Our precious arteries are encased in three layers of protective cells—something to be grateful for, considering that injured vessels can cause an adult to bleed to death in fewer than five minutes. But when extreme trauma does cause an artery to rupture, very few options exist for stemming the flow of blood. Now, a novel short-term approach for closing a hemorrhaging artery is one step closer to helping humans, as researchers have shown that pulses of electricity can make an injured artery constrict, ultimately reducing blood loss.
A team led by Yossi Mandel of Bar-Ilan University, successfully demonstrated this approach in sheep; their results were published on 23 November in IEEE Transactions on Biomedical Engineering.
While working for the Israeli army, Mandel was tasked with studying how to stop severe bleeding from trauma. “Bleeding control is, of course, one of the main aims of every army,” he says. “There were some preliminary reports on the effect of electric fields on blood vessels and I wanted to further explore this phenomenon and its translational potential for treating patients and soldiers wounded in the battlefield.”
For his most recent experiments in sheep, his team first modeled different configurations of electrodes to see which could deliver the most effective electric field to the wall of an artery. This included modeling the electrical properties of each layer of the artery wall, as well as the thermal properties of the surrounding tissues.
Using these data, they created two experimental setups: one with a monopolar electrode that produces an electrical field with a single, large focus, and one with bipolar electrodes that generated two fields, each focused on a different area.
In a series of experiments, the team then tested their customized electrodes by inserting them into the hemorrhaging carotid arteries of sedated sheep. They wanted to see if the electrical fields produced by the electrodes could cause the artery to constrict enough to limit blood loss. The technique worked and, as predicted by modeling, the monpolar electrode caused the blood vessel to constrict at just one site, and the bipolar configuration caused constriction at two sites.
The group then measured how much blood loss occurred when the vessels were restricted by 50 and 100 percent. They reported "moderate" blood loss when the artery was restricted by 50 percent, and a sevenfold reduction in blood loss when the artery was restricted by 100 percent, compared to no treatment. The group could not say that treatment stopped blood loss entirely, because some blood may have leaked undetected through small passages in the artery even when it was restricted by 100 percent.
An analysis of the arteries after treatment revealed no damage, and simulations suggest that temperature increases in nearby tissue from the electrical field do not exceed levels deemed unsafe, the researchers say.
The positive results reported from applying this technique to the carotid arteries of sheep were not replicated when the technique was performed in the femoral arteries of sheep, however. This may have to do with a fundamental difference between the two types of arteries in this animal. Carotid arteries harbor many sympathetic nerves—which respond to the electrical field—and femoral arteries do not.
The role of sympathetic nerves is supported by previous work that Mandel conducted in the femoral arteries of rats, which contain many sympathetic nerves. His earlier work shows that electrical fields can cause the femoral arteries of rats to constrict. Human femoral arteries also contain many sympathetic nerves, suggesting that this technique could work for us as well.
According to Mandel, this is the first demonstration of their technique in large arteries in living animals, and the first evidence supporting the role of sympathetic nerves. Moving forward, he says, “We plan to further explore the potential of this technology on other blood vessels and study the potential effect of electric field application on blood pressure.”
Michelle Hampson is a freelance writer based in Halifax. She frequently contributes to Spectrum's Journal Watch coverage, which highlights newsworthy studies published in IEEE journals.
