INTRODUCTION Despite current generation mechanical assist devices being designed to limit shear stresses and minimise damage to formed elements in blood, severe secondary complications suggestive of impaired rheological functioning are still observed. At present, the precise interactions between the magnitude-duration of shear stress exposure and the deformability of red blood cells (RBC) remain largely undescribed for repeated subhaemolytic shear stress duty-cycles of less than 15 s. Given that the time taken for blood to traverse mechanical devices (e.g., Bio Pump) typically ranges from 1.85-3.08 s, the present study examined the influence of repeated, short duration, supraphysiological shear stress exposure on RBC function. METHODS RBC were exposed to shear stress duty-cycles of 64 Pa × 3 s or 88 Pa × 2 s, for 10 repeated bouts, in an annular Couette shearing system and ektacytometer. Laser diffractometry was used to measure RBC deformability before and after application of each duty-cycle. Free haemoglobin concentration and RBC morphology was also examined following shear exposure to determine cell viability. RESULTS Initial exposure to shear stress duty-cycles decreased RBC deformability and increased RBC sensitivity to mechanical damage. Interestingly, the pattern of change in these variables reversed and returned to baseline values within two successive duty-cycle exposures. Significant improvements in RBC deformability were then observed by the 9th repeated exposure to 64 Pa × 3 s. CONCLUSIONS Repeat applications of short duration supraphysiological, subhaemolytic shear stress induces a biphasic RBC deformability response that appears to progressively improve initially impaired RBC populations.

中文翻译：

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红细胞变形能力的双相性损害，是由于反复的，短期的超生理性，溶血性切应力暴露引起的。

引言尽管当前的机械辅助装置被设计为限制剪切应力并使血液中形成的元素的损害最小化，但仍观察到严重的继发性并发症，提示流变功能受损。目前，对于重复的低于溶血的剪切应力小于15 s的循环，剪切应力暴露的持续时间与红细胞的可变形性之间的精确相互作用仍未得到充分描述。考虑到血液穿过机械装置（例如，生物泵）所花费的时间通常为1.85-3.08 s，因此本研究研究了反复，短时间，超生理切应力暴露对RBC功能的影响。方法RBC暴露于64 Pa×3 s或88 Pa×2 s的剪切应力占空比下，重复10次，在环形Couette剪切系统和ektacytometer中。在应用每个占空比之前和之后，使用激光衍射仪测量RBC的可变形性。剪切暴露后还检查了游离血红蛋白浓度和RBC形态，以确定细胞活力。结果最初暴露于剪切应力占空比会降低RBC的可变形性，并增加RBC对机械损伤的敏感性。有趣的是，这些变量的变化模式在两次连续的占空比暴露中反转并返回到基线值。第9次重复暴露于64 Pa×3 s后，观察到RBC的可变形性有了显着改善。结论重复短时间的超生理学应用，