MODEL STUDIES OF LEUKOCYTE-ENDOTHELIUM-BLOOD INTERACTIONS

Computational fluid dynamics (CFD) and large scale model experiments w ere used to analyze the hemodynamic impact of leukocytes adherent to t he wall of post-capillary venules. Using a large scale model and, with the aid of a finite element package, solving the Navier Stokes equati ons for low Reynolds number flow in a cylinder past an adherent sphere , we have developed a dimensionless correlation which permits the esti mation of the pressure drop across an adherent leukocyte in an in vivo vessel. This relationship is: f . Re = exp[ 2.877 + 4.630(d/D)(4)] wh ere fis the Fanning friction factor, Re is the Reynolds number and d/D is the leukocyte to vessel diameter ratio. The friction factor is pro portional to the pressure drop across the leukocyte, and does not sign ificantly increase until d/D is greater than 0.5, and then increases r apidly with increasing d/D. Computations indicate that the length of t he disturbed flow region generated by an adherent leukocyte increases with decreasing vessel size, The average wall stress in the disturbed flow region remains constant, and equal to the wall stress in the undi sturbed region for d/D less than approximately 0.5. For d/D greater th an 0.5, the average wall stress in the disturbed flow region increases rapidly with increasing d/D. There is an even larger increase, up to five times greater than the average disturbed stress, in the peak wall stress in the disturbed now region, This indicates that significant w all stress gradients can be generated by an adherent leukocyte in post -capillary size vessels. (C) 1997 Elsevier Science Ltd.