Abstract:
The present invention is directed to a system and method for monitoring the intraluminal pressure in a ventricular shunt. The shunt may have one or more measurement nodes housing a pressure-sensitive body that changes dimensions in response to the pressure of the cerebrospinal fluid within the lumen of the shunt. The change in the dimensions of the pressure-sensitive body may be measured transcutaneously using an ultrasonic transducer and processed using a processor to estimate the intraluminal pressure. The shunt may include one or more pressure-measurement nodes distributed along the length of the shunt to enable the detection of shunt occlusions and valve malfunctioning.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 60/778,752, filed Mar. 3, 2006, entitled Methods and devices for pressure measurement and infection reduction in neurosurgical shunts, and U.S. Provisional Patent Application No. 60/796,714, filed May 2, 2006, entitled Methods and devices for non-invasive pressure measurement in ventricular shunts, and incorporates the contents in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a system and method for monitoring the pressure in a ventricular shunt, in particular, a system and method utilizing a pressure-sensitive body that changes shape in response to pressure within the lumen of the ventricular shunt. 
       BACKGROUND OF THE INVENTION 
       [0003]    Hydrocephalus is a condition in which the body is unable to relieve itself of excess cerebrospinal fluid collected in the ventricles of the brain because of infection or disease. The increase in the cerebrospinal fluid pressure may be caused by tumor of the brain or of the membranes covering the brain (e.g. meninges), infection of or bleeding into the cerebrospinal fluid, or congenital malformations of the brain. 
         [0004]    Ventricular shunt is a surgical procedure in which a tube is placed in one of the brain ventricles to drain the excess cerebrospinal fluid and relieve the elevated pressure in hydrocephalus. The ventricular shunt drains fluid from the ventricular system in the brain to the cavity of the abdomen (e.g. peritoneal cavity) or to a large vein in the neck (e.g. the jugular vein). 
         [0005]    The tubing contains unidirectional valves to insure that fluid can only flow out of the brain and not back into it. The valve can be set at a desired pressure to allow cerebrospinal fluid to escape whenever the pressure level is exceeded. 
         [0006]    A small reservoir may be attached to the tubing and placed under the scalp. This reservoir allows samples of cerebrospinal fluid to be removed with a syringe and to check the pressure. 
         [0007]    The pressure of the cerebrospinal fluid should be checked periodically to ensure that the pressure is relieved and the shunt is operating properly, and/or initiate a drug therapy if necessary. Therefore a means for the non-invasive measurement of the cerebrospinal fluid pressure along the length of the shunt is highly desirable to detect the degree and location of tube occlusion(s) and the malfunction of the valve(s). 
       SUMMARY OF THE INVENTION 
       [0008]    The current invention relates to a ventricular shunt (or shunt, used interchangeably herein) including a pressure-sensitive body that changes its dimensions in response to the pressure of the cerebrospinal fluid within the lumen of the shunt. 
         [0009]    The change in the dimensions of the pressure-sensitive body may be measured transcutaneously using an ultrasonic transducer and processed using a processor to estimate the intraluminal pressure at the location of the pressure-sensitive body. 
         [0010]    The pressure-sensitive body may be housed in a pressure-measurement node configured to ensure the proper aiming of the ultrasonic transducer on the pressure-sensitive body to improve the accuracy by which the dimensions of the pressure-sensitive body are measured. 
         [0011]    The shunt may include one or more pressure-measurement nodes distributed along the length of the shunt to enable the detection of occluded shunt segments and/or the detection malfunctioning valves. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  shows an embodiment of a ventricular shunt and a monitoring unit in accordance with the present invention. 
           [0013]      FIG. 2A  shows a front view of the shunt of  FIG. 1 . 
           [0014]      FIG. 2B  shows a side view of the shunt of  FIG. 1 . 
           [0015]      FIG. 2C  shows a front view of a measurement node of the shunt of  FIG. 1 . 
           [0016]      FIG. 2D  shows a side view of a measurement node of the shunt of  FIG. 1 . 
           [0017]      FIG. 3  shows an embodiment of an ultrasound probe positioned on the measurement node of the shunt of  FIG. 1 . 
           [0018]      FIG. 4  shows another embodiment of the ultrasound probe positioned on an embodiment the measurement node of the shunt of  FIG. 1 . 
           [0019]      FIG. 5A  shows a front view of another embodiment of the shunt. 
           [0020]      FIG. 5B  shows a side view of another embodiment of the shunt. 
           [0021]      FIG. 6A  shows a front view of another embodiment of the measurement node. 
           [0022]      FIG. 6B  shows a side view of another embodiment of the measurement node. 
           [0023]      FIG. 7A  shows a front view of another embodiment of the measurement node. 
           [0024]      FIG. 7B  shows a side view of another embodiment of the measurement node. 
           [0025]      FIG. 8A  shows a front view of another embodiment of the shunt. 
           [0026]      FIG. 8B  shows a side view of another embodiment of the shunt. 
           [0027]      FIG. 9  shows a front view of another embodiment of the shunt. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    A shunt monitoring system is shown in  FIG. 1 . The shunt monitoring system may be comprised of a shunt  100  with measurement nodes  106  and  108  and a monitoring unit  141 . The monitoring unit  141  may be comprised of a transducer  130  and a processor  142 . 
         [0029]    The preferred embodiment of the shunt  100  shown in  FIG. 1  and  FIG. 2  may be a flexible tube with a lumen  102 , a set of draining holes  104 , and at least two measurement nodes  106  and  108  positioned along the length of the shunt  100 . The set of draining holes  104  may be located at the distal end  110  (or ventricular end, used interchangeably herein) of the shunt  100 . 
         [0030]    The nodes  106  and  108  may be preferably positioned along the length of the shunt  100  at locations that are accessible for interrogation by the external ultrasonic transducer  130  once the shunt  100  is placed inside the patient&#39;s body. The pressure measured at the node  106  closest to the ventricular end  110  may indicate the ventricular pressure, while a pressure difference between the nodes  106  and  108  may indicate an occlusion  174  between the locations of the nodes  106  and  108 . Although, the above example describes a shunt with the two measurement nodes  106  and  108 , additional measurement nodes may be used to enable the noninvasive detection of occlusion between additional segments of the shunt  100 . 
         [0031]      FIG. 2C and 2D  show the details of the measurement node  106  (or  108 ) which may include a pressure-sensitive body  112  and an acoustic collimator  114 . The pressure-sensitive body  112  may be a gas-filled capsule made of a flexible material such as silicone. The body  112  may be attached to the bottom  116  of the cavity  118  of the measurement node  106  (or  108 ). The cavity  118  may be continuous with the lumen  102 . The body  112  may collapse in the direction  120  under increased pressure in the cavity  118 . The wall thickness of the body  112  and/or the pressure of the gas within the body  112  may be selected to allow a predetermined degree of collapse of the body  112  under a given increase in the pressure within the cavity  118 . Therefore the distance  122  between the upper surface  124  of the body  112  and the acoustically translucent window  126  of the collimator  114  will vary with the pressure within the cavity  118 . A calibration relationship between the distance  122  and the pressure within the cavity  118  may be established and used by the processor  142  for the estimation of the pressure within the cavity  118  from a measured distance  122 . 
         [0032]    The distance  122  may be measured using an external ultrasound transducer  130  placed over the skin  131  covering the node  106  (or  108 ). The transducer  130  may emit ultrasound pulses  132  aimed towards the collimator  114  as shown in  FIG. 3 . The transducer  130  may receive the ultrasound echoes  134  and  136  returning from the acoustically translucent window  126  and the upper surface  124  of the body  112  and converts them into the electronic pulses  138  and  140 , respectively. The electronic pulses  138  and  140  are processed by the processor  142  to determine the time difference  144  between their corresponding echoes  134  and  136 . The time difference  144  between the ultrasound echoes  134  and  136  or their corresponding electronic pulses  138  and  140  is indicative of the distance  122 . The processor  142  may convert the time difference  144  into the value of the pressure within the node  106  (or  108 ) using the established calibration relationship. 
         [0033]    The acoustical collimator  114  may be composed of an acoustically translucent window  126  surrounded by an acoustically opaque annulus  128  as shown in  FIGS. 2C and 2D . The annulus  128  may be made of an acoustically opaque material such as, for example, TYVEK polymer (commercially available from DuPont), a foamy material, or a gas-filled volume to provide high acoustical attenuation. The collimator  114  may be positioned such that its acoustically translucent window  126  is directly above the upper surface  124  of the body  112 . Therefore, the collimator  114  may only allow the passage of ultrasonic pulses  132  that are traveling approximately perpendicular to the upper surface  124 , which may improve the accuracy and repeatability of the measurement of the distance  122 . In addition, this configuration may eliminate the guesswork re the proper aiming of the transducer  130  and ensure that the returned ultrasound echoes  134  and  136  are arising from the pressure-sensitive body  112 . The body of the node  106  (or  108 ) may be made of rigid and/or semi-flexible materials necessary to maintain the dimensions of the cavity  118 . 
         [0034]    Another embodiment of the measurement node  106  (or  108 ) shown in  FIG. 4  includes metallic or magnetic bodies  150  and  152  to help guide the operator to the location of the node  106  (or  108 ) under the skin  131  without having to palpate. The sensing tip  154  of the ultrasound transducer  156  may be equipped with metal and/or magnetic sensors  160  and  162  that may activate an audio tone or a light indicator  164  once the tip  154  is adjacent to the measurement node  106  (or  108 ). For example, a signal strength indicator  164  (e.g. an optical bar graph) may be used to indicate whenever the tip  154  is over the node  106  (or  108 ) and aligned with the acoustical window  126 . 
         [0035]    In a typical application of the shunt  100 , the distal end  110  of the shunt  100  may be inserted through a hole  170  in the skull  172  into the frontal horn of the right ventricle as shown in  FIG. 1 . The shunt  100  may be tunnelized under the skin  131  all the way down to the peritoneal cavity or to a major vein where it drains. The shunt  100  is positioned such that the collimator  114  of the nodes  106  and  108  is facing the skin  131  as shown in  FIG. 1  and  FIG. 3  to enable the easy interrogation of the pressure-sensing body  112  by the ultrasound transducer  130  placed over the skin  131 . The pressure measured from the node  106  positioned close to the ventricular end  110  may represent the intraventricular pressure. A difference in the pressure between the node  106  and the node  108  may indicate the presence of an occlusion  174  between the two nodes. The magnitude of the difference in the pressure between the node  106  and the node  108  may indicate the degree of the occlusion  174  between the two nodes. The occlusion  174  may lead to an increase in the pressure measured at node  106  relative to the pressure measured at node  108 . An equivalent increase in the pressure at both nodes  108  and  106  above the opening pressure of the shunt&#39;s valve may be indicative of valve malfunctioning. 
         [0036]    Another measurement node embodiment is shown in  FIG. 5  where the measurement node  306  (or  308 ) is located on the side of the shunt  300 . The cavity  318  is opened directly to the lumen  302 . This configuration may have several advantages including that the pressure-sensitive body  312  is positioned away from the lumen  302  and hence it does not affect the effective diameter of the lumen  302 . The winged geometry of the node  306  (or  308 ) with respect to the shunt  300  ensures the proper orientation of the node  306  (or  308 ) relative to the surface of the skin where the ultrasound transducer  130  may be placed to interrogate the pressure-sensitive body  312 . In addition, having the node  308  on the side of the shunt  300  does not increase the overall thickness of the shunt  300  while still making it easier to palpate the location of the node  306  (or  308 ) through the skin. The collimator  314  may be elliptical in shape with an off-centered acoustical window  326  surrounded by the acoustically opaque shield  328 . 
         [0037]    Another embodiment of the measurement node is shown in  FIG. 6  where the pressure-sensitive body  402  may be embedded within the wall  404  of the shunt  400 . In this embodiment the pressure-sensitive body  402  may be a hollow rectangular prism filled with biologically compatible fluid  406  such as for example saline. The upper wall  408  of the body  402  may be non-deformable while the lower wall  410  and the sidewalls  412  and  414  may be expansible diaphragms made of a flexible material such as silicone. The lower wall  410  may be bordering the lumen  416  of the shunt  400 . The sidewalls  412  and  414  may be bordering the gas-filled chambers  418  and  420 , respectively. An increase in the pressure within the lumen  416  may press against the lower wall  410  to displace it in the direction  422  and decrease the distance  424  between the lower wall  410  and the upper wall  408 . Simultaneously, the flexible sidewalls  412  and  414  may bulge into the bordering gas-filled chambers  418  and  420  to relieve the fluid volume shifted by the displacement of the lower wall  410 . This configuration may reduce the resistance to fluid shifts and therefore maximize the displacement of the lower wall  410  in response to a given increase in the intraluminal pressure. 
         [0038]    Similar to the other embodiments, the distance  424  may be measured transcutaneously using the ultrasonic transducer  130  and used by the processor  142  to estimate the pressure within the lumen  416 . 
         [0039]    The lower wall  410  may be embedded with micro air or gas bubbles (not shown) to increase its ultrasonic contrast relative to the fluid  406  and improve its detection using the external ultrasound transducer  130 . In addition, ultrasonic contrast and detection of the lower wall  410  may be also improved by using a fluid  406  with acoustical characteristics that are different from that of the material of the diaphragm  410  and/or that of the biological fluid that would be normally filling the lumen  416  (i.e. the cerebrospinal fluid). The presence of air (or gas) in the chambers  418  and  420  may act as an acoustical collimator that would only allow the passage of ultrasonic waves that are almost perpendicular to both the upper wall  408  and the lower wall  410 . 
         [0040]    Although the above embodiment describes a pressure sensitive body that is rectangular in shape, the body may assume any other shape including cylindrical. A cylindrical pressure-sensitive body (not shown) may be encircled all-around by a gas-filled compartment to allow the expansion of the cylinder&#39;s flexible wall into the surrounding compartment and hence facilitate the movement of the cylinder&#39;s flexible bottom (or diaphragm) in response to an increase in the intraluminal pressure. 
         [0041]    Another embodiment of the measurement node is shown in  FIG. 7  where the pressure-sensitive body may be composed of at least the two hydraulically connected chambers  502  and  504  embedded within the wall  506  of the shunt  500 . The pressure-sensing chamber  502  may be composed of non-expansible (e.g. rigid) walls except for a flexible diaphragm  512  bordering the lumen  514  of the shunt  500 . The pressure-reading chamber  504  may be composed of non-expansible (e.g. rigid) walls except for a diaphragm  516  bordering a gas-filled compartment  518 . The chambers  502  and  504  may be interconnected with a non-expansible channel  520  and filled with a fluid  522 . The fluid  522  may hydrostatically transmit the pressure signals from the sensing chamber  502  to the reading chamber  504 . 
         [0042]    An increase in the pressure within the lumen  514  may press against the diaphragm bottom  512  to displace it in the direction  524  and shift some of the fluid  522  into the chamber  504 . The shift of the fluid  522  into the chamber  504  may displace the diaphragm  516  into the gas-filled compartment  518  to increase the distance  526  between the diaphragm  516  and the top wall  528 . A calibration relationship between the distance  526  and the pressure may be established and used for the estimation of the pressure from a measured distance  526 . 
         [0043]    Similar to the other embodiments, the distance  526  may be measured transcutaneously using the ultrasonic transducer  130  and used by the processor  142  to estimate the pressure within the lumen  514 . 
         [0044]    This embodiment may allow the amplification of the displacement of the sensing diaphragm  512  into a larger displacement of the reading diaphragm  516  by making the diameter  530  of the pressure-sensing chamber  502  greater than the diameter  532  of the pressure-reading chamber  504 . This may be helpful in detecting slight changes in pressure and in improving the accuracy of the pressure estimation from diaphragm displacement. 
         [0045]    This embodiment may also allow the placement of the sensing chamber  502  at a distant location from the reading chamber  504 . For example, the sensing chamber  502  may be placed near the ventricular end of the shunt that is inside the skull (inaccessible to ultrasonic interrogation), while the reading chamber  504  may be placed at a location that is outside the skull and is accessible for ultrasonic measurements. 
         [0046]    This embodiment may also enable the sensing of the intraluminal pressure at multiple locations along the length of the shunt while allowing the reading of all these measurements at a single location that is transcutaneously accessible by ultrasonic means. For example, the shunt embodiment  540  shown in  FIG. 8  include a first sensing-chamber  502  that is located near to the ventricular end  542  of the shunt  540  and a second sensing-chamber  503  that is located near the proximal end  544  of the shunt  540 . Both sensing-chambers  502  and  503  are hydraulically connected through the fluid-filled channels  520  and  521  to the adjacent reading-chambers  504  and  505 , respectively. Relative difference in the expansion distances  526  and  527  of the diaphragms  516  and  517  measured at the reading-chambers  504  and  505  may be indicative of pressure differences or an occlusion between the locations of the sensing-chambers  502  and  503 , respectively. An ultrasound array transducer (not shown) operating in B-mode may be used to image the reading chambers  504  and  505  simultaneously and measure the distances  526  and  527 . 
         [0047]    The distances  526  and  527  may be processed by a processor to estimate pressure at the locations of the sensing chambers  502  and  503  and the estimated pressures may be compared to detect the presence of an occlusion between sensing chambers  502  and  503 . Although the above example only describes two sensing-chambers reporting to two adjacent reading-chambers, it is understood that additional reading and sensing chambers may be added to this configuration to enable the monitoring of pressure and occlusion at additional locations along the length of the shunt. 
         [0048]    During the placement of the shunt  540  in the patient, the bending of the shunt  540  may cause the fluid  522  to shift within, for example, the channel  520  and cause an initial offset of the diaphragm  516 . This offset may be corrected by recording the initial distance  526  and use it as baseline for comparison to future measurements of the distance  526 . Alternatively, the offset may be eliminated or minimized by using a second dummy channel  550  (i.e. not connected to a pressure-sensing chamber) running next to the channel  520  and connected to a second reading-chamber  552  as shown in  FIG. 9 . Therefore, the diaphragm displacement of the second reading chamber  552  will be solely caused by pressure-unrelated factors such as the mechanical bending of the shunt  540  and/or abnormal temperature changes. The difference in the displacement distances between the diaphragms of the first and second pressure-reading chambers  504  and  552  may be considered as the actual displacement distance caused by the pressure variation at the location of the pressure-sensing chamber  502 . 
         [0049]    Although the above detailed description describes and illustrates various preferred embodiments, the invention is not so limited. Many modifications and variations will now occur to persons skilled in the art. As such, the preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention. 
         [0050]    Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope.