Setsuo Takatani

Evaluation of the Wear of the Pivot Bearing in the Gyro C1E3 Pump

To estimate the lifetime of the pivot bearing system of the sealless centrifugal Gyro C1E3 pump, pivot bearing wear phenomena of the C1E3 were studied. The pivot bearing system consisted of a male and female pivot made of ceramics and ultrahigh molecular weight polyethylene (UHMWPE), respectively. First, many pumping tests were performed with the C1E3 under various pumping conditions, and the effects of impeller position and fluid on wear were analyzed. Through these preliminary tests, it was found that the wear progress of the pivot bearing consisted of initial wear and stationary wear. Most of this initial wear is caused by the plastic deformation of the polyethylene female pivot. It also was observed that bovine blood was almost comparable to water in its effect on the stationary wear rate at the same rotational speed. Based on these results, a long-term pumping test was performed with the C1E3, and initial and stationary wear rates were determined. At the same time, the maximal loosening distance (LDmax) (permissible total wear) of the C1E3 was determined experimentally from hemolytic and hydraulic performance perspectives. By using experimentally determined parameters the lifetime of the pivot bearing system of the C1E3 pump was estimated for various pumping conditions. The lifetime of the pivot bearing system of the C1E3 was typically 10 years for right ventricular assist, 8 years for left ventricular assist, and 5 years for cardiopulmonary bypass.

Experimental and clinical evaluation of a noninvasive reflectance pulse oximeter sensor

The objective of this study was to evaluate a new reflectance pulse oximeter sensor. The prototype sensor consists of 8 light-emitting diode (LED) chips (4 at 665 nm and 4 at 820 nm) and a photodiode chip mounted on a single substrate. The 4 LED chips for each wavelength are spaced at 90-degree intervals around the substrate and at an equal radial distance from the photodiode chip. An optical barrier between the photodiode and LED chips prevents a direct coupling effect between them. Near-infrared LEDs (940 nm) in the sensor warm the tissue. The microthermocouple mounted on the sensor surface measures the temperature of the skin-sensor interface and maintains it at a preset level by servoregulating the current in the 940-nm LEDs. An animal study and a clinical study were performed. In the animal study, 5 mongrel dogs (weight, 10–20 kg) were anesthetized, mechanically ventilated, and cannulated. In each animal, arterial oxygen saturation (SaO2) was measured continuously by a standard transmission oximeter probe placed on the dogs earlobe and a reflectance oximeter sensor placed on the dogs tongue. In the first phase of the experiment, signals from the reflectance sensor were recorded while the dog was immersed in ice water until its body temperature decreased to 30°C. In the second phase, the animals body temperature was normal, and the oxygen content of the ventilator was varied to alter the SaO2. In the clinical study, 18 critically ill patients were monitored perioperatively with the prototype reflectance sensor. The first phase of the study investigated the relationship between local skin temperature and the accuracy of oximeter readings with the reflectance sensor. Each measurement was taken at a high saturation level as a function of local skin temperature. The second phase of the study compared measurements of oxygen saturation by a reflectance oximeter (SpO2[r]) with those made by a co-oximeter (SaO2[IL]) and a standard transmission oximeter (SpO2[t]). Linear regression analysis was used to determine the degree of correlation between (1) the pulse amplitude and skin temperature; (2) SpO2(r) and SaO2(IL); and (3) SpO2(t) and SaO2(IL). Studentst test was used to determine the significance of each correlation. The mean and standard deviation of the differences were also computed. In the animal study, pulse amplitude levels increased concomitantly with skin temperature (at 665 nm,r=0.9424; at 820 nm,r=0.9834;p<0.001) and SpO2(r) correlated well with SaO2(IL) (r=0.982; SEE=2.54%;p<0.001). The results of the clinical study are consistent with these findings. The proto-type reflectance pulse oximeter sensor can yield accurate measurements of oxygen saturation when applied to the forehead or cheek. It is, therefore, an effective alternative to transmission oximeters for perioperative monitoring of critically ill patients.

In-vivo studies of reflectance pulse oximeter sensor

Reflectance oximetry can offer an advantage of being applicable to any portion of the body. However, the major problem of reflectance oximetry is low pulsatile signal level which prevents prolonged clinical application during extreme situations, such as hypothermia and vasoconstriction. In order to improve the pulsatile signal level of reflectance pulse oximeter and thus its accuracy, three different sensors, with the separation distances (SPD) between light emitting diode (LED) and photodiode being 3, 5, and 7 mm respectively, were studied on nine healthy volunteers. With the increase of the SPD, it was found that both the red (660 nm) and near-infrared (830 nm) pulsatile to average signal ratio (AC/DC) increased, and the standard deviations of (AC/DC)red/(AC/DC)infrared ratio decreased, in spite of the decrease of the absolute signal level. Further clinical studies of 3 mm and 7 mm SPD sensors on seven patients also showed that the (AC/DC)red/(AC/DC)infrared ratio measured by the 7 mm sensor were less disturbed than the 3 mm sensor during the surgery. A theoretical study based on the three-dimensional photon diffusion theory supports the experimental and clinical results. As a conclusion, the 7 mm sensor has the highest signal-to- noise ratio among three different sensors. A new 7 mm SPD reflectance sensor, with the increased number of LEDs around the photodiode, was designed to increase the AC/DC ratio, as well as to increase the absolute signal level.

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.

The Baylor-ABI Electromechanical Total Artificial Heart: Accelerated Endurance Testing

To test the durability of each part or assembled component of the Baylor-ABI total artificial heart (TAH), the authors performed an endurance test under severe conditions. The TAH was immersed in a saline bath at 42 degrees C, which is 4-5 degrees C higher than normal body temperature. This is an accelerated endurance test because of the elevated temperatures. In this accelerated endurance test loop, the 42 degrees C heated saline was circulated not only in the pump but also outside the pump. During pumping, temperatures of the motor and outside surface of the centerpiece were continuously measured. This testing showed that during almost 4 months of pumping no electromechanical troubles were observed. Both inside (motor) and outside temperatures were stable and the differences in both temperatures were only 3-4 degrees C, demonstrating that heat generation is not a problem. The voltage and current required in this system remained constant, indicating stable and reliable performance. Based on these results, this pump is expected to run continuously over a long duration in a normal physiologic environment. This accelerated endurance test system is very suitable for estimating the influence of heat generation by the actuator of blood pumps. It is also quite useful in validating the durability of various cardiac prosthesis.

Baylor Multi-Purpose One-Piece Total Artificial Heart (TAH) System for Short-Term to Long-Term Use

A multi-purpose total artificial heart (TAH) system has been developed for use as both a temporary and permanent device. The blood pump is pneumatically-driven in short-term use and is electro-mechanically-driven in long-term or permanent use. Both versions consist of the same components, except for the actuation mechanism and driving source. The common components are a compact pumping chamber with the same configuration, a biolized blood-contacting surface with gelatin, a pusher-plate, a Hexsyn rubber diaphragm, and bovine pericardial valves. Pump configurations have been designed based on anatomical studies of 26 heart transplant patients. The pump is implanted orthotopically as a long-term or permanent device and actuated electro-mechanically. The pneumatic version of the pump is implanted as a short-term device in the postcardiotomy setting or as a bridge to transplant and is pneumatically-driven by a low pressure pumping unit. The pump has a 63-ml stroke volume and is compact compared with other devices being developed. An 81/min pump output has been realized against 120 mmHg afterload in both in vitro and in vivo tests. Currently 1-week survival has been achieved with the electro-mechanical version without an anticoagulation regimen. The results suggest that the currently developed system could be applied in many patients of various population types as a temporary device for postcardiotomy, a long-term device for bridge to transplant, or a permanent device for endstage heart disease.

Application of computers in development of a total artificial heart

The application of computers in the design, analysis, and control of a completely implantable total artificial heart is discussed. Computing tools are used to perform overall system dynamics modeling and analysis, magnetic coupling finite element analysis, and blood pump sizing numerical optimization. A microprocessor-based hybrid controller that has been developed for closed loop feedback control of the device is also discussed.<<ETX>>

Phase 1 Ex Vivo Studies of the Baylor/NASA Axial Flow Ventricular Assist Device

The Baylor/NASA ventricular assist device (VAD) is a small, electrically driven, valveless axial flow pump that is implantable inside the chest cavity. It is intended to assist a diseased heart. In the phase 1 study of this pump development program, the 2-day pump is intended to produce an assist device for cardiopulmonary bypass (CPB) application. The main focus of this phase of the program was to develop a pump which produced minimum blood trauma. Antithrombogenic features are planned to be incorporated into the phase 2 pump. In this phase 1 study, eight pumps were implanted paracorporeally in two calves as LVADs to assess hemolysis, pump performance, efficiency, and stability, the goal for this study being a 2-day implantation. The pump running times ranged from 18 to 203 (78.1 ± 23.7; mean ± SE) h. Plasma free hemoglobin levels were below 13.7 mg/di, except for one case complicated by inflow cannula obstruction due to pannus formation. Pump speed was maintained between 10100 and 11400rpm. Pump output ranged from 3.6 to 5.11/min. The electrical power required by the system ranged from 10.5 to 12.8W. No detectable organ dysfunction was noted and postmortem evaluations demonstrated no pump-related adverse effects in any of the calves. Thrombus deposition was observed mainly at the hub area and flow straightener. For the next series of experiments (phase 2), the thrombogenic regions in these subacute experiments should be eliminated.

The Baylor Electromechanical Total Artificial Heart

A totally implantable electromechanical total artificial heart (TAH) system has been developed in our institute. This pump is very small (outer diameter, 97 mm; central thickness, 83 mm; and weight, 620 g), demonstrating a good anatomical fit in the pericardial space of 26 heart transplant recipients. The actuation mechanism is simple, and all the components are commercially available with proven longterm durability, thus allowing easier fabrication. The pump can be easily and simply controlled by reliable Hall effect sensors with left master alternate (LMA) mode. Four newly fabricated TAHs demonstrated quite similar pump performances. This TAH has a reproducible high performance with good quality assurance. In vitro performance mapping demonstrated that the pump can provide a maximum flow of 91/ min, with a high sensitivity to preload and a low sensitivity to afterload. During 4 months of accelerated endurance testing in 42°C saline, no electromechanical troubles were observed and power requirement remained constant, indicating a stable and reliable performance. After modification of the inflow valve angle, excellent flow paterns inside the blood chamber were demonstrated in this study, in which laser light and a high-speed camera were used. In vivo feasibility tests were performed successfully in eight calves for up to 1 week, demonstrating the readiness to move forward to longterm in vivo studies. This small, simple, reliable, and durable mechanically driven totally implantable TAH system is suitable for a permanent heart replacement.

Development of a Seal-Less Motor-Driven Centrifugal Blood Pump (Baylor Gyro Pump)

To overcome the seal shaft-related problems of conventional centrifugal blood pumps, a new seal-less centrifugal blood pump capable of more than 2 weeks’ operation was designed by supporting the rotating part of the pump with two pivot bearings. The rotor of a brushless direct current (DC) motor is placed in the inlet side of the pump and is directly connected with the impeller. The blood passes through the gap around the rotor and enters the impeller eye; the rotor impeller rotates as a “gyroscope” in the pump. The pump generated 31/min against 86 mmHg at 2000 rpm. Indices of hemolysis of 0.005 was obtained in hemolysis tests using bovine blood.