Measurements of intravascular pressure, red blood cell (RBC) velocity, and microvessel hematocrit (Hct(micro)) 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 (Hct(sys)) from 5 to 67%, changes in volumetric flux of red cells (Q̇(RBC)) were derived from the product of microvessel bulk flow and Hct(micro). During hemodilution, a heterogeneous response of changes in Q̇(RBC) was found with larger distributing arterioles (43-54 μm) exhibiting a monotonic fall, whereas increases in Q̇(RBC) 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 Q̇(RBC), alterations of Hct(micro) suggested a lessening of the disparity between Hct(sys) and Hct(micro), which was indicative of a more efficient utilization of the remaining circulating RBC volume. In response to hemoconcentration, a decrease in Q̇(RBC) also occurred, which, in concert with the dilution data, suggested that Q̇(RBC) was maximized for a range of 28 < Hct(sys) < 46%. From measurements of the arteriovenous pressure drop across mesenteric modules, regional resistance was found to exhibit a relative plateau as Hct(sys) 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.
|Original language||English (US)|
|Journal||American Journal of Physiology - Heart and Circulatory Physiology|
|State||Published - 1986|
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