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Techniques in Coloproctology
Published in: Techniques in Coloproctology 6/2012

01-12-2012 | Original Article

Defecation 2: Internal anorectal resistance is a critical factor in defecatory disorders

Authors: M. Bush, P. Petros, M. Swash, M. Fernandez, A. Gunnemann

Published in: Techniques in Coloproctology | Issue 6/2012

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Abstract

Background

The aim of this study was to test our hypothesis that the reason why imaging is of little assistance in diagnosing “constipation” causes may be related to the high sensitivity of internal anorectal flow resistance in defecation to small changes in geometry. We applied a mathematical model to describe the effects on flow mechanics of observed changes in the shape of the rectum and anus during defecation.

Methods

Three groups of patients were studied with video proctograms. Group 1 comprised 4 patients with normal defecation studied with video proctography or magnetic resonance imaging (MRI). Group 2 comprised 8 patients with fecal incontinence, studied by video X-ray electromyography. Group 3 comprised 8 patients with constipation evaluated by video MRI.

Results

Three muscle vectors open the anorectal angle prior to defecation, causing the anorectal luminal diameter to increase to approximately twice its resting size. These vectors are forwards (anterior wall), backwards and downwards (posterior wall). Resistance to passage of a fecal bolus through the anorectum is determined by viscous friction against the anorectal wall and by the energy required to deform the bolus as it flows. The observed changes in anorectal geometry serve to reduce both the viscous friction in the anus and the deformation of the bolus, which reduces the force required to facilitate its passage through the anus. For example, if the effective diameter of the anus is doubled during defecation, the frictional resistance is reduced by a factor of 8.

Conclusions

The sensitivity of flow resistance to geometry explains why MRI or computed tomography (CT) scans taken during defecation are not often helpful in diagnosing causation. Small changes in geometry can have a disproportionate affect on flow resistance. Combining accurate directional measurements during dynamic MRI or CT scans taken during defecation with observations of bolus deformation, and if possible, simultaneous anorectal manometry, may provide clinically helpful insights on patients with anorectal evacuation disorders.
Literature
1.
Petros P, Swash M, Bush M, Fernandez M, Gunnemann A, Zimmer M (2012) Defecation 1—Testing a hypothesis for pelvic striated muscle action to open the anorectum. Tech Coloproctol (in press)
2.
Petros PE, Ulmsten U (1997) Role of the pelvic floor in bladder neck opening and closure 1: muscle forces. Int Urogynecol J Pelvic Floor Dysfunct 8:74–80PubMedCrossRef
3.
Bush MB, Petros PEP, Barrett-Lennard BR (1997) On the flow through the human urethra. J Biomechanics 30:967–969CrossRef
4.
Farag A (2009) The use of flow equation in functional coloproctology: a new theory in anorectal physiology. Pelviperineology 8:17–23
5.
White FM (2002) Differential relations for a fluid particle. In: Fluid mechanics, 5th edn. McGraw Hill, Boston, pp 215–275
6.
Bird RB, Armstrong RC, Hassager O (1987) The generalised newtonian fluid. In: Dynamics of polymeric liquids Vol 1. Fluid dynamics, 2nd edn. Wiley, New York, pp 169–233
7.
Ritter AB, Hazelwood V, Valdevit A, Ascione AN (2011) Principles and biomedical applications of hemodynamics. In: Biomedical engineering principles, 2nd edn. Taylor and Francis, Boca Raton, USA, pp 151–205
8.
Bush MB, Moron C, Messner-Pellenc L, Petros PE, Millard R (2005) A mechanical model for the opening of the human female urethra. In: Adlassnig K-P, Bracale M (eds) Proceedings of biomedical engineering 2005. Acta Press, Austria, pp 210–213
9.
Noakes KF, Bissett IP, Pullan AJ, Cheng LK (2006) Anatomically based computational models of the male and female pelvic floor and anal canal. In: Proceedings of the 28th IEEE EMBS annual international conference, New York City, p 3815–3818
10.
11.
Saha P (2000) Fundamentals of extrusion. In: Aluminium extrusion Technology. ASM International, Materials Park, USA, pp 1–23
12.
Swash M, Snooks SJ, Henry MM (1985) A unifying concept of pelvic floor disorders and incontinence. J R Soc Med 78:906–911PubMed
13.
Snooks SJ, Barnes PR, Swash M (1984) Damage to the voluntary anal and urinary sphincter musculature in incontinence. J Neurol Neurosurg Psychiatr 47:1269–1273PubMedCrossRef
14.
Bartolo DC, Macdonald AD (2002) Faecal continence and defecation. In: Pemberton J, Swash M, Henry MM (eds) The Pelvic floor: its functions and disorders. WB Saunders, London, pp 77–83
15.
Shafik A (1982) A new concept of the anatomy of the anal sphincter mechanism and the physiology of defecation. XIV. Anal canal. A fallacious embryological and anatomical entity. Am J Proctol Gastroenterol Colon Rectal Surg 33:14–30PubMed
16.
Petros PE, Swash M (2008) The musculoelastic theory of anorectal function and dysfunction. Pelviperineology 27:89–93
17.
Seow-Choen F, Ho J (1994) Histoanatomy of anal glands. Dis Colon Rectum 17:1215–1218CrossRef
18.
Abendstein B, Brugger BA, Furtschegger A, Rieger M, Petros PE (2008) Role of the uterosacral ligaments in the causation of rectal intussusception, abnormal bowel emptying, and fecal incontinence-a prospective study. Pelviperineology 27:118–121
Metadata
Title
Defecation 2: Internal anorectal resistance is a critical factor in defecatory disorders
Authors
M. Bush
P. Petros
M. Swash
M. Fernandez
A. Gunnemann
Publication date
01-12-2012
Publisher
Springer Milan
Published in
Techniques in Coloproctology / Issue 6/2012
Print ISSN: 1123-6337
Electronic ISSN: 1128-045X
DOI
https://doi.org/10.1007/s10151-012-0860-3

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