Echo Measurements

Continuity Equation

The continuity equation allows you to do a couple of things in echo. As you can measure velocity at the LVOT and the aortic valve, plus cross sectional area at the LVOT, you can use these to work out the cross sectional area of the aortic valve.

With these measurements you can also work out an estimate of the stroke volume. Stroke volume will be mls ejected with each heart beat. The way you can get that is the column of blood ejected, and calculate the volume.

You've calculated the cross sectional area (cm) at the aortic valve (as about). You've measured the average V (cm/s) at the valve. The VTI is then V * S = VTI.

When you then times VTI (at LVOT, you prefer a direct measurement than a calculation) by CSA (of LVOT) you get stroke volume. IF YOU times that by HR you'll get cardiac output (ml/min or l/min(

To do so you need to measure

Velocity

VTI (vti at lvot and vti at aortic valve) (velocity (CM/S) * time (S) = VTI (CM)) The key in the continuity Equation is that pressure has to remain constant.

So if cross sectional area falls velocity has to increase to maintain a steady pressure

Pressure = CSA X V

Next point is that velocity is pulsatile, so you need to take an