A thermoconductive and thermoselective leukocyte filter

Previously, it was reported by our group that the superphysiological temperature of over 43 degrees C affected leukocyte properties. It was speculated that heat treatment might alter the immunological properties of leukocytes. In order to take advantages of this phenomenon, attempts were made to develop a thermoconductive and thermoselective leukocyte filter. A stainless steel fiber was selected for the new material of a leukocyte filter due to its good heat conductance, stability during thermal change, and inertness to any chemicals. Preliminary studies were conducted to evaluate the effect of fiber diameter and temperature on the filtration of blood cells. As a result, more than 99% of white blood cells (WBCs) and platelets were removed utilizing a 4 microns diameter fiber filter. The environmental temperatures of the filtration process were varied to 4, 20, 36, and 50 degrees C for 5 min. Almost 95% of WBCs and platelets were removed at 4, 20, and 36 degrees C. However, the reduction of platelets was remarkably suppressed at 50 degrees C (54%). Additionally, the removal of lymphocytes was significantly lower than that of neutrophils at 50 degrees C (69% vs. 83%; p = 0.0002). These data demonstrate that effective heat treatment and removal of leukocytes are possible with an ultrafine stainless steel fiber filter.

Flow pattern analysis of the Baylor total artificial heart

To obtain an optimal design of the left blood chamber of the total artificial heart (TAH), flow visualization studies were performed. Information on velocities in critical areas of the left chamber was gathered using sectional pulsed laser light. The flow patterns on the entire pumping duration were photographed frame by frame. The inflow port, the opposite of the inflow and outflow of the pump (bottom area), and the diaphragm/housing junction were the focal areas. The pump conditions, such as chamber pressure, preload and afterload pressure, pumping rate and roller screw, and displacement were recorded. Major stagnations and a low washout effect were observed in the bottom region. The closing of the inflow valve was irregular. In order to solve this problem, the inflow valve angle was changed 20 degrees. A comparison study showed a better valve closing characteristic, and no stagnation areas were observed with this new valve angle. Various velocity profiles confirmed the results. The valve closing characteristics is described in relationship to back flow.

Secretory carcinoma of the breast. Correlation of aspiration cytology and histology

We analyzed the fine needle aspiration findings in five cases of secretory carcinoma of the breast in adults to clarify their cytomorphologic features and correlate them with their histology. The cytologic smears revealed grapelike clusters of mucous globular structures (MGSs); single MGSs; clusters and sheets of cells with pale green and slightly granular cytoplasm with or without intracytoplasmic vacuolization; some ordinary duct carcinoma-like arrangements; scattered, single, vacuolated cells; some extracellular mucus; and a clean background. The MGSs were globular structures consisting of distinctive vacuolated cells containing large globules of a secretory product. The cytologic findings showed a similar wide variation in the range of histologic appearances; however, the grapelike clusters of MGSs, which corresponded to a microcystic or microfollicular pattern histologically, were present in most cases and should suggest a diagnosis of secretory carcinoma.

Does hematocrit affect in vitro hemolysis test results? Preliminary study with Baylor/NASA prototype axial flow pump

The effect of hematocrit (Ht) on in vitro hemolysis test results (i.e., index of hemolysis) was evaluated using a Baylor/NASA prototype axial flow pump. Red blood cell suspensions of six different Ht (5, 10, 15, 20, 30, 40%; n = 30) were prepared and used for this evaluation. The pump was operated for 60 min under 5 L/min flow conditions, and blood samples were taken every 10 min to measure plasma free hemoglobin levels. The normalized index of hemolysis (NIH) was calculated using the regression line slope between time and plasma free hemoglobin level, and relationships between NIH and Ht or hemoglobin (Hb) were checked. NIH and Ht had a statistically significant (p < 0.0001) correlation with a coefficient of fit of 0.976, and NIH and Hb had a statistically significant (p < 0.0001) correlation with a coefficient of fit of 0.976. To reduce the effect of Ht, NIH/Ht was proposed and compared with a modified index of hemolysis (MIH), which was normalized by the Hb level of blood. NIH/Ht and MIH had a poor correlation with Ht (coefficient of fit, 0.608) and Hb (coefficient of fit, 0.577), respectively. When blood that has a wide range of Ht or Hb values is used for in vitro hemolysis tests, NIH/Ht is suggested for use as an index of hemolysis to evaluate the hemolysis characteristics of rotary blood pumps because MIH has no dimension and it requires Hb values. In contrast, NIH/Ht has a dimension of g/100 L, which is quite understandable, and it does not require measurement of Hb levels of blood; it is therefore cost-effective.

The Baylor total artificial heart. Flow visualization studies

To analyze the flow patterns of the left blood chamber of the Baylor total artificial heart (TAH) and to evaluate influences of the inflow valve angle to the flow patterns, flow visualization studies were performed. The inflow valve angle of the left housing was changed by 20 degrees orthogonal to the inflow tube, and comparison studies of the modified and unmodified models were made. For evaluating sectional flow patterns, a laser light was used, the clear transparent housing was scanned segmentally, and flow patterns were recorded on high contrast film for measuring flow velocities. A signal was used that synchronized the timing of the camera shutter to the pusher-plate movement signal. With the modified 20 degree inflow valve direction, there were better closing characteristics of the inflow valve leaflets. At the same time, we could successfully reduce the vortex formation at the inflow port, which may cause thrombus formation. We also have improved the washout during the diastolic phase in not only the bottom area, but in the entire pumping chamber. This flow visualization setup is simple and inexpensive. It is useful not only for validation of global flow patterns, but also for validation of local flow velocities of various blood pumps.

An ultimate, compact, seal-less centrifugal ventricular assist device: Baylor C-Gyro pump

We have developed a compact, seal-less, all-purpose centrifugal pump, the Baylor C-Gyro pump, which is intended as a long-term ventricular assist device (VAD) as well as a cardiopulmonary bypass pump. In attaining this goal, we began with eliminating the shaft seals by adopting a pivot bearing system at the impeller shaft. In addition, a ring magnet encased in the bottom of the impeller was coupled magnetically to a driver magnet placed outside the pump housing (C1 Prototype). This first model yielded satisfactory performance in vitro with a flow rate of 8 L/min against 250 mm Hg at 2,400 rpm, and an index of hemolysis (IH) of 0.0083 g/100 L using bovine blood. In the second model, the C1 Eccentric Inlet Port Model, the inlet bearing support bar in the prototype were eliminated without reducing the prototype's performance. These designs for antithrombogenicity are being tested by the first in vivo experiment, which has lasted for more than 2 weeks.

The need for standardizing the index of hemolysis

Hemolysis is one of the most important performance parameters of blood pumps. However, comparative in vitro evaluation of the reported hemolysis effect is difficult owing to the lack of uniformity in the test methods used. Currently, three types of formulas are generally accepted and widely used for the index of hemolysis: the traditionally used index of hemolysis (defined as grams of plasma free hemoglobin released per 100 L of blood pumped); the normalized index of hemolysis (normalized by hematocrit); and the modified index of hemolysis (taking into account not only hematocrit but also hemoglobin). In addition, the tested blood conditions are often not indicated in the reports. To address this confusing situation, all three indices of hemolysis were routinely derived in our laboratory. To avoid further confusion, the tested blood conditions and test loop were defined in each study in our laboratory. If we limit the acceptable range of hemoglobin in human blood, the normalized index of hemolysis is sufficient. Furthermore, using milligrams as the unit of expression would be easier and reasonable for comparing the less hemolytic blood pumps, such as the centrifugal pumps that are currently available clinically. We would like to propose this value of a normalized index of hemolysis in milligrams as the most useful formula for the index of hemolysis in the assessment of various types of rotary blood pumps.

Collective motions in proteins investigated by X-ray diffuse scattering

We have developed theoretical models for analysis of X-ray diffuse scattering from protein crystals. A series of models are proposed to be used for experimental data with different degrees of precision. First, we propose the normal mode model, where conformational dynamics of a protein is assumed to occur mostly in a limited conformational subspace spanned by a small number of low-frequency normal modes in the protein. When high precision data are available, variances and covariances of the normal mode variables can be determined from experimental data using this model. For experimental data with lower degrees of precision, we introduce a series of simpler models. These models express the covariance matrix using relatively simple empirical correlation functions by assuming the correlation between a pair of atoms to be isotropic. As an application of these simpler models, we calculate diffuse-scattering patterns from a human lysozyme crystal to examine how each adjustable parameter in the models affects general features of the resulting patterns. The results of the calculation are summarized as follows. (1) The higher order scattering makes a significant contribution at high resolutions. (2) The resulting simulated patterns are sensitive to changes in correlation lengths of about 1 A, as well as to changes of the functional form of the correlation function. (3) But only the "average" value of the intra- and intermolecular correlation lengths seems to determine the gross features of the pattern. (4) The effect of the atom-dependent amplitude of fluctuations is difficult to observe.

Totally implantable total artificial heart and ventricular assist device with multipurpose miniature electromechanical energy system

A multipurpose miniature electromechanical energy system has been developed to yield a compact, efficient, durable, and biocompatible total artificial heart (TAH) and ventricular assist device (VAD). Associated controller-driver electronics were recently miniaturized and converted into hybrid circuits. The hybrid controller consists of a microprocessor and controller, motor driver, Hall sensor, and commutation circuit hybrids. The sizing study demonstrated that all these components can be incorporated in the pumping unit of the TAH and VAD, particularly in the centerpiece of the TAH and the motor housing of the VAD. Both TAH and VAD pumping units will start when their power line is connected to either the internal power pack or the external battery unit. As a redundant driving and diagnostic port, an emergency port was newly added and will be placed in subcutaneous location. In case of system failure, the skin will be cut down, and an external motor drive or a pneumatic driver will be connected to this port to run the TAH. This will minimize the circulatory arrest time. Overall efficiency of the TAH without the transcutaneous energy transmission system was 14-18% to deliver pump outputs of 4-9 L/min against the right and left afterload pressures of 25 and 100 mm Hg. The internal power requirement ranged from 6 to 13 W. The rechargeable batteries such as NiCd or NiMH with 1 AH capacity can run the TAH for 30-45 min. The external power requirement, when TETS efficiency of 75% was assumed, ranged from 8 to 18 W. The accelerated endurance test in the 42 degrees C saline bath demonstrated stable performance over 4 months. Long-term endurance and chronic animal studies will continue toward a system with 5 years durability by the year 2000.

In vitro and in vivo validation tests for total artificial heart

Properly planned in vitro and in vivo studies are mandatory to validate blood pump performance. However, standard procedures for in vitro and in vivo tests of total artificial heart (TAH) performance still do not exist. At Baylor College of Medicine, standard tests procedures for performance validation of the totally implantable TAH have been established. In this paper, these in vitro tests protocols (performance mapping tests, accelerated endurance test, hemolysis test, flow visualization tests, etc.) are described as well as in vivo test procedures (TAH implantation procedure, including surgical technique, postoperative management and tests, etc.). In addition, pathological protocols are presented. In our experience, these procedures are very simple, easy to perform, and inexpensive. These protocols are proposed as standard in vitro and in vivo tests for a TAH.

Successful thermal management of a totally implantable ventricular assist system

Thermal management of the implantable ventricular assist system (VAS) is important not only from the pathophysiological point of view but also from the standpoint of system endurance. The heat distribution within the Baylor VAS was measured using different motor housing materials and environmental conditions. The temperature of the circulating water in the mock loop was set at 37 degrees and 42 degrees C. A polycarbonate motor housing was not a suitable material because of the high temperature development in the actuation system. An anodized aluminum housing demonstrated excellent heat conductivity. The surface temperature of this motor housing was 41.6 degrees C when immersed in circulating water at 42 degrees C. Heat conduction from the motor to the circulating blood revealed an effective thermal path. In the worst case, the heat flux of the motor to the circulating blood revealed an effective thermal path. In the worst case, the heat flux of the motor housing was calculated to be less than 0.062 W/cm2--an acceptable level for the surrounding tissues.

Flow visualization in the Baylor total artificial heart

To analyze the flow patterns of the left and right blood chambers of the total artificial heart (TAH), flow visualization studies were performed. Two setup levels were used for the flow visualization studies. For estimating the global flow patterns, the pumps were illuminated using incandescent light, and the patterns were recorded by either videotape or photography. To evaluate sectional flow patterns, a laser light was applied, and the pump could be scanned segmentally. The flow patterns were recorded by a high-speed camera. A signal was also used that synchronized the timing of the camera shutter to the pusher-plate movement signal. In the left pump chamber, major stagnations were observed in the middle area of the inflow site. To solve this problem, a modification was made that changed the inflow direction appropriately. After evaluation of the inflow port direction, a proper flow pattern was obtained, which was validated by a global flow visualization study. Furthermore, both pump chambers indicated excellent flow patterns as obtained by a segmental flow visualization study method utilizing a laser light. The Baylor TAH demonstrated excellent flow patterns in flow visualization studies, with antithrombogenicity expected. These flow visualization studies are very useful not only for validations of global flow patterns but also for validations of local areas of stagnation in various blood pumps.

Internal hydraulic loss in a seal-less centrifugal Gyro pump

A new index "loss factor Z" defined by Eq. 1 was introduced as the absolute expression of the mock loop resistance for testing a nonpulsatile pump. [formula: see text] where gamma is specific gravity of the fluid, g is the acceleration of gravity, delta P is total pressure head, and Q is flow. Z is expected to be constant, regardless of the pumping parameters. Z values obtained in the same mock loop but with different rotary blood pumps were almost identical and were defined as Z0. New methods of analysis of the flow-restrictive conditions of various rotary blood pumps are proposed in this paper: namely, differential loss factor delta Z, and loss factor sensitivity delta Z/delta A. The proposed Z-Q curves demonstrated better performance mapping than the conventional delta P-Q curves. Delta Z is the difference between the Z-Q curves of two different pumps. A is a design parameter of the pump; therefore delta Z/delta A is a quantitative expression of the effect of the design change on the hydraulic performance. These various indices were used to analyze the internal hydraulic loss of a centrifugal pump (Gyro pump). The relationship between its gap size (rotor casing) and hydraulic performance was assessed quantitatively by these indices. In this paper, the derivation processes and above-mentioned indices are described.

Axial flow ventricular assist device: system performance considerations

A cooperative effort between Baylor College of Medicine and NASA/Johnson Space Center is under way to develop an implantable left ventricular assist device for either pulmonary or systemic circulatory support for more than 3 months' duration. Using methodical evaluation and testing, an implantable axial pump has been systematically improved. These improvements include the addition of an inducer as a pumping element in front of the impeller and the construction of an efficient brushless direct current motor. To date, less than 10 W of power is required to generate 5 L/min flow against 100 mm Hg. An index of hemolysis of 0.021 g/100 L has been achieved. Two-day in vivo feasibility studies in calves are under way to evaluate the antithrombogenic nature of the pump. Further improvements in system efficiency, hemolytic performance, and the antithrombogenic nature of the pump are expected with the use of empirical studies, computer flow modeling, and in vivo testing in calves.

Development of the Baylor/NASA axial flow ventricular assist device: in vitro performance and systematic hemolysis test results

Our newly developed axial flow pump consists of a flow tube, an internal rotating impeller, and a fixed flow stator (we call the stator) behind the impeller. This pump produces a flow of 3 to 8 L/min against 50 to 150 mm Hg pressure difference, respectively, in the range of 10,000 to 16,000 rpm. An axial flow pump that will be used as a ventricular assist device (VAD) has to have low hemolytic and good antithrombogenic characteristics. This paper will show how to decrease the hemolytic properties of this axial flow pump systematically using a test matrix. The test variables evaluated were impeller blade tip geometry, impeller flow tube clearance (radial clearance), impeller stator clearance (axial clearance), impeller blade number, stator blade number, and impeller length. All in vitro hemolysis tests were performed at 5.0 L/min against 100 mm Hg pressure difference using a total of 83 bags of fresh bovine blood. The results were as follows: the impeller blade tip geometry did not significantly effect hemolysis, a 0.005-inch and a 0.009-inch radial clearance were significantly (p < 0.01 or 0.001) less hemolytic than the other clearances, a 0.075-inch axial clearance was significantly (p < 0.05) more hemolytic than the other clearances, two- and six-bladed impellers were significantly (p < 0.01 and 0.02, respectively) less hemolytic than a four-bladed impeller, a five-bladed stator was significantly (p < 0.05 or 0.01) less hemolytic than the other stators, and the impeller length did not make a significant difference. Currently, the best index of hemolysis is 0.031 +/- 0.018 g/100 L, and using parameters from these results, implantable devices are being fabricated.

A fluid dynamic analysis of a rotary blood pump for design improvement

The proper design of a left ventricular assist device (LVAD) requires an understanding of the pump's fluid dynamic and biocompatible properties. A hydraulically efficient system minimizes the power required for pumping. Biocompatibility refers to the ability to pump blood with minimal hemolysis and thrombus formation. Typically, shear stresses below a threshold level will not damage blood significantly. A fluid dynamic analysis of a prototype centrifugal pump designed for use as an LVAD was performed to establish flow characteristics. A flow visualization technique using Amberlite particles suspended in a glycerin/water blood analogue was used. The system was illuminated with a 1 mm planar beam strobed helium-neon laser, and the results were recorded photographically. An analysis of photographs revealed laminar and turbulent flows with vortices within an illuminated plane in both the inlet and outlet port areas. From these data, velocity and shear stress profiles were generated that showed possible areas of improvement. It was concluded that the outlet port design could be improved by changing its angle and the continuity of its expansion. The inlet port could also be improved by smoothing the transition area between the inlet tube and the pump body to allow for gradual acceleration of the entering fluid.

Baylor Gyro Pump: a completely seal-less centrifugal pump aiming for long-term circulatory support

A seal-less centrifugal pump aiming for long-term circulatory support has been developed. In this model, shaft seals that cause thrombus formation and blood leakage were eliminated. A brushless direct current motor was incorporated as a driving unit, and pivot bearings were used to support the impeller. With reference to its motor-driven system, this pump was named the M-Gyro Pump. The first model (M1) yielded an index of hemolysis of 0.005 g/100 L using bovine blood and demonstrated satisfactory performance as a right heart assist for 2 days (4 L/min, 60 mm Hg, 1,800 rpm). The second model (M2) has been developed for left heart assist by employing a stronger motor. The pump capacity was improved to 6 L/min against 240 mm Hg at 1,800 rpm, but significant heat generation was observed. By optimization of motor efficiency, the M2 model can be improved to meet the requirements of a pump for left heart assist.

In vitro performance of the Baylor/NASA axial flow pump

A cooperative effort between Baylor College of Medicine and NASA/Johnson Space Center is under way to develop an implantable axial flow left ventricular assist device (LVAD). The pump is intended as an assist device for either pulmonary or systemic circulatory support for more than 3 months' duration. Currently, in vitro studies are under way to reduce the hemolysis generated by the axial flow pump. A system utilizing a testing matrix has been developed to analyze the effects of different pump parameters on hemolysis. The following parameters are being investigated: impeller blade tip geometry, impeller/flow tube clearance, impeller/stator clearance, number of impeller blades, number of stator blades, and length of the impeller. To date, an index of hemolysis of 0.038 g/100 L has been achieved. The test matrix is not complete, and further improvements are expected.

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.

Development of the Baylor-Nikkiso centrifugal pump with a purging system for circulatory support

The Baylor-Nikkiso centrifugal pump is a magnetically coupled system with a V-ring seal separating the pump and the actuator chamber. To prevent thrombus formation behind the impeller and to extend the life of the pump to 2 weeks of continuous operation, we incorporated a purging chamber behind the V-ring seal. An external pump connected to this purging chamber infused fluid at a constant rate to wash the shaft-seal area. To evaluate the effectiveness of the purging system, we have carried out biventricular bypass experiments using calves. The purging system was successful in reducing the level of thrombus formation after 2 weeks of operation. The results of these studies confirmed that the Baylor-Nikkiso centrifugal pump with this purging system is suitable for at least 2 weeks of continuous operation as a circulatory support system.

Two-layer membrane model for iontophoretic drug transport through excised rat skin

Iontophoretic and passive transport of an ionized drug (sulfisoxazole) across excised rat skin was studied using a two-chamber cell with four electrodes under successive experimental conditions: without electrical current (stage-I) and with electrical current (stage-II). Two iontophoretic/diffusion models, i.e. a one-layer membrane model and a two-layer membrane model, in which a difference in the electrical potential gradient was taken into account between the stratum corneum and epidermis/dermis layer, were constructed to describe the non-steady-state drug permeation process during ionotrophoresis. The observed iontophoretic lag-time was two times greater than the calculated value based on the one-layer membrane model. According to the two-layer membrane model, the calculated ionotophoretic lag-time agreed with the observed value. It was revealed by model adaptation to the observed data that the stratum corneum fraction of the electro-chemical potential difference across the whole skin caused by the iontophoresis was around 90%. This result was consistent with the observation that the direct current resistance of whole skin was seven times greater than that of stripped skin.

Ethyl all-cis-5,8,11,14,17-icosapentaenoate modifies the biochemical properties of rat very low-density lipoprotein

The biochemical properties of serum very low-density lipoprotein (VLDL) were investigated in rats given highly purified all-cis-5,8,11,14,17-icosapentaenoate (EPA), an ethyl-ester derivative (EPA-E). The elution time (gel filtration) of VLDL from EPA-E-treated serum was increased significantly compared with that of the control. EPA-E-treated VLDL isolated by ultracentrifugation exhibited a marked decrease in triglyceride content with a relative increase in cholesterol. In treated VLDL, a significant increase in the ratio of apo E/apo C was observed. There was a remarkable increase in the content of EPA in all the fractions of phospholipids, cholesteryl esters and triglycerides after EPA-E treatment, resulting in n-3 polyunsaturated fatty acid-rich VLDL. EPA-E also reduced the incorporation of [14C]oleate into triglycerides in hepatic microsomes and the rate of hepatic triglyceride secretion. Moreover, lipoprotein lipase activity in heparin-injected plasma was increased in rats given EPA-E without there being an effect on hepatic triglyceride lipase activity. These findings indicate that EPA-E exerts an inhibitory effect on hepatic triglyceride synthesis/secretion and a stimulatory effect on triglyceride degradation, resulting in a reduction in particle size and an increase in the ratio of apo E/apo C. Triglyceride-poor and EPA-rich VLDL may rapidly be converted into the density of intermediate low-density lipoprotein and low-density lipoprotein and/or may be absorbed into the liver rapidly.