In vitro model for studying the effects of hemodynamics on device induced thromboembolism in human blood

Biomateria related thromboembolism is a complex phenomenon, affected by suc h variables as biomaterial surface chemistry, hemodynamics, and individual donor variations. Thus, isolation of the individual variables would greatly facilitate the understanding and inhibition of this phenomenon. A low volu me in vitro model with this potential has been developed, with the initial focus on studying the influence of hemodynamics on thromboembolism (TE) in human blood. Patterned after a larger in vitro model for bovine blood used successfully in our laboratory, the smaller model directed fresh human bloo d in a single pass through 1/32 inch ID PVC tubing and a flow cell at 3 ml/ min. The flow cell consisted of alternating abrupt expansions and contracti ons of cylindrical tubing that could be modified to study the effects of he modynamic parameters on TE. Thrombus growth in the flow cell was monitored visually by transillumination microscopy. Emboli from the flow cell were de tected continuously by a light-scattering microemboli detector (LSMD), and their strength was assessed by using the constant-pressure filtration (CPF) method. Preliminary studies confirmed the potential of this model. Thrombi were observed visually in the flow cell at sites of high vorticity and at flow separation and reattachment points and were also observed to embolize. Emboli were detected by the LSMD downstream of the flow cell in significan tly greater numbers than upstream and were coincident with the embolization of thrombi observed visually. Emboli collected downstream of the flow cell occluded the CPF fillers at 50 mm Hg, suggesting that they possessed suffi cient strength to occlude microvessels. This model may be used to aid in de veloping a computer model of thromboembolism, which could subsequently be r efined with clinical data.