ECHONOMY Tools for Echocardiographic Calculations Muhamed Saric, MD, PhD
New York University
A moving fluid has 3 types of energy: kinetic (velocity, V), potential
(pressure, P), and thermal (heat loss due to friction, T).
The sum of all energies is constant; an increase in one form of energy
can come only at the expense of other two forms:
E = V + P + T = constant
An increase in fluid velocity leads to a drop in local pressure. This
is the basis of Venturi effect and the lift of an airplane.
As fluid velocity slows down, local pressure increases; i.e. there is
If decrease in fluid velocity is accompanied by an increase in
turbulent flow, there will be an increase in heat loss at the expense of
Flow From LVOT to Aortic Valve to Ascending Aorta
Pressure is high (P1); velocity is low (V1)
AREA (AVA): Pressure is low (P2); velocity (V2) is increased.
AORTA (AscA): Velocity (V3) decreases rapidly. The kinetic energy
is dissipated into pressure (P3) or thermal loss (T).
Normally, as the blood enters from AVA into AscA, turbulence leading to
heat loss prevents significant pressure recovery.
When AVA is moderately stenotic and the diameter of the receiving
AA is small (< 2.0 cm), little turbulence & heat loss occur. Thus the
kinetic energy is converted primarily into pressure; i.e. a
significant pressure recovery occurs.
P1 - P2
= Peak instantaneous pressure gradient by Doppler
P1 - P3
= Peak-to-peak gradient by cardiac cath
P3 - P2 =
The larger the pressure recovery, the lower the peak-to-peak gradient
will be for any given peak instantaneous gradient. In other words, the more
pressure recovery there is, the more overestimation of aortic stenosis by
Doppler will occur compared to cardiac cath.
Peak velocity (Vmax) across aortic valve by continuous
Overestimation of peak gradient by Doppler compared to
P3 - P2 = 4 * Vmax2 *
C = 2 * (AVA / AscAA) * (1- AVA / AscAA)
Niederberger J, Schima H, Maurer G,
Baumgartner H. Importance of pressure recovery for the assessment of aortic
stenosis by Doppler ultrasound. Role of aortic size, aortic valve area, and
direction of the stenotic jet in vitro.
Circulation. 1996 Oct 15;94(8):1934-40.