Colonic motility: practice or research?

Disorders of colonic motility are thought to play a part in several diseases, especially the irritable bowel syndrome, and also ulcerative colitis, diverticular disease, and constipation. The genesis of abdominal pain or disordered bowel habit is generally ascribed to abnormal colonic motor function. Despite research contributions from many countries the normal and pathological motor function of the colon remains poorly understood. This is due in part to the relative inaccessibility of the organ, its regional differences in structure and function,'2 and to the capricious nature of motor events in the large bowel. It is difficult to measure colonic function simultaneously in its various parts and it is erroneous to extrapolate findings from one part to another. Ritchie hoped that manometry would prove a 'safe and reliable method of studying colonic movements'3 and in 1965 Deller and Wangel4 expressed the view that understanding of intestinal motility may progress if pertinent problems were recognised. They pointed out that motility patterns in normal subjects needed to be described in more detail, that the relation between pressure and transit needed to be further investigated, and that the analysis and classification of pressure waves had to be standardised and quantified. Although some of these points have been considered, our understanding of colonic function has not increased much and measurements of colonic pressures have not found their way into routine clinical practice; measurements of transit have a more practical value in selected patients. Why is it that clinical usefulness of colonic pressure measurements remains elusive? The answer is partly methodological and partly dependent on the physiology of colonic smooth muscle. Colonic motility can be conveniently considered under two related aspects, intraluminal pressure activity and transit of intraluminal contents. The second has been measured by studying the movements of barium,5 or radio-opaque shapes6 and more recently radioactive isotopes.7 Radio-opaque shapes are clinically the most useful for quantifying colonic transit; movement of barium involves unacceptably high doses of radiation and radioisotope studies need access to imaging equipment and the patient has to be immobilised during the scans. Formulae have been devised to measure segmental colonic transit with radio-opaque shapes.8 The need for repeated abdominal radiographs can be avoided by a modification of this technique and segmental transit can be measured from a single x ray film taken after the serial ingestion of radio-opaque shapes for three days. This minimises exposure of the patient to radiation. If the stools, rather than the patient's abdomen are screened for the shapes, there is no radiation risk but this approach is inconvenient. Slow transit constipation can be distinguished from outlet obstruction by the ingestion of a capsule containing 20 shapes followed by an abdominal x ray film taken on the fifth day; 80% retention of the markers signifies slow colonic transit. These simple methods can be used clinically to help establish a diagnosis and to measure the effect of treatment; they are also useful in research. Colonic pressures can be measured with balloons, continually perfused catheters, freely mobile pressure sensitive radiotelemetry capsules, or solid state tube mounted strain gauges, each measuring different aspects of colonic motor function. Most studies use water perfused catheters. Solid state transducers have the important advantage that they can be used in the ambulatory patient and are becoming readily available. Hardware and software exist for prolonged computerised collection (including the ambulant patient) and analysis of data.9 The positioning of the recording devices in the colonic lumen and cleansing of the bowel before pressure measurements remain non-standardised. It seems logical to study unprepared bowel in an unsedated patient, but this limits studies to the distal colon or requires invasive and time consuming intestinal transtubation. Morphology of individual colonic pressure waves has eluded reliable classification. This has led to the concept of the motility index (area under the time pressure curve) to describe pressure activity. This has the advantage of being expressed as a number and is thus amenable to statistical analysis, but it does not recognise different types of colonic pressure waves. As pressure measurements obtained from colonic probes 5 cm apart can be very different, some workers have summed the pressure activity from adjacent channels to obtain a value for the colonic segment under study as a whole in an attempt to standardise analysis.9 Colonic motor function has also been investigated with electromyography, the electrodes being attached to the mucosa in the intact human. '0 A background slow variation in electrical potential has been described (basal electrical rhythm) with superimposed shorter duration, larger amplitude potentials (spike potentials or electrical response activity). The basal electrical rhythm controls the occurrence of the electrical response activity, which is thought to correlate with colonic smooth muscle contraction. Normal motility of the small intestine in the fasting state is characterised by the cyclical appearance of the migrating motor complex. This is a high amplitude burst of contractions that start in the stomach and are propagated distally into the lower small bowel. After eating, this regular coordinated activity gives way to irregular, non-propagated pressure 1009