The hemolysis test of the Gyro C1E3 pump in pulsatile mode

Pneumatic driven pulsatile ECMO in vitro evaluation with oxygen tanks

Extracorporeal membrane oxygenation device is a procedure in which mechanical systems circulate blood and supply oxygen to patients with impaired cardiopulmonary function. Current venoarterial systems are associated with low patient survival rates and new treatments are needed to avoid left ventricular dilation, which is a major cause of death. In this study, a new mobile pulsatile ECMO with a pump structure that supplies pulsatile flow by using an oxygen tank as a power source is proposed. In vitro experiments conducted under mock circulation system as like patient conditions demonstrated that 2.8 L oxygen can sustain the outflow of 1 L/min of pulsatile blood flow for 53 min, while a 4.6 L tank was able to sustain the same flow for 85 min. The energy equivalent pressure evaluation index of the pulsatile blood pump shows that the mobile pulsatile ECMO could supply sufficient pulsatile blood flow compared to the existing pulsatile ECMO. Through in vitro experiments performed under mock circulation conditions, this new system was proven to supply sufficient oxygen and pulsatile blood flow using the pressure of an oxygen tank even while transporting a patient.

Preload control of the increased outflow of a dual pulsatile extracorporeal membrane oxygenator

An improved pulsatile extracorporeal membrane oxygenation (ECMO) device is needed to reduce the high risk of complications associated with existing ECMO devices, due to continuous blood outflow (which reduces blood perfusion) and a complex structure that makes setup and management difficult. This study introduces a new pulsatile ECMO device to maintain sufficient pulsatility (an “energy equivalent pressure increment” [EEPI] of at least 20 %) and simplify the structure of the pulsatile pump by removing artificial valves and complex actuators. The hemodynamic characteristics and pulsatility of the proposed pulsatile ECMO device were evaluated in-vitro using a MOCK system. Although the pulsatile ECMO device has the same dual pumping structure as existing pulsatile ECMOs, the newly applied preload control mechanism increases the outflow of the proposed pulsatile ECMO compared to the previous device.

Numerical modeling of pulsatile blood flow through a mini-oxygenator in artificial lungs

While previous in vitro studies showed divergent results concerning the influence of pulsatile blood flow on oxygen advection in oxygenators, no study was done to investigate the uncertainty affected by blood flow dynamics. The aim of this study is to utilize a computational fluid dynamics model to clarify the debate concerning the influence of pulsatile blood flow on the oxygen transport. The computer model is based on a validated 2D finite volume approach that predicts oxygen transfer in pulsatile blood flow passing through a 300-micron hollow-fiber membrane bundle with a length of 254 mm, a building block for an artificial lung device. In this study, the flow parameters include the steady Reynolds number (Re = 2, 5, 10 and 20), Womersley parameter (Wo = 0.29, 0.38 and 0.53) and sinusoidal amplitude (A = 0.25, 0.5 and 0.75). Specifically, the computer model is extended to verify, for the first time, the previously measured O₂ transport that was observed to be hindered by pulsating flow in the Biolung, developed by Michigan Critical Care Consultants. A comprehensive analysis is carried out on computed profiles and fields of oxygen partial pressure (P_O2) and oxygen saturation (S_O2) as a function of Re, Wo and A. Based on the present results, we observe the positive and negative effects of pulsatile flow on P_O2 at different blood flow rates. Besides, the S_O2 variation is not much influenced by the pulsatile flow conditions investigated. While being consistent with a recent experimental study, the computed O₂ volume flow rate is found to be increased at high blood flow rates operated with low frequency and high amplitude. Furthermore, the present study qualitatively explains that divergent outcomes reported in previous in vitro experimental studies could be owing to the different blood flow rates adopted. Finally, the contour analysis reveals how the spatial distributions of P_O2 and S_O2 vary over time.

Hemodynamic performance of a compact centrifugal left ventricular assist device with fully magnetic levitation under pulsatile operation: An in vitro study

Long-term using continuous flow ventricular assist devices could trigger complications associated with diminished pulsatility, such as valve insufficiency and gastrointestinal bleeding. One feasible solution is to produce pulsatile flow assist with speed regulation in continuous flow ventricular assist devices. A third-generation blood pump with pulsatile operation control algorithm was first characterized alone under pulsatile mode at various speeds, amplitudes, and waveforms. The pump was then incorporated in a Mock circulation system to evaluate in vitro hemodynamic effects when using continuous and different pulsatile operations. Pulsatility was evaluated by surplus hemodynamic energy. Results showed that pulsatile operations provided sufficient hemodynamic assistance and increased pulsatility of the circulatory system (53% increment), the mean aortic pressure (65% increment), and cardiac output (27% increment). The pulsatility of the system under pulsatile operation support was increased 147% compared with continuous operation support. The hemodynamic performance of pulsatile operations is susceptible to phase shifts, which could be a tacking angle for physiological control optimization. This study found third-generation blood pumps using different pulsatile operations for ventricular assistance promising.

Haemodynamic evaluation of the new pulsatile-flow generation method in vitro

Continuous-flow ventricular-assist devices are widely used to support patients with advanced heart failure, because continuous-flow ventricular-assist devices are more durable, have smaller sizes and have better survival rates for patients compared to the pulsatile-flow ventricular-assist devices. Nevertheless, continuous-flow ventricular-assist devices often cause complications such as gastrointestinal bleeding, haemorrhagic stroke, and aortic insufficiency and have a negative impact on the microcirculation for both long-time implantable and short-time extracorporeal systems. The aim of this study is the evaluation of the pulsatile-flow generation method in continuous-flow ventricular-assist device without pump speed changes. The method may be used for short-time extracorporeal continuous-flow mechanical circulatory support and long-time implantable mechanical circulatory support. A shunt with a controlled adjustable valve, that clamps periodically, is connected in parallel to the continuous-flow ventricular-assist device. We compared the continuous-flow ventricular-assist device operating with and without the shunt on the mock circulation loop. The continuous-flow ventricular-assist device-shunt system was connected according to the left ventricle-aorta circuit and worked in phase with the ventricle. Heart failure was simulated on the mock circulation circuit. Rotaflow (Maquet Inc.) was used as the continuous-flow pump. Haemolysis studies of the system for generating a pulse flow were carried out at a flow rate of 5 L/min and a pressure drop of 100 mm Hg. To compare the haemodynamic efficiency, we used the aortic pulsation index I_p, the equivalent energy pressure and the surplus haemodynamic energy. These indexes were higher in the pulsatile mode (I_p - 4 times, equivalent energy pressure by 7.36% and surplus haemodynamic energy - 10 times), while haemolysis was the same. The normalised index of haemolysis was 0.0015 ± 0.001. The results demonstrate the efficiency of the pulsatile-flow generation method for continuous-flow ventricular-assist devices without impeller rotation rate changes.

In Vitro Comparative Assessment of Mechanical Blood Damage Induced by Different Hemodialysis Treatments

Gradual deterioration of red blood cells (RBCs) due to mechanical stress (chronic hemolysis) is unavoidable during treatments that involve extracorporeal blood circulation, such as hemodialysis (HD). This effect is generally undetectable and does not generate any acute symptoms, but it leads to an increase in plasma free hemoglobin (fHb). There are no absolute safety levels for fHb increase, indicating the need for an empirical evaluation using comparative testing. The increase in fHb levels was investigated in vitro by applying double‐needle double‐pump HD (HD‐DNDP), a new modality in which arterial and venous pumps both run continuously. fHb was measured during typical and worst‐case simulated dialysis treatments (double‐needle single‐pump HD [HD‐DNSP], hemodiafiltration [HDF‐DN], single‐needle double‐pump HD [HD‐SNDP], and HD‐DNDP) performed in vitro using bovine blood for 4 h. Hemolysis‐related indices (fHb%; index of hemolysis, IH; and normalized IH) were calculated and used for comparison. The increase in fHb during either HDF‐DN or HD‐SNDP with Artis and AK200 dialysis machines was similar, while the fHb at the maximum real blood flow rate (Qb_real) at the completion of the HD‐DNDP treatment on Artis was higher than that for HD‐DNSP using a Phoenix dialysis machine (fHb% = 1.24 ± 0.13 and 0.92 ± 0.12 for the Artis machine with HD‐DNDP at Qb_real = 450 mL/min and Phoenix with HD‐DNSP at Qb_real = 500 mL/min, respectively). However, the fHb levels increased linearly, and no steep changes were observed. The increases observed during HD‐DNDP were the same order of magnitude as those for widely used bloodlines and treatment modes for delivering dialysis treatments. The observed results matched literature findings, and thus the measured fHb trends are not predicted to have clinical side effects. HD‐DNDP treatment with Artis does not merit any additional concern regarding mechanical stress to RBCs compared with that observed for routinely used dialysis treatments, bloodlines and machines. Although the in vitro measurement of the fHb increase in bovine blood does not allow a prediction of the absolute level of blood mechanical damage or the possible effects in humans, such measurements are valuable for assessing hemolytic harm by performing tests comparing the proposed treatment with existing devices.

Blood trauma testing for mechanical circulatory support devices

Preclinical hemolysis testing is a critical requirement toward demonstrating device safety for U.S. Food and Drug Administration (FDA) 510(k) approval of mechanical circulatory support devices (MCSD). FDA and ASTM (formerly known as the American Society for Testing and Materials) have published guidelines to assist industry with developing study protocols. However, there can be significant variability in experimental procedures, study design, and reporting of data that makes comparison of test and predicate devices a challenge. To overcome these limitations, we present a hemolysis testing protocol developed to enable standardization of hemolysis testing while adhering to FDA and ASTM guidelines. Static mock flow loops primed with fresh bovine blood (600 mL, Hematocrit = 27±5%, heparin titrated for ACT >300 sec) from a single-source donor were created as a platform for investigating test and predicate devices. MCSD differential pressure and temperature were maintained at 80 mmHg and 25°±2° C. Blood samples (3 ml) were collected at 0, 5, 90, 180, 270, 360 minutes to measure CBC and plasma free hemoglobin. This protocol led to 510(k) approval of two adult MCSD and has been used to test novel cannulae and a pediatric MCSD. Standardization of hemolysis testing procedures and transparency of results may enable better blood trauma characterization of MCS devices to facilitate the FDA 510(k) and PMA submission processes and improve clinical outcomes.

Durability improvement of polymer chamber of pulsatile extracorporeal life support system in terms of mechanical change

Twin Pulse Life Support, T-PLS has received the CE mark (2003) and Korea Food and Drug Administration (KFDA) approval (2004) for short-term application as an Extracorporeal Life Support system (ECLS). T-PLS's original intention was to apply for not only short-term but also long-term application such as Extracorporeal ventricular assist device (VAD). Hence, a long-term durability test was conducted. The 1-year reliability of the systems tested in this study did not meet the STS/ASAIO standard of 80% reliability with 60% confidence for a 1-year mission life. However, without the disposable units, which are only designed to operate for 6 h, the 1-year reliability exceeded the STS/ASAIO standard of 80% reliability with 60% confidence. In this study, by using the existing analysis methods and analyzing the root cause of the failure used by a numerical analysis. As eliminating or mitigating of the root cause of the failure, we improved the durability of blood chamber and evaluated the performance of the modified system via the hemolysis test.

Application of a pressure-relieving air compliance chamber in a single-pulsatile extracorporeal life support system: an experimental study

Nonpulsatile blood pumps are mainly used in extracorporeal life support systems. Although pulsating blood flow is known to be physiological, a pulsatile pump is not commonly applied in a circuit with a membrane oxygenator because of damage to the blood cells. The hypothesis that the placement of a pressure-relieving compliance chamber in a circuit might reduce blood cell trauma was tested. An extracorporeal life support circuit was constructed in an acute lung injury model of dogs by oleic acid infusion. The animals were divided into three groups. In group I (n = 6) a nonpulsatile centrifugal pump was used as a control. In group II (n = 4) a single-pulsatile pump was used, and in group III (n = 6) a single-pulsatile pump equipped with a compliance chamber was used. Pump flow was maintained at 1.8-2.0 L/min for 2 h. Hemodynamics and blood gas analyses indicated that the pulsatile groups II and III had better results than the nonpulsatile group I. The plasma-free hemoglobin level, which indicates blood cell trauma, was the lowest in group I and the highest in group II but was significantly decreased in group III. A pressure-relieving compliance chamber could significantly reduce high circuit pressures and blood cell trauma.

Mathematical Modeling of Fluid Dynamics in Pulsatile Cardiopulmonary Bypass

The design criteria of an extracorporeal circuit suitable for pulsatile flow are quite different and more entangled than for steady flow. The time and costs of the design process could be reduced if mutual influences between the pulsatile pump and other extracorporeal devices were considered without experimental trial-and-error activities. With this in mind, we have developed a new lumped-parameter mathematical model of the hydraulic behavior of the arterial side of an extracorporeal circuit under pulsatile flow conditions. Generally, components feature a resistant-inertant-compliant behavior and the most relevant nonlinearities are accounted for. Parameter values were derived either by experimental tests or by analytical analysis. The pulsatile pump is modeled as a pure pulsatile flow generator. Model predictions were compared with flow rate and pressure tracings measured during hydraulic tests on two different circuits at various flow rates and pulse frequencies. The normalized root mean square error did not exceed 24% and the model accurately describes the changes that occur in the basic features of the pressure and flow wave propagating from the pulsatile pump to the arterial cannula.

Fractural characteristic evaluation of a microcapsule suspension using a rotational shear stressor

We are developing microcapsule suspensions to evaluate the absolute hemolytic properties of centrifugal blood pumps. Four types of microcapsule suspensions, with maximum diameters of 100 microm or 10 microm, and membranes of polyurethane or melamine resin, were exposed to fluid dynamic shear up to 15,000 s(-1) with a rotating shear stressor developed in our laboratory. As a result, destruction was observed of only the 100 microm microcapsules. The microcapsules with polyurethane membranes broke at a high shear velocity range over 11,250 s(-1), a tendency similar to that observed using bovine blood. The microcapsules with melamine resin ruptured at approximately 7,500 s(-1). These observations could lead to determination of absolute hemolysis from shear stress occurring in centrifugal blood pumps.

Development of a new disposable pulsatile pump for cardiopulmonary bypass: computational fluid-dynamic design and in vitro tests

A newly conceived blood pump for pulsatile cardiopulmonary bypass (CPB) is presented. The new device's main design features (fully disposable pumping head with ring shaped valves) were intended to overcome the factors that today limit the use of pulsatile blood pumps, i.e., the complexity and costs of devices. The pump was designed and analyzed by means of three-dimensional computational models, including solid computer assisted design of the pumping head and computational fluid-dynamic (CFD) analyses of the fluid domain and of its interaction with deformable components. A prototype of the device, integrated with the venous reservoir, was built to perform hydraulic in vitro tests with aims of both validating CFD results and verifying the new device's pumping behavior. Functional evaluation of the pump was carried out by using the device in a model circuit made with standard CPB components plus a mock hydraulic bench representing an adult patient's systemic circulation. A roller pump used in pulsatile mode (RP-PM) was used for comparison. At a 5 L/min flow rate, the pulsatile hydraulic power (<Wpuls>) delivered to the patient was approximately 15 mW for the RP-PM. The new pump proved to be able to deliver <Wpuls> up to 40 mW, thus providing a more physiological condition, closer to the <Wpuls> delivered by the natural heart (90-140 mW).

A preliminary study of microcapsule suspension for hemolysis evaluation of artificial organs

A microcapsule suspension, a substitute for animal blood in hemolysis tests, has been developed for evaluation of the absolute hemolytic properties of circulatory artificial organs. The microcapsule suspension was made by dispersing microcapsule slurry into an ethylene glycol sodium chloride solution. The microcapsule slurry was composed of a leuco dye solution and polyurethane membrane made by the reaction between aliphatic poly-isocyanate and polyamine by interfacial polycondensation. The microcapsule was a small particle containing dye inside. The microcapsule suspension was white; the diameter of the microcapsules was from 5 to 100 microns. The specific gravity of the suspension was 1.024, and the membrane was elastic. The fluid showed Newtonian characteristics, different from animal blood, and its viscosity was approximately 5.8 mPa.s. After the microcapsules were destroyed, the leuco dye was extracted with n-hexane from the suspension and was measured by spectroscopy after being colored with acid ethanol. Hemolysis can be regarded as a fatigue fracture of cell membranes rather than a static fracture. The destruction of microcapsules by a Potter type tissue grinder was observed at a low stroke number region and was compared to rat blood. Moreover, hemolysis tests of a commercially available centrifugal blood pump and the prototype of our centrifugal pump for mechanism checks were carried out with bovine blood. The hemolysis level of the prototype pump increased with time while the hemolysis level of the commercial blood pump did not change as much as that of the control when both pumps were tested with the microcapsule suspension. These results are similar to tests utilizing bovine blood. Therefore, hemolysis tests of circulatory artificial organs completed with microcapsule suspension are expected to provide results similar to tests with animal blood.

The safety system for the rotary blood pump, combination of the valve and LVAD pulsatile mode: in vitro test

The significant amount of regurgitation produced by a stopped rotary blood pump is one of the major considerations for its use as an implantable left ventricular assist device (LVAD), especially if the pump accidentally stops. The installation of a valve is an option for the solution of this potential problem. However, this option may lead to thrombogenic problems, particularly if the valve motion is restricted. This in vitro study analyzes the valve performance and assesses the credibility of a rotary blood pump valve. A pulsatile pump was used as the natural heart and a centrifugal pump as the LVAD. The valve was positioned into the LVAD outflow. In the low speed range (<1,000 rpm in this test condition), normal valve motion was maintained. Also, the valve model provided a higher mean bypass flow than the model without a valve due to reduced regurgitation. However, the valve motion was drastically restricted when in the high speed range (>1,600 rpm in this condition). The pulsatile mode was applied to the LVAD by periodically changing the impeller speed (40 bpm); subsequently, a constant valve motion could be provided. A possibility exists that this pulsatile mode application could eliminate thrombosis formation around the valve. A conclusion was made that the combination of a valve and an LVAD in a pulsatile mode is considered to be a unique safety system for a rotary blood pump.

Hemolysis test of a centrifugal pump in a pulsatile mode: the effect of pulse rate and RPM variance

Centrifugal pumps are generally employed as nonpulsatile blood flow pumps; however, these pumps can produce pulsatile flow by periodically alternating the impeller rotation speed. This study investigates blood trauma due to the effect of pulse frequency and various ranges of pump speed. The hemolysis tests were conducted using the Gyro C1E3 pump. The study was divided into the following categories: Group 1 in a nonpulsatile mode; Group 2 operated at 40 bpm with 30% of speed variance; Group 3, 60 bpm with 30% of speed variance; Group 4, 40 bpm with 70% of speed variance; and Group 5, 60 bpm with 70% of speed variance. A flow rate of 3 L/min and a total pressure head of 200 mm Hg were employed in all groups to simulate a percutaneous cardiopulmonary support condition. There were no significant differences in the hemolysis levels among Groups 1, 2, and 3. However, Groups 4 and 5 exhibited a significantly higher hemolysis rate compared to the other groups. These results indicate that a high rate of speed variance increases hemolysis; however, a range of less than 30% does not affect hemolysis. The pulse rate has no significant effect on hemolysis. In conclusion, the higher speed variance increases the hemolysis level when a pulsatile mode is applied with a centrifugal pump at the given test conditions. However, a speed variance of less than 30% or a pulse rate of less than 60 bpm does not affect hemolysis.