Thoracic Artificial Lung Impedance Studies Using Computational Fluid Dynamics and In Vitro Models

Abstract

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.

Hemodynamic Design Requirements for In-Series Thoracic Artificial Lung Attachment in a Model of Pulmonary Hypertension

“…Recently, Schewe et al, reported artificial lung designs with resistances approximately one-third of previously reported devices. 10,11 It is unclear, however, if this reduction is sufficient for PA-PA attachment. The goal of this study, therefore, was to examine the design constraints of TALs for PA-PA attachment in a model of mild pulmonary hypertension.…”

Design and In Vitro Assessment of an Improved, Low-Resistance Compliant Thoracic Artificial Lung

“…Minor losses are reduced and less recirculation occurs, lowering Z 0 . Comparison of cTAL vector plots with those in an identical device with a hard shell housing 4 confirmed that recirculation regions are smaller and have lower velocity in the cTAL. This resulted in lower impedances compared to the rigid housing TAL.…”

“…In the same device with a rigid housing, Z 0 =0.69 and Z 1 =1.22 mmHg/(L/min). 4 Moreover, unlike TALs with rigid housings, Z 0 decreased slightly with increasing SV in the cTAL. At SV =0.075, Z 0 for the cTAL and TAL were 0.41 ± 0.14 and 0.94 ± 0.09 mmHg/(L/min), respectively.…”

“…Further details are provided elsewhere. 4 A slip wall boundary condition was applied to the bundle walls while a FSI condition was used in the inlet and outlet regions. A pressure of 770 mmHg (absolute pressure) was applied at the outlet and also used for the initial pressure condition.…”

“…A pressure of 770 mmHg (absolute pressure) was applied at the outlet and also used for the initial pressure condition. A time dependent velocity was applied to the inlet face using a previously described pulsatile flow waveform 4 (Figure 2) with average flow rates, Q , of 3 and 5 L/min and a heart rate, HR , of 100 beats/min.…”