Characteristics of blood rheology in patients during Novacor left ventricular assist system support

Mechanical blood trauma in assisted circulation: sublethal RBC damage preceding hemolysis

After many decades of improvements in mechanical circulatory assist devices (CADs), blood damage remains a serious problem during support contributing to variety of adverse events, and consequently affecting patient survival and quality of life. The mechanisms of cumulative cell damage in continuous-flow blood pumps are still not fully understood despite numerous in vitro, in vivo, and in silico studies of blood trauma. Previous investigations have almost exclusively focused on lethal blood damage, namely hemolysis, which is typically negligible during normal operation of current generation CADs. The measurement of plasma free hemoglobin (plfHb) concentration to characterize hemolysis is straightforward, however sublethal trauma is more difficult to detect and quantify since no simple direct test exists. Similarly, while multiple studies have focused on thrombosis within blood pumps and accessories, sublethal blood trauma and its sequelae have yet to be adequately documented or characterized. This review summarizes the current understanding of sublethal trauma to red blood cells (RBCs) produced by exposure of blood to flow parameters and conditions similar to those within CADs. It also suggests potential strategies to reduce and/or prevent RBC sublethal damage in a clinically-relevant context, and encourages new research into this relatively uncharted territory.

The effect of fluid viscosity on the hemodynamic energy changes during operation of the pulsatile ventricular assist device

Blood viscosity during operation of ventricular assist device (VAD) can be changed by various conditions such as anemia. It is known generally that the blood viscosity can affect vascular resistance and lead to change of blood flow. In this study, the effect of fluid viscosity variation on hemodynamic energy was evaluated with a pulsatile blood pump in a mock system. Six solutions were used for experiments, which were composed of water and glycerin and had different viscosities of 2, 2.5, 3, 3.5, 4, and 4.5 cP. The hemodynamic energy at the outlet cannula was measured. Experimental results showed that mean pressure was increased in accordance with the viscosity increase. When the viscosity increased, the mean pressure was also increased. However, the flow was decreased according to the viscosity increase. Energy equivalent pressure value was increased according to the viscosity-induced pressure rise; however, surplus hemodynamic energy value did not show any apparent changing trend. The hemodynamic energy made by the pulsatile VAD was affected by the viscosity of the circulating fluid.

Biomedical engineering management of Novacor left ventricular assist system (LVAS) patients

As the number of cardiac transplant centres increases, there is an associated decrease in the availability of donor organs per centre. Subsequently, hospitals are utilizing cardiac assist systems (total artificial heart and ventricular assist devices) as a bridge to cardiac transplantation. Because of the engineering complexities related to the clinical implantation and follow up of these devices, a successful centre should have a well co-ordinated biomedical engineering programme. These engineers are responsible for the calibration, monitoring, and continued operation of these units. This paper is intended to serve as a guide to any centre interested in utilizing total artificial heart and ventricular assist systems, in particular the Novacor left ventricular assist system, and focuses on the management and function of the biomedical engineering component of our cardiac assist programme.

Reconsideration of total erythrocyte destruction phenomenon

During a particular long-term in vitro hemolysis test, the plasma free hemoglobin suddenly increased even though the hemolysis level had risen linearly for the previous several hours. This phenomenon was dubbed the total destruction of erythrocytes (TDE) phenomenon, and it was hypothesized that this was the result of the accumulation of sublethal damage to erythrocytes. It was suggested that the TDE might demonstrate the hemolytic characteristics of a pump more sensitively than a conventional hemolysis test. However, the previous report did not consider the effects of temperature or contamination. To study these effects, 3 long-term hemolysis tests were concluded under the following conditions. For Study 1 blood temperature was maintained at 27 degrees C (n = 2); for Study 2, at 37 degrees C (n = 4); and for Study 3, at 37 degrees C with gentamicin (n = 4). The BioMedicus and Nikkiso pumps were used as they were in our previous report. Gas sterilization of all circuits and pumps preceded experimentation. In Studies 1 and 3, hemolysis increased linearly for 29 h. However, in Study 2 a sudden increase of hemolysis occurred for both pumps. Possible causes of this were the dramatic changes in environmental factors such as severe acidosis, high O2 and glucose consumption, and CO2 accumulation. In contrast, neither Study 1 nor Study 3 showed a sudden increase in hemolysis. The plasma free hemoglobin increased linearly in both groups until 29 h of pumping. The environmental changes resulting from contamination were considered to be the cause of the sudden increase in hemolysis. In conclusion, the TDE did not reflect mechanical blood cell damage, but rather different environment situations. Hemolysis increased linearly up to 29 h in either 27 degrees C or germ-free conditions.

Experience with the Berlin Heart Assist Device

Different mechanical circulatory support systems (MCSS) have been in clinical use since 1987 to keep patients alive by assisting the heart during cardiac recovery after open heart surgery, myocardial infarction, acute graft failure after heart transplantation, or as a bridge to transplantation in heart transplant candidates. Four different hospitals in Germany used the Berlin Heart Assist Device. Up until 1993, there were 22 patients in the "recovery" group; 4 patients were weaned from the system, and only 1 patient was discharged from the hospital. In 112 patients the Berlin Heart Assist Device was implanted for the purpose of a bridge to transplantation, 68 were transplanted and 46 patients left the hospital. It was concluded that patients may be kept alive with this system for weeks and months after any kind of cardiogenic shock. Complete cardiac recovery may be achieved in patients with early posttransplant graft failure. Reliable prediction of outcome in bridge-to-transplantation patients requires further experience and improvement of system components.