What is a Doppler test?
A Doppler test is a quick and painless way to detect blood flow. Professor Charles McCollum tells Senior Cardiac Nurse Emily McGrath more about Doppler tests.
Why would I have a Doppler test?
A Doppler test is used to detect blood flow. It shows whether a pulse is present and whether there is blood flow to a limb. It can diagnose or help to manage conditions such as peripheral arterial disease (PAD) or diabetic foot ulcer. Compared with feeling the pulse with the fingertips, which can be unreliable, a hand-held Doppler test has far greater value.
It can also be used to check if there is adequate blood flow to the hand or leg following operations or injuries (including fractured bones, which can reduce blood flow to limbs).
If there is any uncertainty about whether a pulse is present, a Doppler test should be carried out
Doppler tests are useful before surgery. For example, every patient coming in for orthopaedic surgery below the hip should have a Doppler test on their ankle. This is because if you have an operation on the leg and there’s poor blood flow, it may not heal well. A Doppler test on the leg is also recommended before heart bypass surgery. This is because a vein may be taken from your leg to use for the bypass, but the leg wound may not heal if there isn’t a good blood supply.
Are there different types of Doppler test?
A Duplex ultrasound is a combination of Doppler and traditional ultrasound. It can be used to identify the best vein from your leg to use for a heart bypass, and can also help to diagnose deep vein thrombosis (DVT).
A special type of Doppler, a transcranial Doppler, is used to look at the arteries supplying the brain.
Do I need to do anything to prepare for a Doppler test?
No, and the only equipment needed is the Doppler instrument and ultrasound jelly.
Is there anyone that a Doppler test wouldn’t be suitable for?
No. However, a Doppler test isn’t usually used on the chest, because ultrasound can’t travel through the air in the lungs.
How does a Doppler test work?
A Doppler ultrasound records sound waves reflecting off moving objects, such as blood cells, to measure their speed and other aspects of how they flow. So it’s slightly different to traditional ultrasound methods, which use sound waves that bounce off organs and body structures, such as blood vessels, to create pictures.
What does a Doppler test involve and how long does it take?
Usually, a blood pressure cuff is applied to one or more limbs, a jelly is applied to your skin, and the ultrasound probe (transducer) is applied to your skin and focused on the relevant artery.
For most healthy people a Dopper test is pain-free. There are no risks or after-effects
The time taken depends on what it is being used for. Applying a Doppler to the arteries of the wrist or the ankle to see if the blood flow is adequate only takes 20 seconds. Measuring the ankle and the wrist’s arterial pressure will take two or three minutes.
Measuring the ankle–brachial pressure index (ABPI), which compares the blood pressure at your ankle with the blood pressure at your wrist, will take six to eight minutes. This can show whether there is a blockage in the artery supplying a limb.
Will a Doppler test hurt?
Usually, no. Sometimes the cuff has to be applied on an injured leg, or a leg with an ulcer that may be sore, but the cuff will only be inflated for 30 seconds. It’s non-invasive. For most healthy people it’s pain-free. There are no risks or after-effects.
What about ‘false positives’?
This can be a risk if your healthcare professional only feels your pulse with their fingertips – they may think they feel a pulse when there isn’t one. This can be because they are imagining it or because they are feeling the pulse in their own fingers. If there is any uncertainty about whether a pulse is present, a Doppler test should be carried out.
What are the latest developments in imaging using ultrasound?
Technology for imaging arteries by ultrasound is developing at an impressive pace. The imaging of artery disease is clearer with duplex ultrasound than it is with MRI and CT angiograms. It also has the advantage of showing the speed (velocity) of blood flow, and any turbulence. The flow velocity tells you how narrow the artery is, making Doppler by far the best test to show the severity of arterial narrowing or disease.
We are just starting to introduce ways to create 3D images of arteries and veins, allowing clinicians to see the extent of arterial disease for themselves.
We are quite close to being able to look at the inside of arteries, like a virtual endoscopy, without the need for invasive tests. This will revolutionise the imaging of arteries outside of your chest.