The Reynolds number is an important indicator of how smoothly blood is flowing through blood vessels. is determined by the length of accumulated plaque , the vessel radius and the blood velocity . If the Reynolds number is below 2300, the flow is laminar, shown by straight arrows exiting the area of congestion (yellow) in the graphic. But if rises above 2300, blood flow can turn turbulent, as shown by curly arrows exiting the congestion. Laminar flow is considered healthy, while turbulent flow can have grave consequences such as heart attacks if occurring in inappropriate regions. This Demonstration shows how important, seemingly small changes can affect our health.
The Reynolds number=(length of congestion)×(blood density)×(flow rate in congested area)/viscosity.
Flow rate is determined as a function of effective vessel radius and incoming velocity due to the conservation relation: (=area of the cross section).
 S. S. Mao, N. Ahmadi, B. Shah, D. Beckmann, A. Chen, L. Ngo, F. R. Flores, Y. L. Gau and M. J. Budoff, "Normal Thoracic Aorta Diameter on Cardiac Computed Tomography in Healthy Asymptomatic Adult; Impact of Age and Gender," Academic Radiology, 15(7), 2008 pp. 827–834. doi:10.1016/j.acra.2008.02.001.