Flow motion in the intestinal villi during hemorrhagic shock: a new method to characterize the microcirculatory changes.

Conventional parameters are often inadequate to describe the dynamic flow changes in microcirculation. We used a novel approach to characterize oscillatory flow conditions in a canine model of hemorrhagic shock. Microcirculation in the ileal mucosal villi was visualized using intravital microscopy with the orthogonal polarization spectral imaging technique. The distribution of red blood cell velocity (RBCV) was estimated from the relative time periods of observed RBCV, and the average RBCV (A-RBCV) and its SD were then computed from the first and second moments of the RBCV distribution, respectively. Hemorrhagic shock (for 60 min) was followed by resuscitation with saline, hypertonic saline-Dextran solution (HSD, 7.2% NaCl-10% Dextran, 4 mL/kg), or HSD supplemented with the selective endothelin-A receptor antagonist ETR-p1/fl peptide (100 nmol/kg), respectively. The macrohemodynamic derangement (70% decrease in cardiac index and ileal blood flow) during shock was associated with the appearance of flow motion in the villi and an enhanced endothelin-1 release. The calculated A-RBCV was decreased by 40%. At resuscitation onset, continuous flow periods were transiently seen in 33%, 40%, and 50% of the experiments after saline, HSD, and HSD + ETR p1/fl treatment, respectively. HSD with or without endothelin-A antagonist treatment resulted in an increased relative duration of high-flow periods (by 20%) and a significant, 20% to 40% rise in A-RBCV. These results demonstrate that time-wise variability of RBCV should be used for the analysis of oscillatory flow conditions. The probabilistic estimation of A-RBCV provides a quantitative basis for comparison of the effectiveness of different resuscitation or vasoactive strategies.