Development of a Disposable Maglev Centrifugal Blood Pump Intended for One-Month Support in Bridge-to-Bridge Applications: In Vitro and Initial In Vivo Evaluation

MedTech Dispo, a disposable maglev centrifugal blood pump with two degrees of freedom magnetic suspension and radial magnetic coupling rotation, has been developed for 1-month extracorporeal circulatory support. As the first stage of a two-stage in vivo evaluation, 2-week evaluation of a prototype MedTech Dispo was conducted. In in vitro study, the pump could produce 5 L/min against 800 mm Hg and the normalized index of hemolysis was 0.0054 ± 0.0008 g/100 L. In in vivo study, the pump, with its blood-contacting surface coated with biocompatible 2-methacryloyloxyethyl phosphorylcholine polymer, was implanted in seven calves in left heart bypass. Pump performance was stable with a mean flow of 4.49 ± 0.38 L/min at a mean speed of 2072.1 ± 64.5 rpm. The maglev control revealed its stability in rotor position during normal activity by the calves. During 2 weeks of operation in two calves which survived the intended study period, no thrombus formation was seen inside the pump and levels of plasma free hemoglobin were maintained below 4 mg/dL. Although further experiments are required, the pump demonstrated the potential for sufficient and reliable performance and biocompatibility in meeting the requirements for cardiopulmonary bypass and 1-week circulatory support.     

Feasibility of a tiny centrifugal blood pump (TinyPump) for pediatric extracorporeal circulatory support

Abstract: In this study, the performances of the TinyPump (priming volume 5 mL) system including the pediatric cannulae (Stöckert Pediatric Arterial Cannulae 2.6, 3.0, and 4.0 mm, Stöckert Instruments GmbH, Munich, Germany; Polystan 20‐Fr Venous Catheter, MAQUET GmbH, Rastatt, Germany) and an oxygenator (Terumo Capiox RX05 Baby‐RX, Terumo Cardiovascular Systems Co., Tokyo, Japan) were studied in vitro followed with preliminary ex vivo studies in 20‐kg piglets. In vitro results revealed that the TinyPump system met the requirements for pump speed, pump flow, and pressure drop as extracorporeal circulatory support during open heart surgery and extracorporeal membrane oxygenation (ECMO) in pediatric patients. In 2‐h ex vivo studies using 20‐kg piglets where the blood contacting surface of the TinyPump was coated with a biocompatible phospholipid polymer, the plasma‐free hemoglobin levels remained less than 5.0 mg/dL and no thrombus formation was observed inside the pump. The TinyPump system including the oxygenator and connecting circuits resulted in an overall priming volume of 68 mL, the smallest ever reported. The TinyPump can be a safe option for pediatric circulatory support during open heart surgery and ECMO without requiring blood transfusion.     

Comparison of a New Miniaturized Extracorporeal Membrane Oxygenation System With Integrated Rotary Blood Pump to a Standard System in a Porcine Model of Acute Lung Injury

Extracorporeal membrane oxygenation (ECMO) is used for severe acute respiratory distress syndrome. However, available ECMO systems are large and not well designed for fast delivery, emergency implantation, and interhospital transfer. Therefore, a new miniaturized oxygenator with integrated rotary blood pump (ILIAS) was developed and compared with a standard ECMO system in a large animal model. Acute lung injury was induced with repeated pulmonary saline lavage in 14 pigs until PaO₂/FiO₂‐ratio was <100 mm Hg with a positive‐end‐expiratory‐pressure of 5 mbar. Pigs were assigned to the following three groups: group 1 (n = 4): control group with conventional ventilation; group 2 (n = 5): standard vv‐ECMO; group 3 (n = 5): vv‐ILIAS. Gas exchange, hemodynamics, hemolysis, and coagulation activation were examined over a period of 8 h. No device failed during the observation period. PaCO₂ decreased from 59.40 ± 4.14 mm Hg to 48.62 ± 4.50 mm Hg after 1 h in the ILIAS group compared with an improvement of PaCO2 from 48.86 ± 7.45 to 40.10 ± 6.02 in the conventional ECMO group (P = not significant [n.s.]). ARDS‐induced respiratory acidosis was controlled promptly with a pH of 7.2 ± 0.1 at baseline increasing to 7.4 ± 0.1 in both study groups after 60 min of ECMO support. Mean carbon dioxide transfer was comparable between the conventional ECMO and ILIAS (211.36 ± 78.39 mL/min vs. 219.99 ± 76.72 mL/min, P = n.s.). PaO₂/FiO₂ increased from 118.4 ± 15.5 mm Hg to 179.1 ± 72.4 mm Hg in the ILIAS group compared with an improvement of oxygenation from 107.1 ± 24.9 mm Hg to 179.0 ± 45.7 mm Hg in the standard ECMO group (P = n.s.). Mean oxygen transfer was calculated with 136.09 ± 30.25 mL/min for the ILIAS and 129.05 ± 36.28 mL/min for the standard ECMO. Hemodynamic instability or significant activation of the plasmatic coagulation was not observed. However, hemolysis was significantly higher in the ILIAS group compared with the conventional ECMO. As the ILIAS prototype provided excellent gas exchange with hemodynamic stability comparable with a standard ECMO system, we believe this study serves as a proof of concept. Further development and design modifications (optimized rotation speed and surface coating of rotor) are already done and another experiment is projected to reduce hemolysis and platelet consumption for clinical application.     

A magnetically levitated centrifugal blood pump with a simple-structured disposable pump head

Abstract:  A magnetically levitated centrifugal blood pump (MedTech Dispo) has been developed for use in a disposable extracorporeal system. The design of the pump is intended to eliminate mechanical contact with the impeller, to facilitate a simple disposable mechanism, and to reduce the blood-heating effects that are caused by motors and magnetic bearings. The bearing rotor attached to the impeller is suspended by a two degrees-of-freedom controlled radial magnetic bearing stator, which is situated outside the rotor. In the space inside the ringlike rotor, a magnetic coupling disk is placed to rotate the rotor and to ensure that the pump head is thermally isolated from the motor. In this system, the rotor can exhibit high passive stiffness due to the novel design of the closed magnetic circuits. The disposable pump head, which has a priming volume of 23 mL, consists of top and bottom housings, an impeller, and a rotor with a diameter of 50 mm. The pump can provide a head pressure of more than 300 mm Hg against a flow of 5 L/min. The normalized index of hemolysis of the MedTech Dispo is 0.0025 ± 0.0005 g/100 L at 5 L/min against 250 mm Hg. This is one-seventh of the equivalent figure for a Bio Pump BPX-80 (Medtronic, Inc., Minneapolis, MN, USA), which has a value of 0.0170 ± 0.0096 g/100 L. These results show that the MedTech Dispo offers high pumping performance and low blood trauma.     

Establishment of a novel miniature veno‐venous extracorporeal membrane oxygenation model in the rat

Recently, veno‐venous extracorporeal membrane oxygenation (V‐V ECMO) has been commonly used in the world to support patients with severe respiratory failure. However, V‐V ECMO is a new technology compared to veno‐arterial extracorporeal membrane oxygenation and cardiopulmonary bypass, and there are few reports of basic research. Although continuing research is desired, clinical research that standardizes conditions such as patients’ background characteristics is difficult. The purpose of this study was to establish a simple and stably maintainable miniature V‐V ECMO model to study the mechanisms of the biological reactions in circulation during V‐V ECMO. The V‐V ECMO system consisted of an original miniature membrane oxygenator, polyvinyl chloride tubing line, and roller pump. The priming volume of this system was only 8 mL. Polyethylene tubing was used to cannulate the right femoral vein as the venous return cannula for the V‐V ECMO system. A 16‐G cannula was passed through the right internal jugular vein and advanced into the right atrium as the conduit for venous uptake. The animals were divided into 2 groups: SHAM group and V‐V ECMO group. V‐V ECMO was initiated and maintained at 50‐60 mL/kg/min, and oxygen was added into the oxygenator during V‐V ECMO at a concentration of 100% (pump flow:oxygen = 1:10). Blood pressure was measured continuously, and blood cells were measured by blood collection. During V‐V ECMO, the blood pressure and hemodilution rate were maintained around 80 mm Hg and 20%, respectively. Hb was kept at >10 g/dL, and V‐V ECMO could be maintained without blood transfusion. It was possible to confirm oxygenation of and carbon dioxide removal from the blood. Likewise, the pH was adequately maintained. There were no problems with this miniature V‐V ECMO system, and extracorporeal circulation progressed safely. In this study, a novel miniature V‐V ECMO model was established in the rat. A miniature V‐V ECMO model appears to be very useful for studying the mechanisms of the biological reactions during V‐V ECMO and to perform basic studies of circulation assist devices.     

Impact of high mechanical shear stress and oxygenator membrane surface on blood damage relevant to thrombosis and bleeding in a pediatric ECMO circuit

The roles of the large membrane surface of the oxygenator and the high mechanical shear stress (HMSS) of the pump in the extracorporeal membrane oxygenation (ECMO) circuit were examined under a pediatric support setting. A clinical centrifugal pump and a pediatric oxygenator were used to construct the ECMO circuit. An identical circuit without the oxygenator was constructed for comparison. Fresh human blood was circulated in the two circuits for 4 hours under the identical pump speed and flow. Blood samples were collected hourly for blood damage assessment, including platelet activation, generation of platelet-derived microparticles (PDMP), losses of key platelet hemostasis receptors (glycoprotein (GP) Ibα (GPIbα) and GPVI), and high molecular weight multimers (HMWM) of von Willebrand factor (VWF) and plasma free hemoglobin (PFH). Platelet adhesion on fibrinogen, VWF, and collagen was further examined. The levels of platelet activation and generation of PDMP and PFH exhibited an increasing trend with circulation time while the expression levels of GPIbα and GPVI receptors on the platelet surface decreased. Correspondingly, the platelets in the blood samples exhibited increased adhesion capacity to fibrinogen and decreased adhesion capacities on VWF and collagen with circulation time. Loss of HMWM of VWF occurred in both circuits. No statistically significant differences were found in all the measured parameters for blood damage and platelet adhesion function between the two circuits. The results indicate that HMSS from the pump played a dominant role in blood damage associated with ECMO and the impact of the large surface of the oxygenator on blood damage was insignificant.     

Extracorporeal membrane oxygenator compatible with centrifugal blood pumps

Coil-type silicone membrane oxygenators can only be used with roller blood pumps due to the resistance from the high blood flow. Therefore, during extracorporeal membrane oxygenation (ECMO) treatment, the combination of a roller pump and an oxygenator with a high blood flow resistance will induce severe hemolysis, which is a serious problem. A silicone rubber, hollow fiber membrane oxygenator that has a low blood flow resistance was developed and evaluated with centrifugal pumps. During in vitro tests, sufficient gas transfer was demonstrated with a blood flow less than 3 L/min. Blood flow resistance was 18 mm Hg at 1 L/min blood flow. This oxygenator module was combined with the Gyro C1E3 (Kyocera, Japan), and veno-arterial ECMO was established on a Dexter strain calf. An ex vivo experiment was performed for 3 days with stable gas performance and low blood flow resistance. The combination of this oxygenator and centrifugal pump may be advantageous to enhance biocompatibility and have less blood trauma characteristics.     

Pulse Conductance and Flow‐induced Hemolysis During Pulsatile Cardiopulmonary Bypass

In this study, the hypothesis was tested that a low‐resistant, high‐compliant oxygenator provides better pulse conductance and less hemolysis than a high‐resistant, low‐compliant oxygenator during pulsatile cardiopulmonary bypass. Forty adults undergoing coronary artery bypass surgery were randomly divided into two groups using either an oxygenator with a relatively low hydraulic resistance (Quadrox BE‐HMO 2000, Maquet Cardiopulmonary AG, Hirrlingen, Germany) or with a relatively high hydraulic resistance (Capiox SX18, Terumo Cardiovascular Systems, Tokyo, Japan). The phase shift between the flow signals measured at the inlet and outlet of the oxygenator was used to assess compliance. Pulse conductance in terms of pressure attenuation was calculated by dividing the outlet pulse pressure of the oxygenator by the inlet pulse pressure. A normalized index was used to assess hemolysis. The phase shifts in time of the flow pulses were 36 ± 6 ms in the low‐resistant (high‐compliant) oxygenator, and 14 ± 2 ms in the high‐resistant (low‐compliant) oxygenator group (P < 0.001). The low‐resistant, high‐compliant oxygenator provided 27% better pulse conductance compared with the high‐resistant, low‐compliant oxygenator (0.84 ± 0.02 and 0.66 ± 0.01, respectively, P < 0.001). Inlet pulse pressures were significantly higher (29%) in the high‐resistant, low‐compliant (Capiox) group than in the low‐resistant, high‐compliant (Quadrox) group (838 ± 38 mm Hg and 648 ± 25 mm Hg respectively, P < 0.001), but no significant difference in hemolysis was found. A low‐resistant, high‐compliant oxygenator provides better pulse conduction than a high‐resistant, low‐compliant oxygenator. However, the study data could not confirm the association of high pressures with increased hemolysis.     

Evaluation of Conventional Nonpulsatile and Novel Pulsatile Extracorporeal Life Support Systems in a Simulated Pediatric Extracorporeal Life Support Model

The objective of this study is to evaluate two extracorporeal life support (ECLS) circuits and determine the effect of pulsatile flow on pressure drop, flow/pressure waveforms, and hemodynamic energy levels in a pediatric pseudopatient. One ECLS circuit consisted of a Medos Deltastream DP3 diagonal pump and Hilite 2400 LT oxygenator with arterial/venous tubing. The second circuit consisted of a Maquet RotaFlow centrifugal pump and Quadrox‐iD Pediatric oxygenator with arterial/venous tubing. A 14Fr Medtronic Bio‐Medicus one‐piece pediatric arterial cannula was used for both circuits. All trials were conducted at flow rates ranging from 500 to 2800 mL/min using pulsatile or nonpulsatile flow. The post‐cannula pressure was maintained at 50 mm Hg. Blood temperature was maintained at 36°C. Real‐time pressure and flow data were recorded using a custom‐based data acquisition system. The results showed that the Deltastream DP3 circuit produced surplus hemodynamic energy (SHE) in pulsatile mode at all flow rates, with greater SHE delivery at lower flow rates. Neither circuit produced SHE in nonpulsatile mode. The Deltastream DP3 pump also demonstrated consistently higher total hemodynamic energy at the pre‐oxygenator site in pulsatile mode and a lesser pressure drop across the oxygenator. The Deltastream DP3 pump generated physiological pulsatility without backflow and provided increased hemodynamic energy. This novel ECLS circuit demonstrates suitable in vitro performance and adaptability to a wide range of pediatric patients.     

Hemolytic performance of a MagLev disposable rotary blood pump (MedTech Dispo): effects of MagLev gap clearance and surface roughness

Mechanical shaft seal bearing incorporated in the centrifugal blood pumps contributes to hemolysis and thrombus formation. In addition, the problem of durability and corrosion of mechanical shaft seal bearing has been recently reported from the safety point of view. To amend the shortcomings of the blood-immersed mechanical bearings, a magnetic levitated centrifugal rotary blood pump (MedTech Dispo Model 1; Tokyo Medical and Dental University, Tokyo, Japan) has been developed for extracorporeal disposable application. In this study, the hemolytic performance of the MedTech Dispo Model 1 centrifugal blood pump system was evaluated, with special focus on the narrow blood path clearance at the magnetic bearing between rotor and stator, and on the pump housing surface roughness. A pump flow of 5 L/min against the head pressure of 100 mm Hg for 4 h was included in the hemolytic test conditions. Anticoagulated fresh porcine blood was used as a working fluid. The clearance of blood path at the magnetic bearing was in the range of 100-250 micro m. Pump housing surface roughness was controlled to be around Ra = 0.1-1.5 micro m. The lowest hemolytic results were obtained at the clearance of 250 micro m and with the polished surface (Ra = 0.1 micro m) yielding the normalized index of hemolysis (NIH) of less than 0.001 g/100 L, which was 1/5 of the Biopump BP-80 (Medtronic Inc., Minneapolis, MN, USA, and 1/4 of the BPX-80. In spite of rough surface and narrow blood path, NIH levels were less than clinically acceptable level of 0.005 g/100 L. The noncontact, levitated impeller system is useful to improve pump performance in blood environment.     

In vitro drug adsorption and plasma free hemoglobin levels associated with hollow fiber oxygenators in the extracorporeal life support (ECLS) circuit

The purpose of this study was to identify the percentage of fentanyl or morphine sulfate lost from adhesion to either the polyvinylchloride (PVC) tubing or the surface of two different hollow fiber oxygenators used in current extracorporeal life support circuits and to identify any difference in the plasma free hemoglobin (PFH) levels generated when using these oxygenator and/or drug combinations. For each drug examined, six simple circuits were assembled; for each drug, two circuits contained tubing without an oxygenator (control), two circuits contained the Jostra Quadrox D (Maquet Cardiopulmonary, AG Hirrlingen, Germany), and two circuits contained the Terumo Baby Rx (Terumo Cardiovascular Systems Corp., Ann Arbor, MI). Fentanyl or morphine sulfate was added to yield initial circuit concentrations equal to 1430 ng/mL, respectively. Throughout the 6-hour in vitro testing, samples to evaluate the drug and PFH levels were drawn at various time intervals. Significance in this study is defined as p < .05. Fentanyl's initial adsorption seems to be 80% in circuits without oxygenators, 86% in the circuits containing the Quadrox D oxygenator, and 83% in the circuits with the Baby Rx oxygenator. Morphine sulfate seems to be initially adsorbed at a rate of 40% in all circuits and does not seem to be adsorbed by either of the tested oxygenators. The PFH levels were significantly (p < .05) elevated in the fentanyl circuits. The type of oxygenator does not seem to play a significant role in drug adsorption. During this in vitro study, the majority of both drugs were lost to the PVC tubing. The type of oxygenator did not seem to significantly affect PFH. However, fentanyl in any combination or alone was associated with increased PFH levels.     

Clinical evaluation of two different extracorporeal membrane oxygenation systems: a single center report

Refinements in extracorporeal membrane oxygenation (ECMO) equipment, including heparin-coated surfaces, centrifugal pump, membrane oxygenator, and more biocompatible pump-oxygenator circuits, have reduced procedure-related complications and have made ECMO a safe and effective therapy for critical patients. The aim of this study was to evaluate the performance of two different ECMO circuit systems in a clinical setting and compare their outcomes. From December 2004 to December 2009, 121 patients required ECMO for primary or postcardiotomy cardiogenic shock at our heart center. We used the Medtronic circuit system in our earlier series (Group M, n = 64), and from July 2007, ECMO was carried out mainly with the Quadrox D PLS circuit system (Group Q, n = 56). We retrospectively summarized and analyzed the data of these patients. The evaluation was based on the comparison between properties of the membrane oxygenators and pumps, anticoagulation therapy, circuit-related complications, and clinical outcomes. Support pump flow rates, platelet counts, and trans-membrane pressure drops (TMPDs) of preoxygenator and postoxygenator pressures were compared between two groups at the time of support established (T1) and support established for 24 h (T2). There were no significant differences between the two groups with regard to patient characteristics and pre-ECMO data. The support pump flow rates and platelet counts at different times were comparable in the two groups. The cannulation technique, ECMO duration, and mean heparin dosage were similar in both groups. There were also no significant differences between the groups in mortality or complications related to bleeding and organ dysfunction. Compared with the M group, the Q group experienced less mechanical failure of the ECMO circuit. The Quadrox PLS circuit system showed less circuit thrombus formation (P < 0.045), less plasma leakage (P < 0.001), and less need for replacement of oxygenators (P < 0.001). Furthermore, frequency of hemolysis during ECMO was significantly lower (P < 0.045). In addition, at T1 and T2, TMPDs were significantly lower in the Q group. Our results suggest that both ECMO circuit systems provide similar effects for safe clinical application, but the Quadrox PLS ECMO circuit system demonstrated partially improved biocompatibility in terms of improved cell preservation, lower TMPDs, less plasma leakage, and thrombus formation.     

Comparison of Centrifugal and Roller Pump Hemolysis Rates at Low Flow

Abstract We compared in vitro rates of hemolysis for a recently developed centrifugal pump with a conventional roller pump (10-10-00; Stöckert, Munich, Germany). Flow rates of 0.3 L/min and 1 L/min and a pressure of 200 mm Hg were chosen to simulate conditions during neonatal extracorporeal membrane oxygenation (ECMO). There was no significant difference in hemolysis rates between centrifugal and roller pumps (p = 0.57) nor between high and low flow (p = 0.86). The centrifugal pump caused no more blood trauma than the roller pump at the low-flow/high-pressure conditions required for neonatal ECMO. The Nikkiso pump is superior to roller pumps in size and priming volume (25 ml) and may permit development of a smaller and simpler ECMO system.     

Laboratory Evaluation of Hemolysis and Systemic Inflammatory Response in Neonatal Nonpulsatile and Pulsatile Extracorporeal Life Support Systems

The objective of this study was to compare the systemic inflammatory response and hemolytic characteristics of a conventional roller pump (HL20‐NP) and an alternative diagonal pump with nonpulsatile (DP3‐NP) and pulsatile mode (DP3‐P) in simulated neonatal extracorporeal life support (ECLS) systems. The experimental neonatal ECLS circuits consist of a conventional Jostra HL20 roller pump or an alternative Medos DP3 diagonal pump, and Medos Hilite 800 LT hollow‐fiber oxygenator with diffusion membrane. Eighteen sterile circuits were primed with freshly donated whole blood and divided into three groups: conventional HL20 with nonpulsatile flow (HL20‐NP), DP3 with nonpulsatile flow (DP3‐NP), and DP3 with pulsatile flow (DP3‐P). All trials were conducted for durations of 12 h at a flow rate of 500 mL/min at 36°C. Simultaneous blood flow and pressure waveforms were recorded. Blood samples were collected to measure plasma‐free hemoglobin (PFH), human tumor necrosis factor‐alpha, interleukin‐6 (IL‐6), and IL‐8, in addition to the routine blood gas, lactate dehydrogenase, and lactic acid levels. HL20‐NP group had the highest PFH levels (mean ± standard error of the mean) after a 12‐h ECLS run, but the difference among groups did not reach statistical significance (HL20‐NP group: 907.6 ± 253.1 mg/L, DP3‐NP group: 343.7 ± 163.2 mg/L, and DP3‐P group: 407.6 ± 156.6 mg/L, P = 0.06). Although there were similar trends but no statistical differences for the levels of proinflammatory cytokines among the three groups, the HL20‐NP group had much greater levels than the other groups (P > 0.05). Pulsatile flow generated higher total hemodynamic energy and surplus hemodynamic energy levels at pre‐oxygenator and pre‐clamp sites (P < 0.01). Our study demonstrated that the alternative diagonal pump ECLS circuits appeared to have less systemic inflammatory response and hemolysis compared with the conventional roller pump ECLS circuit in simulated neonatal ECLS systems. Pulsatile flow delivered more hemodynamic energy to the pseudo‐patient without increased odds of hemolysis compared with the conventional, nonpulsatile roller pump group.     

Mock Circulation Loop to Investigate Hemolysis in a Pulsatile Total Artificial Heart

Hemocompatibility of blood pumps is a crucial parameter that has to be ensured prior to in vivo testing. In contrast to rotary blood pumps, a standard for testing a pulsatile total artificial heart (TAH) has not yet been established. Therefore, a new mock circulation loop was designed to investigate hemolysis in the left ventricle of the ReinHeart TAH. Its main features are a high hemocompatibility, physiological conditions, a low priming volume, and the conduction of blood through a closed tubing system. The mock circulation loop consists of a noninvasive pressure chamber, an aortic compliance chamber, and an atrium directly connected to the ventricle. As a control pump, the clinically approved Medos‐HIA ventricular assist device (VAD) was used. The pumps were operated at 120 beats per minute with an aortic pressure of 120 to 80 mm Hg and a mean atrial pressure of 10 mm Hg, generating an output flow of about 5 L/min. Heparinized porcine blood was used. A series of six identical tests were performed. A test method was established that is comparable to ASTM F 1841, which is standard practice for the assessment of hemolysis in continuous‐flow blood pumps. The average normalized index of hemolysis (NIH) values of the VAD and the ReinHeart TAH were 0.018 g/100 L and 0.03 g/100 L, respectively. The standard deviation of the NIH was 0.0033 for the VAD and 0.0034 for the TAH. Furthermore, a single test with a BPX‐80 Bio‐Pump was performed to verify that the hemolysis induced by the mock circulation loop was negligible. The performed tests showed a good reproducibility and statistical significance. The mock circulation loop and test protocol developed in this study are valid methods to investigate the hemolysis induced by a pulsatile blood pump.     

Development of a disposable magnetically levitated centrifugal blood pump (MedTech Dispo) intended for bridge-to-bridge applications--two-week in vivo evaluation

Last year, we reported in vitro pump performance, low hemolytic characteristics, and initial in vivo evaluation of a disposable, magnetically levitated centrifugal blood pump, MedTech Dispo. As the first phase of the two-stage in vivo studies, in this study we have carried out a 2-week in vivo evaluation in calves. Male Holstein calves with body weight of 62.4–92.2 kg were used. Under general anesthesia, a left heart bypass with a MedTech Dispo pump was instituted between the left atrium and the descending aorta via left thoracotomy. Blood-contacting surface of the pump was coated with a 2-methacryloyloxyethyl phosphorylcholine polymer. Post-operatively, with activated clotting time controlled at 180–220 s using heparin and bypass flow rate maintained at 50 mL/kg/min, plasma-free hemoglobin (Hb), coagulation, and major organ functions were analyzed for evaluation of biocompatibility. The animals were electively sacrificed at the completion of the 2-week study to evaluate presence of thrombus inside the pump,together with an examination of major organs. To date, we have done 13 MedTech Dispo implantations, of which three went successfully for a 2-week duration. In these three cases, the pump produced a fairly constant flow of 50 mL/Kg/min. Neurological disorders and any symptoms of thromboembolism were not seen. Levels of plasma-free Hb were maintained very low. Major organ functions remained within normal ranges. Autopsy results revealed no thrombus formation inside the pump. In the last six cases, calves suffered from severe pneumonia and they were excluded from the analysis. The MedTech Dispo pump demonstrated sufficient pump performance and biocompatibility to meet requirements for 1-week circulatory support. The second phase (2-month in vivo study) is under way to prove the safety and efficacy of MedTech Dispo for 1-month applications.     

A Compact Centrifugal Pump for Cardiopulmonary Bypass

A majority of the cardiopulmonary bypass (CPB) systems still utilize bulky roller pumps. A direct-drive small centrifugal pump intended for second-generation CPB pump has been developed. The pump has a 50 mm diameter impeller and provides a 6 L/min flow at 3,000 rpm against 300 mm Hg. A flexible drive shaft allows us to separate the pump head from the console resulting in easier manipulation. An in vitro study showed that the pump generated less hemolysis (index of hemolysis = 0.0011, comparable to the value for Bio-medicus BP-80). To improve blood flow around the shaft-seal region and to reduce thrombus formation around the shaft, six holes were drilled through the impeller. In biventricular bypass experiments using calves, our pump demonstrated excellent antithrombogenicity and durability for 48 h. And the compact and atraumatic centrifugal pump system showed excellent performance and easy manipulation under actual CPB conditions in animal.     

Non‐invasive Measurements of Energy Expenditure and Respiratory Quotient by Respiratory Mass Spectrometry in Children on Extracorporeal Membrane Oxygenation‐A Pilot Study

Extracorporeal membrane oxygenation (ECMO) provides temporary life‐saving support for pediatric patients with severe cardiac failure, but causes metabolic disturbances and altered nutritional requirements. However, few studies have addressed the optimal energy supply to meet the demand of these children, largely due to technical difficulties with their invasive nature. We have adapted respiratory mass spectrometry to continuously measure O₂ consumption and CO₂ production in the gas exchange across the ECMO oxygenator, as well as that across the ventilator. This study aimed to assess energy expenditure (EE) and respiratory quotient (RQ) in children on ECMO. Five children (aged 0.3 to 36 months, median 20) were studied between Day 1 and Day 6 on ECMO. EE and RQ were measured in sequential fashion at the child's native lungs and ECMO oxygenator using respiratory mass spectrometry. Measurements were collected at 4‐h intervals, with the means in 24 h representing the values of each day. Each child's caloric and protein intakes were recorded for each day. Between ECMO Days 1 and 6, there was a small but significant increase in EE from 40 to 46 kcal/kg/day (P = 0.03). In comparison, the caloric intake significantly increased by twice as much as EE from 30 to 61 kcal/kg/day (P = 0.017). As a result, RQ significantly increased from 0.6 to 1.0 (P < 0.0001). Protein intake significantly increased during ECMO Days 1 to 6 from 0.5 to 1.5 g/kg/day (P = 0.04). Respiratory mass spectrometry is feasible to provide a unique and safe technique to measure EE and RQ in patients on ECMO. Without this knowledge, inadequate feeding may occur. Further studies are warranted in a larger patient population to provide better information to guide clinical practice in this special group of critically ill children.     

Enhancement of Hemocompatibility of the MERA Monopivot Centrifugal Pump: Toward Medium‐Term Use

The MERA monopivot centrifugal pump has been developed for use in open‐heart surgery, circulatory support, and bridge‐to‐decision for up to 4 weeks. The pump has a closed‐type, 50‐mm diameter impeller with four straight paths. The impeller is supported by a monopivot bearing and is driven by a radial‐flux magnet‐coupling motor. Because flow visualization experiments have clarified sufficient pivot wash and stagnation at the sharp corner of the pivot support was suggested, sharp corners were removed in the design stage. The index of hemolysis of the pump operating at more than 200 mm Hg was found to be lower than that of a commercial pump. Four‐week animal tests were then conducted two times; improvement of thrombus formation was seen in the female pivot through modification of female pivot geometry. Overall antithrombogenicity was also recorded. Finally, to assure mid‐term use, an additional 4‐week durability test revealed that the rate of the axial pivot wear was as small as 1.1 µm/day. The present in vitro and in vivo studies revealed that the MERA monopivot centrifugal pump has sufficient hemocompatibility and durability for up to 4 weeks.     

The Aachen Miniaturized Heart‐Lung Machine—First Results in a Small Animal Model

Congenital heart surgery most often incorporates extracorporeal circulation. Due to foreign surface contact and the administration of foreign blood in many children, inflammatory response and hemolysis are important matters of debate. This is particularly an issue in premature and low birth‐weight newborns. Taking these considerations into account, the Aachen miniaturized heart‐lung machine (MiniHLM) with a total static priming volume of 102 mL (including tubing) was developed and tested in a small animal model. Fourteen female Chinchilla Bastard rabbits were operated on using two different kinds of circuits. In eight animals, a conventional HLM with Dideco Kids oxygenator and Stöckert roller pump (Sorin group, Milan, Italy) was used, and the Aachen MiniHLM was employed in six animals. Outcome parameters were hemolysis and blood gas analysis including lactate. The rabbits were anesthetized, and a standard median sternotomy was performed. The ascending aorta and the right atrium were cannulated. After initiating cardiopulmonary bypass, the aorta was cross‐clamped, and cardiac arrest was induced by blood cardioplegia. Blood samples for hemolysis and blood gas analysis were drawn before, during, and after cardiopulmonary bypass. After 1 h aortic clamp time, all animals were weaned from cardiopulmonary bypass. Blood gas analysis revealed adequate oxygenation and perfusion during cardiopulmonary bypass, irrespective of the employed perfusion system. The use of the Aachen MiniHLM resulted in a statistically significant reduced decrease in fibrinogen during cardiopulmonary bypass. A trend revealing a reduced increase in free hemoglobin during bypass in the MiniHLM group could also be observed. This newly developed Aachen MiniHLM with low priming volume, reduced hemolysis, and excellent gas transfer (O₂ and CO₂) may reduce circuit‐induced complications during heart surgery in neonates.