Chronic animal health assessment during axial ventricular assistance: Importance of hemorheologic parameters

Chronic testing of the Nimbus/UOP Axial Flow Pump was performed on 22 calve s for periods of implantation ranging from 27 to 226 days (average, 74 days ). The following parameters were measured: plasma free hemoglobin, blood an d plasma viscosity, erythrocyte deformability and mechanical fragility, oxy gen delivery index (ODI), blood cell counts, hematocrit, hemoglobin, blood urea nitrogen, creatinine, bilirubin, total protein, fibrinogen, and plasma osmolality. Most of the above parameters were stable during the full cours e of support. Compared with baseline, statistically significant differences during the entire period of implantation were only found in: hematocrit (p < 0.001), hemoglobin (p < 0.005), red blood cell (RBC) count (p < 0.001), and whole blood viscosity (p < 0.01). Plasma viscosity and ODI were mostly stable during the period of implantation, In some animals, an acute increas e in fibrinogen concentration, plasma and blood viscosity, and a decrease i n ODI were found to be early signs of the onset of infection. A small (10%) decrease in deformability of RBCs was found during the first 2 weeks after implantation. This alteration in RBC deformability was highly correlated ( r = 0.793) with changes in total plasma protein concentration that fell mor e than 15% (p < 0.001) during the same period. Mechanical fragility of RBCs was found to be slightly increased after implantation. Plasma free hemoglo bin remained close to baseline level (p > 0.2). After the first 2 weeks of the postoperative period, pump performing parameters for all animals were c onsistent and stable. In general, the Nimbus/UOP Axial Flow Pump demonstrat ed basic reliability and biocompatibility and did not produce significant a lterations in the mechanical properties of blood or animal health status. T he pump provided adequate hemodynamics and was well tolerated by the experi mental animal for periods as long as 7.5 months. Monitoring theologic param eters of blood is very helpful for evaluation of health during heart-assist device application.