Patent Publication Number: US-9423049-B2

Title: Reading and adjusting tool for hydrocephalus shunt valve

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/015,195, now U.S. Pat. No. 8,813,757, filed on Jan. 27, 2011, hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     This disclosure relates generally to surgically implanted physiological shunt systems and related flow control devices. More particularly, the present disclosure relates to a position indicator and adjustment tool for such shunt systems having variable pressure or flow settings for the one-way flow control valves controlling the flow of Cerebral Spinal Fluid (CSF) out of a brain ventricle and preventing backflow of fluid into the brain ventricle. 
     2. Description of Related Art 
     A typical adult has a total of about 120-150 cubic centimeters (cc) of CSF with about 40 cc in ventricles in the brain. A typical adult also produces about 400-500 cc/day of CSF, all of which is reabsorbed into the blood stream on a continuous basis. 
     Sometimes, the brain produces excess CSF or there can be a blockage of the normal CSF pathways and or absorption sites resulting in a condition known as hydrocephalus. Hydrocephalus is a condition of excessive accumulation of CSF in the ventricles or brain tissue. Hydrocephalus can result from genetic conditions, from trauma to the brain or as a person ages. 
     Excessive accumulation of CSF, due to hydrocephalus or other causes, manifests itself as increased pressure within the brain. Whatever the cause, over time, this increased CSF pressure causes damage to the brain tissue. It has been found that relieving the CSF pressure is therapeutically beneficial. This relief is usually performed by draining CSF from the ventricles. 
     Patients with hydrocephalus normally require, at least over some time period, continuous drainage of excess CSF to maintain normal CSF pressure in the brain. Excessive CSF accumulated in the ventricles of the brain is typically drained away from the brain using a shunt system. 
     Where hydrocephalus is a chronic condition, the shunt system typically drains the CSF into the patient&#39;s peritoneal cavity or into the patient&#39;s vascular system. Such shunt systems typically have a catheter implanted in the ventricle of the brain. The catheter is connected to a fluid control device which is in turn connected to a catheter which empties in to the patient&#39;s peritoneal cavity or into the patient&#39;s vascular system. An example of a fluid control device is shown in U.S. Pat. No. 5,637,083 issued to William J. Bertrand and David A. Watson on Jun. 10, 1997 entitled “Implantable Adjustable Fluid Flow Control Valve”, the teaching of which is incorporated herein in its entirety by reference. Current fluid control devices include an inlet connector, an outlet connector and a valve positioned between the inlet connector and the outlet connector. The valve includes a mechanism to control fluid flow through the valve. In some instances, the mechanism includes a magnet embedded within the valve. Rotating a rotor or otherwise shifting of the rotor position changes the internal configuration of the mechanism. Changing the internal configuration of the mechanism produces a variety of pressure or flow characteristics for the valve. As the internal configuration of the valve changes, the pressure or flow characteristics of the valve change. 
     In use, the valve is subcutaneously placed on the patient&#39;s skull. The catheter going to the patient&#39;s ventricle is attached to the inlet connector. The catheter going to the patient&#39;s peritoneal cavity or vascular system is attached to the outlet connector. In this way, a direction of flow is established from the inlet connector through the valve to the outlet connector. Changing the internal configuration of the mechanism by coupling the external magnet to the internal magnet and rotating the external magnet effects a movement internal to the shunt and produces a variety of pressure or flow characteristics through the valve. 
     It is desirable to have a number of different settings in order to achieve different pressure and/or flow characteristics of the valve. One complication with current adjustable valves is that once implanted, it is difficult to determine the setting of the valve and/or adjust the setting of the valve. Having more settings for the valve only makes determining and/or adjusting the valve setting more difficult. With some adjustable valves, x-ray images are used to determine the current state or post adjustment state of the valve. By requiring an x-ray, it is time consuming and costly to determine and adjust the valve setting, as well as not being in the best interest of the patient due to x-ray exposure issues. 
     Another complication with current adjustable valves is compatibility with magnetic resonance imaging (MRI) procedures. As many current adjustable valves utilize magnets for adjusting and/or determining a valve setting, their function can be disrupted due to interaction of magnetic components in the valve with the applied magnetic field created during the MRI procedure. In particular, the valve setting can be altered to a random, undesirable setting. If the valve setting is not returned to the desired setting after the MRI procedure, this situation can be extremely harmful to a patient. As such, the valve setting needs to be immediately reset to the desired setting upon conclusion of the MRI procedure. In any event, improvement of valves for the treatment of hydrocephalus can provide great benefit. 
     SUMMARY 
     Concepts presented herein relate to determining and/or adjusting a pressure or flow setting for an implantable medical device. In one embodiment, a reading and adjustment tool for use with a valve having a pressure or flow setting adjustable to a plurality of pressure or flow settings is disclosed. The tool includes a signal generator and an excitation coil coupled to the signal generator. The signal generator includes an adjustment interface configured to generate an adjustment signal to adjust the pressure or flow setting and a reading interface to generate a reading signal to read the pressure or flow setting of the valve. At least one excitation coil is connected to the signal generator and configured to generate an oscillating electromagnetic field based on one of the adjustment signal and the reading signal. 
     In another embodiment, a handheld valve reading and adjustment tool for use with a valve having a pressure or flow setting adjustable to a plurality of pressure or flow settings is disclosed. The tool includes a signal generator and an excitation coil coupled to the signal generator. A reading coil includes a first coil portion positioned on a first side of the excitation coil and a second coil portion positioned on an opposite side of the excitation coil than the first portion. The tool further includes a signal detector coupled to the reading coil. The signal generator is configured to send a reading signal to the valve and the reading coil is configured to receive an indication of the pressure or flow setting based on the reading signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram of an adjustable shunt system. 
         FIG. 2  is a schematic block diagram of a signal generator, coil assembly and signal detector for a handheld tool. 
         FIG. 3  is a schematic side view of a handheld tool in a first position. 
         FIG. 4  is a schematic side view of the handheld tool of  FIG. 3  in a second position. 
         FIG. 5  is a schematic bottom view of the handheld tool of  FIG. 4 . 
         FIG. 6  is a schematic diagram of a user interface for a handheld tool. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic block diagram of an adjustable shunt system  10  including an implantable flow control device  12  (e.g., a shunt) and an electronic valve reader and adjustment tool  14 . In general, device  12  can be implanted in a patient to regulate flow of fluids (e.g., CSF discussed above) within the patient based on a pressure or flow setting (also known as a valve setting) for the device  12 . Tool  14 , in turn, can be a handheld mechanism configured to subcutaneously read and/or adjust the pressure or flow setting of the device  12  when positioned proximate thereto. In particular, the tool  14  can create an oscillating electromagnetic field that is received by device  12 . The field can cause device  12  to adjust the pressure or flow setting and/or provide feedback indicative of a pressure or flow setting as will be discussed below. 
     The device  12  includes a valve  16 , an adjustment circuit assembly  18 , a reading circuit assembly  20  and a connector assembly  22  coupling the valve  16  with the adjustment circuit assembly  18  and the reading circuit assembly  20 . In one embodiment, the adjustment circuit assembly  18  includes an adjustment mechanism that alters a relative position of connector assembly  22  with respect to valve  16 , causing a change in the pressure or flow setting of valve  16 . Additionally, the connector assembly  22  can include an element that alters a resonant frequency of the reading circuit assembly  20  as a function of the relative position of the connector assembly  22  and valve  16 . An exemplary valve is further described in co-pending U.S. patent application Ser. No. 13/015,174 filed on even date herewith, entitled “Adjustment for Hydrocephalus Shunt Valve”, the contents of which are hereby incorporated by reference in their entirety. In general, fluid is allowed to flow through the valve  16  from an inlet connector  24  to an outlet connector  26  depending on a valve setting indicative of a cracking pressure (when valve  16  operates as a check valve) for valve  16 . The valve  16  defines a number of settings to alter pressure and/or flow characteristics of fluid through device  12 . Adjustment circuit assembly  18  is coupled to valve  16  through connector assembly  22  to alter the pressure or flow setting based on signals (e.g., an electromagnetic field) from tool  14 . Reading circuit  20  is also coupled to valve  16  through connector assembly  22  and configured to provide a signal indicative of the pressure or flow setting to tool  14  in response to a signal (e.g., an electromagnetic field) from tool  14 . Device  12  can be formed of biocompatible materials in order to be subcutaneously positioned within a patient. Additionally, the materials can limit the use of magnetic materials such that a pressure or flow setting for device  12  will not be altered during an MRI procedure. 
     Tool  14  includes a power source  30  configured to provide power to a signal generator  32 , a coil assembly  34 , a signal detector  36  and a user interface  38 . Signal generator  32  of tool  14  is adapted to provide output signals (e.g., an electromagnetic field) through coil assembly  34  to adjustment circuit assembly  18  and reading circuit assembly  20  within device  12 . In particular, the signal generator  32  is coupled to coil assembly  34 , which in turn can send output signals that match a resonant frequency of the adjustment circuit assembly  18  and reading circuit assembly  20  in order to induce a current therein. Current induced within the adjustment circuit assembly is used to drive an adjustment mechanism that changes the pressure or flow setting for valve  16 . Additionally, current sensed by tool  14  is used to estimate the coupling of the in vivo adjustment circuit assembly  18  with the coil assembly  34 . This coupling estimate can be used to guide the user to the valve when setting and to limit the power transmitted to the in vivo adjustment circuit assembly  18 . In one embodiment, the adjustment mechanism is a wire formed of shape memory alloy that contracts when current is induced therein, causing the pressure or flow setting to change. In one embodiment, the resonant frequency of adjustment circuit assembly  18  is approximately 100 kHz, although other frequencies can be used. 
     In a similar manner, signal generator  32  is also adapted to send an output signal (e.g., an electromagnetic field) to reading circuit assembly  20  that matches a resonant frequency of the reading circuit assembly  20 . However, the resonant frequency of reading circuit assembly  20  changes as a function of the pressure or flow setting for valve  16 . As a result, signal generator  32  is configured to transmit signals for multiple frequencies (e.g., by performing a scanning operation) and determine which frequency is the resonant frequency for reading circuit assembly  20 . In particular, when the frequency of the signal handheld is close enough to the valve the signal sent by signal generator  32  induces current within the reading circuit assembly  20 , creating a magnetic field that can be sensed by signal detector  36 . Based on a strength of the signal detected by signal detector  36 , a distance from the tool  14  to the device can be estimated. In one embodiment, the resonant frequency of reading circuit assembly  20  is around  1  MHz (nominally), adjustable within a range of frequencies capable of generation by signal generator  32 . Using the resonant frequency information, the pressure or flow setting of valve  16  can be determined, for example using a lookup table. 
     User interface  38  can provide a visual indication of operation for signal generator  32  and signal detector  36 , allow input to the tool  14  and provide a visual indication of proximity of the tool  14  to device  12 . For example, user interface  38  can include a screen to display pressure information, one or more buttons to alter operation of tool  14  and/or a set of indicators. The set of indicators, in one embodiment, can indicate a strength of the signal detected by detector  36 . If the detected signal is too weak, the user can move the tool  14  closer to device  12  until the tool  14  is in an acceptable working range. 
       FIG. 2  is a schematic block diagram of select components within tool  14  operable to adjust and/or read a pressure or flow setting of valve  12 .  FIG. 2  illustrates the signal generator  32 , coil assembly  34  and signal detector  36  of  FIG. 1 . Signal generator  32  includes an adjustment interface  50  and reading interface  52  operably coupled to a relay  54  which is coupled to coil assembly  34 . Coil assembly  34  includes an excitation coil  56  and sense (or reading) coil  58  having a first coil portion  58   a  and a second coil portion  58   b  positioned on opposite sides of the excitation coil  56 . In one embodiment, coil portion  58   a  and  58   b  are equally spaced from excitation coil  56 . As such, flux from an electromagnetic field generated by excitation coil  56  will be cancelled within coil  58  and thus signal detector  36  will not detect a signal within coil  58 . Stated another way, sensing of flux from reading circuit assembly  20  is independent of signals provided by excitation coil  56 . In particular, flux passing through coil part  58   a  will generate a voltage that apposes that generated in coil part  58   b , causing cancellation of signals from excitation coil  56  within sense coil  58 . If the signal from excitation coil  56  is not cancelled, a calibration process can be performed such that coil  58  does not detect a signal upon generation of a signal within excitation coil  56 . Relay  54  is operable to transmit either signals from adjustment interface  50  or reading interface  52  to excitation coil  56 , depending on whether tool  14  is in a mode to adjust pressure or flow setting of device  12  or read a pressure or flow setting of device  12 . In this manner, relay  54  can select one of an adjustment signal from adjustment interface  50  and a reading signal from reading interface  52  as an output signal delivered to coil  56 . In an alternative embodiment, two excitation coils can be utilized, one providing signals from the adjustment interface  50  and one providing signals from the reading interface  52 . In this embodiment, relay  54  can be eliminated. 
     Adjustment interface  50  includes an adjustment drive circuit  60  and one or more capacitors  62 . Adjustment drive circuit  60  and capacitors  62  are configured to generate signals that match a resonant frequency of adjustment circuit assembly  18  of  FIG. 1 . In one example, adjustment drive circuit  60  is embodied as an H-bridge that applies a voltage to the one or more capacitors  62 . When device  14  operates in an adjustment mode, relay  54  transmits current from the capacitors  62  to excitation coil  56 . In turn, excitation coil  56  creates an oscillating electromagnetic field, based on operation of the adjustment drive circuit  60  and capacitors  62 , that is received by device  12  to adjust a pressure or flow setting for the device  12 . 
     Reading interface  52  includes a reading drive circuit  64  inductors  66 . Alternatively, inductors  66  can be replaced by capacitors, as desired. In one example, reading drive circuit  64  is embodied as a direct digital sampler configured to scan a number of different frequencies in order to match a particular frequency of reading circuit assembly  20 . The reading drive circuit  64  is connected via relay  54  to the excitation coil  56  in coil assembly  34 . Current is induced within the reading circuit assembly  20  when the valve is within range of the excitation coil. Current within reading circuit assembly  20  can then be sensed by sense coil  58 . In particular, flux created by current in the reading circuit assembly  20  generates a current in coil  58 . Detector  36  is coupled to coil  58  so as to determine at what frequency reading circuit assembly  20  is resonant (i.e., by sensing the current induced in reading coil  58  from current generated within the reading circuit assembly  20 ). The frequency that is determined is indicative of a pressure or flow setting for device  12 . This setting can be sent to a user of tool  14 , for example via user interface  38 . 
       FIGS. 3-5  are schematic views of one embodiment of tool  14 . Tool  14  includes a housing  100  (referenced generally) that includes a body portion  102  and a coil assembly housing  104  pivotable with respect to body portion  102  about a pivot assembly  108 . The coil assembly housing  104  is positionable among a plurality of positions, including a generally perpendicular position with respect to a length of body portion  102  as shown in  FIG. 3  and a generally parallel position as shown in  FIG. 4 . Alternatively, in other embodiments, the coil assembly  104  is movable with respect to the housing  100 , for example by tethering with a cord or rotatable about the housing  100 . In one embodiment, pivot assembly  108  is a friction hinge that allows selective positioning among a plurality of angles between and including the positions of coil assembly housing  104  in  FIGS. 3 and 4 . Body portion  102  includes a reduced central portion  110  for convenient grasping by a user. As such, the user is able to easily position tool  14  and, in particular, coil assembly housing  104  proximate the device  12  implanted within a patient. 
     Components of tool  14  discussed above are positioned within the housing  100 . Power source  30 , signal generator  32 , signal detector  36  and user interface  38  are all positioned within body portion  102 , while coil assembly  34  is positioned within coil assembly housing  104 . Power source  30 , in the embodiment illustrated, is a battery electrically coupled to a main printed circuit board (PCB)  120  positioned within body portion  102 . A connector  122  is connectable to an AC to DC external power supply such as a conventional  120  volt alternating current (AC) outlet. Connection of connector  122  to a conventional outlet can recharge battery  30 . Signal generator  32  includes a corresponding printed circuit board (PCB)  124  that connects capacitors  62  and inductors  66  to main PCB  120  through a connector  126 . Relay  54 , adjustment drive circuit  60  and reading drive circuit  64 , illustrated in  FIG. 2 , are not illustrated in  FIGS. 3-5 , but can be positioned on PCB  120  or PCB  124 , as desired. Additionally, circuitry for user interface  38  (referenced generally) can be positioned on PCB  120  and is positioned near a top of body portion  102  so as to be readily viewable by a user. Coil assembly  34  is coupled to PCB  120  through a suitable connector  128 . 
     Operation of tool  14  is controlled through user interface  38 , an example of which is illustrated in  FIG. 6 . User interface  38  includes a power button  150 , a read selection button  152 , an adjustment selection button  154  and pressure or flow setting buttons  156  and  158 . Power button  150  selectively power on and off tool  14 . The read selection button  152  and adjustment selection button  154  are configured to select, respectively, a read mode (to read a pressure or flow setting of device  12 ) and an adjust mode (to adjust a pressure or flow setting of device  12 ). Once the adjust mode is selected, pressure or flow setting buttons  156  and  158  can be pressed to adjust the pressure of device  12  up or down, respectively. 
     User interface  38  further includes a set of indicators  160  (herein illustrated as light emitting diodes) (LEDs)) and a display screen  162  (herein illustrated as a liquid crystal display). The set of indicators  160  can provide indication to a user of proximity between tool  14  and device  12 . For example, if all of the indicators are lit, this can be indicative of tool  14  being in close proximity to device  12  such that tool  14  is in a workable range to read and/or adjust a pressure or flow setting of device  12 . If none or less than all of the indicators  160  are lit, this can be an indication to the user to move tool  14  closer to device  12 . Other ways of providing indications to the user can also be used, such as different colors of LEDs. Screen  162  can be used to display pressure or flow setting information received from device  12  and/or indicate adjustments to the pressure or flow setting that will be made. 
     Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present disclosure.