The critical speed at which flow of a liquid of density in a pipe of diameter D changes from laminar to turbulent is determined by the Reynolds number R and the viscosity of the liquid ,

For cylindrical pipes, the Reynolds number corresponding to critical velocity is about 2000.

Density of blood, , and its viscosity at 370 C, . Therefore,

the greatest speed at which blood can flow through an artery of diameter 3.8 mm if the flow is to remain laminar is