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