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

OBJECTIVE: 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. METHODS: 5 mature female minipigs (mean body weight 50 ±â€¯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. RESULTS: 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 (pM2 vs. M1 < 0.0001, pM2 vs. M3 = 0.0005, pM2 vs. M4 = 0.0005) and the adjusted p-values (pM2 vs. M1 < 0.0001, pM2 vs. M3 = 0.0030, pM2 vs. M4 = 0.0030). In the SC, the difference between ischemia and flow reduction was significant according to the unadjusted p-values (pM2 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: pM2 = 0.0001), velocity (inner probe: pM1 < 0.0001, pM2 = 0.0155, pM3 = 0.0027; outer probe: pM1 < 0.0001, pM2 = 0.0045, pM3 = 0.0047, pM4 = 0.0037) and serosal flow (outer probe, methods 1 and 2: p < 0.0001; pM3 = 0.0009, pM4 = 0.0008). The histopathological analysis showed a significant association with time (p = 0.003) but not with the experimental method (p = 0.1386). CONCLUSIONS: 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.

Evaluation of the NMR-MOUSE as a new method for continuous functional monitoring of the small intestine during different perfusion states in a porcine model.

OBJECTIVE: The study aim was to evaluate a small low-field NMR (nuclear magnetic resonance) scanner, the NMR-MOUSE®, for detecting changes in intestinal diffusion under different (patho-) physiological perfusion states. METHODS: Laparotomy was performed on 8 female landrace pigs (body weight 70±6 kg) and the feeding vessels of several intestinal loops were dissected. Successively, the intestinal loops were examined using O2C (oxygen to see, LEA Medizintechnik GmbH, Giessen, Germany) for microcirculatory monitoring and the NMR-MOUSE® for diffusion measurement (fast and slow components). On each loop the baseline measurement (physiological perfusion) was followed by one of the following main procedures: method 1 -ischemia; method 2 -flow reduction; method 3 -intraluminal glucose followed by ischemia; method 4 -intraluminal glucose followed by flow reduction. Additionally, standard perioperative monitoring (blood pressure, ECG, blood gas analyses) and histological assessment of intestinal biopsies was performed. RESULTS: There was no statistical overall time and method effect in the NMR-MOUSE measurement (fast component: ptime = 0.6368, pmethod = 0.9766, slow component: ptime = 0.8216, pmethod = 0.7863). Yet, the fast component of the NMR-MOUSE measurement showed contrary trends during ischemia (increase) versus flow reduction (decrease). The slow-to-fast diffusion ratio shifted slightly towards slow diffusion during flow reduction. The O2C measurement showed a significant decrease of oxygen saturation and microcirculatory blood flow during ischemia and flow reduction (p < .0001). The local microcirculatory blood amount (rHb) showed a significant mucosal increase (pClamping(method 1) = 0.0007, pClamping(method 3) = 0.0119), but a serosal decrease (pClamping(method 1) = 0.0119, pClamping(method 3) = 0.0078) during ischemia. The histopathological damage was significantly higher with increasing experimental duration and at the end of methods 3 and 4 (p < .0001,Fisher-test). CONCLUSION: Monitoring intestinal diffusion changes due to different perfusion states using the NMR-MOUSE is feasible under experimental conditions. Despite the lack of statistical significance, this technique reflects perfusion changes and therefore seems promising for the evaluation of different intestinal perfusion states in the future. Beforehand however, an optimization of this technology, including the optimization of the penetration depth, as well as further validation studies under physiological conditions and including older animals are required.