Follicular fluid rheology and the duration of the ovulatory process

The fluid dynamics of ovulation were investigated to understand the mechani cal role of follicular fluid in oocyte release. A set of equations describi ng the flow of fluid from an evacuating follicle was derived from basic pri nciples. These equations demonstrate that, subject to assumptions about the available pressure differential and the source of the expulsive force, the size and shape of the ovulatory orifice have the largest influences on the rate of fluid loss, although the viscosity of the fluid is also an importa nt variable. A thorough rheological examination of pig, bovine and human fo llicular fluids, performed using a cone-plate viscometer, demonstrated that these fluids have complex, non-Newtonian characteristics. The fluids also undergo time-dependent and spontaneous changes in viscosity at constant she ar rates; some fluids were subject to coagulation-like events. Viscosity ch aracteristics were unrelated to broad parameters of follicle development. T he models used representative viscosity values to demonstrate that variatio ns in the rate and duration of follicle evacuation, as observed by ultrason ography, could be explained largely by variations in fluid viscosity and th e characteristics of the ovulatory orifice.