Robert Jarvik

Study of Flow‐Induced Hemolysis Using Novel Couette‐Type Blood‐Shearing Devices

To assist the development and application of blood-contacting medical devices, two novel flow-through Couette-type blood-shearing devices have been developed to study the quantitative relationship between blood damage indexes and flow-dependent parameters. One device is an axial flow-through Couette-type device supported by a pair of pin bearings adapted from the adult Jarvik 2000 blood pump. The other is a centrifugal flow-through Couette-type device supported with magnetic bearings adapted from the CentriMag blood pump. In both devices, a rotor spindle was used to replace the original impeller blades so that a small gap was created between the housing and the rotating spindle surface. Computational fluid dynamics simulations have shown that a uniform, high shear stress region can be generated inside the small gap while the shear stresses elsewhere are relatively low. The possibility of secondary blood damage caused by mechanical seals was eliminated due to the use of a magnetic rotor system. Blood flow through the gap was driven by an externally pressurized reservoir. By adjusting the rotational speed and blood flow rate, shear-induced hemolysis was quantified at a matrix of exposure time (0.039 to 1.48 s) and shear stress (50 to 320 Pa). All of the experiments were conducted at room temperature using heparinized ovine blood with a hematocrit value of 30%. The measured hemolysis levels were much lower than those published in the literature, and the overestimation of those earlier studies may be attributable to device-related secondary blood-damaging effects. A new set of coefficients for the power law model was derived from the regression of the experimental data.

Early in vivo experience with the pediatric Jarvik 2000 heart.

The need for smaller, more efficient ventricular assist devices that can be used in a more chronic setting have led to exploration of mechanical circulatory support in the pediatric population. The pediatric Jarvik 2000 heart (child size), under development, was implanted in six juvenile sheep and studied for both acute fit and chronic performance evaluation. Daily hemodynamic measurements of cardiac output and pump output at varying pump speeds were taken. In addition, plasma free hemoglobin, lactic acid dehydrogenase, and platelet activation from blood samples were determined at baseline, after implantation, and twice a week thereafter. The measured flow through the outflow graft at increasing speeds from 10,000 rpm to 14,000 rpm with an increment of 1,000 rpm were 1.47 ± 0.43, 1.89 ± 0.52, 2.36 ± 0.61, 2.80 ± 0.73, and 3.11 ± 0.86 (L/min). The baseline plasma free hemoglobin was 11.95 ± 4.76 (mg/dL), with subsequent mean values being <30 mg/dL at postimplantation and weekly postimplantation measurements. Both lactic acid dehydrogenase and platelet activation showed an acute increase within the first week after implantation with subsequent return to baseline by 2 weeks after surgery. Our initial animal in vivo experience with the pediatric Jarvik 2000 heart shows that a small axial flow pump can provide partial to nearly complete circulatory support with minimal adverse effects on blood components.

Pre-clinical Evaluation of the Infant Jarvik 2000 Heart in a Neonate Piglet Model

BACKGROUND The infant Jarvik 2000 heart is a very small, hermetically sealed, intracorporeal, axial-flow ventricular assist device (VAD) designed for circulatory support in neonates and infants. The anatomic fit, short-term biocompatibility and hemodynamic performance of the device were evaluated in a neonate piglet model. METHODS The infant Jarvik 2000 heart with two different blade profiles (low- or high-flow blade design) was tested in 6 piglets (8.8 ± 0.9 kg). Using a median sternotomy, the pump was placed in the left ventricle through the apex without cardiopulmonary bypass. An outflow graft was anastomosed to the ascending aorta. Hemodynamics and biocompatibility were studied for 6 hours. RESULTS All 6 pumps were implanted without complication. Optimal anatomic positioning was found with the pump body inserted 2.4 cm into the left ventricle. Hemodynamics demonstrated stability throughout the 6-hour duration. The pump flow increased from 0.27 to 0.95 liter/min at increasing speeds from 18 to 31 krpm for the low-flow blade design, whereas the pump flow increased from 0.54 liter/min to 1.12 liters/min at increasing speeds from 16 krpm to 31 krpm for the high-flow blade design. At higher speeds, >80% of flow could be supplied by the device. Blood chemistry and final pathology demonstrated no acute organ injury or thrombosis for either blade design. CONCLUSIONS The infant Jarvik 2000 heart is anatomically and biologically compatible with an short-term neonate piglet model. This in vivo study demonstrates the future feasibility of this device for clinical use.

In vivo experience of the child-size pediatric Jarvik 2000 heart: update.

Data from early in vivo experiments demonstrated that the child-size Jarvik heart was capable of providing partial to nearly complete circulatory support with acceptable adverse effects on blood. However, bearing thrombosis was responsible for device malfunction in most cases. To overcome this problem, original pin bearings were replaced with novel conical bearings. This study evaluated chronic in vivo performance of the modified child-size Jarvik heart in the pediatric setting. Six juvenile sheep were implanted with the modified child-size Jarvik heart. Cardiac and pump output were measured daily. Serial blood samples were drawn to evaluate hematology, biocompatibility, and end-organ function. End-organ damage and device thrombosis were examined at necropsy. No device malfunction occurred during animal experiments up to 70 days. Mean cardiac output of the animals was 3.4 L/min. The child-size Jarvik heart was able to deliver a blood flow ranging from 1.4 to 2.5 L/min at speed from 10,000 rpm to 14,000 rpm. Mean plasma-free hemoglobin was 9.8 ± 5.6 mg/dl, indicating no hemolysis. Acute elevation occurred in some organ function tests after the implant surgery but returned to normal range thereafter. These indices and necropsy showed no end-organ damage. No device thrombosis was observed. The current in vivo experience shows that the modified child Jarvik 2000 heart retained its hemodynamic function and excellent biocompatibility, and the conical bearings permitted it to remain free of thrombus.

Venous return of an artificial heart designed to prevent right heart syndrome

AbstractA large number of calves maintained up to two weeks with the Kwan-Gett artificial heart have had elevated central venous pressure with associated ascites, edema, oliguria responding to diuretics, and increased body weight and weight of organs at autopsy. This has been described as right heart failure syndrome and has been a problem limiting survival with the artificial heart. The high venous pressure has been attributed to inadequate pumping characteristics of the heart as well as imperfect fit which obstructs venous return.A new design of an artificial heart was tested on the mock circulation and in one calf with encouraging results. Venous return remained unimpaired during the artificial heart test in the calf.The heart is designed with the following main characteristics.(1)Highly flexible ventricular diaphragm.(2)Low resistance to inflow.(3)Parallel disposition of artificial ventricles and artificial atria for a better anatomical relation to the natural ostia.(4)Artificial atria with air chambers vented to the atmosphere. The increased compliance of the atrial walls prevented reduction of venous return caused by vacuum applied to the ventricles during the filling period. Although the heart compromised lung space, it demonstrated the need for still another new design which will not obstruct venous return and will maintain normal venous pressures without compromising lung space.

Electrical Energy Converters for Practical Human Total Artificial Hearts-An Opinion in Support of Electropneumatic Systems

Until recently, most artificial hearts have served as research tools to acquire further knowledge necessary ultimately to design practical systems for human use. Transcutaneous systems or percutaneous systems utilizing permanently implanted energy converters, batteries, and electronics packages have a number of substantial problems that would not exist if most system elements were kept outside the body. These problems include physiologic control, fit and fixation, foreign body infection, hermetic sealing, cable insulation and fatigue, inherent system complexity, stringent requirements for maintenance-free operation with long-term high reliability, and high cost. Percutaneous systems, particularly those in which only the blood pump is implanted, are an attractive choice for practical systems in the near future. A wearable, battery-powered electropneumatic total heart system should be developed.