Antisiphoning valve

Abstract

A valve for preventing excessive cerebrospinal fluid flow in ventriculoperitoneal shunt, known as 'siphoning', which occurs when a patient rapidly moves from a recumbent to an upright position, is described. The valve includes at least one valve unit containing within a cerebrospinal fluid (CSF)-filled cavity, a freely moveable float which is buoyant in CSF. The valve is subcutaneously implanted in the patient in an upright orientation in which the entrance port of the valve unit is elevated higher than the cavity while the patient is upright. In this orientation, the float rises to the top of the CSF-filled cavity where it seals against a seat of the entrance port. The float thus stops flow until intracranial pressure sufficiently exceeds the buoyant force. The casing generally has a contoured sectional profile. When the patient reclines, the valve orients so that the float rises to a high region of the casing which is away from the entrance seat thereby allowing CSF to flow through. The contour of the casing is selected to increase hydrodynamic force on the float in the direction of flow when flow rate increases. This causes the float to contact a seat of the valve unit exit port when flow exceeds a predetermined amount. The novel valve thus provides the capability to prevent excessive drainage even when the patient is recumbent, for example, caused by coughing or sneezing.