Minimally-invasive procedure for monitoring a physiological parameter within an internal organ

A minimally-invasive surgical procedure for monitoring a physiological parameter within an internal organ of a living body. The procedure entails making a first incision in the body to enable access to the organ. An endoscopic instrument is then inserted through the first incision and a second incision is made therewith through an external wall of the organ and into the internal cavity thereof. A sensing unit is placed in the second incision such that the second incision is occluded by the unit and a proximal end of the unit is outside the organ. The unit includes a sensing device having a sensing element adapted to sense the physiological parameter within the organ, and an anchor to which the sensing device is secured. The first incision is closed, after which a readout device outside the body telemetrically communicates with the sensing device to obtain a reading of the physiological parameter.

BACKGROUND OF THE INVENTION

The present invention generally relates to implantable medical devices, monitoring systems and implantation procedures. More particularly, this invention relates to a minimally-invasive surgical procedure for implanting a sensing device adapted to monitor one or more physiological properties of a living body, such as pressure, temperature, flow, acceleration, vibration, composition, and other properties of biological fluids within an internal organ.

Various implantable devices have been developed to monitor and wirelessly communicate physiological parameters of the heart, as well as physiological parameters of other internal organs, including the brain, bladder and eyes. Such predicate wireless devices can generally be divided into two functional categories: large-sized (pacemaker-type) and smaller-sized telemetric devices. An example of a pacemaker-type wireless pressure sensor is the LVP-1000 Left Ventricular Pressure Monitoring System under development by Transoma Medical, Inc. The LVP-1000 comprises a sensor adapted to be implanted into an external wall of the heart, a wireless transmitting unit adapted to be located elsewhere within the patient, and wiring that physically and electrically connects the sensor and transmitting unit. The sensor of the LVP-1000 is adapted to be secured with sutures to the left side of the heart during an open-chest surgical procedure.

Smaller telemetric sensors include batteryless pressure sensors developed by CardioMEMS, Inc., Remon Medical, and the assignee of the present invention, Integrated Sensing Systems, Inc. (ISSYS). For example, see commonly-assigned U.S. Pat. Nos. 6,926,670 and 6,968,734 to Rich et al., and N. Najafi and A. Ludomirsky, “Initial Animal Studies of a Wireless, Batteryless, MEMS Implant for Cardiovascular Applications,” Biomedical Microdevices, 6:1, p. 61-65 (2004). With such technologies, pressure changes are can be sensed with an implant equipped with a mechanical capacitor (tuning capacitor) having a fixed electrode and a moving electrode, for example, on a diaphragm that deflects in response to pressure changes. The implant is further equipped with an inductor in the form of a fixed coil that serves as an antenna for the implant, such that the implant is able to receive radio frequency (RF) signals from outside the patient and transmit the frequency output of the circuit. The implant can be placed directly within the heart chamber whose pressure is to be monitored, or in an intermediary structure such as the atrial or ventricular septum. Implantation involves a translumenal implantation technique using a placement catheter to deliver the implant to a chamber of the heart or another cardiovascular chamber, after which the implant is secured to an interior wall surface of the chamber.

FIGS. 1aand1brepresent two types of wireless pressure sensing schemes disclosed in the Rich et al. patents. InFIG. 1a, an implant10is shown as operating in combination with a non-implanted external reader unit20, between which a wireless telemetry link is established using a resonant scheme. The implant10contains a packaged inductor coil12and a pressure sensor in the form of a mechanical capacitor14. Together, the inductor coil12and capacitor14form an LC (inductor-capacitor) tank resonator circuit that has a specific resonant frequency, expressed as 1/(LC)1/2, which can be detected from the impedance of the circuit. At the resonant frequency, the circuit presents a measurable change in magnetically-coupled impedance load to an external coil22associated with the reader unit20. Because the resonant frequency is a function of the capacitance of the capacitor14, the resonant frequency of the LC circuit changes in response to pressure changes that alter the capacitance of the capacitor14. Based on the coil12being fixed and therefore having a fixed inductance value, the reader unit20is able to determine the pressure sensed by the implant10by monitoring the resonant frequency of the circuit.

FIG. 1bshows another wireless pressure sensor implant30operating in combination with a non-implanted external reader unit50. A wireless telemetry link is established between the implant30and reader unit50using a passive, magnetically-coupled scheme, in which on-board circuitry of the implant30receives power from the reader unit50. In the absence of the reader unit50, the implant30lays passive and without any internal means to power itself. When a pressure reading is desired, the reader unit50must be brought within range of the implant30.

InFIG. 1b, the implant30contains a packaged inductor coil32and a pressure sensor in the form of a mechanical capacitor34. The reader unit50has a coil52by which an alternating electromagnetic field is transmitted to the coil32of the implant30to induce a voltage in the implant30. When sufficient voltage has been induced in the implant30, a rectification circuit38converts the alternating voltage on the coil32into a direct voltage that can be used by electronics40as a power supply for signal conversion and communication. At this point the implant30can be considered alert and ready for commands from the reader unit50. The implant30may employ the coil32as an antenna for both reception and transmission, or it may utilize the coil32solely for receiving power from the reader unit50and employ a second coil42for transmitting signals to the reader unit50. Signal transmission circuitry44receives an encoded signal generated by signal conditioning circuitry46based on the output of the capacitor34, and then generates an alternating electromagnetic field that is propagated to the reader unit50with the coil42.

The implant30is shown inFIG. 1bwithout a battery, and therefore its operation does not require occasional replacement or charging of a battery. Instead, the energy required to perform the sensing operation is entirely derived from the reader unit50. However, the implant30ofFIG. 1bcould be modified to use a battery or other power storage device to power the implant30when the reader unit50is not sufficiently close to induce a voltage in the implant30, in which case the wireless telemetry link between the implant30and reader unit50uses an active magnetically-coupled scheme.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a minimally-invasive surgical procedure for monitoring one or more physiological parameters within an internal organ of a living body, such as the human heart, brain, kidneys, lungs, bladder, etc. The procedure entails endoscopically placing a miniature implantable sensing device through an external wall of the organ, such as a wall of the heart, blood vessel, kidneys, lungs, bladder, etc., or a wall surrounding the organ, such as the abdominal wall or the meninges surrounding the brain.

The minimally-invasive surgical procedure makes use of at least one sensing unit adapted to be implanted in the living body and attached to an organ therein, and a readout device that is not adapted to be implanted in the living body. The sensing unit includes a sensing device having a sensing element adapted to sense the physiological parameter within the organ, and an anchor to which the sensing device is secured. The sensing unit is adapted for placement in an incision in an external wall of the organ so that when a distal end of the sensing unit is within the wall or extends into the internal cavity, an oppositely-disposed proximal end of the sensing unit is outside the organ and the sensing unit occludes the incision. The readout device telemetrically communicates with the sensing device to obtain a reading of the physiological parameter.

The minimally-invasive surgical procedure generally entails making a first incision in a living body to enable access to the internal organ. An endoscopic instrument is then inserted through the first incision and a second incision is made therewith through an external wall of the organ and into the internal cavity thereof. The sensing unit is then placed in the second incision such that a distal end of the sensing unit is within the wall or extends into the internal cavity. The sensing unit includes a sensing device having a sensing element adapted to sense the physiological parameter within the organ, and an anchor to which the sensing device is secured. The sensing unit is placed in the second incision so that a proximal end of the sensing unit is outside the organ and the sensing unit occludes the incision. The anchor is then secured to the external wall of the organ such that the sensing device is secured within the second incision by only the anchor. The first incision can then be closed, after which the readout device is used outside the living body to telemetrically communicate with the sensing device and obtain a reading of the physiological parameter.

The minimally-invasive surgical procedure is intended to be particularly well-suited for providing safe, fast, detailed, real-time, and continuous measurements for both short-term and long-term applications, such as over a period of hours, days, weeks or longer in an emergency room or hospital. In cases where the patient is moved to a rehabilitation facility, the sensing device can be utilized for much longer periods and data relating to the physiological parameter(s) being monitored can be wirelessly sent to a physician or nurse in order to provide diagnostic tailored treatment of the patient. For patients that need even longer term monitoring, at-home monitoring can be easily accomplished by tying the readout device to the Internet, telephone, or other long-distance communication system. The wireless sensing device can be configured for batteryless operation, allowing the device to potentially function for a patient's lifetime with no maintenance or need for replacement after initial implantation.

Miniaturization of the sensing unit can be effectively achieved by fabricating the sensing element as a miniature MEMS (micro-electromechanical system) sensor, combined with custom electronics and a telemetry antenna. A preferred aspect of the invention is to limit the volume protrusion of the sensing unit into the cavity being monitored. In the case of the heart, the risk of thrombogenesis can be significantly reduced by limiting protrusion of the sensor unit into the blood stream within a heart chamber, in terms of distance into the cavity as well as shape and size of the protruding portion of the sensing unit. For this purpose, the sensing device is preferably configured so that the sensing element is located on a distal surface (relative to insertion direction) of the device, such that only the distal surface of the sensing device need contact the biological fluid being monitored.

The implantation procedure and sensing system of this invention can be used to measure a variety of physiological parameters, a particularly notable example of which is physiological pressures such as cardiovascular pressures, intracranial pressures, intra-sac pressures, radial artery pressure, pulmonary artery pressure, etc. A key advantage of the invention is that only a small portion of the sensing system—namely, the sensing device and its anchor—need be implanted inside the body, with only a portion thereof actually being within the organ, while the remaining members of the system—including the readout unit—are located outside the organ and, in the case of the readout unit, outside the body. As a result, the procedure for implanting the sensing device as well as the device itself are minimally invasive, which allows greater flexibility in the implant location and allows the sensing device to be used in many areas and organs of the body, including the heart. When used in the heart, the sensing device greatly reduces the risk of complications, in particular thrombosis and thrombogenicity.

DETAILED DESCRIPTION OF THE INVENTION

Illustrated inFIGS. 2athrough13are monitoring systems and components thereof that implement one or more implantable sensors configured to be placed through an external wall of an internal organ for monitoring one or more physiological parameters within an internal cavity of the organ. Organs of particular interest include but are not limited to the heart, brain, kidneys, lungs, and bladder. The physical footprint of the implanted portion of each monitoring system is limited to the sensing device, its anchor and optionally a separate antenna, such that the sensing unit can be far smaller than, for example, the Transoma Medical, Inc., LVP-1000 Left Ventricle Pressure Monitoring System, which must be physically connected to a relatively large remote transmitting device.

While the resonant, passive and active schemes described in reference toFIGS. 1aand1bare also within the scope of the invention, sensing devices of this invention are preferably passive and preferably translate a physiologic parameter into a frequency tone and modulate the impedance of an antenna with the frequency tone to communicate the physiologic parameter to an external readout unit.FIG. 2arepresents a wireless implantable sensing device60as comprising a transducer62, electronic circuitry64(e.g., an application specific integrated circuit, or ASIC), and an antenna66. These and any additional or optional components (e.g., additional transducers) of the sensing device60are preferably contained in a single sealed housing72. The antenna66is shown as comprising a coil68(e.g., copper windings) wrapped around a core70(e.g., ferrite), though other antenna configurations and materials are foreseeable. The transducer62is preferably a MEMS device, more particularly a micromachine fabricated by additive and subtractive processes performed on a substrate. The substrate can be rigid, flexible, or a combination of rigid and flexible materials. Notable examples of rigid substrate materials include glass, semiconductors, silicon, ceramics, carbides, metals, hard polymers, and TEFLON. Notable flexible substrate materials include various polymers such as parylene and silicone, or other biocompatible flexible materials. A particular but nonlimiting example of the transducer62is a MEMS capacitive pressure sensor for sensing pressure, such as various blood pressures within the heart, intracranial pressure, intraocular pressure, etc., though other materials and any variety of sensing elements, e.g., capacitive, inductive, resistive, piezoelectric, etc., could be used. For example, the transducer62could be configured to sense temperature, flow, acceleration, vibration, pH, conductivity, dielectric constant, and chemical composition, including the composition and/or contents of a biological fluid, for example, oxygen, carbon dioxide, glucose, gene, hormone, or gas content of the fluid. The sensing device60may be powered with a battery or other power storage device, but in preferred embodiments is powered entirely by a remote device that is not configured for implantation, such as a readout unit80represented inFIG. 2c.

Because the sensing device60is equipped with a built-in antenna66, the device60requires only an anchor for implantation, and does not require a wire, cable, tether, or other physical component that conducts the output of the sensing device60to a separate location where another component utilizes the output of the sensing device and/or transmits the output of the sensing device to a location outside the body of the patient. InFIG. 2b, consistent reference numbers are used to identify functionally equivalent structures of a second wireless implantable sensing device60that differs from the device60ofFIG. 2aby the placement of the antenna66outside the housing72. The antenna66is shown as comprising a conductive coil68patterned on a substrate74, and connected to the device60with wires76. The substrate74can be rigid, flexible, or a combination of rigid and flexible materials such as those described above in reference to the transducer62, and may carry additional electronics. The antenna66can be placed remotely from the sensing device60, such as immediately under the skin, to provide better wireless transmission between the device60and the readout device80ofFIG. 2c. A remotely-placed antenna for use with the invention can also be configured in accordance with the antenna66as shown inFIG. 2a, with a coil68wrapped around a core70and connected to the device60with wires76.

In addition to powering the sensing device60, the readout unit80is represented as being configured to receive an output signal from the sensing device60, process the signal, and relay the processed signal as data in a useful form to a user. The readout unit80is shown equipped with circuitry82that generates a high-frequency (e.g., 13.56 MHz), high-power signal for an antenna84to create the magnetic field needed in communicate with the sensing device60. The readout unit80contains additional circuitry86to receive and demodulate a backscattered signal from the sensing device60, which is demodulated and then processed with a processing unit88using calibration coefficients to quantify the physiological parameter of interest. The readout unit80is further shown as being equipped with a user interface90, by which the operation of the readout unit80can be controlled to allow data logging or other user control and data examination.

FIG. 3represents a block diagram showing particularly suitable components for the electronic circuitry64ofFIGS. 2aand2b. The circuitry64includes an oscillator92, for example a relaxation oscillator, connected to a resistor93and a MEMS mechanical capacitor94. A preferred MEMS capacitor94comprises a fixed electrode and a moving electrode on a diaphragm that deflects relative to the fixed electrode in response to pressure, such that the capacitor94is able to serve as a pressure sensing element for the transducer62. A nonlimiting example of a preferred MEMS capacitor94has a pressure range of about −100 to about +300 mmHg, with an accuracy of about 1 mmHg. Alternatively, a variable resistor transducer could be used with a fixed capacitance, or an inductor could be substituted for the transducer or fixed circuit element. Based on the RC or other time constant (1/(LC)1/2), the oscillator92produces a frequency tone that directly relates to the capacitive value of the capacitor94and, therefore, the physiologic parameter of interest.

The circuitry64is further shown as including a modulator96, with which the frequency tone of the oscillator92is encoded on a carrier frequency, placed on the antenna66, and then transmitted to the readout unit80. This is accomplished simply by opening and closing a switch98and adding a capacitance100to the antenna matching circuit, resulting in an AM (amplitude modulation) LSK (load shift keying) type modulation. This transmission approach is similar to that used in RFID (radio frequency identification) communications, except RFID does not typically encode analog information but instead encodes a few digital bits either on an AM LSK or FSK (frequency shift keying) modulation.

Because the preferred embodiment of the sensing device60does not utilize wires to transmit data or power to the readout unit80, nor contains an internal power source, the circuitry64further includes a regulator/rectifier102to extract its operating power from an electromagnetic (EM) waves generated by the readout unit80or another EM power source. The regulator/rectifier102rectifies incoming power from the inductive antenna66and conditions it for the other circuit components within the circuitry64. Finally, a matching circuit104is shown as comprising a trimmable capacitor bank106to resonate the inductor antenna66, which is energized by the magnetic field and backscatters data as previously described.

As an alternative to the embodiment ofFIG. 3, the modulator96could use a 13.56 MHz (or other frequency) magnetic field as a clock reference to create a second carrier frequency, such as one that is one-quarter or another sub-multiple or multiple of the original frequency. The second carrier frequency can then be amplitude modulated (AM) using the oscillator frequency tone and transmitted to the readout unit80via the same antenna66. In this embodiment, the readout unit80may or may not have a second antenna to receive the second carrier frequency-based AM signal.

The communication scheme described above differs from resonate tank communication systems that use capacitive pressure transducer elements in conjunction with an inductor/antenna. In particular, the circuitry64allows the use of any frequency for the high power readout unit80, which in preferred embodiments utilizes an industrial, scientific, medical (ISM) band frequency. In contrast, the frequencies and potentially large bandwidths required of resonate tank communication systems are subject to FCC emission limitations, likely requiring the use of extra shielding or potentially other measures taken in the facilities where the sensing device60and readout unit80are to be used. Another feature of the circuitry64is the allowance of more combinations of oscillator elements to be used. Because resonator tank systems require an inductive element and a capacitive element in which at least one of the elements serves as a transducer, resonator tank systems do not lend themselves well to resistive-based or other based sensors. Finally, the circuitry64also allows for signal conditioning, such as transducer compensation, which allows for such items as removing temperature dependence or other non-idealities that may be inherent to the transducer62. In the preferred embodiment, a negative temperature coefficient of the MEMS capacitor94can be compensated with simple circuitry relying on the positive temperature coefficient of resistor elements arranged in a trimmable bank of two resistor units with largely different temperature coefficients that can be selectively added in a trimming procedure in production to select the precise level to compensate the transducer variation.

In the past, the restrictive levels of energy available to small implantable medical sensing devices and the desire to maximize data rates to capture more detailed physiological parameter response have been met with a robust type of analog communication that places information on the frequency rather than amplitude of the carrier. In U.S. Pat. No. 6,929,970 to Rich et al., a secondary carrier frequency is used for communication with an interrogator unit, resulting in a technique that consumes substantially more power in the implant and requires a second external antenna to receive the signal. The greater power consumption of the implant necessitates a tradeoff between smaller size and longer communication range. In contrast, the communication scheme described above for this invention draws upon the RFID-type communications, such as those described in U.S. Pat. Nos. 7,015,826 and 6,622,567, whose contents are incorporated herein by reference. However instead of communicating digital data using a fixed rate clock, the present invention transmits analog information as the frequency of the clock to lower power consumption and enhance powering and communication range. In this way, much of the readout unit80can utilize hardware that is commercially available for RFID, except that a different demodulator is required. An early example of RFID can be found in U.S. Pat. No. 4,333,072.

FIG. 4depicts a preferred example of the housing72as having a cylindrical shape with a flat distal face112. (The terms “distal” and “proximal” are used herein in reference to orientation during the implantation procedure described below.) Other shapes are also possible, for example, a torpedo-shape in which the peripheral face114of the housing72immediately adjacent the distal face112is tapered or conical (not shown). The housing72can be formed of glass, for example, a borosilicate glass such as Pyrex Glass Brand No 7740 or another suitably biocompatible material. A biocompatible coating, such as a layer of a hydrogel, titanium, nitride, oxide, carbide, silicide, silicone, parylene and/or other polymers, can be deposited on the housing72to provide a non-thrombogenic exterior for the biologic environment in which the sensing device60will be placed. As can be seen inFIG. 4, the inductive antenna66(comprising the copper coil68surrounding the core70ofFIG. 2a) occupies most of the internal volume of the housing72. The size of the antenna66is governed by the need to couple to a magnetic field to enable telepowering with the readout unit80from outside the body, for example, a transmission distance of about 10 cm or more. The cylindrical shape of the housing72is convenient for the sensing device60to be endoscopically placed with anchors discussed in reference toFIGS. 5 through 15. The circuitry64is disposed between the antenna66and an end of the housing72that preferably carries the transducer62. A nonlimiting example of an overall size for the housing72is about 3.7 mm in diameter and about 16.5 mm in length.

A preferred aspect of the invention is to locate the transducer62on a distal surface of the sensing device60, for example, the flat distal face112of the cylindrical housing72, or on the peripheral face114of the housing72immediately adjacent the distal face112. In a preferred embodiment, the flat distal face112is defined by a biocompatible semiconductor material, such as a heavily boron-doped single-crystalline silicon, in whose outer surface the pressure-sensitive diaphragm (or other sensing element94) is formed. In this manner, only the distal face112of the housing72need be in contact with a biological fluid whose physiological parameter is to be monitored. In the case of monitoring pressure within the heart, this aspect of the invention can be utilized to minimize protrusion of the sensing device60into the heart chamber, thereby reducing the risk of thrombogenesis.

FIGS. 5 through 15represent embodiments for anchors with which the sensing device60ofFIG. 4can be anchored to a wall of an internal organ, for example, by making an incision in the wall from the exterior of the organ, inserting the sensing device60in the incision from the exterior side of the wall, and then securing the sensing device60to the wall. According to a preferred aspect of the invention, access to the organ and implantation of the sensing device60is achieved using an endoscope, for example, via laparoscopic surgery, thoracoscopic surgery, or another similar minimally-invasive procedure, as opposed to translumenal implantation techniques using a placement catheter that places a sensing device within an organ and then secures the device to an interior wall surface of the organ. As an endoscopic procedure, an endoscope or other suitable instrument comprising a rigid or flexible tube is utilized to enable the procedure to be visual observed, as well as the use of instruments for making the incision and securing the anchor as required by the invention. The procedure can be performed through small incisions (on the order of a few centimeters, for example, about three centimeters or less) as compared to much larger incisions needed in traditional surgical procedures. The procedure may entail insufflation of the body cavity surrounding the organ to create a working and viewing space for implantation and securement of the sensing device60.

Together, the sensing device60and the anchors ofFIGS. 5 through 15form sensing units that have minimal protrusion into the organ when implanted through the organ wall from the exterior of the organ. Maximum protrusion of the sensing units is preferably not more than one centimeter, more preferably not more than eight millimeters, for example between about 0.5 to about 2 millimeters, with a preferred volumetric protrusion of not more than about 0.02 cm3. The distal end of the sensing units (for example, as defined by the distal face112of the housing72and/or the distal end of the anchor) may also be slightly recessed below the internal surface of the wall, for example, up to about two millimeters from the internal surface of the wall. Particularly suitable materials for the anchors include but are not limited to NITINOL, TEFLON, polymers such as parylene, silicone and PEEK, metals, glass, and ceramics.

InFIGS. 5 and 6, an anchor120A is shown configured to have a distal tubular portion122partially surrounded by a proximal dome-shaped portion124. The anchor120A is preferably in accordance with the teachings of commonly-assigned U.S. patent application Ser. No. 12/111,954 to Najafi et al., whose contents regarding anchor construction and use are incorporated herein by reference. The sensing device60is axially disposed within the tubular portion122to yield a sensing unit110A in which the distal face112carrying the transducer62protrudes from the tubular portion122. The sensing device60can be secured in the tubular portion122by any suitable means, such as an interference fit, a biocompatible epoxy, glue or cement, or any other type of attachment method or combinations of attachment methods known to those skilled in the art. The dome-shaped portion124generally joins the tubular portion122at an end125opposite the open end126of the tubular portion122through which the sensing device60is received. The dome-shaped portion124defines a substantially tubular section130that circumscribes the tubular portion122and terminates at an edge128short of the open end126of the tubular portion122. Multiple oblong openings132are defined in the tubular section to enable the anchor120A to be secured to a wall of an internal organ, such as with standard surgical sutures or another suitable attachment technique that can be performed during the endoscopic procedure, such as nails, screws, springs, and biocompatible adhesives such as cements, glues, epoxies, etc.

FIG. 6depicts the sensing unit110A ofFIG. 5implanted in an incision in a wall134of an internal organ for the purpose of sensing a physiological parameter of a biological fluid within an internal cavity136of the organ. The wall134may be an exterior wall of the heart, a blood vessel, kidneys, lungs, bladder, etc., or a wall surrounding an organ, such as the abdominal wall or the meninges surrounding the brain. As evident fromFIG. 6, only the tubular portion122of the anchor120A is inserted into the incision, and the dome-shaped portion124remains entirely outside the incision; as such, the tubular and dome-shaped portions122and124are not configured to clamp the wall134therebetween. Furthermore, the anchor120A does not protrude through the wall134, but instead is recessed in the wall134, whereas the distal end112of the sensing device60protrudes into the internal cavity136of the organ. As noted above, the distance the distal end112protrudes from the internal surface138of the wall134(for example, the endocardium lining a chamber of the heart) is preferably not more than one centimeter, and more preferably not more than eight millimeters. As also noted above, the sensing device60and anchor120A could be configured so that the anchor120A, and not the sensing device60, protrudes beyond the wall134, in which case the distal end112of the sensing device60may be recessed up to about two millimeters from the internal surface138of the wall134. Again, the anchor120A preferably does not protrude more than one centimeter, and more preferably not more than eight millimeters, beyond the internal surface138of the wall134. Finally, it is within the scope of the invention that both the anchor120A and the sensing device60could protrude into the internal cavity136, or that neither the anchor120A nor the sensing device60protrudes into the internal cavity136, but instead are recessed in the wall134.

FIG. 6further shows the inclusion of a felt pad140between the peripheral edge128of the anchor120A and the external surface142of the wall134. A suitable material for the felt pad140is standard surgical grade felt. The anchor120A and the felt pad140can be simultaneously attached (e.g., sutured) to the wall134. Depending on the material from which it is formed, the felt pad140may be used to promote cell (tissue) growth and encapsulation of the incision, leading to further stabilization of the sensing unit110A.

FIGS. 7 and 8show an anchor120B that is again configured to have a distal tubular portion152, but with a proximal disk-shaped portion154. Such an anchor is also disclosed in commonly-assigned U.S. patent application Ser. No. 12/111,954 to Najafi et al. As before, the sensing device60is shown axially disposed within the tubular portion152, yielding a sensing unit110B in which the distal face112of the device60carrying the transducer62protrudes from the tubular portion152. Though not shown, the disk-shaped portion154may be formed to have multiple oblong openings to enable the anchor120B to be secured to the wall134of an internal organ, such as with sutures or another suitable attachment technique that can be performed during the surgical procedure. InFIG. 9, a sensing unit110C essentially identical to the unit110B ofFIGS. 7 and 8is shown as further including a tubular insert144secured in the incision prior to placement of the remainder of the unit110C. The insert144can be attached to the wall134with an interference fit, or with the use of a biocompatible cement, glue or epoxy, screws, springs, nails, etc. The tubular portion152of the anchor120C can then be secured within the bore of the insert144. A preferred aspect of this embodiment is that the anchor120C is not permanently joined to the insert144to permit the exchange of the sensing unit110C and/or its sensing device60, and/or the use of a different anchor with additional features.

As evident fromFIGS. 8 and 9, both anchors120B and120C and the sensing device60protrude into the internal cavity136, with the sensing devices60protruding farther, though any of the configurations discussed in reference toFIGS. 5 and 6could also be present in the embodiments ofFIGS. 7 through 9.

FIGS. 10 through 15show anchors that are adapted to clamp a wall of an organ, in contrast to the attachment techniques associated with the anchors120A-C ofFIGS. 5-9. As represented inFIGS. 11,13, and15, the sensing device60is recessed within anchors120D,120E, or120F, and elements of the anchors120D-F providing the clamping action extend farther into the internal cavity136of the organ than the distal face112of the device60carrying the transducer62.

The anchor120D shown inFIGS. 10 and 11is preferably in accordance with the teachings of commonly-assigned U.S. Pat. No. 7,317,951 to Schneider et al., whose contents regarding the anchor construction and use are incorporated herein by reference. The anchor120D is represented as having an annular-shaped central body162that defines a bore in which the sensing device60is received. The central body162has arcuate arms164that extend substantially radially from a distal end of the central body162, and arcuate members166that extend substantially radially and in the opposite direction from the proximal end of the central body162. As can be seen fromFIG. 10, each arm164is axially aligned with one of the arcuate members166so as to lie in the same plane as the arcuate member166. Each arm164terminates with a pad168and each arcuate member166defines a leg170that oppose each other, such that the pads168and legs170cooperate to clamp the wall134as seen inFIG. 11.

The arcuate members166connect a ring172to the central body162. A second ring174is axially spaced by struts176between the central body162and the ring172, forming a cage for containing the sensing device60. The sensing device60is secured within the central body162by crimping fingers178over the opening in which the sensing device60is received. The rings172and174can be configured to allow delivery and placement of the anchor120D and its sensing device60using an appropriately-configured endoscopic instrument (not shown). As with the previous embodiments of the invention, the anchor120D ofFIGS. 10 and 11is configured to place the distal face112of the device60carrying the transducer62in contact with fluid within the internal cavity136with minimal protrusion into the cavity136by either the device60or anchor120D. In the configuration shown inFIGS. 10 and 11, the distal face112of the sensing device60is recessed beneath the internal surface138of the wall134, and the arms164preferably do not protrude more than five millimeters into the cavity136.

The anchors120E and120F ofFIGS. 12 through 15are preferably in accordance with the teachings of commonly-assigned U.S. patent application Ser. No. 11/684,910 to Goetzinger et al., whose contents regarding these anchor constructions and their use are incorporated herein by reference. The anchor120E ofFIGS. 12 and 13is shown as having an annular-shaped base182and retention legs180that cooperate to retain the sensing device60within the anchor120E. Distal arms184and proximal legs186extend from distal and proximal ends, respectively, of the base182. When deployed as shown, the arms184and legs186have arcuate shapes, each terminating with an extremity or tip188and190, respectively. Each arm184and leg186lies in a different radial plane, with the result that the tips188and190of the arms184and legs186do not directly oppose each other when deployed, such that the wall134into which the anchor120E is inserted is not locally compressed by directly opposing arms184and legs186. Furthermore, the tips188and190of the arms184and legs186are preferably capable of piercing the wall134, so that the tips188and190can become embedded in the wall134without puncturing the wall134. The minimized compressive forces applied by the anchor120E to the wall134is believed to reduce tissue killed after implantation, and the configurations of the arms184and legs186and their opposing actions also accommodate walls of differing thicknesses. The anchor120E and its sensing device60can be delivered and placed using an appropriately-configured endoscopic instrument (not shown). As with the previous embodiments of the invention, the anchor120E ofFIGS. 12 and 13is configured to place the distal face112of the device60carrying the transducer62in contact with fluid within the internal cavity136with minimal protrusion into the cavity136by either the device60or anchor120E. In the configuration shown inFIGS. 12 and 13, the distal face112of the sensing device60protrudes not more than two millimeters into the cavity136, and the arms184preferably do not protrude more than five millimeters into the cavity136.

FIGS. 14 and 15identify elements of the anchor120F with the same reference numbers used inFIGS. 12 and 13to identify functionally similar structures. The primary differences evident in the anchor120F are the different configuration of its legs186. The legs186have a compound deployment action, during which they initially spread radially and then travel axially in a distal direction until the tips190of the legs186engage and become embedded in the wall134. As with the previous embodiments of the invention, the anchor120F ofFIGS. 14 and 15is configured to place the distal face112of the device60in contact with fluid within the internal cavity136with minimal protrusion into the cavity136by either the device60or anchor120F. In the configuration shown inFIGS. 14 and 15, the distal face112of the sensing device60is substantially flush with the internal surface138of the cavity136, and the arms184preferably do not protrude more than five millimeters into the cavity136.

To accurately locate the distal face112and its transducer62relative to the internal surface138of the wall134, the thickness of the wall134can be measured using one or more of the following procedures: an echocardiogram; a pressure-sensitive needle inserted through the desired location for the implant, wherein the pressure signal displays atrial waveforms when the needle reaches the inside of the heart; or estimation of the wall thickness by observation of the patient's size and weight. Based on the wall thickness, an appropriate combination of sensing device60and anchor120A-F can be selected to achieve a desired placement of the transducer62relative to the internal surface138of the cavity136. Thereafter, the incision is made at the desired location for the sensing device60. For example, using standard devices and procedures, a tool can be inserted into the incision and a small circular portion (for example, about 3.5 mm diameter) of the wall134is excised. The previously assembled sensing unit110A-F (with the selected sensing device60and anchor120A-F) is then inserted in the resulting circular hole, after which the anchor120A-F is secured to the wall134, for example, sutured to the myocardium and pericardial layer of the heart (FIGS. 5-9) or by deployment of the arms164/184and legs166/186(FIGS. 10-15).

In accordance with a preferred aspect of the invention, the sensing device60can be implanted to monitor a variety of physiological parameters. For example, the device60can be used to monitor radial artery pressure. In this embodiment, the sensing device60can be implanted with an anchor under the skin of the wrist above the radial artery, while the readout unit80is located outside the body. The device60may contain the antenna66(FIG. 2a) or the antenna66may be located elsewhere in the arm or body (FIG. 2b). The readout unit80or portions thereof can be located on the outside of the body in close proximity to the device60, for example, worn on the wrist of the patient similar to a wrist watch.

The sensing device60can also be used to monitor intrasac pressures in an aneurysm sac of a patient who has had surgery to repair an abdominal aortic aneurysm or a thoracic aortic aneurysm. In this embodiment, the sensing device60can be implanted within the aneurysm sac, while the readout unit80is located outside the body. The device60may contain the antenna66(FIG. 2a) or the antenna66may be located elsewhere in the arm or body (FIG. 2b). The readout unit80or portions thereof can be located on the outside of the body in close proximity to the device60, for example, worn on a belt.

Another example is to use the sensing device60to monitor intracranial pressures in patients with traumatic brain injuries (blunt trauma or penetrating trauma), including but not limited to patients with intracranial hemorrhage, closed head injuries, epidural hematoma, subdural hematoma, subarachnoid hemorrhage, diffuse axonal injury, and intracranial hypertension. Depending on the type of injury, the sensing device60can be implanted with one of its anchors120A-F, preferably one of the anchors120A,120B or120C, using a minimally-invasive surgery technique into any area of the brain to place the distal face112of the device60(carrying the transducer62) in contact with either brain tissue or fluid. Portions of the readout unit80and optionally the antenna66of the sensing device60can be implanted between the skull and scalp of the patient.

Still another example is to use the sensing device60to monitor pulmonary artery pressures and other cardiovascular pressures near or within the heart. For example, the sensing device60can be implanted with one of its anchors120A-F, preferably one of the anchors120A,120B or120C, through the outer wall of the right ventricle, left ventricle, right atrium, left atrium, left ventricular apex, right ventricular apex, left atrial appendage, right atrial appendage, pulmonary artery, etc. As particular examples, the sensing device60can be implanted in the ventricular apex (right or left) or the atrial appendage (left or right), with only the distal face112of the device60(carrying the transducer62) being inside the ventricular apex or atrial appendage while the remainder of the sensing device60and its anchor120A-F are either within the heart wall, outside the heart, in a different location within the body, and/or outside the body. In each case, the risk of complications inside the heart, in particular thrombosis and thrombogenicity, are greatly reduced.

In each of the above-noted embodiments and applications, the anchors120A-F can be modified to provide other features beyond those described, for example, a device similar to an RFID tag can be added to the anchor such that it wirelessly transmits ID information concerning the sensing device60. The ID information may include an ID number, ID name, patient name/ID, calibration coefficients/information, range of operation, date of implantation, valid life of the device (operation life), etc. The anchors120A-F may further include additional capabilities such as features for connection to a catheter, shunt, or other device (not shown).

In addition to the sensing units110A-F and reader unit80described above, the monitoring systems of this invention can be combined with other technologies to achieve additional functionalities. For example, the reader unit80can be implemented to have a remote transmission capability, such as home monitoring that may employ telephone, wireless communication, or web-based delivery of information received from the sensing units110A-F by the reader unit80to a physician or caregiver. In this manner, the reader unit80can be adapted for remote monitoring of the organ and patient, closed-loop drug delivery of medications to treat the organ, closed-loop pacemaker parameter tuning to treat congestive heart failure or congestive heart failure related conditions, warning of critical worsening of congestive heart failure or congestive heart failure related conditions, portable or ambulatory monitoring or diagnosis, monitoring of battery operation, data storage, reporting global positioning coordinates for emergency applications, and communication with other medical devices chosen from the group consisting of pacemakers, left ventricular assist devices (LVAD), defibrillators, cardioverter defibrillators, drug delivery systems, non-drug delivery systems, and wireless medical management systems. Furthermore, the placement of the sensing units110A-F can be utilized as part of a variety of different medical procedures, including early diagnosis of a heart failing due to congestive heart failure related conditions, early diagnosis of failure of the organ, early intervention in treatment of congestive heart failure related conditions, tailoring of medications, disease management, identification of complications from congestive heart failure related conditions, identification of complications from cardiovascular disease related conditions, treatment of complications from congestive heart failure related conditions, treatment of complications from cardiovascular disease related conditions, pacing adjustments to the heart, reduction in frequency and severity of hospitalizations due to cardiovascular diseases, reduction in frequency and severity of hospitalizations due to congestive heart failure, tuning of defibrillator or pacemaker parameters to improve congestive heart failure related conditions, identification of mitral valve stenosis, treatment of mitral valve stenosis, feedback regarding the impact of medication on the organ, and chronic disease management of the organ.

While the invention has been described in terms of specific embodiments, it is apparent that other forms could be adopted by one skilled in the art. Therefore, the scope of the invention is to be limited only by the following claims.