In laminar flow blood particles remain in a single layer, while in turbulent flow the particles move erratically between layers. Turbulent flow is less efficient than laminar flow, i.e., a relatively larger pressure difference is required for the same amount of flow. The Reynolds number is a dimensionless number (no units) characterizing the flow. In a straight vessel, when the Reynolds number exceeds the critical value of 2200 flow becomes turbulent. Below the critical Reynolds number flow is laminar. In general, flow in the arterial system is laminar. In the aorta when cardiac output is large, as during exercise, flow can be turbulent. Flow distal to stenoses and stenotic valves is turbulent. Flows in vascular access grafts in hemodialysis patients can also be very high leading to turbulence.
KeywordsReynolds number Stenosis Non-laminar flow
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