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However, if there is blood moving in a vein or artery under the skin, then the ultrasound beam is changed by the Doppler effect. The reflected beam is different from the projected beam and the hand held Doppler machine is calibrated to pick up this change.

In the 1980s and 1990s, when duplex ultrasound scanners were very rare, the hand held Doppler was seen to be magical. A patient could be stood up, a hand held Doppler placed over a vein and when the vein was squeezed, blood flow could be heard.

A hand held Doppler is a small box that can be held in the hand or put in the pocket. It has a wire coming from it leading into a small cylindrical probe, often called a pencil probe.

The biggest problem with the hand held Doppler is that you do not know which vein is being examined. If the Doppler probe is being pointed into the groin, there are several veins that might be at that point under the skin. If only one wooosh is heard, it might make the doctor or nurse think that the vein is normal. However this would be wrong if the Doppler had slipped and the second wooosh was missed simply due to bad positioning. Alternatively, the Doppler may be examining a completely different vein that is working whilst a big varicose vein slips passed unnoticed.

If a wooosh was heard on squeezing, then this meant that the vein was being examined and blood flow going up the vein was being heard. On release of the vein, if the valves were working nothing would be heard. If, however, the valves were not working, then a second wooosh could be heard as blood fell back down the vein.

If nothing is moving, the ultrasound beam that is reflected is the same as the one that was projected and nothing happens.

When the probe is placed on the skin, contact gel is used to make a good connection and then the ultrasound beam is projected directly into the skin and to the underlying structures.

Now with the duplex ultrasound scanner being available in all reputable vein clinics, no one should ever need to use a hand held Doppler to assess varicose veins or recurrent varicose veins ever again.

You will often see a hand held Doppler being used by district nurses or nurses on the ward in hospitals. They are very useful to find pulses in arteries particularly at the ankles in the foot where they can be hard to feel.

Since duplex ultrasound scan has now become more available, it has become much clearer that hand held Dopplers can give the wrong information.