Flow characteristics and required control algorithm of an implantable centrifugal left ventricular assist device

As the clinical application of LVADs has increased, attempts have been made to develop smaller, less expensive, more durable and efficient implantable devices using rotary blood pumps. Since chronic circulatory support with implantable continuous-flow LVADs will be established in the near future, we need to determine the flow characteristics through an implantable continuous-flow LVAD. This study describes the flow characteristics through an implantable centrifugal blood pump as a left ventricular assist device (LVAD) to obtain a simple non-invasive algorithm to control its assist flow rate adequately. A prototype of the completely seal-less and pivot bearing-supported centrifugal blood pump was implanted into two calves, bypassing from the left ventricle to the descending aorta. Device motor speed, voltage, current, flow rate, and aortic blood pressure were monitored continuously. The flow patterns revealed forward flow in ventricular systole and backward flow in diastole. As the pump speed increased, an end-diastolic notch became evident in the flow profile. Although the flow rate (Q [l/min]) and rotational speed (R [rpm]) had a linear correlation (Q = 0.0042R - 5.159; r = 0.96), this linearity was altered after the end-diastolic notch was evident. The end-diastolic notch is considered to be a sign of the sucking phenomenon of the centrifugal pump. Also, although the consumed current (I [A]) and flow rate had a linear correlation (I = 0.212Q + 0.29; r = 0.97), this linearity also changed after the end-diastolic notch was evident. Based upon the above findings, we propose a simple algorithm to maintain submaximal flow without inducing sucking. To maintain the submaximal flow rate without measuring flow rate, the sucking point is determined by monitoring consumed current according to gradual increases in voltage.

Clinical comparative study of cardiopulmonary bypass with Nikkiso and BioMedicus centrifugal pumps

The Nikkiso centrifugal pump was evaluated in elective adult open heart surgery in comparison with the BioMedicus pump. Ten patients using the Nikkiso pump (Group N), and 10 patients using the BioMedicus pump (Group B) were examined for (or to determine) hematobiologic parameters and patient outcome data as well as pump controllability. During cardiopulmonary bypass (CPB), both pumps maintained systemic perfusion satisfactorily without any mechanical adverse event. Rotation speed of the Nikkiso centrifugal pump (3,580 +/- 100 rpm) was significantly higher than that of the BioMedicus pump (3,170 +/- 100 rpm; p < 0.05) whereas changes in free plasma hemoglobin, platelet count, blood urea nitrogen, and creatinine levels showed no significant differences between the two groups. Urine output in Group N for 20 min after the initiation of CPB (7.10 +/- 1.50 ml/kg/h) was significantly higher than that in Group B (3.23 +/- 0.46 ml/kg/h; p < 0.05). Patient outcome data were similar in both groups, such as duration of intensive care unit stay, hospital stay, postoperative intubation time, amount of postoperative bleeding, and amount of blood transfused. These equivalent results with the BioMedicus pump suggested that the Nikkiso pump can be used in open heart surgery as a reliable and atraumatic CPB pump.

Changes in the mononuclear cell subpopulations of rat cardiac transplant recipients administered FK506 for the treatment of ongoing rejection

The inhibitory effect of ongoing rejection and the changes that occurred in mononuclear cell subpopulations were compared between four groups of rats treated with FK506 or steroids. Group 1 was given no immunosuppressive drugs, group 2 was given FK506 from the day of grafting, group 3 was commenced on FK506 on the 4th day after grafting, and group 4 was commenced on methylprednisolone (MP) on the 4th day after grafting. The graft survival times in groups 2 and 3 were significantly longer than those in groups 1 and 4, and there were fewer CD3+ and CD4+ T lymphocytes in the peripheral blood in the groups treated with immunosuppressive drugs than in group 1. In group 4, the levels in both the peripheral blood and thymus were significantly lower than those in the groups treated with FK506 despite the fact that graft rejection occurred soon after the discontinuation of steroid administration. Moreover, the levels of interleukin-2 receptors and macrophages in groups 2, 3, and 4 were significantly lower than that in group 1 postoperatively; however, the number of macrophages in groups 2 and 3 was significantly lower than that in group 4 on the 10th day after transplantation. The findings of this study demonstrated that FK506, even if administered after rejection has begun, might inhibit the subsequent extensive allograft rejection more specifically and effectively than steroids, and that the measurement of a marker for macrophages in the peripheral blood could be useful for the detection of rejection following allograft transplantation in rats.

Effect of dose of cyclosporine or FK506 and antithrombotic agents on cardiac allograft vascular disease in heterotopically transplanted hearts in rats

BACKGROUND

We compared the severity of cardiac allograft vascular disease in rats treated with cyclosporine or FK506 and studied the effect of antithrombotic agents on cardiac allograft vascular disease.

METHODS

One group each was treated with 2 and 5 mg/kg/day of cyclosporine. Two other groups were injected with heparin and dipyridamole, respectively, in addition to cyclosporine. Four other groups were similarly divided by dose of FK506 (0.1 or 0.25 mg/kg/day) and concomitant anticoagulant treatment.

RESULTS

Grade of rejection and percentage stenosis of coronary arteries were lower in groups with high doses of immunosuppressive agents or with heparin. Major histocompatibility class II antigens were expressed by the endothelium of grafted hearts, and IgM and C3 were deposited in the intimal and medial layers in all groups except those administered the higher doses of immunosuppressive drugs. However, no remarkable differences in density of major histocompatibility class II antigens were found between groups demonstrating expression of these antigens. On the other hand, the intensity of IgM or C3 expression grew significantly as coronary stenosis increased in severity.

CONCLUSIONS

A significant difference in severity of cardiac allograft vascular disease was not found between the groups treated with cyclosporine and FK506, and cardiac allograft vascular disease was almost entirely suppressed when doses of cyclosporine and FK506 sufficient to suppress graft rejection were administered. Our findings also showed that concomitant heparin administration reduced the extent of allograft rejection and the incidence of cardiac allograft vascular disease.

[Surgical treatment for postinfarction ventricular septal perforation]

Between August 1981 and August 1992, operation for ventricular septal perforation (VSP) after acute myocardial infarction (AMI) was performed in 12 patients and the results were studied. During this period, medical treatment was attempted as a standard therapy for more than two weeks after AMI, followed by operation. However, only four patients received elective operation two weeks after the onset of AMI. Regarding the relationship between the preoperative circulatory status and timing of surgery, elective operative could not be performed in seven patients showing a pulmonary to systemic flow ratio (Qp/Qs) of more than 3.0, while four out of five patients with a ratio of less than 3.0 received operation more than two weeks after the onset of AMI. Two patients with severe right heart failure after the repair of VSP died on table without weaning from the pump. Ten operative survivors were weaned from the pump without any difficulty of hemostasis and intraaortic balloon pumping was removed after operation. However, three patients died of multiple organ failure which had been deteriorating before operation. Postoperative activity improved to New York Heart Association Functional Class I or II in six survivors for the late follow-up period. In the case of high Qp/Qs due to VSP, early operation is recommended to prevent multiple organ failure.

[Emergency coronary artery bypass grafting with warm blood cardioplegia for a patient with acute myocardial infarction and severe left ventricular dysfunction]

Emergency coronary artery bypass grafting was performed in a 61 year old man who developed acute severe cardiac and respiratory dysfunction after myocardial infarction. At operation cardiac arrest was obtained by warm blood cardioplegia in antegrade intermittent fashion. The left anterior descending artery, diagonal branch, and right coronary artery were revascularized by saphenous vein (SVG). After declamping the aorta, spontaneous heart beating was obtained and postoperative course was uneventful. Postoperative examination showed patent all SVGs and improved cardiac function. Although the delivery of the warm blood cardioplegia was controversial, our recent study revealed that the intermittent antegrade delivery of warm blood cardioplegia showed no ischemic changes of the heart during the procedure.

[The effect of additional albumin with optimal concentration on the reperfusion after preservation of isolated rat hearts]

We studied the effect of additional albumin in preservation solution on reperfusion after immersion of isolated rat hearts by measuring cardiac function, myocardial enzymes and calcium. Male Wistar rats weighing 300 gr to 450 gr were used. Isolated rat hearts were arrested by cardioplegic solution and washed out with preservation solution. Then, the hearts were immersed at 4 degrees C for six hours. The group was divided into four by the concentration of additional albumin in preservation solution which basically consisted of Euro-Collins solution. In control group, the cardiac function was immediately measured after the heart was isolated. Albumin was not added in group I (n = 16), 2% of albumin in group II (n = 18), 5% of albumin in group III (n = 17) and 7% of albumin in group IV (n = 18). There were no significant differences between groups II and III in cardiac function and myocardial enzymes. The levels of myocardial malondialdehyde (nmol/g dry weight) and calcium (mumol/g dry weight) at 15 minutes after reperfusion were 279.3 +/- 38.1, 5.9 +/- 5.3 in group I; 243.3 +/- 86.5, 4.1 +/- 2.0 in group II; 217.1 +/- 106.6, 4.1 +/- 1.3 in group III and 274.9 +/- 77.1, 4.9 +/- 1.2 in group IV, respectively. Although no statistical significances were seen among those results, those data might suggest the relationship between the recovery of cardiac output and myocardial ATP contents. Those results also suggested that additional albumin with optimal concentration might inhibit reperfusion injury.

[Direct implantation of the left coronary artery to the ascending aorta in Bland-White-Garland syndrome]

A seventeen-year-old male with Bland-White-Garland syndrome underwent direct implantation of the left coronary artery to the ascending aorta. Under cardiopulmonary bypass, the main pulmonary artery was completely transected and the left coronary artery (LCA) was excised with a cuff of the pulmonary artery wall. Then the proximal end of LCA was directly anastomosed to the ascending aorta. The postoperative course was excellent. It appears that this surgical procedure might be the most ideal repair both anatomically and hemodynamically to reconstruct the left coronary artery in Bland-White-Garland syndrome.

[Advantage of internal thoracic artery for coronary arterial bypass surgery in patients over 70 years of age]

Between April 1988 and September 1991, 16 among 23 patients over 70 years of age underwent coronary bypass grafting (CABG) with at least one arterial graft. The age ranged from 70 to 77 years (mean, 72.1 years) and involved coronary lesions were two vessels in two patients and three vessels in 14 patients. Seven patients with unstable angina received emergency CABG. The number of distal anastomosis with arterial graft was mean of 1.3 per patient and left internal thoracic artery (ITA) was used as a pedicled graft in all patients. Sequential grafting with left ITA arterial graft was performed in two and right gastroepiploic artery was concomitantly used in three patients. No atherosclerosis was seen in left ITA, however, poor quality saphenous vein graft (SVG) was in five and atherosclerosis of ascending aorta was in five patients. After operation deep vein thrombosis of leg after harvesting SVG occurred in one patient. The angiogram performed within one month of operation in nine patients showed that the patency rate of arterial graft was 100% and that of SVG was 94.4%. The longest follow-up period was 42 months and New York Heart Association Functional Class improved to Class I or II in all patients. The use of pedicled ITA in elderly patient showed advantage for diseased ascending aorta and it seemed to prevent the postoperative complication due to the use of SVG.