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.

FIELD F THE INVENTION 
This invention relates to ventriculoperitoneal shunts, and more 
specifically, to a valve to moderate cerebrospinal fluid flow when the 
patient changes between recumbent and upright positions. 
BACKGROUND OF THE INVENTION 
Treatment of certain medical conditions and diseases such as hydrocephalus 
frequently includes implanting a subcutaneous ventriculoperitoneal (VP) 
shunt to drain cerebrospinal fluid (CSF) from a ventricle of the brain to 
a receiving cavity, such as the heart or peritoneum. A VP shunt typically 
includes a catheter which extends from the ventricle, through a burr hole 
in the skull located behind the ear, and along the side of the body to the 
abdomen. 
Early VP shunts exhibited a performance characteristic known as "siphoning" 
which refers to surging of CSF drainage when the patient changes from a 
recumbent to a sitting or standing position. Siphoning is caused by the 
rapid increase in hydrostatic pressure differential in the catheter due to 
the sudden change in height of the head above the abdomen. In addition to 
temporary discomfort, excessive CSF drainage might cause other adverse 
consequences, for example, distention of the brain, or rupture of the 
blood vessels leading to potentially serious brain hematoma. 
To eliminate siphoning, VP shunts sometimes incorporate an antisiphoning 
valve which continuously senses the patient's attitude (i.e., 
horizontal-to-vertical orientation) and automatically moderates flow when 
the patient moves to an upright position. A weighted ball check valve is 
the operative mechanism frequently used in conventional antisiphoning 
valves. Generally in such valves, one or more spherical balls which are 
more dense than CSF reside within a hollow cavity of an elongated housing 
with a seat at the CSF inlet end. The antisiphoning valve is implanted so 
that the housing is horizontally oriented when the patient lies down. In 
the horizontal orientation, the balls can roll away from the seat, thus 
allowing CSF to pass through the valve. When the patient sits or stands, 
the housing orients vertically with the seat at the bottom. The balls sink 
toward the seat, thereby stopping flow until the aggregate intracranial 
and hydrostatic pressures of fluid in the catheter exceeds the force 
exerted by the weight of the balls against the seat. 
A patient also is susceptible to experience CSF surging while recumbent. 
When a patient coughs or sneezes, for example, which of course can occur 
while lying down, intracranial pressure temporarily increases and produces 
high flow through the catheter. A weighted ball valve does not stop flow 
while the patient is recumbent because the ball can roll away from the 
seat. Therefore, a conventional weighted ball, antisiphoning valve is not 
able to protect against CSF surges while the patient is in a recumbent 
attitude. 
In a weighted ball antisiphoning valve the flow enters from the bottom to 
assure that the ball will sink toward the seat in the upright orientation. 
Bottom entry causes the fluid to follow an S-shaped path from the brain to 
the abdomen. That is, fluid must travel downward to descend below the 
bottom seat, then upward past the seat and ball, and downward again to its 
ultimate destination. The shunt valve disclosed in U.S. Pat. No. 5,042,974 
exemplifies such S-shaped fluid flow path of a bottom entry, weighted 
ball, antisiphoning valve. To accommodate the S-shaped path, conventional 
antisiphoning valves are bulky. Due to its size, the valve tends to remain 
in fixed position when implanted in the patient. As the patient grows, the 
distance between the ends of the catheter and the valve increase which 
stresses the elastic tubing normally used in VP shunts. This stress 
increases the probability that the tubing will disconnect from the shunt 
components and require surgical intervention to correct. 
It is an object of the present invention to provide a streamlined, 
antisiphoning valve in which CSF flows straight through in a 
non-meandering path. Such a valve can have a smaller cross section than a 
conventional valve of equal capacity. The small cross section promotes the 
ability of the valve to move in the axial direction of the catheter within 
the body of the patient to relieve stress caused by the patient's growth. 
It is another object of this invention to provide an attitude responsive, 
antisiphoning valve which can reduce surging fluid drainage even when the 
patient is recumbent. 
SUMMARY OF THE INVENTION 
Accordingly, there is provided an antisiphoning valve for a 
ventriculoperitoneal shunt comprising: 
a hollow body defining at least one internal fluid chamber having a chamber 
wall; 
an outlet port on the body to connect the antisiphoning valve in fluid 
communication between the at least one chamber and a discharge cannula; 
an inlet port on the body distant from the outlet port to connect the 
antisiphoning valve in fluid communication between the at least one 
chamber and a supply cannula; 
at least one freely moving float within each chamber, the at least one 
freely moving float being buoyant in cerebrospinal fluid; and 
a first seat on the chamber wall proximate to the inlet port adapted to 
mate with the at least one freely moving float to stop cerebrospinal fluid 
flow when the antisiphoning valve in use is oriented in an upright 
attitude wherein the inlet port is elevated higher than the at least one 
chamber thereby causing cerebrospinal fluid in the chamber to buoy up the 
float to mate with the seat. 
The present invention also provides an antisiphoning valve as just 
described and further comprising a second seat on the chamber wall distant 
from the first seat adapted to mate with the at least one freely moving 
float to stop cerebrospinal fluid flow when the at least one freely moving 
float mates with the second seat. 
There is further provided a method of shunting cerebrospinal fluid from a 
ventricle of the brain to a receiving cavity which incorporates using the 
above-described antisiphoning valve to prevent excessive fluid drainage 
when a patient moves from a recumbent to an upright attitude.

DETAILED DESCRIPTION 
FIG. 1 illustrates a ventriculoperitoneal (VP) shunt 1 which incorporates 
the antisiphoning valve of the present invention. The shunt includes a 
supply cannula 2 which extends through a burr hole 6 in the skull into a 
ventricle of the brain, not shown. The proximal end 5 of the cannula is 
connected to a tubular shaped inlet port 7 of antisiphoning valve 4. 
Tubular shaped outlet port 3 of the valve provides connection to discharge 
cannula 8 leading to a receiving cavity, such as the peritoneum, in the 
abdomen, not shown. The antisiphoning valve body is elongated and contains 
an internal valve unit, not shown, which aligns with the longitudinal axis 
of the valve such that the entrance port and the exit port of the valve 
unit are proximate and distant from the inlet port, respectively, as will 
be explained in greater detail, below. FIG. 1 thus shows the proper 
orientation of the implanted antisiphoning valve 4 to achieve intended 
performance. That is, the longitudinal axis of the antisiphoning valve is 
oriented in the body to align the entrance port to the top of the valve 
unit when the patient is upright and away from the top of the valve unit 
when the patient is recumbent. 
A basic embodiment of the antisiphoning valve of this invention is shown in 
FIGS. 2-4. Like elements in the figures are provided with the same 
reference designations. The valve is shown as oriented in a patient in an 
upright position in FIG. 2 and in a recumbent position in FIGS. 3 and 4. 
The antisiphoning valve includes an elongated hollow body 22 which defines 
an internal fluid chamber 24. The body preferably has a generally 
cylindrical exterior shape, however, the cross section need not be 
circular or uniform across the length of the valve. The valve includes 
inlet port 21 and outlet port 23 which are tubular extensions of the body 
useful for connecting the valve to supply and discharge cannulae, 25 and 
26, respectively, by inserting the port into the lumen of the cannula. The 
cannulae in VP shunts are normally circular cross section, soft, 
elastomeric tubes. The outer dimensions of the inlet and outlet ports are 
selected to be slightly larger than the inner diameter of the cannula 
which causes the cannula wall to expand when the port is inserted in the 
lumen. This provides a liquid tight seal between the inside surface of the 
cannula and the outside surface of the port. 
The illustrated inlet and outlet ports are generally cylindrical, with a 
circular cross section of constant outer diameter, however, other shapes 
are contemplated. For example, the port can be frustoconical or it can 
have one or more circumferential, outwardly radiating sealing ridges to 
further assure a snug fit between the cannula and the port. The sealing 
ridges can be the same or different size. For example, size of the sealing 
ridge can vary with distance from the end of the port. More specifically, 
the sealing ridge near the end of the port can have the smallest outer 
diameter and the ridge furthest from the end can have the largest outer 
diameter. The peaks of the ridges can be rounded or they may have a 
sharp-tipped, frustoconical cross section. Such sharp-tipped ridges define 
teeth which bite into the cannula wall which increases the resistance of 
the cannula to accidentally disconnect from the port. Mechanical means for 
clamping the cannula to the port, such as ligated sutures, can be used to 
increase resistance of the cannula to disconnect. 
The basic antisiphoning valve has a single valve unit which includes a 
contoured casing 32 and a float 34. The casing defines a concave, 
generally oval cavity 33 that surrounds the float and which normally is 
filled with cerebrospinal fluid in service. The casing has an entrance 
port 36 through which fluid enters the cavity. Similarly, the casing has 
an exit port 38 which leads to the opening of the outlet port 23. 
Preferably, float 34 is spherical. The dimensions of the casing are 
sufficiently larger than those of the float to permit the float to move 
freely within the cavity. However, the entrance and exit port opening 
cross section dimensions are smaller than the float to confine the float 
within the cavity. 
The float material has a lower specific gravity than CSF, and therefore, it 
floats in the fluid. The float can be solid, low density material, such as 
low density or ultra low density polyolefin plastic. It can also be a 
composite of a shell and core of different materials, provided that the 
overall specific gravity is less than that of CSF. The float also can be 
hollow. Preferably, the float and cavity surfaces should be suitably 
lubricious and biocompatible that biological matter and debris which may 
be suspended in the fluid do not appreciably adhere to the surfaces and 
occlude the fluid passage way. The surfaces may be coated with a layer of 
nonadhesive material, such as polytetrafluoroethylene. 
The entrance port meets the cavity in a cross section, preferably circular, 
adapted to form a liquid tight seat for the float. More preferably, the 
seat, 39a, is frustoconical. Due to the low specific gravity of the float, 
buoyant force causes the float to rise to the top of the cavity, as shown 
in FIG. 2. Thus CSF inlet flow is stopped until hydrostatic pressure 
exerted from above the valve, increases sufficiently to overcome the 
buoyant force exerted by the float against the seat. When this condition 
occurs, the float moves downward to permit CSF to flow to the outlet port. 
As fluid drains from the ventricle, intracranial pressure decreases, which 
causes the float to rise upward against the entrance port seat to again 
stop flow through the valve. 
In the recumbent position, the antisiphoning valve orients as seen in FIG. 
3. Generally, the float rises to the ceiling 35 of the cavity which is 
contoured to provide at least a gentle elliptical profile with a region of 
high elevation distant from entrance port 36. Consequently, the float 
moves away from the valve seat to allow CSF to flow freely through the 
valve. Fluid motion produces hydrodynamic force which drags the float in 
the direction of fluid flow represented by the arrow in FIG. 3. While 
fluid flows slowly, the hydrodynamic force is small enough that the float 
continues to hover near the high region. The cavity size and shape are 
preferably selected to effectively increase the hydrodynamic force on the 
float when the patient experiences a sudden high flow-producing event, 
such as coughing or sneezing, that the float is drawn in contact with the 
seat 39b at exit port 38, as seen in the FIG. 4. The hydrodynamic drag on 
the float can be enhanced, for example, by reducing the clearance between 
the float and the casing and by conforming the contour of the casing 
closely to the shape of the float. Once the exit port is closed, high 
pressure maintains the float in contact with the seat. That is, the high 
flow-producing event increases the pressure on the cavity side of the 
float above the pressure on the outlet port side. Consequently, the float 
remains in contact with the seat until the high flow-producing event 
subsides. The surge might also originate in the abdomen, in which case 
force will move the float in the opposite direction to seal against the 
seat at entrance port 36, as shown in phantom in FIG. 4. Therefore, 
whichever direction the flow surges, the float will be forced against a 
seat and flow will be temporarily stopped. Finally, when the pressure 
driving the float against the seat is relieved, the float will move toward 
the ceiling of the cavity and away from the seats to reestablish flow 
through the valve. 
The antisiphoning valve of this invention thus exhibits performance 
features not found on conventional valves with high density balls. First 
it provides a straight-through fluid flow path which enables the valve to 
fit within a streamlined body. Having smaller bulk, the novel 
antisiphoning valve will be less obtrusive under the skin than a 
conventional valve. It will also be less resistant to axial displacement 
so that the valve can more readily move with the cannulae as the patient 
grows. As a result, the cannulae will be subject to less tensile stress 
and will be less likely to accidentally disconnect. Second, the novel 
antisiphoning valve provides the ability to reduce or eliminate sudden CSF 
flow surges which could occur while the patient is in the recumbent as 
well as the upright position. 
Another embodiment of the novel antisiphoning valve is shown in FIG. 5. The 
internal fluid chamber of this valve includes a plurality of valve units 
interconnected serially between inlet port 51 and outlet port 53. Each 
valve unit contains a single float 52a, 52b and 52c, situated within a 
casing defining a elliptically contoured cross section cavity for the 
respective float. The units are separated by chamber sections 55 which 
provide room for seats for entrance ports 56b and 56c, and exit ports 58a 
and 58b. The float and casing of each valve unit can be the same or 
different sizes. The float materials can be selected to provide different 
buoyancies, and therefore, different threshold intracranial pressures for 
stopping flow. 
FIG. 6 illustrates still another embodiment of the novel antisiphoning 
valve which includes multiple valve units. The casing of valve unit 65 is 
elongated so as to provide room for multiple floats 62 and 63 in the 
cavity. The purpose for having more than one float in a single cavity is 
to increase the buoyant force against the entrance port seat and thereby 
to increase the threshold intracranial pressure necessary to unseat the 
float. It is understood that the displacement of heavy fluid by the volume 
of a less dense float produces the buoyant force. Hence, the greater the 
volume of the float, the larger the displacement, and the higher the 
buoyant force. By providing multiple floats a high buoyant force can be 
obtained while maintaining smaller valve cross section dimension than 
might be needed for a single, spherical float. 
Although the shape of the float is preferably spherical, floats of other 
shapes are contemplated. For example, an elongated, torpedo-shaped, float 
71 can be used in an elongated valve unit casing 72, as in FIG. 7. The 
illustrated torpedo float has hemispherical ends 73, 74, however, 
frustoconical ends are also satisfactory. 
The antisiphoning valve of this invention can be manufactured by well known 
methods. For example, with reference to FIG. 8, it is seen that the body 
of the novel antisiphoning valve can be constructed in two clam shell 
sections, 82 and 84. Starting with the sections disassembled, floats are 
inserted in the valve units and the sections are assembled to enclose the 
floats. The assembled valve is then held together with removable 
fasteners, such as screws 86 screwed into predrilled and tapped holes, 
shown in phantom. A seal between the mating surfaces can be achieved by 
polishing the mating surfaces to a fine tolerance finish, by constructing 
the body of sealably deformable plastic, such as polyolefin, polyester or 
polyamide plastic or copolyetherester elastomer, or by placing between the 
clam shell portions an elastomeric gasket 88, the thickness of which is 
exaggerated in the figure. 
Although specific forms of the invention have been selected for 
illustration in the drawings, and the preceding description is drawn in 
specific terms for the purpose of describing these forms of the invention, 
this description is not intended to limit the scope of the invention which 
is defined in the claims.