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Structure-function relationship of the human external anal sphincter.

Amanda M Stewart1, Mark S Cook2, Keisha Y Dyer3,4

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|July 10, 2017
PubMed
Summary
This summary is machine-generated.

This study reveals the human external anal sphincter (EAS) has an intrinsic design optimized for function, despite vaginal delivery not altering its structure-function relationship. Understanding EAS mechanics is key to treating fecal incontinence (FI).

Keywords:
External anal sphincterFecal incontinenceMuscle architecture

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Area of Science:

  • Anatomy and Physiology
  • Pelvic Floor Disorders
  • Gastroenterology

Background:

  • Obstetrical external anal sphincter (EAS) injury is a primary cause of female fecal incontinence (FI).
  • Limited understanding of the EAS structure-function relationship impedes effective treatment strategies.
  • Direct measurement of human EAS intrinsic parameters is needed to elucidate its functional mechanics.

Purpose of the Study:

  • To directly measure functionally relevant intrinsic parameters of the human EAS.
  • To investigate whether vaginal delivery alters the EAS structure-function relationship.
  • To correlate EAS structural design with its physiological function in maintaining continence.

Main Methods:

  • Comparison of in vivo EAS functional parameters (sarcomere length, PCSA, fiber length, stiffness) between vaginally nulliparous (VN) and vaginally parous (VP) cadaveric donors.
  • Analysis included operational sarcomere length (Ls) and optimal length (Lso) for force-length relationship.
  • Statistical analysis using unpaired and paired t-tests (α < 0.05).

Main Results:

  • The human EAS operates at a shorter sarcomere length (Ls) than optimal (Lso), enhancing active and passive tension with stretching.
  • EAS possesses a long fiber length (Lfn) for rapid contraction and intermediate PCSA for maintaining resting tone.
  • No significant differences in EAS structural parameters were found between VN and VP groups.

Conclusions:

  • The human EAS exhibits an intrinsic structural design well-matched to its functional requirements.
  • Vaginal delivery did not appear to alter the fundamental structure-function relationship of the EAS.
  • Understanding EAS intrinsic mechanics is crucial for advancing the diagnosis and treatment of fecal incontinence.