Pressure effects on the flow behavior of sickle (HbSS) red cells in isolated (ex-vivo) microvascular system

Abstract The effect of varying arterial perfusion pressure ( P a ) on flow behavior of human normal (HbAA) and sickle (HbSS) erythrocytes was evaluated in isolated rat mesoappendix vasculature. Red cell velocity ( V rbc ) and wall shear rate in single arterioles (i.d. 20.4 ± 4.5 μm, X and SD) were determined and total peripheral vascular resistance (PRU) calculated. The vasculature initially perfused with Ringer's solution was then perfused with red cells suspended (HCT 2%) in the same medium. At P a of 100 mm Hg, oxy HbSS cells resulted in higher (50%) PRU and lower V rbc (7.1 ± 2.2 mm/sec) and wall shear rates (1800 ± 490 sec −1 ) than those recorded with HbAA cells which show a more rapid microvascular passage, i.e., V rbc (14.4 ± 2.8 mm/sec) and wall shear rates (3810 ± 360 sec −1 ). At the same P a , partial deoxygenation ( P O 2 40 mm Hg) of HbSS cells caused marked (300%) increase in PRU, and decrease in V rbc (3.2 ± 0.9 mm/sec), and wall shear rates (820 ± 440 sec −1 ). During stepwise decrement of P a (100-30 mm Hg), PRU for oxy HbSS cells remains elevated but the overall trend is similar to that for HbAA cells and Ringer's perfusion. At P a of 30 mm Hg, oxy HbSS cells caused some microvascular obstruction. In contrast, with decrement in P a below 80 mm Hg partially deoxy HbSS cells resulted in progressive increase in PRU and drastic decrease in V rbc , coupled with progressive capillary obstruction and stasis. An increased propensity of these cells to cause irreversible vasoocclusion is demonstrated when low-pressure conditions prevail.