Spatiotemporal mapping of ex vivo motility in the caecum of the rabbit
We used high definition radial, strain rate and intensity spatiotemporal mapping to quantify contractile movements of the body and associated structures of the rabbit caecum when the terminal ileum was being perfused with saline at a constant rate. This perfusion caused gradual distension of the caecum as a result of relative restriction of outflow from the ampulla caecalis. The body of the caecum exhibited two patterns of motility that appeared autonomous, i.e. occurred independently of any contractile activity at the inlet or outlet. Firstly, the pattern that we termed ladder activity consisted of an orderly sequential contraction of bundles of axially oriented circular muscle between the spiral turns of longitudinal muscle and proceeded either from base to tip or from tip to base at a similar frequency and velocity. Secondly, less-localised, rapidly propagating synchronous contractions of both circular and longitudinal muscle, which were more common when the caecum was distended, that were termed mass peristalsis. Movements of the ileum and sacculus rotundus occurred at the same frequency and were broadly coordinated. Distension of the distal sacculus occurred synchronously with contraction of the ileum and did not propagate in an orderly manner across the structure, i.e. was instantaneous. This pattern was consistent with hydrostatic distension. Contractions propagated through the ampulla caecalis in either an orad or an aborad direction at a similar frequency to, and broadly correlated with, those in the ileum. The frequencies of distension of the sacculus and of contraction in the ileum and ampulla were momentarily augmented during mass peristalsis. The authors conclude that there was some coordination between the contractile activity of the terminal ileum and the caecal ampulla during periods of ongoing inflow from the ileum and between these structures and the caecum during mass peristalsis.