Related Experiment Video
Updated: Aug 29, 2026

Quantification of Levator Ani Hiatus Enlargement by Magnetic Resonance Imaging in Males and Females with Pelvic Organ Prolapse
Published on: April 17, 2019
Theoretical analysis of the effects of viscous losses and abdominal straining on urinary outlet function
Srboljub M Mijailovich1, Maryrose P Sullivan, Subbarao V Yalla
1Harvard School of Public Health, Boston, Massachusetts 02115, USA. smijailo@hsph.harvard.edu
Aims:
The aim of this study was to theoretically explore the relationship between the tube law (TL) of the urethra and the pressure-flow (p-Q) relationship during micturition. The understanding of this relation is important for the evaluation of outlet obstruction by urodynamic interpretation of p-Q plots.
Methods:
We simulated the outlet function by a lumped theoretical model, and suggested how the TL can be used to quantitatively predict the p-Q relationship of the system. Our analysis considered the relation between the TL and the steady state p-Q plot for various TLs including the hysteresis of the pressure-area relationship.
Results And Conclusions:
The inclusion of pressure losses distal to the flow controlling zone and experimentally measured p-A relations of the urethra in the model lead to the predictions that flow in the flow controlling zone is not always critical but is often in the sub-critical range, that an increase in abdominal pressure can increase the flow under certain conditions, and that hysteresis in the pressure-area relation is correlated to the hysteresis in the p-Q plot.
Related Concept Videos
Urodynamic Studies: Uroflowmetry
Anatomy of the Genitourinary System II: Bladder and Urethra
Urinary Bladder
In males, the bladder is situated in front of the rectum, while in females, it is positioned anterior to the vagina and uterus. The bladder floor contains an inverted triangular area called the trigone, defined by the two ureteric...
Nursing Assessment of the Genitourinary System II: Inspection and Palpation
The Micturition Reflex
The process begins with bladder filling, where the bladder wall stretches as urine accumulates. This stretching activates the urine storage reflex, mediated by the sacral spinal segments and the pontine storage center. Efferent sympathetic impulses stimulate the detrusor muscle to relax and the internal urethral sphincter to contract, facilitating urine...
Imaging Studies VI: Voiding Cystourethrography and Cystography

