Visual parameters define the phase and the load of contractions in isolated guinea pig ileum.

How the movements of the intestinal walls relate to luminal pressures and outflow remains incompletely understood. We triggered the peristaltic reflex in the isolated ileum of the guinea pig and quantified wall movements through computerized measurements of diameter changes. Contractions developed as indentations close to the upstream end of the loop. The indentations deepened and expanded in length. The downstream shoulder of contractions started and stopped to propagate before the upstream shoulder. Shoulders differed in their length and gradient over most of the duration of the contraction, and this gives the contraction an axial asymmetry. Over the course of individual contractions, the length of the indented segment correlated well with the luminal pressure. Contractions in response to large volumes generated long indented segments and high luminal pressures. The onset and the end of pressure waves and of outflow did not necessarily coincide with the onset and end of visual parameters of contractions. These findings indicate that objective visual parameters might be useful to describe and to classify contractions.