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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.

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.

Background There are few reports that demonstrate the chronologic changes in the functional integrity of the internal thoracic artery (ITA) wall after skeletonization. We investigated the impact of skeletonization on ITA wall integrity by immunohistochemical analyses in acute and chronic phases. Methods Nine mongrel dogs underwent bilateral ITA dissection with one skeletonized vessel and the other pedicled. The following studies were performed 1 week (acute phase, n=3) and 12 weeks (chronic phase, n=6) after ITA harvesting. All specimens of the ITAs were stained by antibodies against von Willebrand Factor (VWF), endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and proliferating cell nuclear antigen (PCNA). After observation with confocal laser scanning microscopy, quantitative analyses of the staining signal for VWF and eNOS expressed on endothelial cells were performed. Results There were significantly more microvessels positive for VWF in the adventitia of skeletonized ITAs than in the adventitia of pedicled ITAs but the expression of PCNA in both groups was minimal, as in normal vessels. iNOS was not detected in any specimen. The intensity of VWF and eNOS expressed by endothelial cells had no significant differences between groups at either phase. Conclusions The functional integrity of skeletonized ITA was similar to that of pedicled ITA in both acute and chronic phases. Although skeletonization induced neovascularization in the adventitia it did not induce proliferation of smooth muscle cells in the media, which is supposed to be a feature of vascular remodeling.

Objectives: We have investigated the effects and outcome from grafting the right internal thoracic artery to the left anterior descending artery in coronary artery bypass grafting.Methods: We analyzed the findings in 185 patients who underwent coronary artery bypass grafting involving right internal thoracic artery-left anterior descending artery bypass. The survival rate, cardiac events related to the right internal thoracic artery-left anterior descending artery graft, and graft patency were investigated. In cardiac catheterization, the production of nitric oxide from the endothelium of the internal thoracic artery was measured as the plasma nitrite and nitrate levels by the Griess reaction. The reactions to acetylcholine infusion (5 μg) in the right internal thoracic artery (n = 4) were compared to those in the left internal thoracic artery (n = 9) grafts.Results: The hospital mortality rate was 0.5%. The actuarial survival rate at 11 years after operation was 98.81%. The rate of freedom from cardiac events at 11 years after operation was 92.08%. The rate of patency of the right internal thoracic artery-left anterior descending artery was 97.0% in 133 patients. Nitric oxide production was calculated as (total nitrite plus nitrate production in response to stimulation by acetylcholine-total nitrite plus nitrate level before acetylcholine load) / (total nitrite plus nitrate level before acetylcholine load). There was no significant difference in changes in plasma concentration in response to acetylcholine stimulation between the right internal thoracic artery-left anterior descending artery and left internal thoracic artery-left anterior descending artery groups (20 ± 29% versus 5 ± 10%).Conclusions: The right internal thoracic artery-left anterior descending artery grafts exhibited good patency and release of nitric oxide in response to acetylcholine loading, similar to left internal thoracic artery-left anterior descending artery grafts.

A 66-year-old man was referred for treatment of critical limb ischemia arising with multiple organ dysfunction due to acute pneumonia. Angiographic examinations demonstrated total obstruction of the bilateral external iliac arteries and the bilateral superficial femoral arteries with collateral circulation to the distal vessels. Urgent percutaneous transluminal angioplasty dissolved the obstruction of the left external iliac artery, and subsequent low-density-lipoprotein apheresis ameliorated his progressive ischemia in the lower extremities. Femoro-femoral and bilateral femoro-popliteal bypasses were performed 31 days after the endovascular intervention, which achieved successful limb salvage with the relief of ischemic symptoms related to arteriosclerotic obliterans.

Background . Allograft aortic valve replacement has gained widespread acceptance. However, there is little information about in vivo allograft valve function at rest and during exercise. Methods . Cardiac catheterization was performed to measure hemodynamic variables at rest and during supine bicycle exercise in 44 patients who had had aortic valve replacement using allograft valves or Bicer or St. Jude Medical prosthetic valves 19 to 27 mm in diameter. Sixteen patients received an allograft valve; 17, a Bicer valve; and 11, a St. Jude Medical valve. There were no significant differences between the three groups in age, body surface area, left ventricular end-systolic and end-diastolic volume indices, exercise cardiac index, exercise heart rate, or work load achieved. Left ventricular and ascending aortic pressures were measured simultaneously according to the transseptal method. Results . The mean pressure gradient was generally higher for the Bicer and St. Jude Medical valves than for the allograft valves, both at rest and during exercise. Significant differences were obtained in patients with small-sized valves (21 and 23 mm); pressure gradients were higher in the prosthetic valve groups. In patients with large-sized prosthetic valves (25 mm), there were no significant differences between the three groups at rest and during exercise. However, there was no pressure gradient at all for allograft valves. Conclusions . Exercise cardiac catheterization confirms that the allograft aortic valve is an ideal substitute from the hemodynamic aspect, particularly in patients with a small aortic root and in those who perform strenuous exercise.

During left nephrectomy in a 35-year-old woman with a left renal cell carcinoma extending into the inferior vena cava (IVC) and right atrium, cardiac arrest occurred. Immediate transesophageal echocardiography demonstrated that the event was caused by a pulmonary tumor embolism. Emergent cardiopulmonary bypass (CPB) was established and the tumors in the pulmonary arteries were successfully removed. The left nephrectomy was completed. The patient recovered in the intensive care unit without any neurological deficit. A postoperative pulmonary perfusion scintigram showed no defect in the pulmonary circulation. Transesophageal echocardiography was useful for making a rapid diagnosis of an intraoperative pulmonary embolism originating from a tumor of the IVC or right atrium.

A collaborative effort between Baylor College of Medicine and NASA/Johnson Space Center is underway to develop an axial flow ventricular assist device (VAD). We evaluated inducer/impeller component designs in a series of in vitro hemolysis tests. As a result of computational fluid dynamic analysis, a flow inducer was added to the front of the pump impeller. According to the surface pressure distribution, the flow inducer blades were connected to the impeller long blades. This modification eliminated high negative pressure areas at the leading edge of the impeller. Comparative studies were performed between inducer blade sections that flowed smoothly into the impeller blades (continuous blades) and those that formed discrete separate pumping sections (discontinuous blades). The inducer/impeller with continuous blades showed significantly (p < 0.003) lower hemolysis with a normalized index of hemolysis (NIH) of 0.018 +/- 0.007 g/100 L (n = 3), compared with the discontinuous model, which demonstrated an NIH of 0.050 +/- 0.007 g/100 L (n = 3). The continuous blade model was evaluated in vivo for 2 days with no problems. One of the pumps evaluated ran for 5 days in vivo although thrombus formation was recognized on the flow straightener and the inducer/impeller. As a result of this study, the pump material was changed from polyether polyurethane to polycarbonate. The fabrication method was also changed to a computer numerically controlled (CNC) milling process with a final vapor polish. These changes resulted in an NIH of 0.0029 +/- 0.0009 g/100 L (n = 4), which is a significant (p < .0001) value 6 times less than that of the previous model.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

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.

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.

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.

We used quantitative angiography to determine the postoperative diameter of the internal thoracic artery graft at the point close to the anastomosed site in 147 patients who received the graft for the left anterior descending coronary artery. We performed generalized multiple linear regression analysis (Type I quantification method) to assess the effects of the following factors on the internal thoracic artery graft diameter: age, gender, time of angiography, laterality of the internal thoracic artery used, presence of an undivided major side branch of the internal thoracic artery, presence of a saphenous vein graft having blood flow competition with an internal thoracic artery graft, presence of distal stenosis of the recipient left anterior descending coronary artery, severity of postoperative left anterior descending coronary artery stenosis, and presence of coronary risk factors. The standardized category scores for 25% left anterior descending coronary artery stenosis, 50% left anterior descending coronary artery stenosis, and presence of a saphenous vein graft having blood flow competition with an internal thoracic artery graft were -1.418, -0.767 and -0.622, respectively. Thus, the internal thoracic artery diameter was smaller in patients with well-preserved flow of the recipient coronary artery. The internal thoracic artery diameter had a particularly strong correlation with the degree of left anterior descending coronary artery stenosis (partial correlation coefficient: 0.670). The other factors seemed to have little or no correlation with the postoperative internal thoracic artery diameter. With the criterion that the internal thoracic artery diameter below 1.0 mm represents the "string sign" of internal thoracic artery graft, this phenomenon was observed in nine patients (6.1%). In all of these patients, left anterior descending coronary artery flow was well-preserved, and no ischemia was disclosed in the left anterior descending coronary artery-perfused area. These results indicate that internal thoracic artery grafts have flow adaptability responding to the flow demand of the recipient coronary artery and that the string sign of internal thoracic artery grafts is mainly an outcome of its physiologic characteristics.

Objective: Reoperative coronary artery bypass grafting with cardiopulmonary bypass tends to cause a higher mortality and morbidity than the primary operation. The purpose of this study was to discuss the effectiveness and safety of a minimally invasive coronary artery bypass procedure for patients who had previously undergone coronary artery bypass surgery.Methods: We performed redo single coronary artery bypass grafting to the left anterior descending coronary artery in 9 patients and to the right coronary artery in 3 patients using minimally invasive cardiac surgery. The graft to the left anterior descending coronary artery was taken from the left internal thoracic artery in 5 patients, the right gastroepiploic artery in 3 patients, and from the saphenous vein in the other 1 patient. The graft to the right coronary artery was from the right gastroepiploic artery in all 3 patients.Results: All grafts were patent. There was no major postoperative complication and no surgical or hospital death except one late death.Conclusions: In selected patients, we could safely and completely perform coronary artery bypass re-grafting to the left descending coronary artery or right coronary artery using a minimally invasive operation.

In hypothermic cardiopulmonary bypass (CPB), various vasodilators are used to control the perfusion pressure. These agents, however, often decrease the pressure excessively, and the low perfusion pressure may persist until the end of CPB. In this study we evaluate the safety and characteristics of the regulation of perfusion pressure during CPB using a volatile anesthetic, sevoflurane which has an extremely low partition coefficient. Twenty adult patients who underwent cardiac surgery were studied. Sevoflurane was applied by a vaporizer inserted into the oxygenator gas supply line. Pump flows were fixed at 2.4 L/min/m2 during the hypothermic period. Sevoflurane concentration was adjusted to keep mean arterial pressure (MAP) between 40 and 70 mmHg during CPB. Hemodynamic and metabolic parameters were measured and compared to the group we previously treated with chlorpromazine. In all cases, MAP could be maintained adequately. In the sevoflurane group, systemic vascular resistance indices (SVRI) during the rewarming period and at the end of CPB were higher, and doses of norepinephrine needed at the end of CPB were significantly lower than in the chlorpromazine group. The regulation of perfusion pressure during CPB using sevoflurane was safe and could easily maintain adequate SVRI.

The roles of prostaglandins and catecholamines in the hypotensive hemodynamic change during cardiopulmonary support with a venoarterial bypass (VAB) were investigated in a series of chronic animal experiments of gradually reduced pulmonary arterial blood flow (PAF). The VAB system consisted of a pulsatile ventricular assist device, an artificial lung, and the right atrium uptake and descending aorta return cannulae in four adult goats weighing 49-51 kg. The PAF was adjusted to 50, 10, and 0% of the total systemic blood flow. Indomethacin, an inhibitor of prostaglandin production; phentolamine, an alpha-antagonist of catecholamine; and noradrenaline, an agonist of catecholamine were administered at each PAF condition. The mean aortic pressure (mAoP) and the systemic vascular resistance decreased in proportion to the decrease in PAF. Indomethacin increased the mAoP at all PAF conditions, indicating a relationship between prostaglandins and hypotension. Phentolamine decreased the mAoP at all PAF conditions, indicating a normal response of catecholamine receptors. However, noradrenaline increased the mAoP at 50 and 10% PAF, but did not appreciably increase the value at 0% PAF, indicating complete response of catecholamine receptors to endogenous catecholamines at 0% PAF only. In conclusion, prostaglandins play a substantial role in hypotension during VAB, and catecholamines may subsequently increase in compensation for extreme hypotension.

As percutaneous transluminal coronary angioplasty has become an increasingly common procedure replacing coronary artery bypass grafting (CABG), the clinical profile of the patients referred for CABG has changed markedly. A retrospective study of the changes in the clinical profile and surgical outcome of patients who underwent CABG during the past 10 years was conducted. Between March 1982 and February 1996, 1010 patients underwent isolated CABG at Nara Medical University. The first 100 consecutive patients who underwent CABG in 1984-85 (group 1) were compared with the first 100 consecutive patients who underwent CABG in 1994-95 (group 2). Preoperative risk increased significantly during the decade with respect to patient age (p

This study sought to determine the effects of grafting the internal thoracic artery (ITA) to the left anterior descending coronary artery (LAD) on long-term (10-year) survival, the cardiac death-free rate, and on the cardiac event-free rate in Japanese patients.The use of ITA grafts has been reported to enhance postoperative survival and to decrease the occurrence of cardiac events in the Western literature. However, the survival benefits in Japanese patients, who may have different prognoses with coronary artery disease and a different fate of a saphenous vein graft, have not yet been determined.A total of 954 consecutive patients who underwent coronary artery bypass graft operations (CABG) during the last 12 years at the Nara Medical University were followed and evaluated. Of these, 713 patients underwent ITA-CABG to at least the LAD (ITA group), and 241 patients received a saphenous vein graft (SVG) to the LAD (SVG group). At the time of operation, no significant difference was found between these two groups in age, sex ratio left ventricular ejection fraction, left ventricular end-diastolic pressure, cardiac index, incidence of unstable angina, or in the necessity for an emergency operation. However, those patients who received ITA-CABG had significantly higher incidences of diabetes mellitus, hyperlipidemia, and left main coronary artery disease.The 10-year cumulative graft patency rate for the LAD was 23% higher in the ITA group (90.3%) compared to the SVG group (67.0%), (p.0001). Despite increased preoperative risk factors, patients in the ITA group showed significant improvements in their 5- and 10-year cumulative survival rates as well as in their cardiac death-free and event-free rates. Furthermore, this study demonstrated that ITA grafts improved the prognoses of patients with diabetes mellitus or left ventricular dysfunction and lowered both the long-term postoperative cardiac-death rate and the cardiac-event rate.The use of ITA grafts was effective in improving both the postoperative survival and cardiac event-free rates, and should be recommended in patients with diabetes mellitus or left ventricular dysfunction. ITA grafting to the LAD should be a routine operation in almost all categories of such patients.

In vitro hemolysis tests play a very important role in the development of rotary blood pumps such as the axial flow blood pump. A rotary blood pump that has a high normalized index of hemolysis (NIH) will not have good in vivo test results. In other words, a good in vitro hemolysis test result is required before in vivo evaluations can be initiated. Many factors affect in vitro hemolysis test results, such as the effects of the priming volume, the blood-contacting surface area (BCSA) of the test circuit, throttle usage for the test loop resistance, and blood temperature. Each of these parameters was evaluated in the Baylor/NASA axial flow blood pump; the results are described here. Different priming volumes (small; 402 ± 28 ml, large; 674 ± 26 ml) did not affect hemolysis (NIH was 0.0065 ± 0.0049 and 0.0074 0.0055 g/1001, respectively). Different BCSAs (680 and 2000 cm2) of the test circuit did not show significant differences (in NIH 0.0066 ± 0.0034 and 0.0085 ± 0.0057g/1001, respectively). Different throttle systems (clamp with 1/2-inch tubing and clamp with 1/4-inch tubing) did not show a significant difference compared to the corresponding control value (0.0089 ± 0.0049 vs 0.0096 ± 0.0051 g/1001 and 0.0017 ± 0.0003 vs 0.0020 ± 0.0001 g/1001, respectively). At 37°C, the NIH (0.0168 ± 0.0015 g/1001) was significantly (P < 0.05) higher than that at 25°C (0.0065 ± 0.0056 g/1001). According to these test results, the following test conditions were suggested for in vitro hemolysis tests to evaluate rotary blood pumps: One unit of blood (450–500 ml) for the priming volume, small BCSA (approximately 700 cm2) for the test circuit, utilization of a throttle with a clamp with 1/4-inch tubing to obtain the correct test pressure, and blood temperature of 25°C.

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.

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.

The Baylor/NASA Axial Blood Flow Pump has been developed for use as an implantable 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. To date the pump provides acceptable results in terms of thrombus formation and hemolysis (IH of 0.018 g/100 L). A fluid dynamics analysis using flow visualization was performed to investigate the flow fields and to determine areas within the pump that could be improved. These studies focused upon the inflow area in front of the pump. A prototype axial flow pump assembly was constructed to facilitate the flow visualization studies. Particle image tracking velocimetry techniques were used to measure Amberlite particles suspended in a blood analog fluid composed of 63% water and 37% glycerin. This method used a pulsed (612 Hz) laser light to determine flow velocity profiles, shear stress, Reynolds numbers, and stagnant areas within the axial pump. These studies showed that the flow straightener (a vaned assembly in the pump inflow) reduced Reynolds numbers from 4,640 to 2,540 (at 8.5 L/min) and that the flow straightener exacerbates a discontinuity found between it and the impeller. Within the inflow area, a maximum of 80 N/m2 shear stress was measured, which is well below published blood damage thresholds. Design variations were investigated resulting in a smoother flow transition between flow straightener and impeller. These variations must be investigated further to establish a correlation with hemolysis and thrombus formation.

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 characteristic is described in relationship to back flow.

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.

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.

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.

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.

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.

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.

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.

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.

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.

We attempted to quantify the exercise coronary flow reserve in 20 patients with bilateral internal thoracic artery grafts to the left coronary arteries (group I) who had complete revascularization. The coronary sinus blood flow was measured by the continuous thermodilution method both at rest and during exercise (50 W for 8 to 9 minutes) approximately 1 month after the operation. These results were compared with 30 patients treated with an internal thoracic artery and saphenous vein grafts to the left coronary arteries (group II) and 9 patients with saphenous vein grafts alone to the left coronary arteries (group III). There were no differences among the three groups in age, sex, number of vessels involved, heart rate, double products, left ventricular (LV) end-diastolic pressure, LV ejection fraction, LV end-diastolic volume, or LV mass at the time of study. None of the 59 patients in the study had abnormally enlarged LV end-diastolic volume or increased LV mass. The postoperative coronary sinus blood flow per 100 grams of LV mass at rest was similar among the three groups (73.0 +/- 28.4 mL/min per 100 g LV mass in group I, 73.4 +/- 31.1 mL/min per 100 g LV mass in group II, and 75.9 +/- 28.5 mL/min per 100 g LV mass in group III [not significant]) and significantly (p0.01) increased by exercise, although the differences between groups during exercise were not significant (158.9 +/- 45.9, 153.5 +/- 72.1, and 148.3 +/- 60.0 mL/min per 100 g LV mass, respectively [not significant]).(ABSTRACT TRUNCATED AT 250 WORDS)

We report 2 patients with congenital coronary anomalies (atresia of left main coronary artery and anomalous origin of the left coronary artery from the pulmonary artery) successfully treated with single or double internal thoracic artery grafting. Because the internal thoracic artery has a potential for circumferential as well as longitudinal development, and because of the uncertainty of ultimate vein graft function, we believe that the internal thoracic artery is the best graft material for the treatment of congenital coronary malformations requiring bypass operation in children, adolescents, or even in adults.

We performed myocardial revascularization with bilateral internal mammary arteries in eight children for coronary artery complications consequent to Kawasaki disease. Subjects included seven boys and one girl, ranging in age from 3 to 13 years (mean age, 8.3 +/- 3.4 years). The body surface area ranged from 0.65 to 1.65 m2 (average, 1.08 +/- 0.35 m2). Three patients had a previous myocardial infarction. The right internal mammary artery was anastomosed to the right coronary artery and the left internal mammary artery was sutured to the left anterior descending artery in all patients. The patients received an average of 2.4 grafts. Magnifying loupes of 3.5 X were used for anastomosis with 8-0 monofilament polypropylene sutures. Subjects were followed up from 12 to 38 months (23 +/- 10.8 months) after operation. All were doing well with no recurrence of angina, and body development was normal, including the sternum and thorax according to chest x-ray films and computed tomography of the chest. Patency of the bilateral internal mammary arteries was 100% in the early (within 1 month) postoperative period and remained so in the late (over 1 year) postoperative period. Anastomotic junctions between the internal mammary artery and the coronary artery developed well angiographically in the late postoperative period. The internal mammary artery is the graft of choice for pediatric myocardial revascularization because of its excellent long-term patency and growth potential. Bilateral internal mammary arteries should be used whenever indicated, and the use of bilateral internal mammary arteries did not adversely influence chest wall development in the children.