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Introduction: Our group has developed a paracorporeal artificial lung (PAL) attached in a pulmonary artery (PA) to PA in series configuration to address profound respiratory failure and serve as a bridge to transplant and/or recovery. We recently designed, developed and converted our passive pre-PAL compliance chamber to an active, synchronized, counterpulsating assist device to relieve right heart strain and offset increased work placed on the right ventricle when the PAL is attached. In this study, we evaluated the safety and performance of both a valved and non-valved optional active compliance chamber (OACC) in a PA-PA PAL for right heart assistance in normal adult sheep. Methods : Eleven sheep (30—50 kg) were divided into non-valved OACC (n = 6) and valved (n = 5) OACC groups. To mimic pulmonary hypertension, a C-clamp was placed distal to the OACC-PAL and occluded until a 20% decrease in cardiac output (CO) was achieved. The OACC was activated, and right ventricular pressure (RVP), pulmonary artery pressure (PAP), mean arterial pressure (MAP) and CO were recorded. Results: All eleven animals tolerated the implantation of the OACC PAL. Activation of the OACC resulted in a significant increase in CO. Systolic and diastolic right ventricular pressure decreased in both groups. Lastly, counterpulsation increased the mean PAP in all animals and peak PAP reached 89 mmHg. Despite providing right heart assistance, synchronizing the counterpulsation was technically difficult, and the high peak PA pressures resulted in anastomotic bleeding in all animals and anastomotic breakdown in 4/11 animals. Conclusions: An OACC PAL perfused by the right ventricle applied in series with the pulmonary circulation reduces ventricular load and improves cardiac efficiency. These preliminary data suggest the potential of an artificial lung in unloading the strained right ventricle and acting as a bridge to transplantation. The augmented peak PA pressures, resulting in bleeding and anastomotic breakdown, and complexity in synchronizing the cardiac cycle with the pulsations of the augmented OACC, compromise this configuration. Perfusion (2007) 22, 81—86.

‘The artificial lung especially has lingered behind progress with artificial hearts and ventricular assist devices, not because the need for lungs has not been recognized, but because we have not had a full understanding of the engineering problems and the unique material requirements until recent years.’1 Brack Hattler, MD PhD The development from the first clinical use of haemo-dialysis over five decades ago to widespread chronic treatment took more than two decades. The histories of other artificial organ technologies, such as artificial hearts, follow similar long development paths. For five decades, due to a lack of technology, artificial lungs have been limited to use with a heart-lung machine for cardiopulmonary bypass (CPB) or extracorporeal membrane oxygenation (ECMO). The advent of pumpless biocompatible artificial lungs will open new treatment options for patients with acute or chronic lung failure.

An estimated 16 million Americans are afflicted with some degree of chronic obstructive pulmonary disease (COPD), accounting for 100,000 deaths per year. The only current treatment for chronic irreversible pulmonary failure is lung transplantation. Since the widespread success of single and double lung transplantation in the early 1990s, demand for donor lungs has steadily outgrown the supply. Unlike dialysis, which functions as a bridge to renal transplantation, or a ventricular assist device (VAD), which serves as a bridge to cardiac transplantation, no suitable bridge to lung transplantation exists. The current methods for supporting patients with lung disease, however, are not adequate or efficient enough to act as a bridge to transplantation. Although occasionally successful as a bridge to transplant, ECMO requires multiple transfusions and is complex, labor-intensive, time-limited, costly, non-ambulatory and prone to infection. Intravenacaval devices, such as the intravascular oxygenator (IVOX) and the intravenous membrane oxygenator (IMO), are surface area limited and currently provide inadequate gas exchange to function as a bridge-to-recovery or transplant. A successful artificial lung could realize a substantial clinical impact as a bridge to lung transplantation, a support device immediately post-lung transplant, and as rescue and//or supplement to mechanical ventilation during the treatment of severe respiratory failure.

Introduction: Transmembrane pressure drop reflects the resistance of an artificial lung system to blood transit. Decreased resistance (low transmembrane pressure drop) enhances blood flow through the oxygenator, thereby, enhancing gas exchange efficiency. This study is part of a previous one where we observed the behaviour and the modulation of blood pressure drop during the passage of blood through artificial lung membranes. Methods: Before and after the induction of multi-organ dysfunction, the animals were instrumented and analysed for venous-venous extracorporeal membrane oxygenation, using a pre-defined sequence of blood flows. Results: Blood flow and revolutions per minute (RPM) of the centrifugal pump varied in a linear fashion. At a blood flow of 5.5 L/min, pre- and post-pump blood pressures reached -120 and 450 mmHg, respectively. Transmembrane pressures showed a significant spread, particularly at blood flows above 2 L/min; over the entire range of blood flow rates, there was a positive association of pressure drop with blood flow (0.005 mmHg/mL/minute of blood flow ) and a negative association of pressure drop with temperature (-4.828 mmHg/oCelsius). These associations were similar when blood flows of below and above 2000 mL/minute were examined. Conclusions: During its passage through the extracorporeal system, blood is exposed to pressure variations from -120 to 450 mmHg. At high blood flows (above 2 L/min), the drop in transmembrane pressure becomes unpredictable and highly variable. Over the entire range of blood flows investigated (0 – 5500 mL/min), the drop in transmembrane pressure was positively associated with blood flow and negatively associated with body temperature.

We believe we have fulfilled the five objectives outlined in the introductory section to this text. Unquestionably, the clinical perfusionist will be confronted with a set of conditions that do not match the very specific values proposed for our in vitro performance testing. The in vitro results for a particular brand of oxygenator can serve as a 'performance baseline', predicting oxygen transfer performance under standard conditions. It is encumbant upon the clinical perfusionist to assess the impact that each variable (i.e. Hb, blood flow and SvO2) will have on the overall oxygen transfer performance. Table 5 illustrates how increases or decreases in each of these three variables can influence the resulting VO2/minute. The clinical perfusionist must manipulate these variables in order to satisfy the oxygen transfer demand created by the patient on CPB. In order for the in vitro performance testing to be helpful in the clinical environment, the perfusionist must: (1) be familiar with the results and the conditions under which they were achieved; and (2) be able to assess and interpret how their current set of conditions on cardiopulmonary bypass will impact on the oxygenator's performance. Example Brand Y membrane oxygenator is being used clinically on a patient weighing 115 kg and consuming 320 ml O2/minute. According to Table 4, this VO2/minute exceeds the 277.2 ml O2/minute achieved during its in vitro performance test.(ABSTRACT TRUNCATED AT 250 WORDS)

After a shortened history of conventional closed and open heart surgery, including hypothermia by surface cooling and extracorporeal circulation, the first application of a new membrane oxygenator developed by ML Bramson with an integrated temperature exchange system and a heart-lung machine (HLM) was reported in 1972. The aim was to have an efficient oxygenating and gas exchange artificial lung that allowed prolonged perfusions in patients with cardiogenic shock or acute respiratory insufficiency. After in vitro closed recirculation studies comparing different bubble, vertical screen, and the new membrane oxygenators, the Bramson HLM was used in dog experiments before starting clinical cardiac surgery with routine interventions (closure of an atrial septal defect). The first clinically prolonged support for more than three hours after a double valve replacement in a NYHA class IV patient failed. A partial venoarterial prolonged perfusion for 42 hours and 43 minutes in a 10-year-old girl after surgical correction of a partial av canal defect and postoperative development of consistent lung edema caused by myocardial failure after an ischemic time of 43 minutes was the first successful long-term perfusion case in Europe. These first experiences with the Bramson membrane lung formed the basis, in our group, for further investigations of different perfusion routes and cannulations in animal experiments. Also, scanning electron microscopy studies could be performed with experimentally and clinically used membranes. The development of disposable membrane lung devices, for instance, Lande - Edwards, Kolobow Scimed, and General Electric Peirce membrane lungs, ameliorated and improved the use of these devices considerably. Also, BRAMSON had developed a disposable membrane lung device that had proved to be very effective in animal experiments by 1972, but, unfortunately, this device did not become commercially available.