Time is of the essence in an emergency. When medics are treating trauma patients, every second counts. Yet finding a suitable vein into which to make a lifesav-ing injection can be difficult, and doubly so in the case of someone whose heart is beating only weakly. Michael Gray, of the Georgia Institute of Technology, in Atlanta, and his colleagues hope to change that. They have designed a cheap, handheld device that should be able to detect veins routinely in an emergency. It works using the Doppler effect-the phenomenon that causes a siren to change pitch when the vehicle sounding it drives past.
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