Researchers are using computer simulations to investigate how ultrasound and tiny bubbles injected into the bloodstream might break up blood clots, limiting the damage caused by a stroke in its first hours.
Strokes are the most common cause of long-term disability in the United States and the third most common cause of death. More than 795,000 Americans suffer a stroke every year, which happens when a clot blocks an artery or blood vessel and restricts blood flow to the brain. The longer the clot stays intact, the more brain tissue dies, the higher the chance of severe damage, and the lower a victims chance of survival.
Now, researchers from the Universities of California at Berkeley (UC Berkeley) and San Diego (UCSD) suspect these clots could be broken upwithout surgery or drugsusing a combination of microbubbles and high intensity focused ultrasound (HIFU). The team used supercomputers at the Department of Energys National Energy Research Scientific Computing Center (NERSC) to figure out how this might work. Their findings were published in Journal of the Acoustical Society of America.
One day, HIFU could be a useful medical treatment for people who are stroke victims. But before this can happen, we need to establish some fundamental background work, which includes understanding how HIFU accelerates damage to a clot when bubbles are present, says Andrew Szeri, Professor of Mechanical Engineering at UC Berkeley and co-author of the paper.
According to Szeri, the teams NERSC allocation was incredibly valuable because it allowed them to generate the preliminary data needed to write a research proposal for funding in a new area. Without some kind of preliminary data, its a non-starter; theres just no way for us to find funding, Szeri adds.
Scanning electron micrograph of a human citrate blood clot before HIFU treatment (left column) and after HIFU treatment (right column). The images on the left show a dense fibrin fiber network with numerous cells incorporated into the matrix prior to HIFU exposure. As seen in subfigure (a), right, there is clearly damage to the fibrin network of the blood clot as well as lysis of red blood cells.
Aside from surgery, a drug called tissue plasminogen activator (tPA) is currently the only federally approved treatment for stroke-causing blood clots. But it is estimated that less than five percent of all patients transported to emergency rooms actually receive the clot-dissolving drug. For safety reasons, it can only be administered to some patients and then only within four-and-a-half hours of the initial stroke.
In the early 1990s, researchers noticed that ultrasound scans seemed to enhance the effectiveness of drugs like tPA, but nobody knew why. A clinical trial in 2004 confirmed that obstructed blood vessels cleared more quickly when ultrasound was administered in combination with tPA. In the years after, many researchers built on this result by trying to figure out how to administer ultrasound to maximize the clot-busting effectiveness of tPA.
These experiments never made too much sense to me. With or without ultrasound, tPA is only available to about 3 percent of all stroke victims worldwide. So, regardless of how successful this approach is 97 percent of the population will not benefit from it, says Thilo Hoelscher, Director of UC San Diegos Brain Ultrasound Research Laboratory and co-author on the paper. We are looking for a safe treatment for stroke patients who cannot receive tPA.
Because artificial microbubbles are already widely used as contrasting agents, Hoelscher suspected they could be safely used in combination with HIFU to dissolve blood clots. Ultrathin shells of fat molecules filled with gas, these artificial bubbles are about one-eighth of the size of red blood cells. Once injected into the bloodstream, they only last a few minutes in the blood pool. The gas is exhaled and the fat molecules are metabolized in the liver or the spleen.
Originally posted here:
Clot-dissolving bubbles to treat strokes?