## Case 12

## Continuous Wave Doppler Tracings

**This is a continuous wave Doppler tracing of the tricuspid regurgitation
jet. Normally the peak systolic pressure in the right ventricle is 20 to 25 mm
Hg and the right atrial pressure is less than 5 mm Hg. To make it easy, let's
assume the peak systolic right ventricular pressure in a normal animal is 20 mm
Hg and right atrial pressure is 4 mm Hg. This means the pressure gradient (i.e.,
difference) is 16 mm Hg across the tricuspid valve. Of course in a normal
animal, there is no tricuspid regurgitation of note although in many there is a
trace amount. Using the modified Bernoulli equation, we can calculate the
velocity of a tricuspid regurgitation jet by dividing the pressure gradient by 4
and then taking the square root of that value. In this situation, 16 divided by
4 is 4 and the square root of 4 is 2. This means that if a normal animal has
some tricuspid regurgitation, the velocity of blood flow back across the
tricuspid valve should be 2 meters/second (normal is up to
around 3.2 meters/second). Working the other way in this dog, if
the velocity is 4.5 meters/second the pressure gradient must be 81 mm Hg. We
don't actually know what the right atrial pressure is but since the dog appears
to be in right heart failure, it must be in the 10 to 15 mm Hg range.**

**Similarly, we can measure the velocity of the pulmonic regurgitation jet and estimate
the diastolic pressure in the pulmonary arteries. In the picture above we have done this
and measured the velocity of the jet in early diastole to be about 3.9 meters/second. This
translates into a pressure gradient across the pulmonic valve of 60 mm Hg. In early
diastole, the right ventricular pressure is usually zero so this means the pulmonary
artery early diastolic pressure must be the same as
the gradient or 60 mm Hg. In late diastole you can see that the velocity
decreases. It does this as the pulmonary artery pressure in diastole decreases
and as the right ventricular diastolic pressure increases. The velocity at the
end of diastole on the middle tracing comes down to about 3 meters/second. This
translates into a pressure gradient of 36 mm Hg. If we assume that right
ventricular end-diastolic pressure is 14 mm Hg, this means the diastolic
pressure in the pulmonary arteries is approximately 50 mm Hg. We have now
approximated the pulmonary artery pressure to be 100 mm Hg in systole and 50 mm
Hg in diastole. This is assuming that we were able to line up our continuous
wave Doppler beam parallel with both jets. If we didn't, the velocity would be
less than normal. Remember that it is always easy to underestimate the velocity
of blood flow using Doppler ultrasound. It can never be overestimated. **

##
Quiz

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