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Created: 13/8/2005

Descending aorta waveform

Identification of the descending aortic waveform is essential for the correct use of the oesophageal doppler. Waveforms from other structures e.g. pulmonary artery, azygous vein or coeliac axis may be encountered and confuse the user.

After acquiring the characteristic descending aortic waveform, the signal should be optimised before starting monitoring. This should be accomplished by moving the probe a centimetre up or down until the waveform indicates the best possible velocity and colour intensities and then rotating the probe to see if the signal can improve even more. The Peak Velocity display is used as a reference to the highest identified wave. The use of the audio signal is highly recommended.

A green line termed the Maximum Frequency Follower must trace the waveform accurately between the two white triangles on the baseline and the arrow at the peak, thereby matching the beginning and the end of systolic flow for all the waveforms during a measurement cycle. This Velocity/Time envelope is used by the monitor to make calculations. Following the adjustments, the Auto Gain control completes the optimisation process.

Optimum signal is usually located where the oesophagus lies parallel with the descending aorta at T5 – T6. 

 Audible – sharpest pitch – “whip crack”
 Visual – highest peak – PV (peak velocity)
 Visual – colour – red/yellow on ascending side with traces of white on descending

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