Aspiration of oocytes for in-vitro fertilization

An aspiration system, incorporating a regulated vacuum pump,was used to examine, in vitro, some factors that may affectoocyte collection. In an open aspiration system, as the lengthof the needle was increased, or the internal diameter decreased,the velocity (and flow rate) of aspirated fluid decreased. Therewas a difference, however, between experimental flows and thosepredicted by Hagen-Poiseuille's Law. Upon application of vacuumto a closed aspiration system, employing isolated bovine ovaries,there was an initial rapid increase in the collection tube vacuumto 85% of the selected pump vacuum followed by a more gradualrise to 100%. The vacuum within the needle similarly rose rapidlyto approximately half the selected vacuum, while the vacuumat the needle tip was ~5% of selected vacuum. The vacuums throughoutthe system briefly equilibrated as maximum flow/velocity wasreached. Flow/velocity slowed dramatically as the follicle collapsed,and stopped as the needle tip was blocked. If vacuum was maintainedduring the withdrawal of the needle from the follicle, therewas a dramatic forward flow of fluid toward the collection tube.The morphological appearance of bovine cumulus after in-vitroaspiration was generally unaltered by vacuums commonly utilizedin oocyte collection, providing the cumulus was regular, compactand refractile. The cumulus was less resistant to aspirationif it was damaged or had degenerated. These results suggestthat an intact cumulus may offer protection during ooocyte collection.