Influence of flow variations on capillary hematocrit in mesentery.

JOHNSON, PAUL C.,JON BLASCHKE, KENNETH S. BURTON, AND JOE H. DIAL. Infruence of Jzozo variations on capillary hematocrit in mcsenter-y. Am. J. Physiol. 221(l): 105-l 12. 1971.~Red cell spacing was measured on line in mesenteric capillaries of the cat by counting red cells passing through the capillary and simultaneously measuring red cell velocity. Most capillaries had reasonably stable hematocrit values under control conditions although some showed erratic changes and in a few a well-defined periodicity was apparent. Gross flow to the mesentery was reduced for l-2 min by partial occlusion of the arterial perfusion circuit. Capillary hematocrit was, on the average, unchanged during hypotension although onethird of the capillaries showed a reproducible increase or decrease. These changes were slower than the accompanying reduction of pressure and flow. With sudden restoration of pressure and flow, hematocrit remained essentially unchanged. Vasomotion led in some instances to changes in hematocrit. This appeared to be associated with vasomotion of precapillary sphincters or possibly metarterioles. Our findings are consistent with the hypothesis that flow fractionation at the capillary entrance is an important determinant of capillary hematocrit while the absolute flow rate seems to have little effect.