Patent Description:
Active implantable medical devices are routinely implanted with a patient's body. Such implantable medical devices are often used to provide therapy, diagnostics or both. In some cases, it can be desirable to communicate with such implantable medical devices via the skin, such as via a programmer or the like located outside of the body. Such communication can be though conducted communication, which conducts electrical current through the patient's body tissue from one device to the other. In the programmer example, the programmer may be electrically connected to the patient's body through electrode skin patches or the like. Such communication may facilitate the programmer in programing and/or re-programing the implantable medical device, reading data collected by the implantable medical device, and/or collecting or exchanging any other suitable information. In some instances, two or more implantable medical devices may be implanted with a patient. In such cases, it can be desirable to establish communication between the two or more implanted medical devices using conducted communication. Such communication may facility the implanted medical devices in sharing data, distribution of control and/or delivery of therapy, and/or in performing other desired functions. These are just some example uses of conducted communication in the body.

<CIT> discusses a leadless pacemaker for pacing a heart of a human. When the pacemaker is communicating with an external device or vice versa, the devices can measure the peak average integrated or faulted amplitude of the received signal to set an automatic discriminating threshold for noise rejection.

The present disclosure generally relates to systems, devices, and methods for communicating between medical devices, and more particularly, to systems, devices, and methods for communicating between medical devices using conducted communication.

The invention is defined in the independent claim <NUM>.

Additionally, or alternatively, any of the above described embodiments may further comprise, after determining the counted number of pulses exceeds the pulse count threshold, beginning, by the medical device, a new communication window.

Additionally, or alternatively, any of the above described embodiments may further comprise, by the medical device: tracking a communication session timer, and after determining the communication session timer has reached a threshold value, setting, by the medical device, the receive threshold to a lower predetermined value.

Additionally, or alternatively, any of the above described embodiments may further comprise resetting, by the medical device, the communication session timer after successfully receiving a message.

Additionally, or alternatively, in any of the above described embodiments, adjusting the receive threshold based at least in part on an amplitude of the received conducted communication signal may comprise: after a communication window timer reaches a threshold value, determining, by the medical device, whether a message was received before the communication window timer reached the threshold value, wherein the message represents a predefined sequence of pulses in the communication signal having an amplitude above the receive threshold, and, after determining that no message was received before the communication window timer reached the threshold value, increasing, by the medical device, the receive threshold.

Additionally, or alternatively, in any of the above described embodiments, increasing the receive threshold may comprise increasing the receive threshold by a predetermined amount.

Additionally, or alternatively, any of the above described embodiments may further comprise: before the communication window timer has reached the threshold value, determining, by the medical device, whether a message has been received, and, after determining that a message has been received before the communication window timer has reached the threshold value, resetting, by the medical device, the communication window timer value.

Additionally, or alternatively, any of the above described embodiments, may further comprise: tracking, by the medical device, a communication session timer, and after determining that the communication session timer has reached a threshold value, setting, by the medical device, the receive threshold to a lower predetermined value.

Additionally, or alternatively, any of the above described embodiments may further comprise resetting, by the medical device, the communication session timer after determining that a message has been received.

Additionally, or alternatively, in any of the above described embodiments, adjusting the receive threshold based at least in part on an amplitude of the received conducted communication signal may comprise setting, by the medical device, the receive threshold to a value proportional to a maximum amplitude of a pulse of the communication signal having an amplitude above the receive threshold.

Additionally, or alternatively, in any of the above described embodiments, setting the receive threshold to a value proportional to the maximum amplitude of a pulse of the communication signal having an amplitude above the receive threshold may comprise setting the receive threshold to the maximum value of the amplitude of the pulse of the communication signal having an amplitude above the receive threshold.

Additionally, or alternatively, any of the above described embodiments may further comprising setting, by the medical device, the receive threshold to a value proportional to a maximum amplitude of each pulse of the communication signal having an amplitude above the receive threshold.

Additionally, or alternatively, in any of the above described embodiments, the receive threshold may decay according to a predetermined function.

The disclosure may be more completely understood in consideration of the following description of various illustrative embodiments in connection with the accompanying drawings, in which:.

It should be understood, however, that the intention is not to limit aspects of the disclosure to the particular illustrative embodiments described.

The following description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The description and the drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the disclosure.

This disclosure describes systems, devices, and methods for communicating between medical devices. Some medical device systems of the present disclosure may communicate using conducted communication techniques, which may include delivering electrical communication signals into a body of a patient for conduction through the patient's body. This signal may be received by another medical device, thereby establishing a communication link between the devices.

<FIG> is a conceptual schematic block diagram of an exemplary leadless cardiac pacemaker (LCP) that may be implanted on the heart or within a chamber of the heart and may operate to sense physiological signals and parameters and deliver one or more types of electrical stimulation therapy to the heart of the patient. Example electrical stimulation therapy may include bradycardia pacing, rate responsive pacing therapy, cardiac resynchronization therapy (CRT), anti-tachycardia pacing (ATP) therapy and/or the like. As can be seen in <FIG>, LCP <NUM> may be a compact device with all components housed within LCP <NUM> or directly on housing <NUM>. In some instances, LCP <NUM> may include communication module <NUM>, pulse generator module <NUM>, electrical sensing module <NUM>, mechanical sensing module <NUM>, processing module <NUM>, energy storage module <NUM>, and electrodes <NUM>. While a leadless cardiac pacemaker (LCP) is used as an example implantable medical device, it is contemplated that any suitable implantable medical device may be used, including implantable medical devices that provide therapy (e.g. pacing, neuro-stimulation, etc.), diagnostics (sensing), or both.

As depicted in <FIG>, LCP <NUM> may include electrodes <NUM>, which can be secured relative to housing <NUM> and electrically exposed to tissue and/or blood surrounding LCP <NUM>. Electrodes <NUM> may generally conduct electrical signals to and from LCP <NUM> and the surrounding tissue and/or blood. Such electrical signals can include communication signals, electrical stimulation pulses, and intrinsic cardiac electrical signals, to name a few. Intrinsic cardiac electrical signals may include electrical signals generated by the heart and may be represented by an electrocardiogram (ECG).

Electrodes <NUM> may include one or more biocompatible conductive materials such as various metals or alloys that are known to be safe for implantation within a human body. In some instances, electrodes <NUM> may be generally disposed on either end of LCP <NUM> and may be in electrical communication with one or more of modules <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In embodiments where electrodes <NUM> are secured directly to housing <NUM>, an insulative material may electrically isolate the electrodes <NUM> from adjacent electrodes, housing <NUM>, and/or other parts of LCP <NUM>. In some instances, some or all of electrodes <NUM> may be spaced from housing <NUM> and connected to housing <NUM> and/or other components of LCP <NUM> through connecting wires. In such instances, the electrodes <NUM> may be placed on a tail (not shown) that extends out away from the housing <NUM>. As shown in <FIG>, in some embodiments, LCP <NUM> may include electrodes <NUM>'. Electrodes <NUM>' may be in addition to electrodes <NUM>, or may replace one or more of electrodes <NUM>. Electrodes <NUM>' may be similar to electrodes <NUM> except that electrodes <NUM>' are disposed on the sides of LCP <NUM>. In some cases, electrodes <NUM>' may increase the number of electrodes by which LCP <NUM> may deliver communication signals and/or electrical stimulation pulses, and/or may sense intrinsic cardiac electrical signals, communication signals, and/or electrical stimulation pulses.

Electrodes <NUM> and/or <NUM>' may assume any of a variety of sizes and/or shapes, and may be spaced at any of a variety of spacings. For example, electrodes <NUM> may have an outer diameter of two to twenty millimeters (mm). In other embodiments, electrodes <NUM> and/or <NUM>' may have a diameter of two, three, five, seven millimeters (mm), or any other suitable diameter, dimension and/or shape. Example lengths for electrodes <NUM> and/or <NUM>' may include, for example, one, three, five, ten millimeters (mm), or any other suitable length. As used herein, the length is a dimension of electrodes <NUM> and/or <NUM>' that extends away from the outer surface of the housing <NUM>. In some instances, at least some of electrodes <NUM> and/or <NUM>' may be spaced from one another by a distance of twenty, thirty, forty, fifty millimeters (mm), or any other suitable spacing. The electrodes <NUM> and/or <NUM>' of a single device may have different sizes with respect to each other, and the spacing and/or lengths of the electrodes on the device may or may not be uniform.

In the embodiment shown, communication module <NUM> may be electrically coupled to electrodes <NUM> and/or <NUM>' and may be configured to deliver communication pulses to tissues of the patient for communicating with other devices such as sensors, programmers, other medical devices, and/or the like. Communication signals, as used herein, may be any modulated signal that conveys information to another device, either by itself or in conjunction with one or more other modulated signals. In some embodiments, communication signals may be limited to sub-threshold signals that do not result in capture of the heart yet still convey information. The communication signals may be delivered to another device that is located either external or internal to the patient's body. In some instances, the communication may take the form of distinct communication pulses separated by various amounts of time. In some of these cases, the timing between successive pulses may convey information. Communication module <NUM> may additionally be configured to sense for communication signals delivered by other devices, which may be located external or internal to the patient's body.

Communication module <NUM> may communicate to help accomplish one or more desired functions. Some example functions include delivering sensed data, using communicated data for determining occurrences of events such as arrhythmias, coordinating delivery of electrical stimulation therapy, and/or other functions. In some cases, LCP <NUM> may use communication signals to communicate raw information, processed information, messages and/or commands, and/or other data. Raw information may include information such as sensed electrical signals (e.g. a sensed ECG), signals gathered from coupled sensors, and the like. In some embodiments, the processed information may include signals that have been filtered using one or more signal processing techniques. Processed information may also include parameters and/or events that are determined by the LCP <NUM> and/or another device, such as a determined heart rate, timing of determined heartbeats, timing of other determined events, determinations of threshold crossings, expirations of monitored time periods, activity level parameters, blood-oxygen parameters, blood pressure parameters, heart sound parameters, and the like. Messages and/or commands may include instructions or the like directing another device to take action, notifications of imminent actions of the sending device, requests for reading from the receiving device, requests for writing data to the receiving device, information messages, and/or other messages commands.

In at least some embodiments, communication module <NUM> (or LCP <NUM>) may further include switching circuitry to selectively connect one or more of electrodes <NUM> and/or <NUM>' to communication module <NUM> in order to select which electrodes <NUM> and/or <NUM>' that communication module <NUM> delivers communication pulses. It is contemplated that communication module <NUM> may be communicating with other devices via conducted signals, radio frequency (RF) signals, optical signals, acoustic signals, inductive coupling, and/or any other suitable communication methodology. Where communication module <NUM> generates electrical communication signals, communication module <NUM> may include one or more capacitor elements and/or other charge storage devices to aid in generating and delivering communication signals. In the embodiment shown, communication module <NUM> may use energy stored in energy storage module <NUM> to generate the communication signals. In at least some examples, communication module <NUM> may include a switching circuit that is connected to energy storage module <NUM> and, with the switching circuitry, may connect energy storage module <NUM> to one or more of electrodes <NUM>/<NUM>' to generate the communication signals.

As shown in <FIG>, a pulse generator module <NUM> may be electrically connected to one or more of electrodes <NUM> and/or <NUM>'. Pulse generator module <NUM> may be configured to generate electrical stimulation pulses and deliver the electrical stimulation pulses to tissues of a patient via one or more of the electrodes <NUM> and/or <NUM>' in order to effectuate one or more electrical stimulation therapies. Electrical stimulation pulses as used herein are meant to encompass any electrical signals that may be delivered to tissue of a patient for purposes of treatment of any type of disease or abnormality. For example, when used to treat heart disease, the pulse generator module <NUM> may generate electrical stimulation pacing pulses for capturing the heart of the patient, i.e. causing the heart to contract in response to the delivered electrical stimulation pulse. In some of these cases, LCP <NUM> may vary the rate at which pulse generator <NUM> generates the electrical stimulation pulses, for example in rate adaptive pacing. In other embodiments, the electrical stimulation pulses may include defibrillation/cardioversion pulses for shocking the heart out of fibrillation or into a normal heart rhythm. In yet other embodiments, the electrical stimulation pulses may include anti-tachycardia pacing (ATP) pulses. It should be understood that these are just some examples. When used to treat other ailments, the pulse generator module <NUM> may generate electrical stimulation pulses suitable for neuro-stimulation therapy or the like. Pulse generator module <NUM> may include one or more capacitor elements and/or other charge storage devices to aid in generating and delivering appropriate electrical stimulation pulses. In at least some embodiments, pulse generator module <NUM> may use energy stored in energy storage module <NUM> to generate the electrical stimulation pulses. In some particular embodiments, pulse generator module <NUM> may include a switching circuit that is connected to energy storage module <NUM> and may connect energy storage module <NUM> to one or more of electrodes <NUM>/<NUM>' to generate electrical stimulation pulses.

LCP <NUM> may further include an electrical sensing module <NUM> and mechanical sensing module <NUM>. Electrical sensing module <NUM> may be configured to sense intrinsic cardiac electrical signals conducted from electrodes <NUM> and/or <NUM>' to electrical sensing module <NUM>. For example, electrical sensing module <NUM> may be electrically connected to one or more electrodes <NUM> and/or <NUM>' and electrical sensing module <NUM> may be configured to receive cardiac electrical signals conducted through electrodes <NUM> and/or <NUM>' via a sensor amplifier or the like. In some embodiments, the cardiac electrical signals may represent local information from the chamber in which LCP <NUM> is implanted. For instance, if LCP <NUM> is implanted within a ventricle of the heart, cardiac electrical signals sensed by LCP <NUM> through electrodes <NUM> and/or <NUM>' may represent ventricular cardiac electrical signals. Mechanical sensing module <NUM> may include, or be electrically connected to, various sensors, such as accelerometers, blood pressure sensors, heart sound sensors, piezoelectric sensors, blood-oxygen sensors, and/or other sensors which measure one or more physiological parameters of the heart and/or patient. Mechanical sensing module <NUM>, when present, may gather signals from the sensors indicative of the various physiological parameters. Both electrical sensing module <NUM> and mechanical sensing module <NUM> may be connected to processing module <NUM> and may provide signals representative of the sensed cardiac electrical signals and/or physiological signals to processing module <NUM>. Although described with respect to <FIG> as separate sensing modules, in some embodiments, electrical sensing module <NUM> and mechanical sensing module <NUM> may be combined into a single module. In at least some examples, LCP <NUM> may only include one of electrical sensing module <NUM> and mechanical sensing module <NUM>. In some cases, any combination of the processing module <NUM>, electrical sensing module <NUM>, mechanical sensing module <NUM>, communication module <NUM>, pulse generator module <NUM> and/or energy storage module may be considered a controller of the LCP <NUM>.

Processing module <NUM> may be configured to direct the operation of LCP <NUM>. For example, processing module <NUM> may be configured to receive cardiac electrical signals from electrical sensing module <NUM> and/or physiological signals from mechanical sensing module <NUM>. Based on the received signals, processing module <NUM> may determine, for example, occurrences and types of arrhythmias. Processing module <NUM> may further receive information from communication module <NUM>. In some embodiments, processing module <NUM> may additionally use such received information to determine occurrences and types of arrhythmias. In still some additional embodiments, LCP <NUM> may use the received information instead of the signals received from electrical sensing module <NUM> and/or mechanical sensing module <NUM> - for instance if the received information is deemed to be more accurate than the signals received from electrical sensing module <NUM> and/or mechanical sensing module <NUM> or if electrical sensing module <NUM> and/or mechanical sensing module <NUM> have been disabled or omitted from LCP <NUM>.

After determining an occurrence of an arrhythmia, processing module <NUM> may control pulse generator module <NUM> to generate electrical stimulation pulses in accordance with one or more electrical stimulation therapies to treat the determined arrhythmia. For example, processing module <NUM> may control pulse generator module <NUM>. to generate pacing pulses with varying parameters and in different sequences to effectuate one or more electrical stimulation therapies. As one example, in controlling pulse generator module <NUM> to deliver bradycardia pacing therapy, processing module <NUM> may control pulse generator module <NUM>. to deliver pacing pulses designed to capture the heart of the patient at a regular interval to help prevent the heart of a patient from falling below a predetermined threshold. In some cases, the rate of pacing may be increased with an increased activity level of the patient (e.g. rate adaptive pacing). For instance, processing module <NUM> may monitor one or more physiological parameters of the patient which may indicate a need for an increased heart rate (e.g. due to increased metabolic demand). Processing module <NUM> may then increase the rate at which pulse generator <NUM> generates electrical stimulation pulses.

For ATP therapy, processing module <NUM> may control pulse generator module <NUM> to deliver pacing pulses at a rate faster than an intrinsic heart rate of a patient in attempt to force the heart to beat in response to the delivered pacing pulses rather than in response to intrinsic cardiac electrical signals. Once the heart is following the pacing pulses, processing module <NUM> may control pulse generator module <NUM> to reduce the rate of delivered pacing pulses down to a safer level. In CRT, processing module <NUM> may control pulse generator module <NUM> to deliver pacing pulses in coordination with another device to cause the heart to contract more efficiently. In cases where pulse generator module <NUM> is capable of generating defibrillation and/or cardioversion pulses for defibrillation/cardioversion therapy, processing module <NUM> may control pulse generator module <NUM> to generate such defibrillation and/or cardioversion pulses. In some cases, processing module <NUM> may control pulse generator module <NUM> to generate electrical stimulation pulses to provide electrical stimulation therapies different than those examples described above.

Aside from controlling pulse generator module <NUM> to generate different types of electrical stimulation pulses and in different sequences, in some embodiments, processing module <NUM> may also control pulse generator module <NUM> to generate the various electrical stimulation pulses with varying pulse parameters. For example, each electrical stimulation pulse may have a pulse width and a pulse amplitude. Processing module <NUM> may control pulse generator module <NUM> to generate the various electrical stimulation pulses with specific pulse widths and pulse amplitudes. For example, processing module <NUM> may cause pulse generator module <NUM> to adjust the pulse width and/or the pulse amplitude of electrical stimulation pulses if the electrical stimulation pulses are not effectively capturing the heart. Such control of the specific parameters of the various electrical stimulation pulses may help LCP <NUM> provide more effective delivery of electrical stimulation therapy.

In some embodiments, processing module <NUM> may further control communication module <NUM> to send information to other devices. For example, processing module <NUM> may control communication module <NUM> to generate one or more communication signals for communicating with other devices of a system of devices. For instance, processing module <NUM> may control communication module <NUM> to generate communication signals in particular pulse sequences, where the specific sequences convey different information. Communication module <NUM> may also receive communication signals for potential action by processing module <NUM>.

In further embodiments, processing module <NUM> may control switching circuitry by which communication module <NUM> and pulse generator module <NUM> deliver communication signals and/or electrical stimulation pulses to tissue of the patient. As described above, both communication module <NUM> and pulse generator module <NUM> may include circuitry for connecting one or more electrodes <NUM> and/<NUM>' to communication module <NUM> and/or pulse generator module <NUM> so those modules may deliver the communication signals and electrical stimulation pulses to tissue of the patient. The specific combination of one or more electrodes by which communication module <NUM> and/or pulse generator module <NUM> deliver communication signals and electrical stimulation pulses may influence the reception of communication signals and/or the effectiveness of electrical stimulation pulses. Although it was described that each of communication module <NUM> and pulse generator module <NUM> may include switching circuitry, in some embodiments, LCP <NUM> may have a single switching module connected to the communication module <NUM>, the pulse generator module <NUM>, and electrodes <NUM> and/or <NUM>'. In such embodiments, processing module <NUM> may control the switching module to connect modules <NUM>/<NUM> and electrodes <NUM>/<NUM>' as appropriate.

In some embodiments, processing module <NUM> may include a pre-programmed chip, such as a very-large-scale integration (VLSI) chip or an application specific integrated circuit (ASIC). In such embodiments, the chip may be pre-programmed with control logic in order to control the operation of LCP <NUM>. By using a pre-programmed chip, processing module <NUM> may use less power than other programmable circuits while able to maintain basic functionality, thereby potentially increasing the battery life of LCP <NUM>. In other instances, processing module <NUM> may include a programmable microprocessor or the like. Such a programmable microprocessor may allow a user to adjust the control logic of LCP <NUM> after manufacture, thereby allowing for greater flexibility of LCP <NUM> than when using a pre-programmed chip.

Processing module <NUM>, in additional embodiments, may include a memory circuit and processing module <NUM> may store information on and read information from the memory circuit. In other embodiments, LCP <NUM> may include a separate memory circuit (not shown) that is in communication with processing module <NUM>, such that processing module <NUM> may read and write information to and from the separate memory circuit. The memory circuit, whether part of processing module <NUM> or separate from processing module <NUM>, may be volatile memory, non-volatile memory, or a combination of volatile memory and non-volatile memory.

Energy storage module <NUM> may provide a power source to LCP <NUM> for its operations. In some embodiments, energy storage module <NUM> may be a non-rechargeable lithium-based battery. In other embodiments, the non-rechargeable battery may be made from other suitable materials. In some embodiments, energy storage module <NUM> may include a rechargeable battery. In still other embodiments, energy storage module <NUM> may include other types of energy storage devices such as capacitors or super capacitors.

To implant LCP <NUM> inside a patient's body, an operator (e.g., a physician, clinician, etc.), may fix LCP <NUM> to the cardiac tissue of the patient's heart. To facilitate fixation, LCP <NUM> may include one or more anchors <NUM>. The one or more anchors <NUM> are shown schematically in <FIG>. The one or more anchors <NUM> may include any number of fixation or anchoring mechanisms. For example, one or more anchors <NUM> may include one or more pins, staples, threads, screws, helix, tines, and/or the like. In some embodiments, although not shown, one or more anchors <NUM> may include threads on its external surface that may run along at least a partial length of an anchor member. The threads may provide friction between the cardiac tissue and the anchor to help fix the anchor member within the cardiac tissue. In some cases, the one or more anchors <NUM> may include an anchor member that has a cork-screw shape that can be screwed into the cardiac tissue. In other embodiments, anchor <NUM> may include other structures such as barbs, spikes, or the like to facilitate engagement with the surrounding cardiac tissue.

In some examples, LCP <NUM> may be configured to be implanted on a patient's heart or within a chamber of the patient's heart. For instance, LCP <NUM> may be implanted within any of a left atrium, right atrium, left ventricle, or right ventricle of a patient's heart. By being implanted within a specific chamber, LCP <NUM> may be able to sense cardiac electrical signals originating or emanating from the specific chamber that other devices may not be able to sense with such resolution. Where LCP <NUM> is configured to be implanted on a patient's heart, LCP <NUM> may be configured to be implanted on or adjacent to one of the chambers of the heart, or on or adjacent to a path along which intrinsically generated cardiac electrical signals generally follow. In these examples, LCP <NUM> may also have an enhanced ability to sense localized intrinsic cardiac electrical signals and deliver localized electrical stimulation therapy.

<FIG> depicts an embodiment of another device, medical device (MD) <NUM>, which may operate to sense physiological signals and parameters and/or deliver one or more types of electrical stimulation therapy to tissues of the patient. In the embodiment shown, MD <NUM> may include a communication module <NUM>, a pulse generator module <NUM>, an electrical sensing module <NUM>, a mechanical sensing module <NUM>, a processing module <NUM>, and an energy storage module <NUM>. Each of modules <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> may be similar to modules <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> of LCP <NUM>. Additionally, energy storage module <NUM> may be similar to energy storage module <NUM> of LCP <NUM>. However, in some embodiments, MD <NUM> may have a larger volume within housing <NUM>. In such embodiments, MD <NUM> may include a larger energy storage module <NUM> and/or a larger processing module <NUM> capable of handling more complex operations than processing module <NUM> of LCP <NUM>.

While MD <NUM> may be another leadless device such as shown in <FIG>, in some instances MD <NUM> may include leads, such as leads <NUM>. Leads <NUM> may include electrical wires that conduct electrical signals between electrodes <NUM> and one or more modules located within housing <NUM>. In some cases, leads <NUM> may be connected to and extend away from housing <NUM> of MD <NUM>. In some embodiments, leads <NUM> are implanted on, within, or adjacent to a heart of a patient. Leads <NUM> may contain one or more electrodes <NUM> positioned at various locations on leads <NUM> and various distances from housing <NUM>. Some leads <NUM> may only include a single electrode <NUM>, while other leads <NUM> may include multiple electrodes <NUM>. Generally, electrodes <NUM> are positioned on leads <NUM> such that when leads <NUM> are implanted within the patient, one or more of the electrodes <NUM>-<NUM> are positioned to perform a desired function. In some cases, the one or more of the electrodes <NUM> may be in contact with the patient's cardiac tissue. In other cases, the one or more of the electrodes <NUM> may be positioned subcutaneously but adjacent the patient's heart. The electrodes <NUM> may conduct intrinsically generated electrical cardiac signals to leads <NUM>. Leads <NUM> may, in turn, conduct the received electrical cardiac signals to one or more of the modules <NUM>, <NUM>, <NUM>, and <NUM> of MD <NUM>. In some cases, MD <NUM> may generate electrical stimulation signals, and leads <NUM> may conduct the generated electrical stimulation signals to electrodes <NUM>. Electrodes <NUM> may then conduct the electrical stimulation signals to the cardiac tissue of the patient (either directly or indirectly). MD <NUM> may also include one or more electrodes <NUM> not disposed on a lead <NUM>. For example, one or more electrodes <NUM> may be connected directly to housing <NUM>.

Leads <NUM>, in some embodiments, may additionally contain one or more sensors, such as accelerometers, blood pressure sensors, heart sound sensors, blood-oxygen sensors, and/or other sensors which are configured to measure one or more physiological parameters of the heart and/or patient. In such embodiments, mechanical sensing module <NUM> may be in electrical communication with leads <NUM> and may receive signals generated from such sensors.

While not required, in some embodiments MD <NUM> may be an implantable medical device. In such embodiments, housing <NUM> of MD <NUM> may be implanted in, for example, a transthoracic region of the patient. Housing <NUM> may generally include any of a number of known materials that are safe for implantation in a human body and may, when implanted, hermetically seal the various components of MD <NUM> from fluids and tissues of the patient's body. In such embodiments, leads <NUM> may be implanted at one or more various locations within the patient, such as within the heart of the patient, adjacent to the heart of the patient, adjacent to the spine of the patient, or any other desired location.

In some embodiments, MD <NUM> may be an implantable cardiac pacemaker (ICP). In these embodiments, MD <NUM> may have one or more leads, for example leads <NUM>, which are implanted on or within the patient's heart. The one or more leads <NUM> may include one or more electrodes <NUM> that are in contact with cardiac tissue and/or blood of the patient's heart. MD <NUM> may be configured to sense intrinsically generated cardiac electrical signals and determine, for example, one or more cardiac arrhythmias based on analysis of the sensed signals. MD <NUM> may be configured to deliver CRT, ATP therapy, bradycardia therapy, and/or other therapy types via leads <NUM> implanted within the heart. In some embodiments, MD <NUM> may additionally be configured to provide defibrillation/cardioversion therapy.

In some instances, MD <NUM> may be an implantable cardioverter-defibrillator (ICD). In such embodiments, MD <NUM> may include one or more leads implanted within a patient's heart. MD <NUM> may also be configured to sense electrical cardiac signals, determine occurrences of tachyarrhythmias based on the sensed electrical cardiac signals, and deliver defibrillation and/or cardioversion therapy in response to determining an occurrence of a tachyarrhythmia (for example by delivering defibrillation and/or cardioversion pulses to the heart of the patient). In other embodiments, MD <NUM> may be a subcutaneous implantable cardioverter-defibrillator (SICD). In embodiments where MD <NUM> is an SICD, one of leads <NUM> may be a subcutaneously implanted lead. In at least some embodiments where MD <NUM> is an SICD, MD <NUM> may include only a single lead which is implanted subcutaneously but outside of the chest cavity, however this is not required.

In some embodiments, MD <NUM> may not be an implantable medical device. Rather, MD <NUM> may be a device external to the patient's body, and electrodes <NUM> may be skinelectrodes that are placed on a patient's body. In such embodiments, MD <NUM> may be able to sense surface electrical signals (e.g. electrical cardiac signals that are generated by the heart or electrical signals generated by a device implanted within a patient's body and conducted through the body to the skin). MD <NUM> may further be configured to deliver various types of electrical stimulation therapy, including, for example, defibrillation therapy via skinelectrodes <NUM>.

<FIG> illustrates an embodiment of a medical device system and a communication pathway through which multiple medical devices <NUM>, <NUM>, <NUM>, and/or <NUM> of the medical device system may communicate. In the embodiment shown, medical device system <NUM> may include LCPs <NUM> and <NUM>, external medical device <NUM>, and other sensors/devices <NUM>. External device <NUM> may be a device disposed external to a patient's body, as described previously with respect to MD <NUM>. In at least some examples, external device <NUM> may represent an external support device such as a device programmer, as will be described in more detail below. Other sensors/devices <NUM> may be any of the devices described previously with respect to MD <NUM>, such as ICPs, ICDs, and SICDs. Other sensors/devices <NUM> may also include various diagnostic sensors that gather information about the patient, such as accelerometers, blood pressure sensors, or the like. In some cases, other sensors/devices <NUM> may include an external programmer device that may be used to program one or more devices of system <NUM>.

Various devices of system <NUM> may communicate via communication pathway <NUM>. For example, LCPs <NUM> and/or <NUM> may sense intrinsic cardiac electrical signals and may communicate such signals to one or more other devices <NUM>/<NUM>, <NUM>, and <NUM> of system <NUM> via communication pathway <NUM>. In one embodiment, one or more of devices <NUM>/<NUM> may receive such signals and, based on the received signals, determine an occurrence of an arrhythmia. In some cases, device or devices <NUM>/<NUM> may communicate such determinations to one or more other devices <NUM> and <NUM> of system <NUM>. In some cases, one or more of devices <NUM>/<NUM>, <NUM>, and <NUM> of system <NUM> may take action based on the communicated determination of an arrhythmia, such as by delivering a suitable electrical stimulation to the heart of the patient. One or more of devices <NUM>/<NUM>, <NUM>, and <NUM> of system <NUM> may additionally communicate command or response messages via communication pathway <NUM>. The command messages may cause a receiving device to take a particular action whereas response messages may include requested information or a confirmation that a receiving device did, in fact, receive a communicated message or data.

It is contemplated that the various devices of system <NUM> may communicate via pathway <NUM> using RF signals, inductive coupling, optical signals, acoustic signals, or any other signals suitable for communication. Additionally, in at least some embodiments, the various devices of system <NUM> may communicate via pathway <NUM> using multiple signal types. For instance, other sensors/device <NUM> may communicate with external device <NUM> using a first signal type (e.g. RF communication) but communicate with LCPs <NUM>/<NUM> using a second signal type (e.g. conducted communication). Further, in some embodiments, communication between devices may be limited. For instance, as described above, in some embodiments, LCPs <NUM>/<NUM> may communicate with external device <NUM> only through other sensors/devices <NUM>, where LCPs <NUM>/<NUM>. send signals to other sensors/devices <NUM>, and other sensors/devices <NUM> relay the received signals to external device <NUM>.

In some cases, the various devices of system <NUM> may communicate via pathway <NUM> using conducted communication signals. Accordingly, devices of system <NUM> may have components that allow for such conducted communication. For instance, the devices of system <NUM> may be configured to transmit conducted communication signals (e.g. current and/or voltage pulses, referred herein as electrical communication pulses) into the patient's body via one or more electrodes of a transmitting device, and may receive the conducted communication signals via one or more electrodes of a receiving device. The patient's body may "conduct" the conducted communication signals from the one or more electrodes of the transmitting device to the electrodes of the receiving device in the system <NUM>. In such embodiments, the delivered conducted communication signals may differ from pacing pulses, defibrillation and/or cardioversion pulses, or other electrical stimulation therapy signals. For example, the devices of system <NUM> may deliver electrical communication pulses at an amplitude/pulse width that is sub-threshold. That is, the communication pulses may have an amplitude/pulse width designed to not capture the heart. In some cases, the amplitude/pulse width of the delivered electrical communication pulses may be above the capture threshold of the heart, but may be delivered during a refractory period of the heart and/or may be incorporated in or modulated onto a pacing pulse, if desired. In some cases, the delivered electrical communication pulses may be notches or other disturbances in a pacing pulse.

Unlike normal electrical stimulation therapy pulses, the electrical communication pulses may be delivered in specific sequences which convey information to receiving devices. For instance, delivered electrical communication pulses may be modulated in any suitable manner to encode communicated information. In some cases, the communication pulses may be pulse width modulated and/or amplitude modulated. Alternatively, or in addition, the time between pulses may be modulated to encode desired information. In some cases, a predefined sequence of communication pulses may represent a corresponding symbol (e.g. a logic ''<NUM>'' symbol, a logic "<NUM>" symbol, an ATP therapy trigger symbol, etc.). In some cases, conducted communication pulses may be voltage pulses, current pulses, biphasic voltage pulses, biphasic current pulses, or any other suitable electrical pulse as desired.

<FIG> shows an illustrative medical device system <NUM> that may be configured to operate according to techniques disclosed herein. For example, the system may include multiple devices connected to a patient represented by heart <NUM> and skin <NUM>, where at least some of the devices are configured for communication with other devices. In the exemplary system <NUM>, an LCP <NUM> is shown fixed to the interior of the right ventricle of the heart <NUM>, and external support device <NUM> and external defibrillator <NUM> are shown connected to skin <NUM> through skin electrodes <NUM> and <NUM>, respectively. External support device <NUM> can be used to perform functions such as device identification, device programming and/or transfer of real-time and/or stored data between devices using one or more of the communication techniques described herein. In at least some embodiments, LCP <NUM> and external support device <NUM> are configured to communicate through conducted communication.

In some embodiments, external defibrillator <NUM> may be configured to deliver a voltage and/or current signal into the patient through skin <NUM> as a patch-integrity signal, and may further sense the patch-integrity signal in order to determine information about the contact between electrodes <NUM> and skin <NUM>. External defibrillator <NUM> may be configured to display or emit an alarm if the received patch-integrity signal indicates insufficient contact between electrodes <NUM> and skin <NUM> to achieve sufficient sensing by the patch electrodes <NUM> of cardiac electrical signals of heart <NUM> and/or for safe delivery of defibrillation and/or cardioversion pulses. In some embodiments, the patch-integrity signal may represent a continuous signal, such as a sine-wave, square-wave, saw-tooth wave, or the like. Additionally, and in some cases, the patch-integrity signal may have a frequency of between about <NUM> and about <NUM>, but this is not required. In some instances, this patch-integrity signal may interfere with the conducted communication signals delivered and received by LCP <NUM> and external support device <NUM>. Accordingly, the LCP <NUM> and/or external support device <NUM> may employ one or more techniques for enhancing the effectiveness of their conducted communication scheme, as described in more detail below.

It should be understood that the system of <FIG> is just one example system that may benefit from the techniques disclosed herein. Other system may include additional and/or different devices, but may still include a device delivering a conducted signal into the body of a patient that may interfere with conducted communication signals delivered into the patient's body for inter-device communication. Additionally, other systems may have different communication schemes that use additional communication modalities and/or include intermediary devices that receive conducted communication signals from a first device and relay received messages to a second device.

<FIG> depicts an example conducted communication signal <NUM> that may be received by LCP <NUM>. Although the description of the following examples uses external support device <NUM> as a transmitter and LCP <NUM> as a receiver, it should be understood that this is only for ease of description. The below described techniques may be implemented by any device of a system, such as system <NUM>, with any of the devices of the system acting as the transmitter and any of the devices of the system acting as the receiver. This may include inter-device communication between, for example, two or more implanted medical devices, such as LCP <NUM> and another LCP (not shown in <FIG>. ) and/or other implanted device.

In the example shown in <FIG>, conducted communication signal <NUM> includes signal component <NUM> and noise component <NUM>. In the example shown, signal component <NUM> represents a series of communication pulses <NUM> delivered by external support device <NUM> (or other internal or external device). In the example shown, noise component <NUM> represents a patch-integrity signal delivered by external defibrillator <NUM>. Once LCP <NUM> receives the conducted communication signal, LCP <NUM> may perform initial amplification and/or filtering. Conducted communication signal <NUM> of <FIG> may represent the output of the initial amplification and/or filtering. LCP <NUM> may provide the conducted communication signal <NUM> to a comparator circuit, which may be part of a communication module of LCP <NUM>. The comparator circuit may compare the conducted communication signal <NUM> to a receive threshold, such as a programmable receive threshold <NUM>. In some cases, the comparator circuit may produce a pulse each time the conducted communication signal <NUM> is above the programmable receive threshold <NUM>, resulting in a conducted communication signal <NUM> such as shown in <FIG>. That is, in the example shown, the comparator circuit may generate a high signal (e.g. one of pulses <NUM>) whenever the amplitude of conducted communication signal <NUM> is higher than the receive threshold <NUM>.

As described, in some conducted communication schemes, the specific characteristics or spacing of received pulses, such as pulses <NUM> of conducted communication signal <NUM>, may convey information. In some embodiments, LCP <NUM> and external support device <NUM> may be configured according to a specific communication protocol, whereby specific patterns of pulse characteristics and/or pulse spacing may represent predefined messages. Some example messages may include identification messages, commands, requests for data, and the like. If a received set of pulses do not have the characteristics that correspond to a recognized message format, the device may determine that a valid message has not been received, and conversely if a received set of pulses do have the characteristics that correspond to a recognized message formats, the device may determine that a valid message has been received.

In at least some instances, LCP <NUM> and/or external support device <NUM> may also determine whether a received message is valid by checking a received message for errors. For instance, the receiving device, even after receiving a series of pulses that correspond to a recognized message format, may employ one or more error checking schemes, such as repetition codes, parity bits, checksums, cyclic redundancy checks (CRC), or the like. When so provided, the device may only determine that a received message is valid if the error checking algorithm determines that there are no errors, or no significant errors, in the received message.

As can be seen in <FIG>, conducted communication signal <NUM> includes pulses <NUM> generated from both signal component <NUM> and noise component <NUM> of conducted communication signal <NUM>. Accordingly, and in some instances, LCP <NUM> may determine that conducted communication signal <NUM> is not a valid message as the pulse pattern will not match a recognized message format. In this example, receive threshold <NUM> is set too low such that portions of noise component <NUM> have an amplitude high enough to pass through the comparator circuit and generate pulses <NUM> in conducted communication signal <NUM>.

<FIG> is a flow diagram of an illustrative method <NUM> that LCP <NUM> (or another device) may implement in order to adjust receive threshold <NUM> based, at least in part, on the amplitude of conducted communication signal <NUM>. Adjusting receive threshold <NUM> to be above the amplitude of noise component <NUM> of conducted communication signal <NUM> may allow only signal component <NUM> to pass through the comparator circuit resulting in a conducted communication signal that only includes pulses due to signal component <NUM>. This may produce a valid message received at LCP <NUM>.

In the example method <NUM>, LCP <NUM> may begin by setting receive threshold <NUM> to an initial value, as shown at <NUM>. The initial value may be set such that, under most conditions, receive threshold <NUM> is below the amplitude of signal component <NUM> of conducted communication signal <NUM>. Next, LCP <NUM> may reset and begin a communication window timer, as shown at <NUM>, and reset and begin a communication session timer, as shown at <NUM>. In some embodiments, LCP <NUM> may begin the communication window timer only at predefined times. For instance, the communication window timer may be synchronized to line up with one or more features of a sensed cardiac electrical signal, such as an R-wave. In such an example, once LCP <NUM> resets the communication window timer, LCP <NUM> may wait to start the communication window timer until sensing a particular feature in the cardiac electrical signal. In at least some instances, LCP <NUM> may start the communication window timer after a predefined time after sensing the particular feature. As one example, LCP <NUM> may wait between about <NUM> and about <NUM> after sensing an R-wave to begin the communication window timer.

In some cases, LCP <NUM> may count the number of received pulses in a received conducted communication signal, as shown at <NUM>. For instance, received conducted communication signal <NUM> may be passed through the comparator circuit using receive threshold <NUM>, resulting in conducted communication signal <NUM>. As one example implementation, LCP <NUM> may increment a pulse count value every time LCP <NUM> detects a pulse in conducted communication signal <NUM>.

Next, LCP <NUM> may determine whether the communication session timer has exceeded the communication session timer threshold, as shown at <NUM>. If the communication session timer has exceeded the communication session timer threshold, LCP <NUM> may begin method <NUM> again back at <NUM>. The communication session timer may help ensure that if receive threshold <NUM> ever gets set above the maximum amplitude of signal component <NUM> of conducted communication signal <NUM>, receive threshold <NUM> is reset to a lower value. Although step <NUM> includes setting receive threshold <NUM> back to its initial value, in some instances, if LCP <NUM> arrives at step <NUM> through block <NUM>, LCP <NUM> may set receive threshold <NUM> to a lower value that is different than the initial value. For instance, LCP <NUM> may simply reduce the value of receive threshold <NUM> instead of setting it back to its initial value.

If LCP <NUM> determines that the communication session timer has not exceeded the communication session timer threshold, LCP <NUM> may determine whether the communication window timer has exceeded the communication window timer threshold, as shown at <NUM>. If LCP <NUM> determines that the communication window timer exceeded the communication window timer threshold, LCP <NUM> may reset the pulse count and reset and begin the communication window timer, as shown at <NUM>, and then begin again with counting received pulses at <NUM>.

If LCP <NUM> determines that the communication window timer does not exceed the communication window timer threshold, LCP <NUM> may determine whether a valid message was received, as shown at <NUM>. For example, LCP <NUM> may compare the pattern of received pulses to predefined pulse patterns that represent messages. In some instances, LCP <NUM> may run one or more error checking schemes before or after determining whether the pattern of received pulses corresponds to one of the predefined pulse patterns. LCP <NUM> may determine that a valid message has been received after determining that the pattern of received pulses corresponds to one of the predefined pulse patterns, and if so provided, after determining that t there are no errors, or significant errors, in the received pulse pattern. If LCP <NUM> determines that a valid message has been received, LCP <NUM> may begin the method again at block <NUM>, such as by following the 'YES' branch of block <NUM>.

If no valid message has yet been received, LCP <NUM> may determine whether the pulse count is greater than the pulse count threshold, as shown at <NUM>. The pulse count threshold may be set to above a maximum number of pulses that LCP <NUM> could possibly receive in a valid message. For instance, if each message may correspond to a predefined pulse pattern or sequence, there may be a maximum number of pulses that may be sent in a given message. Accordingly, if LCP <NUM> receives a number of pulses that is above the pulse count threshold within a communication window, LCP <NUM> may conclude that the conducted communication signal <NUM> has been corrupted by noise. Therefore, if LCP <NUM> determines that the pulse count has exceeded the pulse count threshold, LCP <NUM> may increase the value of receive threshold <NUM> and reset the pulse count, as shown at <NUM>, and begin method <NUM> again at step <NUM>. LCP <NUM> may increase the value of receive threshold <NUM> by a predetermined amount, based on how long it took for the number of received pulses to exceed the pulse count threshold, based on how much the number of received pulses exceeded the pulse count threshold, and/or based on any other suitable criteria. If the pulse count has not exceed the pulse count threshold, LCP <NUM> may loop back to step <NUM> and continue counting received pulses.

In some instances, LCP <NUM> may wait until the end of a communication window to determine whether a valid message was received and whether the pulse count exceeded the pulse count threshold. For instance, blocks <NUM> and <NUM> may be connected to the 'YES' branch block <NUM>, such that LCP <NUM> only determines whether a valid message was received and whether the pulse count exceeded the pulse count threshold after the communication window timer exceeds the communication window timer threshold. Block <NUM> may then be connected to the 'NO' branch of block <NUM>.

The LCP <NUM> may be configured to adjust receive threshold <NUM> based at least in part on the amplitude of conducted communication signal <NUM>. Setting receive threshold <NUM> at an appropriate level effectively filters out noise component <NUM> in conducted communication signal <NUM>. In operation, method <NUM> may work to increase receive threshold <NUM> above the peak amplitude of noise component <NUM> such that the peaks of noise component <NUM> are below receive threshold <NUM> such that the comparator circuit does not produce corresponding pulses in conducted communication signal <NUM>. However, receive threshold <NUM> may remain below the peak amplitude of signal component <NUM>, such that the comparator circuit does produce pulses in conducted communication signal <NUM> that correspond to the pulses in signal component <NUM>.

<FIG> depicts conducted a communication signal 550a, which represents the output of the comparator circuit when the receive threshold <NUM> had been set higher than the maximum amplitude of noise component <NUM> but lower than the maximum amplitude of signal component <NUM>. As can be seen, conducted communication signal <NUM> only includes pulses due to signal component <NUM> of conducted communication signal <NUM>. When so provided, LCP <NUM> may interpret conducted communication signal 550a as a valid message.

<FIG> depicts a flowchart of another illustrative method <NUM> that LCP <NUM> (or another device) may use to adjust the receive threshold <NUM>. In this case, the receive threshold <NUM> may be adjusted based, at least in part, on the amplitude of conducted communication signal <NUM>. In the illustrative method <NUM>, LCP <NUM> may receive regular messages from another device, such as external support device <NUM>. In one example, at least one message may be received during each communication window.

LCP <NUM> may begin, as shown in method <NUM>, by setting receive threshold <NUM> to an initial value, resetting and beginning a communication window timer, and resetting and beginning a communication session timer, as shown at <NUM>, <NUM>, and <NUM>, respectively. Next, LCP <NUM> may determine whether the communication session timer has exceeded the communication session timer threshold, as shown at <NUM>.

If LCP <NUM> determines that the communication window session timer has not exceeded the communication window session threshold, LCP <NUM> may determine whether the communication window timer has exceeded the communication window timer threshold, as shown at <NUM>. If LCP <NUM> determines that the communication window timer has not exceeded the communication window timer threshold, LCP <NUM> may determine whether a valid message has been received, as a shown t <NUM>. If no valid messaged has been received, LCP <NUM> may loop back to block <NUM>. In this manner, LCP <NUM> may continue to check whether a valid message has been received during a communication window.

If LCP <NUM> determines that the communication window timer has exceeded the communication window timer threshold, LCP <NUM> may determine whether at least one valid messaged was received during the communication window. If no valid message was received, LCP <NUM> may increase receive threshold <NUM> and reset and begin the communication window timer, as shown at <NUM>, and begin method <NUM> again at <NUM>. LCP <NUM> may increase the value of receive threshold <NUM> by a predetermined amount, based on how long it took for the number of received pulses to exceed the pulse count threshold, or based on other criteria. If LCP <NUM> determines that at least one valid message has been received, LCP <NUM> may begin method <NUM> again at block <NUM>.

In this manner, if receive threshold <NUM> is set too low, e.g. below the maximum amplitude of noise component <NUM>, LCP <NUM> will not readily receive valid messages and will then increase the receive threshold <NUM>. This will continue until receive threshold <NUM> is set above the amplitude of noise component <NUM> and LCP <NUM> may begin to receive valid messages based on only the signal component <NUM>.

In some instances, LCP <NUM> may wait until after the communication window timer has exceeded the communication window timer threshold before determining whether a valid message has been received. For example, method <NUM> may not include block <NUM> at all. Instead, the 'NO' branch of block <NUM> may connect directly to block <NUM>.

In some instances, LCP <NUM> may wait longer than a single communication window period before determining whether a pulse count exceeds a pulse count threshold or whether a valid message was received. For example, LCP <NUM> may wait until two, three, or even four communication windows have elapsed before making any determinations. These are just some example alternatives to the method shown in <FIG>.

<FIG> depicts another method for adjusting the receive threshold <NUM>. <FIG> depicts conducted communication signal <NUM> along with a dynamic receive threshold 505A, where the dynamic receive threshold 505A is reset to a new value on each of the peaks of conducted communication signal <NUM> that exceed the then present dynamic receive threshold 505A.

In the example of <FIG>, dynamic receive threshold 505A may be set to an initial value and may be configured to decay over time to lower values. It should be understood that the decay shape of dynamic receive threshold 505A depicted in <FIG> is an example only. In one non-limiting example, dynamic receive threshold 505A may decay to about half of its initial value after <NUM>, and then decay to about one-quarter of its initial value over the subsequent <NUM>. The specific decay values and time periods may differ. It is contemplated that dynamic receive threshold 505A may decay in a logarithmic or natural logarithmic fashion, in an exponential fashion, in a step wise fashion, or any other desirable way.

As can be seen, dynamic receive threshold 505A is configured to decay after the conducted communication signal <NUM> reaches a peak amplitude that is above the then existing dynamic receive threshold 505A. For example, in <FIG>, the dynamic receive threshold 505A begins to decay at peak <NUM> and at the end of peak <NUM>. LCP <NUM> may reset the dynamic receive threshold 505A to a new higher value when conducted communication signal <NUM> reaches a new peak amplitude that is above the then existing dynamic receive threshold 505A. In some embodiments, LCP <NUM> may continually reset dynamic receive threshold 505A to a new, higher value as conducted communication signal <NUM> keeps providing peaks that exceed the decaying dynamic receive threshold 505A. As can be seen, once conducted communication signal <NUM> begins to drop in amplitude, dynamic receive threshold 505A will begin to decay. In some embodiments, dynamic receive threshold 505A may be configured to wait to decay for a short predefined time period after being set to a new value. In some cases, instead of continually resetting dynamic receive threshold 505A to a new, higher value, LCP <NUM> may wait to determine a peak of conducted communication signal <NUM>. In some cases, resetting a new, higher value for dynamic receive threshold <NUM> A may lag conducted communication signal <NUM> by a short period of time.

In some instances, instead of setting dynamic receive threshold 505A to the value of the most recent peak of conducted communication signal <NUM>, LCP <NUM> may set dynamic receive threshold 505A to a value that is proportional to the most recent peak of conducted communication signal <NUM>. For instance, LCP <NUM> may set dynamic receive threshold 505A to a value that is between <NUM>%-<NUM>% of the maximum value of the most recent peak. This is just one example. Other examples include between <NUM>%-<NUM>%, <NUM>%-<NUM>%, or <NUM>%-<NUM>% of the maximum value of the most recent peak of conducted communication signal <NUM>.

In some cases, the decay characteristics of the dynamic receive threshold 505A may be based, at least partially, on the characteristics of the conducted communication signal <NUM>. For example, dynamic receive threshold 505A may be configured to decay more quickly for higher values of the dynamic receive threshold 505A. In another example, dynamic receive threshold 505A may be configured to decay more quickly the longer it has been since the dynamic receive threshold 505A has been reset, which would correspond to a longer period of low amplitude activity of conducted communication signal <NUM>. These are just examples.

In some alternative embodiments, LCP <NUM> may adjust the receive threshold to a value where LCP <NUM> detects that it successfully receives communication signals but does not receive noise signals. For instance, LCP <NUM> may initiate a search algorithm in order to adjust a receive threshold, such as threshold <NUM> or 505a. In some embodiments, the algorithm may have the receive threshold decay in a step-wise manner, and the time between decay steps may range from between about <NUM> to about <NUM>,<NUM>. The <NUM> value may represent the shortest length communication. The <NUM>,<NUM> value may represent a slow respiratory cycle which could impact a signal to noise ratio. However, in other embodiments, the time between decay steps may have any value between <NUM> and <NUM>,<NUM>. In some embodiments, the decay at each step may occur in binary ratios, such as <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, or <NUM>/<NUM> or the like. For instance, at each decay step, receive threshold 505a may decay by the chosen <NUM>/<NUM> (or other chosen binary ratio) of the current value of receive threshold 505a. In further embodiments, the decay value may change at successive steps. For instance, the first decay amount may be <NUM>/<NUM> of receive threshold 505a, the second decay amount may be <NUM>/<NUM> of receive threshold 505a, the third decay amount may be <NUM>/<NUM> of receive threshold 505a, and the like. Once LCP <NUM> sets the receive threshold to a value where LCP <NUM> determines that it is receiving both a signal component and a noise component in received communication signals, LCP <NUM> may set the receive threshold to the previous value where LCP <NUM> did not detect both signal components and noise components in received communication signals. One particularly useful embodiments may include setting the time between decay steps at <NUM> and the decay value to <NUM>/<NUM>. However, this is just one example.

In some cases, LCP <NUM> may employ an adaptive filter to help filter out noise component <NUM>. As described, the patch-integrity signal of an external defibrillator <NUM> may be a continuous signal having generally static characteristics, such as frequency and/or amplitude. In such cases, LCP <NUM> may sense, outside of a communication period, the patch-integrity signal. LCP <NUM> may then process the patch-integrity signal to determine at least the frequency of the signal and may configure an adaptive filter into a notch filter centered at the frequency of the patch-integrity signal. In cases where patch-integrity signal has a single frequency, or a narrow frequency spectrum, the notch filter may be particularly effective in filtering out, or at least reducing in amplitude, the noise component <NUM>.

Although the techniques were generally described separately, in instances, LCP <NUM> may employ multiple of the disclosed techniques simultaneously. For example, LCP <NUM> may implement the pulse-counting method described above in addition to a dynamic receive threshold. In another example, LCP <NUM> may implement the pulse counting method along with an adaptive filter. In general, in different embodiments, LCP <NUM> may include all combinations of the above described techniques.

It should be understood that although the above methods were described with LCP <NUM> as a receiver and external support device <NUM> as a transmitter, this was just for illustrative purposes. In some cases, external support device <NUM> may act as a receiver and may implement any techniques described with respect to LCP <NUM>. Additionally, it should be understood that the described techniques are not limited to system <NUM>. Indeed, the described techniques may be implemented by any device and/or system that uses conducted communication.

In some cases, one or more of the devices of system <NUM> (or other system) may be configured to actively cancel the patch-integrity signal. For instance, in the example of <FIG>, instead of (or in addition to) devices of system <NUM> adjusting receive thresholds or adaptive filters, one or more of the devices of system <NUM> may inject a cancelling or inverse signal into the patient body in order to cancel out, or at least reduce the amplitude of, the patch-integrity signal delivered by external defibrillator <NUM>. The below description uses external support device <NUM> only as an example of a device that may perform the described techniques. It should be understood, however, that the techniques described herein may be applied by any of the devices of system <NUM>, or by other devices in other systems as desired.

<FIG> depicts an example patch-integrity signal <NUM> signal that may be delivered by an external defibrillator <NUM>. External support device <NUM> may sense signals propagating through a patient's body, including patch-integrity signal <NUM>, during a period of relative electrical quietness within the patient's body. For instance, external support device <NUM> may sense propagating electrical signals in the patient via electrodes <NUM> between heartbeats of the patient and while no conducted communication signals are propagating through the patient's body. Where patch-integrity signal <NUM> is sufficiently different from other signals propagating through the patient's body, external support device <NUM> may employ one or more filters to filter out signals other than patch-integrity signal <NUM>, leaving only patch-integrity signal <NUM>. For instance, external support device <NUM> may employ one or more low-pass, high-pass, bandpass, notch, and/or any other suitable filter. External support device <NUM> may determine various characteristics of patch-integrity signal <NUM>. For instance, external support device <NUM> may determine the frequency components, the amplitude, and/or the phase of patch-integrity signal <NUM>.

In some instances, external support device <NUM> may include a pulse generator module whereby external support device <NUM> may generate varied waveforms. After external support device <NUM> senses patch-integrity signal <NUM>, external support device <NUM> may generate a cancelling or inverse signal <NUM> (see <FIG>) using the determined characteristics. For instance, external support device <NUM> may generate inverse signal <NUM> to have a similar amplitude and frequency as patch-integrity signal <NUM>. However, external support device <NUM> may generate inverse signal <NUM> at a phase that is shifted relative to inverse signal <NUM> by one-hundred eighty degrees. An example of inverse signal <NUM> is depicted in <FIG>. If the patch-integrity signal <NUM> is not a regular signal as shown in <FIG>, the external support device <NUM> may simply generate an inverse signal <NUM> that will cancel out, or at least reduce the amplitude of, the patch-integrity signal <NUM>. Other example inverse signals may include signals that are not true inverses of the patch-integrity signal. For instance, the inverse signal, when added to the patch-integrity signal, may reduce the amplitude of the patch-integrity signal received at a device of the system which includes external support device <NUM>. Alternatively, the inverse signal, when added to the patch-integrity signal, may produce a signal that is received by a device of the system that include external support device <NUM> having an increased frequency than the original patch-integrity signal. This increased frequency of the patch-integrity signal may allow the signal to be more easily filtered out by the receiving device. Accordingly, although the description throughout this disclosure may focus on or discus an inverse signal that is a true inverse signal of the patch-integrity signal, or a close analog to a true inverse signal, it should be understood that this is merely for ease of description. In general, external support device <NUM> may generate an inverse signal that is not a true inverse signal, but interferes or changes the patch-integrity signal sufficiently to allow a receiving device to distinguish between the patch-integrity signal and communication signals or to filter the patch-integrity signal without filtering communication signals.

External support device <NUM> may deliver the generated inverse signal <NUM> into the body of the patient, for example through electrodes <NUM>. Since inverse signal <NUM> has similar but opposite characteristics of patch-integrity signal <NUM>, inverse signal <NUM> may destructively interfere with patch-integrity signal <NUM>, thereby canceling out and/or at least reducing the amplitude of patch-integrity signal <NUM> sensed by other devices connected to the patient, such as LCP <NUM>. In some examples, inverse signal <NUM> may be the exact opposite of patch-integrity signal <NUM> and may fully cancel inverse signal <NUM> such that LCP <NUM> does not sense patch-integrity signal <NUM>. In other examples, inverse signal <NUM> may only be similar to patch-integrity signal <NUM> and may only reduce the amplitude of patch-integrity signal <NUM> sensed by LCP <NUM>. In any case, the delivered inverse signal <NUM> may reduce the amplitude of patch-integrity signal <NUM> sensed by LCP <NUM>, which can enhance the signal-to-noise ratio (SNR) of conducted communication between external support device <NUM> and LCP <NUM> (and/or between LCP <NUM> and another implanted devices). An example of a signal sensed by LCP <NUM> while external support device <NUM> is delivering inverse signal <NUM> is shown in <FIG> as signal <NUM>.

In at least some embodiments, instead of attempting to match the amplitude of patch-integrity signal <NUM>, external support device <NUM> may generate inverse signal <NUM> having a different amplitude than patch-integrity signal <NUM>. The amplitude of patch-integrity signal <NUM> sensed by devices connected to the patient other than external support device <NUM>, such as LCP <NUM>, may differ than the amplitude of patch-integrity signal <NUM> sensed by external support device <NUM>. Accordingly, delivering inverse signal <NUM> into the patient with an amplitude similar to patch-integrity signal <NUM> sensed by external support device <NUM> may cancel out patch-integrity signal <NUM> sensed by LCP <NUM>, but may additionally introduce noise in the form of inverse signal <NUM>, which was not fully cancelled out by patch-integrity signal <NUM>. Accordingly, in some instances, external support device <NUM> may generate inverse signal <NUM> having an amplitude higher, or lower, than the amplitude of patch-integrity signal <NUM> sensed by external support device <NUM>. External support device <NUM> may attempt to match the amplitude of inverse signal <NUM> sensed by LCP <NUM> to the amplitude of patch-integrity signal <NUM> sensed by LCP <NUM>. For example, external support device <NUM> may adjust the amplitude of inverse signal <NUM> based on feedback received from LCP <NUM>, or based on a presence or absence of received messages from LCP <NUM>. In other embodiments, external support device <NUM> may include a physical dial or gain adjuster <NUM> that a user may adjust to increase or decrease the amplitude of generated inverse signal <NUM> (see <FIG>).

Delivering inverse signal <NUM> into the patient's body may enhance the signal-to-noise ratio (SNR) of conducted communication with the body by removing or reducing the patch-integrity signal <NUM> in the body. In some embodiments, external support device <NUM> may deliver inverse signal <NUM> into the patient's body continuously. In other cases, the delivered inverse signal <NUM> may cause external defibrillator <NUM> to generate or emit an alarm as patch-integrity signal <NUM> sensed by external defibrillator <NUM> may be fully cancelled or reduced in amplitude below a certain alarm threshold. Accordingly, in some cases, external support device <NUM> may only selectively deliver inverse signal <NUM> into the patient's body. For example, external support device <NUM> may only deliver inverse signal <NUM> into the patient's body while external support device <NUM> or LCP <NUM> are delivering conducted communication signals into the patient's body. In some cases, LCP <NUM> may have an easier time discriminating between the delivered conducted communication signals from patch-integrity signal <NUM>. In some cases, the conducted communication scheme of external support device <NUM> and LCP <NUM> may include only delivering conducted communication signals during predefined time periods. For instance, external support device <NUM> and LCP <NUM> may be configured to only deliver conducted communication signals during communication windows lasting about <NUM>, with each communication window separated by <NUM>. These numbers are just examples. The communication window lengths and spacing may be any suitable values.

In some cases, the communication windows may be synchronized to one or more features of the cardiac electrical signals. For instance, external support device <NUM> and LCP <NUM> may be configured to communication during communication windows that occur about <NUM>-<NUM> after each detected R-wave. External support device <NUM> may be configured to only deliver inverse signal <NUM> into the patient's body during these communication windows. Both external support device <NUM> and LCP <NUM> may benefit from enhanced discrimination between sensed conducted communication signals and patch-integrity signal <NUM>.

The patch-integrity signal <NUM> depicted in <FIG> is only one example. Different external defibrillators currently on the market may use differently shaped patch-integrity signals. Accordingly, in some embodiments, instead of having a general waveform generator capable of generating any, or a large number of different types of waveforms, external support device <NUM> may include hardware or circuitry that may generate inverse signals of various different known patch-integrity signals used in available external defibrillators.

<FIG> depicts an example interface of an external support device <NUM>. External support device <NUM> may include a dial, switch, or other mechanical selector, such as dial <NUM>, or a menu option in graphical user interface <NUM>, that allows a user to select a particular inverse waveform from a set of preprogrammed inverse waveforms that correspond to the different available external defibrillators. The preprogrammed inverse waveforms may be stored in a memory of external support device <NUM>. Each selectable waveform may have an identifier correlating the waveform to a particular brand or product to easily identify the appropriate inverse waveform. These features may allow external support device <NUM> to be less complex and less costly to manufacture than when the external support device <NUM> is required to sense the patch-integrity signal and then generate an inverse signal using a general waveform generator.

<FIG> depicts system <NUM> which may help enhance discrimination between conducted communication signals and noise signals such as patch-integrity signals. System <NUM> may include external support device <NUM>, external defibrillator <NUM>, and switching unit <NUM>. External defibrillator <NUM> may be connected to switching unit <NUM> through wires <NUM>, and external support device <NUM> may be connected to switching unit <NUM> by wires <NUM>. Switching unit <NUM> may be connected to electrodes <NUM> attached to patient skin <NUM> through wires <NUM>.

In system <NUM>, a switching unit <NUM> may be configured to switch between wires <NUM> from external support device <NUM> and wires <NUM> from external defibrillator <NUM> to connect/disconnect each device to electrodes <NUM>. Switching unit <NUM> may initially connect wires <NUM> to electrodes <NUM>, allowing external defibrillator <NUM> to deliver a patch-integrity signal through electrode <NUM> and into the patient through skin <NUM>. In some cases, when external support device <NUM> is to deliver conducted communication signals into the patient, switching unit <NUM> may disconnect wires <NUM> of external defibrillator <NUM> from the electrodes <NUM> and connect wires <NUM> from external support device <NUM> to the electrodes <NUM>. In this configuration, external support device <NUM> may deliver conducted communication signals into the patient through electrodes <NUM>. With the external defibrillator <NUM> disconnected from the electrodes <NUM>, the patch-integrity signal is effectively blocked from entering the patient, and devices may communicate through conducted communication signals without interference from the patch-integrity signal. Once the conducted communication signals have been sent and received, switching unit <NUM> may disconnect wires <NUM> of the external support device <NUM> from the electrodes <NUM> and connect wires <NUM> of the external defibrillator <NUM> to the electrodes <NUM>. The patch-integrity signal of the external defibrillator <NUM> may then be delivered to the patient, verifying to the external defibrillator <NUM> that the patch electrodes <NUM> are sufficiently in electrical communication with the skin. If the communication period is kept short enough, a patch verification alarm of the external defibrillator <NUM> may not be triggered.

In some instances, external support device <NUM> may control switching unit <NUM> to connect/disconnect wires <NUM>, <NUM> from wires <NUM>. In other instances, external defibrillator <NUM> may control switching unit <NUM>, a different device may control switching unit <NUM>, or both of external defibrillator <NUM> and external support device <NUM> may control switching unit <NUM>. For ease of description, the techniques are described below from the perspective of external support device <NUM> controlling switching unit <NUM>.

In operation, external defibrillator <NUM> may normally be connected to electrode <NUM> to deliver a patch-integrity signal and/or sense cardiac electrical signals. Before external support device <NUM> delivers conducted communication signals into the patient, external support device <NUM> may command switching unit <NUM> to disconnect wires <NUM> of the external defibrillator <NUM> from the electrodes <NUM> and connect wires <NUM> of the external support device <NUM> to the electrodes <NUM>, thereby blocking the patch-integrity signal from external defibrillator <NUM> from being delivered to the patient. Once external support device <NUM> is finished delivering the conducted communication signals, external support device <NUM> may command switching unit <NUM> to reconnect wires <NUM> of the external defibrillator <NUM> to the electrodes <NUM>.

In some instances, instead of only commanding switching unit <NUM> to connect wires <NUM> of the of the external support device <NUM> to the electrodes <NUM> before external support device <NUM> delivers conducted communication signals into the patient, external support device <NUM> may cause switching unit <NUM> to switch at regular intervals. For instance, in some cases where external support device <NUM> and another device, such as an LCP device, are connected to the patient and are configured to communicate using conducted communication only during predefined communication windows, external support device <NUM> may command switching unit <NUM> to connect wires <NUM> of the external support device <NUM> to the electrodes <NUM> during each of the communication windows.

When wires <NUM> of the external defibrillator <NUM> are disconnected from the electrodes <NUM>, wires <NUM> may form an open circuit which may cause external defibrillator <NUM> to generate or emit an alarm, as external defibrillator <NUM> may no longer sense the patch-integrity signal. In some embodiments, in order help prevent external defibrillator <NUM> from generating an alarm, when switching unit <NUM> disconnects wires <NUM> of the external defibrillator <NUM> from the electrodes <NUM>, switching unit <NUM> may connect wires <NUM> directly together, or may connect wires <NUM> together through a resistive or other network contained within switching unit <NUM>. In these embodiments, switching unit <NUM> may maintain a closed loop for the patch-integrity signal, which may help prevent external defibrillator <NUM> from generating or emitting an alarm.

Although system <NUM> is depicted as including external defibrillator <NUM>, switching unit <NUM>, and external support device <NUM>, it is contemplated that system <NUM> may include fewer or more devices. For instance, the support functions of external support device <NUM> and the switching functions of switching unit <NUM> may be built into external defibrillator <NUM>. When so provided, external defibrillator <NUM> may have an internal switching mechanism and can control the switching mechanism to help support conducted communication via other devices within the patient.

Claim 1:
A method of communicating with a medical device implanted within a patient comprising:
receiving, at the medical device via electrodes connected to the patient, a conducted communication signal, wherein the conducted communication signal comprises a signal component and a noise component; and
adjusting, by the medical device, a receive threshold based at least in part on an amplitude of the received conducted communication signal,
wherein the receive threshold is adjusted for at least partially reducing an amplitude of the noise component of the conducted communication signal,
wherein adjusting the receive threshold based at least in part on the amplitude of the received conducted communication signal comprises:
counting, by the medical device, a number of pulses in the conducted communication signal having an amplitude greater than the receive threshold during a communication window;
determining, by the medical device, whether the counted number of pulses exceeds a pulse count threshold; and
after determining the counted number of pulses exceeds the pulse count threshold, increasing, by the medical device, the receive threshold;
wherein the pulse count threshold is set to above a maximum number of pulses in a valid message.