ABSTRACT

Constipation and incontinence are associated with several diseases and cause major impairment on social life. To be faecal continent is a complex process involving integration of somatic and visceral muscle function with sensory information under local, spinal and central nervous system control.

A new probe based on the principle of impedance planimetry was developed and validated in vitro and in vivo in order to investigate dynamic rectal motility patterns at several levels simultaneously. The probe was able to outline complex configurations in vitro and when applied in vivo, in the Göttingen Minipig, spontaneous events accompanied with passage of flatus were observed. The rectal configuration during these events demonstrated a complex configuration with a decrease in cross sectional area (CSA) in the proximal part of the rectum and an increase in the distal part. The results indicate that the probe as well as the animal model might be an alternative to other established methods.

Neurohumeral control of ano-rectal motililty is complex and poorly understood. Stimulation of the pelvic nerve (PN) elicited a differentiated response in the rectum identical to the spontaneous events during basal conditions, which seemed to facilitate defecation. A decrease in anal pressure observed in the majority of experiments during PN stimulation supports this. Stimulation of the hypogastric nerve (HGN) elicited an increase in anal pressure and no response in the rectum, which was abolished after the administration of phentolamine. Additionally, the anal pressure increase to pudendal nerve (PuN) stimulation was abolished after the administration of pancouronium. The results indicate an excitatory as well as inhibitory effect of PN stimulation to the rectum. The HGN and the PuN exert an excitatory effect on the internal anal sphincter (IAS) and the external anal sphincter (EAS) respectively. The differentiated rectal response and the interaction with the anal canal obtained with the probe indicate that the probe may have a place in future investigations concerning ano-rectal motility.

Selective activation of the rectum without activation of the EAS was feasible. Selectivity was obtained by blocking, distal to the excitation side, the induced neural activity in the large fibres innervating the EAS, using an anodal block. The result was a reduction of the anal pressure increase to stimulation showing that the undesirable contraction of the EAS in response to sacral root stimulation can largely be reduced. The technique used may allow a more physiological defecation in patients with spinal cord injuries. However, future investigations may elucidate whether defecation can be achieved. Another important issue to investigate is how the technique works in an implanted system.