Introduction: Machine perfusion preservation is expected to be effective in small intestine transplantation, but there are few methods to evaluate its effectiveness, and it largely relies on histology. Histology has focused primarily on the mucosal layer of the small intestine, but the muscularis layer has not been evaluated. Therefore, we developed a method for evaluating the small intestinal muscular layer. This study aims to compare and evaluate Cold Storage (CS) and Hypothermic Machine Perfusion (HMP). We evaluated the viability of the muscularis layer by focusing on the serosal electrical　potential and peristalsis during ex vivo blood reperfusion, and also focused on the pathological evaluation of the small intestinal mucosa.
Methods:Pig small intestines were extracted with 0 minutes of Warm Ischemia Time　and were preserved in the CS group (CS 6 hours) or HMP group (CS 4 hours + HMP 2 hours), and then ex vivo blood reperfusion was performed for 2 hours. HTK was used as the preservation solution, and diluted autologous blood was used for reperfusion. Pathological evaluation was based on the Swerdlow Classification. In addition, the electrical potential difference between the mesentery and the intestinal surface during reperfusion was measured as the intestinal serosal potential, and peristalsis was measured from the captured video using Digital Image Correlation method.
Results: Small intestinal serosal potential was 4.4 vs 12.6 [-] (CS vs MP) at 100 minutes of reperfusion, and small intestinal peristalsis was 0.20 vs 0.35 [mm/s] (CS vs MP) at 90 minutes of reperfusion. There was a positive correlation of 0.8 between serosal electrical potential and peristalsis at 100 minutes of reperfusion. Serosal electrical potential and peristalsis during reperfusion tended to be greater in the MP group, and muscular layer was more active than in the CS group.  In the pathological examination, the mucosal tissue after preservation was Grade 1 in both CS group cases and Grade 0 and Grade 2 in both MP group cases. After reperfusion, mucosal necrosis was confirmed in two CS cases and one MP case, while the mucosa was preserved in the MP case. Damage to the intestinal mucosa by MP was non-inferior to CS.
Conclusion: The serosal electrical potential and peristalsis during reperfusion were shown to be useful methods for assessing small intestinal muscularis function.