PRESSURE INDICATOR

Abstract: A shunt valve system includes an implantable shunt valve and a device for obtaining pressure setting information from the shunt valve after it is implanted under the scalp of a patient. The device includes a housing that is externally mountable on the patient's head proximate the shunt valve. A fluid-filled chamber is formed in the housing in which a ferromagnetic indicator is movable. The position of the ferromagnetic indicator corresponds to an indicator magnet located within the implanted shunt valve. In one embodiment, the indicator magnet is affixed to a cam which forms a portion of a stepping motor used to select a pressure setting for the shunt valve. From the position of the ferromagnetic indicator, which corresponds to the indicator magnet and the cam, the pressure setting of the shunt valve can be determined.

Description: PRESSURE INDICATOR CROSS REFERENCE TO RELATED APPLICATION Not Applicable. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH Not Applicable. HELD OF THE INVENTION The present invention relates to devices for obtaining information from an apparatus and more particularly to a system including an implantable apparatus and a device for obtaining pressure setting information of the apparatus after implantation. BACKGROUND OF THE INVENTION Many types of medical apparatus are implanted at various locations in the body on a permanent or semi-permanent basis. However, after implantation it is often difficult to obtain information from the implanted apparatus. One such type of implantable apparatus is a shunt valve and catheter used in the treatment of hydrocephalus, a condition where cerebrospinal fluid (CSF) collects in the ventricles of the brain of a patient. CSF is produced by die ventricular system and is normally absorbed by the venous system. However, if the CSF is not absorbed, the volume of CSF increases thereby elevating the intracranial pressure. This excess CSF can result in abnormally high epidural and intradural pressures. Left untreated, hydrocephalus can result in serious medical conditions, including subdural hematoma, compression of the brain tissue and impaired blood flow. •1- Various drainage catheters or shunt systems have been developed to remove excess CSF and thereby reduce the elevated intracranial pressure. Generally, fluid shunt systems include a valve mechanism for controlling or regulating the flow rate of fluid through the system. Shunt systems typically permit fluid flow only when the fluid pressure reaches a threshold pressure for the shunt valve. The threshold pressure should be such that excessive fluid is allowed to drain without creating an undesirable overdrainage condition in which too much fluid is drained from the ventricle. Thus, the shunt system should have a threshold pressure that is balanced to reduce excessive intracranial pressure and avoid overdrainage conditions. To achieve optimal drainage conditions, it may be desirable to periodically adjust the threshold pressure. For example, a surgeon may initially select a relatively low threshold pressure to trigger fluid flow. Over time, the initial threshold pressure may not be ideal. For example, it could lead to excess fluid flow, creating an undesirable overdrainage condition in which too much fluid is drained from the ventricle. Such a situation may give rise to a need to increase the threshold pressure to afford a fluid flow rate that is balanced to avoid both excessive intracranial pressure and overdrainage conditions. One prior art shunt valve that allows threshold pressure adjustment without removal of the device is disclosed in U.S. Patent Nos. 4,615,691 and 4,772,257, both of which are incorporated by reference herein. These patents disclose a cerebrospinal fluid shunt valve that is externally adjustable by means of a programming device. The shunt valve includes a stepping motor having rotor and stator elements. The stator elements are composed of a magnetically soft and permeable material shaped and positioned with respect to the rotor. The external programming device applies a magnetic field causing the rotor to rotate about a central axis so as to adjust the threshold pressure. After programming the shunt valve and during examinations, the pressure setting of the device should be verified to ensure proper fluid drainage occurs. The pressure setting is generally ascertained using X-ray examination of the device. Known shunt valves and stepping motors generally include radiopaque elements that are observable on a display or other device. From the observed positions of the radiopaque elements, the pressure to which the device has been programmed can be verified. However, X-ray examination can be cumbersome and time consuming. Furthermore, access to X-ray equipment may be limited or the equipment may be unavailable. It would, therefore, be desirable to provide a system including an apparatus and a device for obtaining information from the implanted apparatus without invasive surgical procedures and/or X-ray examination. SUMMARY OF THE INVENTION The present invention provides a shunt system including an implantable apparatus and a device for obtaining pressure information from the apparatus after implantation. Although primarily shown and described as a system for obtaining pressure information from an implanted shunt valve, it is understood that the invention has other applications as well. In one embodiment, a device for deteπmning the pressure setting of an implanted shunt valve includes a housing having a fluid-filled chamber and a ferromagnetic indicator that is freely movable within the chamber. The housing is adapted to be externally mountable upon the patient's body at a location proximate the implanted shunt valve. A plurality of markings can be affixed on the housing such that each marking corresponds to a specific pressure setting of the shunt valve. The markings can also include a centrally located marking for positioning the device relative to the shunt valve. To effectively position the ferromagnetic indicator of the device in relation to a pressure setting of the shunt valve, the shunt valve includes an indicator magnet. The indicator magnet generates a magnetic field that biases the ferromagnetic indicator to a particular orientation in relation to the location of the magnetic poles of the indicator magnet. In one embodiment, the indicator magnet is affixed to a cam which forms a portion of a stepping motor for programming the shunt valve to a selected pressure setting. The positions of the cam and the indicator magnet correspond to the pressure setting of die shunt valve. In operation, after the shunt valve is implanted under the scalp of the patient the device is used to determine me pressure setting of the shunt valve. The housing is mounted on me scalp of a patient over a protrusion corresponding to die implanted shunt valve. The device should be positioned such that the ferromagnetic indicator is aligned witii the central marking to ensure that die device is properly positioned in relation to the shunt valve. The position of me ferromagnetic indicator of the device is determined by me relative position of the indicator magnet in the shunt valve which corresponds to die pressure setting of the shunt valve. The pressure setting of the shunt valve is then visually deteπnined based on die orientation of the ferromagnetic indicator with respect to the markings on me housing. More particularly, the ferromagnetic indicator will be generally aligned witii one of the markings, each of which indicate a particular pressure setting of the shunt valve. In another embodiment, a device for determining pressure setting information from an implanted shunt valve includes a ferromagnetic indicator that is secured to the housing at a pivot point. The ferromagnetic indicator, which is disposed widiin a chamber formed in the housing, is freely rotatable about the pivot point. A ferromagnetic material is contained in cavities formed in me side -4- walls of the housing. The position of me ferromagnetic material is influenced by an indicator magnet disposed wimin the shunt valve. Based on the position of the ferromagnetic material, me device can be manipulated to align me ferromagnetic indicator with die indicator magnet in the shunt valve. More particularly, the pivot point of die ferromagnetic indicator should be aligned widi the ferromagnetic material in the cavities formed in me side walls of die housing. Once me device is properly positioned, die pressure setting of the shunt valve is determined based on the position of the ferromagnetic indicator wfth respect to a plurality of markings on the housing, each of which corresponds to a particular pressure setting of the shunt valve. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood from the following detailed description taken in conjunction wim die accompanying drawings, in which: Figure 1 is a perspective view of an implanted shunt valve and a device for obtaining information from the shunt valve in accordance with die present invention; Figure 2 is a perspective view of the device of Figure 1; Figure 3 is a perspective view of the shunt valve of Figure 1 shown without an exterior portion of die shunt valve; Figure 4 is a top view of die device of Figure 1; Figure 5 is a side view of die device of Figure 1; Figure 5A is a side view of an alternative embodiment of die device of Figure 1; Figure 6 is a top view of another embodiment of a device in accordance widi the present invention; Figure 7 is a side view of die device of Figure 6; Figure 8 is a top view of the shunt valve of Figure 3; Figure 9 is a cross-sectional view of die shunt valve of Figure 3 along lines 9-9; Figure 10 is a top view of the device and shunt valve of Figure 1 shown in a first position; and Figure 11 is a further top view of die device and shunt valve of Figure 1 shown in a second position. DETAILED DESCRIPTION OF THE INVENTION The drawings are understood to be illusttative of the concepts disclosed herein to facilitate comprehension of me invention. Further, the drawings are not to scale, and die scope of die invention is not to be limited by die relative dimensions of various components of the particular embodiments shown and described herein. FIGS. 1-3 show a system 100 including a shunt valve 200 and a device 300 for determining a pressure setting of me shunt valve 200. The shunt valve 200 is implanted under the scalp (not shown) of a patient 10 proximate the skull -6- 12. The device 300 is adapted for being externally mounted on die patient's head over the protrusion corresponding to die implanted shunt valve 200. As shown in FIGS. 4-5 in conjunction with FIGS. 1-3, die device 300 includes a housing 302 having a geometry adapted for placement against the body of a patient. It is understood d at die housing 302 can have a variety of configurations mat allow die device 300 to be positioned in relation to an implanted apparatus. In one embodiment adapted for use widi the implanted shunt valve 200, die housing 302 includes opposed first and second side walls 304a,b and a top portion 306. The side walls 304 and die top portion 306 togedier form a channel 308 mat is sized to accommodate a protrusion on a patient's scalp corresponding to die implanted shunt valve 200. Disposed widiin the top portion 306 of the housing is a chamber 310 (FIG. 5) in which a ferromagnetic indicator 312 is freely movable. The chamber 310 can contain a fluid 314, such as a clear oil, that allows the ferromagnetic indicator 312 to freely move within die chamber 310. The ferromagnetic indicator 312 can float on the fluid 314 or die fluid can facilitate movement of the ferromagnetic indicator by reducing frictional forces. A plurality of markings 316 indicative of a pressure setting of me implanted apparatus can be affixed on die housing 302. The markings 316 can also include a central marking 318 that can facilitate proper positioning of me device in relation to the implanted shunt valve. As shown in FIG. 5 A, me housing 302 can further include a magnifying element 320, such as a lens, mat is effective to enhance a visual deteπnination of the position of die relatively small ferromagnetic indicator 312. It is -7- understood diat die magnifying element 320 can be affixed to die device or it can be a separate component, such as a loupe type instrument. FIGS. 6-7 show an alternative embodiment of me device 300' wherein the ferromagnetic indicator 312 is secured to die housing 302 at a pivot point 322. The ferromagnetic indicator 312 is freely rotatable about die pivot point 322. A ferromagnetic material 324, such as iron filings, is contained within first and second cavities 326a,b located in respective first and second wall portions 304a,b of the housing. The ferromagnetic material 324 provides an indication of die relative alignment of me device 300' in relation to the shunt valve 200. That is, when die pivot point 322 is aligned widi the ferromagnetic material 324 in the first and second cavities 326a,b, die device 300' is properly positioned in relation to the shunt valve 200. The ferromagnetic indicator 312 dien rotates about the pivot point 322 and points to one of die markings 316 on me housing. Referring now to FIGS. 8-9, viewed in conjunction with FIGS. 1-3, the shunt valve 200 is typically implanted under die scalp in fluid communication witii a ventricular catheter (not shown) located in me ventricles of the patient's brain. The shunt valve 200 is effective to drain excess cerebrospinal fluid (CSF) to reduce elevated intracranial pressure. The shunt valve 200 includes a stepping motor 202 that is actuable by means of an external programmer (see U.S. Patent No. 4,772,257) to set a threshold pressure above which CSF flows dirough the shunt valve. The stepping motor 202 includes a rotor 204 diat is effective to rotate a cam 206 having a series of steps 208 formed tiiereon. The steps 208 sequentially increase in height witii respect to the rotor 204. A spring 210 has a first end 210a in contact witii the cam 206 and a second end 210b in biased contact witii a spherical element 212. The particular step 208 on which the first end 210 of die spring rests determines the pressure applied to die spherical element 212 by the second end 210b of the spring. By rotating tiie rotor 204 and -8- the cam 206 to position die spring 210 on a particular step 208, one can select a threshold pressure above which CSF will flow through the shunt valve. The shunt valve 200 includes an indicator magnet 214 to allow the pressure setting of tiie shunt valve 200, e.g., the position of the cam 206, to be determined by die externally mountable device 300. The indicator magnet 214 is secured witiiin the shunt valve 200 in a fixed position relative to the cam 206 and/or rotor 204. In one embodiment, tiie indicator magnet 214 is secured to a top portion 216 of the cam such that the indicator magnet is coaxial with both the cam 206 and tiie rotor 204. The poles of the indicator magnet 214 can be positioned to correspond to a predetermined pressure setting of the shunt valve. The overall dimensions of die device and shunt valve can vary. In an exemplary embodiment, the device housing 302 has a length LH (FIG. 4) that can range from about 10 millimeters to about 16 millimeters and a widtii WH diat can range from about 8 millimeters to about 24 millimeters. The height HH can vary from about 5 millimeters to about 10 millimeters. The chamber 310 is generally centered between die sidewalls 304 with a diameter ranging from about 3 millimeters to about 7 millimeters. The deptii DC (FIG. 5) of the chamber 310 can vary from about 0.5 millimeter to about 1.5 millimeter and is preferably about 1.0 millimeter. The ferromagnetic indicator 312 can be formed in a variety of geometries that enhance a visual deteπnination of the position of die indicator. In an exemplary embodiment, die ferromagnetic indicator 312 is elongate or needle- shaped witii a lengtii of about 1.3 millimeter. The indicator magnet 214 housed witiiin the shunt valve 200 is, in an exemplary embodiment, circular with a diameter ranging from about 1.0 millimeter to about 1.2 millimeter with a thickness of about 0.3 millimeter. The indicator magnet 214 generates a magnetic field having a strength in the range from about 100 Gauss to about 500 Gauss. As shown in FIGS. 10-11, to obtain tiie pressure setting of the implanted shunt valve 200, die device 300 is mounted upon die patient's scalp such that die protrusion corresponding to die shunt valve is generally witiiin the channel 308 of die housing. An arrow 313 indicates die direction of fluid flow for proper longitudinal orientation of the device. It is understood diat CSF flows in a direction from the patient to tiie shunt valve. After initial placement on die scalp, the device 300 typically needs to be more accurately positioned witii respect to the shunt valve 200. As shown in FIG. 10, for example, after initial placement of tiie device 300 over die scalp protrusion (not shown) die ferromagnetic indicator 312 is not aligned witii the center marking 318. The position of the ferromagnetic indicator 312 is determined by die relative position of die indicator magnet 214 and die cam 206 which correspond to die pressure setting of die shunt valve 200. The device 300 should be manipulated until die ferromagnetic indicator 312 is within die center marking 318 on die housing, as shown in FIG. 11. After the device is properly positioned, die ferromagnetic indicator 312 points to one of die markings 316. Each of these markings corresponds to a particular pressure setting of die shunt valve 200. It is understood diat ferromagnetic, as used herein, refers to a property exhibited by certain metals, alloys, and compounds characterized by an attraction to a magnetized body. The ferromagnetic indicator, for example, may be -10- comprised of a ferrite steel in one embodiment. Alternatively, the ferromagnetic indicator can be a composite material containing ferromagnetic and non- ferromagnetic materials. One skilled in the art will appreciate further features and advantages of die invention based on the above-described embodiments. Accordingly, die invention is not to be limited by what has been particularly shown and described, except as indicated by die appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety. What is claimed is: ■11-

Claims: 1. A device for obtaining parameter setting information from a surgically implanted apparatus that includes a stepping motor having a rotor for rotating a cam with an indicator magnet in a fixed position in relation to the cam, the device comprising: an externally mountable housing having a chamber and a contact surface adapted to be mountable on the patient's body proximate die implanted apparatus; and a ferromagnetic indicator disposed witiiin the chamber such that a position of tiie ferromagnetic indicator corresponds to a position of the indicator magnet which is indicative of a position of die cam and die pressure setting of the apparatus 2. The device according to claim 1, wherein die ferromagnetic indicator is freely movable within tiie chamber. 3. The device according to claim 1, wherein the implanted apparatus is an externally programmable shunt valve implanted beneatii the patient's scalp. 4. The device according to claim 1, wherein the housing includes first and second side walls and a top portion, diat together define a channel diat is sized to accommodate a protrusion on a patient's scalp corresponding to the implanted apparatus. 5. The device according to claim 1, wherein die chamber has a fluid disposed dierein. 6. The device according to claim 1, further including a plurality of markings affixed to die housing, each marking corresponding to a specific pressure setting of the apparatus. -12- 1 7. The device according to claim 6, wherein die markings include a central marking for aligning the ferromagnetic indicator with the indicator magnet. ι 8. The device according to claim 1, wherein me ferromagnetic indicator is rotatably affixed to die housing at a pivot point. ι 9. The device according to claim 8, further including a ferromagnetic material 2 disposed witiiin tiie housing tiiat is effective to align tiie ferromagnetic indicator 3 witii die indicator magnet. 1 10. The device according to claim 1, further including a magnifying element 2 disposed on die housing, die magnifying element being effective to enhance a 3 visual determination of a position of die ferromagnetic indicator. 1 11. An implantable shunt valve effective to provide pressure setting 2 information to an externally positioned device, die shunt valve comprising: 3 a stepping motor having a rotor for rotating a cam, wherein a position of 4 die cam corresponds to a pressure setting of the shunt valve; and 5 an indicator magnet in a generally fixed position witii respect to the cam, 6 wherein the position of the indicator magnet is effective to influence a position 7 of a ferromagnetic indicator that forms part of tiie externally positioned device 8 such diat die position of die ferromagnetic indicator corresponds to die pressure 9 setting of the shunt valve. i 12. The shunt valve according to claim 11, wherein die indicator magnet has 2 a magnetic pole orientation corresponding to a predetermined pressure setting of 3 the shunt valve. -13- 13. The shunt valve according to claim 11, wherein the indicator magnet generates a magnetic field having a strength in die range from about 100 gauss to about 500 gauss. 14. A shunt valve system, comprising: an implantable shunt valve including a stepping motor having a rotor and a cam, wherein a position of die cam corresponds to a pressure setting of tiie shunt valve; and an indicator magnet secured to and substantially coaxial with the rotor; and an externally mountable device for deterπ-iπing die pressure setting of die shunt valve when it is implanted beneatii a patient's scalp, the externally mountable device including a housing defining a chamber; and a ferromagnetic indicator freely movable within die chamber such tiiat a position of tiie ferromagnetic indicator corresponds to the pressure setting of die shunt valve. 15. The system according to claim 14, wherein die indicator magnet is substantially coaxial witii the cam. 16. The system according to claim 14, further including a plurality of markings located in the housing wherein each of the plurality of markings corresponds to a predetermined pressure setting of die shunt valve. ■14-

Inventors: KRAUS ROBERT G, KRAUS, ROBERT, G.
Applicants: JOHNSON & JOHNSON PROFESSIONAL, JOHNSON & JOHNSON PROFESSIONAL, INC.
Application year: 1999
Main classification: A61M27
IPC codes: A61B5, A61F2, A61M27