Perfusion-related changes in intestinal diffusion detected by NMR-MOUSE® monitoring in minipigs

The aim was to investigate perfusion-related changes in the intestinal diffusion assessed by NMR-MOUSE monitoring in minipigs. This was a follow-up study of previous experiments on landrace pigs demonstrating the feasibility of NMR-MOUSE monitoring in large animals.

5 mature female minipigs (mean body weight 50 ± 2 kg) underwent laparotomy with exposition of several small intestinal loops and their feeding vessels. The loops were examined consecutively using NMR-MOUSE monitoring for assessment of intestinal proton diffusion (fast diffusion component [FC] and slow diffusion component [SC]) and oxygen to see monitoring (O2C, LEA Medizintechnik GmbH, Giessen, Germany) for microcirculatory evaluation. Following a baseline measurement on each loop under physiological perfusion, measurements were continued as one of the following main treatments were performed per loop: method 1 - ischemia; method 2 - flow reduction; method 3 - intraluminal glucose followed by ischemia; method 4 - intraluminal glucose followed by flow reduction. Perioperative monitoring was supplemented by blood gas analyses and histopathological assessment of H.E. stained intestinal biopsies.

The NMR-MOUSE measurement showed a significant difference in the change to baseline values in the FC during flow reduction compared to the other treatments according to the unadjusted (p_{M2 vs. M1} < 0.0001, p_{M2 vs. M3} = 0.0005, p_{M2 vs. M4} = 0.0005) and the adjusted p-values (p_{M2 vs. M1} < 0.0001, p_{M2 vs. M3} = 0.0030, p_{M2 vs. M4} = 0.0030). In the SC, the difference between ischemia and flow reduction was significant according to the unadjusted p-values (p_{M2 vs. M1} = 0.0397). Whereas the FC showed a trend towards ongoing increase during ischemia but towards ongoing decrease during flow reduction, the SC showed contrary trends. These effects seemed to be attenuated by prior glucose application. According to the results of O2C monitoring, ischemia as well as flow reduction caused a significant decrease of microcirculatory oxygen saturation (inner probe: methods 1-4 and outer probe methods 1, 2: p < 0.0001; outer probe: p_M2 = 0.0001), velocity (inner probe: p_M1 < 0.0001, p_M2 = 0.0155, p_M3 = 0.0027; outer probe: p_M1 < 0.0001, p_M2 = 0.0045, p_M3 = 0.0047, p_M4 = 0.0037) and serosal flow (outer probe, methods 1 and 2: p < 0.0001; p_M3 = 0.0009, p_M4 = 0.0008). The histopathological analysis showed a significant association with time (p = 0.003) but not with the experimental method (p = 0.1386).

Intestinal diffusion is affected significantly by perfusion changes in mature minipigs. As shown by NMR-MOUSE monitoring, ischemia and flow reduction have contrary effects on intestinal diffusion and, additionally, the fast and slow diffusion components show opposite trends during each of those pathological perfusion states. Prior intraluminal glucose application seems to attenuate the effects of malperfusion on intestinal diffusion.