Doppler echocardiographic findings are strongly influenced by
the pressure gradients between chambers according to the Bernoulli
equation. This relationship is simplified to:
p2-p1=4V2
 |
| Fig.2.3 |
and is very important to understand for further appreciation
of the wealth of information available in the Doppler velocity
spectral display. The Doppler spectral recordings from mild and
severe mitral regurgitation are shown in
Figure 2.3 to illustrate this point further. As describes
above, small degrees of mitral regurgitation produce very high
pressure differences between the left ventricle and the left atrium.
Minor degrees of regurgitation will, therefore, result in very
high velocity jets as a consequence of these great pressure differences.
Severe mitral regurgitation results in relatively smaller differences
between the two chambers. These smaller pressure gradients result
in relatively lower velocity jets. This, of course, assumes that
the systolic pressures within the ventricles are similar in both
situations.
Thus, the severity of valvular regurgitation is not reflected
in an increase in the velocity of the regurgitant jet as detected
by Doppler echocardiography. As will be demonstrated in more detail
later, the inverse is usually the case. With greater degrees of
regurgitation, pressures will rise in the chamber receiving the
regurgitant volume leading to a general decrease in the velocity
of the resultant Doppler spectral recording.
Another important implication of the increase in velocity in
regurgitant jets is that almost all degrees of valvular regurgitation
result in a velocity increase above 1.5 m/sec. The practical effect
of these higher velocities on Doppler recordings is that aliasing
is almost always produced in pulsed wave Doppler interrogations
of valvular regurgitation. This is results in the fact that pulsed
Doppler echocardiography may be used for detection of the location
of the turbulence (or area of the jet) but not its peak velocity.
 |
| Fig.2.4 |
This is demonstrated in the idealized drawing of spectral recordings
resulting from a mitral insufficiency jet shown in
Figure 2.4. The left panel shows systolic turbulent flow moving
away from a transducer positioned at the apex. The full profile
is recorded by CW Doppler. When the same jet is interrogated by
PW Doppler, aliasing occurs.
2004