Three stage valve

An implantable valve for allowing the passage of cerebrospinal fluid (CSF) from a ventricle of the brain to a suitable drainage location in the body includes a movable diaphragm, one side of which is in pressure communication with the drainage location of the body and the other side of which is in pressure communication with the ventricular spaces of the brain. A valve assembly, actuable by displacement of the diaphragm in response to a pressure differential applied thereto, regulates passage of CSF from the ventricular spaces to the drainage location. When differential pressure is relatively small, the valve is actuated to a constant pressure mode in which a predetermined differential pressure across the valve is maintained. In response to a sudden increase in differentail pressure, the valve mechanism is actuated to a constant flow mode in which a desired relatively constant rate of fluid flow is maintained. Above a predetermined pressure differential, the valve is actuated once again to a constant pressure mode in which differential pressure above a predetermined maximum is prevented.

BACKGROUND OF THE INVENTION 
The present invention relates to an intracranial pressure relief valve and, 
more particularly, to a three stage valve which provides either constant 
pressure or constant flow characteristics in accordance with a fluid 
pressure differential applied across the valve. 
Hydrocephalus is a condition in which the body, for any one of a variety of 
reasons, is unable to relieve itself of excess cerebrospinal fluid (CSF) 
collected in the ventricles of the brain. The excessive collection of CSF 
in the ventricular spaces results in an increase in both epidural and 
intradural pressures. This in turn causes a number of adverse 
physiological effects including compression of brain tissue, impairment of 
blood flow in the brain tissue and impairment of the brain's normal 
metabolism. 
Treatment of a hydrocephalic condition frequently involves relieving the 
abnormally high intracranial pressure. Accordingly, a variety of CSF 
pressure regulator valves and methods of controlling CSF pressure have 
been developed which include various forms of check valves, servo valves 
or combinations thereof. Generally, such valves serve to divert CSF from 
the ventricles of the brain through a discharge line to some suitable 
drainage area of the body such as the venous system or the peritoneal 
cavity. Check valves operate by opening when the difference between CSF 
pressure and pressure in the discharge line exceeds a predetermined value. 
One drawback to the use of a simple check valves in the treatment of 
hydrocephalus is that such a valve might open in response to normal 
variations in differential pressure between CSF ventricular pressure and 
pressure in the discharge line, resulting in hyperdrainage of the 
ventricular spaces. For example, when a patient stands after lying in a 
recumbent position, the differential pressure will normally increase by 
reason of the resulting increased ventricle height of the fluid column 
existing between the head and the selected drainage location. Though such 
an increase in differential pressure is quite normal, a check valve might 
respond by opening, thereby allowing undesired hyperdrainage of the 
ventricular spaces, which, in turn, may result in a potentially serious 
brain hematoma. Accordingly, it is desirable to provide a hydrocephalus 
pressure relief valve which is effective in shunting CSF in response to 
abnormal intracranial pressures while avoiding hyperdrainage in the event 
of normal variations in body fluid pressures. 
The present invention is directed to a pressure relief valve which prevents 
the excessive flow of CSF in the event of sudden increases in differential 
pressure. In such a valve, the differential pressure between CSF and fluid 
in the drainage location acts to displace a movable area of a diaphragm. 
Such movement of the diaphragm actuates a valve regulating the passage of 
CSF to the drainage area. When the pressure differential is relatively 
small, the valve allows the passage of fluid at a flow rate sufficient to 
maintain a desired ventricular CSF pressure. However, a sudden increase in 
differential pressure, as would occur when the patient stands, causes the 
valve to operate essentially as a constant flow device in which passage of 
fluid is maintained at a relatively constant desired flow rate. A very 
high differential pressure, as might occur as a result of undesired 
clogging of the valve, causes the valve to once again operate in a 
constant pressure mode this time at a higher pressure, thereby preventing 
CSF pressure from building above a predetermined maximum safe value. 
In view of the foregoing, it is a general object of the present invention 
to provide a new and improved pressure regulator valve for relieving 
intracranial pressure caused by the presence of excess CSF in the 
ventricles of the brain. 
It is a more specific object of the present invention to provide a pressure 
regulator valve which avoids undesired hyperdrainage of the ventricular 
spaces as a result of normal increases in differential pressure. 
SUMMARY OF THE INVENTION 
A valve for controlling the passage of body fluids from one location in the 
body to another location includes a housing having first and second 
interior chambers. An inlet port establishes fluid communication between 
the first chamber and the one location while an outlet port establishes 
fluid communication between the second chamber and the other location. A 
valve mechanism between the first chamber and the second chamber regulate 
the passage of fluid between the chambers. The valve may be actuated to 
any one of four conditions. In the first of these conditions, fluid 
communication between the first and second chambers is prevented. In the 
second condition fluid communication is provided between the first and 
second chambers at a flow rate sufficient to maintain a desired constant 
first pressure differential between the first and second chambers. In the 
third condition, fluid communication is provided between the first and 
second chambers sufficient to maintain a desired relatively constant flow 
rate of fluid between the chambers while in the fourth condition fluid 
communication between the chambers is provided at a fluid flow rate 
sufficient to maintain a constant desired second pressure differential 
between the first and second chambers. The valve includes partition means 
in the housing which include a movable member separating the first and 
second chambers and which moves in response to the pressure differential 
therebetween. The movable member is associated with the valve mechanism 
such that motion of the member in response to an increasing pressure 
differential between fluids in the first and second chambers sequentially 
conditions the valve mechanism from the first condition through the second 
and third conditions to the fourth condition. Accordingly, the valve 
mechanism will be sequentially conditioned to one of the four conditions 
in response to an increasing pressure differential between fluid at the 
one location of the body and fluid at the other location of the body.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, and particularly to FIG. 1, a hydrocephalus 
system 10 for maintaining a desired predetermined intracranial pressure in 
a patient 11 is illustrated. The system shown includes a three stage 
pressure relief valve 12 constructed in accordance with the present 
invention for maintaining the desired intracranial pressure. 
Cerebrospinal fluid (CSF) 14 is drained from a ventricle 15 of the brain 16 
by means of a ventricular catheter 17. Preferably, the catheter is 
radio-opaque in order to facilitate its accurate placement within the 
brain. The distal end 18 of the catheter is provided with a plurality of 
apertures 20 allowing the passage of CSF therethrough and is positioned in 
a suitable brain ventricle as illustrated. The other end of the catheter 
is coupled to the inlet port 21 of the valve thereby establishing fluid 
communication between the valve and the ventricle. The outlet port 22 of 
the valve is attached to one end of a drain catheter 23, the opposite end 
of which discharges into an appropriate location of the patient's body. As 
illustrated, the drain catheter is threaded through an appropriate vein 24 
to terminate within the right atrium of the heart 25. Another drainage 
location, for example, the peritoneal cavity, could also be selected. When 
open, the valve allows passage of CSF from the brain ventricles to the 
selected discharge location thereby relieving CSF pressure caused by 
excessive accumulation of CSF. 
Normally, a pressure differential exists between CSF within the ventricle 
and fluid in the selected drainage location. Accordingly, a differential 
pressure will exist between fluids applied to the inlet and outlet ports 
of the valve. The valve illustrated is of the type which opens when the 
pressure differential exceeds a predetermined threshold value. Typically, 
the valve 12 includes means for adjusting the differential pressure 
threshold at which it opens so that the hydrocephalus system may be 
adjusted to suit the specific requirements of an individual patient. 
While an increased differential pressure may result from the excessive 
accumulation of CSF in the brain ventricles, such an increase may be a 
perfectly normal response to ordinary physical activity of the patient. 
For example, when a patient stands after lying for some time in a 
recumbent position as illustrated in phantom in FIG. 1, the differential 
pressure will suddenly increase by reason of the sudden increase in 
vertical height H of the fluid column existing between the distal end of 
the ventricular catheter 17 and the drainage location. If the relief valve 
were to open and permit unrestrained fluid flow during this period, 
hyperdrainage of the ventricle, and a drain hematoma, are possible 
results. Accordingly, the valve includes means for preventing such 
unrestricted fluid flow to the drainage location in the event of a sudden 
increase in the differential pressure. 
The internal construction and operation of the three stage valve may best 
be understood by reference to FIGS. 2-6. As illustrated, the valve 
includes a disc-shaped inner housing 26 fashioned from a durable, 
biologically compatible material, such as thermoplastic polymers of 
polyethersulfone or polycarbonates. The inner housing 26 is received 
within an outer housing comprising two members 27 and 28 formed of 
silicone rubber or similar material bonded together over the inner 
housing. The dimensions of the inner and outer housings are selected so as 
to be compatible with subcutaneous implantation of the valve over the 
cranium 29. 
As is best illustrated in FIGS. 3 and 4, the inner housing includes two 
circulat cup-shaped members 30 and 31, each including a single port 32 and 
33 respectively, by means of which fluid can pass to or from the interior 
region of the housing. In this regard, outer ousing members 27 and 28 are 
provided with internal conduits 35 and 36 respectively, which allow fluid 
communication between the inlet and outlet ports and the housing 26. 
Upper housing member 30 is provided with an aperture 37 through the upper 
surface thereof. As illustrated, the aperture 37 includes a region of 
relatively larger diameter 38 coaxially aligned above a region of 
relatively smaller diameter 40. Both the relatively larger diameter and 
smaller diameter regions of the aperture are internally threaded as 
illustrated. In order to seal the aperture while still allowing ready 
access to the interior region of the housing, the upper housing member 30 
also includes a removable cap 41 having a domed upper surface 42 and an 
externally threaded cylindrical lower portion 43 dimensioned as to engage 
the threads of the relatively larger diameter segment 38 of the aperture 
37. To allow a tight seal between the cap and the housing, the upper 
housing member includes a raised annular seat 44 adjacent the periphery of 
the aperture against which the cap bears as it is screwed into the upper 
housing member. 
Referring further to FIGS. 3 and 4, the valve includes partition means in 
the form of a movable member or diaphragm 45 extending laterally across 
the interior region of the inner housing thereby dividing that region into 
first and second interior chambers 46 and 47, respectively. The diaphragm 
45 is fashioned from a flexible biocompatible material, such as silicone 
rubber, and, as best seen in FIG. 3, comprises a disc-shaped member having 
an aperture 48 provided centrally therethrough. The operative surface 50 
of the diaphragm is provided with an annular groove 51 concentrically 
aligned with the center aperture which allows the operative surface to 
travel vertically in response to differential pressure across the 
diaphragm such as might result from a difference in pressures in the first 
and second interior chambers. Toward its center, and in the region 
immediately surrounding the aperture, the thickness of the diaphragm is 
increased to form a raised area 52, while both the upper and lower 
surfaces of the raised area, 53 and 54 respectively, are undercut to form 
a circular, rectangular cross-sectioned channel 55 therebetween as is best 
seen in FIG. 6. The diaphragm 45 also includes an integrally formed raised 
circular edge 56 projecting both above and below the operative surface 50 
along its outer circumference. This edge, in a manner to be developed, 
facilitates installation of the diaphragm within the housing. 
The manner in which the diaphragm is held in position relative to both the 
upper and lower housing members is best illustrated in FIGS. 4 and 6. 
Referring to those Figures, it will be seen that the lower edge of the 
upper housing member is provided with a rectangular cross section channel 
57 thereby forming inner and outer sleeves 58 and 60 respectively. As 
illustrated, the vertical dimension of the inner sleeve 58 is less than 
that of the outer sleeve 60 while the channel 57 is dimensioned to receive 
the outer raised edge 56 of the diaphragm. The upper edge surface of the 
lower housing member is provided with a pair of raised steps 61 and 62 
thereby forming concentric annular ledges 64, 65 and 65 thereon. When 
assembled, the lower edge of the outer sleeve 60 contacts the first ledge 
64, while the second ledge 65 is dimensioned so as to contact the lower 
edge 56 of the diaphragm when the diaphragm is in place. Similarly, the 
inner ledge 64 is dimensioned as to allow the diaphragm to be received in 
the space formed between the upper edge thereof and the lower edge of the 
interior sleeve 60. Thus, when assembled, upper housing member 30 
interlocks with lower housing member 31 by engagement of their 
corresponding edges, while the diaphragm 45 is received in the spaced 
provided therebetween thereby rigidly affixing the outer periphery of the 
diaphragm relative to the two interior housing members. When mounted in 
this manner, the operative surface 50 of the diaphragm is free to travel 
vertically in response to a pressure differential existing between fluids 
contained in the first and second chambers. 
To regulate the passage of fluid from the first chamber 46 to the second 
chamber 47 and hence from a brain ventricle to the selected drainage area 
of the body, the valve includes valving means for regulating fluid 
communication between the first and second chambers. Such valving means 
take the form of a valve seat 67 mounted for movement between valve 
closure means and fluid restrictor means. In the embodiment illustrated, 
such valve closure means take the form of a sphere 68, fashioned from 
ruby, sapphire or similar hard, biocompatible material, while the fluid 
restrictor means take the form of a generally cylindrical restrictor 70 
also fashioned from ruby, sapphire or similar such material. The valve 
seat 67, formed of the same material selected for the sphere and the 
restrictor, comprises a disc having flat, parallel, upper and lower faces 
71 and 72. As is best seen in FIG. 6, the valve seat is received within 
the channel 55 formed in the raised segment 52 of the diaphragm adjacent 
the aperture provided centrally therethrough whereby the valve seat 
travels with movement of the diaphragm. The ruby valve closure sphere 68 
is positioned directly above the valve seat and is held in position by 
means of a cylindrical collar 74 externally threaded and dimensioned to 
engage the threads of the relatively narrow diameter segment 40 of the 
aperture provided in the upper surface of upper housing member 30 directly 
beneath the cap 41. The cylindrical collar 74 includes a central hollow 
region 75 dimensioned to receive the ruby sphere 68 and may be engagingly 
or disengagingly rotated relative to the upper housing member whereby the 
vertical position of the sphere relative to the valve seat 67 may be 
adjusted. As may further be seen in FIG. 6, the valve seat 67 includes an 
orifice 76 extending centrally therethrough which provides fluid 
communication between the first and second chambers. As illustrated, the 
orifice 76 is located directly beneath the sphere 68 so that when the 
sphere contacts the upper surface of the valve seat 67, as would occur 
when the diaphragm 45 is deflected upwardly, it totally occludes the 
orifice thereby precluding the passage of fluid between the first and 
second chambers. The restrictor extends perpendicularly upward from the 
lower interior surface of the inner housing and is positioned directly 
beneath the valve seat orifice so that downward travel of the diaphragm 
and the valve seat results in the introduction of the restrictor 70 into 
the orifice thereby partially occluding the passage between the first and 
second chambers. 
It will be observed that the orifice 76 provided in the valve seat is not a 
simple cylindrical aperture but rather is tapered so that the orifice 76 
is narrowest at the upper surface 71 of the valve seat 67 and widest at 
its lower surface 72. The restrictor 70 is generally cylindrical in form 
and includes a segment of relatively larger diameter 77 above and 
coaxially aligned with a segment of relatively narrower diameter 78 the 
lower edge of which is received in a suitable recess 80 provided in the 
lower interior surface of housing member 31 thereby affixing the 
restrictor perpendicularly relative to that surface. The dimension of the 
restrictor is selected so that it will barely pass through the orifice at 
its narrowest point. By way of example, in one embodiment of the valve, 
the valve seat orifice had a diameter of 0.040 inches at its narrowest 
point and the clearance between the restrictor and the orifice at the 
narrowest point was on the order of 0.001 inches. 
The operation of the valve may best be understood by reference to FIGS. 
6-10 and the description which follows. FIG. 10 is a graphical depiction 
of pressure versus flow characteristics of a valve constructed in 
accordance with the invention. Briefly, the valve operates to maintain a 
desired differential pressure P.sub.1 between fluids in the brain 
ventricles and at the selected discharge location of the body. The valve 
accomplishes this by adjusting the fluid flow rate Q so that the desired 
pressure P.sub.1 is maintained. Such operation of the valve occurs within 
the region designated I on the graph of FIG. 10. 
When differential pressure rapidly increases, such as when the patient 
stands, a flow rate greater than a pre-selected rate Q.sub.1 will be 
necessary to maintain the desired first pressure P.sub.1. However, such a 
flow rate may create risks of undesirable hyperdrainage of the brain 
ventricles. Accordingly, when such a rapid increase in differential 
pressure occurs, the valve automatically serves to maintain a relatively 
constant desired rate of fluid flow despite changes in differential 
pressure. In a practical valve, the flow rate will not be entirely 
independent of the applied differential pressure but rather will increase 
from a lower flow rate Q.sub.1 to a higher flow rate Q.sub.2 as 
differential pressure increases between first pressure P.sub.1 and a 
second pressure P.sub.2 as indicated by the solid line in FIG. 10. A valve 
operating in this condition is operating in region II of FIG. 10. Flow 
rates Q.sub.1 and Q.sub.2 are sufficiently low so that during a temporary 
rapid increase in differential pressure, pressure will return to normal 
before a quantity of CSF sufficient to cause adverse side effects may flow 
through the valve. In a typical valve Q.sub.1 and Q.sub.2 might be 0.4 
ml./min and 0.8 ml./min. respectively, while first and second pressures, 
P.sub.1 and P.sub.2 may have values of 80 and 350 millimeters of water 
respectively. 
While it is desirable to avoid high flow rates through the valve in order 
to avoid hyperdrainage of the ventricles, it may, under certain emergency 
conditions, be desirable to allow rapid shunting of CSF in order to avoid 
possible brain damage. When the valve is operating in region II, increases 
in differential pressure tend to close the valve between the first and 
second interior chambers. To avoid the possibility of building extremely 
high ventricular CSF pressure, the valve is constructed so that when 
differential pressure exceeds a second pressure P.sub.2 substantially 
higher than first pressure P.sub.1, the valve once again operates to allow 
a fluid flow rate sufficient to maintain a differential pressure no higher 
than second pressure P.sub.2. Such operation is that which would occur in 
region III of FIG. 10. When the valve is operating in this region, further 
increases in differential pressure result in an increase in fluid flow 
through the valve thereby stabilizing differential pressure. 
FIGS. 6-9 illustrate operation of the valve in each of the regions 
previously described. CSF applied to the inlet port 21 of the valve 
completely fills the first chamber 46 and exerts a downwardly directed 
force on the diaphragm 45 by reason of the CSF pressure within the brain 
ventricle. Since the second chamber 47 is in fluid communication with the 
selected drainage location in the body, the pressure of the CSF therein 
exerts an upwardly directed force on the lower surface of the diaphragm. 
Accordingly, the differential pressure between CSF in the brain ventricle 
and fluid at the drainage location results in verticle deflection of both 
the diaphragm and the valve seat 67 rigidly attached thereto. As shown in 
FIG. 6, when valve seat 67 contacts sphere 68, the orifice 76 is totally 
occluded, thereby preventing fluid flow between chambers 46 and 47. When 
differential pressure is relatively low, such as when the valve is 
operating in region I FIG. 10, the resulting slight downward displacement 
of the diaphragm is sufficient to displace the valve seat 67 relative to 
the sphere 68 thereby allowing fluid to pass through the orifice 76 from 
the first interior chamber 46 to the second interior chamber 47. The 
valving means in this condition are illustrated in FIG. 7. As shown, 
downward deflection of the diaphragm is sufficient to allow the passage of 
fluid through the orifice, yet the upper surface of the restrictor 70 is 
sufficiently removed from the orifice so as not to interfere with the flow 
of fluid between the chambers. In this condition, the valve acts primarily 
as a constant presure device whereby a constant pressure differential is 
maintained between the fluids in the first and second chambers. A slight 
increase in differential pressure results in slight downward deflection of 
the diaphragm thereby further opening the valve means to allow greater 
fluid flow between the chambers with the results that the increased 
pressure in the first chamber is rapidly relieved. Similarly, a decrease 
in the pressure of fluid in the first chamber allows the diaphragm to move 
toward the sphere, thereby restricting the fluid flow between the 
chambers, thus allowing pressure in the first chamber to increase. 
FIG. 8 illustrates the condition of the valve when a sudden increase in 
differential pressure is applied to the valve. When such an event occurs, 
the pressure differential exceeds the first desired pressure P.sub.1 and 
consequently the valve operates in region II of FIG. 10. When such a 
differential pressure is applied to the valve, the downward displacement 
of the diaphragm 45 is sufficient to cause the valve seat 67 to descend 
over the restrictor 70 thereby causing the restrictor to partially occlude 
the orifice 76 therein. Because the orifice is tapered, additional 
downward travel of the valve seat results in a further occlusion of the 
orifice. The orifice is shaped such that the additional occlusion occuring 
orifice by reason of increasing differential pressure is sufficient to 
offset the higher flow rate ordinarily resulting from increased pressure 
thereby resulting in a relatively uniform rate fluid flow between the 
chambers despite increase in differential pressure. Accordingly, in this 
condition, the valve acts primarily as a constant flow device permitting 
the passage of fluid from the first to the second chamber at a relatively 
constant desired rate despite changes in applied differential pressure. 
FIG. 9 illustrates operation of the valve in region III of FIG. 10 such as 
would occur when differential pressure exceeds the desired second pressure 
P.sub.2. In this condition, differential pressure displaces the diaphragm 
to a degree sufficient to cause the large diameter end 77 of the 
restrictor 70 to protrude past the upper surface of the valve seat thereby 
allowing fluid to easily flow past the restrictor and through the orifice 
76. It will be noted, that in this condition, the orifice is not nearly as 
restricted as it was in FIG. 8 when the large diameter end of the 
restrictor 70 was received within the tapered region of the valve seat 67. 
When the valve is operating in this manner, increases in differential 
pressure cause the valve seat to be further displaced away from the 
restrictor, thereby further opening the orifice, and allowing a greater 
fluid flow rate. Thus, the valve once again operates essentially as a 
constant pressure device whereby differential pressure greater than a 
desired maximum pressure P.sub.2 is prevented. A further advantage of this 
construction, is that as the restrictor passes through the orifice, it 
tends to remove foreign materials which may tend to clog the valve. Thus, 
should clogging occur, the resulting increased differential pressure will 
eventually cause the restrictor to pass through the orifice thereby 
providing the valve with a self-cleaning feature. 
While a particular embodiment of the invention has been shown and 
described, it will be obvious to those skilled in the art that changes and 
modifications may be made without departing from the invention in its 
broader aspects, and, therefore, the aim in the appended claims is to 
cover all such changes and modifications as fall within the true spirit 
and scope of the invention.