Current thoracic artificial lungs (TALs) have blood flow impedances greater than the natural lungs, which can result in abnormal pulmonary hemodynamics. This study investigated the impedance and gas transfer performance of a TAL with a compliant housing (cTAL). Fluid-structure interaction (FSI) analysis was performed using ADINA to examine the effect of the inlet and outlet expansion angle, θ, on device impedance and blood flow patterns. Based on the results, the θ=45° model was chosen for prototyping and in vitro testing. Glycerol was pumped through this cTAL at 2, 4, and 6 L/min at 80 and 100 beats/min, and the zeroth and first harmonic impedance moduli, Z0 and Z1, were calculated. Gas transfer testing was conducted at blood flow rates of 3, 5, and 7 L/min. FSI results indicated that the 45° model had an ideal combination of low impedance and even blood flow patterns, and was thus chosen for prototyping. In vitro, Z0=0.53 ± 0.06 mmHg/(L/min) and Z1=0.86 ± 0.08 mmHg/(L/min) at 4 L/min and 100 beats/min. Outlet PO2 and SO2 values were above 200 mmHg and 99.5%, respectively, at each flow rate. Thus, the cTAL had lower impedance than hard-shell TALs and excellent gas transfer.

Current thoracic artificial lungs (TALs) possess blood flow impedances greater than the natural lungs, resulting in abnormal pulmonary hemodynamics when implanted. This study sought to reduce TAL impedance using computational fluid dynamics (CFD). CFD was performed on TAL models with inlet and outlet expansion and contraction angles, θ, of 15°, 45°, and 90°. Pulsatile blood flow was simulated for flow rates of 2–6 L/min, heart rates of 80 and 100 beats/min, and inlet pulsatilities of 3.75 and 2. Pressure and flow data were used to calculate the zeroth and first harmonic impedance moduli, Z0 and Z1, respectively. The 45° and 90° models were also tested in vitro under similar conditions. CFD results indicate Z0 increases as stroke volume and θ increase. At 4 L/min, 100 beats/min, and a pulsatility of 3.75, Z0 was 0.47, 0.61, and 0.79 mmHg/(L/min) for the 15°, 45°, and 90° devices, respectively. Velocity band and vector plots also indicate better flow patterns in the 45° device. At the same conditions, in vitro Z0 were 0.69 ± 0.13 and 0.79 ± 0.10 mmHg/(L/min), respectively, for the 45° and 90° models. These Z0 are 65% smaller than previous TAL designs. In vitro, Z1 increased with flow rate but was small and unlikely to significantly affect hemodynamics. The optimal design for flow patterns and low impedance was the 45° model.

A silicone hollow fiber oxygenator was evaluated to characterize gas transfer and biocompatibility. The device's fiber bundle was composed of MedArray's silicone hollow fibers with a 320 microm outside diameter, a 50 microm wall thickness, a surface area of 0.45 m, and a 0.49 void fraction. An in vitro gas exchange study was performed comparing the MedArray device (n = 9) with the Medtronic 0600 oxygenator (n = 6) using Association for the Advancement of Medical Instrumentation standards and blood flow rates of 0.5-1.75 L/min, and an oxygen to blood flow ratio of two. Biocompatibility and resistance studies were performed in vivo using a swine venovenous extracorporeal membrane oxygenation model (MedArray n = 5, Medtronic n = 5). Average O(2) transfer at 1 L/min was 86 ml/min/m in the MedArray device and 101.1 ml/min/m in the Medtronic device. At 0.5 L/min the MedArray and Medtronic device average resistance was 15.5 and 148.5 mm Hg/(L/min), respectively. Both devices had similar platelet consumption and hemolysis. Results indicate that the MedArray device has lower O(2) transfer efficiency, similar biocompatibility, and lower resistance than the Medtronic 0600 oxygenator. Optimization of the MedArray fiber bundle and housing design is necessary to improve O(2) transfer efficiency while maintaining lower device resistance than the Medtronic oxygenator.

The compliant Thoracic Artificial Lung (cTAL) has been studied in acute in vivo and in vitro experiments. The cTAL’s long term function and potential use as a bridge to lung transplantation are assessed presently. The cTAL without anti-coagulant coatings was attached to sheep (n=5) via the pulmonary artery and left atrium for 14 days. Systemic heparin anticoagulation was utilized. cTAL resistance, cTAL gas exchange, hematologic parameters, and organ function were recorded. Two sheep were euthanized for non-device related issues. The cTAL’s resistance averaged 1.04±0.05 mmHg/(L/min) with no statistically significant increases. The cTAL transferred 180±8 mL/min of oxygen with 3.18±0.05 L/min of blood flow. Except for transient surgical effects, organ function markers were largely unchanged. Necropsies revealed pulmonary edema and atelectasis, but no other derangements. Hemoglobin levels dropped with device attachment but remained steady at 9.0±0.1 g/dL thereafter. In a fourteen day experiment, the cTAL without anti-coagulant coatings exhibited minimal clot formation. Sheep physiology was largely unchanged, except for device attachment related hemodilution. This suggests that patients treated with the cTAL shouldn’t require multiple blood transfusions. Once tested with anti-coagulant coatings and plasma resistant gas exchange fiber, the cTAL could serve as a bridge to transplantation.

Background Previous thoracic artificial lungs (TALs) had blood flow impedances greater than the natural lungs, which could cause abnormal pulmonary hemodynamics. New, compliant TALs (cTALs), however, have an impedance lower than the natural lung. Methods In this study, a new cTAL design was attached between the pulmonary artery and left atrium in five sheep (60.2 ± 1.9 kg). A distal pulmonary artery band was placed to control the percentage of cardiac output routed to the cTAL. Rest and exercise conditions were simulated using a continuous dobutamine infusion of 0 and 5 mcg/kg/min, respectively. At each dose, a hemodynamic data set was acquired at baseline (no flow to the cTAL) and 60, 75, and 90% of CO shunted to the cTAL. Results Device resistance did not vary with blood flow rate, averaging 0.51 ± 0.03 mmHg/(L/min). Under all conditions, cardiac output was not significantly different from baseline. Pulmonary system impedance only increased above baseline with 5 mcg/kg/min of dobutamine and 90% of cardiac output diverted to the cTAL. Conclusion Results indicate minimal changes in pulmonary hemodynamics during pulmonary artery – left atrium cTAL attachment for high device flows under rest and exercise conditions.