Anaes SAQs · Measurement & monitoring physics
Fluid flow: laminar, turbulent and the Reynolds number
Primary — Poiseuille: Q = delta-P pi r^4 / (8 viscosity length); radius to the fourth (halve radius = 1/16 flow); laminar (smooth, parabolic profile, pressure proportional to flow) vs turbulent (chaotic, flat profile, pressure proportional to flow squared); Reynolds number Re = density velocity diameter / viscosity (< 2000 laminar, 4000 turbulent, 2000-4000 transitional); turbulence favoured by high velocity, large diameter, low viscosity (anaemia = murmur), kinks; clinical: IV cannula size, ETT resistance, large-airway turbulence vs small-airway laminar, aneurysm/valve turbulence.
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State the Hagen-Poiseuille equation and explain its clinical significance. Define the Reynolds number and give the threshold values for laminar and turbulent flow. Give two clinical examples of each flow type.
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