We conducted numerical experiments to study the influence of non-propagating longitudinal and circular contractions, i.e. pendular activity and segmentation, respectively, on flow and mixing in the proximal duodenum. A lattice-Boltzmann numerical method was developed to simulate the fluid mechanical consequences for each of 22 randomly selected sequences of high-definition video of real longitudinal and radial contractile activity in the isolated proximal duodenum of the rat and guinea pig. During pendular activity in the rat duodenum, the flow was characterized by regions of high shear rate. Mixing was so governed by shearing deformation of the fluid that increased the interface between adjacent domains and accelerated their interdiffusion (for diffusion coefficients approx. less than 10 28 m 2 s 21). When pendular activity was associated with a slow gastric outflow characteristic of post-prandial period, the dispersion was also improved, especially near the walls. Mixing was not promoted by isolated segmentative contractions in the guinea pig duodenum and not notably influenced by pylorus outflow. We concluded that pendular activity generates mixing of viscous fluids 'in situ' and accelerates the diffusive mass transfer, whereas segmentation may be more important in mixing particulate suspensions with high solid volume ratios.

Localized contractions during segmental and pendular activity had some features of the spike patches that are normally associated with slow wave propagation. However, the commencement of propagation following administration of neural blocking agents and cholinergic inhibitors indicates their localization is maintained by inhibitory elements of the enteric nervous system.

We describe a mechanism by which peripheral mixing may be engendered by mucosal microfolds without requiring the coordinated contraction of individual villi or groups of villi.

We studied the caecal contractile activity of the chicken (Gallus gallus) using single caeca that had been cannulated at their proximal and distal ends, and in paired caeca, maintained in situ on excised segments of gut that were cannulated at the colonic and small intestinal ends. Longitudinal and circular contractile patterns were characterised using high-definition spatiotemporal mapping. Low amplitude longitudinal contraction waves of frequency 14.1 cycles/min occurred in the absence of major contractile events. These were termed fast phasic and appeared to be mediated by slow waves. The nature of major spontaneous contractions occurring in the single caecum varied with the level of caecal distension. Type A contractions occurred when the caecum was not distended, originated from variable sites and propagated in both directions. Type B or C contractile events occurred when the caecum was moderately or fully distended, originated from a predominantly distal site and propagated proximally. On diameter maps, each type B event comprised a succession of contractions which had similar propagation speeds, frequency and direction to fast phasic contractions. Type C events were comprised of a succession of higher amplitude contractions with no appreciable propagation. Perfusion of saline via the colon resulted in fluid entering both caeca and the onset of aborad contractions in their proximal canals. Saline was also seen to flow between caeca during contractile events however no saline was seen to enter the small intestine as has been postulated by other workers.

ObjectivesTo characterise the area and movements of ongoing spontaneous localised contractions in the resting porcine urinary bladder and relate these to ambient intravesical pressure (P ves ), to further our understanding of their genesis and role in accommodating incoming urine. Materials and MethodsWe used image analysis to quantify the areas and movements of discrete propagating patches of contraction (PPCs) on the anterior, anterolateral and posterior surfaces of the urinary bladders of six pigs maintained ex vivo with small incremental increases in volume. We then correlated the magnitude of P ves and cyclic changes in P ves with parameters derived from spatiotemporal maps. ResultsContractile movements in the resting bladder consisted only of PPCs that covered around a fifth of the surface of the bladder, commenced at various sites, and were of %6 s in duration. They propagated at around 6 mm/s, mainly across the anterior and lateral surface of the bladder by various, sometimes circular, routes in a quasi-stable rhythm, and did not traverse the trigone. The frequencies of these rhythms were low (3.15 cycles/min) and broadly similar to those of cyclic changes in P ves (3.55 cycles/min). Each PPC was associated with a region of stretching (positive strain rate) and these events occurred in a background of more constant strain. The amplitudes of cycles in P ves and the areas undergoing PPCs increased after a sudden increase in P ves but the frequency of cycles of P ves and of origin of PPCs did not change. Peaks in P ves cycles occurred when PPCs were traversing the upper half of the bladder, which was more compliant. The velocity of propagation of PPCs was similar to that of transverse propagation of action potentials in bladder myocytes and significantly greater than that reported in interstitial cells. The size of PPCs, their frequency and their rate of propagation were not affected by intra-arterial dosage with tetrodotoxin or lidocaine. ConclusionsThe origin and duration of PPCs influence both P ves and cyclic variation in P ves . Hence, propagating rather than stationary areas of contraction may contribute to overall tone and to variation in P ves . Spatiotemporal mapping of PPCs may contribute to our understanding of the generation of tone and the basis of clinical entities such as overactive bladder, painful bladder syndrome and detrusor overactivity.