 Secondary Objective: To analyze the collected data and establish maximal allowable injection pressure and flow rate. The collected data segments for each patient will be analyzed and maximal values for pressure and the saline injection rate will be recorded in a spreadsheet. Inter-patient variation in the results, presumably due to different degrees of occlusion, will be statistically evaluated. We will also determine if any of the catheters which appear occluded in the operating room resume flow with the flushing maneuvers. 