White blood cell (WBC) margination and rolling were studied in venules (20-60 microns in diameter) in rat mesentery to examine the relationship between WBC rolling velocity (Vwbc), flux (Fwbc, cells/min), and deformation; and red blood cell (RBC) velocity (Vrbc), wall shear rate (gamma), and microvessel hematocrit (Hmicro). For a range of 1.0 less than or equal to Vrbc less than or equal to 5.0 mm/s, Vwbc remained constant (congruent to 50 microns/s). The volume flux of WBCs rolling along the venular wall (normalized to systemic WBC concentration) decreased nonlinearly from 30 to 5% of total luminal flux as gamma ranged from 50 to 800 s-1 and was more strongly correlated with gamma compared with Fwbc vs. gamma. As indicated by the rolling volumetric flux, margination was weakly affected by Hmicro, except for Hmicro greater than 50% where margination increased. Deformation of WBCs was quantitated during their rolling contact with the endothelium (EC) in terms of their length and height. As gamma increased from 50 to 800 s-1, WBCs elongated to 140% of their estimated undeformed diameter, and the contact area between WBC and EC increased 3.6-fold. These data suggest that with increased gamma rolling of WBCs along the EC decreases, since only the most deformable WBCs of the circulating population persist in maintaining contact with the endothelium. It is concluded that Vwbc is invariant with elevations in gamma, since the greater deformations of rolling WBCs at high shear result in greater adhesive forces attendant to increased WBC-EC contact area, which attenuate increases in Vwbc.

The purpose of this study was to determine which parameters were the best measure of nerve regeneration, assuming that the sciatic functional index (SFI) represented the "gold standard." Three different sciatic functional indexes and 11 commonly used electrophysiologic and morphologic indicators of regeneration were all determined in 24 rats 12 weeks after one of three lesions was created in the sciatic nerve. With linear regression analysis, only fiber/axon diameter ratio (D/d) and myelin thickness/axon diameter ratio showed statistically significant correlations with sciatic functional index (r = 0.55 and 0.53, respectively). The other 11 parameters had poorer correlation. Therefore, if sciatic functional index is the best measure of comprehensive nerve function, then other parameters are not. It is probable that each parameter measures some different component of the regeneration process. A stepwise multiple linear regression analysis produced a model that included D/d, nerve conduction velocity, and nerve action potential amplitude that gave a slightly better correlation (r = 0.67). The relatively poor correlation between sciatic functional index and the other parameters of nerve function indicates that all nerve regeneration studies must be interpreted carefully before comparisons are made. Furthermore, the best measure of nerve function remains unproved or undiscovered in the experimental animal.

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Measurements of intravascular pressure, red blood cell (RBC) velocity, and microvessel hematocrit (Hctmicro) were made in arterioles and venules of the cat mesenteric microvasculature during systemic hemodilution (cell-free plasma) and hemoconcentration (packed cells). For a range of systemic hematocrits (Hctsys) from 5 to 67%, changes in volumetric flux of red cells (QRBC) were derived from the product of microvessel bulk flow and Hctmicro. During hemodilution, a heterogeneous response of changes in QRBC was found with larger distributing arterioles (43-54 microns) exhibiting a monotonic fall, whereas increases in QRBC above control were found in smaller arterioles that were indicative of a potential enhancement of oxygen delivery. Although the dilution response of all arterioles and venules averaged for all calibers of vessels demonstrated a decline in QRBC, alterations of Hctmicro suggested a lessening of the disparity between Hctsys and Hctmicro, which was indicative of a more efficient utilization of the remaining circulating RBC volume. In response to hemoconcentration, a decrease in QRBC also occurred, which, in concert with the dilution data, suggested that QRBC was maximized for a range of 28 less than Hctsys less than 46%. From measurements of the arteriovenous pressure drop across mesenteric modules, regional resistance was found to exhibit a relative plateau as Hctsys was increased above its control value. This behavior was attributed to a decrease in vascular hindrance of the principal resistance vessels and an invariance of blood viscosity at the capillary level due to RBC redistribution and the attendant viscous behavior of blood.