Studies on the Rectosigmoid Brake and its Therapeutic Significance

Abstract

Colonic motility disorders and faecal incontinence affect at least one-third of the adult population. However, patient satisfaction with treatment outcomes is often poor. This lack of effective therapies is largely due to incomplete understanding of colonic motor patterns and their underlying control mechanisms. A distal braking mechanism in the colon, or rectosigmoid brake, has been hypothesised for many decades; however, descriptions remain vague. This thesis aimed to clarify the physiology and clinical significance of the ‘rectosigmoid brake’. Narrative and systematic reviews of existing literature on the rectosigmoid brake were undertaken. A porcine model was developed, and high-resolution (HR) recordings and sacral nerve stimulation were applied to this model. While technical success was achieved, as opposed to the stomach and small intestine, it was determined that an anaesthetised pig is not a suitable model for the study of colon motility. The anatomical correlation of ‘rectosigmoid brake’ activity was defined using HR manometry. The most likely motor pattern involved in the brake in healthy colon is the cyclic motor pattern most prominently seen in the rectosigmoid region travelling in the retrograde direction. This motor pattern appears to occur independent to proximal propagating sequences but is strongly associated with a meal, suggesting an underlying neurogenic control mechanism. The electrophysiological basis of the rectosigmoid brake was studied using intraoperative recordings in patients undergoing abdominal operations. While prominent cyclic activity was shown manometrically, no consistent slow waves were observed in the corresponding region of the colon, suggesting—in contrast to the current theory that the interstitial cells of Cajal and associated slow waves are responsible for the cyclic motor pattern—that a neurogenic mechanism predominates. The potential role of the rectosigmoid brake as a therapeutic target in faecal incontinence was investigated. Patients have altered cyclic motor patterns, and sacral nerve stimulation increases the number of retrograde propagating motor patterns. Last, an objective automated method was developed for high-throughput HR manometry data analysis, and validated using the current manual analysis method. Overall, this thesis presents the rectosigmoid brake as a potential therapeutic target for colonic motility disorders, as well as various advances in the study of colonic motility, and serves as a platform for future research.