On Structure-Function Relationships in the Female Human Urethra: A Finite Element Model Approach

Area of Science:

• Biomedical Engineering
• Urology
• Physiology

Background:

• Limited understanding of urethral striated/smooth muscle and vascular plexus roles in continence and micturition.
• Current hypotheses on equal muscle contribution to urethral closure pressure (UCP) lack detailed evidence.

Purpose of the Study:

• To develop and utilize a 3-D multiphysics finite element model to investigate the impact of individual urethral muscle layer contractions on UCP.
• To challenge and refine existing theories regarding the functional roles of urethral muscles in maintaining continence and initiating micturition.

Main Methods:

• Construction of a 3-D finite element model based on MR images of a healthy female urethra.
• Simulation of contractions in individual urethral muscle layers (striated and smooth).
• Modeling of age-related muscle atrophy and vascular plexus contributions to urethral closure.

Main Results:

• The urethra model exhibited a curved and asymmetric geometry.
• Contraction of outer striated muscle increased UCP; inner smooth muscle contraction reduced UCP and urethral length, suggesting a role in micturition initiation.
• Simulated posterior striated muscle atrophy led to reduced and asymmetric UCP. Vascular plexus and arteriovenous pressure are crucial for proximal urethral closure.

Conclusions:

• The current hypothesis of equal striated and smooth muscle contribution to UCP is rejected.
• Urethral smooth muscle may play a key role in initiating micturition.
• Vascular pressure is vital for maintaining proximal urethral closure and functional urethral length.