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Biomedical subjects

S Takatani

Publications and source records attributed to S Takatani.

98 records · Page 6Linked to original sources
PubMedDate not supplied

Intraoperative determination of mediastinal constraints for a total artificial heart.

The anatomic constraints to mediastinal fit of a total artificial heart (TAH) were largely neglected during the early developmental stages, precipitating failure due to compression or torsion of intrathoracic conduits and vascular structures. Cadaveric studies quantifying anatomic constraints are limited by postmortem factors causing distortion of critical structures. This study defines the anatomic constraints and parameters necessary for designing an implantable TAH. Importantly, these parameters were measured in 12 consecutive patients undergoing orthotopic cardiac transplant (mean body surface area, 2.0 +/- 0.1 m2) after native heart amputation. A full sized contour model of the cylindrical TAH (diameter, 97 mm; width, 78 mm) was inserted into the pericardial cavity to verify fit, which was found adequate in each case, with no identifiable compression of adjacent vascular structures. Intraoperative measurements obtained define intrathoracic and pericardial constraints for a cardiac prosthesis (mean pericardial dimensions: length, 133.0 mm; width, 154.0 mm; depth, 129.0 mm). The parameters measured will provide useful reference for other prosthetic devices, since they were obtained intraoperatively rather than postmortem. The current dimensions of our TAH were found to be acceptable for orthotopic implantation.

Adult↗
PubMedDate not supplied

Development of the E4T electrohydraulic total artificial heart.

A completely implantable total artificial heart (TAH) is being developed based on many years of research performed at the Cleveland Clinic Foundation and Nimbus, Inc. The pumping unit consists of biolized surface-treated pusher plate blood pumps powered by an interventricular electrohydraulic energy converter. A variable volume device references the back side of the pusher plates to lung pressure. Electrical power is supplied by a transcutaneous energy transmission system, integrated with a wearable external battery pack. An implanted internal battery provides back-up power. System design and optimization efforts have resulted in a compact pumping unit package and an overall TAH that meets anatomic, physiologic, and engineering requirements. Overall pumping unit basic dimensions are 98 mm diameter and 80 mm thick. The blood pumps have a truncated conical shape and are separated by a thin interventricular septum 21 mm thick. Theoretical stroke volume is 64 ml, and maximum stroke length is 13.2 mm. Normal pump operation is at 90% of full stroke, which yields a net output of 53 ml, with valve regurgitation taken into account.

Cardiac Output↗
PubMedDate not supplied

Altered humoral control of circulating volume during artificial circulation.

UNLABELLED: Plasma atrial natriuretic polypeptide (ANP) levels and plasma renin activity (PRA) were measured in six left ventricular assist device (LVAD) goats, four single artificial heart (SAH) goats, i.e., LVAD animals with fibrillated hearts, and 3 total artificial heart (TAH) calves. During the 4 week experiment, the ANP levels in the SAH goats increased to 516 pg/ml from the control value of 61.8 pg/ml because of an elevated CVP of 13-21 mmHg, while those of the LVAD goats were near the lower limit of the control values. The TAH calves had slightly decreased ANP levels at 23-46 pg/ml after the third postoperative week, which did not increase after the steep increase in CVP induced by the changes in the driving conditions. The PRA levels were 10-50 times higher than control in the SAH goats and a TAH calf whose CVP rose to 19 mmHg, although the cardiac output was within normal limits. IN CONCLUSION: 1) The secretion of ANP secondary to alteration in CVP was preserved in the LVAD recipients and enhanced diuresis, while it was compromised in the TAH cases. 2) The PRA levels in cases with elevated CVPs were high enough to suppress diuresis.

Animals↗
PubMedDate not supplied

Optical sensor for hemoglobin content and oxygen saturation. Application to artificial heart research.

A hybrid optical sensor that can measure both hemoglobin content ([ Hb]) and oxygen saturation (OS) of whole blood has been developed. The measurement errors in [Hb] and OS are 0.5 g% and 1.2%, respectively, over an hematocrit range of 25 to 45%. The oxygen content derived from the optical sensor yielded a standard error of 0.1 to 0.2 vol%. The sensors were mounted in the outflow ports of left and right artificial hearts that maintained the entire circulation and were used to chronically monitor arterial and mixed venous [Hb] and OS. In combination with pump output and pressure measurements, oxygen delivery and oxygen consumption of the animal was derived on-line using a microprocessor. In the experiment that lasted 40 days, both sensors functioned well, with stable measurements, and no thrombus formation around the sensor at the time of autopsy. The optical sensors are useful for monitoring cardiopulmonary function and metabolic status of patients without requiring blood samples. In addition, the pump output may be controlled through the level of mixed venous OS or in combination with the arterial OS.

Animals↗
PubMedDate not supplied

Anatomic constraints for a total artificial heart in orthotopic heart transplant recipients.

The anatomic constraints and design parameters for a heart prosthesis have not yet been defined in heart transplant recipients (i.e., the population most eligible for total artificial heart implantation). The parameters regarding anatomic constraints were measured in 26 consecutive patients undergoing orthotopic heart transplantation (median body surface area 1.9 m2) after cardiectomy. A full-sized contour model of the cylindric total artificial heart (diameter 97 mm; width 81 mm) was inserted into the pericardial cavity to decide the pump configuration and to verify its fit. The dimensions of this model were based on the miniature electromechanical total artificial heart that is currently under development. Fit was found to be adequate in most of the cases with no identifiable compression of adjacent vascular structures. The median intraoperative measurements that define pericardial constraints for a heart prosthesis were pericardial length (130 mm), width (160 mm), and depth (140 mm). We also took measurements from the excised hearts, which should provide a useful reference for other prosthetic devices. The current dimensions of our implantable total artificial heart were found acceptable for orthotopic implantation. Length of the pericardium and cardiothoracic ratio were identified as variables related to adequacy of fit.

Adult↗
PubMedDate not supplied

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.

Heart, Artificial↗
PubMedDate not supplied

Flow visualization evaluation of secondary flow in a centrifugal blood pump.

To design a less hemolytic and more antithrombogenic centrifugal blood pump, secondary flow, i.e., vortex and turbulent flow, must be properly controlled. An irregular stream pattern is a cause of hemolysis, and good wash-out around the shaft minimizes thrombus formation. In this study, flow visualization methods were applied to evaluate secondary flow in a centrifugal blood pump. Correlation with results of in vitro hemolysis tests was investigated. Separation of the stream lines from the vanes and patterns implying the existence of vortices were observed in the impeller that showed high hemolysis. By adjustment of vane angles, these irregular patterns could be minimized, and hemolysis decreased as well. Using a similar technique, the flow pattern at the back of the impeller could be visualized, which enabled further investigation of the effects of secondary flow on thrombus formation. This flow visualization was effective in examining secondary flow patterns.

Animals↗