Biomedical subjects
Publications and source records attributed to B Lestar.
We determined the maximum closing capability of the internal anal sphincter muscle ring in vitro and in vivo. The internal sphincter, 4 to 6 mm thick, cannot close the anal canal hermetically, not even during maximal contraction. The blood-filled anal cushions have to fill up an intrasphincteric gap of at least 7 to 8 mm in diameter.
The human IAS has particular structural and functional characteristics. This smooth muscle constantly generates rhythmic electrical slow waves, but no action potentials. The slow waves are linked to calcium fluxes and both are essential for mechanical activity, i.e. the ASPW. The IAS is pharmacologically characterized by the presence of alpha excitatory and beta inhibitory adrenergic receptors. Cholinergic drugs have an indirect effect through the release of an inhibitory neurotransmitter, very probably VIP, from NANC nerves. The myogenic activity of the IAS is enhanced by its extrinsic sympathetic innervation. Thus, at rest, the IAS is in a state of partial tetanus and contributes approximately 55% of the MABP. Because the IAS ring cannot be completely closed, the anal mucosa and the haemorrhoidal plexuses fill the gap. By compressing these tissues, the IAS perfectly closes the anal canal to retain not only solids but also fluid stool and gas. Acute rectal distension and rectal activity, mainly through intramural pathways, induce reflex IAS relaxation, permitting the rectal contents to be sampled by receptors in the upper anal canal while continence is temporarily maintained by EAS activity and by expansion of the haemorrhoidal cushions. There is a correlation between the volume of rectal distension and the parameters of IAS relaxation. At maximal IAS relaxation, ASPW are absent, indicating the completeness of the inhibition. Although this RAIR is not essential for defecation, insufficient relaxation may be implicated in constipation. Hyperactivity of the IAS resulting in a high MABP and AUSPW has been considered both as a cause and as an effect in haemorrhoids and anal fissure. Continence for fluids and gas is impaired if IAS activity is decreased (i.e. a low MABP), either by direct trauma or by damage of its sympathetic innervation. Severe faecal incontinence will develop when the contractility of both the IAS and the EAS is affected.
Seven experts drew the rectal axes of 18 representative proctographic images on two occasions, with a 1-year interval, in order to assess intraobserver variation in the determination of the anorectal angle (ARA). Intraobserver variation (6%) and interobserver variation (17%) were smallest when the central rectal axis was used to determine the ARA. A strong relation was found between inter- and intraobserver variation (r = 0.77). Intraobserver variation tended to be rather small for pictures made during straining, but a relation with the magnitude of the ARA was not found. Although none of the seven experts could reproduce the rectal axes with less than or equal to 10% variation in all 18 pictures, redrawing of the central rectal axis delivered less than or equal to 10% variation in 86% of determinations. It is concluded that intraobserver variation is influenced by the expertise of the investigator, the method of analysis, and the anorectal configuration to be analyzed. Radiologic assessment of the ARA may yield reliable data on the dynamics of the anorectum if performed by a single investigator on x-ray films that allow confident analysis.
Determination of the anorectal angle (ARA) and the position of the pelvic floor is, theoretically, very important in understanding the mechanisms of anorectal continence and defaecation. The variability in the measurement of the ARA was analyzed. Nine experts drew ther rectal axis either as a line along the posterior wall of the distal rectum or as the central axis of the rectal lumen on the outlines of 18 representative proctographic images. The standard deviations and ranges of the mean values of each ARA were comparable but large in both methods. On average, the S.D. was 8 degrees and the range value about 23 degrees. Inter-observer variation was not related to the magnitude of the ARA, but rather to the anorectal configuration. Drawing a line along the posterior distal rectal wall is difficult when it is irregular or when the puborectalis impression is indistinct. The central rectal axis is difficult to draw when the junction between the upper and lower rectum is ill defined or when the outlines of the distal rectum are asymmetric e.g. by the presence of a rectocele. Thus, the variability of both methods was not strongly interrelated (r = 0.68 for the median values). It is concluded that, in general, radiologic assessment of the ARA is not reliable enough for comparative investigation of the dynamics of the anorectum.
Explore the source record for details and available documents.
The maximal anal basal pressure (MABP) was measured with probes of 0.3, 1, 2 and 3 cm diameter in 21 subjects, 60 years old, without anal pathology. The components of MABP were analyzed by inducing a maximal internal sphincter (IS) relaxation, taking pressure measurements in the conscious state and during narcosis with curarization. In seven cases pressure measurements were done on isolated anorectum after abdominoperineal rectum amputation. MABP increases with probe diameter before as well as during anaesthesia with curarization. The contribution of the striated sphincter tonic activity is constant within the range of probe diameters used. At rest, i.e. when the 0.3 cm diameter pressure recording probe is used, 30% of MABP is made up by striated sphincter tonic activity, 45% of it is due to nerve induced IS activity, 10% to purely myogenic IS activity and 15% can be attributed to the expansion of the haemorrhoidal plexuses. Although MABP is mainly based on active forces generated by the smooth and striated sphincter apparatus, the presence of the anal cushions is essential for perfect anal continence, as they have to fill the gap within the IS ring to hermetically close the anal canal. The global IS activity, contributing 50-60% of MABP at rest, can completely be inhibited by a maximal rectoanal inhibitory reflex. Stretching of passive elements starts at 1 cm anal distension, but steeply increases thereafter, accounting for 65% of the MABP at 3 cm anal distension. It is deduced that optimal stool diameter is about 2 cm.
Explore the source record for details and available documents.