Patent Publication Number: US-2020289803-A1

Title: Cerebrospinal Fluid Shunt Valve System

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/473,126, filed Mar. 29, 2017, and hereby incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     BACKGROUND OF THE INVENTION 
     The present invention relates to neurosurgical devices used for treating hydrocephalus and, more specifically, to ventriculoperitoneal (VP) shunts that relieve pressure on the brain caused by excess fluid accumulation within the brain. 
     Hydrocephalus is a condition caused by an abnormal accumulation of cerebrospinal fluid (CSF) within the ventricles of the brain. Cerebrospinal fluid is produced in the choroid plexuses of the ventricles of the brain and circulates through the ventricular system of the brain to the subarachnoid spaces in the cranium and spine to be absorbed into the bloodstream. The fluid is used to surround the brain and spinal cord and acts as a protective cushion or buffer against injury. It also contains nutrients and proteins for nourishment and functioning of the brain while clearing away waste products. 
     Hydrocephalus occurs when there is an imbalance between the amount of CSF that is produced and the amount that is absorbed. When CSF builds up within the brain, it causes the ventricles to enlarge and increases the pressure inside the skull. 
     Hydrocephalus is typically treated through the surgical placement of a shunt system within the brain. The shunt system places a drainage tube between the brain&#39;s ventricles or the subarachnoid space and another body region, typically the abdominal cavity (or pleural cavity, heart atrium, and others), where the CSF can be absorbed. This creates an alternative route for removal of CSF buildup within the brain. Valves may be positioned within the shunt pathway to regulate flow based upon differential pressure, i.e., the pressure difference at the proximal catheter tip and the pressure at the drainage end. 
     Shunt failure is a very common complication requiring immediate shunt revision (the replacement or reprogramming of the pre-existing shunt). A shunt malfunction that does not receive immediate medical attention can be life-threatening or result in permanent neurologic injury. The shunt failure rate is relatively high (in the pediatric population, the shunt failure rate after one year is 40-50% and after five years is at nearly 100%) and it is not uncommon for patients to have multiple shunt revisions within their lifetime. 
     A leading cause of shunt failure is partial or complete blockage of the shunt. Both the proximal catheter placed in the brain and the distal catheter that provides the draining may become blocked. Typically when there is a blockage, the shunt must be replaced. 
     Under-drainage due to shunt blockage can cause the ventricles to increase in size and fail to remedy the symptoms of hydrocephalus. However, over-drainage is also undesired since it decreases the size of the ventricles and creates slit like ventricles. Over-drainage has also been found to increase the likelihood of shunt blockages. 
     SUMMARY OF THE INVENTION 
     While the inventors do not wish to be bound by a particular theory, there is now evidence that blockage of the shunt may be caused by the continuous over-draining of CSF to relieve CSF buildup, even at low levels. Over time the ability of the tissue to rebound diminishes causing the tissue to be permanently deformed and lodged within the catheter holes. Tissue entering the catheter can tear or break off and create blockages within the catheter over time. 
     The present invention operates to significantly reduce the time during which draining occurs allowing tissue surrounding the catheter to rebound from the catheter holes returning to its normal position for a sufficient amount of time to recover its normal shape. Intracranial pressure (ICP) is the differential pressure between ICP and ambient pressure. Ambient pressure may be measured by an ambient pressure sensor in an external reader or implanted. Instead of allowing CSF to drain at a nearly constant flow rate, the present invention monitors the ICP over a portion of a monitoring cycle to calculate short intervals of drainage for every monitoring cycle necessary to produce the desired pressure correction. By continuously alternating between valve fully open and valve fully closed, the system can allow the brain tissue to retain its normal shape with reduced blockage. 
     Specifically, in one embodiment, the invention provides a cerebral shunt used to treat an abnormal accumulation of cerebrospinal fluid (CSF) in a brain of a patient, comprising: a catheter implanted within the brain of the patient with a proximal portion within the brain opposite a distal portion diverting CSF out of the brain to another region of the patient; a pressure sensor implanted within the brain of the patient and producing a signal representing an ICP; a valve that permits excess CSF to drain out of the brain through the catheter in an open position and prevents the excess CSF from passing out of the brain through the catheter in a closed position; and a valve driver receiving the signal representing the ICP controlling the valve to switch the valve between the open position and closed position in a cycle for successive cycles so that the relative time that the valve is in the open position versus the closed position is a function of ICP. 
     It is thus a feature of at least one embodiment of the invention to electrically control operation of the valve according to measured ICP to permit sophisticated control of the valve operation that can minimize long periods of drainage such as can cause tissue distortion. 
     The valve driver may be adapted to open the valve during each cycle for a period of time that is less time than a period of time that the valve is closed. The valve driver may be adapted to open the valve less than 10% of the time over each cycle. The valve driver may be adapted to open the valve less than 2% of the time over each cycle. 
     It is thus a feature of at least one embodiment of the invention to increase the time during which the valve is in a closed position to minimize tissue deformation. 
     The valve driver may be adapted to open the valve for a continuous period of time. The continuous period of time may be less than 5 seconds. The valve may be open for a period of time limited to a predetermined time permitting tissue surrounding the valve to be released from the valve without irreversible shape change. 
     It is thus a feature of at least one embodiment of the invention to permit the tissue to recover between drainage sessions, preventing permanent deformation. 
     A controller may receive the signal from the pressure sensor over a period of time and averaging the signal over the period of time. The period of time may be between 2 and 10 minutes. 
     It is thus a feature of at least one embodiment of the invention to provide continuous monitoring without the need for continuous drainage. 
     The valve driver may operate to attenuate an effect of sudden changes in the signal representing the ICP. 
     It is thus a feature of at least one embodiment of the invention to prevent sudden pressure changes or spikes (for example, caused by patient movement, sneezing, coughing) to cause over-drainage. 
     The pressure sensor may provide a pair of opposed conductive plates at least one plate flexing in response to ICP enabling circuitry detecting flexure according to at least one of varying resonant frequency, capacitance and piezo-resistance. 
     It is thus a feature of at least one embodiment of the invention to monitor an absolute pressure change to discount gravitational effects which influence pressure difference valves. 
     A biocompatible holder may comprise a disk having a broad face supporting an elongated tube extending downwardly therefrom and supporting the pressure sensor on a distal end of the tube. 
     It is thus a feature of at least one embodiment of the invention to allow for implantation of the pressure sensor to a desired depth within the skull while communicating with pressure sensor electronics outside of the skull. 
     The valve comprises a piezo bender actuator receiving electrical signals from the valve controller to be electrically actuated to reposition the piezo bender actuator to open or close the valve. 
     It is thus a feature of at least one embodiment of the invention to utilize piezoelectric qualities of materials in creating simplified electrically actuated valves. 
     The piezo bender actuator may be a cantilever repositioning to change a position of a collar extending around a tube having an orifice in series with the catheter to block the orifice. The piezo bender may be a cantilever repositioning to change a position of a plug removably insertable within an orifice of the catheter wherein the orifice permits CSF to drain. 
     It is thus a feature of at least one embodiment of the invention to utilize simple on-off valves. 
     A wireless transmitter may communicate the signal to an external wireless reader. The wireless transmitter may be an RFID device or other suitable wireless communication method. 
     It is thus a feature of at least one embodiment of the invention to permit external communication and control with the pressure sensing and valve control systems. 
     The present invention also provides a method of treating hydrocephalus where there is an abnormal accumulation of cerebrospinal fluid (CSF) in a brain of a patient comprising the steps of: providing a cerebral shunt comprising a catheter having a proximal portion opposite a distal portion; a pressure sensor producing a signal representing an ICP; a valve limiting flow through the catheter between an open and closed position; implanting the proximal portion of the catheter within the brain of the patient and the distal portion outside the brain of the patient; implanting the sensor within the brain of the patient; and receiving the signal representing the ICP controlling the valve to switch the valve between the open position and closed position in a cycle for successive cycles so that the relative time that the valve is in the open position versus the closed position is a function of ICP. 
     These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic of a cerebral shunt system of one embodiment of the present invention showing with a pressure sensor system installed within a patient; 
         FIG. 2  is an external telemeter device wirelessly communicating with the pressure sensor system within the patient; 
         FIG. 3A  is a side elevation view of a pressure sensor system having upper and lower spiral metal coils/plates spaced apart in parallel alignment 
         FIG. 3B  is the side elevation view of the pressure sensor system of  FIG. 3A  and showing a pressure applied to the top plate causing deflection of the upper metal coil/plate; 
         FIG. 4  is an exploded view of the pressure sensor having a first deflecting plate and a second non-moveable plate; 
         FIG. 5  is an exploded view of the plates of  FIG. 4  bonded together and inserted within a protective sleeve and exposing the silicon membrane; 
         FIG. 6  is the bonded plates of  FIG. 5  installed within a biocompatible holder; 
         FIG. 7  is a flow diagram of a valve control system; 
         FIG. 8  is a graph showing the measurement cycle of the valve control system over time; 
         FIG. 9  is a valve of one embodiment of the present invention installed within a housing; 
         FIG. 10  is an enlarged schematic of the valve of  FIG. 9  showing a cantilevered piezo bender actuator sliding a collar to block or expose a tubular orifice permitting CSF flow into the housing; 
         FIG. 11  is a schematic of a valve of an alternative embodiment of the present invention showing a cantilevered piezo bender actuator having a plug to block or expose a tubular orifice permitting CSF flow into the housing; and 
         FIG. 12  is a simplified depiction of the cerebral shunt system installed within a skull of a patient. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIGS. 1 and 12 , a cerebral shunt system  10  of the present invention may be partially implanted within a human patient  12 . The cerebral shunt system  10  may include embedded devices  16  installed beneath the scalp and/or skull  13  of the human patient  12  communicating with an external reader or telemeter device  14  to be discussed below. 
     The embedded devices  16  assist with drainage of excess cerebrospinal fluid (CSF) surrounding the brain of the patient  12 . The CSF may be drained from within the brain to another location within the patient&#39;s body, such as the abdominal cavity, peritoneal cavity, pleural cavity, or heart, able to absorb the excess CSF. 
     The embedded devices  16  include a proximal catheter  18  that may be surgically implanted in the cranium or spine to approach the ventricle or other CSF space where CSF resides so that CSF may be drained from the patient&#39;s brain or spinal canal. The proximal catheter  18  may be closed at the tip but include a number of small drainage holes, approximately 1 mm in diameter, running along a length of the proximal catheter  18 . The holes may be arranged in rows and are generally positioned at a distal end of the catheter allowing the CSF to flow from the ventricles or subarachnoid space through the holes and into the proximal catheter  18 . The CSF is drained from the brain&#39;s ventricles or the subarachnoid space by flowing through the proximal catheter  18  leading away from the brain. The proximal catheter  18  extends from the brain through a small hole in the skull  13  to the outside of the skull  13 . 
     A distal catheter  20  fluidly communicates with the proximal catheter  18  and typically runs underneath the scalp of the patient  12  and to a drainage site such as the abdominal cavity, peritoneal cavity, pleural cavity, or heart. The distal catheter  20  may have a closed tip and also contain a number of small drainage holes, approximately 1 mm in diameter, running along a length of the distal catheter  20 . The holes may be arranged in rows and are mostly positioned at a distal drainage end of the catheter allowing the CSF to drain out of the distal catheter  20  into the drainage site. The catheter may be open ended with or without slits. 
     A valve  22  is located between the proximal catheter  18  and the distal catheter  20 , facilitating the fluid communication therebetween and regulating the flow rate of CSF through the catheter system. In one embodiment of the present invention, the valve  22  may be installed outside the skull  13  of the patient  12  but underneath the skin of the patient  12  and coupling the proximal catheter  18  to the distal catheter  20 . It is understood that the valve  22  may be positioned anywhere along the catheter system to regulate flow rate in a similar manner. For example, the valve  22  may be located at the proximal catheter  18 , distal catheter  20 , or anywhere between the two catheters. 
     Operation of the valve  22  may be controlled by a valve driver  24  in the form of a microcontroller providing an electrical drive signal to the valve  22  according to a valve control program  132 . The valve control program  132  may be processed by a valve driver  24  determining whether the valve  22  should be open or closed according to a sensed ICP. The valve driver  24  may include a digital processor, electronic memory holding the valve control program  132 , an electrical interface circuit for communicating between the valve driver  24  and other devices as is generally understood in the art. According to the valve control program  132 , the valve driver  24  will send a signal to the valve  22  to open or close the valve  22  thus allowing CSF to flow out of the skull  13  of the patient  12  or not flow out of the skull  13  of the patient  12 . For example, when the valve  22  is open, CSF may drain through the distal catheter  20  whereas when the valve  22  is closed, CSF is not drained through the distal catheter  20 . 
     The ICP may be determined by a pressure sensor  26  (to be described in more detail below) implanted within the skull  13  of the patient  12 , e.g., in the brain parenchyma. The pressure sensor  26  may sense an absolute ICP, or condition representative of pressure, and deliver that sensed signal to the valve driver  24 . 
     The valve driver/microcontroller  24  may also communicate with an RFID circuit  25  (or other wireless communication method) providing two-way communication through an antenna  27  with a handheld telemeter device  14 . The antenna  27  may also communicate with a battery system  30  providing power to the other elements of the embedded devices  16  using standard wireless power transmission techniques such as radio-frequency identification (RFID) and resonance based inductive coupling technology. 
     As noted above, and referring to  FIG. 2 , the cerebral shunt system  10  may also include an external reader such as a handheld telemeter device  14  that may be positioned outside the patient&#39;s skull  13  to receive ICP data from the pressure sensor  26  and to program the valve control program  132  as well as to provide electrical charging current for batteries  30  communicating with the pressure sensor  26  and the valve driver  24 . 
     In one embodiment, the telemeter device  14  may be a handheld wand having a base  15  attached to a handle  17  for gripping, where in use, the base  15  has a broad face  19  positioned in close proximity to the patient&#39;s skull  13  so that the telemeter device  14  may wirelessly communicate with the embedded devices  16  within the patient  12 . The telemeter device  14 , e.g., within the base  15  portion, may contain an antenna  27  to facilitate the wireless communication therebetween. In one embodiment, telemeter device  14  may make use of a standard RFID circuit  25  (or other wireless communication device) for communicating with the RFID circuit  25  (or other wireless communication device) of the embedded devices  16  such as may communicate with the valve driver  24 . 
     The telemeter device  14  may connect to a computer (e.g., PC or laptop) through an electrical conductor, such as a USB cable. Physicians may control the cerebral shunt system  10  on a Graphical User Interface (GUI) of the computer to set parameters or thresholds for the valve, as will be further discussed below. 
     It is understood that the telemeter device  14  may communicate with the embedded devices  16  through a wired or wireless connection and instead of being an external device, the telemeter device  14  may also be implanted or embedded device within the patient  12 . 
     Sensing System 
     Referring now to  FIGS. 3A and 3B , the pressure sensor  26  may include a housing  28  having a deformable upper plate  29  opposite and substantially parallel to a non-deformable lower plate  31 . The upper plate  29  and lower plate  31  are held in separation by standoffs  33  extending at the outer edges between the two plates which seal between the upper plate  29  and lower plate  31  at a predetermined pressure for example atmospheric pressure or vacuum. The lower surface of the upper plate  29  and upper surface of the lower plate  31  support two oppositely disposed metal electrodes  36 ,  37  in parallel separation to each other. The metal electrodes  36 ,  37  may be made of copper, silver, gold, or a material which may elastically deform with deformation of the upper plate  29 . 
     When pressure (P) is applied to the upper plate  29  due to increased ICP caused by CSF buildup, the upper metal electrode  36  (center diaphragm) bends toward the lower metal electrode  37 . In response to the physical repositioning of the upper metal electrode  36  with respect to the lower metal electrode  37 , the capacitance between the upper metal electrode  36  and lower metal electrode  37  changes. This variation may be detected by a capacitive sensing routine executed by the valve driver  24  for example such as measures a change of charging time of the capacitance or a change in frequency when the capacitance is made part of a tuned resonant circuit. 
     The change in capacitance for small deflections may be proportional or otherwise functionally related to the applied ICP on the center diaphragm thus an ICP can be calculated. 
     Referring now to  FIG. 4 , in one embodiment of the pressure sensor  26  the upper plate  29  may be made of a thin silicon membrane. The first plate  29  contains a T-shaped well  72  extending within the upper plate  29  for supporting a similarly shaped diaphragm or metal electrode  36  that deforms under pressure. The T-shaped well  72 , and correspondingly the metal electrode  36 , has a vertical channel or stem  74  of the T extending downward from a middle of the upper plate  29  toward a bottom of the upper plate  29  and a horizontal arm  76  extending across the top of the stem  74  forming the top of the T. The horizontal arm  76  is rectangular and is substantially centered within the upper plate  29  to define a center diaphragm. The metal electrode  36  fits within the T-shaped well  72  and has a substantially identical shape as the T-shaped well  72  and fitting therein so as to fully encompass the T-shaped well  72 . 
     The non-deformable lower plate  31  may be a thick glass plate providing a “ground plane” that does not deform under ICP. A front side  81  of the plate  31  supports an electrode  37  in a similar manner as the upper plate  29 . The second plate  31  may contain an upside down T-shaped well  82  supporting the electrode  37  but not necessarily extending all the way through the glass plate but just at a surface. The T-shaped well  82 , and correspondingly the electrode  37 , has a vertical channel or stem  84  of the T extending upward from a middle of the plate toward a top of the second plate  31  and a horizontal arm  86  extending across the bottom of the stem  84  at the bottom of the upside down T. The horizontal arm  86  is rectangular and substantially centered within the second plate  31  to correspond in relative position with the horizontal arm  76  of the first plate  29 . The T-shaped well  82  carries the T-shaped electrode  37  having a substantially similar shape as the T-shaped well  82  and fitting therein so as to fully encompass the T-shaped well  82 . 
     Referring now to  FIG. 5 , the plate  29  is bonded to the front side  81  of the second plate  31  to create a bonded plate  90 . When the first plate  70  and second plate  31  are bonded together, the plates  29  and  31  are aligned such that the horizontal arms  76 ,  86  of the first plate  29  and second plate  31  overlap and align such that the center diaphragms of the metal electrodes  36  and  37  are positioned in substantially parallel separation to create what is known as a parallel plate capacitor arrangement. The metal plates  29 ,  31  may be separated by a vacuum to prevent electric transfer between the plates. 
     As shown, in the bonded plate  90 , holes  92  may be drilled through the bonded plate  90  within the vertical stem  74  of the T of the first plate  29  and vertical stem  84  of the T of the second plate  31  respectively so that each metal plate  36  and  37  may be electrically communicated with through wires  116 . 
     The bonded plate  90  may be covered by a protective sleeve such as parylene or silastic  94  having a front, back, and side walls corresponding with the walls of the bonded plate  90  and slid over the bonded plate  90  to provide a protective layer to the bonded plate  90 . The sleeve  94  includes a rectangular opening  96  allowing the horizontal arm  76  (center diaphragm) of the first plate  70  to be exposed to an applied ICP. 
     ICP (P) may be applied to the metal diaphragm through the rectangular opening silicon membrane  96  of the sleeve  94  causing the metal plate  36  to deflect while the electrode  37  remains non-movable within the glass plate  31 . The deflection of the metal plate  29  varies a distance between the two metal plates  36  and  37  changing the capacitance when a voltage is applied. The voltage may be applied to the plates through wires  116  attached to the holes  92  allowing electricity to flow from the wires  116  to the conductive plates and allowing a capacitance to be recorded. Detection of the capacitance is proportional to the applied ICP on the center diaphragm thus an ICP may be calculated. 
     Referring to  FIG. 6 , the bonded plate  90  held within the sleeve  94  may be carried by a biocompatible holder  100  that is installed within the skull of the patient  12  to measure ICP changes. The biocompatible holder  100  may include a disk  102  supporting a downwardly extending tube  104 . 
     The disk  102  may be circular in shape and flattened to provide a top surface  108  opposite a bottom surface  110  to fit a human skull shape. A perimeter of the disk  102  may include a U-shaped cutout  106 . 
     A tube  104  extends downwardly from the bottom surface  110  of the disk  102  providing an oblong support structure with a rounded tip for carrying the pressure sensor  26 , for example, the bonded plate  90 . The tube  104  may have a rectangular receiving socket  112  within an outer surface of the tube  104  for receiving the pressure sensor  26 . The receiving socket  112  may be sized to receive the pressure sensor  26  therein and may include fastening or bonding means to secure the pressure sensor  26  in place. The pressure sensor  26  is installed within the receiving socket  112  such that the center diaphragm of the pressure sensor  26  is exposed allowing ICP pressure to be applied thereon. 
     The electrical wires  116  coupled to the pressure sensor  26 , for example, to each plate  29 ,  31  of the bonded plate  90 , may run from a distal end of the tube  104 , through the tube  104 , and to the disk  102  where the electrical components are held so as to communicate an electrical signal and a capacitance measurement. The electrical wires  116  may communicate with the valve microcontroller  24 , RFID circuit  25  (or other wireless communication device), and other electronics for transmission to and from the implanted or external RFID circuit  25  (or other wireless communication device). 
     In an alternative embodiment, it will be understood that the capacitance formed by the electrical plates  36  and  37  may be incorporated into an electrically resonant circuit that may be interrogated remotely, for example using wireless signals from the telemeter device  14  which by measuring the frequency of this circuit (in the manner of a grid dip meter) can determine the ICP. Thus the pressure sensor  26  may be used independently as an ICP sensor or may communicate with the valve controller  24  wirelessly. The resonant circuit may be formed in part by shaping the electrical plates  36  and  37  into spiral coils acting both as antennas and inductors for the purpose of creating the resonant circuit. In this case the pressure sensor  26  does not need to be wired or powered by an external power source, instead relying upon an external reader to detect and respond to physical changes within the pressure sensor  26 . 
     In an alternative embodiment, the pressure sensor  26  may be a commercially available piezoresistive sensor, e.g., where a silicon diaphragm is exposed to the ICP. A silicon diaphragm is used in which an ICP pressure difference across the diaphragm leads to a change of resistivity which may be measured by the valve controller  24 . For example, the piezoresistive sensor may be Amphenol P330 series or All Sensors DS-0287 series, both of which are commercially available. 
     It is understood that the pressure sensor  26  may be biocompatible and MRI compatible and may be used in conjunction with a holder  100  that is also biocompatible and MRI compatible. The RFID (or other wireless communication device) circuit  25  and antenna  27  may by isolated by a magnetic switch or reed switch that when in the presence of a magnetic field, such as when within an MRI machine, the antenna  27  will disable. The magnetic switch opens the circuit in high magnetic fields in each orthogonal plane. This prevents overheating and overcharging of the system in magnetic environments. Alternatively, various voltage threshold circuit such as back to back diodes or the like may be used to shunt the antenna  27  for example by detuning it. 
     Valve Control System 
     Referring now to  FIGS. 7 and 8 , the valve driver  24  executing the valve control program  132 , may receive the electrical signal indicating an ICP measurement of the pressure sensor  26  wirelessly or through a wired connection. The ICP measurement may consists of pulse waveforms having up to five peaks for a single pulse. The first three peaks (P1, P2, P3) generally determine the main waveform called a “P wave”. P1 is due to the arterial pulse, P2 is due to cerebral compliance, and P3 is due to closure of the aortic valve, which causes the dicrotic notch. 
     The valve microcontroller  24  operates a program  132  comprising a number of steps to be described. The program may operate a “sleep mode” whereby the control program  132  does not record the incoming ICP sensor signals as indicated by the process step  134 . The sleep mode helps to conserve energy consumption and battery life. 
     After a predetermined amount of time (T1) has passed or when a predetermined condition occurs, such as when the patient  12  moves or during certain times of the day, the program proceeds to an “active mode” during which the control program  132  executes a measurement cycle  131  during which it records the incoming ICP sensor signals during a monitoring time  135  (T2) to determine an ICP over a predetermined time period as indicated by the process step  136 . For example the active mode may record the incoming ICP sensor signals during a monitoring time  135  (T2). In one embodiment, the monitoring time  135  may be for a five or ten minute period or a period between five and ten minutes. 
     During or after the monitoring time  135  (T2) has passed, the recorded data is processed using de-noising and smoothing algorithms and techniques, for example, moving average, low pass filter, exponential smoothing, etc. In one embodiment, the algorithm is a local regression method as indicated by the process step  137 . In one embodiment, the local regression algorithm assigns regression weights to the value within a dynamic range with a length chosen to be 5: 
     
       
         
           
             
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     where x is the predicted value associated with the original signal data to be smoothed, x i  is the neighbor of x in the dynamic range, and d(x) is half of the dynamic range length at the x-axis. Based on these weights, the weighted linear least-squares regression is performed. The regression uses a second degree polynomial. 
     It is understood that other filtering techniques, e.g., moving average, low pass filter, exponential smoothing, etc., may be applied to the recorded data to remove outlier data and/or noise. For example, the filtering techniques may be used to attenuate or remove spikes within the incoming ICP sensor signals, for example, when the patient  12  stands up or coughs. 
     After the signal de-noising step, a wavelet transform will be applied to the signal to get the frequency range of the signal as indicated by process step  141 . The process then proceeds to process step  143  where the frequency range of the resulting signal is determined. 
     If the frequency range is a high frequency range, the signal information is outputted to the medical professional for further evaluation as indicated by process step  145 . For example, the high frequency may indicate a critical patient condition or system failure that requires human intervention. If the frequency range is a low frequency range (e.g., DC level), then the shunt will be controlled depending on the signal and proceed to averaging step  138 . 
     As indicated by process step  138 , when the frequency range is in the low frequency range, the filtered recorded data is averaged over the recording time period. 
     The averaged ICP is compared against a threshold value (TH) which may be set by the operator (for example, 12 mmHg). If an average ICP pressure value is over the threshold value, it is considered “high” and requires CSF draining and if an average ICP pressure value is under the threshold value is considered “normal” or “low” and does not require CSF draining as indicated by process step  140 . If the averaged ICP is above the threshold value, the process continues to step  142  to open the valve  22  for a short control time  139  (T3) depending on the amount of difference between the averaged ICP and the threshold value, allowing the CSF to drain for the short period of time and then re-closing the valve immediately after. In one embodiment, the control time  139  may be between two and five seconds. This functional relationship between the error between the averaged ICP and the threshold value may use a known control algorithm such as proportional/integral/derivative algorithms for stability. The process then loops back to sleep mode  134  or active mode  136 . If the averaged ICP is within a predetermined acceptability zone of the threshold pressure, the process automatically loops back to sleep mode  134  or active mode  136  with the valve  22  remaining closed. If the process loops back to active mode, the incoming electrical signals are recorded for the next predetermined time period and the cycle is repeated. If the process loops back to sleep mode  134 , the process remains dormant until the program proceeds to active mode. 
     The operator may determine the parameters (TH, T1, T2, T3) associated with the control program  132 . These parameters may be conveyed to the valve microcontroller  24  through the telemeter device  14  or may be preprogrammed into the device. For example the operator may determine when and how long the control system remains in sleep mode  134 . The operator may also determine when the system proceeds to active mode  136 . The operator may also determine the threshold value (step  140 ) and the amount of time the valve  22  is opened (step  142 ). 
     In an alternative embodiment of the present invention, instead of exceeding a pressure threshold level, the valve may open based upon a pressure elevation over time. For example, the pressure elevation may be determined by an accelerometer or altimeter used to measure changes in altitude, vertical velocities, or altitudes of the device above a fixed level. In this respect, the valve may open as a function of intracranial pressure elevation and time. The valve may close as a function of a lower intracranial pressure parameter. 
     A cycle may be defined as switching from a closed valve  22  to an open valve  22  for successive cycles. It is understood that the valve  22  remains closed for the majority of time of the cycle whereas the valve  22  is opened for only short periods of time within the cycle when a high ICP is detected. In one embodiment, the valve may be opened 2 to 3 seconds or less than five seconds. In this respect, drainage of the CSF occurs for only short periods of time, minimizing the possibility of over drainage and allowing the tissue surrounding the catheter to rebound from a deformed position within the holes of the catheter when the valve  22  is off (i.e., tissue recovery period). The valve  22  may be opened for a period of time limited to a predetermined time permitting tissue surrounding the catheter to be release from the catheter without irreversible shape change. In one embodiment, the valve  22  may remain open for less than 25% of the cycle time or less than 10% of the cycle time or less than 2% of the cycle time. 
     Although the closed valve  22  may indicate zero flow, it may also mean low flow allowing the tissue to be released form the catheter. In this respect, the open valve  22  may indicate a flow rate that substantially holds the tissue in the holes of the catheter. 
     Electrically Actuated Valves 
     Referring now to  FIGS. 9, 10 and 11  the valve microcontroller  24  may receive a signal from the pressure sensor  26 , through a wired or wireless communication, indicating an ICP signal. The valve microcontroller  24  then runs the valve control program  132  to determine whether the valve should be on or off. The on-off instruction is then sent to the valve driver  24  to regulate the valve  22  of the cerebral shunt system  10  between an on and off state. 
     In one embodiment of the present invention, the electrical signal causes a piezo bender actuator  152  to bend between a first position and a second position, opening and closing the valve  22 . The piezo bender actuator  152  may be a cantilevered finger having at least one piezoelectric layer of material permitting the finger to displace in at least one direction, for example, providing 1 to 2 mm displacement. The piezo bender actuator  152  may be made of a ceramic, crystal, composite material, or known piezoelectric material and include side surface electrodes attached to electrical wires  116  that may communicate with the valve driver  24 . 
     Referring specifically to  FIGS. 9 and 10 , the valve&#39;s on and off state may be actuated by an electrical signal delivered from the valve driver  24  to the valve  22  to electrically actuate the valve  22 . 
     The valve  22  may provide for an enclosed chamber  150  (as shown in  FIG. 9 ) communicating with the proximal catheter  18 . An inflow tube  151  spans the enclosed chamber  150  and passes through one wall of the chamber  150  to the distal catheter  20 . The proximal catheter  18  may be connected in series with the inflow tube  151  regulating CSF flow to a drain tube  159  connected in series to the distal catheter  20 . The transverse inflow tube  151  and drain tube  159  may be constructed of stainless steel and may have a diameter less than the catheter  18 ,  20  allowing the catheter  18 ,  20  to couple to the tubes  151 ,  159  by sliding thereover. 
     As seen best in  FIG. 10 , the inflow tube  151  has a small orifice  154  normally covered by a blocking collar  156  that prevents flow between the proximal catheter  18  and distal catheter  20  (for example, prevents flow from the orifice  154  into the chamber  150  and to the drain tube  159 ). 
     A piezo electric bender  152  is fixed within the chamber  150  and extends in cantilevered fashion between bender guides  133  which allow the piezo electric bender  152  to slide the collar  156  along the inflow tube  151  in order to open and close the orifice  154 . The piezo bender actuator  152  extends toward the transverse inflow tube  151  and is displaced in one direction along axis  149  when a voltage is applied and in an opposite direction along axis  149  when a second voltage is applied. 
     When the piezo bender actuator  152  is in a first closed position, the collar  156  is in a position whereby the collar  156  covers the orifice  154  preventing CSF to drain from the inflow tube  151 . When the piezo bender actuator  152  is in a second open position, the collar  156  is in a position whereby an orifice  154  of the transverse inflow tube  151  is exposed allowing CSF to drain from the transverse inflow tube  151 . It is understood that various gaskets or other sealing means may be used to prevent leakage. 
     Referring now to  FIG. 11 , in an alternative embodiment of the present invention, the valve  22  may receive CSF from the proximal catheter  18  through an inflow tube  151  in a similar manner. The valve  22  may control flow from the inflow tube  151  to a drain tube  159  in series with the distal catheter  20  permitting CSF to drain. 
     The valve  22  may provide a housing with a chamber ( FIG. 9 ) supporting the inflow tube  151  and having an orifice  154  extending along an axis  161  used to drain CSF to the drain tube  159 . The housing may support a piezo bender actuator  152  defined by a cantilevered finger supported at one end and unrestricted on the opposite end  153  to become displaced in one direction substantially along axis  161  when a voltage is applied and in the opposite direction substantially along axis  161  when a second voltage is applied. 
     The free end  153  of the piezo bender actuator  152  may include a polymer gasket material  155  wrapped around the free end  153  and also including a flexible pin  157  extending from the gasket material  155  toward the orifice  154  substantially along axis  161  when displaced. The flexible pin  157  is sized and positioned to fit within the orifice  154  so as to plug the orifice  154  preventing the flow of CSF therethrough. 
     When the piezo bender actuator  152  is in a first closed position, the free end  153  is positioned toward the orifice  160  and the pin  157  is plugged within the orifice  160  preventing CSF to drain from the inflow tube  151 . When the piezo bender actuator  152  is in a second open position, the free end  153  is positioned away from the orifice  160  and the orifice  160  is unblocked allowing CSF to drain from the inflow tube  151 . 
     It is understood that many types of electrically actuated valves  22  may be used in conjunction with the present invention for regulating the flow rate of CSF out of the brain and into a drainage site. While the valve  22  is generally described as an on-off valve it is understood that the valve  22  may also regulate the flow rate (varied flow rate above 0) when in the on position. 
     Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference, which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. When elements are indicated to be electrically connected, that connection may be direct or through an intervening conductive element. 
     When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.