title: Theoretical analysis of the effects of viscous losses and abdominal straining on urinary outlet function.
abstract: OBJECTIVE
  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.
  
  
  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.
authors.affiliation: Harvard School of Public Health, Boston, Massachusetts 02115, USA. smijailo@hsph.harvard.edu
authors.forename: Srboljub M
authors.initials: SM
authors.lastname: Mijailovich
authors.forename: Maryrose P
authors.initials: MP
authors.lastname: Sullivan
authors.forename: Subbarao V
authors.initials: SV
authors.lastname: Yalla
authors.forename: Jose G
authors.initials: JG
authors.lastname: Venegas
mesh_terms: D000005:Abdomen / Q000502:physiology*; D006801:Humans; D008954:Models, Biological; D011312:Pressure; D013314:Stress, Mechanical; D014521:Urethra / Q000502:physiology*; D014563:Urodynamics; D014783:Viscosity