medicine Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pract ...

, Esophageal Doppler or Oesophageal Doppler uses a small ultrasound probe inserted into the

esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...

through the

nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passes th ...

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...

to measure

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...

velocity in the

descending aorta In human anatomy, the descending aorta is part of the aorta, the largest artery in the body. The descending aorta begins at the aortic arch and runs down through the chest and abdomen. The descending aorta anatomically consists of two portions o ...

. It is minimally invasive (does not break the skin) and is used to derive

hemodynamic Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously mo ...

parameters such as

stroke volume In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from the left ventricle per beat. Stroke volume is calculated using measurements of ventricle volumes from an echocardiogram and subtracting the volume of the blood i ...

(SV) and

cardiac output In cardiac physiology, cardiac output (CO), also known as heart output and often denoted by the symbols Q, \dot Q, or \dot Q_ , edited by Catherine E. Williamson, Phillip Bennett is the volumetric flow rate of the heart's pumping output: t ...

(CO). A properly constructed and calibrated probe is approved for use on adults and children in many parts of the world.

How it Works

From the probe tip, a beam of

continuous wave A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or particle ...

ultrasound Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...

is directed through the esophageal wall into the

aorta The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes ...

and reflects off the moving blood back to the probe; the

Doppler effect The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

is used to directly measure the velocity of the blood (by the shift in frequency of the reflected ultrasound signal compared to the original beam).

Esophageal Doppler Monitor

An Esophageal Doppler Monitor (EDM) or Oesophageal Doppler Monitor (ODM) is a cardiac output monitor using an esophageal positioned ultrasound sensor. It usually displays a graph of real-time aortic blood velocities and recognized main flow against time. It provides instantaneous values of hemodynamic parameters for the just past beat, such as heart rate (HR), stroke distance (SD), maximum acceleration (MA), flow-time (FT) and peak velocity (PV); also values calculated from these, such as stroke volume (SV), flow-time corrected (FTc) and cardiac output (CO). Using manual input of age, weight and height; body surface area (BSA) and body mass index (BMI) estimates are calculated, so that indexed values may be calculated and displayed, such as cardiac output index (CI) and stroke volume index (SVI or SI). Often available is recording of instantaneous values and display of a long-term trend graph.

Instantaneous Values

In an Esophageal Doppler Monitor (EDM) or Oesophageal Doppler Monitor (ODM), during the time the

aortic valve The aortic valve is a valve in the heart of humans and most other animals, located between the left ventricle and the aorta. It is one of the four valves of the heart and one of the two semilunar valves, the other being the pulmonary valve. The ...

is open (ejection time or flow 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). Flow time (FT) is the time difference between the sudden increase in velocity (T0) and the return to near zero velocity (T1). Stroke distance (SD) can calculated from the plug flow like velocity (v(t)): :

SD = \int_^ v(t)\,dt

. An estimate of the aortic cross-sectional area is calculated from a function of age, weight and height. The cross-sectional area is adjusted to give more accurate cardiac output and renamed to aortic constant (AC). The product of stroke distance and aortic constant gives stroke volume (how much blood was ejected from a heartbeat into the

arteries An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...

). The heart rate (HR) can be calculated from the time difference between the current peak velocity and the previous one.

Cardiac output In cardiac physiology, cardiac output (CO), also known as heart output and often denoted by the symbols Q, \dot Q, or \dot Q_ , edited by Catherine E. Williamson, Phillip Bennett is the volumetric flow rate of the heart's pumping output: t ...

(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.

Parameters

The Doppler frequency shift signal is processed to produce a list of signal power against frequency samples, 180 times a second. This list is analysed to identify the velocities of the

plug flow In fluid mechanics, plug flow is a simple model of the velocity profile of a fluid flowing in a pipe. In plug flow, the velocity of the fluid is assumed to be constant across any cross-section of the pipe perpendicular to the axis of the pipe. T ...

like movement down the centre of the aorta. The plug flow velocities can be differentiated and integrated against time to derive acceleration, peak velocity and stroke distance. With an aortic constant based on age, weight and height; stroke volume (SV) is calculated.

References

{{reflist Medical equipment Intensive care medicine