Paulo Arratia, a professor in the Department of Mechanical Engineering and Applied Mechanics at the School of Engineering and Applied Science, conducted the study with two Penn students and professor Christian Wagner from Saarland University in Germany.
The results of the study pose important questions for the behavior of blood under various conditions in the body, which also has implications in healthcare.
Atherosclerosis, or hardening of the arteries, is one of today’s major healthcare problems. Cholesterol, fats, and age contribute to the hardening, which leads to thickening of the vessel walls, and subsequently, plaque formation.
Because of this, blood has a harder time pushing through the blood vessels to get to and from the heart. The heart, which functions as a pump, now has to work harder to generate more force to get blood through the smaller arteries and to the tissues, resulting in a higher blood pressure.
Arratia’s findings suggest that plasma is an important contributing factor to the ease of blood flow.
Blood is about 55 percent plasma; the rest is made up of fats and chemical substances. So the plasma contributes largely to the blood makeup. Arratia and his team found that plasma actually exhibits a “higher flow resistance,” according to the article posted on Penn’s website.
“Our experiments showed that the blood plasma forms threads,” Wagner said. “That is, it exhibits an extensional viscosity.”
Arratia points out that altering the resistance of blood, however slightly, can have a large impact in a system as sensitive as the human body.
Blood flows through many different types of vessels – elastic arteries, valved veins, and small-diameter vessels known as capillaries, where red blood cells can often only pass one at a time.
So this plasma component of blood, exhibiting a higher flow resistance, becomes important in these smaller vessels.
In addition, these properties are very different from that of water, and yet water composes 92 percent of blood plasma. The other eight percent is made up of nutrients and proteins.
For this reason, “nobody thought plasma could be a complex fluid,” Arratia said.
These results have opened the door into further investigations of blood plasma properties that might be different than previously imagined. They also pose interesting questions for an already complex health issue.