Erythrocyte Aggregation in Hyperthermic Hypoxic Conditions Significantly Related to Self‐identified Race

Abstract

Our purpose was to identify the kinetics of erythrocyte (RBC) reversible aggregation (Agg) during stop flow (SF) experiments as a function of temperature and O2 for RBC from healthy subjects self-identified as Black (B, n=8), Hispanic (H, 4) or Caucasian (C, 4) (48+/- 9 y). Whole blood (EDTA, BioIVT, Westbury, NY), vendor verified to be viral free, and used within 1 week of donation, was centrifuged and the platelet poor plasma (PPP) was recovered. All RBCs were resuspended in autologous PPP, and incubated at specified temperatures (37, 41, 45, 49 C) and O2 (0, 5, 10%, saturating). Flow was initiated in a microchannel system at 0.1-0.2 Re, then stopped while recording the entire microchannel width. The greyscale range of the images showed a significant Fahraeus effect with flow (cell free layer at wall). With SF, as Agg proceeded, the aggregates accumulated within the centerline of the microchannel, increasing the variability of the greyscale range from white at the microchannel wall to black in the centerline. The change in variability indicated kinetics of Agg that occurred over 3 min of recording. The primary data of greyscale vs time (custom software) was fit to a sigmoid (dose response) curve, where the fitted EC50 was the T1/2 for Agg and with the fitted slope (p) indicated the kinetics of Agg. At 37 C the T1/2 was 93 s in 0% O2, 75 s with venous (5%) or arterial (10%) and was not different by group. As temperature increased, the T1/2 became significantly faster in blood from B or H (to 65 s), but not C. Correlation between temperature and the fitted T1/2 were significant in B (slope, R2; -2.9, 0.92), H (-2.7, 0.97) and C (-1.1, 0.6), but the F-test on the slope was significant for B (p=0.02) and H (0.04) not C (0.6). This coincided with a significantly steeper p for B and H. At venous, arterial or saturating O2, the effect of increasing temperature to decrease the T1/2 was much less pronounced, and not different between groups. This data shows that in only hypoxic conditions, with temperatures of 41 C (105.8 F) or higher, RBC from self-identified B or H subjects aggregates more readily than C. These results pertain to our focus of microvascular compromise in thermal burn injury progression, but also clinical conditions of localized cautery to control bleeding, high fevers or malignant hyperthermia.