Blood flow affects clot formation
Australian researchers have found the mechanism that stops some stroke and heart attack patients responding to blood thinning treatments such as aspirin.
The research, published today in Nature Medicine, reveals the shape of blood vessels plays a significant role in the formation of platelets after an injury or accumulation of plaque in vessels.
Biologist and lead author Warwick Nesbitt, from Monash University in Melbourne, says anything that changes the shape of the vessel will change the way the blood flows through it.
He says as blood flows over an obstruction it affects the way platelets, cells that form blood clots or thrombus, behave.
The obstruction causes the blood to accelerate and then rapidly decelerate, he says.
"Think of it like a plane wing. As the air is flowing over the top of the wing it has to increase in speed and then it decreases on the other side."
Nesbitt says it's during the slowdown of the blood flow that platelets become reactive.
When the platelets sense the change in blood flow they start to extend tethers, small arm like membranes that are visible under a microscope, and attach to the damaged surface, he says.
"When the flow decelerates the tether starts to act like a little muscle and contract, reeling the platelet into the surface."
Nesbitt says before his research the formation of blot clots was thought to be caused solely by proteins released into the blood stream after an injury, causing platelets to clump together.
"In the past people assumed that the blood was flowing through at a fairly constant rate."
Nesbitt says they discovered the effect of blood flow on clot formation by using drugs to block chemicals normally released during platelet aggregation.
He says aggregation still occurred when there was a change in the vessel.
Nesbitt says 10% to 12% of stroke or heart attack sufferers that show aspirin resistance may form clots in vessels due to changed blood flow caused by injury or plaque build up.
Aspirin, an anti-clotting treatment, reacts with chemicals released by platelets to thin the blood.
Nesbitt says the study has shown that because aggregation can form without these chemicals, aspirin doesn't always help.
Nesbitt is now developing a device that can mimic blood flow behaviour to use as a diagnostic tool.
"You can flow blood through this device and then measure the amount of platelet thrombus that's formed to see whether they're hyper-responsive or they have a defect in their platelet function," he says.
Nesbitt also says they're looking into drug treatments that inhibit this new type of platelet aggregation.