Bp. Helmke et al., MECHANISMS FOR INCREASED BLOOD-FLOW RESISTANCE DUE TO LEUKOCYTES, American journal of physiology. Heart and circulatory physiology, 42(6), 1997, pp. 2884-2890
Despite the small number of leukocytes relative to erytkrocytes in the
circulation, leukocytes contribute significantly to organ blood flow
resistance. The present study was designed to investigate whether inte
ractions between leukocytes and erythrocytes affect the pressure-flow
relationship in a hemodynamically isolated rat gracilis muscle. At con
stant arterial flow rate, arterial pressure was increased significantl
y when relatively few physiological counts of leukocytes were added to
a suspension containing erythrocytes at physiological hematocrits. Ho
wever, the arterial pressure after perfusion of similar numbers of iso
lated leukocytes without erythrocytes was only slightly increased. An
increase in resistance was also observed when leukocytes were replaced
with 6-mu m microspheres. We propose a new mechanism for increasing t
he hemodynamic resistance that involves hydrodynamic interactions betw
een leukocytes and erythrocytes. In the presence of larger and less de
formable leukocytes, erythrocytes move through capillaries more slowly
than without leukocytes. Therefore erythrocytes are displaced from th
eir axial positions. Slowing and radial displacement of erythrocytes s
erve to increase the relative apparent viscosity attributable to eryth
rocytes, thereby causing a significant elevation of organ blood flow r
esistance.