WO2025144800A1

WO2025144800A1 - Implantable sensor system

Info

Publication number: WO2025144800A1
Application number: PCT/US2024/061724
Authority: WO
Inventors: J. Freddy HANSEN
Original assignee: TC1 LLC
Current assignee: TC1 LLC
Priority date: 2023-12-29
Filing date: 2024-12-23
Publication date: 2025-07-03
Anticipated expiration: 2026-06-29

Abstract

An implantable medical device for determining a change in pressure of a lumen in a body. The implantable medical device includes a first sensor that can be configured to detect variances in a first capacitance of a first capacitor based on changes in pressure in the lumen and changes in the environment of the lumen. The implantable medical device can also include a second sensor configured to detect variances in a second capacitance of a second capacitor based on changes in the environment of the lumen, and one or more processors. When executing program instructions, the one or more processors are configured to determine a change in pressure of the lumen based on the variances in the first capacitance and the variances in the second capacitance.

Description

IMPLANTABLE SENSOR SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims priority to U.S. Provisional Patent Application No. 63/616,480, filed 29-December-2023, entitled “IMPLANTABLE WIRELESS PRESSURE SENSOR”, the subject matter of which is incorporated herein be reference in its entirety.

TECHNICAL FIELD

[0002] Embodiments herein relate to implantable devices for wirelessly sensing pressure and other physical properties within the human body.

BACKGROUND

[0003] The measurement of blood pressure within the human heart and its vasculature provides critical information regarding the organ's function. Many methods and techniques have been developed to give physicians the ability to monitor heart function to properly diagnose and treat various diseases and medical conditions. For example, a sensor placed within the chambers of the heart can be used to record variations in blood pressure based on physical changes to a mechanical element within the sensor. This information is then transferred through a wire from the sensor to an extracorporeal device that is capable of translating the data from the sensor into a measurable value that can be displayed. The drawback of this type of sensor is that there must be a wired connection between the sensor and the extracorporeal device, thus limiting its use to acute settings.

[0004] U.S. Pat. No. 6,111 ,520, U.S. Pat. No. 6,855,115, and U.S. Publication No. 2003/0136417, each of which is incorporated herein by reference, all describe wireless sensors that can be implanted within the body. These sensors can be used to monitor physical conditions within the heart or an abdominal aneurysm. An abdominal aortic aneurysm (AAA) is a dilatation and weakening of the abdominal aorta that can lead to aortic rupture and sudden death. In the case of a repaired abdominal aneurysm, a sensor can be used to monitor pressure within the aneurysm sac to determine whether the intervention is leaking. [0005] Fabrication methodologies that have been developed in the field of Micro- Electro-Mechanical Systems ("MEMS") such that a capacitor can be utilized as an indicator of pressure. Such a sensor includes two parallel plates that are spaced apart from one another and surrounded by a dielectric. The pressure within a lumen of a patient can then deform a portion of the sensor to push one plate towards the second plate resulting in a change in the capacitance of the capacitor. This change in capacitance can then be correlated to the change in pressure of the lumen to determine the pressure change. However, the fundamental physics of a capacitor causes its capacitance value to change when there is a change in the dielectric value of the medium surrounding the capacitor electrodes (e.g., plates). This is an important limitation on implanted sensors that use capacitance readings to measure pressure, because dielectric changes cause ambiguity in the pressure readings. This effect may be enhanced in "split-plate" capacitor designs. Typical capacitors are calibrated based on the assumption that the dielectric material surrounding the plates is air. However, the environment of the implanted capacitor includes blood, tissue, fluids, etc. that collectively function as an environmental dielectric that surrounds the capacitor plates. Environmental changes alter the properties of the environmental dielectric, which can undesirably change the capacitance detected by the implanted sensor. These capacitance changes can be mistakenly interpreted as caused by pressure changes in the patient lumen, leading to misdiagnosis and/or incorrect treatment.

SUMMARY

[0006] The embodiments described herein are directed toward an implantable sensor system for determining a change in pressure of a lumen in a body. The implantable medical device includes a first sensor that can be configured to detect variances in a first capacitance of a first capacitor based on changes in pressure in the lumen and environmental changes of the lumen. The implantable medical device can also include a second sensor configured to detect variances in a second capacitance of a second capacitor based on environmental changes of the lumen, and one or more processors. When executing program instructions, the one or more processors are configured to determine a change in pressure of the lumen based on the variances in the first capacitance and the variances in the second capacitance.

[0007] Optionally, the implantable medical device can also include a body that includes the first sensor and the second sensor and is configured to couple to the lumen. In one aspect, the body may include a cavity defined in part by a first wall adjacent to the first sensor, the first wall configured to deform in response to the changes in pressure in the lumen. In another aspect, the body can include a second wall adjacent to the second sensor, the second wall configured to prevent detection of the changes in pressure in the lumen. In one example, the first wall may have a first thickness, and the second wall may have a second thickness, and the first thickness can be less than the second thickness. In another example, the first wall can have a lower modulus of elasticity than the second wall.

[0008] Optionally, the first sensor can include a first capacitor with first and second spaced apart plates, and the second sensor may include a second capacitor with first and second spaced apart plates. In an example, the first plate of the second capacitor can be coupled to the second plate of the second capacitor to move together. A size and shape of each of the first and second spaced apart plates of the first capacitor may be the same as a size and shape of each of the first and second spaced apart plates of the second capacitor. In one aspect, the one or more processors can be further configured to subtract a variance of the first capacitance detected by the first sensor by a variance of the second capacitance detected by the second sensor to determine the change in pressure of the lumen. In another aspect, subtracting the variance of the first capacitance by the variance of the second capacitance results in a pressure-based capacitance, and the pressure-based capacitance can be converted into a pressure variation to determine the change in pressure of the lumen. In one example, the second capacitor can be a reference capacitor configured to only detect variances in the second capacitance of the second capacitor based on the environmental changes of the lumen. In another example, the implantable medical device can also include an LC circuit electrically coupled to the first sensor and the second sensor.

[0009] In one or more embodiments a method of determining a variance of pressure within a lumen is provided. The method can include detecting, with a first sensor device, a first capacitance variance based on a combination of changes in pressure in the lumen and changes in an environment of the lumen. The method can also include detecting, with a second sensor device, a second capacitance variance based on changes in an environment of the lumen. The method can also include determining the variance of pressure of the lumen by reducing the second capacitance variance from the first capacitance variance.

[0010] Optionally, the detecting, with the first sensor, the first capacitance variance based on the changes in pressure in the lumen can include deforming, with the changes in pressure, a first wall in a body containing the first sensor to cause a first plate of a first capacitor to move towards a second plate of the first capacitor; and detecting a change in capacitance responsive to the movement of the first plate towards the second plate. In one aspect, the reducing the second capacitance variance from the first capacitance variance can result in a pressure based capacitance, and the pressure based capacitance is converted into a pressure variation to determine the variance of pressure of the lumen. In another aspect, the environmental changes of the lumen may include changes to electric permittivity within the lumen.

[0011] In accordance with one or more embodiments an implantable wireless sensor for determining a pressure of a lumen in a body is provided. The sensor can include a first sensor device coupled to an LC resonant circuit. The first sensor capacitance of the LC resonant circuit can be configured to vary in response to changes in pressure in the lumen and changes in an environment of the lumen. The sensor also may include a second sensor device coupled to the LC resonant circuit. The second sensor capacitance of the LC resonant circuit can be configured to vary only in response to environmental changes of the lumen.

[0012] Optionally, the sensor can also include a control system within the LC resonant circuit that includes one or more processors that, when executing program instructions, are configured to subtract the first sensor capacitance by the second sensor capacitance to determine a pressure capacitance. In one aspect, the one or more processors may be further configured to convert the pressure capacitance into a change in pressure of the lumen. In another aspect, the sensor can also include a body that includes the first sensor and the second sensor and is configured to couple to the lumen. In yet another aspect, the body may include a cavity defined in part by a first wall adjacent to the first sensor, the first wall configured to deform in response to the changes in pressure in the lumen, and a second wall adjacent to the second sensor, the second wall configured to prevent detection of the changes in pressure in the lumen.

[0013] These and other aspects, features and advantages may be more clearly understood and appreciated from a review of the following detailed description of the disclosed embodiments and by reference to the appended drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a fop view showing an implantable medical device (IMD) lodged within a lumen.

[0015] FIG. 2 is a perspective view of an implantable wireless sensor according to an embodiment, with the sensor body shown as transparent to reveal interior detail.

[0016] FIG. 3 is a schematic view of two pressure sensitive capacitor plates being formed in recessed trenches on two substrate wafers.

[0017] FIG. 4 is a schematic view showing the wafers of FIG. 3 imposed in face- to-face relation.

[0018] FIG. 5 is a schematic view showing the imposed wafers of FIG. 4 being laser-cut around their peripheries.

[0019] FIG. 6 is a schematic view of an alternate embodiment of two imposed wafers in which only one of the wafers has a recessed trench.

[0020] FIG. 7 is a schematic view illustrating a first step in a process for manufacturing wafers with capacitor plates formed thereon.

[0021] FIG. 8 is a schematic view illustrating a second step in the process for manufacturing wafers with capacitor plates formed thereon.

[0022] FIG. 9 is schematic view illustrating a third step in the process or manufacturing wafers with capacitor plates formed thereon.

[0023] FIG. 10 is a schematic view illustrating a fourth step in the process for manufacturing wafers with capacitor plates formed thereon.

[0024] FIG. 11 shows another embodiment in which two capacitor plates are formed on one wafer. [0025] FIG. 12 illustrates the embodiment of FIG. 11 showing the two capacitor plates on the single wafer connected to opposite ends of a helical inductor coil.

[0026] FIG. 13 is a schematic view of a sensor system for measuring the pressure of a lumen.

[0027] FIG. 14 is a schematic view of a control system for measuring the pressure of a lumen.

[0028] FIG. 15 is a flow block diagram of a method for determining a change in pressure in a lumen.

[0029] FIG. 16 is a block diagram of an exemplary system for communicating with a wireless sensor in accordance with an embodiment.

[0030] FIG. 17 is a block diagram of an exemplary base unit in accordance with an embodiment.

DETAILED DESCRIPTION

[0031] It will be readily understood that the components of the embodiments as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations in addition to the described example embodiments. Thus, the following more detailed description of the example embodiments, as represented in the figures, is not intended to limit the scope of the embodiments, as claimed, but is merely representative of example embodiments.

[0032] Reference throughout this specification to “one embodiment” or “an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment.

[0033] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the various embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obfuscation. The following description is intended only by way of example, and simply illustrates certain example embodiments.

[0034] The methods described herein may employ structures or aspects of various embodiments (e.g., systems and/or implantable leads and/or IMDs) discussed herein. In various embodiments, certain operations may be omitted or added, certain operations may be combined, certain operations may be performed simultaneously, certain operations may be performed concurrently, certain operations may be split into multiple operations, certain operations may be performed in a different order, or certain operations or series of operations may be re-performed in an iterative fashion. It should be noted that, other methods may be used, in accordance with an embodiment herein. Further, wherein indicated, the methods may be fully or partially implemented by one or more processors of one or more IMDs, devices, or systems. While the operations of some methods may be described as performed by the processor(s) of one device, additionally, some or all of such operations may be performed by the processor(s) of another device described herein.

[0035] All references cited herein, including publications, patent applications, and patents, are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0036] Embodiments set forth herein describe an implantable sensor system that includes a first sensor and a second sensor. The first and second sensors are designed to be implanted within a lumen of a patient body. The first sensor measures a first capacitance variance within the lumen. The first capacitance variance is based on both pressure-based changes in the lumen and material-based changes in the lumen. The pressure-based changes may be attributable to movement of the wall(s) of the lumen. The material-based changes may be attributable to blood flow and blood consistency. The second sensor measures a second capacitance variance within the lumen. The second capacitance variance is based on the material-based changes in the lumen. In an embodiment, the second capacitance variance is not based on the pressure-based changes in the lumen. For example, the second capacitance variance may be only based on the material-based changes. In an embodiment, the first sensor includes a first capacitor, and the second sensor includes a second capacitor. For example, the pressure-based changes may be based on lumen wall movement that causes a first conductive plate of the first capacitor to move relative to a second conductive plate of the first capacitor. In an example, the second capacitor of the second sensor may not be affected by the lumen wall movement. For example, the second capacitor may be spaced apart from, and not coupled to, the lumen wall.

[0037] The implantable sensor system also includes one or more processors. The one or more processors receive the first capacitance variance and the second capacitance variance. For example, the one or more processors may receive a value or signal representing the first capacitance variance and another value or signal representing the second capacitance variance. The one or more processors may determine a pressure-based capacitance value of the lumen based on the first and second capacitance variances. The pressure-based capacitance value may be a measured change in pressure within the lumen. The pressure-based capacitance value may be used to monitor a status of the patient and select or modify treatment of the patient.

[0038] The capacitance of a parallel plate capacitor, in a textbook example, is C = s-A/d, where A is the plate area, d is the plate-to-plate distance, and £ is the electric permittivity of the dielectric material between the plates. In real-world capacitors, the relationship between capacitance and the three parameters can be more complicated. For example, the capacitor electrodes (the “plates”) may not be flat, the plates may have differences sizes, and/or a dielectric medium may surround the plates instead of only being between the plates. In general, the capacitance is affected by the geometry of the plates and nearby dielectric media.

[0039] The implantable sensor system described herein utilizes a second “reference” sensor (e.g., capacitor) that is part of the sensor body. The first and second sensors may include respective first and second capacitors. The second capacitor can be made identical to the first capacitor in terms of plate area, nominal plate-to-plate distance, connecting leads, etc. The first capacitor may be mounted on a thin wall of the sensor body. The second, or reference, capacitor may be mounted on a thick wall that is not sensitive to ambient pressure changes. The reference sensor may subject to identical (or nearly identical) changes in ambient dielectric values. During operation of the implantable sensor system, from time to time the first capacitor may be switched out (open circuit) and the second (e.g., reference) capacitor is switched in. This allows a measurement of the capacitance that only depends on the ambient dielectric materials (e.g., blood, biological tissue, or air when the system is bench-tested/calibrated). The effect of changes in the dielectric materials on capacitance can be accounted and compensated for in the values recorded from the first capacitor, yielding capacitance data that is only dependent on pressure. For example, the pressure-based capacitance value can be determined by subtracting the capacitance attributable to dielectric material-based changes in the lumen, as measured by the reference (second) sensor, to the capacitance measured by the first sensor. The result of the subtraction is a capacitance value that is attributable to pressure-based changes in the lumen alone (e.g., not attributable to dielectric material-based changes in the lumen).

[0040] In one example, the compensation can be made locally in the electronics of the implantable sensor system, or the capacitance data (e.g., values) can be transmitted to an external reader device which performs the calculation. In an example embodiment, both the first capacitor and the second capacitor are located on opposite walls of an electronics package. In other embodiments, both capacitors may be located on the same wall, on perpendicular walls, or on opposite sides of the electronics package (on other the same or different walls of the sensor housing).

[0041] A first conductive plate of the reference capacitor may be mounted on a relatively thick wall of a sensor housing that holds the first capacitor and the reference capacitor. In an embodiment, a spacer can be placed between a first conductive plate of the first capacitor and a wall of the lumen of the patient. The wall of the lumen is thinner than the thick wall of the sensor housing. This spacer is constructed so that it transfers the motion of the wall of the lumen to the first capacitor plate without significantly preventing the lumen wall from moving and flexing. The spacer may be designed to make the first and second capacitors have approximately the same distance between the ambient dielectric medium and the conductive plate of the respective capacitor. The material of the spacer may be selected to have an electric permittivity that is approximately the same as that of the thick wall of the sensor housing.

[0042] In an example, the second capacitor has the same size and shape as the first capacitor. Providing two capacitors with the same nominal geometry makes it easier to subtract out the dielectric material-based effects to isolate the pressure-based effects. In another example, however, the second capacitor may have a different size than the first capacitor. In this case, a multiplying factor could be applied to the second capacitor values. This implantable sensor system can work with both "full-plate" and "split-plate" capacitor designs.

[0043] The term “lumen” as used herein refers to the cavity of a tubular structure of a blood vessel of a patient. The blood vessel directs blood flow to or from the heart of the patient. In one example, the lumen can be of the superior vena cava. The environment of the lumen can include blood, tissue, and/or the like. The tubular structure is defined by one or more walls (also referred to herein as lumen walls).

[0044] The term “environment” as used herein refers to the makeup, consistency, surroundings, or the like of a part or component. For example, when used in relation to a lumen, such as the environment of the lumen, environment can include all materials within that lumen, including but not limited to blood, tissue, walls, artificially introduced objects, and/or the like. For example, artificially introduced objects in the lumen may have a metallic or magnetic character (e.g., a pacemaker introduced in close proximity to a sensor). In an example, variances in capacitance of a capacitor may be based on the changes to electric permittivity within the lumen as a result of changes in the blood, tissue, walls, etc. within the lumen. In one example, a change in the electric permittivity of a lumen can be representative of a change in the environment of the lumen.

[0045] The term “pressure-based capacitance value” as used herein refers to a value representative of the change in capacitance of a sensor that is based only on a pressure change within a lumen. Changes in pressure in a lumen can move a first plate of a capacitor towards or away from a second plate, resulting in the capacitor detecting a variance in capacitance (e.g., a capacitance variance). However, changes in materials (blood, fluid, etc.), or electric permittivity, in a lumen can also result in changes in capacitance detected by a sensor. In one example to determine a pressure-based capacitance value, a value of a second capacitance variance that is based on capacitance variance due to electric permittivity can be subtracted from a value of a first capacitance variance that is based on capacitance variance due to pressure and electric permittivity. A value of the first capacitance variance, as measured by the capacitor, can be determ ined via the use of a lookup table, a decision tree, an algorithm , a mathematical function, a model, and/or the like. A value of the second capacitance variance can also be determ ined via the use of a lookup table, a decision tree, an algorithm , a mathematical function, a model, and/or the like.

[0046] The terms “variance,” “variation,” and “change” are used interchangeably herein. The term “capacitor” as used herein refers to an electronic component that can store an electrical charge using spaced-apart first and second electrically conductive plates. The term “sensor” as used herein is a device that includes multiple electronic components and measures a property. The term “sensor” can encompass all electronic components that result in a property reading. The electronic components of a sensor include at least one or more sensor components (or devices), circuitry (e.g., circuit components), and electrical power components. The sensor component (or device) of a sensor may be a capacitor, a transistor, or the like. For example, the electronic components of a first sensor described herein may include a first capacitor and circuitry that must be used to detect the capacitance variance in the first capacitor. The circuitry may be an inductive capacitive (LC) resonant circuit that is electrically connected to the first capacitor. In an example, a first capacitor and a second capacitor may be part of an LC resonant circuit within a sensor. Multiple sensors and/or capacitors may be commonly mounted on a single housing, such as a body of an IMD, or may be mounted on different, discrete housings.

[0047] FIG. 1 illustrates an implantable medical device (IMD) 100 that is configured to determine a pressure-based capacitance value in a lumen 102 of a patient according to an embodiment. Blood flows left to right through the lumen 102 in Figure 1 as indicated by the arrow 104. The IMD 100 optionally includes a wire 107 that secures the IMD 100 to the walls of the lumen 102. The IMD 100 can include a sensor system 106 that includes a first sensor 108 and a second sensor 110. In various embodiments, the sensor system

a wireless pressure sensor. Although the sensor system 106 is part of the IMD 100 in Figure 1 , in another embodiment the sensor system 106 may be a discrete implantable pressure sensor, which lacks one or more components of the IMD 100.

[0048] The sensor system 106 includes the first sensor 108 and the second sensor 110, which is also referred to herein as a reference sensor. In an embodiment, the first sensor 108 and the second sensor 110 are held by a body 109 of the sensor system 106. The body 109 may be a housing, substrate, or other structural component. The first sensor 108 may be spaced apart from the second sensor 110 along the body 109. The first sensor 108 in one example can include a first capacitor and can be configured to sense or detect changes, or variances, in capacitance in real time, as a result of pressure changes and environmental changes of the IMD 100. In one example the environmental changes can be detected via a detection of a change in electric permittivity within the lumen 102. The first capacitor can include a first plate and a second plate that are parallel plates spaced apart from one another and a body (e.g., housing) that is deformable (e.g., elastic). In an example, the first sensor 108 can be coupled to the lumen 102 of the patient such that when the lumen 102 exerts pressure on the deformable body, the body pushes the first plate of the first capacitor closer to the second plate resulting in a first capacitance variance. The first capacitance variance can be measured and the value converted to a pressure measurement. As such, the first sensor 108 may include movable components that dynamically move in real time. In example embodiments, the first sensor 108 may be one or more of the sensors described in U.S. Patent Application No. 17/184,717, filed 25-February-2021 entitled “Wireless Sensor for Measuring Pressure” (now U.S. Patent 11 ,103,146); U.S. Patent Application No. 17/184,755, filed 25-February-2021 entitled “Method and System for Determining a Lumen Pressure” (now U.S. Patent 11 ,103,147); U.S. Patent Application No. 17/184,775, filed 25- February-2021 entitled “System and Method for Developing an Implant Assembly” (now U.S. patent 11 ,179,048); U.S. Patent Application No. 16/194,103, filed 16-November- 2018 entitled “Wireless Sensor for Measuring Pressure” (now U.S. Patent 11 ,033,192); U.S. Patent Application No. 14/733,450, filed 08-June-2015 entitled "Method of Manufacturing Implantable Wireless Sensor for In Vivo Pressure Measurement” (now U.S. Patent 10,143,388); U.S. Patent Application No. 12/612,070, filed 04-November- 2009 entitled "Method of Manufacturing Implantable Wireless Sensor for In Vivo Pressure Measurement " (now U.S. Patent 9,078,563); U.S. Patent Application No. 11/204,812 filed 16-August-2005 entitled “Method of Manufacturing Implantable Wireless Sensor for In Vivo Pressure Measurement" (now U.S. 7,621 ,036); and/or U.S. Patent Application No. 11/157,375, filed 21-June-2005, entitled "Implantable Wireless Sensor for In Vivo Pressure Measurement" (now abandoned), the complete subject matter of each of which is expressly incorporated herein by reference in its entirety.

[0049] By having components such as plates that move relative to one another, the first sensor 108 can detect and measure capacitance variance as a result of pressure changes in the lumen 102. In an example, the environment 114 of the lumen 102, which can include blood and other organic fluid, tissue, and/or the like, can also experience changes that affect the capacitance variance measured by the first sensor 108. The material in the environment may function as a dielectric that surrounds the first sensor 108. When properties of this dielectric material change, the capacitance detected by the first sensor 108 also varies or changes. The changing properties of the environmental dielectric material, such as changes in the blood/fluid composition, flow rate, tissue, walls, etc. within the lumen 102, alter the measured capacitance by changing the electric permittivity within the lumen 102. In one example a change in electric permittivity within a lumen 102 can be representative of a change in the environment of the lumen.

[0050] In an embodiment, the second sensor 110 , when installed in the lumen 102, does not have movable components, in contrast to the first sensor 108. For example, the second sensor 110 may include a second capacitor that has a third plate and fourth plate that are parallel conductive plates that are fixed in place relative to one another. In one embodiment, the third plate and parallel fourth plate do not move in relation to one another because of the material utilized in forming the second sensor 110. In another example, the first sensor 108 is identical to the second sensor 110, only the second sensor 110 is located at a thicker area of the body 109 pressure changes do not affect the second sensor 110. In another embodiment, the second sensor 110 may be discrete and spaced apart from the first sensor 108 within the lumen 102. In one example a spacer 111 can be provided to provide spacing similar to the first sensor 108 while still not being sensitive to pressure changes in the lumen 102. In one example, the second sensor 110 can include a reference capacitor that provides a reference capacitance measurement. The reference capacitance measured by the second sensor 110 can be subtracted, or reduced, from the capacitance measured by the first sensor 108 to obtain a pressure-based capacitance value, which is only affected by pressure. In other words, to determine a pressure-based capacitance value, a value of a second capacitance variance that is based on capacitance variance due to only electric permittivity (e.g., the reference capacitance) can be subtracted from a value of a first capacitance variance that is based on capacitance variance due to pressure and electric permittivity.

[0051] In an example, the second sensor 110 detects capacitance variances only resulting from material-based environmental changes of the lumen 102. The second sensor 110 functions as a control such that when changes happen as a result of environmental changes of the lumen, the second sensor 110 can be utilized to detect this capacitance change and ensure it is not mistaken for a pressure change. The more alike the first sensor is to the second sensor, the more effective the sensor system is at only detecting pressure changes. For example, the plates of each of the first and second sensors can have the same geometry, be made of the same materials, or the like. The dielectric materials of each of the first and second sensors 108, 110 can also be the same. In yet another example the materials of the plates and dielectrics can be different and can have different shapes. The second sensor 110 does not have moving components such that changes in capacitance in the environment can be detected and accounted for when determining whether pressure changes have occurred.

[0052] Referring now to the drawings, in which like numerals indicate like elements throughout the several views, FIG. 2 illustrates a first sensor 210 that is configured to measure variances in capacitance resulting from both the environment surrounding the sensor 210 (e.g., the environment of the lumen) and pressure exerted by a lumen that deforms the sensor 210 by pushing two plates (e.g., the first plate and second plate of the first sensor 210) of the sensor (e.g. pressure sensitive capacitor) closer to one another. The sensor 210 can be fabricated using micro-machining techniques and is small, accurate, precise, durable, robust, biocompatible, and insensitive to changes in body chemistry, or biology. In one example, the sensor 210 can incorporate radiopaque features to enable fluoroscopic visualization during placement within the body. In an example, this sensor 210 can be encased in a hermetic, unitary package of electrically insulating material where the package is thinned in one region so as to deform under a physiologically relevant range of pressure. In one example an LC circuit may be contained in the packaging and be configured so that one electrode of the capacitor is formed on a thinned region of a lumen. This first sensor 210 does not require the use of external connections to relay pressure information externally and does not need an internal power supply to perform its function. The first sensor 210 can be attached to the end of a catheter to be introduced into a human body and delivered to an organ or vessel using catheter-based endovascular techniques.

[0053] Referring to FIG. 2, the first sensor 210 includes a body 212 (also referred to herein as sensor body). The body 212 is formed from electrically insulating materials, preferably biocompatible ceramics. In a preferred embodiment, the body is comprised of fused silica. The sensor 210 comprises a deflectable region 214 at the lower end of the body 212. The body 212 further comprises a lower chamber 219 and an upper chamber 221.

[0054] An LC resonator may be hermetically housed within the sensor body 212 and comprises a capacitor 215 and an inductor 220. As used herein, the term "hermetic" will be understood to mean "completely sealed, especially against the escape or entry of air and bodily fluids." The capacitor 215 is located within the lower chamber 219 and comprises at least two electrically conductive plates, or first plate 216 and second plate 218 that are disposed in parallel, spaced apart relation. The inductor 220 comprises a coil disposed within the upper chamber 221 and which is in conductive electrical contact with the capacitor 215.

[0055] The lower capacitor, or second plate 218 of the capacitor 215 may be positioned on an inner surface of the deflectable region 214 of the sensor body 212. The upper capacitor, or first plate 216 of the capacitor 215 may be positioned on a fixed region of the sensor body 212. A change in ambient pressure at the deflectable region 214 of the sensor 210 causes the deflectable region 214 to bend, thereby displacing the second plate 216 with respect to the first plate 218 and changing the capacitance measured by the first sensor 210. Because the change in capacitance of the LC resonator changes its resonant frequency, the resonant frequency of the sensor 210 is pressure dependent.

[0056] U.S. Pat. Nos. 6,111 ,520 and 6,278379 cover fundamental operating principles of wireless pressure sensors, but further miniaturization may be desired and/or needed to achieve an acceptable size for implantation into the heart or the vasculature. The sensor outer dimensions are constrained by the lumen size of the delivery catheter that is used to introduce the sensor. Catheter inner diameters typically range from 1-5 mm. Also, the size and shape of the sensor should minimally interfere with mechanical or hemodynamic function of the heart or vessel where it is located.

[0057] With these physical size constraints in mind, one challenge is achieving adequate coupling to the sensor inductor coil from the external readout device at the distance from the outside of the body to the implant site. One method for achieving enhanced coupling is to add magnetic material to the inductor. However, this approach is not feasible in a sensor intended for in vivo use, as the magnetic material would be averse to magnetic resonance imaging, for example. For a limited coil cross-sectional area, an increased coupling coefficient is also achievable by using a three-dimensional inductor coil configuration, as opposed to two-dimensional designs. For these reasons, the inductor 220 in an embodiment is a three-dimensional helical coil.

[0058] The sensor 210 may include a completely passive inductive-capacitive (LC) resonant circuit, or LC circuit 213 with a pressure varying capacitor 215. Because the sensor 210 is fabricated using completely passive electrical components and has no active circuitry, it does not require on-board power sources such as batteries, nor does it require leads to connect to external circuitry or power sources. These features create a sensor 210 which is self-contained within the packaging material and lacks physical interconnections traversing the hermetic packaging, such interconnects frequently being cited for failure of hermeticity. In an example, other sensing capabilities, such as temperature sensing, can be added using the same manufacturing techniques. For example, temperature sensing capability can be accomplished by the addition of a resistor with known temperature characteristics to the basic LC circuit 213.

[0059] The capacitor in the sensor system includes at least two conductive elements separated by a gap. If a force is exerted on the sensor, a portion of the sensor deflects, changing the relative position between the at least two conductive elements. This movement can have the effect of reducing the gap between the conductive elements, which will consequently change the capacitance of the LC circuit. An LC circuit is a closed loop system whose resonance is proportional to the inverse square root of the product of the inductor and capacitor. Changes in pressure alter the capacitance and, ultimately, cause a shift in the resonant frequency of the sensor. The pressure of the environment external to the sensor is then determined by referencing the value obtained for the resonant frequency to a previously generated curve relating resonant frequency to pressure.

[0060] The presence of the inductor can allow the LC circuit to couple to the sensor electromagnetically and to induce a current in the LC circuit via a magnetic loop. This characteristic allows for wireless exchange of electromagnetic energy with the sensor and the ability to operate it without the need for an on-board energy source such as a battery. The pressure surrounding the sensor can be determined by a non-invasive procedure by remotely interrogating the sensor, recording the resonant frequency, and converting this value to a pressure measurement.

[0061] One method of sensor interrogation is explained in U.S. Patent No. 7,245,117, incorporated herein by reference. The interrogating system may energize the sensor with a low duty cycle, gated burst of RF energy having a predetermined frequency or set of frequencies and a predetermined amplitude. The energizing signal is coupled to the sensor via a magnetic loop. The energizing signal induces a current in the sensor that is maximized when the frequency of the energizing signal is substantially the same as the resonant frequency of the sensor. The system receives the ring down response of the sensor via magnetic coupling and determines the resonant frequency of the sensor, which is then used to determine the measured physical parameter. The resonant frequency of the sensor is determined by adjusting the frequency of the energizing signal until the phase of the ring down signal and the phase of a reference signal are equal or at a constant offset. The energizing signal frequency is locked to the resonant frequency of the sensor and the resonant frequency of the sensor is known. The pressure of the localized environment can then be ascertained. [0062] The body of the implantable sensor may be composed of one or more ceramics such as, but not limited to, fused silica, quartz, pyrex and sintered zirconia, that provide the required biocompatibility, hermeticity and processing capabilities. These materials are considered dielectrics, that is, they are poor conductors of electricity but are efficient supporters of electrostatic or electroquasistatic fields. Dielectric materials have the ability to support such electrostatic or electroquasistatic fields while dissipating limited energy.

[0063] With regard to operation within the human body, blood and body fluids are conductive mediums and are thus particularly lossy. As a consequence, when a sensor is immersed in a conductive fluid, energy from the sensor will dissipate and the capacitance of the sensor can vary accordingly.

[0064] There are various manufacturing techniques that can be employed to realize the sensors according to the embodiments described herein. Capacitors and inductors made by a variety of methods can be manufactured separately, joined through interconnect methods and encapsulated in hermetic packaging. In one embodiment, the pressure sensitive capacitor 215 and the three-dimensional inductor coil 220 are formed separately and joined together to form the LC circuit. In another embodiment, the capacitor and inductor coil can be manufactured integral with one another. Additionally, there are several methods to create these discrete elements and to join each discrete element to create the final sensor. The following examples are provided to illustrate important design considerations and alternative methods for creating these discrete sensor elements, but should not be construed as limiting the inventive subject matter in any way.

[0065] Referring now to FIG. 3, the pressure sensitive capacitor plates 216, 218 are formed on two separate substrate wafers 240, 242 in recessed trenches 244. At least one of the wafers 240 has a substrate thickness in the region 246 of the first plate 216 such that sufficient pate deflection occurs due to external pressure change, resulting in a sufficient change in resonant frequency per unit pressure (mm Hg) once the LC circuit has been created. If necessary, the thickness of the wafer 240 in the region 246 can be reduced by suitable chemical or mechanical means, as indicated by the dashed line 247, to provide the desired range of deflection. [0066] As shown in FIG. 4, the wafers 240, 242 are bonded together such that the capacitive plates are 216, 218 parallel and separated by a gap in the order of 0.1-10 microns, preferably 0.1-2 microns.

[0067] The performances of the sensor, especially the propensity of its capacitance and, in turn, its resonant frequency to change as a response to an environmental pressure change, are closely related to few fundamental geometrical considerations. Widening or elongating the deflective region will augment its mechanical flexibility, and, in turn, the pressure sensitivity of the sensor. Decreasing the thickness of the deflective area will result in similar improvements. However, thinner deflective region can become too fragile or otherwise more sensitive to systemic response from the host-organism other than changes in mean and pulsatile blood pressure (ex: hyperplasia, tissue overgrowth, etc.). Reducing the gap, while maintaining adequate deflective region thickness, offers a complementary alternative to insufficiently low sensitivity. As the initial value of the gap is shrinking, the motion of the deflective region relative to the initial gap becomes proportionally more important. This results in a greater change in capacitance for a given stimulus, therefore enhancing the pressure sensitivity. While relevant sensitivity can be achieved with initial airgap ranging from 0.1 to 10 micrometers, initial airgaps ranging from a 0.1 to 2 micrometers are preferable.

[0068] To ensure adequate pressure range, the value of the maximum deflection under maximum load (indexed, for example, on physiologically relevant maximum pulsatile blood pressure values, at relevant location in the host-organism) ought to be, in theory, inferior or equal to the value of the initial gap. In practice, limiting the maximum deflection under maximum bad to represent only a fraction of the initial gap (ex: 0.6 micrometer for a 1 micrometer initial gap) will ease the fabrication constraints and result in a more robust and versatile sensor.

[0069] One suitable method for creating the pressure sensitive capacitor is by electroplating the individual plates 216, 218 in the recessed trenches 244 on a substrate wafer 240, 242 to a given height H1 , H2 that is less than or equal to the depth D1 , D2 of the respective trench 244. When the wafers are bonded together the first plate 216 and second plate 218 are generally separated by the difference between the sum of the trench depths and the sum of the plate heights, (D1 +D2)-(HI+H2). An inherent variation in the height of the plates and the required range of deflection for the full operating pressure range are parameters which determine the initial separation distance (a.k.a. the gap).

[0070] FIG. 5 illustrates the assembled wafers and capacitor plates laser-cut around their peripheries 248, reducing the capacitor to its final size and hermetically fusing the two wafers together at 250. A C0.sub.2 laser can be used at a peak wavelength of about 10 microns if the substrate is fused silica. Power must be sufficiently large to cut and fuse the wafers together, while at the same time being sufficiently small that the internal components of the sensor are not damaged by excessive heat.

[0071] In an alternate method, the wafers are pre-bonded using glass frit to produce a hermetic seal around the cavities. In this method, the laser cut only releases the sensors from the wafer and does not provide the primary means of creating the hermetic seal. Other suitable methods of hermetically sealing the wafers include, but are not limited to, adhesives, gold compression bonding, direct laser bonding, and anodic bonding.

[0072] In an alternate embodiment illustrated in FIG. 6, second plate 218 is formed on a substrate wafer 642 having a trench 644 with a depth greater that of the trench 244 in the substrate wafer 240. The other, or first plate 216 is formed on the inner surface of a wafer 640 without a trench. When imposed in face-to-face relation, the first plate 216 is received into the lower end of the trench 644 with the first plate 216 and second plate 218 disposed in parallel, spaced-apart relation.

[0073] To achieve smaller gap separation distances on the order of 0.1-2 microns, revised processing methods are employed to bring additional control to the variation in height across the first plate 216 and second plate 218. One method is as follows: the conductive plates 216, 218 are built to a target height that slightly exceeds the depth of the recess trench 644, as shown in FIG. 7. In the disclosed embodiment the first plate 216 and second plate 218 are formed by electroplating. Preferred materials for the plates are copper, gold, and alloys thereof. After building the plates, each conductive plate 216, 218 is polished using chemical/mechanical polishing (CMP) to planarize and reduce the height of the plate until it is less than the depth of the trench by the desired amount, as shown in FIG. 10. [0074] Another method also begins with the first plate 216 and second plate 218 formed to a height that slightly exceeds the depth of the trenches 244, as shown in FIG. 7. In one example the first plate 216 and second plate 218 are metal capacitor plates that can be mechanically polished to planarize the metal surface down to the surface of the substrate 240, 242, as shown in FIG. 8. Following this step, the metal plates are chemically etched by a selective etchant to the height indicated by the dashed line 256 in FIG. 9 to achieve the desired difference in height between the height of the first plate 216 and second plate 218 and the depth of the trench 244, as shown in FIG. 10.

[0075] Another method for forming the first plate 216 and the second plate 218 is physical vapor deposition (PVD), also known as thin film deposition, in conjunction with photolithography. PVD is used to deposit a uniform layer of metal, sub-micrometer to tens of micrometers thick, on a wafer. Subsequently a layer of photoresist is deposited, a mask is used to pattern the photoresist, and a selective etching technique is utilized to etch away the extra metal and to define the desired pattern. Other methods of defining the metal pattern can be utilized, such as shadow masking, a method well known in the art.

[0076] In one approach, shown in FIGS. 11 and 12, a pressure sensitive capacitor

615 can be formed by separating the bottom conductive pad into two separate regions 618A, 618B that capacitively couple to one another via a common third conductive region

616 on the pressure sensitive deflective region. The inductor coil 220 is then electrically connected as shown in Ha 211 , one lead 222 of the coil 220 to the first region 618A, and the other lead 224 of the coil 220 to the second region 618B.

[0077] When the split-plate design is employed for one side of the capacitor, as shown in FIG. 12, the spat plates 618A, 618B are preferably located on the fixed side of the capacitor (i.e., opposite the pressure-sensitive side), because the electrical/mechanical interconnects made to the spot plates in order to complete the LC circuit are less prone to mechanical failure when the surface to which they are mechanically attached does not deflect or move repetitively.

[0078] FIG. 13 illustrates an example sensor system 1300 for obtaining pressure data related to a lumen 1302 that is disposed within the lumen. The lumen 1302 can be any lumen within a patient, and in particular a lumen associated with the heart of the patient. The sensor system 1300 also includes a sensor body 1304 or housing that holds a control system 1306 (FIG. 14). The control system 1306 in one example has an electronics package that includes a charging or resonance coil, a transceiver or communication antenna, an energy storage device such as a battery/capacitor, memory, one or more processors, etc.

[0079] The sensor body 1304 additionally can have a cavity 1308 formed as an indentation in the housing. The cavity 1308 is positioned above a first capacitor 1310 to form a first wall 1312 between the cavity 1308 and the first capacitor 1310. In an example the first wall 1312 is considered a thin wall as a result of its reduced thickness as a result of the cavity 1308. In one example the first capacitor 1310 can be formed utilizing MEMS manufacturing techniques.

[0080] The first capacitor 1310 can include a first plate 1314 that is in parallel spaced relation to a second plate 1316. In one example, the first plate 1314 is a first electrode and the second plate 1316 is a second electrode. In an embodiment, the first plate 1314 can be formed so the first plate 1314 can be moved in relation to the second plate 1316. For example, the first plate 1314 can be coupled to the first wall 1312 of the body 1304, where the first wall 1312 can deform or deflect as pressure increases within the lumen 1302. Because the first wall 1312, in the example embodiment of FIG. 13 is a thin wall, the first wall 1312 can move in relation to the second plate 1316. To this end, when referring to the first wall 1312 as a thin wall, “thin wall” does not pertain to a particular measured thickness such as less than 1 mm. Instead, the measured thickness and consistency of the first wall 1312 is such that internal pressure within the lumen 1302 can cause movement of the first plate 1314. This thickness may thus vary depending on the material utilized for the body 1304 or size of a cavity 1308 (e.g., opening) of a lumen 1302 in which the sensor system 1300 is implanted. The first capacitor 1310 may be configured to detect changes in capacitance as a result of changes in pressure in the lumen 1302 along with changes in capacitance as a result of environmental changes within the lumen 1302. In one example changes in electric permittivity detected by either the first capacitor 1310 or second capacitor 1318 can be representative of a change in the environment of the lumen. [0081] In one example, disposed below the first capacitor 1310 is a second capacitor 1318. The second capacitor 1318 functions as a reference capacitor that detects changes in capacitance only resulting from environmental changes. The environmental changes (e.g. blood, tissue, fluid, air, etc.) cause the dielectric properties surrounding the first capacitor 1310 and second capacitor 1318 to change, resulting in a change in capacitance being detected by both the first capacitor 1310 and second capacitor 1318. The second capacitor 1318 can be utilized to calibrate the first capacitor 1310 by negating any changes in capacitance detected by the first capacitor 1310 that are due to environmental changes. The sensor system 1300 ensures the pressure determination being made by the one or more processors of the control system 1306 is only being made based on capacitance changes resulting from pressure changes, and not based on changes due to environmental changes.

[0082] While in this example the second capacitor 1318 is aligned with the first capacitor 1310, in other example embodiments the second capacitor can be located at different locations within the body 1304. To this end, the first capacitor 1310, control system 1306 and second capacitor 1318 can be arranged in any manner with respect to one another to facilitate manufacturing or improve attachment within the lumen 1302. As an example, there may be a location in the lumen that is less likely to be affected by pressure, while another location is more likely to be affected by pressure. In such a case the first capacitor 1310 and second capacitor can be arranged and spaced in relation to one another such that the first capacitor is adjacent to the area of the lumen most affected by pressure and the second capacitor 1318 is least affected by pressure. In another example a spacer may be utilized in association with the second capacitor 1318 such that the first capacitor 1310 and second capacitor 1318 can be in side-by-side alignment with one another. In yet another example the second capacitor 1318 can be located in a second body spaced from the body 1304 of the first capacitor 1318. Indeed, the first capacitor 1310 and second capacitor 1318 are located within the same environment as the lumen so both can detect changes in capacitance resulting from environmental changes.

[0083] In one example the second capacitor 1318 can be formed utilizing MEMS manufacturing techniques. In another example the second capacitor 1318 includes a third plate 1320 that is in parallel spaced relation to a fourth plate 1322. In one example the third plate 1320 is a first electrode and the fourth plate 1322 is a second electrode. In one example the third and fourth plates 1320, 1322 of the second capacitor 1318 have the same or similar size, shape, and material as the first and second plates 1314, 1316 of the first capacitor 1310. In addition, in an embodiment the distance between the third and fourth plates 1320, 1322 of the second capacitor 1318 is the same or similar to the initial distance between the first and second plates 1314, 1316 of the first capacitor 1310 before any movement as a result of pressure within the lumen 1302. In one example the only difference between the first capacitor 1310 and the second capacitor is that the first capacitor has plates 1314, 1316 that can move relative to one another as a result of changes in pressure within the lumen whereas the plates 1320, 1322 are static and do not move as a result of the changes in pressure within the lumen. In one example to prevent capacitance changes in the second capacitor 1318 because of pressure changes is to connect, or couple, third and fourth plates 1320, 1322 together so that they move together when the fourth plate 1322 moves with the second wall 1324. In such an embodiment the second wall can be a thin wall similar to first wall 1312.

[0084] In an embodiment the third plate 1320 can be formed so the third plate 1320 cannot be moved in relation to the fourth plate 1322. For example, the third plate 1320 can be coupled to a second wall 1324 of the body 1304, where the second wall 1324 is of size and shape that the second wall 1324 does not deform or deflect as pressure increases within the lumen 1302. In one example the second wall 1324 can be considered a thick wall. Because the second wall 1324 is thick, the second wall 1324 can absorb pressure increases and dissipate the pressure forces throughout the rest of the body 1304 to ensure the third plate 1320 does not move as a result of pressure increases in the lumen 1302. The thick wall, similar to the thin wall does not necessarily pertain to a particular measured thickness such as more than 1 mm. Instead, the measured thickness and consistency of the thick wall is such that internal pressure within the lumen 1302 does cause movement of the either the third or fourth plates 1320, 1322 of the second capacitor 1318. This thickness may thus vary depending on the material utilized for the body 1304 or size of the cavity 1308 (e.g. , opening) of the lumen 1302 in which the sensor system 1300 is implanted. In another example the thickness of the second wall 1324 is at least twice the thickness of the first wall 1312. In an alternative embodiment the thickness of the first wall 1312 and second wall 1324 are approximately the same and instead the mechanical properties associated with each wall 1312 or 1324 differ. For example, in one embodiment the first wall 1312 can be made of a material that has smaller modulus of elasticity and is more reactive to pressure than the material of the second wall 1324. In another example, the first wall 1312 has a first thickness, and the second wall 1324 has a second thickness and the first thickness is less than the second thickness. In an example, pressure increases of the lumen 1302 result in the plates of the first capacitor to move toward one another because of the material of the first wall 1312, while the material of the second wall 1324 prevents movement of the plates of the second capacitor 1318, despite the two walls 1312, 1324 having similar thicknesses. In yet another alternative embodiment the body 1304 manufactured to have additional mechanical supports surrounding the second wall 1324, including in some examples a spacer, preventing movement of the plates of the second capacitor 1318 despite having a similar thickness to the first capacitor 1310. In all, the body 1304 is designed such that the first capacitor 1310 has plates that move relative to one another because of changes in pressure within the lumen 1302, while the second capacitor 1318 has plates that do not move relative to one another because of changes in pressure within the lumen 1302.

[0085] FIG. 14 illustrates a control system 1400 that in one example embodiment can be the control system 1306 of FIG. 13. The control system 1400 includes components such as one or more wireless transceivers 1402, one or more processors 1404 (e.g., a microprocessor, microcomputer, application-specific integrated circuit, etc.), and one or more local storage medium (also referred to as a memory portion) 1406. [0086] Each transceiver 1402 can utilize a known wireless technology for communication. Exemplary operation of the wireless transceivers 1402 in conjunction with other components of the control system 1400 may take a variety of forms and may include, for example, operation in which, upon reception of wireless signals, the transceiver 1402 demodulates the communication signals to recover incoming information received by the wireless signals. The one or more processors 1404 format outgoing information and convey the outgoing information from one or more of the wireless transceivers 1402 for modulation to communication signals. The wireless transceiver(s) 1402 conveys the modulated signals to a remote device, such as a cell tower or a remote server (not shown).

[0087] The local storage medium 1406 can encompass one or more memory devices of any of a variety of forms (e.g., read only memory, random access memory, static random-access memory, dynamic random-access memory, etc.) and can be used by the one or more processors 1404 to store and retrieve data. The data that is stored by the local storage medium 1406 can include, but need not be limited to, operating systems, applications, including a pressure application, or the like. Each operating system includes executable code that controls basic functions of the device, such as interaction among the various components, communication with external devices via the wireless transceivers 1402, and storage and retrieval of applications to and from the local storage medium 1406. All of these components (e.g., transceiver, one or more processors, local storage medium, etc.) of the control system 1400 can be operatively coupled to one another, and can be in communication with one another, by way of one or more internal communication links, such as an internal bus.

[0088] The control system 1400 also includes a pressure application 1420 that configures the one or more processors of the control system to determine changes in pressure within a lumen. In one example the pressure application 1420 includes instructions for the one or more processors to use obtained sensor data or information that is received from a first sensor 1416 that includes a first capacitor 1422 and a second sensor 1418 that includes a second capacitor 1424 to determine the change in pressure within the lumen. In one example the first capacitor 1422 measures variances in a capacitance of the first capacitor 1422 while the second capacitor 1424 measures variances in capacitance of the second capacitor 1424. In one example the first capacitor 1422 obtains data and information related to variances or changes in capacitance of the first capacitor as a result of pressure changes in the lumen and as a result of environmental changes in the lumen resulting in a change in dielectric properties surrounding the plates of the first capacitor 1422. Meanwhile the second capacitor 1424 functions as a reference capacitor that only obtains data and information related to variances or environmental changes of the lumen. [0089] The pressure application 1420 can include instructions to utilize the data obtained by both the first and second capacitors 1422, 1424 to determine changes in pressure within the lumen. In one example, the change in capacitance measured by the second capacitor (e.g., due to environmental changes) is subtracted, or reduced from the change in capacitance measured by the first capacitor (e.g. , due to pressure changes and environmental changes). In one example to determine a pressure-based capacitance value, a value of a second capacitance variance (obtained from the second capacitor 1424) that is based on capacitance variance due to only electric permittivity can be subtracted from a value of a first capacitance variance (obtained from first capacitor 1422) that is based on capacitance variance due to both pressure and electric permittivity. By accounting for the changes in capacitance as a result of environmental changes of the lumen, only the changes in capacitance resulting from pressure are considered.

[0090] FIG. 15 illustrates a method 1500 for determining a change in pressure in a lumen of a patient. In one example the sensor system, capacitors, control systems, etc. previously described in relation to FIGS. 1 -14 can be utilized to implement one or more operations described related to the method 1500.

[0091] At 1502, one or more processors obtain capacitance data from a first sensor of a sensor system. The first sensor can be configured to measure or detect changes in capacitance as a result of both changes in pressure in the lumen and environmental changes within the lumen. In one example the first sensor includes first and second plates that can each be electrodes that are located in parallel spaced relation to one another. At least one of the plates is placed by a first wall of the body of the sensor system that has mechanical or electrical properties that cause the wall to move at least one plate in response to pressure changes in the lumen. In one example, the first wall is a thin wall that deforms in response to the pressure changes. In another example, the first wall can be formed of a material that has a modulus of elasticity that allows deformation of the material as a result of the pressure changes accordingly. In yet another example, the first wall is placed in a location against a wall of a lumen that is thin and reactive to pressure changes within the lumen. Indeed, the first sensor not only detects changes in capacitance as a result of environmental changes, but also as a result of the pressure changes in the lumen.

[0092] At 1504, the one or more processors obtain capacitance data from a second sensor of the sensor system where the second sensor is configured to only measure or detect changes in capacitance as a result of environmental changes of the lumen. In one example the second sensor includes two plates (e.g., third plate and fourth plate), and the body of the sensor system is configured to prevent movement of either of the plates as a result of pressure changes in the lumen. In one embodiment preventing the movement of the plates accomplished by providing a second wall that is a thick wall (e.g. thicker than the wall adjacent the first sensor) that absorbs pressure changes within the lumen and dissipates the pressure throughout the body to prevent any deformation and consequential effect on the plates of the second sensor. Alternatively, the material of the body around at least one of the plates is stiffer or is not as elastic as the material adjacent to at least one of the plates of the first sensor. In yet another example additional supports, spacers, or structure can be placed adjacent to at least one of the plates of the second sensor to prevent movement of a plate of the second sensor relative to the other plate of the second sensor as a result of pressure changes within the lumen. In one embodiment, a first capacitor of the first sensor can be identical in size and shape to a second capacitor of the second sensor. To this end the shape and size of the plates can be identical, the initial distance between the plates can be identical, the material of the plates can be identical, or the like. In other embodiments, the first capacitor of the first sensor and the second capacitor of the second sensor have plates that differ in size, shape, material and/or etc.

[0093] At 1506, the one or more processors determine whether the second sensor is detecting or measuring a change in capacitance as a result of environmental changes. For example, if changes in the fluid, blood, tissue, etc. within the environment occur the dielectric properties surrounding the second capacitor of the second sensor are changing. Consequently, a change in the capacitance sensed by the second sensor can be detected and measured. If no change in capacitance is being detected or measured at the second sensor, then at 1508, the one or more processors determine the change in capacitance in the lumen based only on capacitance changes being detected by the first sensor. Because changes in the lumen environment are not occurring, any change in capacitance is only the result of a change in pressure within the lumen.

[0094] Alternatively, if at 1506 a change in capacitance is detected by the second sensor, then at 1510 the one or more processors modify the capacitance detected by the first sensor based on the capacitance obtained by the second sensor to determine the capacitance change resulting from a change in the pressure of the lumen (e.g., the capacitance pressure). If changes in capacitance resulting from environmental changes are detected, such change can be negated from the change in capacitance being detected by the first sensor. So, in one example, when a change in capacitance is detected at the second sensor as a result of changes to the environment of the lumen and the first sensor detects the identical change in capacitance, such capacitance change is negated such that a reading is provided that no change in pressure has occurred. False detections of pressure changes due to environmental changes can be eliminated accordingly.

[0095] At 1512, the one or more processors convert the changes in capacitance into capacitance pressure of the lumen. In one example, historical data related to changes in capacitance that correlate to changes in pressure are provided. Such corresponding changes can be provided in a lookup table, decision tree, or the like. The capacitance pressure is the pressure lumen pressure such that changes in the capacitance pressure reflect the changes in pressure in the lumen.

Exemplary System

[0096] FIG. 16 illustrates an exemplary system for communicating with a wireless sensor implanted within a body. The system includes a coupling loop 1600, a base unit 1602, a display device 1604 and an input device 1606, such as a keyboard.

[0097] The coupling loop 1620 is formed from a band of copper. In one embodiment, the loop is eight inches in diameter. The coupling loop includes switching and filtering circuitry that is enclosed within a shielded box 1601. The loop charges the sensor and then couples signals from the sensor into the receiver. The antenna can be shielded to attenuate in-band noise and electromagnetic emissions. [0098] Another possible embodiment for a coupling loop 1620 can have separate loops for energizing and for receiving, although a single loop can be used for both functions. PIN diode switching inside the loop assembly is used to provide isolation between the energizing phase and the receive phase by opening the RX path pin diodes during the energizing period and opening the energizing path pin diodes during the coupling period. Multiple energizing loops can be staggered tuned to achieve a wider bandwidth of matching between the transmit coils and the transmit circuitry.

[0099] The display 1604 and the input device 1606 are used in connection with the user interface for the system. In the embodiment illustrated in FIG. 16 the display device and the input device are connected to the base unit. In this embodiment, the base unit also provides conventional computing functions. In other embodiments, the base unit can be connected to a conventional computer, such as a laptop, via a communications link, such as an RS-232 link. If a separate computer is used, then the display device and the input devices associated with the computer can be used to provide the user interface. In one embodiment, LABVIEW software is used to provide the user interface, as well as to provide graphics, store and organize data and perform calculations for calibration and normalization. The user interface records and displays patient data and guides the user through surgical and follow-up procedures.

[0100] An optional printer 1608 is connected to the base unit and can be used to print out patient data or other types of information. As will be apparent to those of ordinary skill in the art, other configurations of the system, as well as additional or fewer components, can be utilized with the inventive subject matter.

[0101] Patient and system information can be stored within a removable data storage unit, such as a portable USB storage device, floppy disk, smart card, or any other similar device. The patient information can be transferred to the physician's personal computer for analysis, review, or storage. An optional network connection can be provided to automate storage or data transfer. Once the data is retrieved from the system, a custom or third-party source can be employed to assist the physician with data analysis or storage.

Operation of the Base Unit [0102] FIG. 17 is a block diagram of the signal processing components within an exemplary base unit. The base unit determines the resonant frequency of the sensor by adjusting the energizing signal so that the frequency of the energizing signal matches the resonant frequency of the sensor. In the embodiment illustrated by FIG. 17, two separate processors 1702, 1722 and two separate coupling loops 1740, 1742 are shown. In one embodiment, processor 1702 is associated with the base unit and processor 1722 is associated with a computer connected to the base unit. In other embodiments, a single processor is used that provides the same functions as the two separate processors. In other embodiments a single loop is used for both energizing and for coupling the sensor energy back to the receiver. As will be apparent to those skilled in the art, other configurations of the base unit are possible that use different components.

[0103] Additional alternative embodiments will be apparent to those skilled in the art to which the present inventive subject matter pertains without departing from its spirit and scope. For example, the system can operate with different types of sensors, such as non-linear sensors that transmit information at frequencies other than the transmit frequency or sensors that use backscatter modulations.

[0104] It should be clearly understood that the various arrangements and processes broadly described and illustrated with respect to the Figures, and/or one or more individual components or elements of such arrangements and/or one or more process operations associated of such processes, can be employed independently from or together with one or more other components, elements and/or process operations described and illustrated herein. Accordingly, while various arrangements and processes are broadly contemplated, described and illustrated herein, it should be understood that they are provided merely in illustrative and non-restrictive fashion, and furthermore can be regarded as but mere examples of possible working environments in which one or more arrangements or processes may function or operate.

[0105] Some or all of the Figures herein illustrates various methods and processes implemented in accordance with embodiments herein. The operations herein may be implemented by hardware, firmware, circuitry and/or one or more processors housed partially an/or entirely within an IMD, a local external device, remote server or more generally within a healthcare system. Optionally, the operations herein may be partially implemented by an IMD and partially implemented by a local external device, remote server or more generally within a healthcare system. For example, the IMD includes IMD memory and one or more IMD processors, while each of the external devices/systems (ED) (e.g., local, remote or anywhere within the healthcare system) include ED memory and one or more ED processors.

[0106] As will be appreciated by one skilled in the art, various aspects may be embodied as a system, method or computer (device) program product. Accordingly, aspects may take the form of an entirely hardware embodiment or an embodiment including hardware and software that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects may take the form of a computer (device) program product embodied in one or more computer (device) readable storage medium(s) having computer (device) readable program code embodied thereon.

[0107] Any combination of one or more non-signal computer (device) readable medium(s) may be utilized. The non-signal medium may be a storage medium. A storage medium may be, for example, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of a storage medium would include the following: a portable computer diskette, a hard disk, a random access memory (RAM), a dynamic random access memory (DRAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0108] Program code for carrying out operations may be written in any combination of one or more programming languages. The program code may execute entirely on a single device, partly on a single device, as a stand-alone software package, partly on single device and partly on another device, or entirely on the other device. In some cases, the devices may be connected through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made through other devices (for example, through the Internet using an Internet Service Provider) or through a hard wire connection, such as over a USB connection. For example, a server having a first processor, a network interface, and a storage device for storing code may store the program code for carrying out the operations and provide this code through its network interface via a network to a second device having a second processor for execution of the code on the second device.

[0109] Aspects are described herein with reference to the figures, which illustrate example methods, devices and program products according to various example embodiments. The program instructions may be provided to a processor of a general- purpose computer, special purpose computer, or other programmable data processing device or information handling device to produce a machine, such that the instructions, which execute via a processor of the device implement the functions/acts specified. The program instructions may also be stored in a device readable medium that can direct a device to function in a particular manner, such that the instructions stored in the device readable medium produce an article of manufacture including instructions which implement the function/act specified. The program instructions may also be loaded onto a device to cause a series of operational steps to be performed on the device to produce a device implemented process such that the instructions which execute on the device provide processes for implementing the functions/acts specified.

[0110] The units/modules/applications herein may include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set computers (RISC), application specific integrated circuits (ASICs), field- programmable gate arrays (FPGAs), logic circuits, and any other circuit or processor capable of executing the functions described herein. Additionally, or alternatively, the modules/controllers herein may represent circuit modules that may be implemented as hardware with associated instructions (for example, software stored on a tangible and non-transitory computer readable storage medium, such as a computer hard drive, ROM, RAM, or the like) that perform the operations described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term “controller.” The units/modules/applications herein may execute a set of instructions that are stored in one or more storage elements, in order to process data. The storage elements may also store data or other information as desired or needed. The storage element may be in the form of an information source or a physical memory element within the modules/controllers herein. The set of instructions may include various commands that instruct the modules/applications herein to perform specific operations such as the methods and processes of the various embodiments of the subject matter described herein. The set of instructions may be in the form of a software program. The software may be in various forms such as system software or application software. Further, the software may be in the form of a collection of separate programs or modules, a program module within a larger program or a portion of a program module. The software also may include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to user commands, or in response to results of previous processing, or in response to a request made by another processing machine.

[0111] It is to be understood that the subject matter described herein is not limited in its application to the details of construction and the arrangement of components set forth in the description herein or illustrated in the drawings hereof. The subject matter described herein is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. To the extent embodiments herein are described to apply certain mathematical combinations of select variables, the same variables may be combined in other mathematical combinations that are also indicative of the same result. For example, when a single data point is utilized for a particular variable, additionally or alternatively, a mean, average, sum, or other mathematical combination of multiple data points may be utilized for the same variable.

[0112] It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings herein without departing from its scope. While the dimensions, types of materials and coatings described herein are intended to define various parameters, they are by no means limiting and are illustrative in nature. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the embodiments should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein." Moreover, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects or order of execution on their acts.

Accordingly, the scope of the present inventive subject matter is described by the appended claims and is supported by the foregoing description. Finally, it is to be understood that the preferred embodiment is disclosed by way of example, and that modifications to the preferred embodiment may occur without departing from the scope and spirit of the appended claims.

Claims

WHAT IS CLAIMED IS:

1 . An implantable sensor system comprising: a first sensor configured to detect variances in a first capacitance of a first capacitor based on changes in pressure in a lumen and environmental changes of the lumen; a second sensor configured to detect variances in a second capacitance of a second capacitor based on environmental changes of the lumen; and one or more processors that, when executing program instructions, are configured to: determine a change in pressure of the lumen based on the variances in the first capacitance and the variances in the second capacitance.

2. The implantable sensor system of claim 1 , further comprising a body that contains the first sensor and the second sensor and is configured to couple to a wall of the lumen.

3. The implantable sensor system of claim 2, wherein the body includes a cavity defined in part by a first wall of the body, the first wall configured to deform in response to the pressure-based changes in the lumen, wherein the first sensor is coupled to the first wall.

4. The implantable sensor system of claim 3, wherein the body includes a second wall configured to prevent deformation of the second wall in response to the pressure-based changes in the lumen, wherein the second sensor is coupled to the second wall.

5. The implantable sensor system of claim 4, wherein the first wall of the body is thinner than the second wall.

6. The implantable sensor system of claim 4, wherein the first wall of the body has a lower modulus of elasticity than the second wall.

7. The implantable sensor system of claim 1 , wherein the first sensor includes a first capacitor with a first plate and a second plate spaced apart from each other, and the second sensor includes a second capacitor with a third plate and a fourth plate spaced apart from each other, wherein the first, second, third, and fourth plates have a same size and shape.

8. The implantable sensor system of claim 7, wherein the third plate of the second capacitor is coupled to the fourth plate so that the third and fourth plates move together.

9. The implantable sensor system of claim 1 , wherein the one or more processors are configured to determine a pressure-based capacitance value by subtracting a value of a second capacitance variance from a value of a first capacitance variance.

10. The implantable sensor system of claim 1 , wherein the second capacitor is a reference capacitor configured to only detect variances in the second capacitance of the second capacitor that are based on the environmental changes of the lumen.

11 . The implantable sensor system of claim 1 , further comprising an inductive- capacitive (LC) resonant circuit electrically connected to the first sensor and the second sensor.

12. A method of determining a pressure-based capacitance value within a lumen of a patient, the method comprising: detecting, with a first sensor of a sensor system implanted within a lumen of a patient, a first capacitance variance based on both pressure-based changes in the lumen and environmental changes in an environment of the lumen; detecting, with a second sensor of the sensor system within the lumen, a second capacitance variance based on environmental changes in the lumen; and subtracting a value of the second capacitance variance from a value of the first capacitance variance to determine a pressure-based capacitance value.

13. The method of claim 12, wherein the detecting, with the first sensor, includes deforming, with the changes in pressure, a first wall in a body containing the first sensor to cause a first plate of a first capacitor to move towards a second plate of the first capacitor; and detecting a change in capacitance responsive to the movement of the first plate towards the second plate.

14. The method of claim 12, wherein the environmental changes include changes to electric permittivity within the lumen.

15. An implantable sensor system comprising: an inductive-capacitive (LC) resonant circuit configured to be implanted within a lumen of a patient; a first sensor configured to be implanted within the lumen and electrically connected to the LC resonant circuit, the first sensor configured to determine a first capacitance variance based on both pressure-based changes in the lumen and environmental changes in the lumen; and a second sensor configured to be implanted within the lumen and electrically connected to the LC resonant circuit, the second sensor component configured to determine a second capacitance variance based only environmental changes in the lumen.

16. The implantable sensor system of claim 15, further comprising a control system including one or more processors configured to execute program instructions to: subtract a value of the second capacitance variance from a value of the first capacitance variance to determine a pressure-based capacitance value.

17. The implantable sensor system of claim 16, further comprising a body that contains the first sensor and the second sensor.

18. The implantable sensor system of claim 17, wherein the body includes a cavity defined in part by a first wall of the body and a second wall of the body, the first wall configured to deform in response to the pressure-based changes in the lumen, wherein the first sensor component is coupled to the first wall.

19. The implantable sensor system of claim 18, wherein the second wall is configured to not deform in response to the pressure-based changes in the lumen, and the second sensor component is coupled to the second wall.

20. The implantable sensor system of claim 19, wherein the first sensor is contained within the body adjacent the first wall, and the second sensor is contained within the body adjacent the second wall.