referring to the drawings , which are provided by way of example , and not by way of limitation , the present invention provides for a valve such as a shunt valve 10 adapted to be surgically implanted in a tissue space of a body of a mammal for draining fluid from one portion of the body to another for controlling hydrostatic siphon effect , to prevent excessive drainage which may be caused by the siphoning effect of hydrostatic pressure in a distal shunt catheter ( not shown ). the valve includes a housing 12 , formed to have a shape of a disc when viewed from the top or bottom , for example , although the housing can also be configured to have a cylindrical shape when viewed from the top or bottom . the valve includes an inlet connector 14 configured to be connected to an proximal catheter ( not shown ) such as surgical tubing or a ventricular catheter , and an outlet connector 16 configured to be connected to a distal catheter ( not shown ) such as surgical tubing or a peritoneal catheter . the housing can be made of polypropylene or a silicone elastomer , or any other similar suitable material . the housing defines a fluid flow path comprising an inlet port 18 and an outlet port 22 . in one presently preferred aspect , the fluid flow path will contain drainage fluids , or saline ( from pre - flushing the valve by the physician prior to implantation ), or may initially contain flushing saline , and through physiologic flow through the valve outlet chamber , will ultimately contain the drainage fluids that are meant to be drained from the patient after implantation of the valve . an inner wall structure 20 , typically having a generally cylindrical or tubular shape , is disposed substantially within the fluid flow path in the housing , and defines the outlet port 22 that is in fluid communication with the outlet connector . the inner wall structure typically includes an exterior surface defining at least one valve seat 24 against which at least a portion 25 of at least one movable , resilient flow control membranes 26 is biased to be seated in the presence of downstream negative hydrostatic fluid pressure in the outlet port to form a movable seal against the valve seat ( s ) to control fluid flow from the inlet port and the outlet port . the pair of movable , resilient flow control membranes preferably are attached at their outer edges to the inner surface 27 of the housing wall 28 , and have partial inner surfaces 30 that define an outer surface of the inlet port . the generally remaining inner surface 25 of the movable , resilient flow control membranes along with the valve seat in the housing wall separate the inlet port , from the outlet port . the movable membranes interact with the valve seat to control fluid flow through the valve in response to any combination of pressures acting on said movable membranes . the movable membranes are referenced to ambient ( atmospheric ) pressure on their outer surfaces 31 . pressures greater than the reference ambient pressure acting in the inlet port on the inner surface 30 will bias the movable membranes away from the seat to provide for flow though the valve . negative pressure ( as referenced to the ambient pressure ) in the outlet port acting on the inner surface 25 of the movable membrane will bias the movable membrane against the valve seat thereby restricting flow . the movable membrane therefore moves in response to the three changing pressures acting upon it . the valve seat is configured such that the area of negative pressure acting on the movable membranes is minimized in comparison to the area acted upon by the pressure in the inlet port so as to minimize the magnitude of inlet pressure necessary to overcome the sealing pressures caused by negative pressure in the outlet port . the movable membranes are highly effected by any external pressures acting on the outer surfaces of the movable membranes , including ambient pressure and any physical pressure from direct mechanical contact . although a reference to atmospheric pressure is required for the proper function of the valve , any mechanical pressures or forces acting on the movable membranes can adversely affect the function of the valve . therefor according to one presently preferred aspect this invention , a means to protect the movable membranes from physical contact while allowing atmospheric ambient pressure is provided . porous outer anti - fouling membranes 32 are attached to the housing externally of the movable , resilient flow control membranes to prevent such external mechanical pressures contacting against the movable membranes thereby allowing proper regulated flow through the improved fluid shunt valve due primarily to the gradient of inlet pressure and hydrostatic pressure ( as referenced to the ambient pressure acting on the outer surface of the membranes ) between the inlet and outlet of the valve . the porous outer anti - fouling membranes are preferably spaced apart from the movable , resilient flow control membranes to define a fluid filled space 34 , having an volume defined by the outer surfaces of the movable , resilient flow control membranes and the inner surface of the housing and the inner surfaces 36 of the porous outer anti - fouling membranes . in one presently preferred aspect , the fluid filled space 34 may contain one or more extra - cellular fluids , or a gas , or may initially contain a gas , such as air ( as supplied at time of manufacture ), and through diffusion across the outer anti - fouling membranes , may ultimately contain extra - cellular fluids after implantation of the valve . because the porous outer anti - fouling membranes are also somewhat flexible and movable , they are configured to allow an atmospheric reference pressure to be communicated to the fluid filled space that then references said pressure in the fluid filled space against the outer surfaces of the pair of movable , resilient flow control membranes to provide reference atmospheric pressure to the shunt valve at all times . since the porous outer anti - fouling membranes , are permeable to fluid flow though the pores , hydraulic lock within the fluid filled space is avoided if the porous outer anti - fouling membranes are being mechanically constrained by overlying tissue , which is unavoidable when the valve is implanted within tissue spaces of mammals . when the housing has a tubular configuration , a single tubular porous outer anti - fouling membrane may be provided displaced around the outside of the housing having a substantially tubular shape and encasing a single substantially tubular movable membrane and defining the fluid filled space there between . the inner surface of the tubular movable membrane in conjunction with a generally radially configured inner wall with one or more valve seats define the fluid flow path from the inlet port to the outlet port through one or more valve seats provided by the inner wall structure . it is also envisioned that the porous membranes that are configured to facilitate and protect the movement of underlying membranes could also be used to protect the delicate surfaces of implantable mechanisms such as implantable pressure sensors . it will be apparent from the foregoing that while particular forms of the invention have been illustrated and described , various modifications can be made without departing from the spirit and scope of the invention .
an improved shunt valve for the control of hydrocephalus provides for physiological atmospherically - referenced siphon control that is not adversely affected by overlying tissue . the valve includes one or more porous outer anti - fouling membranes to protect the flow control membranes from external mechanical tissue pressure , while permitting free movement of the flow control moveable membranes and permitting positive inlet pressure to regulate flow through the improved fluid shunt valve of the invention . the porous membranes are configured to prevent tissue ingrowth into the membranes pores while allowing adequate fluid flow across so as not to inhibit movement of the movable membrane .