Age Determines How a Human Aorta Stretches
When repairing blood vessels, clinicians often use polyester-based tubes known as aortic prostheses. Unfortunately, the tubes are so stiff that they can induce cardiovascular problems when implanted into patients, says Marco Amabili of McGill University in Canada. On learning of this problem from a heart surgeon, Amabili and his colleagues set out to study the material properties of the human aorta. The researchers identified a strong correlation between an aorta’s age and its response to a pulsing flow, information that’s key to improving future designs of life-sustaining prostheses.
The largest artery in the body, the aorta is the first port of call for blood exiting the heart. Despite its key role in blood transportation, few experiments have studied the behavior of this soft, rubbery tube under its normal conditions. Amabili’s team remedied this problem by inserting pieces of human aorta into a “mock” circulatory loop; the pieces were taken from 11 healthy organ donors, aged between 25 and 84. They then sent pulses of a blood-like liquid through the loop at rates of between 60 and 180 beats-per-minute.
The team observed that the diameter of a natural aorta expands and contracts, after a slight delay, with the rise and fall of the flow rate. This delay decreases with the aorta’s age. They found that the “dynamic stiffness”—a parameter linked to how a material responds to a changing load—increases tenfold from the youngest aorta to the oldest. And they determined that the expansion of the aorta decreases from 10% for the youngest aorta to 2% for the oldest. Making similar measurements on a prosthetic tube, they detected no expansion. This difference, Amabili says, means that implanting a prosthesis into a patient is equivalent to giving them a sick aorta rather than a healthy one.
This research is published in Physical Review X.
Katherine Wright is a Senior Editor for Physics.