Intraventricular Axial Flow Blood Pump Research Articles

Dispositivo de assistência circulatória mecânica intraventricular de fluxo axial: estudo in vitro

É apresentado estudo in vitro de um dispositivo de assistência circulatória totalmente implantável no ventrículo esquerdo, de fluxo axial e de tamanho pequeno (30 cc - 7 cm comprimento). Apesar dessas características foi capaz de gerar fluxos entre 5 - 8 l/min com motor, operando em 8 W, sem causar hemólise em período de até 12 horas. O custo de produção, excetuando-se o sistema de baterias, foi projetado entre 5 - 8 mil dólares, o que o torna viável para utilização clínica rotineira em nosso país.

Sealing properties of mechanical seals for an axial flow blood pump.

A miniature intraventricular axial flow blood pump for left ventricular support is under development. One of the key technologies required for such pumps is sealing of the motor shaft. In this study, to prevent blood backflow into the motor side, mechanical seals were developed and their sealing properties investigated. In the experimental apparatus, the mechanical seal separated the bovine blood on the chamber side from the cooling water on the motor side. A leakage of the blood was measured by inductively coupled plasma (ICP) light emission analysis. The rate of hemolysis was measured by the cyanmethemoglobin method. Frictional torque acting on the shaft was measured by a torque transducer. In the experiments, the rotational speed of the shaft was changed from 1,000 to 10,000 rpm, and the contact force of the seal faces was changed from 1.96 to 4.31 N. To estimate lubrication regimes, the Stribeck curve, a diagram of the coefficient of friction against the bearing characteristic G number, was drawn. The results of the experiments showed that both the leakage of blood and the rate of hemolysis were very small. The friction loss was also very small. The mechanical seal was operated in various lubrication regimes, from a fluid lubrication regime to a mixed lubrication regime.

Long Term Animal Experiments With an Intraventricular Axial Flow Blood Pump

A miniature intraventricular axial flow blood pump (IVAP) is undergoing in vivo evaluation in calves. The IVAP system consists of a miniature (phi 13.9 mm) axial flow pump that resides within the left ventricular (LV) chamber and a brushless DC motor. The pump is fabricated from titanium alloy, and the pump weight is 170 g. It produces a flow rate of over 5 L/min against 100 mmHg pressure at 9,000 rpm with an 8 W total power consumption. The maximum total efficiency exceeds 17%. A purged lip seal system is used in prototype no. 8, and a newly developed "Cool-Seal" (a low temperature mechanical seal) is used in prototype no. 9. In the Cool-Seal system, a large amount of purge flow is introduced behind the seal faces to augment convective heat transfer, keeping the seal face temperature at a low level for prevention of heat denaturation of blood proteins. The Cool-Seal system consumes < 10 cc purge fluid per day and has greatly extended seal life. The pumps were implanted in three calves (26, 30, and 168 days of support). The pump was inserted through a left thoracotomy at the fifth intercostal space. Two pursestring sutures were placed on the LV apex, and the apex was cored with a myocardial punch. The pump was inserted into the LV with the outlet cannula smoothly passing through the aortic valve without any difficulty. Only 5 min elapsed between the time of chest opening and initiation of pumping. Pump function remained stable throughout in all experiments. No cardiac arrhythmias were detected, even at treadmill exercise tests. The plasma free hemoglobin level remained in the acceptable range. Post mortem examination did not reveal any interference between the pump and the mitral apparatus. No major thromboembolism was detected in the vital organs in Cases 1 or 2, but a few small renal infarcts were detected in Case 3.

The Cool Seal System

A critical issue facing the development of an implantable, rotary blood pump is the maintenance of an effective seal at the rotating shaft. Mechanical seals are the most versatile type of seal in wide industrial applications. However, in a rotary blood pump, typical seal life is much shorter than required for chronic support. Seal failure is related to adhesion and aggregation of heat denatured blood proteins that diffuse into the lubricating film between seal faces. Among the blood proteins, fibrinogen plays an important role due to its strong propensity for adhesion and low transition temperature (approximately 50 degrees C). Once exposed to temperature exceeding 50 degrees C, fibrinogen molecules fuse together by multi-attachment between heat denatured D-domains. This quasi-polymerized fibrin increases the frictional heat, which proliferates the process into seal failure. If the temperature of the seal faces is maintained well below 50 degrees C, a mechanical seal would not fail in blood. Based on this "Cool-Seal" concept, we developed a miniature mechanical seal made of highly thermally conductive material (SiC), combined with a recirculating purge system. A large supply of purge fluid is recirculated behind the seal face to augment convective heat transfer to maintain the seal temperature below 40 degrees C. It also cools all heat generating pump parts (motor coil, bearing, seal). The purge consumption has been optimized to virtually nil (< 0.5 cc/day). An ultrafiltration unit integrated in the recirculating purge system continuously purifies and sterilizes the purge fluid for more than 5 months without filter change. The seal system has now been incorporated into our intraventricular axial flow blood pump (IVAP) and newly designed centrifugal pump. Ongoing in vivo evaluation of these systems has demonstrated good seal integrity for more than 160 days. The Cool-Seal system can be applied to any type of rotary blood pump (axial, diagonal, centrifugal, etc.) and offers a practical solution to the shaft seal problem and heat related complications, which currently limit the use of implantable rotary blood pumps.

Development of an Implantable Ventricular Assist System

Background. This study describes the present state of progress in the development of the Jarvik 2000 ventricular assist system.Methods. Designed for implantation in the human thorax, the system consists of a small (25 cm3, 90 g) intraventricular axial-flow blood pump that transmits power and data via internal electronics and a transcutaneous energy transfer system. The pump is powered by portable internal and external polymer lithium ion batteries. The only moving part, the pump rotor, contains a permanent magnet of a brushless direct-current motor that mounts an axial-flow impeller and partial magnetic thrust support, with blood-immersed radial and thrust bearings. The motor uses a redundant coil and electric lead design, which permits continued operation in case of wire breakage.Results. Seven calves have been supported for an average of 107 days (range, 40 to 162 days) with prototypes of the Jarvik 2000 ventricular assist system. No physiologic complications have occurred. When its user is at rest, the pump produces flows of 5 to 6 L/min with a decreased arterial pulse contour. Renal and hepatic functions have remained normal throughout the duration of all studies. Mean plasma free hemoglobin levels ranged from 4.3 to 11.4 mg/dL (mean, 6.3 mg/dL) for each study. Pathologic analyses of the heart and kidneys revealed no damage related to the device.Conclusions. These studies indicate that the Jarvik 2000 ventricular assist system is feasible in animals and holds promise for long-term support of patients.(Ann Thorac Surg 1997;63:367–70)

Five month survival in a calf supported with an intraventricular axial flow blood pump.

We are studying in vivo an intraventricular axial flow blood pump (Jarvik 2000) designed for long-term left ventricular support. The small (25 cc, 85 g) valveless pump has been placed intraventricularly in seven calves; pumps have functioned for as long as 5 months. In the four most recent long-term studies completed, calves have survived for 70, 120, 155, and 162 days (in that order); weight gain has averaged 0.56 kg/day. One study is ongoing at more than 30 days. Under resting physiologic conditions in the normal calf, the continuous flow pump produces flows of 5-6 L/min with a decreased arterial pulse contour. The device has caused no physiologic complications. Calves in the completed studies had mean free plasma hemoglobin levels of 11.4, 7.1, 6.5, and 4.3 mg/dl, respectively. We have modified the inflow structures of the device, and these results suggest that a thrombus free design with no pannus at or around the inlet of the pump can be achieved. Histopathologic analyses of the heart and kidneys in studies of as long as 5 months show no deleterious effects of this device. These studies demonstrate the feasibility of a small implanted intraventricular blood pump for long-term use. Future developments for permanent implantation will include implanted physiologic control systems, transcutaneous energy transmission systems, and implanted batteries.

An intraventricular axial flow blood pump integrated with a bearing purge system.

The future development of implantable axial flow blood pumps must address two major issues: mechanically induced hemolysis and shaft seal reliability. The recent revisions to our miniature intraventricular axial flow left ventricular assist device (LVAD) were aimed particularly at addressing these concerns. To improve hemocompatibility, a new impeller has been designed according to the following criteria: 1) gradual pressure rise along the blade chord; 2) minimized local fluid acceleration to prevent cavitation; 3) minimum surface roughness; and 4) radius edges. Subsequent in vitro hemolysis tests conducted with bovine and ovine blood have demonstrated very low hemolysis (normalized index of hemolysis = 0.0051 +/- 0.0047 g/100 L) with this new impeller design. To address the need for a reliable seal, we have developed a purged seal system consisting of a miniature lip seal and ceramic pressure groove journal bearing that also acts as a purge pump. Several spiral grooves formed on the bearing surface provide viscous pumping of the purge fluid, generating more than 3,000 mmHg at 10,000 rpm. This purge flow flushes the lip seal and prevents blood backflow into the bearing. We have found this purge pump to offer several advantages because it is simple, compact, durable, does not require separate actuation, and offers a wide range of flow, depending upon the groove design. In vivo animal tests demonstrated the potential of the purged seal system.

Development of a Miniature Intraventricular Axial Flow Blood Pump

A new intraventricular axial flow blood pump has been designed and developed as a totally implantable left ventricular assist device (LVAD). This pump consists of an impeller combined with a guide-vane, a tube housing, and a DC motor. The pump is introduced into the LV cavity through the LV apex, and the outlet cannula is passed antegrade across the aortic valve. Blood is withdrawn from the LV through the inlet ports at the pump base, and discharged to the ascending aorta. Our newly developed axial flow pump system has the following advantages: 1) it is a simple and compact system, 2) minimal blood stasis both in the device and the LV cavity, 3) minimal blood contacting surface of the pump, 4) easy accessibility with a less invasive surgical procedure, and 5) low cost. A pump flow > 5 L/min was obtained against 100 mmHg differential pressure in the mock circulatory system. The pump could produce a passive pulsatile flow effect with a beating heart more efficiently than other non-pulsatile pumps because of minimal pressure drop and inertia along the bypass tract. Anatomic fit studies using dissected hearts of dilated cardiomyopathy (DCM) cadavers showed that this pump could smoothly pass through the aortic valve without any interference with mitral valve function. Recently, a dynamic pressure groove bearing and a miniature lip seal have been developed. The dynamic pressure groove bearing has a simple structure and acts as a pressure resistant sealing mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

A Miniature Intraventricular Axial Flow Blood Pump That is Introduced Through the Left Ventricular Apex

A new intraventricular axial flow blood pump has been designed and developed as an implantable left ventricular assist device (LVAD). The pump consists of a tube housing (10 cm in length and 14 mm in diameter), a three-vane impeller combined with a guide vane, and a DC motor. This pump is introduced into the LV cavity through the LV apex, and the outlet cannula is passed antegrade across the aortic valve. Blood is withdrawn from the LV through the inlet ports at the pump base, and discharged into the ascending aorta. A pump flow of > 8 L/min was obtained against 90 mmHg differential pressure in the mock circulatory system. In an acute dog model, this pump could produce a sufficient output of 200 ml/kg/min. In addition, the pump flow profile demonstrated a pulsatile pattern, although the rotation speed was fixed. This is mainly due to the changes in flow rate during a cardiac cycle--that is, during systole, the flow rate increases to the maximum, while the differential pressure between the LV and the aorta decreases to the minimum. Thus, this simple and compact axial flow blood pump can be a potential LVAD, with prompt accessibility and need for less invasive surgical procedures.