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How it Works

How it Works

How the EDM works

The EDM is unique in its ability to directly measure central blood flow with a minimally invasive disposable probe. The probe is placed in the patient’s esophagus and uses Doppler ultrasound to measure the velocity of blood flow in the descending aorta. The esophagus is easy to access for placement of the ultrasound probe as it is close to the patient’s aorta at the level of T5/T6.

Ultrasound explained

Ultrasound emitted by the probe is directed into the aortic blood flow at angle of 45o. The ultrasound will be reflected by the blood’s red cells. As the blood is moving away from the probe tip each reflected wave is emitted from a position further from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency. The distance between successive wave fronts is increased, so the waves “spread out”. The EDM receives the reflected frequency shifted wave and compares its frequency to that of the transmitted wave. The result of this calculation is that the velocity of the blood can be measured during each cardiac cycle.

Ultrasound Waveform

The ultrasound waveform is displayed in red and white with a dark center and it is encapsulated by a green line, which follows the maximal velocity at that point in time. The monitor places three arrows on the screen; the first at the start of systole (on the baseline); the second at the peak velocity (at the top of the waveform) and the third at the end of systole (on the baseline).


The EDM+ directly measures central blood flow in the same way as the EDM. In addition, the device also takes the standard Arterial Blood Pressure (ABP) measurement and calculates a range of Pressure Based Parameters. It is unique in that it can take the Cardiac Output as measured by Doppler flow to calibrate a Pulse Pressure Waveform Analysis (PPWA) algorithm. The PPWA algorithm provides secondary pressure based measures of Stroke Volume (SV) and Cardiac Output (CO) as well as new flow and pressure combined parameters.

By combining both flow and pressure based measurements, the EDM+ allows the user to reduce the inherent weaknesses of PPWA with a quick and simple calibration and recalibration from the Doppler flow based measurements of CO.

For further information relating to probes or for any sales inquiries please call 864-527-5913 or email our Corporate Office