Abstract
Pressure drops in cannulas for hemodialysis have been measured in vitro in both flow directions for five different viscosities and up to 600 mL/min flow. Cannula dimensions were 15, 16 and 17 gauge and 15, 20 and 25 mm nominal length. The measurements were taken at room temperature with glycerin solutions as test fluid.
Results
The pressure drops can be described by a second order function but not by the Hagen-Poiseuille law even when corrected for inlet and outlet effects as described by Bernoulli's law. Pressure drops depend on flow direction. Back-eyes and cannula tips have no influence on the pressure drop. Pressure drops and especially flow direction asymmetry are influenced by the hydraulic design of the connection piece between cannula and tubing. The results can be used for prediction of pressure drops in cannulas allowing better use of pressures already measured in the extracorporeal circuit of hemodialysis machines.
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