A Calf Model for Left Ventricular Centrifugal Mechanical Assist

Abstract: The increased use of centrifugal mechanical assist (CMA) for treatment of refractory postcardiotomy cardiogenic shock highlights the need for experimental testing to improve clinical results. This report describes the preoperative conditioning, anesthetic and surgical technique, and postoperative management of a reliable calf model refined in this laboratory for in vivo sub-chronic (96 h) testing of CMA. Holstein bull calves (2 to 3 months old; mean body weight, 78 kg; n = 35) were instrumented for left ventricular CMA; 4 of these calves were sham-operated controls. Anesthetic recovery and postoperative restraint were accomplished in a specially designed crate to which each calf was preconditioned extensively. Younger calves were more readily conditioned and more tolerant of postoperative restraint than older calves. One calf died of ventricular fibrillation in-traoperatively. One calf that had been heparinized developed uncontrollable hemothorax and died 12 h postoperatively. One calf prematurely dislodged his aortic cannula 15 h postoperatively and exsanguinated. Six calves developed pelvic limb paresis or paralysis because of lumbar spinal cord thromboembolism by 36 h postoperatively, and 3 of these calves were sacrificed by 42 h postoperatively. Fifteen calves required sedation in the first 12 h after the operation. Tachycardia associated with bottle feeding occurred in 15 calves. Second-degree atrioventricular block was noted frequently during deep relaxation. Postmortem examination demonstrated the absence of surgical wound and distant infection, security of cannulae in all but the calf that prematurely dislodged the aortic cannula, absence of thrombus formation at cannu-lation sites, and presence of thromboembolism in 51% of the calves. The incidence of thromboembolic lesions was not influenced by the need for chemical restraint, by the occurrence of feeding-associated tachycardia, or by the presence of atrioventricular block. There were no thromboembolic lesions in any of the sham-operated controls.     

Subchronic Use of the St. Jude Centrifugal Pump as a Mechanical Assist Device in Calves

Abstract: The purpose of this experiment was to study the effects of the St. Jude Lifestream centrifugal pump on hemodynamic and hematologic parameters and the incidence of postmortem findings in a subchronic ex vivo left ventricular assist animal model. Five calves were implanted with the pump as a left ventricular assist device (left atrial to thoracic aorta bypass) and studied for 96 h of continuous pumping under identical conditions. Heparin (100 IU/kg) was administered only in the initial saline pump prime. Throughout the protocol, mean arterial and central venous pressures averaged 102.1 ± 4.6 and 3.4 ± 2.2 mm Hg, respectively. Pump flow was 47.8 ± 8.4 ml/kg/min at a mean pump speed of 1,676.3 ± 106.1 rpm. No clinical abnormalities or mechanical malfunctions attributable to the pump were detected during the 96 h of continuous pumping for each calf. Mean plasma-free hemoglobin after 96 h was 3.9 ± 3.7 u, mol/L (p = 0.337 compared to baseline). At post mortem, renal infarctions were detected in 1 calf. No other pump-associated lesions were detected in any of the other calves. We have concluded that the St. Jude Lifestream centrifugal pump functions reliably during 96 h of continuous left heart bypass in a calf model.     

Effect of Pulsatile and Nonpulsatile Assist on Heart and Kidney Microcirculation with Cardiogenic Shock

Abstract: To estimate microcirculation of the heart and kidney in pulsatile and nonpulsatile-assisted circulation, a comparison study was done using a swine model. Acute myocardial infarction was made by ligation of the left coronary artery branches. After cardiogenic shock, animals were divided into 3 groups as follows: Group C (n = 6), no assist provided; Group NP (n = 6), assisted by a nonpulsatile pump (Bio-Medicus BP-80); Group P (n = 6), supported by a pulsatile pump (Nippon Zeon). Left coronary artery flow, endocardial and epicardial regional flows, and renal cortex and medulla tissue blood flows were measured. Left coronary artery flow and endocardial and epicardial tissue blood flows decreased in cardiogenic shock, and they recovered to the control level soon after support in both Group N and Group P. Renal medulla and cortex tissue blood flows decreased in cardiogenic shock, and these flows did not recover in either Group N or P. However, cortex blood flow in Group P did improve, but it did not improve in Group N. These results suggested that pulsatile assist was more effective than nonpulsatile assist for microcirculation after cardiogenic shock to avoid deterioration of major organ functions.     

Development of a Pivot Bearing Supported Sealless Centrifugal Pump for Ventricular Assist

Abstract Since 1991, in our laboratory, a pivot bearing-supported, sealless, centrifugal pump has been developed as an implantable ventricular assist device (VAD). For this application, the configuration of the total pump system should be relatively small. The C1E3 pump developed for this purpose was anatomically compatible with the small-sized patient population. To evaluate an-tithrombogenicity, ex vivo 2-week screening studies were conducted instead of studies involving an intracorpore-ally implanted VADs using calves. Five paracorporeal LVAD studies were performed using calves for longer than 2 weeks. The activated clotting time (ACT) was maintained at approximately 250 s using heparin. All of the devices demonstrated trouble-free performances over 2 weeks. Among these 5 studies, 3 implantations were subjected to 1-month system validation studies. There were no device-induced thrombus formations inside the pump housing, and plasma-free hemoglobin levels in calves were within the normal range throughout the experiment (35, 34, and 31 days). There were no incidents of system malfunction. Subsequently, the mass production model was fabricated and yielded a normalized index of hemolysis of 0.0014, which was comparable to that of clinically available pumps. The wear life of the impeller bearings was estimated at longer than 8 years. In the next series of in vivo studies, an implantable model of the C1E3 pump will be fabricated for longer term implantation. The pump-actuator will be implanted inside the body; thus the design calls for substituting plastic for metallic parts.     

Findlay Implantable Two-Stage Centrifugal Pump

Abstract The Findlay centrifugal pump is unique in its two-stage pumping mechanisms and in its complementary interrelationship of the stages to each other and to the exit system, and it forms an extremely efficient unit. The first stage is a lift force pump as an inlet. The second and major stage is a shear force pump. Twenty-six prototypes, many multiply modified, have been hand fabricated, and most have had classic pump function analyses. Six pumps have demonstrated minimal hemolysis (3.5-5 h). At modest rotation speeds, it pumps water up to 10 L/min. Forty-four acute studies in normal dogs have been performed with the Findlay pump in a ventricular assist system. Blood flows through the pump ranged from 1.2 to 4.5 L/min. The conclusion is that the Findlay pump has the ability to operate with low blood damage, performs at acceptable rotational speed with reasonable hydraulic and mechanical efficiency, and is small and implantable.     

Clinical Use of Centrifugal Pumps and the Roller Pump in Open Heart Surgery: A Comparative Evaluation

Abstract: Centrifugal pumps have been used widely as the main pump in open heart surgery to reduce damage to blood elements and to reduce the activation of the coagulation system. The purpose of this study was the evaluation and comparison of the effects of two types of centrifugal pumps and of one type of roller pump on blood elements, the coagulation system, complements, and immunoglobulins. Two types of centrifugal pumps (Lifestream; St. Jude Medical, Chelmsford, Massachusetts; and BP-80; Medtronic, BioMedicus, Inc., Eden Prairie, Minnesota, U.S.A.) and one roller pump (Mera Co.) were used separately as the main pump for cardio-pulmonary bypass (CPB) in 29 patients. Platelet counts, lactate dehydrogenase, antithrombin III, thrombin-antithrombin complex (TAT), complements (C3, C4, and CH50) and immunoglobulins G, A, and M values were measured before and after CPB and compared. Values, except those for TAT, showed no significant difference among the three groups. The TAT values increased less in each of the centrifugal pump groups than in the roller pump group. This finding suggests that thrombin synthesis might be suppressed by the use of a centrifugal pump.     

Anatomical Consideration for an Implantable Centrifugal Biventricular Assist System

Abstract: A miniaturized pivot bearing-supported centrifugal blood pump (Gyro PI) has been developed as a long-term biventricular assist system (BiVAS). In this study we determined the anatomical configuration of this system using a bovine model. Under general anesthesia, a left lateral thoracotomy was performed to open the chest. Two Gyro PI-601 pumps for left and right assists were placed in the preperitoneal pocket by a subcostal abdominal incision. The left pump could be placed along the dome of the diaphragm just beneath the apex of the left ventricle. The right pump could be placed next to the left pump. The inlet and outlet ports of both pumps penetrated the diaphragm. The inlet port of the left pump, with a length of 55 mm, was inserted directly into the apex of the left ventricle. A woven Dacron graft (150 mm long, 11 mm inner diameter) was placed between the outlet port of the left pump and the descending aorta. As for the right pump. a 100 mm long and 120 degree angled inflow conduit was placed between the inlet port and the right ventricular infundibulum. The outlet port of the right pump was connected to the main trunk of the pulmonary artery using a 90 mm long, 11 mm inner diameter Dacron graft. We could perform biventricular assistance to confirm the anatomical feasibility of the Gyro implantable centrifugal BiVAS.     

In-Vitro Assessment of Centrifugal Pumps for Ventricular Assist

Abstract: Currently two major types of centrifugal pumps are commercially available for ventricular assist: the Biomedicus-cone (Group I) and the Centrimed-impeller pump (now Sarns 3M)(Group II). To compare them for blood trauma and hemolysis, an in-vitro experiment was designed with a Stöckert roller pump as a standard control (Group III). The in-vitro circuit was constructed consisting of a pump head, electromagnetic flow probe, polyvinyl chloride tubing and a reservoir, identical for all groups. Human ACD blood was used for priming and was circulated with a flow rate of 2 L/min for 24. h. Blood samples were taken at 0, 1, 3, 6, 12, and 24. h and zero control values were subtracted from the resulting data per time interval. Among the 16 parameters studied, a highly significant difference in favor of Group I was found for glutamate oxalacetate transaminase (GOT) and lactate dehydrogenase (p < 0.0001) and for the free plasma hemoglobin (p < 0.0001) after 12 and 24. h, respectively. The hemolytic index (Allen) again was lowest for group I in contrast to Groups II and III (0.012 versus 0.060 and 1.70) after 24. h. All other parameters studied did not render significant differences between the systems tested. The authors conclude that the Biomedicus pump currently is the least traumatic centrifugal pump for ventricular assist.     

Clinical Experience with the Nikkiso Centrifugal Pump

Abstract: The Nikkiso HPM-15 is a minimally sized centrifugal pump. Preliminary results regarding clinical use of this pump for cardiopulmonary bypass (CPB) procedures have been reported previously. Recently, we have managed some additional cases using a newly developed controller. This article reports our clinical experiences with the use of this pump. We have managed 23 cases with a Nikkiso centrifugal pump. Twenty-two patients underwent CPB and 1 patient with fulminant viral myocarditis underwent percutaneous cardiopulmonary support (PCPS). With this pump, the circuit was extremely easy to prepare and deaeration was achieved readily. Hemodynamics during CPB and PCPS were stable in all cases. The increase in serum-free hemoglobin levels during CPB with this pump was as low as that seen in preliminary tests. A decrease in the platelet count was observed after the initiation of CPB with this pump; however, platelet counts returned to preoperative values 7 days after surgery. Moreover, urine output during CPB with this pump was as high as that seen in preliminary tests. No abnormalities in renal or liver function occurred during CPB. It appears that this new centrifugal pump is safe and easy to operate, and we conclude that it is useful for CPB and PCPS.     

Improving Clinical Outcome with Centrifugal Mechanical Assist for Postcardiotomy Ventricular Failure

Abstract: Between October 1986 and May 1994, 65 patients undergoing cardiac surgery required centrifugal mechanical assist devices to separate from cardiopulmo-nary bypass. This experience was arbitrarily divided into early (n = 33) and recent (n = 32) groups for the purpose of comparing trends in morbidity and mortality. The incidence of mechanical assist application decreased from 2.19% in the early group to 0.96% in the recent group (p < 0.0001). Ability to wean patients from centrifugal assist increased from 33% in the early group to 53% in the more recent group, and hospital survival increased from 15 to 28%. The median chest tube drainage during the first 24 h decreased from 3,245 ml to 1,535 ml, and the incidence of renal failure decreased from 39.4% and 18.8% in the more recent group. Clinically relevant improvement in patient outcome following application of centrifugal mechanical assist for postcardiotomy ventricular failure is being observed.     

Use of a Rate-Limited Ultrafiltration Circuit with Centrifugal Ventricular Assist

Abstract: Renal insufficiency and pulmonary edema are frequently observed in patients who require centrifugal ventricular assist for postcardiotomy ventricular failure. We describe a technique of using a rate-limited ultrafiltration device in parallel with the assist device circuit to remove excess intravascular volume.     

Estimating Mechanical Blood Trauma in a Centrifugal Blood Pump: Laser Doppler Anemometer Measurements of the Mean Velocity Field

Abstract A laser Doppler anemometer (LDA) was used to obtain the mean velocity and the Reynolds stress fields in the inner channels of a well-known centrifugal vaneless pump (Bio-pump). Effects of the excessive flow resistance against which an occlusive pump operates in some surgical situations, such as cardiopulmonary bypass, are illustrated. The velocity vector field obtained from LDA measurements reveals that the constraint-forced vortex provides pumping action in a restricted area in the core of the pump. In such situations, recirculating zones dominate the flow and consequently increase the damage to blood cells and raise the risk of thrombus formation in the device. Reynolds normal and shear stress fields were obtained in the entry flow for the channel formed by two rotating cones to illustrate the effects of flow disturbances on the potential for blood cell damage.     

Hemocompatibility of Axial Versus Centrifugal Pump Technology in Mechanical Circulatory Support Devices

The hemocompatible properties of rotary blood pumps commonly used in mechanical circulatory support (MCS) are widely unknown regarding specific biocompatibility profiles of different pump technologies. Therefore, we analyzed the hemocompatibility indicating markers of an axial flow and a magnetically levitated centrifugal device within an in vitro mock loop. The HeartMate II (HM II; n = 3) device and a CentriMag (CM; n = 3) adult pump were investigated in a human whole blood mock loop for 360 min using the MCS devices as a driving component. Blood samples were analyzed by enzyme‐linked immunosorbent assay for markers of coagulation, complement system, and inflammatory response. There was a time‐dependent activation of the coagulation (thrombin–antithrombin complexes [TAT]), complement (SC5b‐9), and inflammation system (polymorphonuclear [PMN] elastase) in both groups. The mean value of TAT (CM: 4.0 μg/L vs. 29.4 μg/L, P < 0.001; HM II: 4.5 μg/L vs. 232.2 μg/L, P < 0.05) and PMN elastase (CM: 53.4 ng/mL vs. 253.8 ng/mL, P < 0.05; HM II: 28.0 ng/mL vs. 738.8 ng/mL, P < 0.001) significantly increased from baseline until the end of the experiments (360 min). After 360 min, TAT and PMN values were significantly higher in the HM II group compared with the values in the CM adult group. The values of SC5b‐9 increased from baseline to 360 min in the CM group (CM: 141.8 ng/mL vs. 967.9 ng/mL, P < 0.05) and the HM II group. However, the increase within the HM II group (97.3 vs. 2462.0, P = 0.06) and the comparison of the 360‐min values between CM group and HM II group did not reach significance (P = 0.18). The activation of complement, coagulation, and inflammation system showed a time‐dependent manner in both devices. The centrifugal CM device showed significantly lower activation of coagulation and inflammation than that of the HM II axial flow pump. Both HM II and CM have demonstrated an acceptable hemocompatibility profile in patients. However, there is a great opportunity to gain a clinical benefit by developing techniques to lower the blood surface interaction within both pump technologies and a magnetically levitated centrifugal pump design might be superior.     

Computational Prediction of Hemolysis in a Centrifugal Ventricular Assist Device

Abstract: This paper describes the use of computational fluid dynamics (CFD) to predict numerically the hemolysis in centrifugal pumps. A numerical hydrodynamical model, based on the full Navier-Stokes equation, was used to obtain the flow in a vaneless centrifugal pump (of corotating disks type). After proper postprocessing, critical zones in the channel were identified by means of two-dimensional color-coded maps of %Hb release. Simulation of different conditions revealed that flow behavior at the entrance region of the channel is the main cause of blood trauma in such devices. A useful feature resulting from the CFD simulation is the visualization of critical flow zones that are impossible to determine experimentally with in vitro hemolysis tests.     

Tandem Operation of a Turbo Blood Pump (BP-80-Type Centrifugal Pump) to Reduce Hemolysis

Abstract When operating turbo blood pumps in tandem, the strength of shear stress is reduced, but the exposure duration of the stress is increased. The purpose of this experiment was to compare the degree of contribution of these two factors on hemolysis as well as to evaluate the effectiveness of the tandem operation of turbo blood pumps. Tandem operation of two Bio-pumps (BP-80; Medtronics Bio-medicus, Inc., Eden Prairie, Minnesota, U.S.A.) were compared with single operation of a BP-80 in in vitro hemolysis tests in three different driving conditions, that is, pumping heads of 200, 350, and 500 mm Hg under a pump flow rate of 5 L/min. The Allen's hemolytic indexes of the tandem operation at pumping heads of 200, 350, and 500 mm Hg were 0.014, 0.020, and 0.080 mg/dl, respectively. The hemolytic indexes of the single operation at pumping heads of 200, 350, and 500 mm Hg were 0.014, 0.056, and 0.12 mg/dl, respectively. These results indicate that tandem operation is a useful method of reducing hemolysis with the BP-80 under high pumping heads and that the effect on hemolysis of exposure to higher shear stresses may be more serious than that of longer durations of exposure to shear stress in turbo blood pumps.     

Model for a General Mechanical Blood Damage Prediction

Abstract: Knowledge of the correlation between mechanical loading of formed blood elements and the amount of their destruction is important for the prediction of blood trauma in artificial circulatory devices as well as in natural circulation. A hemodynamic assessment and optimization of artificial organs to minimize trauma could be undertaken in the design phase given a comprehensive mechanical blood damage model. A theory to determine blood trauma theoretically as a combination of a mechanical loading analysis and a phenomenological blood damage resistance hypothesis is presented. Arbitrary stress-time functions of blood particles predicted by flow analysis are reduced to a set of simple time functions for which the damage behavior may, in principle, be obtained from mechanical blood damage tests. A classification of those stress functions into damaging and nondamaging parts is followed by an overall trauma prediction considering cumulative effects by means of a damage accumulation hypothesis. Theoretical determination of blood destruction caused by mechanical stresses in a centrifugal pump is one possible application of the proposed theory. The strategy of hemolysis prediction is demonstrated for the Aries Medical Isoflow Pump. Irregular stress-time loading functions of particles passing the pump domain obtained by three-dimensional numerical flow simulations were reduced and classified into harmonic components. To relate these functions to their hemolytic response can only be done in a qualitative manner since blood damage behavior under transient stress loading has not been sufficiently investigated. Accurate prediction of blood trauma using the proposed theory will require detailed study of the influence of frequency and amplitude of harmonic stress loading on formed blood elements.     

Study of Secondary Flow in Centrifugal Blood Pumps Using a Flow Visualization Method with a High-Speed Video Camera

Abstract Four pump models with different vane configurations were evaluated with flow visualization techniques using a high-speed video camera. These models also were evaluated through in vivo hemolysis tests using bovine blood. The impeller having the greatest fluid velocity relative to the impeller, the largest velocity variance, and the most irregular local flow patterns in the flow passage caused the most hemolysis. Even if the pumps were operated at almost the same speed (rpm) at the same output, the impeller showing more irregular flow patterns had a statistically greater rate of hemolysis. This fact confirms that the existence of local irregular flow patterns in a centrifugal blood pump deteriorates its hemolytic performance. Thus, to optimize the design of the pump, it is very important to examine the secondary flow patterns in the centrifugal blood pump in detail using flow visualization with a high-speed video camera.     

Frequency of Seal Disruption with the Sarns Centrifugal Pump in Postcardiotomy Circulatory Assist

Abstract: We have used the Sarns centrifugal pump for uni- or biventricular assist in 58 patients with postcardiotomy cardiogenic shock. This device utilizes a spinning impeller pump that is magnetically coupled to a motor imparting rotary motion to incoming perfusate. Nine patients (16%) experienced 22 device failures, which consisted of a nonvisible disruption of the seal within the pumphead. This allowed fluid to accumulate between the pumphead and the motor necessitating change of the pumphead. The time to seal disruption was 10–149 h (median 48). Of the 22 seal disruptions, 18 occurred in 73 left ventricular pumps (25%), and 4 occurred in 38 right ventricular pumps (11%) p = 0.015. Left ventricular pumps failed at 10–144 h (median 48), and right ventricular pumps failed at 48–149 h (median 83) p = 0.02. The Sarns centrifugal pump is dependable for its intended use of cardiopulmonary perfusion. However, when used for postcardiotomy assist, seal disruption should be expected. It occurs sooner and is more common during left ventricular assist. We recommend inspection of the magnet chamber for evidence of seal disruption every 12 h with left ventricular assist and every 24 h with right ventricular assist.     

Characteristics of a Blood Pump Combining the Centrifugal and Axial Pumping Principles: The Spiral Pump

Abstract: Two well-known centrifugal and axial pumping principles are used simultaneously in a new blood pump design. Inside the pump housing is a spiral impeller, a conically shaped structure with threads on the surface. The worm gears provide an axial motion of the blood column through the threads of the central cone. The rotational motion of the conical shape generates the centrifugal pumping effect and improves the efficiency of the pump without increasing hemolysis. The hydrodynamic performance of the pump was examined with a 40% glycerin-water solution at several rotation speeds. The gap between the housing and the top of the thread is a very important factor: when the gap increases, the hydrodynamic performance decreases. To determine the optimum gap, several in vitro hemolysis tests were performed with different gaps using bovine blood in a closed circuit loop under two conditions. The first simulated condition was a left ventricular assist device (LVAD) with a flow rate of 5 L/min against a pressure head of 100 mm Hg, and the second was a cardiopulmonary bypass (CPB) simulation with a flow rate of 5 L/min against 350 mm Hg of pressure. The best hemolysis results were seen at a gap of 1.5 mm with the normalized index of hemolysis (NIH) of 0.0063 ± 0.0020 g/100 L and 0.0251 ± 0.0124 g/100 L (mean ± SD; n = 4) for LVAD and CPB conditions, respectively.     

Evaluation of Hemolysis in a Pulsatile Assist Device for Centrifugal Pump

Abstract: To evaluate the blood trauma caused by a new device for producing a pulsatile flow of the centrifugal pump, the pulsatile assist device for the centrifugal pump (PAD-CP) that we have developed, a hemolysis study was performed in vitro and in animal experimentation. For the in vitro testing, 2 identical sets of hemolysis test circuits were prepared with 2,400 ml of bovine blood. The 2 circuits were pumped simultaneously. Plasma total hemoglobin levels were less than 40 mg/dl after 3 h, under a pump flow of 2 L/min. Hemolysis increased to a severe level after 4 h of 4 L/min pump flow. The cause of this hemolysis was thought to be a vibration of the circuit because of incomplete compression of the polyurethane tube in the PADCP. Five adult sheep (average body weight, 47 kg) were used for in vivo evaluation of hemolysis. Hemolysis was less than 30 mg/dl of plasma hemoglobin after 4 h of open chest extracorporeal circulation with 3.0–3.6 Limin of flow rate using the PAD-CP. Other hematologic changes after PAD-CP driving were within normal limits. We conclude that the PAD-CP has proven to have possible clinical applications.