Relation between flow-pressure-diameter studies in experimental stenosis of rabbit and human small bowel.

Abstract

Patients with inflammatory and ischaemic bowel diseases seem to tolerate narrowing of the gut lumen to a critical degree of stenosis without obstructive symptoms. To determine the physical factors involved in bowel occlusion, we created an experimental model using New Zealand rabbits in acute experiments under general anaesthesia. At operation a loop of small bowel was isolated and canulated, proximally for perfusion and pressure recording and distally to monitor flow. Having established the physiological pressure and flow conditions in a normal loop of gut, a stenosis was created using circular adjustable rings of determined widths. Pressure and flow were measured constantly and the variables studied were luminal diameter, stenosis length, and perfusate viscosity. This experimental model was reproduced using resected segments of human small bowel. We found a critical pointat 60% ofthe original diameter -down to which the small bowel is able to maintain normal flow. At a diameter smaller than this, the physiological parameters are rapidly altered up to the point of complete obstruction. In the rabbit model bowel rupture occurs at 30% of the initial size. Increased viscosity of the fluid and length of the stenosis alter this critical point inducing a larger critical diameter. We did not observe any cumulative effect of multiple identical stenoses.

Effects of feeding large amounts of grain on colonic contents and feces in horses

“…Results of a study 44 in rabbits indicate that gastrointestinal flow depends on intraluminal pressure, luminal diameter, and the viscoelastic properties of intestinal contents. Coordinated intestinal contractions generate pressure gradients to overcome the resistance to flow.…”

“…Coordinated intestinal contractions generate pressure gradients to overcome the resistance to flow. 44 The luminal diameter and rheologic properties of RDC contents are major factors that determine the resistance to flow. 42 Decreased intestinal diameter and increased viscosity of the contents increase resistance to flow up to a point where flow is interrupted.…”

“…42 Decreased intestinal diameter and increased viscosity of the contents increase resistance to flow up to a point where flow is interrupted. 44 Considering that these same principals may be valid for horses, it is likely that viscosity, not hydration, of contents is the key factor for the formation of gastrointestinal impaction. If dehydration of colonic contents was the only effect of grain ingestion, an increase in colonic content viscosity would be expected to occur.…”

Long-Term Results of Stapled and Hand-Sewn Anastomoses in Patients with Crohn’s Disease

“…Some reports, however, show that stapled anastomoses have a higher bursting pressure and a better blood supply than anastomoses made with sutures [9, 10, 11, 12]. Furthermore, an edematous anastomosis narrows the intestinal lumen, and the intraluminal pressure rises proximal to an intestinal stricture [13]. …”

Renal artery diameter, renal function and resistant hypertension in patients with low-to-moderate renal artery stenosis

“…Arterial remodeling limits change in wall shear stress [7]. Animal models suggested that the minimal diameter and luminal narrowing were related to pressure and flow [14] and that the relation between luminal narrowing and renal blood flow could be not linear [15].…”