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2004
The Changing Left Ventricle

2003
Aortic Valve Disease: New Dimensions in Evaluation and Management

2002
Heart Failure: Echo's Role in and Emerging Health Crisis

2001
Chest Pain in Children & Adults: The Role of Echo

2000
Mitral Regurgitation: New Concept

1998
The Falling Left Ventricle: Diastolic & Systolic Function

1997
Changing the Outcome of Coronary Artery Disease
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Changing the Outcome of CAD

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Pulse and Continuous Wave Doppler
The Bernoulli Equation

There is clear justification for concern over accurate recording of very high velocity jets within the heart. As will be discussed in more detail later, the presence of an obstruction to flow, such as aortic stenosis, will result in a significant increase in velocity across the aortic valve in systole. In practice, these jets attain speeds of up to 7 m/sec.

Fig.1.31

The Bernoulli equation is a complex formula that relates the pressure drop (or gradient) across an obstruction to many factors, as is seen in Figure 1.31. For practical use in Doppler echocardiography this formula has been simplified to: p1-p2=4V2

As we shall see later, Doppler recordings of velocity may, in certain situations, be used to estimate pressure gradients within the heart. When used for this purpose, it is important to keep in mind that the angle the Doppler beam is incident to any given jet may not be known since these examinations are frequently done blindly by CW. In these cases the operator always tries to orient a beam as parallel to flow as possible so that the full velocity recording is obtained (this assumes cosine Ø =1).

Fig.1.32

Note that the full Bernoulli equation requires velocity data from below (V1) and above (V2) any given obstruction. Since V1 is normally much smaller than V2 (Fig. 1.32) it can usually be ignored in the calculation of a pressure gradient.

In the example cited, the peak velocity is approximately 3.5 m/sec and this would correspond to an aortic gradient of 48 mmHg by the simplified Bernoulli equation. Obviously, faithful recording of abnormal velocities has great importance, not only for clear identification and recognition of abnormal profiles but also for quantitative purposes.

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