Pressure Volume Plots

Question 1

LV P-V Relationships

Answer 1

Force=Pressure

Distance = Volume

Area= Net work done by the heart

Question 2

Stoke Volume

Answer 2

SV = EDV-ESV

Ex: SV=120-50 = 70

Question 3

Phases of Cardiac Cycle (P-V Plot)

Answer 3

1. Diasolic filling: generation of preload
2. Isovolumetric contraction stage os sytole
3. Systolic ejection
4. Isovolumetric relaxation

Question 4

ESPVR

Answer 4

End systolic pressure-volume relationship: maximum ventricular pressure developed at a given inotropic state

Question 5

Increase in EDV

Answer 5

Increase in EDV:

• increase in preload
• incrase in systolic intraventricular pressure (IVP)
• slightly increase ESV
• increased SV

Question 6

Increased Afterload

Answer 6

• increase systolic IVP and ESV
• greater ESV than would increased preload alone

Question 7

Positive Inotropy

Answer 7

Potential Causes: heightened SNS tone; digoxin

• Reduced ESV
• Increased SV

maximal systolic pressure is increased with decrease in ESV –> systolic phase shifts leftward and upward –> generates a new ESVPR

Question 8

Velocity of Myocyte Shortening and LV Volume Relationship

Answer 8

Phases

1. Muscle fiber velocity is zero: ventricular myocardium is relaxing
2. Isovolumetric contraction that terminates upon aortic valve opening
   
   • myocyte tension rises dramatically here
   • proves generation of force required to snap open aortic valve and overcome afterload
   • allows rapid ejection of blood from LV
3. Systole: rapid decline in myocyte fiber shortening

Question 9

Positive Inotropin

(positive inotropic compounds)

Answer 9

ie: adrenergics or digitalis

Increase:

1. ventricular contractile force
2. EDV
3. contraction velocity
4. may or may not alter time btwn excitation episodes

*thus they may increase CO (as long as HR doesn’t increase such that time for ventricular filling isn’t compromised

Question 10

When do the valves/open close on the P V plot?

Answer 10