Thrombosis threatens prosthetic rotary pumps

When a heart fails and there are no donors for a new heart, what options are there to explore? The best option is to receive a rotary pump or prosthetic tubes. These are great options except for one major caveat, a little effect known as thrombosis. Thrombosis is the formation of a blood clot inside a blood vessel. Vincent Turitto gave his “Around the World Talk” to describe this effect in detail. He opened with, “The reason why I call this my ‘Around the World Talk’ is because whenever I give this talk, people always ask me to talk in another country.”

A major cause of thrombosis are rotary pumps that act as assistant devices for people who have dysfunctional hearts. The fact of the matter is that any device stuck into the blood causes thrombotic events. “Until the mid-80s, cardiologists used to not believe thrombosis was a significant problem,” explained Turrito. Prosthetic devices used as a replacement for the heart come with many complications including surface infections, abnormal shear forces, and transport rates to name a few. Thrombotic events occur mostly in prosthetic heart valves, vascular stenoses, and rotary pumps. The joke in the medical community is that all of these parts are “guaranteed for life” because once one of these parts is inside of the body, the patient has, at most, two years to live.

Human blood is approximately 40% red blood cells, about 1% blood platelets, and a few coagulation proteins. All of these cells are affected by high shear stresses. “You want to avoid these high stress situations,” said Turrito, “[since] this is how you get leakages.” The leakages Turrito is speaking of are hemoglobin leaking out of red blood cells at high pressures caused by the large shear stresses. The red blood cells play a major role in the production of thrombosis. Red blood cells enhance the transport of blood platelets, affect the heterogeneity of local platelet formation, and they may even have a chemical factor that affect the platelets. Turrito stated, “I have not yet been able to determine if red blood cells have a chemical effect on thrombosis.” The shear stresses also cause platelets to stick together more, which causes a more severe thrombosis.

Another cell affected by shear pressures are smooth muscle cells. This is known as tissue factor activity. This process is directly responsible for micro-particle formulation. However, Turrito feels that this is a misnomer, “Micro-particles are misnamed, they are smaller than a micron, they are more like nano-particles.” Shear forces, however, remove the tissue factor of thrombosis. This raises a very important question; Is thrombosis in prosthetic devices related to surface contact of tissue factor mechanisms? Turrito answered this question by stating, “You are likely to see a lot of cellular debris formed near the pump.” This simply means that micro-particles will show considerably more tissue activity. They are the cells that can activate events that are not intended.

In conclusion, shear flow influences thrombosis formation through a variety of mechanisms. The extent that shear forces have on thrombosis still remains to be determined. This is one prosthetic body part that still needs a lot of research, and if any chemical engineers are up to the task, many lives will be saved.