Abstract:
Cerebrospinal fluid shunts (implantable devices for diversion of excess fluid from the brain to other body cavities) used to treat hydrocephalus often malfunction. A common etiology of shunt malfunction is obstruction of the distal catheter tip by accumulating particulate matter such as fat or proteinaceous debris. The proposed implantable device maintains the patency of the cerebrospinal fluid shunt with mechanical energy which serves to “scrub” the catheter lumen of particulate debris. The proposed device accomplishes this by housing a source of mechanical energy which is coupled to the external aspect of the catheter, itself traversing through a bore in the device. The energy source secondarily induces a waveform in the cerebrospinal fluid flowing through the catheter. The fluid waveform exerts shearing forces on the catheter wall and serves to disrupt the formation and accumulation of debris that potentially could occlude the shunt catheter, thereby maintaining patency of the shunt.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit under 35 U.S.C § 119( e ) of U.S. Provisional Patent Application No. 60/594,517, filed Apr. 14, 2005, and of U.S. Provisional Patent Application No. 60/596,196, filed Sep. 7, 2005. The entire content of each of these applications is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a shunting system, and more particularly, to an implantable anti-clogging device used to maintain cerebrospinal fluid shunt patency.  
       BACKGROUND OF THE INVENTION  
       [0003]     Hydrocephalus is the pathologic accumulation of cerebrospinal fluid (CSF) in the brain. The disease entity has a variety of clinical manifestations ranging from the more benign triad of normal pressure hydrocephalus (gait ataxia, dementia and urinary incontinence) to those secondary to elevated intracranial pressure. The latter may follow a more malignant course and in fact, prove fatal. Hydrocephalus is treated by diverting excess cerebrospinal fluid from the brain to an alternate body cavity. Most commonly, this is the peritoneal cavity (abdominal compartment). The diversion of fluid is accomplished by a shunting device (described in the prior art) which is surgically implanted into the patient. The proximal limb of the shunt system is introduced into the fluid cavities of the brain (“ventricles”) and the distal end into the peritoneal cavity. Through small apertures, excess CSF can enter the shunt (intracranially) and drain into the peritoneal cavity. There exists an interposed valve which broadly serves to regulate CSF flow through the system.  
         [0004]     Cerebrospinal fluid shunts, commonly molded from silicone tubing, are susceptible to failure. In fact, 30-40% of cerebrospinal shunts malfunction after primary placement in the adult population. Such malfunctions, while often benign, may prove dangerous or, if left untreated, fatal. Therefore, the maintenance of cerebrospinal fluid shunt patency is essential to patient wellness. Presently, patients with a malfunctioning shunt undergo revision surgery to reestablish flow through the occluded shunt system. In the adult population, this often requires removal of the shunt catheter from the abdominal compartment, resecting the distal 3-4 cm of the catheter and relocating the catheter within the abdomen. The procedure and the inpatient hospitalization have associated risks and morbidity.  
         [0005]     The majority of shunt malfunctions in the adult population are the direct result of an occlusion at the distal shunt catheter tip (outlet). The distal catheter tip, often located in the peritoneal cavity, is susceptible to blockage by proteinaceous debris or fat. Prevention of such blockage (i.e., maintenance of CSF shunt patency) is desired and an object of the present invention.  
         [0006]     No current implantable device exists to maintain CSF flow in the distal limb of a shunt catheter. U.S. Pat. No. 5,405,316 describes a cerebrospinal fluid shunt that includes plural openings (at the distal tip) through which the fluid flows. As disclosed in this patent, the openings are arranged so tissue growth through the openings does not occlude flow of the fluid within the catheter. However, such designs have been associated with high failure rates. U.S. Pat. No. 5,584,314 describes a self-cleaning inlet head for a fluid. This patent describes an in-line device for the ventricular (proximal) catheter that by combining mechanical and hydraulic action, effectively loosens and sweeps away debris within the catheter lumen. The mechanism is based upon a piston which slides within the catheter lumen in direct contact with potentially debris-laden cerebrospinal fluid. Though elaborate in design, such a mechanism, by virtue of its intricate structure and reliance on small mobile components (see, e.g.  FIG. 7 ), may be susceptible to mechanical failure. An external (extraluminal) method is therefore necessary to maintain fluid flow.  
         [0007]     The prior art also includes external energy sources that have been utilized for similar rationale. U.S. Pat. Nos. 4,698,058 and 5,061,255 provide a self-cleaning catheter system for use in protracted transfer of fluid between a patient&#39;s body and a point outside the body. The system includes a catheter and a source of mechanical vibration which serves to disintegrate undesirable substances within the catheter lumen and maintain the protracted fluid transfer relatively free from obstruction and contamination by the undesirable substance. Similarly, various forms of energy have been utilized to maintain patency of coronary stents and endovascular grafts (U.S. Pat. Nos. 6,231,516; 6,361,554; and 6,585,763) and to prevent post-interventional neointimal hyperplasia and resultant restenosis (U.S. Pat. Nos. 6,210,393 and 6,755,853).  
         [0008]     Other prior art devices which purportedly serve or include methods of utilizing energy to treat or maintain flow of a fluid include those described in U.S. Pat. Nos. 4,509,947; 5,735,811; 5,957,882; and 6,852,097.  
         [0009]     Although the prior art has included numerous devices utilizing externally applied energy to maintain flow of fluid in a lumen, there remains a need in the art for a discrete implantable device used to maintain flow of fluid in the distal cerebrospinal fluid shunt limb. This should be differentiated from a shunt system which, as an integrated component, includes an anti-clogging agent. Failure of integrated components in such unitized systems may necessitate replacement of the entire shunt system (both cranial and abdominal limbs), exposing the patient to added surgical risk. It is optimal therefore to utilize a discrete device with an integrated energy source that is surgically implanted in juxtaposition to the distal shunt catheter. A device distinct from the shunt catheter, the proposed invention may be implanted at time of initial shunt placement or during distal catheter revision procedure.  
         [0010]     It is an object of the invention to provide an implantable device that maintains cerebrospinal fluid shunt patency.  
         [0011]     It is a further object of the invention to provide a device that is implanted in-line with a cerebrospinal fluid shunt.  
         [0012]     It is another object of the invention to provide an implantable device that supplies pulsatile energy to the external aspect of a shunt catheter.  
         [0013]     It is yet another object of the invention to provide an implantable device capable of inducing a waveform in the cerebrospinal fluid flowing within a shunt catheter.  
       SUMMARY OF THE INVENTION  
       [0014]     In accordance with the present invention, there is provided an implantable device that maintains cerebrospinal fluid shunt patency. The device includes a housing made of a biocompatible material and enclosing a compartment therein. The housing has a passageway therethrough with entry and exit ports. The lumen of the passageway is configured and dimensioned to receive a section of the shunt tube. The device also includes an energy generator contained within the compartment. The energy generator generates vibratory energy transmitted to the section of the shunt tube to thereby maintain fluid flow in the shunt.  
         [0015]     The energy generator can include a transducer that converts electrical energy into the vibratory energy. In one embodiment, the transducer produces ultrasonic vibratory energy. In other embodiments, other forms of energy such as sonic, subsonic, and electromagnetic radiation (e.g. light) are used. An impedance-matched elastic membrane can couple the transducer to the section of the shunt tube. The energy generator can also include a signal generator connected to the transducer for generating an electrical signal, a control unit connected to the signal generator for controlling the electrical signal, and a power source for powering the control module.  
         [0016]     In one embodiment, the power source is a rechargeable battery and the energy generator further includes an induction loop connected to the rechargeable battery and responsive to an external energy source to charge the rechargeable battery.  
         [0017]     In order to provide a snug connection, each of the entry and exit ports can include a cuff configured and dimensioned to establish contact areas with the section of the shunt tube. The housing can include fixation tabs for attaching the device to tissue.  
         [0018]     The present invention also relates to a method of maintaining patency of a shunt implanted in a patient. The anti-clogging device is implanted in the patient such that a section of shunt tube is received in the passageway of the housing. The section of the shunt located within the device is excited with energy generated by the energy generator. This secondarily induces a waveform in the fluid flowing within the shunt tube lumen. The fluid waveform propagates the length of the shunt tube and mechanically impedes the accumulation of proteinaceous debris or fat within the lumen, thereby maintaining patency of the shunt.  
         [0019]     The energy generated by the energy generator can be ultrasonic vibratory energy that is generated by a transducer that converts electrical energy into the ultrasonic vibratory energy. In other embodiments, different forms of energy such as sonic, subsonic, and electromagnetic radiation (e.g. light) are generated by the transducer. Regardless of the type of energy, the electrical energy can be stored by a power source, such as a rechargeable battery, that is implanted as a component of the anti-clogging device. The rechargeable battery can be recharged by an extra-corporeal energy source.  
         [0020]     The anti-clogging device can be implanted in the patient during the same procedure that the shunt is implanted. Alternatively, the anti-clogging device is implanted in the patient in a procedure subsequent to the procedure that the shunt is implanted.  
         [0021]     If the shunt is a cerebrospinal fluid shunt, the section of the tube contained within the housing can be located in the peritoneal cavity of the patient. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when considered in conjunction with the subsequent detailed description in which:  
         [0023]      FIG. 1  is a top detail view of the implantable device in accordance with the invention;  
         [0024]      FIG. 2  is a top partial view of the implantable device in accordance with the invention;  
         [0025]      FIG. 3  is an electronic schematic of an embodiment of an electrical circuit for the implantable device in accordance with the invention;  
         [0026]      FIG. 3A  is a schematic representation of an electrical signal input to the implantable device and the resulting mechanical signal output;  
         [0027]      FIG. 4  is a sectional view of the implantable device in accordance with the invention;  
         [0028]      FIG. 5  is a front sectional view of the implantable device in accordance with the invention;  
         [0029]      FIG. 6  is an in situ view of the implantable device in accordance with the invention; and  
         [0030]      FIG. 7  is a sectional view of a prior art shunt head that can be used with the implantable device in accordance with the invention. 
     
    
       [0031]     For purposes of clarity and brevity, like elements and components will bear the same designations and numbering throughout the Figures.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0032]      FIG. 1  shows an anti-clogging device  90  of the present invention. Anti-clogging device  90  maintains patency of tube  100  of a shunt. Anti-clogging device  90  includes a housing  102  that may be composed of titanium or any other suitable biocompatible material. Housing  102  provides a protective outer shell for the implantable device and has a hollow core thereby defining a compartment  92  to accommodate the device components. Housing  102  can be provided with smooth or otherwise blunted edges to minimize tissue trauma and may be variously shaped in alternate embodiments. In an exemplary embodiment, housing  102  has a flat bottom surface to maximize contact with the tissue to which it is secured. Shunt catheter tube  100  is traversing device  90  through central bore or passageway  103  which has a lumen configured and dimensioned to receive a section of tube  100 .  
         [0033]     Passageway  103  can be cuffed with a rubber bushing  104  (at points of entry  105   a  and exit  105   b  ports) to encourage tight coupling between tube  100  and the inner lumen of passageway  103 . Tube  100  is fed through passageway  103  and subsequently into the chosen body cavity at time of implantation. Alternatively, housing  102  can be provided with a door or other opening so that tube  100  can be inserted or removed without having to be fed through entry  105   a  and exit  105   b  ports. As shown, suture tabs  101  are firmly affixed to the corners and top surface of housing  102 , but placement may be varied in alternate embodiments. In an exemplary embodiment, suture tab  101  is comprised of flexible material (e.g. silicone) with a central hole that allows for surgical fixation of the device to local tissue at time of implantation.  
         [0034]      FIG. 2  is a top partial view of implantable anti-clogging device  90  in accordance with the invention. Shunt catheter  100  is traversing device  90  through passageway  103  en route to its final destination in the selected body cavity. Device  90  has both entry  105   a  and exit  105   b  ports for traversing shunt catheter  100 . Shunt catheter  100 , by virtue of its position in passageway  103 , is juxtaposed to elastic membrane  118 . Elastic membrane  118 , which may be composed of any deformable substance (e.g. rubber) is tightly coupled to the active surface of transducer  107 . “Active surface” herein refers to the portion of transducer  107  which emits various energy forms. Elastic membrane  118  can be transparent or translucent for visualization of the underlying transducer  107  and can be impedance-matched to the vibrations produced by transducer  107 .  
         [0035]     Transducer  107  is a component of energy generator  94  that generates vibratory energy transmitted to the section of tube  100  that traverses through device  90  to thereby maintain fluid flow in the shunt. Energy generator  94  is completely contained within compartment  92 , and as described in more detail below, can include other components.  
         [0036]     For example and as shown in  FIGS. 2 and 3 , energy generator  94  can include a circuit board  106  that serves a dual purpose. It functions as a base structure to which the internal components of device  90  are mounted. Circuit board  106  can be made of coated copper or other suitable conductive material such as gold. Energy generator  94  can also include a control unit or module  108  that has wiring etched into circuit board  106 . Surface-mount electronic components are utilized in an exemplary embodiment. Alternate embodiments may employ different wiring substrates and components. Coupling leads  110  transmit generated signals from control module  108  to transducer  107 .  
         [0037]     Control module  108  can include a signal generator  109 , a charging unit  112 , a rechargeable battery  111 , and an induction loop  113 . Signal generator  109  is microprocessor-based and comprises an oscillator, gating circuitry, and an amplifier. Control module  108 , a functional unit and not a discrete component, generates the amplified waveforms that will ultimately be gated or directed into transducer  107  via coupling leads  110 . Transducer  107  which may be sonic, ultrasonic or vibrational emits energy upon its activation and secondarily induces a similar waveform in elastic membrane  118 . Coupled to traversing shunt catheter  100 , elastic membrane  118  evokes yet a similar waveform in the cerebrospinal fluid flowing within the catheter lumen. Alternate embodiments may utilize electromagnetic radiation and a varied signal transduction scheme to apply light energy to the external aspect of shunt catheter  100 .  
         [0038]     Charging unit  112  governs the charging of rechargeable battery  111 . The circuitry regulates the transfer of energy from induction loop  113  to rechargeable battery  111 . In an embodiment, rechargeable battery  111  is charged by exposing inductive loop  113  to an extracorporeal magnetic field source. In an alternate embodiment, rechargeable battery  111  may be substituted for a fuel cell.  
         [0039]      FIG. 3  is an electronic schematic view of energy generator  94 . Specifically, the basic interconnections of control module  108  are depicted. Rechargeable battery  111  which is the power source is connected in parallel to charging unit  112  and signal generator  109 . Induction loop  113  is similarly wired in parallel to charging unit  112 . Conducting the waveform from signal generator  109  to transducer  107  are coupling leads  110 .  
         [0040]     Signal generator  109  comprises an oscillator, gating circuitry and an analog amplifier. The oscillator is capable of generating various waveforms. Generated analog waveforms are gated into transducer  107  at various intervals. The gating circuitry, functionally a square wave generator in series with a digital switch, controls the interval between analog pulses and the pulse width of the analog waveform gated into transducer  107 . The former is a function of the duty cycle of the gating pulse and the latter is a function of the frequency of the gating pulse. The frequency of the analog waveform gated into transducer  107  may be varied. In an exemplary embodiment an ultrasonic transducer  107  is utilized, and accordingly analog waveforms with ultrasonic frequencies are gated into transducer  107 . Alternate embodiments may utilize sonic or subsonic transducers and driving frequencies. Yet other embodiments may utilize vibrational transducers and appropriate driving frequencies.  
         [0041]      FIG. 3A  depicts an analog waveform that is gated into transducer  107  by the digital gating pulse. The amplified waveform is gated into transducer  107  via coupling leads  110  at a certain duty cycle and frequency.  
         [0042]      FIG. 4  is a sectional view of device along the longitudinal axis and parallel to the traversing shunt catheter  100 . The base of transducer  107  is affixed to the supporting circuit board  106 . Elastic membrane  118  is coupled to the active surface of transducer  107 . Elastic membrane  118  is positioned in juxtaposition to traversing shunt catheter  100 . Fluid waveform  114  within shunt catheter  100  is induced by energy transfer from elastic membrane  118 . Retaining screw  119  secures elastic membrane  118  to circuit board  106 . Circuit board  106  is encapsulated in epoxy  120  or similar substrate and affixed to the device housing  102  with mounting hardware.  
         [0043]      FIG. 5  is a sectional view of device  90  perpendicular to traversing shunt catheter  100  in the vertical plane.  
         [0044]      FIG. 6  is an in situ view of device  90 . As shown, device  90  is affixed to locally available abdominal fascia. Alternate embodiments of smaller dimension may be implanted in the thoracic region in the case of ventriculopleural or ventriculoatrial shunts. Proximal portion  117  of shunt  100  is located in the ventricular system of the brain. Cerebrospinal fluid enters proximal portion  117  through orifices at its tip. The fluid flows through intervening shunt valve  121  into distal portion  116  of shunt  100 . Distal portion  116  is the subcutaneous catheter segment distal to shunt valve  121 . Distal shunt catheter  116  prior to its termination in the peritoneal cavity traverses device  90  via passageway  103 . Within passageway  103 , the external aspect of the catheter is exposed to an energy source which induces a waveform in the flowing cerebrospinal fluid.  
         [0045]      FIG. 7  is a section view of a prior head that can be used on shunt  100  in conjunction with device  90 .  
         [0000]     Operation  
         [0046]     Device  90  maintains the patency of the distal shunt catheter  116  and may be implanted during initial shunt placement or during revision surgery. In the case of a vertriculoperitoneal shunt, the surgeon positions device  90  in-line with the distal shunt catheter  116  prior to its passage into the peritoneal cavity. The surgeon has the option of coupling the catheter with the device before or after the laparotomy is performed. “Laparotomy” refers to the act of surgically entering the peritoneal cavity. Regardless of the selected method, final implantation of the device entails inserting the catheter through passageway  103  and subsequently into the peritoneal cavity.  
         [0047]     As optimal function of device  90  relies upon tight coupling between the external aspect of distal shunt catheter  116  and internal elastic membrane  118  for adequate energy transfer, the distal catheter must be pulled through passageway  103  as it is of smaller internal diameter than the external diameter of distal shunt catheter  116 . Initially a suture can be passed through passageway  103  and tied to the end of distal catheter  116 . The catheter  100  is then pulled through passageway  103  utilizing the passed suture. In another embodiment and as previously discussed, device  90  can be made so that passageway  103  is accessible without having to feed catheter  100 . For example, device  90  made be provided in two halves that allow catheter  100  to be placed in passageway  103 . The catheter is then directed into the peritoneal. The standard closing procedure involves re-approximating all anatomical layers, deepest to most superficial. Upon closure of the fascia deep to device  90 , the surgeon secures device  90  to it utilizing suture tab  101 . This prevents subcutaneous migration of the device.  
         [0048]     The device requires intermittent recharging (or replacement of the power source) which can be performed with an extracorporeal magnetic field generator. This is placed over the implantation site for a determined time interval.  
         [0000]     Advantages  
         [0049]     From the description above, a number of advantages of the proposed invention become evident: 
        (a) By reducing the incidence of shunt malfunctions, the proposed device reduces the number of revision procedures necessary. This translates to a potential reduction in surgical morbidity (as an absolute number) and cost.     (b) Such a device is easily implanted either at time of initial surgery or during revision procedures.     (c) The proposed device may be placed in-line with existing shunt catheters in the case of distal revision surgery during which the catheter is removed from the peritoneal cavity and relocated to another site within the same cavity.     (d) As the proposed device is externally coupled to the shunt catheter  100 , there are no intraluminal components capable of causing a shunt malfunction.     (e) Similarly, the proposed device is, in itself, not subject to malfunction as caused by accumulation of proteinaceous debris and/or fat within the distal catheter lumen.        
 
         [0055]     Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the example chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. All references identified are incorporated herein by reference.