Helmholtz Ventricular Assist Devices (VAD) are pneumatically driven polyurethane membrane pumps with various volumes. The pumps are placed paracorporeally and connected with commercially available cannulas between the left atrium and aorta (left ventricular assist device) and/or right atrium and pulmonary artery (right ventricular assist device, bi-ventricular assist device). The pumps can be driven with a stand-alone driving system or with a Helmholtz IABP-console interface. Seventeen animal experiments (on calves) with Helmholtz VAD's were performed to evaluate experimental protocols, to optimize surgical techniques, and to improve design and manufacturing techniques. Blood chemistry and cell counts demonstrated that the tested HIA-70 produces low mechanical blood damage. In the course of the animal experiments the Helmholtz VAD's were made totally transparent, whereby they became easy to de-air, efficient, and affordable.

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The blood compatibility of ventricular assist devices developed by the Helmholtz Institute Aachen (HA-VAD's) was tested on calves. Seven calves received a non-coated HIA-VAD (control) and three a Bioline heparin coated device. The circulatory support of these HIA-VAD's lasted one week. Mechanical blood cell trauma estimated by hematocrit (Hct), hemoglobin (total Hb) and free plasma hemoglobin (free Hb) levels did not differ in either group. All HIA-VAD's in the control group remained thrombus free, except on one occasion when an inflow cannula was obstructed by a thrombus located in the tip. After circulatory support, the animals in this group seemed clinically healthy. However, thrombus formation was observed in the three heparin coated HIA-VAD's. One animal in this group died from complications after re-operation for pneumothorax on the fifth day of support, whereas the other two animals seemed clinically healthy. In these three animals, a stronge decrease in platelet numbers was measured even after 24 hours of support which recovered after 72 hours. This decrease in platelet numbers was associated with a lower degree of platelet aggregation ability stimulated by ADP (p<0.05). Fibrin(ogen) degradation products (FDP) increased significantly immediately after the implantation procedure (p<0.05). Fibrinogen levels initially decreased during the implantation procedure, but increased thereafter in both groups. The FDP levels remained high in this group, although the FDP levels in both groups were decreased after the implantation procedure. The ex vivo measured circulating heparin levels were lower in the heparin coated HIV-VAD group despite the equally administrated heparin doses in both animal groups. No differences were measured in either group with regard to white blood cell (WBC) numbers and complement hemolytic activity (CH50). Despite these hemostatic changes, no mechanical trauma could be demonstrated after seven days of circulatory support.