Esophogeal doppler
In medicine, Esophageal Doppler or Oesophageal Doppler uses a probe inserted into the esophagus through the nose or mouth to measure blood velocity in the descending aorta. From the probe tip, a beam of continuous wave ultrasound is directed through the esophageal wall into the aorta and reflects off the moving blood back to the probe; the Doppler effect is used to measure the velocity of the blood.[1]
In an Esophageal Doppler Monitor (EDM) or Oesophageal Doppler Monitor (ODM), during the time the aortic valve is open (ejection time), the average aortic blood velocity is calculated. The product of average velocity and ejection time gives the stroke distance (how far the blood travels in each heart cycle). An estimate of the aortic cross-sectional area is calculated from a function of physiological parameters (e.g., age, weight, and height). The product of stroke distance and cross-section area gives stroke volume (how much blood was ejected from a heartbeat into the arteries). The heart rate (HR) can be calculated from the time difference between the current peak velocity and the previous one. Cardiac output (CO) is the product of stroke volume and heart rate. Although CO is available beat by beat, it is usually averaged over a number of beats (typically 5) to reduce the variation in displayed value.