Fistula size and hemodynamics: an experimental model in canine femoral arteriovenous fistulas.

PURPOSE: The objective was to evaluate the impact of anastomosis diameter on blood flow in an arteriovenous fistula (AVF), comparing two different anastomosis sizes with a modified side-to-side technique in canine femoral arteries. METHODS: Ten mongrel dogs were subjected to two AVFs each, both using a modified side-to-side technique. On one side, the anastomosis diameter was 1.5 times the arterial diameter and on the other side 3.0 times the arterial diameter. Mean proximal and caudal blood flow and mean venous flow were measured using an electronic flowmeter 15, 20 and 25 min after surgery. The Mann-Whitney, Friedman and Wilcoxon non-parametric tests were used for data analysis (alpha < or = 0.05). RESULTS: Femoral artery flow cranial to the fistula became 5.6 times greater in the 1.5 arterial diameter group, and 8.4 times greater in the 3.0 arterial diameter group, when compared to initial arterial flow. The mean flow in the cranial vein was greater in the 3.0 group (10.09 times greater vs. 6.46 times greater in the 1.5 group). Both in the proximal artery and in the vein there was a significantly greater flow in the group with the larger anastomosis diameter (Wilcoxon test). In the femoral artery caudal to the fistula, the flow in most of the animals was reversed: 3.5 times greater in the 1.5 group and 1.2 times greater in the 3.0 group, without statistical difference. CONCLUSIONS: These results suggest that 3.0 times the arterial diameter for the AVF size in dogs leads to greater venous flow than with 1.5 times the arterial diameter, without increasing the reversed flow.

Evaluation of the longitudinal musculature of segments of the distal colon interposed following extended jejunum-ileum resection.

Several morbid conditions may necessitate extensive intestinal resection, leading to short-bowel syndrome. When clinical treatment becomes inefficient, a surgical approach is necessary. Distal colon interposition is one of the viable techniques. The interposition of colon segments between remnants of the small bowel improved lifestyle, increased transit time, and diminished diarrhea. The aim of this study is to observe the longitudinal muscular contractions after distal colon interposition. Sixteen male Wistar rats (EPM-1) were submitted to an 80% small bowel resection associated with a partial colectomy of the distal colon immediately after the bifurcation of the middle colic artery followed by a 3-cm isoperistaltic distal colon interposition. After 70 days, the animals were submitted to euthanasia and segments of the jejunum, ileum, remnant colon, and interposed colon were prepared for pharmacological tests. The isometric contractions were measured by a polygraph. After 30 minutes, the dose/effect curves were obtained for both metacholine and barium chloride stimulation through the extraluminal surface (serosa). After this period, we observed a significant increase in the length, diameter, and thickness of the intestinal wall. Regarding the sensibility (pD(2)), no difference was found (interposed colon = 7.21 +/- 0.2; remnant colon = 7.65 +/- 0.1; remnant jejunum 7.46 +/- 0.1; and remnant ileum 7.57 +/- 0.1), even though the animals were submitted to different procedures. In relation to the maximal effect (E(max)), the longitudinal muscle contraction responses (interposed colon = 11.79 +/- 0.1; remnant jejunum = 15.42 +/- 0.2; and remnant ileum = 11.48 +/- 0.2) were lower than those of the remnant colon (E(max) = 22.42 +/- 0.1). This means that there was a possible adaptation of colonic segments to their new location.