The U.S. military has begun developing an ultrasonic tourniquet in an effort to stop life-threatening bleeding during combat.
Called the Deep Bleeder Acoustic Coagulation (DBAC) program, it aims to create a cuff-like device that wraps around a wounded limb. Rather than applying pressure to the wound to stem the flow of blood, the device would use focused beams of ultrasound (sound waves above the audible frequencies) to non-invasively clot vessels no matter how deep they are.
If a major blood vessel is hit and a lot of blood lost quickly, a person can die in a few minutes, says Michael Pashley, head of Ultrasound Imaging and Therapy at Philips Research in Briarcliff Manor, NY, one of the groups taking part in the program.
According to the Pentagon’s Defense Advanced Research Projects Agency (DARPA), “these internal bleeding injuries are the leading cause of death for soldiers in the battlefield,” says Pashley. In light of this, DARPA is committing up to $51 million for the project over four years, to be spread among a number of different research organizations.
The ultrasound tourniquet is intended to buy time, so that a medic can get the patient to a better-equipped medical facility, says Lawrence Crum, director of the Center for Industrial and Medical Ultrasound at the University of Washington’s Applied Physics Laboratory in Seattle, who has been working in this field for more than a decade.
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.