Artificial lung: progress and prototypes

Artificial lungs--Where are we going with the lung replacement therapy?

Lung transplantation may be a final destination therapy in lung failure, but limited donor organ availability creates a need for alternative management, including artificial lung technology. This invited review discusses ongoing developments and future research pathways for respiratory assist devices and tissue engineering to treat advanced and refractory lung disease. An overview is also given on the aftermath of the coronavirus disease 2019 pandemic and lessons learned as the world comes out of this situation. The first order of business in the future of lung support is solving the problems with existing mechanical devices. Interestingly, challenges identified during the early days of development persist today. These challenges include device-related infection, bleeding, thrombosis, cost, and patient quality of life. The main approaches of the future directions are to repair, restore, replace, or regenerate the lungs. Engineering improvements to hollow fiber membrane gas exchangers are enabling longer term wearable systems and can be used to bridge lung failure patients to transplantation. Progress in the development of microchannel-based devices has provided the concept of biomimetic devices that may even enable intracorporeal implantation. Tissue engineering and cell-based technologies have provided the concept of bioartificial lungs with properties similar to the native organ. Recent progress in artificial lung technologies includes continued advances in both engineering and biology. The final goal is to achieve a truly implantable and durable artificial lung that is applicable to destination therapy.

Extracorporeal Membrane Oxygenation for Respiratory Failure

This review focuses on the use of veno-venous extracorporeal membrane oxygenation for respiratory failure across all blood flow ranges. Starting with a short overview of historical development, aspects of the physiology of gas exchange (i.e., oxygenation and decarboxylation) during extracorporeal circulation are discussed. The mechanisms of phenomena such as recirculation and shunt playing an important role in daily clinical practice are explained.Treatment of refractory and symptomatic hypoxemic respiratory failure (e.g., acute respiratory distress syndrome [ARDS]) currently represents the main indication for high-flow veno-venous-extracorporeal membrane oxygenation. On the other hand, lower-flow extracorporeal carbon dioxide removal might potentially help to avoid or attenuate ventilator-induced lung injury by allowing reduction of the energy load (i.e., driving pressure, mechanical power) transmitted to the lungs during mechanical ventilation or spontaneous ventilation. In the latter context, extracorporeal carbon dioxide removal plays an emerging role in the treatment of chronic obstructive pulmonary disease patients during acute exacerbations. Both applications of extracorporeal lung support raise important ethical considerations, such as likelihood of ultimate futility and end-of-life decision-making. The review concludes with a brief overview of potential technical developments and persistent challenges.

Development of a self-pumping extracorporeal blood oxygenation device characterized by a rotating shaft with embedded fiber packages

Introduction:

To offer respiratory support for patients with lung disease, a novel technological solution for blood pumping and oxygenation is being developed. The pump–lung system was designed to integrate fiber membranes into six packages radially embedded in a rotating hollow shaft placed along the longitudinal axis of the device. Fiber packages are inclined with respect to the rotation axis so that the rotational motion of the rotating shaft allows a self-pumping system to be obtained.

Method:

Both hemodynamic and gas transfer performances were investigated using both in vitro experiments and in silico flow analyses.

Results:

The predicted flow velocity in the pump chamber was smooth and characterized by high peripheral velocities near the housing wall. As the blood flow enters the inlet, the static pressure increased with the angular momentum imparted to the fiber packages. Experiments confirmed that the proposed pump–lung system can provide adequate blood flow and oxygen transfer over the range of intended operating conditions (0.5–5 L/min and 500–1500 r/min).

Conclusion:

Although the study did not include animal testing, the novel pump-oxygenator solution is feasible for respiratory support in patients with lung diseases.

Mechanical circulatory support in lung transplantation: Cardiopulmonary bypass, extracorporeal life support, and ex-vivo lung perfusion

Lung transplant is the standard of care for patients with end-stage lung disease refractory to medical management. There is currently a critical organ shortage for lung transplantation with only 17% of offered organs being transplanted. Of those patients receiving a lung transplant, up to 25% will develop primary graft dysfunction, which is associated with an 8-fold increase in 30-d mortality. There are numerous mechanical lung assistance modalities that may be employed to help combat these challenges. We will discuss the use of mechanical lung assistance during lung transplantation, as a bridge to transplant, as a treatment for primary graft dysfunction, and finally as a means to remodel and evaluate organs deemed unsuitable for transplant, thus increasing the donor pool, improving survival to transplant, and improving overall patient survival.

Surface modification of silicone tubes by functional carboxyl and amine, but not peroxide groups followed by collagen immobilization improves endothelial cell stability and functionality

Surface modification by functional groups promotes endothelialization in biohybrid artificial lungs, but whether it affects endothelial cell stability under fluid shear stress, and the release of anti-thrombotic factors, e.g. nitric oxide (NO), is unknown. We aimed to test whether surface-modified silicone tubes containing different functional groups, but similar wettability, improve collagen immobilization, endothelialization, cell stability and cell-mediated NO-release. Peroxide, carboxyl, and amine-groups increased collagen immobilization (41-76%). Only amine-groups increased ultimate tensile strength (2-fold). Peroxide and amine enhanced (1.5-2.5 fold), but carboxyl-groups decreased (2.9-fold) endothelial cell number after 6 d. After collagen immobilization, cell numbers were enhanced by all group-modifications (2.8-3.8 fold). Cells were stable under 1 h-fluid shear stress on amine, but not carboxyl or peroxide-group-modified silicone (>50% cell detachment), while cells were also stable on carboxyl-group-modified silicone with immobilized collagen. NO-release was increased by peroxide and amine (1.1-1.7 fold), but decreased by carboxyl-group-modification (9.8-fold), while it increased by all group-modifications after collagen immobilization (1.8-2.8 fold). Only the amine-group-modification changed silicone stiffness and transparency. In conclusion, silicone-surface modification of blood-contacting parts of artificial lungs with carboxyl and amine, but not peroxide-groups followed by collagen immobilization allows the formation of a stable functional endothelial cell layer. Amine-group-modification seems undesirable since it affected silicone's physical properties.

Extracorporeal life support as a bridge to lung transplantation

Patients who are excellent candidates for lung transplantation often die on the waiting list because they are too sick to survive until an organ becomes available. Improvements in lung transplant outcomes, patient selection, and artificial lung device technologies have made it possible to bridge these patients to successful life-saving transplantation. Extracorporeal life support (ECLS) should be tailored to minimize morbidity and provide the appropriate mode and level of cardiopulmonary support for each patient's physiologic requirements. Novel device refinements and further development of ECLS in an ambulatory and simplified manner will help maintain these patients in better condition until transplantation.

An Investigation of Pulsatile Flow Past Two Cylinders as a Model of Blood Flow in an Artificial Lung

Pulsatile flow across two circular cylinders with different geometric arrangements is studied experimentally using the particle image velocimetry method and numerically using the finite element method. This investigation is motivated the need to optimize gas transfer and fluid mechanical impedance for a total artificial lung, in which the right heart pumps blood across a bundle of hollow microfibers. Vortex formation was found to occur at lower Reynolds numbers in pulsatile flow than in steady flow, and the vortex structure depends strongly on the geometric arrangement of the cylinders and on the Reynolds and Stokes numbers.

The evolution of patient selection criteria and indications for extracorporeal life support in pediatric cardiopulmonary failure: next time, let's not eat the bones

Bill James, baseball statistician and author, tells the story of hungry cavemen sitting about a campfire, waiting for tomatoes to ripen. One has the inspiration to throw an ox on the fire, and the first barbecue ensued and was endured. After eating, the conversation goes something like this. "There were some good parts." "Yeah, but there were some bad parts." And the smart one says, "This time, let's not eat the bones." The evolution of patient selection criteria for the use of extracorporeal support (ECLS) is a bit like those cavemen and their first barbecued ox. Extracorporeal life support technology and application to patient care is the unique result of a long standing history of ambitious attempt, evaluation, debate, collaboration and extension.

[Extracorporeal lung assist in severe respiratory failure and ARDS. Current situation and clinical applications]

Despite improvements in ventilation support techniques, lung protection strategies, and the application of new support treatment, acute respiratory distress syndrome continues to have a high mortality rate. Many strategies and treatments for this syndrome have been investigated over the last few year. However, the only therapeutic measure that has systematically shown to be able to improve survival is that of low volume lung protective ventilation. Thus, using a low tidal volume prevents added lung damage by the same mechanical ventilation that is essential for life support. In this context, the use of extracorporeal lung assist systems is considered an exceptional use rescue treatment in extreme cases. On the other hand, it could be a potentially useful complementary method for an ultra-protective ventilation strategy, that is, by using even lower tidal volumes. The currently available extracorporeal lung assist systems are described in this article, including high flow systems such as traditional extracorporeal membrane oxygenation, CO₂ removal systems (interventional lung assist or iLA, with or without associated centrifugal pumps), and the new low flow and less invasive systems under development. The aim of this review is to update the latest available clinical and experimental data, the indications for these devices in adult respiratory distress syndrome (ARDS), and their potential indications in other clinical situations, such as the bridge to lung transplantation, multiple organ dysfunction syndrome, or COPD.

[Extracorporeal lung assist in severe respiratory failure and ARDS. Current situation and clinical applications]

Despite improvements in ventilation support techniques, lung protection strategies, and the application of new support treatment, acute respiratory distress syndrome continues to have a high mortality rate. Many strategies and treatments for this syndrome have been investigated over the last few year. However, the only therapeutic measure that has systematically shown to be able to improve survival is that of low volume lung protective ventilation. Thus, using a low tidal volume prevents added lung damage by the same mechanical ventilation that is essential for life support. In this context, the use of extracorporeal lung assist systems is considered an exceptional use rescue treatment in extreme cases. On the other hand, it could be a potentially useful complementary method for an ultra-protective ventilation strategy, that is, by using even lower tidal volumes. The currently available extracorporeal lung assist systems are described in this article, including high flow systems such as traditional extracorporeal membrane oxygenation, CO₂ removal systems (interventional lung assist or iLA, with or without associated centrifugal pumps), and the new low flow and less invasive systems under development. The aim of this review is to update the latest available clinical and experimental data, the indications for these devices in adult respiratory distress syndrome (ARDS), and their potential indications in other clinical situations, such as the bridge to lung transplantation, multiple organ dysfunction syndrome, or COPD.

Clinical experience with the iLA Membrane Ventilator pumpless extracorporeal lung-assist device

Extracorporeal gas exchange by extracorporeal membrane oxygenation has been established clinically in patients with acute lung failure. The interventional lung-assist (iLA) Membrane Ventilator device (Novalung) is a sophisticated representative of a new generation of pumpless extracorporeal lung-assist devices that are driven by the patient's cardiac output and therefore, do not require extracorporeal pump assistance. The system is characterized by a new membrane gas exchange system with optimized blood flow that is integrated in an arteriovenous bypass established by vascular cannulation. This particular pumpless extracorporeal lung-assist device was applied in 1800 patients for artificial lung assistance with easy use and low cost. This article reviews the present state of clinical Novalung device implementation focusing on encountered limitations and conceivable future developments in the field.