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

The effect of varying arterial perfusion pressure (Pa) on flow behavior of human normal (HbAA) and sickle (HbSS) erythrocytes was evaluated in isolated rat mesoappendix vasculature. Red cell velocity (Vrbc) and wall shear rate in single arterioles (i.d. 20.4 +/- 4.5 Microns means 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 Pa of 100 mm Hg, oxy HbSS cells resulted in higher (50%) PRU and lower Vrbc (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., Vrbc (14.4 +/- 2.8 mm/sec) and wall shear rates (3810 +/- 360 sec-1). At the same Pa, partial deoxygenation (PO2 40 mm Hg) of HbSS cells caused marked (300%) increase in PRU, and decrease in Vrbc (3.2 +/- 0.9 mm/sec), and wall shear rates (820 +/- 440 sec-1). During stepwise decrement of Pa (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 Pa of 30 mm Hg, oxy HbSS cells caused some microvascular obstruction. In contrast, with decrement in Pa below 80 mm Hg partially deoxy HbSS cells resulted in progressive increase in PRU and drastic decrease in Vrbc, coupled with progressive capillary obstruction and stasis. An increased propensity of these cells to cause irreversible vasoocclusion is demonstrated when low-pressure conditions prevail.