Patent Application
20070208390
This subject matter pertains to implantable medical devices such as cardiac pacemakers, cardioverter/defibrillators and sensors. In particular, the subject matter relates to an apparatus and method for monitoring biological and physiological sounds.
Implantable medical devices (IMD), including cardiac rhythm management devices such as pacemakers and cardioverter/defibrillators, may be capable of communicating data with an external device, such as a programmer, via a radio frequency (RF) or other telemetry link. A clinician may use an external programmer to program the operating parameters of an implanted medical device. For example, the pacing mode and other operating characteristics of a pacemaker may be modified after implantation of the pacemaker into the body in this manner. IMDs may include the capability of bidirectional communication or information may be transmitted to the external programmer from the IMD for monitoring purposes. Data transmitted from an IMD to the external programmer may include various operating parameters and physiological data, either collected in real-time or stored from previous internal monitoring operations. In certain circumstances, the information gathered may warrant an immediate response from in order to avoid potential damage to the monitored body. In such circumstances the IMD may have the ability to make certain changes in the operating characteristics of the IMD within the limits of an allowable range of variables. This may be referred to as a closed circuit control loop, and, for example, may be applied in the case where a dangerous cardiac arrhythmia is detected.
The implanted medical device may have electrical electrodes or leads used to detect or sense the timing and strength of the various portions of a heart beat, or of a long series of heart beats. There may be analysis software included in the implanted device to characterize the measured values from the implanted sensors, to determine if immediate action is required, or whether an immediate alert to the external programmer should be sent, or whether to record the data until a scheduled download occurs.
A clinician may use a stethoscope to listen to heart and lung sounds when examining a patient. This may provide valuable information on the conditions found within the body. However, there may be problems with external human monitoring of heart and lung sounds, since the body may be considered as essentially a liquid in which sounds are transmitted easily and efficiently, and the body-to-stethoscope boundary may be a location where the sound waves of interest may be reflected, attenuated and distorted. Thus, listening to body sounds from the outside may result in a failure to capture the desired information due to poor sound transmission at the boundary. Further, it would be beneficial to be able to listen to body sounds, in particular biological and physiologically produced sounds, in a more continuous fashion (i.e., chronically) than is practical with current methods.
Further, listening to body sounds using a human ear from the outside of the body, may result in misinterpreted sound analysis due to human error, the short duration of listening, and the unreliable body to sound detector interface. The present inventors have recognized a need for more continuously, or chronically, detecting biologically generated sounds from inside the body. This permits either electronically storing the sound signatures, or performing an evaluation and comparison on the sounds to determine a current state of the body (e.g., as compared to past values), or to established normal values for the particular body.
This document describes, among other things, an implanted sound sensor, which may be known as a pod, that may be placed in a large blood vessel. The present inventors have recognized a need for an implantable sound detector, for having electronic storage capability within the body, and for sound evaluation capability to enable closed-loop feedback variation within prescribed limits of the operational settings of an implanted medical device, such as a pacer, defibrillator, or other cardiac function management device.
A disclosed implantable medical device (IMD) has an acoustic wave detector that is communicatively coupled to an implantable medical device housing. The acoustic wave detector may be situated to detect biologically generated sounds from areas of interest. The IMD may include an electronic circuit configured to communicate with either an external programmer, an external communications center, or an external emergency center, such as by using RF, inductive, or other telemetry. The IMD may include a cardiac function management device, a diagnostic analysis circuit, a memory circuit, or a closed-loop controller for adjusting the settings and performance of the implantable device.
The acoustic wave detector may be formed of a biocompatible material and implanted in the body, such as adjacent to, or even remote from the IMD. In various examples, the acoustic wave detector is coupled to the IMD housing by modulated electromagnetic radiation, modulated radio frequency radiation, modulated acoustic radiation, modulated ultrasonic waves, modulated e-field, electrical wires or by inductive coupling. There maybe a plurality of such acoustic wave detectors located either in or on the body, each of the detectors being a part of a communications network that includes the IMD as either a communications hub, or as a controller, or an analysis and storage center, or as a port for communications to an external location, such as a physician. The acoustic wave detector is typically battery-powered, and may be recharged by externally applied ultrasonic waves acting on a ultrasonic wave detector/generator, or by inductive coupling through the skin.
The acoustic wave detector is typically made of a biocompatible material or located inside a hermetic biocompatible pod. In certain examples, the pod may be formed of titanium or glass. In one illustrative example, the pod is formed of titanium having a wall thickness of between 0.001 to 0.002 inches—for example, thin enough such that a desired acoustic wave will pass easily through the walls. In an alternative example, the pod is formed of titanium having a greater wall thickness, such as between 0.011 to 0.012 inches, and having a diaphragm portion near the acoustic wave detector, the diaphragm portion having a thickness of between 0.001 to 0.002 inches so as to allow acoustic waves to pass through the diaphragm to reach the detector (or the diaphragm may form part of the detector). The pod may have a shape such as a cylinder, a can, a pill, a capsule or a tube, and may be small enough to fit within a blood vessel, such as the pulmonary artery. For example, the pod may have a diameter or similar dimension of less than 3.5 mm in at least one direction so as to reduce or minimize interference with blood flow. In another example, the pod may have a diameter or similar dimension of less that 2.0 mm in at least one direction, such as for implantation in a blood vessel smaller than the pulmonary artery.
In certain examples, the pod is anchored to the desired location inside the blood vessel by an expandable stent or stent-like mesh. The stent may be manually expanded by a catheter balloon or it may be self expanding. In certain examples, the stent is drug-coated. Examples of drugs used in stent coatings include Sirolimus, Paclitaxel, and Everlimus. The pod is typically attached to the mesh, such as in-between an inside wall of the blood vessel and an outside wall of the mesh, or inside the inner wall of the mesh, for example. In various examples, the acoustic detector pod may be introduced into a blood vessel, an esophagus, a trachea, a bronchus, a lung, a peritoneum, a pericardium or one of the alimentary organs.
In certain examples, the pod encloses the acoustic wave detector, an ultrasonic communication device, an acoustic impedance matching material (e.g., to improve the conduction efficiency of the detector), and a rechargeable battery. The acoustic impedance matching material may be a silicone gel or oil, or one or more other types of oils, such as hydrocarbon or fluorocarbon liquids, that substantially completely fills the pod, or at least an area about the enclosed acoustic wave detector. The acoustic impedance matching material typically has a viscosity that is selected to match a desired acoustic wavelength, such as to provide high acoustic conductance across the body-to-microphone interface, preferably with losses of no more than 80%. In one illustrative example, the acoustic wave detector is directional, such that it can be aimed at a selected location, such as the heart or a lung. The directional sound detector may be aimed in any direction during implantation, for example by turning the delivery catheter. Fluoroscopic markers may be used to allow a physician to see the direction of the sensor during implantation. Sound level measurements during implantation may also be used to help determine the proper detector placement. In another example, the acoustic detector is substantially omni-directional. The acoustic wave detector is typically used to monitor one or more of a heart sound, a mitral valve regurgitation sound, an S3 heart sound, a lung sound (e.g., rasps, rales, cough, etc.) or blood vessel flow sounds (e.g., resulting from an aneurism or vessel constriction).
The implantable medical housing typically receives biological and physiological sound information transmitted from the pod. It may store or process such sound information. For example, the IMD may store the heart or other recorded physiological sounds, transmit information about such sounds to an external programmer, perform a fast Fourier transform on such sounds, compare current sounds to previously-recorded sounds in the same patient, compare current sounds to a stored template sound, perform an analysis of detected sounds, or perform a closed-loop regulation of an interventional device, such as a cardiac function management device, which may be included in the IMD.
The biological sound detector may be remotely communicatively coupled to the IMD in a body, such as by using modulated ultrasonic waves. The IMD in the body may also include an accelerometer, a position detector, a temperature detector, or logic, such as to evaluate the detected biological sounds in conjunction with the measured body position. This may be useful for a patient with breathing difficulty in a supine position, or with sleep apnea. The accelerometer can be used to determine the body's physical posture, such as standing, sitting, prone, supine, or recumbent. The IMD will typically include a processor with analysis software that may use the posture information together with the sound information, such as to attenuate the influence of changes in posture on the sound information, for example. The IMD may then evaluate posture-corrected sound data, for example, and may communicate with an external programmer, an external communications center, or an external emergency center, such as by using RF or another communication technique.
In various examples, the biological sound detector will include a solid-state microphone, a unidirectional microphone, a multidirectional microphone, an omni-directional microphone, a carbon microphone, a piezoelectric microphone, a piezoresistive microphone, or a capacitive microphone. The sound detector is typically in a sealed pod with an ultrasonic or other transmitter or transceiver and a battery. The biological sound detector (pod) may be surrounded with a fluid, gel, or other acoustic impedance-matching material to improve acoustic coupling with the body.
Other aspects of the present systems and methods will be apparent upon reading the following detailed description and viewing the drawings that form a part thereof
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the present subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the subject matter, and it is to be understood that the embodiments may be combined, or that other embodiments may be utilized and that structural, mechanical, logical and electrical changes may be made without departing from the scope of the present subject matter. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present subject matter is defined by the appended claims and their equivalents.
The present inventors have recognized, among other things, a need for an implantable biological and physiological sound sensor, for example, which can be separately located from an implantable medical device (IMD), such as a cardiac function management device (which may be known as a pulse generator, PG), and which can have wireless communication with such an implantable medical device. In certain examples, this will enable a closed loop response to physiological sound information. In certain examples, this will permit reporting of physiological sound information to an external location, such as for clinician review.
The sound sensor may be located within the IMD, outside the IMD, or preferably, at a location remote from the IMD. The location will typically depend upon what physiological sounds the biological sound sensor is intended to listen to. For example, it may be useful to listen to heart sounds using a microphone located in the pulmonary artery. Similarly, it may be useful to listen to lung sounds using an axillary microphone location. If the biological sound sensor is located inside a major blood vessel, it may be anchored in place by an expandable stent-like device, such as a self-expanding stent, or a catheter balloon expanded stent. The stent may be drug coated, such as to inhibit or prevent local stenosis, for example using Everlimus (Guidant's Xience V stent), Paclitaxel (Boston Scientific Taxus stent), and Sirolimus (J&J Cypher stent), or other drugs.
The biological sound sensor may be a solid-state microphone. In certain examples, the microphone has a directional sound-receiving characteristic. By aiming a directional microphone at a selected portion of the heart, lung, or other location generating sounds of interest, physiological sound noise from other locations may be reduced. The biological sound sensor may be aimed during implantation using the delivery catheter to place the sensor, and adjusting the direction in response to received sound levels, or radiographic markers may be used to allow visualization of the sensor. There may be more than one sound sensor implanted in a body, which allows each biological sound sensor to listen to a different area of interest, if desired. Multiple biological sound sensors can form a local area network with an implantable cardiac function management device or other implantable medical device. This would permit the various biological sound sensors to communicate with the implantable medical device as desired. The sound information may be analyzed, filtered, transformed, compared to a template or recent sound, stored in volatile or non-volatile memory, or communicated to an external location. The implantable medical device will typically perform such processing, storage, or communication to an external location. The implantable medical device may also use the biological sound information to initiate or adjust an electrostimulation or other therapy by the implantable medical device, such as by implementing a closed-loop control system.
Each of the locations of interest, the heart 102, the lungs 104 and 106 in this illustrative example, may use a separate biological sound detector. In this illustrative example, sound detector 112 is positioned at a location favorable for obtaining readings for all or a selected portion of the heart 102. Similarly, sound detectors 114 and 116 are positioned to obtain favorable biological sound readings from the right and left lung respectively. The sound detectors 112, 114 and 116 may be either omnidirectional microphones, or unidirectional microphones oriented for receiving sound information from a region of specific interest. For example, the acoustic information may be transmitted to the IMD 108 as part of a local area network, or another method of group communication. In certain examples, the biological sound detectors 112, 114 and 116 communicate wirelessly with the IMD 108 using bidirectional communication. Such wireless communication may use communication means such as modulated ultrasonic waves, or modulated electromagnetic waves such as radio frequency modulation.
The IMD 108 may analyze the biological sound information by various techniques, such as by using Fast Fourier Transform (FFT), other mathematical transformations, filtering, comparison with one or more template or actual time or frequency domain acoustic patterns. The IMD 108 may include electronic circuitry to declare that a particular physiological condition has occurred, to determine the correct response (e.g., cardiac defibrillation in response to a detected fibrillation), or to transmit an alert or other information to an external location, such as by using of radio wave or other communication. The external location may include a processor to perform similar analysis or processing of the sound information as the IMD 108. If the IMD 108 does not detect an immediate problem, it may store the acoustic information, analyzed or in original form or both, in an included electronic storage medium, such as RAM, flash memory, or in a magnetic storage medium.
An illustrative biological sound detector system 200 is shown with a sealed sound detector pod 202 attached to an inside surface of a blood vessel 204. The pod 202 may be attached to the vessel using a stent (or like-structure), which typically includes an open-ended wire tube that may be expanded upon insertion at the desired position, such as by using a balloon catheter. Alternatively, a self-expanding stent may be used, or other methods known in the art. The pod 202 may be attached to the stent either before or after the stent is inserted and anchored in position by means of adhesives, clamps and mechanical attachments. To prevent or inhibit the tissue of the inside wall of the blood vessel 204 from reacting to the presence of the foreign body represented by the pod 202, the stent may be drug coated using any of a number of well known materials.
The pod 202 typically includes a pod shell formed of a bio-compatible material such as glass or titanium, and will typically have at least a portion of the pod shell that is conductive to acoustic waves. One or more portions of the inside of pod 202 may be filled with a liquid or gel that is conductive to acoustic waves. The acoustic impedance (affected by the viscosity, density and other physical characteristics) of the liquid or gel may be selected to obtain good or maximum acoustic conduction, for example, greater than 80% efficient acoustic transmission across the blood-pod interface. Illustrative examples of liquid and gel materials include silicone, hydrocarbon or fluorocarbon materials.
The walls of the pod 202 are generally thick enough to maintain the desired shape, in this illustrative example, a streamlined shape that provides low or minimum interference with blood flow. At least a portion of the walls of the pod 202 is not so thick that acoustic conduction efficiency declines beyond acceptable limits. In an illustrative example, the pod 202 includes a titanium wall that is about 0.012 inches thick, with a thinner portion of the wall being about 0.002 thick. The thinner portion forms an acoustically transmissive membrane near an acoustic pickup or microphone within the pod. The actual thickness of the pod 202 walls needed to maintain the desired shape will depend upon the forces the pod 202 needs to withstand, and whether the interior portion of the pod (about any sound detector, battery or other internal components carried by the pod) is essentially completely filled with an incompressible material such as fluorocarbon oil.
Non-biocompatible materials may be used inside the sealed pod 202. Non-biocompatible materials may even be used for the pod walls if suitably sealed with a bio-compatible material, such as a layer of polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (ETFE), polyetheretherketone (PEEK), parylene, silicone, polyurethane, Tecothane, aromatic polyether thermoplastic, or glass. In this illustrative example, the pod 202 could be formed using a thinner and more acoustically conductive material, which is also uniform, well-controlled, and more inexpensive than biocompatible titanium. The pod 202 includes an acoustic pickup or microphone 206. The microphone 206 may be any type of acoustic pickup, such as an electronic microphone, a piezoelectric acoustic pickup, piezoresistive acoustic pickup, a carbon microphone, a capacitor or other microphone system, and may be either omnidirectional or directional. The microphone is coupled to a transmitter or transceiver for unidirectional or bidirectional communication with the implantable medical device 108 of
In certain illustrative examples, the battery 212 is rechargeable, such as by occasional inductive coupling to receive power from an external source, or by externally applied ultrasonic waves that are picked up by the ultrasonic element 208, converted into an electrical charge, and directed to the battery 212. The circuitry 210 may also include a controller or communications interface with a wireless local area network, such as found in patent application 10/913,118 filed on Aug. 4, 2004, entitled System and Method for Providing Digital Data Communications Over a Wireless Intra-Body Network, incorporated herein, where multiple sensor pods communicate with an implantable medical device (IMD), to coordinate communication by the various sensor pods. This will avoid collisions of data from the various sensor pods.
The IMD housing 302 may also include an ultrasonic receiver or transceiver 310 for either unidirectional or bidirectional communication with one or more of the biological sound sensor pods 200 of
In certain examples, the internal communication between the IMD housing 302 and the separate sound detector pod(s) typically use one or more modulated ultrasonic signals, such as disclosed in patent application 10/888,956 filed Jul. 9, 2004, entitled System and Method of Acoustic Communication for Implantable Medical Device, incorporated herein. The communication between the IMD housing 302 and an external location is typically performed using modulated radio frequency or other electromagnetic or magnetic signals. The circuitry 304 may also include logic and memory elements, such as for comparing one or more of the biological sound recordings to one or more previously stored recordings of the specific individual's normal or abnormal heart or lung sounds, or for comparing a current sound to a template or other standardized biological sound pattern. In certain examples, a deviation from an allowable specified limit will trigger an alert to an external location, or a responsive therapy delivery or adjustment by the implantable medical device. Such responsive therapy may include cardiac function management therapy, such as bradycardia pacing, cardiac resynchronization, cardioversion or defibrillation, anti-tachyarrhythmia pacing, or the like. The circuitry may also include logic or performed instructions that process the received sound information, such as an FFT, high pass, low pass or band pass filtering, or frequency analysis, such as to determine if a physiological condition is detected. If the detected physiological condition is not so severe as to warrant providing an immediate alert to an external location, the circuitry 304 may store in an accompanying memory element either or both of the recorded sound and information obtained from the analysis. Such information can then be transmitted to an external location, if desired, at a later time, such during prescribed time periods.
The housing 302 may also contain one or more accelerometers or position sensors, such as to determine the recent activity level of the patient and the position of the body, including, for example, one or more of supine, prone, recumbent, sitting, standing, or leaning, or to provide information on position-dependent conditions, such as night coughing or wheezing, exercise-induced dyspnea or heart rhythm abnormalities.
The above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the present invention should not be limited to the described embodiments, and is set forth in the following claims.
