How Computational Modeling can Help to Predict Gas Transfer in Artificial Lungs Early in the Design Process

Abstract

Wearable extracorporeal membrane oxygenation (ECMO) circuits may soon become a viable alternative to conventional ECMO treatment. Common device-induced complications, however, such as blood trauma and oxygenator thrombosis, must first be addressed to improve long-term reliability, since ambulatory patients cannot be monitored as closely as intensive care patients. Additionally, an efficient use of the membrane surface can reduce the size of the devices, priming volume, and weight to achieve portability. Both challenges are linked to the hemodynamics in the fiber bundle. While experimental test methods can often only provide global and time-averaged information, computational fluid dynamics (CFD) can give insight into local flow dynamics and gas transfer before building the first laboratory prototype. In this study, we applied our previously introduced micro-scale CFD model to the full fiber bundle of a small oxygenator for gas transfer prediction. Three randomized geometries as well as a staggered and in-line configuration were modeled and simulated with Ansys CFX. Three small laboratory oxygenator prototypes were built by stacking fiber segments unidirectionally with spacers between consecutive segments. The devices were tested in vitro for gas transfer with porcine blood in accordance with ISO 7199. The error of the predicted averaged CFD oxygen saturations of the random 1, 2, and 3 configurations relative to the averaged in-vitro data (over all samples and devices) was 2.4%, 4.6%, 3.1%, and 3.0% for blood flow rates of 100, 200, 300, and 400 ml/min, respectively. While our micro-scale CFD model was successfully applied to a small oxygenator with unidirectional fibers, the application to clinically relevant oxygenators will remain challenging due to the complex flow distribution in the fiber bundle and high computational costs. However, we will outline our future research priorities and discuss how an extended mass transfer correlation model implemented into CFD might enable an a priori prediction of gas transfer in full size oxygenators.

Design, Control, Modeling, and Simulation of Mechanical Ventilator for Respiratory Support

“…In the initial stage, it is necessary to mention the model of breathing mechanics. Regarding the electrical representation, when a circuit only contains a resistor and a capacitor (RC circuit), this means that the sum of the voltage drops, as the resistance (R) and the capacitance (C), is equal to the applied voltage E(t) according to Kirchhoff's second law [43,44]. Additionally, the voltage drop across a capacitor of capacitance C is q(t)/C, where q is the charge on the capacitor.…”

In silico simulation of the liquid phase pressure drop through cylindrical hollow‐fiber membrane oxygenators using a modified phenomenological model

“…By using oxygen admixture in the gas phase of an HFMO, venous blood captures oxygen and releases a part of its carbon dioxide content, converting to arterial blood 5,6 . Therefore, an oxygenator, as a synonym for an artificial lung, can substitute the role of natural lung, which is crucially important during various therapeutical procedures, for example, cardiopulmonary bypass (CPB) surgeries and extracorporeal membrane oxygenation (ECMO) 3,7–10 …”

“…A hollow-fiber membrane contactor (HFMC) is an instrument principally comprised of a housing and bundle of hollow-fibers. [1][2][3] Basically, in an HFMO, a typical gasliquid HFMC, blood flows outside of hollow-fibers while gas flows through the fibers' lumens in a counter-current manner. 4,5 Gas transfer occurs as a result of partial pressure gradient of a common solute particle between gas and liquid phases.…”

“…5,6 Therefore, an oxygenator, as a synonym for an artificial lung, can substitute the role of natural lung, which is crucially important during various therapeutical procedures, for example, cardiopulmonary bypass (CPB) surgeries and extracorporeal membrane oxygenation (ECMO). 3,[7][8][9][10] Hemodynamic through an oxygenator module has significant influences on the performance characteristics of an HFMO. [11][12][13] Conventionally, the blood pressure drop is considered as one of those characteristics.…”

Long-Term Venovenous Connection for Extracorporeal Carbon Dioxide Removal (ECCO2R)–Numerical Investigation of the Connection to the Common Iliac Veins

“…8 However, these new integrated and wearable devices designed for ambulatory long-term treatment are in need of improved connections to the patient's vessels. 23 Currently used cannulae are associated with several complications and disadvantages, which prolong applications. These include cannula thrombosis, 6,9,24 limb ischemia, 13,21,22,27,38,42,51 risk of dislocation, 21,38 infection of the cannulation site, 13,22,38 limitation of patient's mobility, 13,21,22,38 high effort of ambulation, 13,21,22,49 and arguably a low quality of life.…”