Progress has been made toward developing an intravenous gas exchange catheter to provide temporary pulmonary support for patients in acute respiratory failure.

Background Conventional ECMO is cumbersome and is associated with high morbidity and mortality. We are developing the Paracorporeal Ambulatory Assist Lung (PAAL), designed to ambulate lung failure patients during bridge to transplant or recovery. In this study, we investigated the in-vitro and acute in-vivo performance of the PAAL. Methods The PAAL features a 1.75 inch diameter cylindrical HFM bundle of stacked sheets, with a surface area of 0.65 m2 integrated with a centrifugal pump. The PAAL was tested on the bench for hydrodynamic performance, gas exchange and hemolysis. The PAAL was then tested in 40–60 kg adult sheep (n=4) for 6h. The animals were cannulated with an Avalon Elite 27 Fr. DLC inserted through the right external jugular into the SVC, RA and IVC. Results The PAAL pumped over 250 mmHg at 3.5 L/min at a rotation speed of 2100 RPM. Oxygenation performance met the target of 180 ml/min at 3.5 L/min of blood flow in vitro, resulting in a gas exchange efficiency of 278 ml/min/m2. The normalized index of hemolysis (NIH) for the PAAL and cannula was 0.054 g/100L (n=2) at 3.5 L/min, as compared to 0.020 g/100L (n=2) for control (DLC cannula and a Centrimag pump). Plasma-free hemoglobin (pfHb) was below 20 mg/dL for all animals. Blood left the device 100% oxygenated in vivo and oxygenation reached 181 ml/min at 3.8 L/min. Conclusions The PAAL met in vitro and acute in vivo performance targets. 5 day chronic sheep studies are planned in the near term.

Many industrial and biomedical devices (e.g. blood oxygenators and artificial lungs) use bundles of hollow fiber membranes for separation processes. Analyses of flow and mass transport within the shell-side of the fiber bundles most often model the bundle for simplicity as a packed bed or porous media, using a Darcy permeability coefficient estimated from the Blake-Kozeny equation to account for viscous drag from the fibers. In this study, we developed a simple method for measuring the Darcy permeability of hollow fiber membrane bundles and evaluated how well the Blake-Kozeny (BK) equation predicted the Darcy permeability for these bundles. Fiber bundles were fabricated from commercially available Celgard® ×30-240 fiber fabric (300 μm outer diameter fibers @ 35 and 54 fibers/inch) and from a fiber fabric with 193 μm fibers (61 fibers/inch). The fiber bundles were mounted to the bottom of an acrylic tube and Darcy permeability was determined by measuring the elapsed time for a column of glycerol solution to flow through a fiber bundle. The ratio of the measured Darcy permeability to that predicted from the BK equation varied from 1.09 to 0.56. A comprehensive literature review suggested a modified BK equation with the “constant” correlated to porosity. This modification improved the predictions of the BK equation, with the ratio of measured to predicted permeability varying from 1.13 to 0.84.