Page 3, Turbulence & Rheology, Dr. D. Penney

Turbulence (continued..)

In physiological systems there are at least three important factors causing turbulence:

1) Increased velocity of flow resulting from stenosis or coarctation, exercise, patent ductus arteriosus, and a cuff pressure between the systolic and the diastolic pressures (during B.P. measurement) predispose to turbulence. Because velocity is in the numerator of the Reynolds equation, anything that increases it, increases the Reynolds number.

2) A change in radius also produces changes in velocity, so the relationship between velocity and radius is most important.

3) Blood viscosity has the potential to change the Reynolds number. It is usually constant in normal people from day to day, but in some instances, as during severe anemia, hematocrit drops sharply and therefore also viscosity. Since viscosity is in the denominator, a smaller value raises the Reynolds number. Specific gravity or density of the blood is not clinically important, because blood density does not change even when blood becomes extremely viscous.

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