How the ODM works

The CardioQ-ODM is unique in its ability to directly measure central blood flow by way of a minimally invasive disposable probe. The probe is placed in the patient’s oesophagus and uses Doppler ultrasound to measure the velocity of blood flow in the adjacent aorta, hence the name of the technology which is abbreviated to ODM. The oesophagus 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.

Access the Training Workbook for a deeper understanding of how to use this technology.

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 farther 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 ODM 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 centre 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).

Technical Review

The Technical Review is ideal for those seeking a deeper understanding of the ODM technology and contains information on:

  • A short history of the development of oesophageal Doppler monitoring
  • How oesophageal Doppler measures blood flow velocity in the aorta
  • Comparative results compared to pulmonary artery catheter data
  • Accuracy of measurement
  • Probe placement and focussing
  • Waveform and parameter explanation
  • A summary of haemodynamic management
  • Results of clinical application
  • Limitations of use


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