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Unsteady Blood Flow Promotes Arteriosclerosis Development

It is often more turbulent in the human bloodstream than is actually good for the human body. That is what an international research team led by Dr. Duo Xu from the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen has found out.

Can we actually assume that our heart pumps blood through our arteries so slowly that a steady, turbulence-free stream of blood is created? Not really. An international research team recently published a paper in Proceedings of the National Academy of Sciences of the USA (PNAS), which points to it often being more turbulent in our bloodstream than previously thought. This is not advantageous for the human body, as irregularities in the bloodstream have been shown to promote infection and functional disorders of the blood vessels’ inner layer – the endothelium. Infection of the endothelial layer can then lead to the development of arteriosclerosis, the civilization disease, which is the number one cause of death globally. Dr. Duo Xu, who has been researching flows at the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen for the past four years, contributed to the paper and submitted it to PNAS for publication.

“Pulsating flows through tubular geometries are laminar provided that velocities are moderate.” That is how the abstract of the paper that has now been published in one of the worldwide most renowned scientific journals begins. It means that no turbulence develops in a liquid if it is pumped through a tube slowly enough. Generally, pulsating flows are more prone to turbulence that steady flows. However, it was always assumed that no turbulence develops in the human circulatory system due to the low velocity and the high level of viscosity of blood.

Dr. Duo Xu has now shown that turbulence-free behavior of blood is only ever attained under ideal conditions. The research team’s core finding is that pulsating flows react extremely sensitively to geometric disorders and thus already become turbulent at a flow velocity that is lower than the velocity that initiates turbulence in a non-pulsating, constant mass flow. With regard to human blood flow, this means that turbulence occurs far more frequently than is to be expected based on the classic fluid mechanics theory, as there are frequently curves, uneven areas, or constrictions in the human bloodstream, for example due to arteriosclerotic lesions (arterial calcification).

Experimental Proof

The research team has shown, both theoretically using simulations and experimentally, that bloodstreams with geometric unevenness trigger turbulence. In the experiments it can be clearly seen how swirls develop in such critical areas within the phases during which the pulsating blood flow slows down. Said swirls then rapidly develop further into turbulence. It is only thanks to the new acceleration from the next heartbeat that the flow calms once more: it becomes laminar. This means that a blood flow disruption can occur in blood vessels that are not ideally formed during each individual pulse cycle.

Why Is Turbulence Dangerous to Health?

The inner lining of blood vessels – the endothelium – reacts very sensitively to shear stress. In this case, the term “shear stress” refers to the friction that develops on the inner wall of the vessels due to the flow of blood. Usually, the endothelial cells are attuned to a constant flow in one direction. When there is now turbulence with related shear stress fluctuations and reverse flow during each pulse cycle it can initiate cellular disfunctions that can lead to an endothelial infection and to arteriosclerosis in the long-term.

For people with cardiovascular diseases, the research findings mean that they are exposed to a higher risk of arteriosclerosis developing or progressing due to the occurrence of turbulence in areas of available unevenness or constriction. However, turbulence can also occur in healthy people, which clearly shows us the high complexity and sensitivity of our blood circulation system – and also that this research is not yet concluded.

The research was carried out by scientists from the Institute of Science and Technology Austria, the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen, the Friedrich-Alexander University Erlangen-Nuremberg, and the Center for Applied Mathematics at Tianjin University. The experiments were carried out at the Institute of Science and Technology Austria under the leadership of Professor Björn Hof and the simulations were undertaken by Professor Marc Avila’s research group at ZARM.

Scientific Contact:

Dr. Duo Xu
Center of Applied Space Technology and Microgravity (ZARM)
University of Bremen
Email: duo.xuprotect me ?!zarm.uni-bremenprotect me ?!.de

Prof. Dr. Marc Avila
Center of Applied Space Technology and Microgravity (ZARM)
University of Bremen
Email: marc.avilaprotect me ?!zarm.uni-bremenprotect me ?!.de

Press Contact:

Birgit Kinkeldey
Center of Applied Space Technology and Microgravity (ZARM)
University of Bremen
Email: birgit.kinkeldeyprotect me ?!zarm.uni-bremenprotect me ?!.de
Phone: +49 (0)151 23684370

 

Blutstrom
Visualization of the numerical simulation of turbulent blood flow.