Helmut Schmallegger

LONG-TERM IN VIVO LEFT VENTRICULAR ASSIST DEVICE STUDY WITH A TITANIUM CENTRIFUGAL PUMP

A totally implantable centrifugal artificial heart has been developed. The plastic prototype, Gyro PI 601, passed 2 day hemodynamic tests as a functional total artificial heart, 2 week screening tests for antithrombogenicity, and 1 month system feasibility. Based on these results, a metallic prototype, Gyro PI 702, was subjected to in vivo left ventricular assist device (LVAD) studies. The pump system employed the Gyro PI 702, which has the same inner dimensions and the same characteristics as the Gyro PI 601, including an eccentric inlet port, a double pivot bearing system, and a magnet coupling system. The PI 702 is driven with the Vienna DC brushless motor actuator. For the in vivo LVAD study, the pump actuator package was implanted in the preperitoneal space in two calves, from the left ventricular apex to the descending aorta. Case 1 achieved greater than 9 month survival without any complications, at an average flow rate of 6.6 L/min with 10.2 W input power. Case 2 was killed early due to the excessive growth of the calf, which caused functional obstruction of the inlet port. There was no blood clot inside the pump. During these periods, neither case exhibited any physiologic abnormalities. The PI 702 pump gives excellent results as a long-term implantable LVAD.

Flow characteristics and required control algorithm of an implantable centrifugal left ventricular assist device.

SummaryAs the clinical application of LVADs has increased, attempts have been made to develop smaller, less expensive, more durable and efficient implantable devices using rotary blood pumps. Since chronic circulatory support with implantable continuous-flow LVADs will be established in the near future, we need to determine the flow characteristics through an implantable continuous-flow LVAD. This study describes the flow characteristics through an implantable centrifugal blood pump as a left ventricular assist device (LVAD) to obtain a simple non-invasive algorithm to control its assist flow rate adequately. A prototype of the completely seal-less and pivot bearing-supported centrifugal blood pump was implanted into two calves, bypassing from the left ventricle to the descending aorta. Device motor speed, voltage, current, flow rate, and aortic blood pressure were monitored continuously. The flow patterns revealed forward flow in ventricular systole and backward flow in diastole. As the pump speed increased, an end-diastolic notch became evident in the flow profile. Although the flow rate (Q [1/min]) and rotational speed (R [rpm]) had a linear correlation (Q=0.0042R−5.159;r=0.96), this linearity was altered after the end-diastolic notch was evident. The end-diastolic notch is considered to be a sign of the sucking phenomenon of the centrifugal pump. Also, although the consumed current (I [A]) and flow rate had a linear correlation (I=0.212Q+0.29;r=0.97), this linearity also changed after the end-diastolic notch was evident. Based upon the above findings, we propose a simple algorithm to maintain submaximal flow without inducing sucking. To maintain the submaximal flow rate without measuring flow rate, the sucking point is determined by monitoring consumed current according to gradual increases in voltage.

Current progress in the development of a totally implantable gyro centrifugal artificial heart

A totally implantable centrifugal artificial heart has been developed using a miniaturized pivot bearing supported centrifugal pump (Gyro Pl pump). The authors report current progress in its development. The Gyro Pl-601 has a priming volume of 20 ml, weighs 100 g, has a height of 60 mm, and has a diameter of 65 mm. This pump can provide 8 L/min against 150 mmHg at 2,250 rpm. It is driven by an miniaturized DC brushless motor with the coils fixed in a plastic mold that is waterproof and made of titanium (weight, 204 g; height, 18 mm; diameter, 65 mm). In this centrifugal artificial heart, two Gyro PI pumps are implanted independently to replace cardiac function without resecting the native heart. Its anatomic and surgical feasibility were confirmed experimentally. The Gyro Pl-601 was implanted as a right or left ventricular assist device in the preperitoneal space of five calves. All five tests proceeded without any thromboembolic symptoms. One of five tests was extended more than 1 month to confirm the long-term feasibility of the Gyro Pl-601 pump system. Based on the satisfactory results of the in vivo tests, the material conversion of the Gyro Pl from polycarbonate to titanium alloy (Ti-6A1–4V) was undertaken to improve its biocompatibility for long-term implantation. ASAIO Journal 1998; 44:207–211.

Recent advances in the gyro centrifugal ventricular assist device

The gyro pump was developed as an intermediate-term assist pump (C1E3) as well as a long-term centrifugal ventricular assist device (VAD). The antithrombogenic design concept of this pump was confirmed throughout three 1 month ex vivo studies. The normalized index of hemolysis (NIH) of this gyro C1E3 model was lower than that of the BP-80. In the next step, a miniaturized centrifugal blood pump (The Gyro permanently implantable model PI-601) has been developed for use as a permanently implantable device after design optimization. A special motor design of the magnet circuit was utilized in this system in collaboration with the University of Vienna. The priming volume of this pump is 20 ml. The overall size of the pump actuator package is 53 mm in height, 65 mm in diameter, 145 ml of displacement volume, and 305 g in weight. This pump can provide 5 L/min against 120 mm Hg total pressure head at 2,000 rpm. The NIH value of this pump was comparable to that of the BP-80. The gyro PI-601 model is suitable for a VAD. The expected life from the endurance study is approximately 8 years. The evolution from C1E3 to the PI-601 converts this pump to a totally implantable centrifugal pump. Recent technologic advances in continuous flow devices are likely to realize a miniaturized and economical totally implantable VAD.

A PIVOT BEARING-SUPPORTED CENTRIFUGAL PUMP FOR A LONG-TERM ASSIST HEART

A pivot bearing-supported centrifugal blood pump has been developed. It is a compact, cost effective, and anti-thrombogenic pump with anatomical compatibility. A preliminary evaluation of five paracorporeal left ventricular assist studies were performed on pre-conditioned bovine (70-100 kg), without cardiopulmonary bypass and aortic cross-clamping. The inflow cannula was inserted into the left ventricle (LV) through the apex and the outflow cannula affixed with a Dacron vascular graft was anastomosed to the descending aorta. All pumps demonstrated trouble free performance over a two-week screening period. Among these five studies, three implantations were subjected for one month system validation studies. All the devices were trouble free for longer than 1 month. (35, 34, and 31 days). After achieving one month studies, all experiments were terminated. There was no evidence of device induced thrombus formation inside the pump. The plasma free hemoglobin levels were within normal ranges throughout all experiments. As a consequence of these studies, a mass production model C1E3 of this pump was fabricated as a short-term assist pump. This pump has a Normalized Index of Hemolysis of 0.0007 mg/100L and the estimated wear life of the impeller bearings is longer than 8 years. The C1E3 will meet the clinical requirements as a cardiopulmonary bypass pump. For the next step, a miniaturized pivot bearing centrifugal blood pump PI-601 has been developed for use as a permanently implantable device after design optimization. The evolution from C1E3 to the PI-601 converts this pivot bearing centrifugal pump as a totally implantable centrifugal pump. A pivot bearing centrifugal pump will become an ideal assist pump for the patients with failing heart.

FORTSCHRITTE UND OFFENE FRAGEN BEI DER ENTWICKLUNG IMPLANTIERBARER ROTATIONSPUMPEN FÜR DIE LANGFRISTIGE HERZUNTERSTÜTZUNG

Obwohl einige der pulsatil betriebenen Heizunterstützungssysteme bereits zum langfristigen Einsatz geeignet sind und die Entlassung von Patienten über mehrere Monate erlauben, weisen sie doch inhärente Nachteile wie die große Baugröße, einen komplexen und damit teuren Aufbau und die Notwendigkeit des Luft-Ausgleichs durch die Haut auf. Deshalb wird weltweit intensiv an Rotationspumpen gearbeitet, die wesentlich kleiner und mit nur wenig bewegten Teilen ausfuhrbar sind. Das früher beträchtliche Problem der Hämolyse ist mittlerweile gelöst, derzeit stehen die Fragen der Thromben-Freiheit, der Regelung und der Langzeitstabilität im Mittelpunkt der Forschung. Im Tierversuch wurden bereits Einsätze von parakorporalen Systemen bis zu zwei Jahren und von implantierbaren Pumpen bis zu zehn Monaten erreicht Unsere Gruppe konnte dazu mit einem Antriebssystem beitragen, das derzeit den Weltrekord bei einer langzeit-implantierten Rotationspumpe hält

Miniaturisierter Hochdruckantrieb für den pneumatischen Herzersatz

Z U S A M M E N F A S S U N G : Die übl ichen pneumat ischen Antr iebe fü r küns t l iche Ventr ikel arbeiten mit relativ n ied r igem Betr iebsdruck und dadurch großen Druckspe ichern und großlumigen Venti len. Zugleich muß die Schlauchverbindung zwischen Antr iebsgerä t und Patient b z w . Versuchstier kurz ( 1 . 5 m ) gehalten werden. Demgegenüber ermöglicht ein aufschnallbarer oder eventuell implantierbarer Hochdruckant r ieb eine lange und dünnlumige Preß lu f tzu le i tung , sehr kleine Druckspeicher und le is tungsarme pneumatische Servovent i le . Mehrere derar t ige Antriebe wurden in mehreren Schritten unter Kontrolle am Kreislaufmodel l entwickelt und exper imentel l getestet. Sie arbeiten entweder mit einem kleinen Hochdruckspeicher ( G O c c m ) oder mit einem sehr schnellen Kugelventil (SOOHz) . Die Systeme ermöglichen eine sehr variable Gestaltung der Druckkurven und weisen eine ausgezeichnete Steuerbarkeit auf .