Evaluation of Rotational Mechanisms to Enhance Performance of a Respiratory Assist Catheter

摘要

A percutaneous respiratory assist catheter is being developed to partially support native lung function in patients with acute respiratory distress syndrome (ARDS) and acute exacerbations of chronic obstructive pulmonary disease (COPD). Current clinical therapies include pharmacotherapy, mechanical ventilation, and ECLS, but are associated with high mortality rates. The catheter is intended for insertion through the femoral vein for placement in the vena cava where it actively processes venous blood. The artificial lung device consists of a hollow fiber membrane (HFM) bundle that supplements oxygenation and carbon dioxide removal through diffusional processes.The catheter is a second generation concept of the Hattler Catheter with a design goal of size reduction to accommodate percutaneous insertion. The tradeoff in available HFM surface area requires the catheter to be more efficient in removing CO2 per unit surface area. Two prototypes utilizing rotational mechanisms to actively mix the blood and reduce mass transfer boundary layers were evaluated. The first prototype consisted of a rotating HFM bundle capable of rates of 10,000 RPM but required a structure for vessel wall protection. The second prototype employed a rotating impeller within a stationary HFM bundle to internalize rotational components within the device. The prototypes were evaluated in vitro and in vivo to assess design and performance. Development of impeller geometries, a saline seal purge, and device flexibility were notable design highlights. Acceptable hemolysis levels were observed in testing the concept of using a high-speed rotational HFM bundle. Standard gas exchange characterization tests in DI water showed over a two-fold increase in CO2 removal efficiency of 450 and 529 ml CO2/min/m2, rotational catheter and impeller catheter respectively, over the Hattler Catheter. The impeller catheter was evaluated in a bovine model and an average efficiency of 513 ± 20 ml CO2/min/m2 was attained at 20,000 RPM. Catheter size reduction and CO2 removal efficiency enhancements were successfully achieved. A separate novel method to augment CO2 concentration gradients is being researched to integrate with HFMs and attain overall gas exchange project goals.