We’ve got more on the ultrasonic tourniquet, the device that combines two of our favorite things in the Emergency department: ultrasound, and stopping bleeders. The MIT Technology Review has the story on DARPA’s new bid for using high-intensity focused sound waves to heat and cauterize deep vessels — these major limb arteries or veins are big enough to require minutes or hours of pressure, normally, but the ultrasound tourniquet can stop the bleeding in seconds:
Once applied to a wounded limb, the cuff would automatically detect and then seal damaged blood vessels or arteries, by focusing beams of ultrasonic waves at the wound to clot it, in a process known as high-intensity focused ultrasound, or HIFU.
Ultrasonic waves are usually innocuous, bouncing off tissue. This is the principle behind sonograms, says Crum. But when the ultrasonic waves are focused, the effect is radically different. “If you concentrate ultrasound in the same way as light, you can raise the temperature, particularly if the wave is absorbed by the tissue,” he says.
To achieve this effect, the frequency has to be geared to increase its absorption by the tissue, while the intensity must be roughly one million times greater than imaging ultrasound. When applied to a bleeding wound, the effect is similar to cauterization, Crum says.