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Artificial Organs Jun 2018Design of contemporary oxygenators requires better understanding of the influence of hydrodynamic patterns on gas exchange. A decrease in blood path width or an increase...
Design of contemporary oxygenators requires better understanding of the influence of hydrodynamic patterns on gas exchange. A decrease in blood path width or an increase in intraoxygenator turbulence for instance, might increase gas transfer efficiency but it will increase shear stress as well. The aim of this clinical study was to examine the association between shear stress and oxygen and carbon dioxide transfer in different contemporary oxygenators during cardiopulmonary bypass (CPB). The effect of additional parameters related to gas transfer efficiency, that is, blood flow, gas flow, sweep gas oxygen fraction (FiO ), hemoglobin concentration, the amount of hemoglobin pumped through the oxygenator per minute-Qhb, and shunt fraction were contemplated as well. Data from 50 adult patients who underwent elective CPB for coronary artery bypass grafting or aortic valve replacement were retrospectively analyzed. Data included five different oxygenator types with an integrated arterial filter. Relationships were determined using Pearson bivariate correlation analysis and scatterplots with LOESS curves. In the Capiox FX25, Fusion, Inspire 8F, Paragon, and Quadrox-i groups, mean blood flows were 4.8 ± 0.9, 5.3 ± 0.7, 4.9 ± 0.7, 5.0 ± 0.6, and 5.7 ± 0.6 L/min, respectively. The mean O transfer/m membrane surface area was 44 ± 14, 51 ± 9, 60 ± 10, 63 ± 14, and 77 ± 18, respectively, whereas the mean CO transfer/m was 26 ± 14, 60 ± 22, 73 ± 29, 74 ± 19, and 96 ± 20, respectively. Associations between oxygen transfer/m and shear stress differed per oxygenator, depending on oxygenator design and the level of shear stress (r = 0.249, r = 0.562, r = 0.402, r = 0.465, and r = 0.275 for Capiox FX25, Fusion, Inspire 8F, Paragon, and Quadrox-i, respectively, P < 0.001 for all). Similar associations were noted between CO transfer/m and shear stress (r = 0.303, r = 0.439, r = 0.540, r = 0.392, and r = 0.538 for Capiox FX25, Fusion, Inspire 8F, Paragon, and Quadrox-i, respectively, P < 0.001 for all). In addition, O transfer/m was strongly correlated with FiO (r = 0.633, P < 0.001), blood flow (r = 0.529, P < 0.001), and Qhb (r = 0.589, P < 0.001). CO transfer/m in contrast was predominately correlated to sweep gas flow (r = 0.567, P < 0.001). The design-dependent relationship between shear stress and gas transfer revealed that every oxygenator has an optimal range of blood flow and thus shear stress at which gas transfer is most efficient. Gas transfer is further affected by factors influencing the O or CO concentration gradient between the blood and the gas compartment.
Topics: Aged; Blood Flow Velocity; Carbon Dioxide; Cardiopulmonary Bypass; Equipment Design; Hemoglobins; Humans; Middle Aged; Oxygen; Oxygenators; Stress, Mechanical
PubMed: 29473675
DOI: 10.1111/aor.13084 -
Transactions - American Society For... 1972
Topics: Blood Flow Velocity; Capillary Action; Carbon Dioxide; Oxygen; Oxygenators, Membrane; Partial Pressure; Rheology; Silicone Elastomers; Time Factors; Ventilation-Perfusion Ratio
PubMed: 4679893
DOI: 10.1097/00002480-197201000-00096 -
Artificial Organs Feb 2018Extracorporeal membrane oxygenation (ECMO) is a life support system that circulates the blood through an oxygenating system to temporarily (days to months) support heart...
Extracorporeal membrane oxygenation (ECMO) is a life support system that circulates the blood through an oxygenating system to temporarily (days to months) support heart or lung function during cardiopulmonary failure until organ recovery or replacement. Currently, the need for high levels of systemic anticoagulation and the risk for bleeding are main drawbacks of ECMO that can be addressed with a redesigned ECMO system. Our lab has developed an approach using microelectromechanical systems (MEMS) fabrication techniques to create novel gas exchange membranes consisting of a rigid silicon micropore membrane (SμM) support structure bonded to a thin film of gas-permeable polydimethylsiloxane (PDMS). This study details the fabrication process to create silicon membranes with highly uniform micropores that have a high level of pattern fidelity. The oxygen transport across these membranes was tested in a simple water-based bench-top set-up as well in a porcine in vivo model. It was determined that the mass transfer coefficient for the system using SµM-PDMS membranes was 3.03 ± 0.42 mL O min m cm Hg with pure water and 1.71 ± 1.03 mL O min m cm Hg with blood. An analytic model to predict gas transport was developed using data from the bench-top experiments and validated with in vivo testing. This was a proof of concept study showing adequate oxygen transport across a parallel plate SµM-PDMS membrane when used as a membrane oxygenator. This work establishes the tools and the equipoise to develop future generations of silicon micropore membrane oxygenators.
Topics: Animals; Diffusion; Dimethylpolysiloxanes; Equipment Design; Extracorporeal Membrane Oxygenation; Oxygen; Oxygenators, Membrane; Permeability; Porosity; Respiratory Insufficiency; Silicon; Swine
PubMed: 28800389
DOI: 10.1111/aor.12972 -
Annals of Biomedical Engineering Mar 2024We demonstrate a methodology which both improves oxygen transport and reduces or eliminates bubble formation in a novel hyperbaric membrane oxygenator catheter model...
We demonstrate a methodology which both improves oxygen transport and reduces or eliminates bubble formation in a novel hyperbaric membrane oxygenator catheter model system. Angular oscillations were introduced to a bundle of hollow fiber membranes (HFMs) supplied with hyperbaric 100% oxygen at average gauge pressures up to 0.35 barg. Oscillating bundles enabled delivery of an oxygen flux of up to 400 mL min m in an aqueous solution, a doubling over a previous non-oscillating setup. Similarly, the addition of angular oscillations facilitated a five-fold reduction in pressure to achieve similar oxygen flux. The increased angular speed of oscillation improved flux, while the addition of angular micro-oscillation variations resulted in flux reductions of 7-20% compared to continuous macro-oscillation only, depending on mixing conditions. However, semi-quantitative visual observation demonstrated that angular oscillations reduced or eliminated the instance of oxygen bubble formation on the HFMs. The modeled mass transfer coefficients indicated a quasi linear relationship between rotational velocity and flux, suggesting that faster oscillation speeds could further improve oxygen mass transport allowing for HFM bundles to maintain high oxygen fluxes while eliminating bubble formation. This encourages further development of our compact oxygenating catheter that could be used intravascularly.
Topics: Oxygenators; Oxygen; Catheters; Equipment Design; Oxygenators, Membrane
PubMed: 38062312
DOI: 10.1007/s10439-023-03411-x -
Lab on a Chip Dec 2021We have developed and tested a novel microfluidic device for blood oxygenation, which exhibits a large surface area of gas exchange and can support long-term sustainable...
We have developed and tested a novel microfluidic device for blood oxygenation, which exhibits a large surface area of gas exchange and can support long-term sustainable endothelialization of blood microcapillaries, enhancing its hemocompatibility for clinical applications. The architecture of the parallel stacking of the trilayers is based on a central injection for blood and a lateral injection/output for gas which allows significant reduction in shear stress, promoting sustainable endothelialization since cells can be maintained viable for up to 2 weeks after initial seeding in the blood microchannel network. The circular design of curved blood capillaries allows covering a maximal surface area at 4 inch wafer scale, producing high oxygen uptake and carbon dioxide release in each single unit. Since the conventional bonding process based on oxygen plasma cannot be used for surface areas larger than several cm, a new "wet bonding" process based on soft microprinting has been developed and patented. Using this new protocol, each 4 inch trilayer unit can be sealed without a collapsed membrane even at reduced 15 μm thickness and can support a high blood flow rate. The height of the blood channels has been optimized to reduce pressure drop and enhance gas exchange at a high volumetric blood flow rate up to 15 ml min. The simplicity of connecting different units in the stacked architecture is demonstrated for 3- or 5-unit stacked devices that exhibit remarkable performance with low primary volume, high oxygen uptake and carbon dioxide release and high flow rate of up to 80 ml min.
Topics: Carbon Dioxide; Equipment Design; Lung; Microfluidics; Oxygen; Oxygenators
PubMed: 34309615
DOI: 10.1039/d1lc00356a -
ASAIO Journal (American Society For... Sep 2023In this retrospective observational cohort study, we aimed to describe the rate of extracorporeal membrane oxygenation (ECMO) circuit change, the associated risk factors... (Observational Study)
Observational Study
In this retrospective observational cohort study, we aimed to describe the rate of extracorporeal membrane oxygenation (ECMO) circuit change, the associated risk factors and its relationship with patient characteristics and outcome in patients receiving venovenous (VV) ECMO at our center between January 2015 and November 2017. Twenty-seven percent of the patients receiving VV ECMO (n = 224) had at least one circuit change, which was associated with lower ICU survival (68% vs 82% p=0.032) and longer ICU stay (30 vs . 17 days p < 0.001). Circuit duration was similar when stratified by gender, clinical severity, or prior circuit change. Hematological abnormalities and increased transmembrane lung pressure (TMLP) were the most frequent indication for circuit change. The change in transmembrane lung resistance (Δ TMLR) gave better prediction of circuit change than TMLP, TMLR, or ΔTMLP. Low postoxygenator PO 2 was indicated as a reason for one-third of the circuit changes. However, the ECMO oxygen transfer was significantly higher in cases of circuit change with documented "low postoxygenator PO 2 " than those without (244 ± 62 vs. 200 ± 57 ml/min; p = 0.009). The results suggest that circuit change in VV ECMO is associated with worse outcomes, that the Δ TMLR is a better predictor of circuit change than TMLP, and that the postoxygenator PO 2 is an unreliable proxy for the oxygenator function.
Topics: Humans; Extracorporeal Membrane Oxygenation; Retrospective Studies; Prevalence; Oxygen; Oxygenators
PubMed: 37159512
DOI: 10.1097/MAT.0000000000001977 -
Perfusion May 2022Monitoring oxygen delivery to the oxygenator of a heart lung machine (HLM) is typically accomplished with an O analyzer connected to the gas inflow line. It is assumed...
BACKGROUND
Monitoring oxygen delivery to the oxygenator of a heart lung machine (HLM) is typically accomplished with an O analyzer connected to the gas inflow line. It is assumed when the FiO is greater than 21% that oxygen is being delivered to the oxygenator. However, this assumption is imperfect because the connection of the inflow line to the oxygenator is downstream from the O analyzer. FiO monitoring will not alert the perfusionist if the inflow line is not actually connected to the oxygenator. Measuring the fraction of expired oxygen (FEO) is a more reliable way of monitoring O delivery.
METHODS
An O analyzer was placed on the scavenging line that is attached to the exhaust port of oxygenator (FEO).
RESULTS
Whenever the FiO is greater than 21%, and the inflow line is properly connected, the FEO exiting the oxygenator is greater than 21%. The FEO falls to 21% when the inflow line is not functioning.
CONCLUSION
Monitoring the FEO is a more reliable way to verify O delivery to an oxygenator. An alarm can be set on the FEO monitor to alert the perfusionist if the FEO falls below a predetermined threshold so any issue with O delivery will always be recognized.
Topics: Cardiopulmonary Bypass; Heart-Lung Machine; Humans; Monitoring, Physiologic; Oxygen; Oxygenators
PubMed: 33739181
DOI: 10.1177/02676591211001594 -
Biotechnology and Bioengineering Jan 2021Despite hypoxic respiratory failure representing a large portion of total hospitalizations and healthcare spending worldwide, therapeutic options beyond mechanical...
Despite hypoxic respiratory failure representing a large portion of total hospitalizations and healthcare spending worldwide, therapeutic options beyond mechanical ventilation are limited. We demonstrate the technical feasibility of providing oxygen to a bulk medium, such as blood, via diffusion across nonporous hollow fiber membranes (HFMs) using hyperbaric oxygen. The oxygen transfer across Teflon® membranes was characterized at oxygen pressures up to 2 bars in both a stirred tank vessel (CSTR) and a tubular device mimicking intravenous application. Fluxes over 550 ml min m were observed in well-mixed systems, and just over 350 ml min m in flow through tubular systems. Oxygen flux was proportional to the oxygen partial pressure inside the HFM over the tested range and increased with mixing of the bulk liquid. Some bubbles were observed at the higher pressures (1.9 bar) and when bulk liquid dissolved oxygen concentrations were high. High-frequency ultrasound was applied to detect and count individual bubbles, but no increase from background levels was detected during lower pressure operation. A conceptual model of the oxygen transport was developed and validated. Model parametric sensitivity studies demonstrated that diffusion through the thin fiber walls was a significant resistance to mass transfer, and that promoting convection around the fibers should enable physiologically relevant oxygen supply. This study indicates that a device is within reach that is capable of delivering greater than 10% of a patient's basal oxygen needs in a configuration that readily fits intravascularly.
Topics: Catheters; Equipment Design; Membranes, Artificial; Oxygen; Oxygenators
PubMed: 32959889
DOI: 10.1002/bit.27574 -
ASAIO Journal (American Society For... 2006Thrombogenicity, a problem with long-term artificial lungs, is caused by blood-biomaterial interactions and is made worse by nonuniform flow, which also causes decreased... (Comparative Study)
Comparative Study
Thrombogenicity, a problem with long-term artificial lungs, is caused by blood-biomaterial interactions and is made worse by nonuniform flow, which also causes decreased gas exchange. To overcome these obstacles, we changed the inlet and added a uniform flow pump to our previous oxygenator design. Conventional membrane oxygenators have a (1/2)-inch port for the inlet of blood. These port structures make it difficult for the blood to flow uniformly in the oxygenator. In addition, the complex blood flow patterns that occur in the oxygenator, including turbulence and stagnation, lead to thrombogenicity. A cross-flow pump (CFP) can result in uniform blood flow to the inlet side of an oxygenator. In this study, we evaluated the usefulness of an integrated oxygenator with a fiber bundle porosity of 0.6 and a membrane surface area of 1.3 m2. The inlet part of the oxygenator is improved and better fits the outlet of the CFP. Each of the three models of the improved oxygenator has a different inlet taper angle. The computational fluid dynamics analysis showed that, compared with the original design, uniform flow of the integrated oxygenator improved by 88.8% at the hollow fiber membrane. With the integrated oxygenator, O2 transfer increased by an average of 20.8%, and CO2 transfer increased by an average of 35.5%. The results of our experiments suggest that the CFP, which produces a wide, uniform flow to the oxygenator, is effective in attaining high gas exchange performance.
Topics: Blood Flow Velocity; Carbon Dioxide; Equipment Design; Evaluation Studies as Topic; Extracorporeal Membrane Oxygenation; Infusion Pumps, Implantable; Oxygen; Oxygenators, Membrane; Porosity; Surface Properties; Thrombosis
PubMed: 16760718
DOI: 10.1097/01.mat.0000216165.21432.ee -
Analytica Chimica Acta Aug 2022Microfluidics provides enabling platforms for various cell culture, drug testing and synthesis of drug carriers using chip-based microsystems. In this study, we present...
Microfluidics provides enabling platforms for various cell culture, drug testing and synthesis of drug carriers using chip-based microsystems. In this study, we present a novel integrated whole-thermoplastic microfluidic chip to provide a platform for on-chip cell culture at static and dynamic conditions. The whole chip was made of polymethyl methacrylate (PMMA) and thermoplastic polyurethane (TPU) using high precision micromilling and laser micromachining, assembled by thermal fusion bonding. Prior to fabricate the integrated microchip, a pneumatic solo diffuser-nozzle micropump was fabricated and characterized to evaluate its functionality for on-chip pumping. Then the micropump was integrated with a microbioreactor and an oxygenator in a microchip for flow pumping required for on-chip cell culture. Oxygenator, made of a thin TPU membrane and a reservoir, was implemented in the microchip because of low oxygen permeability of PMMA. To design the oxygenator for sufficient oxygen delivery to the chip, numerical simulation was performed using COMSOL Multiphysics® to evaluate oxygen concentration distribution inside the microchip. Finally, the diffuser-nozzle micropump was integrated with the oxygenator and a bioreactor on the microchip for cell culture with on-chip pumping. Culture of DFW cells was performed on the integrated chip for three days, and cell survival was evaluated with Trypan Blue assay. The findings reveal that the proposed integrated chip with on-chip pumping could be employed for conducting various cell culture studies.
Topics: Bioreactors; Cell Culture Techniques; Equipment Design; Microfluidics; Oxygen; Oxygenators; Polymethyl Methacrylate
PubMed: 35934343
DOI: 10.1016/j.aca.2022.340093