Effects of Motility and Luminal Distension on Dog Small Intestine Hemodynamics

Abstract

The effects of spontaneous intestinal motor activity and artificial luminal distension on mesenteric hemodynamics were studied on isolated canine jejunal loops perfused at normothermia under pulsatile flow with heparinized and oxygenated dogs whole blood. To each increase in intestinal tonic activity or intraluminal distension there is a corresponding linear increase in arterial pressure (under constant flow). The hemodynamic effect of distension is less potent than that produced by spontaneous motility. In the luminal pressure range explored (<25 mm Hg) distension does not modify the intestinal O₂ consumption. Spontaneous rhythmic contractions produce oscillations of the venous outflow of the same periodicity as the phasic activity of the bowel and having a magnitude proportional to the strength of the contractions. These results show that intestinal motility or gut lumen distension affects mesenteric hemodynamics by increasing the resistance to blood flow. The linearity of the responses and the absence of any readjustment of the vascular resistance during either tonic contraction or distension seem to indicate a vascular effect resulting only from a mechanical compressing action on the blood vessels. No drastic and irreversible hemodynamic and functional impairments, however, could be observed when the intraluminal pressures involved remain moderate ( < 25 mm Hg). On the other hand the periodic fluctuations of the venous outflow produced by the rhythmic activity may contribute to the mixing and to the propulsion of the mesenteric blood to the portal circulation.

Gastrointestinal circulation and motor function

“…The failure of distension to reduce oxygen consumption was attributed to higher resting blood flow in the denervated gut. In the constant-flow preparation, distension to lumen pressures of below 25 mmHg (the level similar to that of the previous study) did not significantly alter intestinal oxygen consumption (109). These findings seem to indicate that the decreased oxygen consumption observed in the innervated gut (121) is secondary to distension-induced decrease in blood flow.…”

“…The effect of luminal distension in decreasing blood flow is less than that of the contraction for the same increment in lumen pressure (16, 1.09). Kachelhoffer et al (109) have shown that for each 1-mmHg rise in lumen pressure, the rise in vascular resistance produced by sustained spontaneous tonic contractions was 1.61 times that produced by luminal distension. There are other reasons for the more limited effect of luminal distension in decreasing total intestinal blood flow.…”

“…With the constant-flow preparation, Kachelhoffer et al (109) found that stepwise distension of the jejunal loops to a constant lumen pressure produced corresponding increases in perfusion pressure and that there was a linear relationship between the rises in distension pressure and the corresponding rises in perfusion pressure (A perfusion pressure, 0.57; A lumen pressure, 0.21). The study was performed with a basal lumen pressure of -7 mmHg, and the increases in lumen pressure ranged between 2 and 15 mmHg.…”

Interaction between blood flow and motility in normal and inflamed ileum

“…A few studies 1 –5 have investigated the relationship between individual contractions of the small intestine and blood flow. These studies were done mostly on anaesthetized animals using intact or isolated segments.…”

Evaluation of Techniques That Measure Hydrogen and Methane Levels in Breaths of Horses with Gastrointestinal Diseases

“…Thus, GI tract disorders, such as ileus, can cause stagnation of gases and contents as well as dilation of the GI tract. The resulting increase in pressure in the GI tract may impair circulation and cause ischemia in the GI tract [5,9]. Therefore, the decrease in gas levels in breaths that was observed in horses with GI diseases in this study may have been due to impairment of circulation.…”