The Role of Red Blood Cells in Microvascular Blood Flow Alterations Caused by Gut Ischemia-Reperfusion Injury

Gut ischemia-reperfusion injury caused by various critical conditions (e.g. trauma-hemorrhagic shock, burn or sepsis) leads to the development of early multiple organ dysfunction syndrome (MODS). Microvascular blood flow alterations play an important role in initiation and manifestation of MODS. There are limited data showing that splanchnic hypoperfusion is associated with red blood cell (RBC) dysfunction. The role of RBCs in microvascular blood flow disorders caused by this acute state remains unknown. We tested the hypothesis that there is an interconnection between RBC deformability and shape abnormalities resulted from gut ischemia-reperfusion injury and alterations in microvascular blood flow and oxygen delivery in distant organs and tissues. Rat model of superior mesenteric artery occlusion (SMAO) lasting for 45 minutes, and followed by 3 hours of reperfusion was used to re-create gut ischemia-reperfusion injury. Rats subjected to sham SMAO were anesthetized, had a laparotomy, and had their superior mesenteric artery looped with a suture, but the vessel was not occluded.  End-point parameters were determined at the end of a reperfusion period. Microvascular blood flow in the liver and femoral muscle, as well as muscle pO₂ were measured by Oxyflow and Oxylite monitors. RBC shape and deformability were determined by scanning electron microscopy and laser ectacytometry, correspondingly. Bessis' classification was used to evaluate RBC shape changes. Elongation index (EI) served as a measure of RBC deformability. SMAO followed by 3 hour reperfusion period resulted in significantly decreased microvascular blood flow in the liver and femoral muscle, compared to sham SMAO (see Table). Muscle PO₂ was also significantly decreased. SMAO-induced microvascular blood flow and oxygen delivery disorders were associated with RBC deformability and shape alterations. RBC Elongation Index was significantly decreased 3 hours after SMAO. The percentage of abnormal RBCs was significantly increased in SMAO animals, whereas the percentage of normal discocytes was decreased. Abnormal RBCs were mainly presented by echinocytes and spheroechinocytes. Linear regression showed a tight inverse correlation between the percentage of abnormal RBCs and the levels of hepatic and muscular microvascular blood flow (r = -0.82 and -0.84, correspondingly, p<0.01). There was also a correlation between RBC Elongation Index and microvascular blood flows in the liver and muscle (r = 0.76 and 0.78, correspondingly, p<0.01).  These data indicate that microvascular disorders in the liver and femoral muscle resulted from gut ischemia-reperfusion injury are caused at least in part by RBC deformability and shape alterations.

Parameters	Groups of Animals
	SMAO (n=8)	Sham SMAO (n=8)
Liver Blood Flow (units)	509.6±138.8*	1211.7±272.4
Muscle Blood Flow (units)	163.5±82.1*	483.9±238.7
Muscle PO2 (mm Hg)	32.0±7.2*	66.2±7.3
Percentage of Normal Discocytes (%)	88.65±3.42*	94.07±1.93
Percentage of Abnormal Shaped RBC (%)	11.35±3.57*	5.93±2.08
RBC Elongation Index	0.051±0.009*	0.064±0.005

* p<0.05 vs. Sham SMAO