Understanding Pressure Volume Loop
Ventricular volumes are plotted against simultaneously occurring ventricular pressuresduring a normal cardiac cycle
Let us first understand PV loop –now since it is a pressure volume loop, to generate pressure first volume has to come in the LV so mitral valve has to open
So Phase1 starts with mitral valve opening MVO and blood coming into the LV means LV filling .This is preload.So u see the volume has increased and the line which we draw is going to right but not upwards as pressure is not increasing
Now, mitral valve has to close and aortic valve is still to open so it is the isovolumic contraction that is occurring so only pressure increasing and line going upwards while volume not changing so line is going only straight up and not rightwards.This is Phase 2.
When this pressure increases more than the aortic pressure, the aortic valve opens and ejection starts. This is Phase 3 – SEP means systolic ejection period.
After this the aortic valve closes and until opening of mitral valve is the isovolumic relaxation period wherein pressure decreases so again steep straight line.This is Phase 4.
It helps understand the index of contractility ESPVR
PV loop in AS- main differences
Peak pressure generated during systole is much greater because of high pressure gradient
Slope of diastolic limb is steep because of decreased diastolic compliance due to LVH
This means small changes in diastolic volume produce large increase in ventricular filling pressure
Systolic limb shows preservation of pump function (SV & EF)
When right side of PV loop goes to the right that means more volume is coming in so it means preload is increasing
And when right side line is going up means pressure is increasing means after load is increasing
So a tall PV loop tells increased afterload and a fat PV loop tells increased preload.
The area in the loop is the Stroke work or the kinetic energy for a single cardiac cycle.
This PV loops allow estimation of contractility index – ESPVR end systolic pressure volume relation.
It also allows end diastolic pressure volume relation that tells us compliance of LV which determines LV filling.