Central venous catheters are widely used as a hemoaccess method for dialysis therapy. In this study, the performance parameters (velocities, pressure drop, shear rates, access recirculation) of the Niagara catheter are analyzed using computational fluid dynamics. Side holes are left open, closed, or reduced in size to assess the influence of this design feature. Initially the catheter is inserted in a tube which represents the vena cava. In the "arterial" luminal tip, wall shear rates over 20,000 s(-1) are common and peaks attain 55,000 s(-1) at a 300 mL/min blood flow rate. The presence of side holes appears to affect the location but not the level of these elevated shear rates. Halving their diameter causes elevated shear rates to appear in a more extended region with peaks up to 80,000 s(-1). Simulated recirculation percentage is nil in normal catheter use, but attains 30% with reversed catheter connections. The results of the tube model are compared to those of an anatomically realistic right atrium model, which was three-dimensionally reconstructed. It is concluded that most catheter's specific hemodynamic properties can be deduced from the tube model.

The high velocity of blood flow exiting aortic arch cannulae may erode atherosclerotic material from the aortic intima causing non-cardiac complications such as stroke, multiple organ failure and death. Five 24 Fr cannulae from the Sarns product line (straight open tip, angled open tip with and without round side holes, straight and angled closed tip with four rectangular, lateral side holes), and a flexible cannula used at the University Hospital of Gent (straight open tip) are compared in an in vitro steady flow setup, to study the spatial velocity distribution inside the jet. The setup consists of an ultrasound Doppler velocimeter, mounted opposite to the cannula tip in an outflow reservoir. An elevated supply tank supplies steady flow of 1.3 L/min of water. Exit forces at various distances from the tip are calculated by integrating the assessed velocity profiles. The pressure drop across the cannula tip is measured using fluid filled pressure transducers. The four sidehole design provides the lowest exit velocity (0.85 versus 1.08 m/s) and force per jet (0.03 vs 0.15-0.20 N). The round sideholes are useless as less than 1% of the flow is directed through them. Furthermore, the use of angled tip cannulae is suggested because the force exerted on the aortic wall decreases the more the angle of incidence of the jet deviates from 90 degrees. Pressure drop is the lowest for the 4 side hole design and highest for the open tip and increases when an angled tip is used.

To investigate the haemolysis in haemodialysis cannulae, an in-vitro set up is built, using a unipuncture dialysis system. This system is connected to a bag with fresh calf's blood, by the cannula under test, mounted in a large bloodline (5mm diameter). The blood characteristics are kept constant by means of a bicarbonate dialysate in the dialyser. During a 6h period, haematological parameters are regularly sampled. Flow through the cannulae is recorded, which is about 500mUmin. Four different cannulae are tested and compared to the results obtained without any cannula in the circuit. In all cases a linear increase in plasma free haemoglobin levels is found after 6h. The cannulae can be ranked from 8F catheter over 13G, 14G to 16G cannula, the latter producing the highest degree of haemolysis. When using plastic cannulae at high blood flows, their haemolytic effect may not be neglected.

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An artificial lung is used during cardiopulmonary bypass to oxygenate blood and control blood temperature. The oxygen transfer rate-flow rate characteristics of three hollow fiber membrane artificial lungs (Sarns Turbo 440, Cobe Optima, Dideco Compactflo) were determined in vitro to characterize design features. Results are presented as a unique dimensionless relationship between Sherwood number, NSh (ratio of convective to diffusive mass transfer), Schmidt number, NSc (ratio of momentum to diffusive transport), and Reynolds number, NRe (ratio of inertial to viscous forces). This relationship is a function of device porosity, epsilon, and characteristic device length, xi, defined as the ratio of the mean blood path and manifold length: Nsh/NSc(1/3) x xi(1/2) = phi x (epsilon(1/m) x NRe)(m) where phi = 0.26 and m = 1.00 for NPe < 3,200 and phi = 0.47 and m = 0.64 for NPe > 3,200 where NPe is the dimensionless Péclet number defined as NRe x NSc. We found good correspondence between the model predictions and in vitro blood oxygen transfer rates. We conclude that this dimensionless approach allows us (1) to compare artificial lungs independently, (2) to relate water tests to blood, and (3) to predict the oxygen transfer rate of a new artificial lung design.