Light scattering detection of microemboli in an extracorporeal LVAD bovine model

Thromboembolization studies were performed on two calves supported by extracorporeal left ventricular assist devices (LVAD) using a light scattering (He Ne Laser) microemboli detector (LSMD). The LSMD system was placed on the outflow cannula of the LVAD in the extracorporeal loop of each animal. The measurements included the size, number, and rate of production of circulating microemboli in the range 20 microns less than microemboli diameter less than 1,000 microns. These data were compared to independently and concurrently obtained measurements of emboli shear rate (CPF), platelet count, red blood count (RBC), leukocyte count (WBC), plasma free hemoglobin, factors XIII, X, and V, and sorbitol dehydrogenase. Embolic number and volume were seen to be most dynamic in the very early phases of acute thromboembolization (0-40 minutes) with a peak embolic response within the first 30 minutes. The dynamics of reduced emboli volume, rather than number, may be implicated in the later stages of the thromboembolic passivation of these ventricles. The LSMD results generally showed an inverse correlation of microemboli volume rate with CPF measurements for each ventricle. LSMD, CPF, and leukocyte and platelet counts, showed a direct correlation with reduced counts for each additional ventricle for both calves. Factor XII was seen to have a more direct correlation in time with LSMD measurements for each ventricle than other parameters under investigation. This study represents the first time laser scattering and filtration methods have been applied simultaneously with hematologic assays in order to study the dynamics of device associated thrombogenesis.