Cardiac Volume Loop

Question 1

force or tension in muscle

Answer 1

pressure in heart

Question 2

length change in muscle

Answer 2

volume change in heart

Question 3

work is force times distance

Answer 3

work is pressure times volume change

Question 4

power is work over time

Answer 4

still work over time

Question 5

isometric contractions in muscle

Answer 5

isovolumetric contractions in heart

-still isotonic contractions

Question 6

cycle

Answer 6

• in terms of ventricular volume and pressure
• heart cycles counterclockwise on the volume pressure plot
• ventricle fills at bottom/low pressure
• isovolumic contraction
• ejection at top at high pressure
• isovolumic relaxation

Question 7

volume vs pressure

Answer 7

• filling and emptying shown by horizontal changes in length or volume
• tension and relaxation shown by vertical changes in pressure

Question 8

MVO to MVC

Answer 8

• ventricle fills with blood
• increase in pressure due to increase in passive tension as the muscle stretches- preload
• ventricle will fill until is reaches end diastolic volume and mitral valve closes

Question 9

MVC to AVO

Answer 9

• ventricular muscle fibers contracts isometrically and the ventricle undergoes isovolumetric contraction (pressure increases without changing volume)
• mitral valve and aortic closed, pressure increases

Question 10

AVO to AVC

Answer 10

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

Question 11

ACV to MVO

Answer 11

• isovolumetric relaxation

- twitch ends an tension and pressure decrease with no change in volume

Question 12

compliance

Answer 12

• deltaV/deltaP
• compliant vessel is easy to fill
• healthy ventricle is compliant during diastole and not during systole

Question 13

elastance

Answer 13

• deltaP/deltaV

- low elastance ventricle is easy to fill

Question 14

ESVPR

Answer 14

• end systolic volume pressure relationship
• curve that describes the maximal pressure that can be developed at any given LV volume
• PV loop can’t cross it, and end diastolic volume is at intersection point
• represents end systolic elastance
• insensitive to changes in preload, afterload, heart rate
• improved index of systolic function
• steeper and shifts to the left as contractility increases (norepi)
• flatter and shifts to the right as inotropy decreases

Question 15

EDPVR

Answer 15

• end diastolic pressure volume relationship
• passive filling curve for the ventricle and passive properties of myocardium
• slope is the reciprocal of compliance (diastolic elastance)
• if compliance decreased, stiffer, higher end diastolic pressure at any end diastolic volume
• at given EDP, EDV smaller-impaired filling
• if compliance increases, end volume high but pressure might not change

Question 16

cardiac cycle

Answer 16

• pressure vs volume has volume increasing (causes stretching-and preload-frank-starling law increases sensitivity) then isovolumetric contraction then ejection then isovolumetric relaxatoin
• muscle tension vs length- passive stretching, isometric tension, shortening, isometric relaxation
• afterload is work the heart must do
• preload is EDV
• work is pressure (afterload) times volume change

Question 17

stroke volume

Answer 17

• volume of blood ejected by ventricle in a single contraction
• difference between end diastolic volume and end systolic volume
• SV=EDV-ESV
• affected by changes in preload, afterload, inotropy
• in normal hearts not greatly influenced by afterload, it is in failing hearts

Question 18

ejection fraction

Answer 18

• fraction of end diastolic volume that is ejected out of the ventricle during each contraction
• EF=SV/EDV
• healthy usually greater than 55%, dependent on loading
• MI causes damage to myocardium which impairs ability to eject blood and reduces ejection fraction
• low EF indicates systolic dysfunction
• used as clinical indicator of the contractility, increasing inotropy increases EF

Question 19

preload

Answer 19

-end diastolic volume- load heart must get rid of

Question 20

afterload

Answer 20

• ventricular pressure at the end of systole

- at time of aortic valve closure- can use for approximation of aortic pressure at this point

Question 21

sensitization/starling law

Answer 21

• larger preload
• more shortening (because more stretching)
• increased tension and stroke volume
• increased end diastolic volume

Question 22

increasing afterload

Answer 22

• decreases stroke volume
• less shortening, larger total load
• increases pressure needed to eject blood

Question 23

increased contractility-norepi

Answer 23

• increase in stroke volume
• more shortening
• more tension generated
• more volume ejected
• shifts ventricular function curve up
• Po increases with increased initial length
• EF increases
• see summary slide

Question 24

cardiac output

Answer 24

• amount of blood pumped by the ventricle in unit time
• CO=SVxHR
• indicator of how well heart is performing
• regulated principally by demand for oxygen by the cells of the body
• hypertension and heart failure associated with changes in CO
• increases with SNS activation