPVR for any given contractile state

Question 8

what is compliance and its relationship to elastance?

Answer 8

compliance = dV/dP
-a highly compliant ventricle is “easy” to fill (healthy ventricles during diastole)

elastance = dP/dV (they are inverse)
-a low elastance ventricle is “easy” to fill

Question 9

what does the slope of ESPVR represent? what does this provide?

Answer 9

the end-systolic elastance (dV/dP), which provides index of myocardial contractility

Question 10

how does ESPVR change with changes in:
-preload
-afterload
-HR
-increased inotropy (contractility)
-decreased inotropy
what does this mean?

Answer 10

• relatively insensitive to changes in preload, afterload, and HR
• -makes it improved index of systolic function over other parameters like EF, CO, and SV
• becomes steeper and shifts to left if inotropy increases
• becomes flatter and shifts to the right as inotropy decreases

Question 11

EDPVR

• what is it and what does it describe?
• what is its slope mean?

Answer 11

end-diastolic pressure volume relationship

• describes passive filling curve for the ventricle, thus the passive properties of the myocardium
• the slope at any point along curve is reciprocal of ventricular compliance (or stiffness)

Question 12

what happens if ventricle compliance is decreased? when does this happen?

Answer 12

the ventricle is stiffer (elastance is higher)

• this may happen in ventricular hypertrophy
• higher ventricular end-diastolic pressures at a given end-diastolic volume, or smaller EDV at a given EDP

Question 13

what happens if ventricle compliance decreases? when does this happen?

Answer 13

ventricle is easier to fill (elastance is lower)

• this may happen in dilated cardiomyopathy where ventricle is highly dilated w/o appreciable thickening of wall
• EDV may be very high, but the EDP may not be greatly elevated

Question 14

what happens at EDV (end-diastolic volume?)

Answer 14

• the ventricle is done passively filling with blood from diastole
• the ventricle has been stretched, which increases tension (preload)
• this stretching increases sensitivity of cardiomyocetes via Frank-Starling law

Question 15

what happens to the ventricular afterload if aortic blood pressure is high?

Answer 15

the ventricular afterload (pressure) rises

Question 16

is stroke volume affected by changes in preload, afterload, and inotropy?

Answer 16

yes, but SV is not strongly influenced by afterload in normal hearts; highly sensitive in failing hearts

Question 17

how is stroke volume related to EDV and ESV?

Answer 17

SV = EDV - ESV

Question 18

ejection fraction and normal EF

-what is the equation for EF?

Answer 18

fraction of end-diastolic volume ejected out of the ventricle during each contraction

• healthy ventricles have 55-60%
• EF = SV/EDV

Question 19

what are reasons that ejection fraction would decrease?q

Answer 19

myocardial infarction or cardiomyopathy (damage to myocardium), systolic dysfunction and severe heart failure
-can lead to EF lower than 20%

Question 20

what can EF be used as a clinical indicator of?

Answer 20

the inotropy (contractility) of the heart
-increasing inotropy causes increase of EF, while decreasing inotropy decreases EF

Question 21

preload in terms of ventricles

Answer 21

end diastolic volume at the beginning of systole

Question 22

afterload in terms of ventricles

Answer 22

ventricular pressure at the end of systole, meaning at the time of aortic valve closure

Question 23

when does ventricular pressure equal aortic pressure?

Answer 23

at the end of systole (when ventricle is done emptying)

Question 24

what happens to SV with increasing EDV (preload)?

Answer 24

SV increases, and there may be sensitization and Starling law in action

Question 25

what happens to SV with increasing afterload?

Answer 25

SV decreases, b/c the ventricle has to raise its pressure to meet the aortic pressure (main problem with HTN)

Question 26

what is CO an indicator of, and how is it regulated?

Answer 26

indicates how well the heart is performing its function

-regulated by demand for O2 by cells of body

Question 27

what effects do cardiomyopathy, HTN, heart failure, or sepsis have on CO?

Answer 27

heart diseases cause decreased CO, but sepsis increases CO