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.