Koji Kawahito

Can we develop a nonpulsatile permanent rotary blood pump? Yes, we can.

For many years, it was thought that nonpulsatile perfusion produced physiological and circulatory abnormalities. Since 1977, Yukihiko Nosé and his colleagues have challenged this misconception. Toward that end, they did show that if a 20% higher blood flow uses more than that required for a pulsatile blood pump, then there would be no circulatory or physiological abnormalities. These experimental findings confirm that there is no difference in clinical outcome using either a pulsatile or nonpulsatile blood pump. Furthermore, the nonpulsatile rotary blood pump demonstrates efficient and reliable performance in various clinical situations. The nonpulsatile blood pump is a simple and reliable design that is manufactured easily and that has several desirable features. There is no need to incorporate heart valves, which are the most thrombogenic and blood trauma-inducing component. A continuous flow pump does not require a large orifice inflow conduit and proves to be easier to implant in patients with minimal damage to the myocardium. There is no need to incorporate a compliance volume-shifting device, which is essential for a pulsatile blood pump. The nonpulsatile device is a continuous blood pumping system; therefore, the control system is simpler and more reliable than that of a pulsatile pump. Because of the rotary blood pumps structure, only one moving part is necessary for the blood-pumping motion. By using durable components for this moving part, a durable system becomes possible. Because the electrical motor operates continuously, the on-and-off motion required for a pulsatile pump is not necessary; therefore, it is a more efficient and durable system. Thus, this group is working on the development of a nonpulsatile blood pump as a permanently implantable assist device. To achieve this goal, it is necessary to incorporate seven features into the system: small size, atraumatic features, antithrombogenic features, antiinfection features, a simple and durable design, and low energy requirement with easy controllability.

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

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.

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

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.

Development of a non-pulsatile permanent rotary blood pump.

For many years, a common belief was that non-pulsatile perfusion produced physiological and circulatory abnormalities. Since 1977 our group has reported, if a 20% higher blood flow was used more than required for a pulsatile blood pump, there would be no circulatory or physiological abnormalities. These experimental findings confirmed that there was no difference in clinical outcome when using a pulsatile or non-pulsatile blood pump. Furthermore, the non-pulsatile rotary blood pump has demonstrated efficient and reliable performance in various clinical situations. The non-pulsatile blood pump is a simple and reliable design, that can be easily manufactured, and has the following desirable features. There is no need to incorporate heart valves, a large orifice inflow conduit, or a compliance volume-shifting chamber. Since an electrical motor operates continuously, the on-and-off motion required for a pulsatile pump is not necessary; therefore, it becomes a more efficient and durable system. Further, the control algorism is simpler and more reliable than a pulsatile pump. Considering these factors, the non-pulsatile blood pump can be selected for a permanently implantable assist device. To develop an implantable non-pulsatile cardiac device, it is necessary to incorporate seven features in the system such as: small size, atraumatic features, anti-thrombogenic features, anti-infection features, durable and simple design, and low energy requirement with easy controllability.

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.

Acute Occlusion of the Descending Thoracic Aorta: Report of a Case

This report describes the unusual case of an acute occlusion of the descending thoracic aorta in a 52-year-old woman. The patient underwent successful extraanatomical bypass with intraoperative hemodialysis.

Development of an Implantable Centrifugal Ventricular Assist Device (CVAD)

The centrifugal ventricular assist device (CVAD) was developed for long-term circulatory support, and is capable of either intracorporeal implantation or paracorporeal placement. The pump was designed based on our antithrombogenic concepts: (1) sealless pump casing, (2) elimination of stationary parts, and (3) blood flow acceleration under the impeller. To meet conditions (1) and (2), a pivot bearing system was adopted to support the impeller. The inlet port was placed slightly off-center and inclined 60° towards the same direction as the outlet port. This port configuration not only yielded a space where an inlet cup bearing could be directly embedded but also allowed for a significant reduction of the pump height, hence, resulting in easier placement inside the body cavity. Two small secondary vanes were installed in the bottom of the impeller to satisfy condition (3). Five paracorporeal left ventricular (LV) AD studies, using calves, were performed to evaluate the antithrombogenic design of the pump. The first two cases were subjected to 2-week tests. With the activated clotting time (ACT) kept at 250 s with heparin, the initial two cases had trouble-free performances over the 2 weeks. Following these successful results, another three cases were subjected to 1-month validation studies, in which there was no device-induced thrombus formation inside the pump housing. These results confirm that the CVAD, the C1E3, meets the requirements for a 1-month paracorporeal LVAD.