Over the past five years, many studies have demonstrated that patients who receive blood transfusions have higher incidences of heart attack, heart failure, stroke, and even death. While it is known that the banked blood is not the same as blood in the body, the reasons behind banked blood's association with worse outcomes have not been well-understood.
But Duke Medical Center researchers have now discovered a property of banked blood that they believe may account for its questionable utility, and at the same time, uncovered a possible solution.
Almost immediately after it is donated, the researchers found, human blood begins to lose nitric oxide, a key gas that opens up blood vessels to facilitate the transfer of oxygen from red blood cells to oxygen-starved tissues.
"It doesn't matter how much oxygen is being carried by red blood cells, it cannot get to the tissues that need it without nitric oxide," says Jonathan Stamler, a professor of cardiovascular and pulmonary medicine and senior author of one of two papers published by the researchers in the Proceedings of the National Academy of Sciences. "If the blood vessels cannot open, the red blood cells back up in the vessel, and tissues go without oxygen. The result can be a heart attack or even death."
They also found that as nitric oxide levels decrease, the red blood cells become stiffer, making it more difficult for them to deform their shape in order to squeeze through tiny blood vessels. "The issue of transfused blood being potentially harmful to patients is one of the biggest problems facing American medicine," Stamler says.
"Most people do not appreciate that blood has the intrinsic capacity to open blood vessels, thereby enabling oxygen to get to tissues. Banked blood cannot do this properly."
However, Stamler adds, transfusions, and therefore banked blood, are still critically important. In the studies, his team found that adding nitric oxide gas to stored blood before transfusion appears to restore red blood cells' ability to transfer oxygen to tissues, though he cautions that the practice still needs to be proved in a clinical trial.
Transfusion Mystery Solved
January 31, 2008