Flow structure associated with generic configurations of hemodialysis catheters.

摘要

Central venous catheters (CVC), which are typically positioned within the superior vena cava (SVC), play an important role in the process of hemodialysis. Simultaneous extraction and injection of blood generally occur through one or more side holes at the catheter tip, where complex flow patterns are generated. These jet characteristics are significantly influenced by the ratio of the jet velocity Vj from the side hole to the throughflow velocity U, i.e., V j/U, the ratio of the side hole diameter d to the catheter diameter D, the number of side holes, and the location of the catheter within the SVC.; A technique of high-image-density particle image velocimetry is employed, in conjunction with a scaled-up water facility, to characterize the structure of single and multiple jets in the presence of a steady throughflow. In addition, the effects of a pulsatile throughflow on the jet structure are determined during the systole-diastole cycle, corresponding to actual blood flow in a normal adult.; Patterns of mean (time-averaged) velocity, vorticity (shear rate), Reynolds stress correlation and streamline topology are assessed in the region immediately adjacent to the catheter surface, as well as in the flow through the simulated SVC. Regions of flow separation, large-scale recirculation of flow, and stagnated flow, as well as patterns of jet flow from single and multiple holes, and jet impingement on the wall of the SVC, are characterized. Taken together with the corresponding patterns of shear rates/stresses, they form a basis for evaluating the design performance of a hemodialysis catheter. In a general sense, the ideal catheter should maximize the injection and extraction flow rates, while minimizing hole inlet/outlet area. In addition, these flow rates should be delivered with minimal disturbance to the flow through the SVC. Although a catheter design that meets these stringent demands is not yet available, certain configurations of catheter tips investigated herein generate flow patterns that are favorable to catheter performance, and thereby provide a basis for improved design.