Effect of catheter placement on 3-D velocity profiles in curved tubes resembling the human coronary system.

Novel measurement techniques based on intravenous ultrasound (IVUS) technology ('IVUS-Flowmetry') require the location of a catheter inside the coronary bed. The present study quantifies disturbances in the 3-D velocity profile induced by catheter placement inside a tube, applying computational fluid dynamics. Two curved, circular meshes (radius K = 0.025 m and K = 0.035 m) with and without a catheter inside the lumen were applied. The catheter was located at the inner curve, the outer curve and at the top position. Boundary conditions were: no slip on the wall, zero stress at the outlet, uniform inflow with entrance velocities of 0.1, 0.2 and 0.4 m/s. Curvature-associated centrifugal forces shifted the maximal velocity to the outer curve and introduced two symmetrical vortices. Additional catheter placement redistributed the 3-D axial velocity field away from the catheter, which was accompanied by the appearance of multiple low-strength vortices. In addition, peak axial velocity increased, peak secondary velocities decreased, axial pressure drop increased and shear stress increased. Flow calculations simulated to resemble IVUS-based flowmetry changed by only 1% after considering secondary velocity. In conclusion, placement of a catheter inside a curved tube resembling the human coronary system changes the velocity field and reduces secondary patterns. The present study supports the usefulness of catheter-based flowmetry during resting flow conditions. During hyperemic flow conditions, flow measurements might be accompanied by large axial pressure drops because the catheter, itself, might act as a significant stenosis.