Determining cardiac condition status using subcutaneous impedance measurements

Abstract

Techniques are described for acquiring impedance data to provide early warning of decompensated heart failure. An example device can be configured to measure subcutaneous impedance values and increase an impedance score. In some examples, the device can use an adaptive threshold and a fluid index in increasing the impedance score. In some examples, the impedance score is compared to a threshold to determine a heart failure status of a patient.

Description

Technical Field

[0001] This disclosure relates to medical devices, and more specifically, to medical devices for detecting or monitoring cardiac conditions. Background Technology

[0002] Various medical devices have been used or proposed for delivering treatment to patients and / or monitoring their physiological condition. As examples, such medical devices can deliver treatment and / or monitor conditions related to the heart, muscles, nerves, brain, stomach, or other organs or tissues. Medical devices for delivering treatment include those that deliver one or both of electrical stimulation or therapeutic agents to the patient. Some medical devices have been used or proposed for monitoring heart failure or detecting heart failure events.

[0003] Heart failure (HF) is the most common cardiovascular disease, causing a significant economic burden, morbidity, and mortality. In the United States alone, approximately 5 million people suffer from HF, resulting in a large number of hospitalizations. Heart failure can cause dilation of the heart chambers, increased blood volume in the lungs, and fluid retention in the lungs. Often, the first sign of heart failure that a doctor notices in a patient is when it becomes a physical manifestation of swelling or difficulty breathing, at which point the patient doesn't take it seriously and is examined by a doctor. This is undesirable because heart failure patients may need to be hospitalized at such a time to remove excess fluid and relieve symptoms. Summary of the Invention

[0004] This disclosure describes techniques for providing early warning of various cardiac conditions (e.g., decompensated heart failure, worsening heart failure, etc.) based on impedance measurements of subcutaneous tissue in a patient's body. Subcutaneous impedance is an example of impedance that can be monitored to detect worsening heart failure, such as changes in impedance values, where changes in interstitial fluid within the patient's subcutaneous layer are measured. These techniques can be implemented using subcutaneously implanted implantable medical devices (IMDs), such as leaded or lead-free (also referred to as "lead-free") subcutaneous implants coupled to multiple electrodes (e.g., lead-loaded electrodes and / or electrodes on the device housing) for measuring subcutaneous impedance.

[0005] A device (e.g., a subcutaneous IMD or a remote computing device, such as a network device) compares the measured impedance to a reference impedance to accumulate evidence of changes in impedance levels in the patient's subcutaneous interstitial tissue. This evidence is known as the fluid index and can reflect the level of pulmonary or peripheral edema, increased ventricular filling pressure, or other morbidities that may be associated with worsening heart failure experienced by the patient. For example, a patient with peripheral edema associated with a fluid overload condition may also have pulmonary edema associated with the same fluid overload condition. Therefore, according to the techniques disclosed herein, subcutaneous impedance measurements and fluid index values ​​can detect such fluid overload.

[0006] Fluidity index is one example of an index indicating worsening heart failure. Other examples include indices or measures of increased ventricular filling pressure or other morbidities associated with worsening heart failure experienced by the patient. In general, any parameter indicating worsening heart failure can be monitored according to the techniques described herein, and an index indicating worsening heart failure can be any index determined to indicate a trend reflecting a parameter of worsening heart failure, wherein such an index can be based on a measurement of a parameter in the patient's subcutaneous layer.

[0007] The reference impedance can be determined based on previously measured impedance. In some cases, the device can represent the reference impedance as a statistical model designed to track the relative change of impedance values ​​over time. In another instance, the device can interpolate or extrapolate impedance data, predict future data points, generate regression models of accumulated data, deploy machine learning models, etc., to determine the reference impedance value. For example, the reference impedance value can include the mean, median, mode, and range of collected impedance information. In other instances, the reference impedance value can include other useful data analyses that provide a representation of ideal or baseline impedance data points, for example, when regulating cellular activity, the body should attempt to track these data points. The reference impedance can be based on a slope value that changes over time (e.g., upward and downward drift parameters). As discussed below, the upward and downward drift parameters can be varied in a piecewise linear manner to accommodate the rapid rise in impedance that may result in the initial months after a given IMD implantation. Example reference impedance line in Figure 9 The middle line is shown as a dashed line.

[0008] In some instances, the device increases the fluid index based on the difference between the measured impedance and a reference impedance. In one instance, the device can determine the fluid index value by calculating the difference between the daily average impedance value and the daily reference impedance value. Alternatively, the device can determine the fluid index value by summing or accumulating such differences stored in a buffer over time. In some instances, the difference can be modified by subtracting a variability value (e.g., a time-dependent variability value) from the difference before storing the modified difference in the buffer.

[0009] As long as the measured impedance is less than its respective reference impedance, the device can modify or adjust the fluid index value based on such a comparison. The resulting fluid index can be used to determine an impedance score. In some instances, the IMD or another computing device can compare the fluid index with an adaptive threshold to determine a modification to the impedance score. The adaptive threshold can be determined using the average (e.g., average or median) of impedance values ​​determined within a specific time window (e.g., within the most recent 30 days). The adaptive threshold may also include the average (e.g., average or median) of the differences between one or more maximum impedance values ​​and one or more minimum impedance values ​​determined within a specific time window (e.g., within the most recent 30 days), or another measure of the variability of the impedance measurement results. In such instances, the maximum and minimum values ​​can be daily maximums and daily minimums for each day. In other instances, the maximum value can be the maximum value calculated for the previous few days, where an average of up to 30 days is calculated each day to determine the 30-day average. In yet another instance, the average can be the average of the daily variability of impedance values ​​measured over a specific time window. In any case, the adaptive threshold can be proportional to the absolute impedance value and the intraday variation of the impedance.

[0010] In some instances, the IMD or another computing device may compare the impedance score with one or more risk thresholds to determine whether to generate an alarm (e.g., notification, status indicator, warning, etc.). In non-limiting instances, the alarm may contain text or graphical information conveying cardiac condition (e.g., heart failure) or patient status. In some instances, the IMD may transmit the alarm to another computing device. In some instances where a computing device other than the IMD determines the impedance score, the computing device may simply generate an alarm or may further transmit the alarm to another device. In some instances, the computing device may transmit an alarm to the IMD in response to an impedance score that meets one or more risk thresholds, the alarm instructing the IMD to take some action in response to the current cardiac condition status. In any case, the alarm may indicate the status level of the cardiac condition. For example, the risk threshold may trigger one alarm for high risk, a different alarm for medium risk, and another alarm for low risk. The alarm may be communicated directly to the patient or clinician through a variety of methods, including notifications, audio, handheld devices, and automatic or on-demand telemetry to computer communication networks. In some instances, the alarm may contain warnings, such as audible or visual warnings.

[0011] Various techniques are used to enable fluid indices and impedance scores to accurately represent changes in patient condition over time and to better correspond alerts to clinically significant deterioration of patient condition. In some instances, these techniques involve varying parameters that affect the slope of the index over time to address time-related or other factors that may affect the accuracy of the fluid index.

[0012] In some instances, the increase is reduced based on the variability of the measured impedance. In cases of high variability, less accumulation of the fluid index can improve its accuracy by reducing the accumulation during periods of impedance instability that are not directly related to worsening heart failure. Increased accumulation over time can allow for a sustained decrease in impedance, leading to an alarm more quickly.

[0013] In some instances, the way the reference impedance is determined varies over time. Specifically, the amount by which the reference impedance can increase or decrease may be different for different days after implantation, and then may change over time. In this way, the reference impedance may be able to respond to rapid changes (e.g., an increase in impedance typically observed after implantation) or to changes following surgical modifications to the implantation system (such as lead changes / corrections or device alterations).

[0014] In some instances, the device adaptively calculates the fluid index over time by accumulating it based on a finite number of previous comparisons between the measured impedance and a reference impedance (e.g., over a finite time period, such as the most recent X days). For example, the device could sum a finite number of differences between the measured impedance and the reference impedance, which could be stored in a finite-sized first-in-first-out (FIFO) buffer. The finite number of comparisons can serve as a sliding window with respect to previous comparisons. By using a finite memory limit to determine the number of comparisons used to determine the fluid index, the fluid index may be more sensitive to recent events involving changes in subcutaneous tissue impedance, as opposed to events occurring outside the sliding time window. Such algorithms can provide a more accurate representation of a patient's health status on a given date. As will be further described, such algorithms can be further improved by accumulating the fluid index less frequently in patients with high diurnal variability in impedance values ​​due to clinically insignificant impedance changes and transient impedance shifts, such as due to poor adherence to medication regimens or dietary restrictions. Alerts responding to such relatively less important events are also limited. Additionally, limiting the accumulation of fluid index in this way can restrict alerts to responses to recent events, for example, to avoid issuing alerts due to past compliance issues that may have already been resolved.

[0015] As discussed herein, determining an impedance score using subcutaneous impedance involves determining the absolute value of the impedance and the relative change in impedance. The device can determine the impedance score using a fluid index value and an average impedance determined over time. The impedance score can serve as a valuable indicator of a patient's cardiac condition or other health conditions (e.g., edema, preeclampsia, hypertension, etc.). The impedance score can be increased or decreased in some cases by a first number (e.g., one point), and in other cases by a second number (e.g., two points).

[0016] In some instances, the impedance score is compared to two thresholds to provide lag in alarm decision-making. An alarm is generated when the impedance score exceeds a first, higher threshold. The alarm is terminated when the impedance score subsequently exceeds a second, lower threshold. By generating alarms in this manner, the device can generate fewer “casual” alarms that might be misinterpreted by patients or clinicians when the impedance score fluctuates around higher alarm thresholds. Additionally, the device can provide multiple alarms of varying degrees related to risk levels. For example, the alarms could have lag thresholds with high-risk, intermediate-risk, and / or low-risk thresholds.

[0017] In one example, this disclosure provides a system for detecting the state of a heart condition. The system includes an implantable medical device (IMD) comprising a plurality of electrodes and configured for subcutaneous implantation. The implantable medical device is configured to receive one or more subcutaneous tissue impedance signals from the electrodes. The system further includes a processing circuitry configured to determine, at least partially, at least one first tissue impedance value corresponding to a first time period based on the one or more subcutaneous tissue impedance signals. The processing circuitry is further configured to: determine, at least partially, at least one second tissue impedance value corresponding to a second time period different from the first time period based on the one or more subcutaneous tissue impedance signals; determine, at least partially, one or more reference impedance values ​​based on the at least one first tissue impedance value; determine, at least partially, an average impedance value or at least one or more fluid index values ​​based on the one or more reference impedance values ​​and the at least one second tissue impedance value; determine an impedance score based on at least one of the one or more fluid index values ​​or the average impedance value; and determine the patient's heart condition state based at least partially on the impedance score.

[0018] In another instance, this disclosure provides a method for detecting the state of a heart condition, the method comprising: determining at least one reference impedance value at least in part based on one or more subcutaneous tissue impedance signals received from at least one electrode disposed in the subcutaneous layer of a patient during a first time period; determining at least one additional impedance value at least in part based on the one or more impedance signals received from the at least one electrode during a second time period other than the first time period; determining at least one of the following at least in part based on the at least one reference impedance value and the at least one additional impedance value: one or more fluid index values ​​of the patient or a statistical representation of the one or more subcutaneous tissue impedance signals received from the at least one electrode; determining an impedance score at least in part based on the fluid index value or the statistical representation of the one or more subcutaneous tissue impedance signals received from the at least one electrode; and determining the state of the patient's heart condition at least in part based on the impedance score.

[0019] In another instance, this disclosure provides a computer-readable storage medium having instructions stored thereon that, when executed, cause one or more processors to perform at least the following operations: determining at least one reference impedance value at least in part based on one or more subcutaneous tissue impedance signals received from at least one electrode disposed in the subcutaneous layer of a patient during a first time period; determining at least one other impedance value at least in part based on the one or more subcutaneous tissue impedance signals received from the at least one electrode during a second time period other than the first time period; determining an impedance score of the patient at least in part based on the at least one reference impedance value and the at least one other impedance value; and outputting the patient's cardiac condition status at least in part based on the impedance score.

[0020] This disclosure also provides means for performing any of the techniques described herein, and a non-transitory computer-readable medium containing instructions for causing a programmable processor to perform any of the techniques described herein.

[0021] This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the systems, apparatus, and methods described in detail in the following drawings and specification. Further details of one or more embodiments of this disclosure are set forth in the following drawings and specification. Other features, objectives, and advantages will become apparent from the description, drawings, and claims. Attached Figure Description

[0022] Figure 1 The patient demonstrated the environment of the example healthcare system.

[0023] Figure 2 It shows in more detail Figure 1A conceptual side view of an implantable medical device (IMD) for a medical system.

[0024] Figure 3 It is a demonstration Figure 1 and 2 A functional block diagram of an example configuration for an IMD.

[0025] Figure 4 It is a demonstration Figure 1 A functional block diagram of an example configuration of an external device.

[0026] Figure 5 This is a block diagram illustrating an example system that includes an access point, a network, an external computing device (such as a server), and one or more other computing devices that can be coupled to... Figure 1-4 IMD and external devices.

[0027] Figure 6 This is a flowchart illustrating example operations for determining a patient's cardiac condition status based on one or more techniques disclosed herein.

[0028] Figure 7 This is a flowchart illustrating an example operation for determining an impedance score based on subcutaneous tissue impedance values, according to one or more techniques disclosed herein.

[0029] Figure 8 This is a flowchart illustrating an example operation for determining a fluid index based on subcutaneous tissue impedance values, according to one or more techniques disclosed herein.

[0030] Figure 9 This is an example timing diagram illustrating the use of a finite buffer to limit the accumulation of the fluid exponent over time according to one or more techniques disclosed herein.

[0031] Figure 10 This is a flowchart illustrating an example method based on one or more techniques disclosed herein, the example method being... Figure 1 One or both of the IMD and external devices shown are used to provide the patient with an alert regarding the patient's cardiac condition.

[0032] Throughout the specification and drawings, the same reference numerals denote the same elements. Detailed Implementation

[0033] Generally, through electrodes in the subcutaneous space (e.g., such as...) Figure 1 and 2Impedance measurements performed by electrodes on a subcutaneously implanted medical device (as shown) can be measurements of the impedance of interstitial fluid and subcutaneous tissue. In one instance, during a decompensated event of heart failure, a decrease in cardiac output tends to increase venous pressure. This increase in venous pressure, compared to the interstitial space, tends to result in an increase in pressure relative to the capillaries. The combination of these trends can then lead to net fluid outflow from the capillaries into the patient's interstitium or interstitial space. In this case, fluid accumulation increases in the interstitium. This increase in fluid accumulation tends to decrease the impedance measured between the electrodes.

[0034] Implantable medical devices (IMDs) can sense and monitor impedance signals and use these signals to determine a patient's cardiac condition or other health conditions (e.g., edema, preeclampsia, hypertension, etc.). Electrodes used by the IMD to sense impedance signals are typically integrated into the IMD's housing and / or coupled to the IMD via one or more thin leads. An example IMD containing electrodes includes the Reveal LINQ, developed by Medtronic, Inc., Minneapolis, Minnesota. TM Insertable cardiac monitors (ICMs) can be inserted subcutaneously. These IMDs facilitate relatively long-term monitoring of patients during normal daily activities and can periodically transmit collected data to network services, such as those developed by Medtronic, a company based in Minneapolis, Minnesota. network.

[0035] Medical devices configured to measure impedance via implanted electrodes, including the examples identified herein, can implement the techniques of this disclosure for measuring impedance changes in a patient's interstitial fluid to determine whether the patient is experiencing worsening heart failure or decompensation. The techniques involve evaluating impedance values ​​using criteria configured to provide the desired sensitivity and specificity for heart failure detection. The techniques of this disclosure for identifying worsening heart failure can facilitate the determination of cardiac health and risk of sudden cardiac death, and can lead to clinical interventions that inhibit the worsening of heart failure, such as the use of medication.

[0036] Figure 1 An example medical system 2 according to one or more technologies of this disclosure is illustrated with a patient 4. Patient 4 is typically a person, but not necessarily a person. For example, patient 4 may be an animal requiring continuous monitoring of its cardiac condition. System 2 includes an implantable medical device (IMD) 10. IMD 10 may contain one or more electrodes (not shown) on its housing, or may be coupled to one or more leads carrying one or more electrodes. System 2 may also include an external device 12. Example system 2 can be used to measure subcutaneous impedance to provide early warning of the onset of heart failure decompensation events to other users of patient 4.

[0037] The example technology can be used with IMD 10, which can be used with external device 12 and Figure 1 At least one of the other devices not depicted herein performs wireless communication. In some instances, the IMD 10 can be implanted outside the chest cavity of patient 4 (e.g., subcutaneously). Figure 1 (As shown in the pectoral muscle location). IMD 10 can be positioned near the sternum at or just below the patient's heart level, for example, at least partially within the heart contour. IMD 10 contains multiple electrodes ( Figure 1 (Not shown in the image). Therefore, the IMD 10 may contain multiple electrodes and may be configured for subcutaneous implantation, such as in the thoracic region of patient 4 (e.g., outside the thoracic cavity of patient 4) or in other regions of patient 4's body.

[0038] IMD 10 is configured to measure the impedance value within the interstitial fluid of patient 4. For example, IMD 10 may be configured to receive one or more signals indicating a subcutaneous tissue impedance electrode. In some instances, IMD 10 may be a purely diagnostic device. For example, IMD 10 may be a device that simply measures the subcutaneous impedance value of patient 4. IMD 10 may also use the impedance measurement results to determine one or more fluid index values, impedance scores, and / or various thresholds, such as adaptive thresholds, scoring thresholds, threshold weighting factors, and / or cardiac risk thresholds.

[0039] Subcutaneous impedance can be assessed through electrical pathways between electrodes ( Figure 1 (Not shown) The signal is delivered for measurement. In some instances, the housing of IMD 10 can be used as an electrode in combination with electrodes positioned on the leads. For example, system 2 can measure subcutaneous impedance by establishing an electrical path between the leads and one of the electrodes. In additional instances, system 2 may include additional leads or lead segments having one or more electrodes positioned subcutaneously or within the subcutaneous layer for measuring subcutaneous impedance. In some instances, two or more electrodes for measuring subcutaneous impedance may be formed on or integrally with the housing of IMD 10.

[0040] System 2 measures patient 4's subcutaneous impedance and processes the impedance data to accumulate evidence of impedance reduction. This accumulated evidence is called the fluid index and can be determined as a function of the difference between the measured impedance value and a reference impedance value. The fluid index can then be used to determine an impedance score indicative of patient 4's cardiac condition. For example, the impedance score can be measured against cardiac risk thresholds that identify high, intermediate, or low risk of a deteriorating cardiac condition.

[0041] In some instances, the IMD 10 can also sense electrocardiogram (EGM) signals via multiple electrodes and / or operate as a treatment delivery device. For example, the IMD 10 can also operate as a treatment delivery device (such as an implantable pacemaker, cardioverter, and / or defibrillator) that delivers electrical signals to the heart of patient 4, a drug delivery device that delivers therapeutic substances to patient 4 via one or more catheters, or a treatment device that delivers a combination of electrical signals and therapeutic substances.

[0042] In some instances, system 2 includes any suitable number of leads coupled to IMD 10, and each of these leads may extend to any location within or near the heart or chest of patient 4. For example, other example treatment systems may include three transvenous leads and an additional lead located within or near the left atrium of the heart. As other examples, the treatment system may include a single lead extending from IMD 10 into the right atrium or right ventricle, or two leads extending into one of the corresponding right ventricle and right atrium.

[0043] In some instances, the IMD 10 can be subcutaneously implanted in patient 4. Additionally, in some instances, the external device 12 can monitor subcutaneous impedance values ​​according to the techniques described herein. In some instances, the IMD 10 employs Reveal LINQ. TM ICM or similar systems such as LINQ TM An ICM version or a modified form of ICM that can be inserted subcutaneously. Such IMDs can facilitate relatively long-term monitoring of patients during normal daily activities and can periodically transmit collected data to network services such as Medtronic. network.

[0044] External device 12 may be a computing device having a user-viewable display and an interface (e.g., a user input mechanism) for providing input to external device 12. The user may be a physician technician, surgeon, electrophysiologist, clinician, or patient. In some instances, external device 12 may be a laptop computer, tablet computer, computer workstation, one or more servers, cellular phone, personal digital assistant, handheld computing device, networked computing device, or another computing device that can run an application enabling the computing device to interact with IMD 10. External device 12 is configured to communicate with IMD 10 via wired or wireless communication and optionally with another computing device. Figure 1 (Not shown in the image). For example, the external device 12 can communicate via near field communication (NFC) technology (e.g., inductive coupling, NFC, or other communication technologies that can operate within a range of less than 10–20 cm) and far field communication technology (e.g., radio frequency (RF) telemetry according to 802.11 or...). The external device 12 may communicate with a standard set of technologies, or other communication technologies that can operate beyond the range of NFC technology. In some instances, the external device 12 may include a programming head that can be positioned close to the patient 4 near the implantation site of the IMD 10 in order to improve the quality or security of communication between the IMD 10 and the external device 12.

[0045] External device 12 can be coupled to an external electrode or, via a percutaneous lead, to an implanted electrode. In some instances, external device 12 can monitor subcutaneous tissue impedance measurements from IMD 10 according to the techniques described herein.

[0046] The user interface of external device 12 can receive input from the user. The user interface may include, for example, a keypad and a display, which may be, for example, a cathode ray tube (CRT) display, a liquid crystal display (LCD), or a light-emitting diode (LED) display. The keypad may take the form of an alphanumeric keypad or a simplified set of keys associated with specific functions. External device 12 may additionally or alternatively include a peripheral pointing device, such as a mouse, through which the user interacts with the user interface. In some instances, the display of external device 12 may include a touchscreen display, through which the user interacts with external device 12. It should be noted that the user can also interact remotely with external device 12 via a networked computing device.

[0047] External device 12 can be used to configure operating parameters of IMD 10. For example, external device 12 can provide a parameter resolution for IMD 10, which indicates the resolution of the data that IMD 10 should acquire. Examples of resolution parameters may include the frequency at which the electrodes process impedance measurement results or the frequency at which impedance measurement results should be considered when determining a patient's cardiac condition. In some instances, resolution parameters include filters specifying what type of data or data quality should flow into determining a patient's cardiac condition. For example, data type may specify that impedance measurements collected during a certain time period (e.g., daytime, nighttime, high activity, low activity, etc.) should be excluded from condition determination, such as by using non-excluded data to determine a statistical representation of historical data. Data quality may refer to any characteristic used to characterize the acquired signal measurements, such as signal-to-noise ratio (SNR), repeated data entries, weak signal readings, etc.

[0048] In some instances, the user can use the external device 12 to program impedance measurement parameters, such as selecting the electrode and waveform used to measure subcutaneous impedance, or programming scoring parameters, threshold parameters, and / or resolution parameters. The external device 12 can also be used to program the treatment process, select electrodes to deliver defibrillation pulses, select waveforms for defibrillation pulses, or select or configure fibrillation detection algorithms for the IMD 10. The user can also use the external device 12 to program other aspects of the treatment provided by the IMD 10, such as cardioversion or pacing therapy. In some instances, the user can activate certain features of the IMD 10 by entering a single command via the external device 12, such as pressing a single key or combination of keys on the keypad or performing a single-point selection action using a pointing device.

[0049] External device 12 can be used to retrieve data from IMD 10. The retrieved data may include impedance values ​​measured by IMD 10, impedance scores determined by IMD 10, values ​​of physiological parameters measured by IMD 10, indications of arrhythmias or other illnesses detected by IMD 10, and physiological signals recorded by IMD 10. For example, external device 12 can retrieve information related to sudden impedance shifts detected by IMD 10, such as counts or other quantifications of impedance fluctuations, for example, within a time period since the last time information was retrieved by external device 12. External device 12 can also retrieve cardiac EGM segments recorded by IMD 10, for example, because IMD 10 determines that an arrhythmia or other illness occurred during said segment, or in response to a request to record segments from patient 4 or other users. In other instances, a user may also use external device 12 to retrieve information from IMD 10 about other sensed physiological parameters of patient 4, such as activity or posture. (See below for more details.) Figure 5 In more detail, one or more remote computing devices may interact with IMD 10 via a network in a manner similar to external device 12, for example, to program IMD 10 and / or retrieve data from IMD 10.

[0050] The processing circuitry of medical system 2, such as the processing circuitry of IMD 10, external device 12, and / or one or more other computing devices, can be configured to perform the techniques disclosed herein for, for example, measuring subcutaneous impedance values ​​in interstitial fluid to determine cardiac condition status. In some instances, the processing circuitry of medical system 2 analyzes the impedance values ​​sensed by IMD 10 to determine whether changes in interstitial fluid impedance meet multiple criteria. As described herein, criteria may include noise criteria, depolarization interval (e.g., RR interval) criteria, morphological criteria, fluid index criteria, and / or impedance scoring criteria.

[0051] Although described in the context of instances where IMD 10 includes an insertable or implantable IMD, example systems comprising one or more external devices of any type configured to sense subcutaneous tissue impedance can be configured to implement the techniques of this disclosure. In some instances, IMD 10 or external device 12 may use one or more of subcutaneous tissue impedance measurements and intravascular impedance. In some instances, the processing circuitry of external device or IMD 10 may receive intravascular impedance measurements. In one instance, IMD 10 may be configured to measure intravascular impedance and transmit the intravascular impedance to external device 12 or to locally store the intravascular impedance measurement results in IMD 10.

[0052] In some instances, the IMD 10 or external device 12 may determine an impedance score using one or more of intravascular impedance measurements and subcutaneous tissue impedance measurements (e.g., tissue impedance values). For example, intravascular impedance measurements may be used to determine a fluid index value. In some instances, the IMD 10 or external device 12 may determine a fluid index value based on one or more of intravascular impedance measurements and subcutaneous impedance measurements. For example, the IMD 10 or external device 12 may average a fluid index value based on intravascular impedance and a fluid index value based on subcutaneous impedance. In other instances, intravascular impedance may be used to determine an impedance score similar to how subcutaneous impedance is used according to the techniques of this disclosure. Impedance scores may be combined, such as by averaging impedance scores, to determine the impedance score for patient 4. In some instances, the IMD 10 may transmit the impedance score for patient 4, and / or the raw data used to determine the impedance score, to the external device 12 for subsequent use, or vice versa.

[0053] In some instances, the IMD 10 may have one or more electrodes disposed within one layer of the patient 4 (e.g., the subcutaneous layer), while at least one other electrode may be disposed within another layer of the patient 4 (e.g., the dermis, muscle layer, etc.). In this case, the IMD 10 can track the shift in impedance values ​​according to certain impedance scoring techniques, regardless of whether the impedance values ​​are measured using electrode 16, where one of the electrodes 16 is disposed within a tissue layer rather than the subcutaneous layer.

[0054] When the fluid index indicates the onset of a decompensated heart failure event, system 2 provides an alert to patient 4 and / or other users. The process for determining when to issue an alert to patient 4 involves comparing the fluid index to one or more thresholds, as described in more detail below. The alert may be an audible alert generated by IMD 10 and / or external device 12, a visual alert generated by external device 12 such as a text prompt or a flashing button or screen, or a tactile alert generated by IMD 10 and / or external device 12 such as vibration or a vibration pattern. Additionally, alerts may be provided to other devices, for example, via a network. Several different levels of alerts may be used based on the risk level detected by the techniques described herein.

[0055] In instances where the IMD 10 also functions as a pacemaker, cardioverter, and / or defibrillator, or otherwise monitors cardiac electrical activity, the IMD 10 can sense electrical signals associated with cardiac depolarization and repolarization in the patient 4 via electrodes coupled to at least one lead. In some instances, the IMD 10 can deliver pacing pulses to the heart of the patient 4 based on the electrical signals sensed within the heart of the patient 4. The electrodes used by the IMD 10 for sensing and pacing can be configured as unipolar or bipolar. The IMD 10 can also provide defibrillation and / or cardioverter-reducing therapy via electrodes positioned on at least one lead and a housing electrode. The IMD 10 can detect arrhythmias in the heart of the patient 4, such as ventricular fibrillation, and deliver defibrillation therapy to the heart of the patient 4 in the form of electrical pulses. In some instances, the IMD 10 can be programmed to deliver a treatment process, for example, pulses with increasing energy levels, until the fibrillation in the heart of the patient 4 ceases. The IMD 10 employs one or more fibrillation detection techniques known in the art to detect fibrillation.

[0056] Figure 2 This is a conceptual side view showing an example configuration of IMD, as shown in the reference. Figure 1 Example IMD 10 is described. Conceptual side view – The diagram shows a muscle layer 20 and a skin layer 18. The region between the muscle layer 20 and the skin layer 18 contains a subcutaneous space 22. The subcutaneous space contains blood vessels 24, such as capillaries, arteries, or veins, and interstitial fluid in the interstitial fluid 28 of the subcutaneous space 22. The subcutaneous space 22 contains interstitial fluid typically found between the skin layer 18 and the muscle layer 20. The subcutaneous space 22 may contain interstitial fluid surrounding the blood vessels 24. For example, the interstitial fluid surrounds capillaries and allows capillary components (e.g., nutrients) to pass through the interstitial fluid 28 between different layers of the body.

[0057] In some instances, IMD 10 can sense impedance changes with respect to interstitial fluid. In another instance, IMD 10 can sense impedance changes with respect to extravascular fluid and other conductive tissues adjacent to electrode 16. In any case, regardless of the conductive tissue layer and / or fluid type, IMD 10 can track impedance shifts or changes in these layers because impedance changes can occur during adverse health events such as worsening heart failure, even if some of these electrodes 16 are located in layers outside the subcutaneous space 22 or in contact with fluids other than interstitial fluid.

[0058] exist Figure 2 In the example shown, IMD 10 may comprise a leadless, subcutaneously implantable monitoring device having a housing 15 and an insulating cover 76. Electrodes 16A–16N (collectively, “electrodes 16”) may be formed or placed on the outer surface of the cover 76. Although the illustrated example includes three electrodes 16, in some examples, IMDs comprising or coupled to more or fewer than three electrodes 16 may implement the techniques of this disclosure. For example, in some cases, electrodes 16N or additional electrodes may not be necessary, for instance, in which case the housing 15 is conductive and serves as an electrode for IMD 10. The following discusses… Figure 3 The described circuit systems 50-62 can be formed or placed on the inner surface of the cover 76 or within the housing 15. In the illustrated example, the antenna 26 is formed or placed on the inner surface of the cover 76, but in some examples, it can be formed or placed on the outer surface. In some examples, one or more of the sensors 62 can be formed or placed on the outer surface of the cover 76. In some examples, the insulating cover 76 can be positioned over the open housing 15 such that the housing 15 and the cover 76 surround the antenna 26 and the circuit systems 50-62, and protect the antenna and circuit systems from fluids (such as interstitial fluids or other fluids).

[0059] IMD 10 can be directed outward toward the skin layer 18, inward toward the muscle layer 20, or perpendicular in any direction (e.g., left, right, or inward). Figure 2 Page, leave Figure 2 (The page). For example, IMD 10 can be oriented outwards towards the skin, such as... Figure 2 As shown. In some instances, the IMD 10 can be vertically oriented relative to the skin layer 18 and the muscle layer 20, such that the electrode faces... Figure 2 left side of the page or Figure 2 On the right side of the page. In other instances, the IMD 10 can be oriented diagonally or horizontally (e.g., Figure 2 (As shown). Although in Figure 2 IMD 10 is shown in a specific orientation, but those skilled in the art will understand that it can have various orientations and Figure 2The orientation in the text is for illustrative purposes. Similarly, those skilled in the art will understand that IMD 10 may be positioned closer to muscle layer 20 than to the outer layer of skin layer 18 (e.g., dermis or epidermis), while at other times, IMD 10 may be closer to the outer layer of skin layer 18 (e.g., dermis or epidermis).

[0060] IMD 10 can also be any shape (e.g., circle, square, rectangle, trapezoid, etc.). For example, as Figure 2 As shown, the IMD 10 has a specific shape with a rounded edge across the housing 15. Additionally, the electrode 16 can be positioned around the periphery of this shape or around a portion of the periphery of this shape (e.g., Figure 2 (As shown).

[0061] In some cases, the configuration of electrode 16 is chosen to maximize the accuracy of impedance measurements based on the relative positions of circuit systems 50-62. The position of circuit systems 50-62 can be based on form factors and other considerations (charging, electromagnetic noise reduction, etc.), allowing electrode 16 to be positioned as an indirect influence of the selected configuration of circuit systems 50-62. In other instances, electrode positioning may be independent of the configuration of circuit systems 50-62 and can be based on other design considerations, such as the relative position of blood vessels 24 within the implantation area. For example, electrode 16 can be positioned facing a capillary or capillary group of interest, which can be used to provide an even more accurate depiction of impedance changes over time. For example, IMD 10 can determine that optimal impedance readings are obtained closer to certain blood vessels 24 compared to other blood vessels 24. IMD 10 may allow self-repositioning to utilize the optimal readings, for example, through remote control operation, magnetic repositioning, etc. For example, IMD 10 can receive remote control signals or magnetic pulses, causing IMD 10 to rotate in a desired direction (clockwise, counterclockwise, etc.) to achieve such optimal readings.

[0062] IMD 10 can be configured to float within interstitial space 28 or can be fixed in place, for example, using a lead as a tether, thus allowing controlled degrees of freedom depending on the lead configuration. For example, a lead with greater slack could allow IMD 10 to have more degrees of freedom to float within interstitial space 28.

[0063] In some instances, at least one of the electrodes 16 of the IMD 10 may be disposed within another layer, such as the muscle layer 20 or the skin layer 18. In other instances, all of the electrodes 16 may be disposed within a single layer, such as the subcutaneous space 22. In any case, at least one of the electrodes 16 will be in contact with the interstitial fluid in the subcutaneous space 22, while other electrodes 16 may not be in contact with the interstitial fluid. In other instances, each or at least two of the electrodes 16 will be in contact with the interstitial fluid in the subcutaneous space 22. Additionally, at least two of the electrodes 16 may be positioned approximately 3-5 cm apart, such as 4 cm apart. In another instance, some or all of the electrodes 16 may be positioned closer or farther than 4 cm.

[0064] One or more of antenna 26 or circuit systems 50-62 may be formed on the inside of insulating cover 76, such as by using flip-chip technology. Insulating cover 76 may be flipped onto housing 15. When flipped and placed onto housing 15, the components of IMD 10 formed on the inside of insulating cover 76 may be positioned in the gap 78 defined by housing 15. Electrode 16 may be electrically connected to switching circuit system 58 through one or more through-holes (not shown) formed in insulating cover 76. Insulating cover 76 may be formed of sapphire (i.e., corundum), glass, parylene, and / or any other suitable insulating material. Housing 15 may be formed of titanium or any other suitable material (e.g., biocompatible material). Electrode 16 may be formed of stainless steel, titanium, platinum, iridium, or alloys thereof. Additionally, electrode 16 may be coated with materials such as titanium nitride or fractal titanium nitride, but other suitable materials and coatings for such electrodes may be used.

[0065] Figure 3 This is a functional block diagram illustrating an example configuration of an IMD 10 according to one or more technologies described herein. In the example shown, the IMD 10 includes an electrode 16, an antenna 26, a processing circuit system 50, a sensing circuit system 52, an impedance measurement circuit system 60, a communication circuit system 54, a storage device 56, a switching circuit system 58, a sensor 62, and a power supply 91.

[0066] Processing circuitry system 50 may include fixed-function circuitry systems and / or programmable processing circuitry systems. Processing circuitry system 50 may include any one or more of the following: microprocessors, controllers, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or equivalent discrete or analog logic circuitry systems. In some instances, processing circuitry system 50 may include multiple components (such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, or one or more FPGAs) and other discrete or integrated logic circuitry systems. The functionality attributed herein to processing circuitry system 50 may be embodied in software, firmware, hardware, or any combination thereof.

[0067] Sensing circuitry 52 can be selectively coupled to electrode 16 via switching circuitry 58, for example, to select electrode 16 and the polarity of a sensing vector, controlled by processing circuitry 50, for sensing impedance and / or cardiac signals. Sensing circuitry 52 can sense signals from electrode 16, for example, to generate a cardiac EGM or subcutaneous electrocardiogram (ECG) to monitor cardiac electrical activity. As an example, sensing circuitry 52 can also monitor signals from sensor 62, which may include one or more accelerometers, pressure sensors, and / or optical sensors. In some instances, sensing circuitry 52 may include one or more filters and amplifiers for filtering and amplifying signals received from electrode 16 and / or sensor 62.

[0068] In some instances, the processing circuitry 50 may use a switching circuitry 58, for example via a data / address bus, to select which available electrodes will be used to obtain the impedance measurement results of the interstitial fluid. The switching circuitry 58 may comprise a switch array, switch matrix, multiplexer, transistor array, microelectromechanical switch, or any other type of switching device suitable for selectively coupling the sensing circuitry 58 to selected electrodes. In some instances, the sensing circuitry 52 comprises one or more sensing channels, each of which may include an amplifier. In response to a signal from the processing circuitry 50, the switching circuitry 58 may couple an output from a selected electrode to one of the sensing channels.

[0069] In some instances, one or more channels of the sensing circuitry 52 may include an R-wave amplifier that receives signals from electrode 16. In some instances, the R-wave amplifier may take the form of an automatic gain control amplifier that provides an adjustable sensing threshold based on the measured R-wave amplitude. Additionally, in some instances, one or more channels of the sensing circuitry 52 may include a P-wave amplifier that receives signals from electrode 16. The sensing circuitry system can use the received signals to perform pacing and sensing in the heart of patient 4. In some instances, the P-wave amplifier may take the form of an automatic gain control amplifier that provides an adjustable sensing threshold based on the measured P-wave amplitude. Other amplifiers may also be used. In some instances, the sensing circuitry 52 includes channels containing amplifiers with a passband relatively wider than that of the R-wave or P-wave amplifiers. Signals from selected sensing electrodes chosen for coupling to this broadband amplifier may be provided to a multiplexer and then converted by an analog-to-digital converter into multi-bit digital signals for storage in storage device 56. The processing circuit system 50 can use digital signal analysis techniques to characterize the digitized signals stored in the storage device 56 in order to detect and classify arrhythmias from the digitized electrical signals.

[0070] Sensing circuitry 52 includes impedance measurement circuitry 60. Processing circuitry 50 can control impedance circuitry 60 to periodically measure electrical parameters to determine impedance, such as subcutaneous impedance indicating fluid found in interstitial fluid 28. For subcutaneous impedance measurement, processing circuitry 50 can control impedance measurement circuitry 60 to deliver electrical signals between selected electrodes 16 and measure the current or voltage amplitude of the signals. Processing circuitry 50 can select any combination of electrodes 16, for example, by using switching circuitry 58 and sensing circuitry 52. ​​Impedance measurement circuitry 60 includes sampling and holding circuitry or other suitable circuitry for measuring the amplitude of the resulting current and / or voltage. Processing circuitry 50 determines the impedance value based on the amplitude value received from impedance measurement circuitry 60. In some instances, processing circuitry 50 may include switching circuitry 58 to switch between ECG and impedance measurements across the same electrodes 16. For example, switching circuitry 58 may use multiplexing to switch between measurements, allowing processing circuitry 50 to perform various measurements (e.g., impedance, ECG, etc.) using electrodes 16. In such instances, the processing circuitry 50 may use electrodes 16 to receive multiple signals, including at least one electrocardiogram (ECG) and / or one or more subcutaneous tissue impedance signals.

[0071] In some instances, IMD 10 may include a measurement circuitry system with an amplifier design configured to switch between impedance measurements and other physiological parameter measurements (e.g., ECG) in real-time and continuously. Additionally, IMD 10 may briefly activate the impedance measurement circuitry system 60 to convert power. In one instance, IMD 10 may use amplifier circuitry, such as a chopper amplifier, based on certain techniques described in U.S. Application No. 12 / 872,552, filed August 31, 2010, entitled “Chopper-stabilized Instrumentation Amplifier for Impedance Measurement” by Denison et al.

[0072] Because the IMD 10 or external device 12 can be configured to include the sensing circuitry system 52, the impedance measurement circuitry system 60 can be implemented in one or more processors, such as the processing circuitry system 50 of the IMD 10 or the processing circuitry system 80 of the external device 12. (See reference...) Figure 3 In the described example, the sensing circuitry system 52 in conjunction with IMD 10 illustrates an impedance measurement circuitry system 60. Similar to the processing circuitry systems 50, 80, 98 and other circuitry systems described herein, the impedance measurement circuitry system 60 can be embodied as one or more hardware modules, software modules, firmware modules, or any combination thereof. The impedance measurement circuitry system 60 can periodically analyze impedance measurement data to identify a decrease in subcutaneous impedance in patient 4 and alert patient 4 when this decrease indicates the onset of a possible heart failure decompensation event.

[0073] In some instances, the impedance measurement circuitry 60 can measure a current or impedance value other than a previously determined impedance value in response to a signal received from one or more other medical devices (e.g., the communication circuitry 54). In some instances, the one or more other medical devices may include sensor devices such as activity sensors, heart rate sensors, wearable devices worn by the patient, temperature sensors, etc. That is, in some instances, the one or more other medical devices may be external to the IMD 10. In such instances, the other medical devices can be connected to the IMD 10 via the communication circuitry 54.

[0074] In some instances, IMD 10 may contain one or more other medical devices, such as by including them within housing 15 or otherwise attaching them to the interior or exterior of IMD 10. For example, the other medical devices may contain one or more sensors attached to an interior or exterior portion of IMD 10. In any case, processing circuitry 50 may receive one or more signals from one or more medical devices that trigger processing circuitry 50 to control impedance measurement circuitry 60 to perform impedance measurement. In this way, processing circuitry 50 may determine a current impedance value (e.g., a daily average) or an impedance value other than a previously determined impedance value in response to receiving one or more signals from another medical device (such as a sensor device).

[0075] For example, the impedance measurement circuit system 60 can determine that the received signal contains a trigger that causes the impedance measurement circuit system 60 to measure one or more impedance values ​​using the electrode 16. In a non-limiting example, the impedance measurement circuit system 60 can receive a signal indicating when the patient 4's activity level is low. In response to receiving a signal indicating an activity level, the impedance measurement circuit system 60 can use the electrode 16 to measure one or more impedance values. In another example, the impedance measurement circuit system 60 can receive a signal indicating when the patient 4's heart rate is below or above a heart rate threshold, or a signal indicating when the patient 4's body temperature becomes too low or too high compared to certain temperature thresholds, etc. In any case, the impedance measurement circuit system 60 can determine whether the received signal contains trigger information that communicates to the impedance measurement circuit system 60 that the impedance measurement circuit system 60 will perform a physiological parameter measurement using the electrode 16.

[0076] In some instances, processing circuitry system 50 can determine whether a combination of one or more signals received from one or more transmission devices contains trigger information. Processing circuitry system 50 can determine that one or more signals individually contain trigger information. In some instances, processing circuitry system 50 can determine that a combination of one or more signals contains trigger information. In response to determining the presence of trigger information, processing circuitry system 50 can cause impedance measurement circuitry system 60 to measure one or more impedance values ​​using electrode 16. In some instances, processing circuitry system 50 can additionally use timing information. For example, processing circuitry system 50 can start a timer based on trigger information. In some instances, processing circuitry system 50 can cause impedance measurement circuitry system 60 to measure impedance values ​​according to timing constraints following the trigger event (e.g., performing measurements only at night), regardless of when the trigger event occurs during the day. In any case, processing circuitry system 50 can cause IMD 10 to determine one or more tissue impedance values ​​in response to a trigger event, such as in response to receiving a signal from a sensor device, wherein in some cases, IMD 10 may include a sensor device or the sensor device may be independent of IMD 10.

[0077] In some instances, the impedance measurement circuit system 60 can measure impedance values ​​periodically, such as hourly, daily, or weekly. In one instance, the impedance measurement circuit system 60 can measure impedance values ​​during a specific part of the day. For example, the impedance measurement circuit system 60 can measure impedance values ​​every twenty minutes within a predetermined number of hours, such as between noon and 5 p.m. The processing circuit system 50 can determine the final measured impedance value by calculating the average of the measurement results. In this case, the daily value could be the average of the impedances measured by the impedance measurement circuit system 60 during the day (e.g., over a 24-hour period, where measurements are selectively performed at specific times and / or in response to certain triggers, etc.).

[0078] The final value can then be stored in storage device 56 as a measured impedance value. For example, the measured impedance value may include a final average impedance value. In some instances, the impedance value may be stored in a buffer of impedance values, wherein the buffer is configured to store multiple impedance values ​​used to calculate the final average. The measured impedance value may also include buffers of multiple past final averages. That is, the measured impedance value may include buffers of impedance values ​​measured daily in the past.

[0079] In some instances, the impedance measurement circuitry 60 can be configured to sample impedance measurement results at a specific sampling rate. In such instances, the impedance measurement circuitry 60 can be configured to perform downsampling of the received impedance measurement results. For example, the impedance measurement circuitry 60 can perform downsampling to reduce throughput or decrease the amount of data transmitted to the processing circuitry 50. This can be particularly advantageous when the impedance measurement circuitry 60 has a high sampling rate when active.

[0080] In some instances, the processing circuitry 50 performs impedance measurements by causing the impedance measurement circuitry 60 (via the switching circuitry 58) to deliver voltage pulses between at least two electrodes 16 and examining the resulting current amplitude value measured by the impedance measurement circuitry 60. In some instances, the switching circuitry 58 delivers signals that actually stimulate the heart of the patient 4. In other instances, these signals may be delivered during the refractory period, in which case they may not stimulate the heart of the patient 4.

[0081] In other instances, processing circuitry 50 can perform impedance measurements by delivering current pulses across at least two selected electrodes 16 via impedance measurement circuitry 60 (through switching circuitry 58). Impedance measurement circuitry 60 maintains the measured voltage amplitude value. Processing circuitry 50 determines the impedance value based on the amplitude of the current pulses and the amplitude of the resulting voltage measured by impedance measurement circuitry 60. IMD 10 can use defined or predetermined pulse amplitudes, widths, frequencies, or electrode polarities for the pulses delivered for these various impedance measurements. In some instances, the pulse amplitude and / or width can be subthreshold, for example, below the threshold necessary to capture or otherwise activate tissue (such as cardiac tissue, subcutaneous tissue, or muscle tissue).

[0082] In some cases, the IMD 10 can measure subcutaneous impedance values ​​that include resistive and reactive components (e.g., X, XL, XC), as in an impedance triangle. In such cases, for example, the IMD 10 can measure subcutaneous impedance during the delivery of a sinusoidal or other time-varying signal through the impedance measurement circuitry system 60. Therefore, as used herein, the term "impedance" is used broadly to indicate any collected, measured, and / or calculated value that may contain one or both resistive and reactive components. In some instances, the subcutaneous tissue impedance value is derived from a subcutaneous tissue impedance signal received from electrode 16.

[0083] exist Figure 3 In the example shown, the processing circuit system 50 is capable of performing... Figure 6The various techniques described in –9. To avoid confusion, the processing circuit system 50 is described as performing various impedance processing techniques prohibited by IMD 10, but it should be understood that these techniques may also be performed by other processing circuit systems (e.g., the processing circuit system 80 of external device 12, etc.).

[0084] In various instances, the processing circuitry system 50 can perform one, all, or any combination of a variety of impedance scoring techniques discussed in more detail below. When performing the scoring technique, the IMD 10 can generate an alarm when it determines that a decrease in impedance indicates that patient 4 may be experiencing a decompensated event of heart failure. For example, the IMD 10 can provide an auditory or tactile alarm in the form of a buzzer or vibration pattern. Alternatively, the IMD 10 can send an alarm signal to an external device 12, causing the external device 12 to provide an alarm to patient 4. The external device 12 can provide an auditory, visual, or tactile alarm to patient 4. Once an alarm is issued to patient 4, patient 4 can then seek medical care, for example, by going to a hospital or clinic for examination. Alarms can be categorized into different degrees of severity, as indicated by the impedance score.

[0085] The sensing circuitry 52 can also provide one or more impedance signals to the processing circuitry 50 for analysis, such as for determining an impedance score according to the techniques of this disclosure. In some instances, the processing circuitry 50 can store impedance values, impedance scoring factors (e.g., fluid index, average impedance value, reference impedance value, buffer value, etc.), and impedance scores in a storage device 56. According to the techniques of this disclosure, the processing circuitry 50 of the IMD 10 and / or the processing circuitry of another device retrieving data from the IMD 10 can analyze impedance values ​​to determine the cardiac condition of the patient 4.

[0086] The communication circuitry 54 may include any suitable hardware, firmware, software, or any combination thereof for communicating with another device (such as external device 12), another networked computing device, or another IMD or sensor. Under the control of the processing circuitry 50, the communication circuitry 54 may receive downlink telemetry from external device 12 or the other device via an internal or external antenna (e.g., antenna 26), and transmit uplink telemetry to said external device or the other device. Additionally, the processing circuitry 50 may communicate with external devices (e.g., external device 12) and devices such as Medtronic... Computer networks, such as networks, communicate with networked computing devices.

[0087] Antenna 26 and communication circuit system 54 can be configured to be connected via inductive coupling, electromagnetic coupling, NFC technology, RF communication, Wi-Fi TMOr other proprietary or non-proprietary wireless communication schemes to transmit and / or receive signals. In some instances, processing circuitry 50 can provide data to be transmitted uplink to external device 12 via communication circuitry 54 and control signals using an address / data bus. In another instance, communication circuitry 54 can provide received data to processing circuitry 50 via a multiplexer.

[0088] In some instances, the processing circuitry 50 can transmit impedance data to the external device 12 via the communication circuitry 54. For example, the IMD 10 can transmit impedance measurement results collected by the external device 12, which will then analyze them. In such instances, the external device 12 performs the processing techniques described herein. Alternatively, the IMD 10 can perform the processing techniques and transmit the processed impedance data to the external device 12 for reporting purposes, such as providing an alert to patient 4 or another user.

[0089] In some instances, storage device 56 contains computer-readable instructions that, when executed by processing circuitry system 50, cause IMD 10 and processing circuitry system 50 to perform various functions pursuant to this document. Storage device 56 may contain any volatile, non-volatile, magnetic, optical, or electrical medium. For example, storage device 56 may contain random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), erasable programmable ROM (EPROM), flash memory, or any other digital medium. As an example, storage device 56 may store programmed values ​​of one or more operating parameters of IMD 10 and / or data collected by IMD 10 for transmission to another device using communication circuitry system 54. As an example, data stored by storage device 56 and transmitted by communication circuitry system 54 to one or more other devices may include impedance values ​​and / or a digitized cardiac EGM.

[0090] The various components of IMD 10 are coupled to a power source 91, which may include a rechargeable or non-rechargeable battery. For example, a non-rechargeable battery may be able to maintain its charge for several years, while a rechargeable battery may be inductively charged daily, weekly, or yearly from an external device (such as external device 12).

[0091] Figure 4 This is a block diagram illustrating an example configuration of the components of external device 12. In some instances, external device 12 includes a processing circuitry 80, a communication circuitry 82, a storage device 84, and a user interface 86.

[0092] The processing circuitry system 80 may include one or more processors configured to implement functions and / or processing instructions for execution within the external device 12. For example, the processing circuitry system 80 may be capable of processing instructions stored in the storage device 84. The processing circuitry system 80 may include, for example, a microprocessor, DSP, ASIC, FPGA, or equivalent discrete or integrated logic circuitry system, or a combination of any of the foregoing devices or circuitry systems. Therefore, the processing circuitry system 80 may include any suitable structure, whether in hardware, software, firmware, or any combination thereof, for performing the functions attributed herein to the processing circuitry system 80.

[0093] The communication circuitry 82 may include any suitable hardware, firmware, software, or any combination thereof for communicating with another device (such as IMD 10). Under the control of the processing circuitry 80, the communication circuitry 82 can receive downlink telemetry from IMD 10 or another device, and send uplink telemetry to it. The communication circuitry 82 may be configured to communicate via inductive coupling, electromagnetic coupling, NFC technology, RF communication, etc. Wi-Fi TM Or other wireless communication schemes to transmit or receive signals. The communication circuit system 82 can also be configured to communicate with devices other than IMD 10 via any of various forms of wired and / or wireless communication and / or network protocols.

[0094] Storage device 84 can be configured to store information within external device 12 during operation. Storage device 84 may comprise a computer-readable storage medium or a computer-readable storage device. In some instances, storage device 84 comprises one or more of short-term or long-term memory. Storage device 84 may comprise, for example, RAM, DRAM, SRAM, magnetic disk, optical disk, flash memory, or various forms of EPROM or EEPROM. In some instances, storage device 84 is used to store data indicating instructions executed by processing circuitry system 80. Storage device 84 can be used by software or applications running on external device 12 to temporarily store information during program execution. Storage device 84 may also store historical impedance data, timing information (e.g., the number of days since IMD implantation, the number of days since the self-fluid index has exceeded a certain threshold, etc.).

[0095] The data exchanged between external device 12 and IMD 10 may include operating parameters (e.g., resolution parameters). External device 12 may transmit data containing computer-readable instructions that, when implemented by IMD 10, can control IMD 10 to change one or more operating parameters and / or export collected data. For example, processing circuitry 80 may transmit instructions to IMD 10 requesting IMD 10 to export collected data (e.g., impedance data, fluid index values, and / or impedance scores) to external device 12. In turn, external device 12 may receive collected data from IMD 10 and store the collected data in storage device 84. Processing circuitry 80 may implement any of the techniques described herein to analyze the impedance values ​​received from IMD 10, for example, to determine fluid index values, impedance scores, etc. Using the impedance analysis techniques disclosed herein, processing circuitry 80 may then determine the cardiac condition status of patient 4 and / or generate alarms based on the cardiac condition status.

[0096] Users such as clinicians or patients can interact with external devices 12 through user interface 86. User interface 86 includes a display (not shown), such as an LCD or LED display or other type of screen, which the processing circuitry 80 can utilize to present information related to the IMD 10, such as cardiac EGM, indications of impedance change detection, and quantification of impedance changes, such as impedance scores or fluid indices. Additionally, user interface 86 may include input mechanisms for receiving input from the user. Input mechanisms may include, for example, buttons, a keypad (e.g., an alphanumeric keypad), a peripheral pointing device, a touchscreen, or another input mechanism that allows the user to navigate the user interface presented by the processing circuitry 80 of external device 12 and provide input. In other instances, user interface 86 may also include an audio circuitry for providing auditory notifications, instructions, or other sounds to the user, receiving voice commands from the user, or both.

[0097] Power source 108 delivers operating power to components of external device 12. Power source 108 may include a battery and power generation circuitry for generating operating power. In some embodiments, the battery may be rechargeable to allow for extended operation. Recharging can be accomplished by electrically coupling power source 108 to a bracket or plug connected to an AC outlet. Alternatively, recharging can be accomplished via proximal-end inductive interaction between an external charger and an inductive charging coil within external device 12. In other embodiments, conventional batteries (e.g., nickel-cadmium or lithium-ion batteries) may be used. Additionally, external device 12 may be directly coupled to an AC power outlet to power external device 12. Power source 108 may include circuitry for monitoring the remaining charge in the battery. In this way, user interface 86 can provide a current battery charge indicator or a low battery charge indicator when the battery needs to be replaced or recharged. In some cases, power source 108 may be able to estimate the remaining operating time using the current battery.

[0098] Figure 5 This is a block diagram illustrating an example system according to one or more techniques described herein. The example system includes an access point 90, a network 92, an external computing device (such as a server 94), and one or more other computing devices 100A–100N (collectively, “Computing Device 100”), which can be coupled to IMD 10 and external device 12 via network 92. In this example, IMD 10 can communicate with external device 12 via a first wireless connection and with access point 90 via a second wireless connection using communication circuitry 54. Figure 5 In this example, access point 90, external device 12, server 94, and computing device 100 are interconnected and can communicate with each other via network 92. Network 92 can include a local area network (LAN), a wide area network (WAN), or a global network such as the Internet. In some respects, it can be used with Medtronic... The network provides general network technologies and functions similar to those used in its implementation. Figure 5 The system.

[0099] Access point 90 may include a device connected to network 92 via any of a variety of connections, such as dial-up, digital subscriber line (DSL), or cable modem connections. In other instances, access point 90 may be coupled to network 92 via different forms of connection, including wired or wireless connections. In some instances, access point 90 may be a user device that can be co-located with the patient, such as a tablet or smartphone. IMD 10 may be configured to transmit data, such as impedance information, impedance scores, and / or electrocardiograms (EGMs), to access point 90. Access point 90 can then transmit the retrieved data to server 94 via network 92.

[0100] In some cases, server 94 can be configured to provide a secure storage site for data already collected from IMD 10 and / or external device 12. In some cases, server 94 can compile the data into web pages or other documents via computing device 100 for viewing by trained professionals (such as clinicians). Figure 5 One or more aspects of the system shown may be compatible with those of Medtronic. The network provides general network technologies and functions similar to those used in its implementation.

[0101] In some instances, server 94 can monitor impedance, for example, based on measured impedance information received from IMD 10 and / or external device 12 via network 92, to detect worsening heart failure in patient 4 using any of the techniques described herein. Server 94 can provide alerts related to the worsening heart failure in patient 4 to patient 4 via access point 90 via network 92 or to one or more clinicians via computing device 100. In the instance of impedance monitoring by IMD 10 and / or external device 12 as described above, server 94 can receive alerts from IMD 10 or external device 12 via network 92 and provide alerts to one or more clinicians via computing device 100. In some instances, server 94 can generate web pages to provide alerts and information about impedance, and may include memory for storing alerts and diagnostic or physiological parameter information for multiple patients.

[0102] In some instances, one or more computing devices in computing device 100 may be tablets or other smart devices located with a clinician, through which the clinician can program, receive alerts, and / or query IMD 10. For example, the clinician can access data collected by IMD 10, such as when patient 4 is between clinician visits, to check the status of the patient's medical condition via computing device 100. In some instances, the clinician can input instructions for medical interventions for patient 4 into an application executed by computing device 100, such as based on the status of the patient's condition determined by IMD 10, external device 12, server 94, or any combination thereof, or based on other patient data known to the clinician. Device 100 can then transmit the instructions for medical interventions to another computing device in computing device 100 located with patient 4 or patient 4's caregiver.

[0103] In some instances, instructions for medical intervention may include instructions to change medication dosage, timing, or selection; to schedule a clinician visit; or to seek medical care. In other instances, computing device 100 may generate alerts to patient 4 based on the status of patient 4's medical condition, enabling patient 4 to proactively seek medical care before receiving instructions for medical intervention. In this way, patient 4 can be authorized to take action as needed to address their medical condition, which can help improve patient 4's clinical outcomes.

[0104] In the Figure 5 In the example shown, server 94 includes, for example, a storage device 96 and a processing circuitry 98 for storing data retrieved from IMD 10. Although Figure 5 Not shown, but computing device 100 may similarly include storage devices and processing circuitry. Processing circuitry 98 may include one or more processors configured to implement functions and / or processing instructions for execution within server 94. For example, processing circuitry 98 may be capable of processing instructions stored in storage device 96. Processing circuitry 98 may include, for example, a microprocessor, DSP, ASIC, FPGA, or equivalent discrete or integrated logic circuitry, or a combination of any of the foregoing devices or circuitry. Therefore, processing circuitry 98 may include any suitable structure, whether in hardware, software, firmware, or any combination thereof, for performing the functions attributed herein to processing circuitry 98. The processing circuitry 98 of server 94 and / or the processing circuitry of computing device 100 may implement any of the techniques described herein to analyze impedance values ​​received from IMD 10, for example, to determine the cardiac condition of patient 4 (e.g., worsening heart failure).

[0105] Storage device 96 may comprise a computer-readable storage medium or a computer-readable storage device. In some instances, storage device 96 comprises one or more of short-term memory or long-term memory. Storage device 96 may comprise, for example, RAM, DRAM, SRAM, magnetic disk, optical disk, flash memory, or various forms of EPROM or EEPROM. In some instances, storage device 96 is used to store data indicating instructions to be executed by processing circuitry system 98.

[0106] Figure 6 This is a flowchart illustrating an example method for determining the cardiac condition status of patient 4 using a reference impedance value, a fluid index value, and an impedance score, according to one or more techniques of this disclosure. Although described as being performed by IMD 10, the reference... Figure 6One or more of the various example technologies described may be executed by any one or more of the IMD 10, external device 12, or server 94, for example, by the processing circuitry system of any one or more of these devices.

[0107] In some instances, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, may use absolute impedance values ​​and statistical representations of impedance values ​​when determining an impedance score. In some instances, absolute impedance values ​​may typically refer to average impedance values. In some instances, processing circuitry system 50 may determine whether the statistical representations of fluid index values ​​and impedance values ​​meet their respective thresholds. As discussed herein, thresholds may include adaptive thresholds. For example, processing circuitry system 50 may compare fluid index values ​​to adaptive thresholds. In some instances, adaptive thresholds are determined based on intraday variations in impedance values ​​and absolute impedance. In any case, processing circuitry system 50 may determine an impedance score indicative of the cardiac condition status of patient 4.

[0108] In some instances, the processing circuitry 50 can trigger a fluid index alarm on a day when the fluid index is greater than or equal to a threshold (such as an adaptive threshold, a fixed, predefined threshold, or a user-selected threshold). In such instances, the fluid index alarm may stop when the current fluid index value drops below half the threshold. In this way, after triggering a fluid index alarm, the fluid index value can hover around the threshold without resetting the fluid index alarm.

[0109] refer to Figure 6 The processing circuitry 50 can determine a first impedance value (110) based on the subcutaneous tissue impedance signal. The IMD 10 can be implanted in the subcutaneous space 22 of the patient 4. For example, the IMD 10 can be implanted in the interstitial space 28, such as... Figure 2 As shown, the subcutaneous tissue impedance signal can indicate the degree of fluidity in the interstitium. In some instances, the processing circuitry 50 can detect the subcutaneous tissue impedance signal via electrodes 16. In some instances, only one electrode of electrodes 16 is within the subcutaneous space 22, while at least one other electrode of electrodes 16 is within another layer of the patient 4. In either case, the processing circuitry 50 can determine at least one first tissue impedance value corresponding to a first time period, at least in part, based on the subcutaneous tissue impedance signal.

[0110] The first impedance value may include historical impedance values ​​received over a period of time. For example, the processing circuitry system 50 may receive the first impedance value over 10 days, 13 days, 30 days, or any number of days. In some cases, the processing circuitry system 50 may receive at least one first impedance value starting from the date of implantation. In other instances, the processing circuitry system 50 may collect but discard impedance values ​​to prevent them from being included as first impedance values ​​until a specific number of days after implantation. For example, the processing circuitry system 50 may impose a predetermined delay of a number of days, such as 10 days, 13 days, 30 days, etc., before determining the first impedance value. In other instances, the delay may only affect when the processing circuitry system 50 estimates a first reference value among multiple reference values, which are discussed in further detail below.

[0111] In some instances, the first impedance value may comprise raw signal data received from electrode 16, which may be conditioned and processed using signal processing techniques before being stored. Those skilled in the art will understand that impedance values ​​are typically described in ohms. In some instances, processing circuitry 50 may store the first impedance value in storage device 56. In some instances, processing circuitry 50 may transmit the first impedance value via communication circuitry 54. For example, processing circuitry 50 may transmit the first impedance value to external device 12. External device 12 may store the first impedance value in storage device 84. In such instances, processing circuitry 80 may determine the impedance score of patient 4 or may transmit or relay data to server 94 via communication circuitry 82, where server 94 may determine the impedance score of patient 4. Therefore, although many of the techniques described herein are described as being performed by IMD 10, these methods may be performed wholly or partially by any one or more of IMD 10, external device 12, or server 94, for example, by the processing circuitry of any one or more of these devices.

[0112] The processing circuit system 50 can also determine a second impedance value (112) based on the subcutaneous tissue impedance signal. The second impedance value may correspond to a second time period different from the time period corresponding to the first impedance value. For example, the first and second time periods may be offset from each other. In some instances, the first and second time periods may overlap, while in other instances, the time periods, and consequently the impedance values, may be mutually exclusive. In a non-limiting instance, one or more second impedance values ​​can be determined from a pool of first impedance values. For example, the second impedance value may correspond to an impedance value measured during the first time period, where the second impedance value corresponds to a second time period falling within the first time period. For example, the second impedance value may correspond to the daily impedance value for the current date, where the first time period contains values ​​related to the current date and the number of days prior to the current date. In this way, in addition to at least some of the second impedance values, the first impedance value may correspond to a short-term average containing one or more impedance values.

[0113] In some cases, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, may incorporate a second impedance value when determining a first impedance value, wherein the second impedance value corresponds to the current tissue impedance of patient 4, and the first impedance value corresponds to a historical impedance value that includes or does not include the current tissue impedance value (e.g., the second impedance value). For example, at least one first tissue impedance value may include multiple historical tissue impedance values. Therefore, processing circuitry system 50 may determine at least one second tissue impedance value corresponding to a second time period different from the first time period (e.g., deviating from the first time period) based at least in part on one or more subcutaneous tissue impedance signals. Processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, may store and / or transmit the second impedance value for subsequent analysis, just as the first impedance value does.

[0114] In some instances, the processing circuitry 50 can determine the second impedance value as a short-term average (or other average) impedance value. The short-term average can be the average or weighted average of current impedance values ​​from multiple days or hours (e.g., the most recent 12 hours, the most recent day, two days, three days, or four days, etc.). To determine the current impedance and the average impedance, the processing circuitry 50 can employ the techniques described in U.S. Application No. 10 / 727,008, filed December 3, 2003, by Stadler et al., entitled “Method and Apparatus for Detecting Change in Intrathoracic Impedance.” In some instances, the processing circuitry 50 can perform averaging of the impedance values ​​over multiple cardiac cycles. In this way, the processing circuitry 50 can obtain a less noisy signal and / or filter respiration (the AC component of the signal) to obtain the impedance (the DC component of the signal).

[0115] In some instances, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can identify the presence of missing subcutaneous impedance measurement data (e.g., corrupted data, gaps in the data series, etc.). For example, processing circuitry system 80 can identify the presence of missing data. In some instances, processing circuitry system 80 can identify the presence of missing data, such as when certain data cannot be accessed from the intended storage location of storage device 84 or when a missing transmission occurs. In another instance, processing circuitry system 80 can determine that the data series contains data gaps indicating the presence of missing data (e.g., corrupted data). Processing circuitry system 80 can identify data gaps, for example, based on a known transmission rate. In one instance, IMD 10 can periodically (e.g., daily) transmit impedance values ​​to processing circuitry system 80. In such instances, processing circuitry system 80 can determine the presence of missing data based on missing data within a specific time range, where impedance data is available before and / or after the specific time range. In another instance, the processing circuitry 80 may determine that some data is corrupted or contains anomalous data that could indicate a transmission error or data retrieval error. In either case, the processing circuitry 80 may transmit a request for missing data to the IMD 10 or may simply notify the IMD 10 of the identified discrepancy.

[0116] Missing data can occur for any number of different reasons, such as failed data transmission or if the IMD 10 is unavailable when performing impedance measurements within a specific measurement cycle. For example, the IMD 10 may fail to perform certain impedance measurements because the processing circuitry 50 is responding to competing measurement requests. In one instance, the processing circuitry 50 may respond to higher priority measurement requests, such as ECG requests in certain situations, in which case the sensing circuitry 52 may fail to perform impedance measurements as expected.

[0117] In one instance involving missing data, processing circuitry 80 or 98 may determine that one or more impedance values ​​were expected to be received from IMD 10, but were not received from IMD 10. In some instances, processing circuitry 80 or 98 may determine that one or more impedance values ​​were not received from IMD 10, such as by detecting one or more dropped data packets or by identifying gaps in the data received from IMD 10. In some instances, external device 12 or server 94 may determine data inconsistencies indicating corrupt, misleading, or otherwise inconsistent data. For example, external device 12 may compare data received from IMD 10 with data received from other devices to determine if the data is aligned or consistent. In instances where external device 12 or server 94 identifies missing data, external device 12 or server 94 may transmit a notification to IMD 10 (e.g., via communication circuitry 54) to identify the discrepancy or otherwise indicate the presence of missing data. In response, the processing circuit system 80 may attempt to correct the discrepancy, for example, by identifying the cause of the missing data and / or by trying to change the IMD 10 to avoid future data loss.

[0118] In some instances, upon identifying the presence of one or more missing impedance values, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can be configured to interpolate or extrapolate data from one or more known tissue impedance values. For example, processing circuitry system 80 can interpolate or extrapolate from known data points to complete the data series of impedance values ​​measured over time. In some instances, processing circuitry system 80 can interpolate or extrapolate upon identifying the presence of corrupted data and / or outlier data points. Although described below as being performed by processing circuitry system 80, these techniques, as well as other techniques of this disclosure, can be performed by any one or more of IMD 10, external device 12, or server 94, for example, by the processing circuitry systems of any one or more of these devices.

[0119] In some cases, the processing circuitry 80 may include interpolated or extrapolated data as part of one or more tissue impedance values ​​used to determine the impedance score. That is, the processing circuitry 80 may attempt to use various interpolation or extrapolation techniques to complete the data series of impedance measurements, covering missing gaps in the data. In some instances, the processing circuitry 80 may use a weighted average of data corresponding to the number of days with valid impedance measurements. The processing circuitry 80 may use the weighted average data and the interpolated or extrapolated data to determine the fluid index.

[0120] In some instances, the processing circuitry 80 can identify fluid index reset conditions that cause the fluid index value to be reset to the baseline value based on the identification of missing data. In an illustrative example, the processing circuitry 80 can determine that the number of days with missing impedance data (e.g., daily impedance average, etc.) is less than X days. In this case, the processing circuitry 80 can perform interpolation or extrapolation techniques as discussed above. However, if the processing circuitry 80 determines that the number of days with missing impedance data meets a missing data threshold (e.g., 7 days of missing data, 14 days of missing data, etc.), the processing circuitry 80 can automatically cause the reference impedance value to be reset, so that the reference impedance value restarts at the initial value, which causes the fluid index value to be reinitialized to zero (or some other user-defined or fixed and previously defined baseline value). In some instances, the processing circuitry 80 can reset the fluid index value to a baseline value of zero. In such instances, the processing circuitry 80 can restart the fluid index calculation from the baseline value. That is, in some cases, the baseline value of the fluid index reset condition may be zero.

[0121] Although described as being performed by external device 12, the techniques involving fluid index reset and missing data determination can be performed by any one or more of IMD 10, external device 12, or server 94, for example, by the processing circuitry of any one or more of these devices. For example, server 94 can determine the presence of missing data, corrupted data, or outlier data. In such instances, server 94 can perform interpolation or extrapolation techniques to attempt to complete the data series, or otherwise reset the fluid index value when too much data is missing or corrupted. Thus, server 94 can communicate to external device 12 or IMD 10 that a fluid index reset condition has occurred, or, where server 94 performs techniques of this disclosure (such as determining an impedance score), server 94 can reset the fluid index and determine an impedance score using a baseline fluid index value.

[0122] In some instances, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can determine reference impedance values ​​(114) based on a first impedance value. For example, processing circuitry system 50 of IMD 10 can determine one or more reference impedance values ​​based at least in part on at least one first tissue impedance value. The reference impedance values ​​can provide a statistical representation of the values ​​based on the first impedance values. For example, in determining one or more reference impedance values, processing circuitry system 50 can determine a statistical representation of at least one first tissue impedance value corresponding to a first time period. In determining the statistical representation of at least one first tissue impedance value, processing circuitry system 50 can determine a mean, mode, median, range, regression model, or standard deviation to represent at least one first tissue impedance value. Figure 9 The reference impedance value was discussed in further detail.

[0123] When calculating the reference impedance value, the processing circuitry 50 can adjust the slope of the reference value to accommodate the rapid rise in impedance during the initial months (e.g., upward and downward drift parameters). In some instances, the processing circuitry 50 can adaptively calculate the reference impedance value over time. For example, the processing circuitry 50 can adjust the upward and downward drift parameters in a piecewise linear manner to accommodate the rapid rise in impedance during the initial months. Therefore, the processing circuitry 50 can calculate the reference impedance in a way that adapts to different rates of change in impedance over time. In other words, the reference impedance value can be calculated differently over different time periods. For example, the reference impedance value can be calculated to allow for greater changes in reference impedance between days 34 and 60 after implantation or system modification than between days 61 and 120. The reference impedance value can then be calculated to allow for smaller changes in the value over the extended period of 120 days compared to the previous time period.

[0124] For example, processing circuitry 50 can adjust the reference slope value by adjusting upward and downward drift parameters scaled from nominal drift values ​​(e.g., upward drift nominal and downward drift nominal). In some instances, the nominal drift value for the upward drift reference may be 0.18 ohms per day. In another instance, the nominal drift value for the downward drift reference may be 0.05 ohms per day. In an instance where fluid index calculation begins on day 34 post-implantation, processing circuitry 50 can calculate the upward drift parameters from day 34 to day 60 as nominal upward drift values ​​scaled by a predetermined multiplier. In some instances, the predetermined multiplier from day 34 to day 60 may be between 9 and 11 (e.g., 10). In other instances, the predetermined multiplier from day 34 to day 60 may be less than or greater than 10.0. For example, the predetermined multiplier from day 34 to day 60 may be 3.5.

[0125] In some instances, the processing circuitry 50 can calculate the down-drift reference parameter as a nominal down-drift value scaled by a predetermined multiplier. In some instances, the predetermined multiplier from day 34 to day 60 can be a negative fraction (e.g., -0.01). In other instances, the predetermined multiplier can be a positive fraction (e.g., +0.25).

[0126] From day 61 to day 120, the processing circuitry 50 can calculate the upward drift parameter as a nominal upward drift value scaled by different multipliers. For example, the upward drift multiplier for day 61 to day 120 can be a positive fractional value (e.g., positive 2.5). For example, in some instances, the upward drift parameter for day 61 to day 120 can be 0.45, which is the nominal value of 0.18 multiplied by 2.5. From day 61 to day 120, the downward drift multiplier can be a positive fractional value (e.g., positive 0.5), which would result in a downward drift parameter of 0.025. In some instances, the cutoff point for the days may differ. For example, in some instances, the cutoff may be day 61 to day 100 instead of day 120, where day 120 is used only as a baseline for certain instances. In any case, when determining the reference impedance value within the first 60 days, the processing circuit system 50 may utilize a first upward drift parameter and a first downward drift parameter within the first 60 days of implantation, and when determining the reference impedance value within the first 100 days or 120 days of implantation, the processing circuit system may utilize a second upward drift parameter and a second downward drift parameter within the first 100 days or 120 days of implantation.

[0127] Therefore, the processing circuit system 50 can identify a first fluid index calculation to determine at least a first subset of one or more fluid index values ​​and identify a second fluid index calculation to determine at least a second subset of one or more fluid index values. As discussed herein, the identification of which calculation is used is based at least in part on the number of days the fluid index value has been greater than zero. Thus, for this fluid index calculation, day 61 indicates that the fluid index value has been greater than zero for 61 consecutive days.

[0128] Although described below as being performed by processing circuitry system 50, these techniques can be performed by any one or more of IMD 10, external device 12, or server 94, for example, by the processing circuitry system of any one or more of these devices. In some instances, the processing circuitry system, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can determine a reference impedance value according to the techniques described in U.S. Applications No. 12 / 184,149 and No. 12 / 184,003 (both filed July 31, 2008) entitled “Using multiple diagnostic parameters for predicting heart failure events” and “Detecting worsening heart failure based on impedance measurements” by Sarkar et al.

[0129] Still referencing Figure 6 Processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can compare a second impedance value with a reference impedance value (116). For example, processing circuitry system 50 can use a comparator to determine whether the second impedance value is greater than, less than, or equal to the reference impedance value. An example visual depiction of impedance value comparison is shown in... Figure 9 The following is an illustration and will be discussed in further detail below. In some instances, the processing circuitry 50 can determine the difference between a reference value and a second impedance value. In an instance where the second impedance value represents a daily average, the processing circuitry 50 can compare the daily average with a reference value.

[0130] In some instances, the processing circuitry 50 can identify a resolution parameter for determining at least one of the following: a first tissue impedance value, a reference impedance value, and a second tissue impedance value. For example, the processing circuitry 50 can identify the resolution parameter for impedance measurement as performing impedance measurements at a specified IMD 10 per hour, or in other instances, the processing circuitry 50 can average impedance measurements performed within a day into a single impedance measurement. In some instances, the resolution parameter can be implemented using filters based on time constraints or activity levels.

[0131] For example, processing circuitry 50 can derive a single daily impedance measurement result from impedance measurements performed only during the day, only at night, or in sub-time periods within a 24-hour period. Furthermore, processing circuitry 50 can calculate an overall daily measurement result using only impedance measurements captured during periods of low activity. In some instances, when determining a first or second tissue impedance value, processing circuitry systems, such as processing circuitry 50 of IMD 10, processing circuitry 80 of external device 12, or processing circuitry 98 of server 94, can exclude a subset of tissue impedance signals from the subcutaneous tissue impedance signal based on resolution parameters or appropriate filters.

[0132] In some instances, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can determine one or more sub-time periods corresponding to a first time period or a second time period. For example, processing circuitry system 50 can identify the resolution parameter as a measurement specifying 10 seconds per hour. In other instances, processing circuitry system 50 can identify the resolution parameter as a measurement specifying a period of low activity counts, where all hourly measurements with low activity counts are averaged to determine the daily impedance value over a 24-hour period. Therefore, processing circuitry system 50 can apply a filter to the subcutaneous tissue impedance signal based on the sub-time period specified by the filter. It should be noted that although described as being performed by processing circuitry system 50, the resolution parameter and filtering techniques can be performed by any one or more of IMD 10, external device 12, or server 94, for example, by the processing circuitry systems of any one or more of these devices.

[0133] In some instances, the patient's body position can alter the impedance measurement results. For example, when the patient changes position, electrode 16 can move within the subcutaneous space 22. In such instances, the processing circuitry 50 can use resolution parameters or filters to reject impedance values ​​associated with impedance changes due to the patient's body position. In some instances, the processing circuitry 50 can ignore or reject certain subcutaneous tissue impedance signals based on specific changes in body position. In another instance, the processing circuitry 50 can reset the reference impedance based on the new body position. In any case, the body position filter can be programmed by a user (e.g., a physician). For example, the processing circuitry 50 can receive body position filter parameters indicating that the impedance score will be based on subcutaneous tissue impedance values ​​received during periods such as when the patient is lying down or standing upright.

[0134] In some instances, the processing circuitry system 50 may determine, based on the patient 4's position, not to classify the patient 4's heart or health status for a period of time. For example, the processing circuitry system 50 may determine whether the patient 4 is standing upright or lying down, and therefore, when the patient 4 is in a particular position, it may refrain from classifying the patient 4's health status. In some instances, the specific position may be programmable by the user.

[0135] In some instances, the resolution parameter or filter can be based on the processing circuitry system 50 that identifies the orientation of the IMD 10. For example, the processing circuitry system 50 or the impedance measurement circuitry system 60 can be configured to obtain impedance measurements when the patient 4 has a specific posture that causes the IMD 10 to orient in a particular direction. The processing circuitry system 50 can use one of the sensors 62, such as a 3-axis accelerometer, to determine the orientation of the IMD 10. In such instances, the processing circuitry system 50 can be configured to obtain impedance measurements when the patient 4 is in a desired position. For example, the processing circuitry system 50 can be configured to obtain impedance measurements when the patient 4 is lying down, such that the accelerometer value of the IMD 10 indicates that the patient 4 is lying down.

[0136] In one instance, a processing circuitry system, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can identify one or more accelerometer values ​​from one or more accelerometers corresponding to IMD 10 and / or another medical device (such as a wearable medical device with an accelerometer). In some cases, processing circuitry system 50 can determine that accelerometer values ​​from one or more accelerometer values ​​satisfy an orientation threshold. For example, processing circuitry system 50 can set an orientation threshold such that the threshold is satisfied when the orientation of IMD 10 indicates that patient 4 is upright, lying down, tilted, or lying face down. For example, processing circuitry system 50 can initialize IMD 10 with a specific orientation relative to patient 4 and a reference plane (such as the ground plane). Thus, accelerometer data can indicate the orientation of patient 4. In some instances, processing circuitry system 50 can determine that a relative change in one or more accelerometer values ​​indicates the orientation of patient 4 that satisfies an orientation threshold. Therefore, a single accelerometer value can be based on multiple accelerometer values ​​to indicate the relative change in orientation of IMD 10 and / or patient 4.

[0137] In some instances, the processing circuitry system 50 can determine that the accelerometer value meets an orientation threshold. In such instances, the processing circuitry system 50 can determine the tissue impedance value based at least in part on this determination that the accelerometer value meets the orientation threshold. For example, the processing circuitry system 50 can control the impedance measurement circuitry system 60 to perform an impedance measurement in response to determining that the accelerometer value indicates the desired orientation of the patient 4 for performing the impedance measurement.

[0138] In another example, the processing circuitry 50 can be configured to apply a delay period between impedance measurements after the processing circuitry 50 has detected that the IMD 10 is correctly oriented and / or the patient 4 is in the desired position. In a non-limiting example, the processing circuitry 50 can apply a 30-minute or one-hour delay after the processing circuitry 50 detects that the patient 4 has lain down, to allow time for the fluid in the patient 4 to redistribute after the position change.

[0139] In some instances, the processing circuitry system 50 may use filters or resolution parameters with different night / day thresholds, different location thresholds, orientation thresholds, or different activity level thresholds. For example, the processing circuitry system 50 may ignore certain impedance measurements taken during periods when the patient 4's activity level exceeds an activity level threshold, such as when the processing circuitry system 50 or another sensor device connected to the IMD 10 indicates a specific activity level of the patient 4. In another instance, the processing circuitry system 50 may determine that the IMD 10 meets a predefined orientation threshold. For example, the predefined orientation threshold may be based on orientation indicating that the patient 4 is in a desired location for impedance measurement. In response to the IMD 10 meeting the predetermined orientation threshold, the processing circuitry system 50 may determine one or more tissue impedance values. For example, the processing circuitry system 50 may determine a tissue impedance value by causing the impedance measurement circuitry system 60 to perform an impedance measurement.

[0140] The processing circuitry system 50 of IMD 10, the processing circuitry system 80 of external device 12, or the processing circuitry system 98 of server 94 can then determine the fluid index of patient 4 at least in part based on comparison (117). In some instances, IMD 10 can determine the fluid index value according to the techniques described in U.S. Applications No. 12 / 184,149 and No. 12 / 184,003 (both filed July 31, 2008) entitled “Using multiple diagnostic parameters for predicting heart failure events” and “Detecting worsening heart failure based on impedance measurements” by Sarkar et al. For example, as described and applicable, IMD 10 can transmit various input data to external device 12 and / or server 94, where external device 12 and / or server 94 determines the fluid index of patient 4 on any given date. In such an example, external device 12 or server 94 can output the fluid index value to a storage location (e.g., storage device 96) or return it to IMD 10, such that processing circuitry 50 can store the fluid index value in storage device 56.

[0141] In some cases, at least three forms of impedance reduction have been observed in patients. The first form of impedance reduction represents a gradual and sustained decrease in impedance over a longer period of time. This type of impedance reduction lasts for more than a month. This type of impedance reduction is closely associated with worsening heart failure.

[0142] The second form of impedance reduction is characterized by a sudden drop in impedance, followed by a tendency for impedance to increase back to baseline. Such events may be caused by changes in patient compliance, such as medication or dietary indiscretions, or by acute decompensation that may lead to medical intervention. Therefore, some of these crossovers may be critical, while others may be less so.

[0143] A third form of impedance reduction is caused by small DC shifts in the impedance. Since these small shifts can occur multiple times, they can eventually lead to a threshold crossover if the fluid index accumulates over a long period. For example, a sustained impedance shift of even two or three ohms can cause a crossover if it persists long enough. The standard deviation of diurnal impedance variation has been observed to be approximately three ohms. Therefore, this type of impedance reduction is not clinically significant, but it can lead to false alarms if the treatment technique is poorly designed.

[0144] Another notable characteristic of the implantation procedure is the trend in patient impedance. This is that daily impedance increases in the months following implantation, and the rate of increase slows over time as daily impedance approaches baseline. This phenomenon is thought to be due to the drying of the device pouch and the encapsulation of the leads after implantation. In other words, because the device pouch is immediately filled with fluid after implantation, the measured impedance is relatively low because the fluid's resistance is less than that of body tissue. However, as the fluid dissipates over time, resistance increases and the rate of fluid dissipation decreases over time. This can result in daily impedance often being higher than the reference impedance in the initial months after implantation. Consequently, the fluid index may be less sensitive to the actual decrease in daily impedance. This is undesirable.

[0145] IMD 10, such as processing circuit system 50, can address these issues through adaptive processing techniques. Adaptive processing techniques can limit small-amplitude deviations in the measured impedance from the fluid index threshold crossover, limit the increase in the fluid index as the daily impedance recovers or increases towards the baseline value, and allow the rate of change of the reference impedance value to vary over time.

[0146] In one example, processing circuitry system 50 can calculate a fluid index based on the variability of measured impedance values. Specifically, system 2 can determine the fluid index in a manner that mitigates the accumulation of impedance reduction when significant variability exists daily. Processing circuitry system 50 can also assign greater weight to variability based on the time elapsed since implantation or a previously detected event.

[0147] In an additional example, processing circuit system 50 can calculate the fluid index by accumulating the fluid index over a finite time period using a finite number of differences between the measured impedance and the reference impedance. That is, system 2 can use a sliding window technique to calculate the fluid index. This technique can prevent the fluid index from accumulating to alarm conditions when the baseline impedance attempts to "catch up" with the baseline offset in the measured impedance.

[0148] In another instance, the processing circuit system 50 can calculate the fluid index over time by taking into account time-related values. In this way, the time-related values ​​can be used to increase the value of the fluid index after the measured impedance has been below a reference impedance for a threshold duration (e.g., one month), which can indicate a significant clinical deterioration in the patient's condition.

[0149] In some instances, the processing circuit system 50 may consider the following factors when determining the fluid index value: variability, limited memory, duration, and reference slope adjustment as discussed herein. The variability consideration typically refers to the fact that the IMD 10 accumulates the fluid index value less frequently in patients with high diurnal variability in impedance measurements. The limited memory consideration typically refers to the fact that the IMD 10 accumulates the fluid index value over a limited time period, rather than from the start of an impedance drop (e.g., a fluid index event) until the end of the fluid index event (e.g., when a second impedance value is higher than a reference value). The duration consideration typically refers to the fact that the IMD 10 accumulates the impedance value over a prolonged impedance drop. Techniques used to illustrate these considerations in calculating the fluid index are referenced herein, for example, to [reference needed]. Figure 8 This will be discussed. Although some techniques herein are described as being performed by the processing circuitry system 50, the techniques disclosed herein are not limited thereto, and these techniques may be performed by any one or more of the IMD 10, external device 12, or server 94, for example, by the processing circuitry system of any one or more of these devices.

[0150] Still referencing Figure 6 Processing circuit systems, such as processing circuit system 50 of IMD 10, processing circuit system 80 of external device 12, or processing circuit system 98 of server 94, can use fluid index values ​​to determine impedance scores (118). For example, processing circuit system 50 can determine the impedance score from an absolute impedance value or from a daily average impedance value. In some instances, processing circuit system 50 calculates the fluid index value as the sum of the differences between a reference impedance value and daily impedance values. In some instances, the impedance score can be based on a daily average or an absolute impedance value. For example, if the fluid index value is zero on a given date, the impedance score can be increased based on the absolute impedance value for that day or based on the daily average impedance value. In any case, processing circuit system 50 can use absolute impedance (e.g., average impedance) to determine the impedance score and the fluid index value, where the fluid index for that day is a non-zero value.

[0151] In some instances, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can initialize the impedance score with an initial starting value. In some instances, processing circuitry system 50 can set the initial starting value to a baseline value of zero (e.g., impedance score = 0). In other instances, processing circuitry system 50 can initialize the impedance score with a non-zero value. For example, processing circuitry system 50 can receive a command from an external server that the impedance score should be initialized with an initial value of 1 to bias the impedance score. This can be done based on the patient's history or whether IMD 10 is a replacement for a previous IMD 10 that has already increased the impedance score above zero.

[0152] In some instances, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can increase the impedance score based on triggering events indicative of subcutaneous tissue impedance events in patient 4. In some instances, processing circuitry system 50 can increase the impedance score by a first value in response to one or more triggering events from a first set. Processing circuitry system 50 can increase the impedance score by a second value in response to one or more triggering events from a second set. In some instances, the first value can increase the impedance score by one point. In some instances, the second value can increase the impedance score by two points. Other point values ​​greater than or less than the first or second value can be used.

[0153] In some instances, the processing circuitry 50 can detect multiple trigger events during a single iteration of the scoring cycle, in which case the sum of the values ​​can be applied to the impedance score. In one instance, when the processing circuitry 50 determines the presence of two trigger events, it can increase the impedance score by four points, where one trigger event corresponds to a two-point increment and the other also corresponds to a two-point increment. In some instances, the processing circuitry 50 can determine the total impedance score between the low-end value 0 and the high-end value 7, as discussed below. Reference Figure 7 The techniques used to determine impedance scores are further discussed.

[0154] In some instances, the processing circuitry 50 can reduce or reset the impedance score when certain other predefined conditions are met. In one instance, the processing circuitry 50 can determine that the subcutaneous impedance is higher than a reference impedance value. In this case, the processing circuitry 50 can determine the occurrence of a dryness index event, which is the opposite of a fluid index event. In some instances, when the subcutaneous impedance is higher than the reference impedance value, the processing circuitry 50 can determine the dryness index value by accumulating the difference between the subcutaneous impedance and the reference impedance value. Therefore, according to one or more techniques disclosed herein, similar to how a higher fluid index value can increase the impedance score, a higher dryness index value can decrease the impedance score.

[0155] In some instances, the processing circuitry system 50 can determine the cardiac condition status of patient 4 based on an impedance score (119). For example, the processing circuitry system 50 can periodically compare the impedance score to one or more risk thresholds. In some instances, the processing circuitry system 50 can perform the impedance score versus risk threshold comparison at the same time each day (e.g., at the end of the day). In another instance, the processing circuitry system 50 can determine the cardiac or health condition status of patient 4 at multiple intervals each day. In yet another instance, the processing circuitry system 50 can determine the cardiac or health condition status of patient 4 at even longer intervals, such as once a week or once every two weeks. The intervals can be determined based on certain cardiac risk factors of patient 4.

[0156] In some instances, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can determine cardiac condition status as a heart failure risk status. For example, processing circuitry system 50 can use risk status categories such as low, moderate, and high. In some instances, processing circuitry system 50 can use different numbers of risk categories, such as including categories that are very high risk (in some cases) or very low risk. Alternatively, processing circuitry system 50 may exclude certain categories, such as the moderate risk category, and instead monitor only the low and high risk categories. In some instances, processing circuitry system 50 can compare impedance scores to risk thresholds to determine cardiac condition status.

[0157] In non-limiting examples, processing circuit systems, such as processing circuit system 50 of IMD 10, processing circuit system 80 of external device 12, or processing circuit system 98 of server 94, may use different numbers of risk categories. In one example, processing circuit system 50 may determine risk levels as follows: low risk if the impedance score is 0, medium risk if the impedance score is greater than or equal to 1 but less than or equal to 6, and high risk if the impedance score is greater than or equal to 7. Risk thresholds may be set based on optimization considerations (e.g., user-programmable settings) and may be based on specific values ​​used to determine the fluid index. For example, various different constants may be used to determine reference impedance values ​​that would result in a medium risk corresponding to an impedance score between 1 and 5 or a high risk corresponding to an impedance score greater than or equal to 6 (e.g., different values ​​of upward and downward drift parameters, etc.). In any case, IMD 10 will use the same algorithmic techniques to determine the fluid index value, impedance score, and risk category, regardless of the user-programmable constants. In some cases, the user may use a user interface to set the user-programmable constants. For example, users may be able to set what impedance scores constitute high risk, medium risk, and low risk.

[0158] Based on impedance scores, the IMD 10 can determine the state level of one or more health conditions, such as edema, preeclampsia, hypertension, etc. In such instances, the IMD 10 can identify various risk thresholds for each health monitoring condition. For example, the risk threshold for decompensated heart failure may differ from that for other heart-related conditions. In some cases, the number of risk categories may also differ. For example, the IMD 10 can identify high and low risk levels for preeclampsia, which may correspond to different variable risk thresholds at different stages of pregnancy. In any case, the impedance score can indicate conditions that appear to alter the level of impedance within the subcutaneous space 22 prior to warranting medical intervention.

[0159] In some instances, the IMD 10 can utilize impedance measurements to determine the respiratory rate (RR) of patient 4. For example, subcutaneous tissue impedance values ​​may contain low-frequency fluctuations corresponding to RR. Subcutaneous impedance is sensitive to the conductivity of the fluid surrounding electrode 16. With each inhalation, the intrathoracic pressure decreases, increasing pulmonary blood volume. This increase in pulmonary blood volume tends to lead to a decrease in pulmonary artery pressure. A decrease in pulmonary artery pressure tends to lead to a decrease in right artery pressure and increased venous return. This may result in a reduction in extracellular / vascular extracellular volume, thus leading to an increase in impedance. The reverse sequence of events leads to a decrease in expiratory impedance. In another instance, movement of the chest wall of patient 4 may also cause changes in the measured impedance. In some instances, the IMD 10 can determine the respiratory rate (RR) according to U.S. Application No. 16 / 450,250, entitled “Sensing Respiration Parameters Based on an Impedance Signal,” filed June 24, 2019, by Sarkar et al.

[0160] IMD 10 can be used to determine, on any given date, the risk of heart failure (HF) in patient 4 based on subcutaneous impedance. Risk categories can also indicate the risk level for various heart-related conditions that may include subcategories of HF (e.g., valvular heart failure, cardiac arrest, etc.) or other organ complications such as lung, liver, or kidney failure.

[0161] Despite regarding the execution reference Figure 6-9The IMD 10 describes one or more of the various example techniques described, but it should be understood that any number of different components of System 2 and their combinations can perform the disclosed techniques. For example, IMD 10 can transmit raw impedance data to external device 12, where external device 12 can determine a first impedance value, a second impedance value, a reference impedance value, a fluid index value, etc. In some instances, external device 12 may include multiple computing devices (e.g., a remote cloud server) that collectively determine the cardiac condition of patient 4. Furthermore, it should be understood that components of System 2 (e.g., processing circuit system 50, impedance measurement circuit system 60, processing circuit system 80, etc.) can perform reference measurements in parallel or in combination. Figure 6-9 Some or all of the techniques described in the example techniques.

[0162] It should be noted that, for reference Figure 7 The described example techniques can also be performed periodically. For example, a health or cardiac condition status can be determined based on the resolution parameters set for the IMD 10 (e.g., resolution parameters used to represent the frequency at which the electrode 16 should detect impedance measurements). In other instances, a health or cardiac condition status can be calculated without considering the resolution parameters, which may be applied, for example, to the determination of fluid indices, impedance scores, impedance detection frequencies, and / or reference impedance values, but not to the determination of a health or cardiac condition status. For example, the IMD 10 can calculate a health or cardiac condition status daily at several time intervals (e.g., once in the morning, once in the afternoon, once in the evening, once after meals, etc.). The IMD 10 can calculate a health or cardiac condition status daily, weekly, bi-weekly, monthly, etc.

[0163] In some instances, IMD 10 may also calculate a health or cardiac status in response to a user command (e.g., from a physician, from a user interface) or in response to the fulfillment of another condition, such as upon receiving or determining a new impedance score or a modification to the impedance score. IMD 10 may also trigger a health or cardiac status calculation when activity level or other physiological parameters meet a threshold (e.g., low activity when patient 4 is resting or sleeping). In another instance, IMD 10 may determine patient 4's health or cardiac status on a per-measurement basis, such as on a per-fluid index determination or on a per-impedance measurement. Those skilled in the art will understand that when IMD 10 or external device 12 can... Figure 6 There may be various time periods involved in determining, transmitting, and receiving health or heart condition statuses.

[0164] Figure 7This is a flowchart illustrating an example method for determining an impedance score. In some cases, the processing circuitry system 50 can determine the impedance score of patient 4. The processing circuitry system 50 can determine the impedance score periodically at various intervals. In some instances, the processing circuitry system 50 can determine the impedance score in response to a user's request for the current impedance score. In some instances, an external device 12 can determine the impedance score of patient 4. For brevity, refer to... Figure 3 The IMD 10 and its components are described in this document to illustrate certain techniques. However, those skilled in the art will understand that in some instances, the external device 12 and its components may utilize input from the IMD 10 to determine impedance scores. In some instances, the server 94 (e.g., a cloud server) may receive data from the external device 12 or directly from the IMD 10 and perform certain techniques of this disclosure.

[0165] refer to Figure 7 The processing circuitry system 50 can determine an adaptive threshold (120). The adaptive threshold incorporates various attributes of the patient 4 and a threshold that determines the time-varying nature of the adaptive threshold. As described above, in some instances, a device, such as external device 12, can determine the adaptive threshold and transmit it to another device, such as IMD 10. In such instances, the processing circuitry system 50 can determine the adaptive threshold received from external device 12 to determine an impedance score.

[0166] In some instances, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can use formulas that take into account statistics of the detected impedance signal changing over time to determine an adaptive threshold. In some instances, the formula chosen for calculating the adaptive threshold produces a threshold proportional to the absolute impedance value and the intraday variation of the impedance. For example, the formula may take into account the median and / or average (e.g., statistical representation) of the impedance signal received from electrode 16.

[0167] In illustrative and non-limiting examples, the processing circuitry system 50 can determine the adaptive threshold for any given date as the sum of (a) the average impedance value over the most recent X days and {(b1) the average difference between the maximum and minimum impedance values ​​tracked over the most recent X days, or (b2) the average or median day-to-day impedance difference}. In some examples, the processing circuitry system 50 can select between (b1 / 2) components such that the selection between (b1 / 2) components is based on achieving greater variability in the data while simultaneously reducing patient recovery time. In the examples above, X can be 7 days, 10 days, 30 days, 40 days, etc. In some examples, the processing circuitry system 50 can receive user input specifying the adaptive threshold. In other words, the adaptive threshold can be programmed by the user.

[0168] In some instances, the processing circuitry system 50 may determine the statistical representation by referring to the time since implantation or the time since the fluid index value became greater than zero (e.g., the first fluid index event). In some instances, the processing circuitry system 50 may determine the average of the daily impedance values ​​based on all impedance values ​​received during the course of a day or a subset of all impedance values. The processing circuitry system 50 may then calculate the median of the daily averages over a predetermined time period, such as within X days of the first fluid index event, within X days of implantation, or within the most recent X days, where X can be a predetermined number of days. In a non-limiting example, X may be selected as 30 days or 31 days. For example, the processing circuitry system 50 may determine the median of 30 daily averages determined within the most recent 30 days, starting from the current date or from another date of interest.

[0169] In one instance, the adaptive threshold formula may also consider the median difference between the maximum and minimum impedance values ​​measured within X days post-implantation, within X days of the first fluid index event, or within the most recent X days from the current date or from another date of interest. In a non-limiting instance, X may be chosen as 30 days or 31 days. For example, the formula may calculate a range between the maximum and minimum impedance values ​​each day and determine the median of that range over a predetermined time period. In some instances, the range of maximum and minimum impedance values ​​may include the difference between the maximum impedance value measured within a predetermined time period (e.g., the most recent 30 days) and the minimum impedance value measured within the same time period (e.g., the most recent 30 days). In other instances, the range may include the difference between the daily maximum impedance value and the daily minimum impedance value. In such instances, the adaptive threshold formula may consider the median of the range of impedance values ​​measured over a predetermined time period. For example, the adaptive threshold formula may use the median of the daily maximum and daily minimum impedance values ​​measured within the most recent 30 or 31 days. Therefore, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can determine the adaptive threshold at least in part based on the median of the difference between one or more maximum tissue impedance values ​​and one or more minimum tissue impedance values.

[0170] In one instance, the adaptive threshold can be based on a combination of the considerations discussed above. For example, the adaptive threshold can be based on the sum of the calculated median of the average impedance over the most recent 30 or 31 days and the median of the difference (or range) between the daily maximum and daily minimum impedance values ​​measured over the most recent 30 or 31 days. In other words, the two medians of each part of the equation can be added together to determine the adaptive threshold.

[0171] Still referencing Figure 7 Processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can determine fluid index values ​​and average impedance values ​​(122) within a first time period. The first time period can be measured from the current date (e.g., within 10 days of today) or from another time of interest (e.g., from 5 p.m. of the previous day, etc.). For example, processing circuitry system 50 can determine multiple fluid index values ​​within the most recent X days, starting from the current date or from another time of interest. In such instances, processing circuitry system 50 can determine at least one of the average impedance values ​​and one or more fluid index values ​​of one or more subcutaneous tissue impedance signals measured over a period of time, based at least in part on one or more reference impedance values ​​and at least one second tissue impedance value.

[0172] In some instances, the processing circuit system 50 can also determine multiple average impedance values ​​over the most recent X days. In some instances, the first time period can be set to include the most recent 30 days. In some instances, the processing circuit system 50 can determine the average impedance value based on at least a subset of the first organizational impedance values. For example, the processing circuit system 50 can determine the impedance values ​​for day 1, day 2, and through day 30 to determine the average impedance values ​​for days 1-30.

[0173] Similarly, the processing circuitry 50 can determine the fluid index value and the average impedance value (124) within a second time period. The second time period may encompass a shorter period than the first time period. For example, the first time period may include the most recent 30 days, while the second time period may include the most recent 7 days. Although described as being performed by the processing circuitry 50, the fluid index value can be determined by any one or more of the IMD 10, the external device 12, or the server 94, for example, by the processing circuitry of any one or more of these devices.

[0174] Still referencing Figure 7 The processing circuitry 50 can determine a weighting factor (126) for the adaptive threshold. In some embodiments, the weighting factor can be a value between 0.1 and 4.5. In other instances, the weighting factor can be greater than or less than this general range, for example, depending on the specific formula used to calculate the adaptive threshold. The IMD 10 can use the weighting factor to scale the adaptive threshold to determine one or more scoring thresholds based on the type of comparison being performed. Thus, the scoring threshold contains an adaptive threshold scaled by one or more weighting factors. For example, the IMD 10 can multiply the adaptive threshold by different weighting factors before comparing the fluid index value with the adaptive threshold. In some instances, the weighting factor and adaptive threshold can be used only for the fluid index value, while the average impedance value can be compared with different thresholds that do not depend on the weighting factor.

[0175] On a given date, when the fluid index value during the first time period meets an adaptive threshold multiplied by the corresponding weighting factor, the processing circuit system 50 can redetermine or modify the impedance score (128). Additionally, when the average impedance meets an impedance threshold during the first time period, the processing circuit system 50 can redetermine or modify the impedance score.

[0176] In some instances, the processing circuitry 50 can modify the impedance score by increasing it by a set value. For example, the processing circuitry 50 can modify the impedance score by adding a positive integer value to it. In a non-limiting instance, the processing circuitry 50 can modify the impedance score by adding the value 1 to it in response to some triggering event. The processing circuitry 50 can redetermine the impedance score if it has already reset it to zero or if it has not yet increased it by any amount.

[0177] In some instances, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can determine the satisfaction of at least one of the following with respect to one or more time windows: a scoring threshold and an impedance threshold. For example, processing circuitry system 50 modifies the impedance score in response to one or more fluid index values ​​satisfying one or more scoring thresholds in at least one of the following: a predetermined amount of time and a predetermined number of time periods (e.g., days, etc.). In an illustrative example, processing circuitry system 50 can increase the impedance score by one point (e.g., 1 point) in response to the following example conditions (e.g., scoring thresholds) being met with respect to a first time period: (1) the fluid index value for the most recent 30 days is greater than or equal to an adaptive threshold (multiplied by 0.6) for one or more days; (2) the fluid index value for the most recent 30 days is greater than or equal to an adaptive threshold (multiplied by 1.7) for one or more days; or (3) the fluid index value for the most recent 30 days is greater than or equal to an adaptive threshold (multiplied by 3.2) for one or more days. In this example, the processing circuit system 50 determines the weighting factors to be 0.6, 1.7, and 3.2. In this example, the first time period is the most recent 30 days. However, as discussed herein, for example, the time period and weighting factors can vary depending on the specific circumstances associated with patient 4.

[0178] In another instance, the processing circuitry 50 may also increase the impedance score by a point value greater than one (e.g., two points) in response to the average impedance meeting an impedance value threshold and the fluid index meeting various scoring thresholds. In some instances, the processing circuitry 50 may modify the impedance score in response to the average impedance value meeting an impedance value threshold. In some instances, the impedance value threshold may be less than or equal to approximately 600 ohms or another comparable ohmic value. In any case, the impedance value threshold may be a user-defined variable.

[0179] For example, the processing circuit system 50 may increase the impedance score by two points in response to the following example conditions (e.g., a scoring threshold and an impedance value threshold) being met with respect to a first time period: (1) the fluid index value over the most recent 30 days is greater than or equal to an adaptive threshold (multiplied by 1.5) for 24 or more days; or (2) the average impedance over the most recent 30 days is less than or equal to approximately 600 ohms. In the first case, 24 or more days can be a consecutive number of days or a cumulative 24 days. For the average impedance, the average impedance over the most recent 30 days may refer to the set of daily average impedances over the most recent 30 days. In other instances, the average impedance over the most recent 30 days may refer to a single average of impedance values ​​measured over time. In other instances, the average impedance may refer to a single average of daily average impedance values ​​determined over time. In any case, the average impedance value may be the average of some impedance values ​​measured by the IMD 10 over time. For example, the average may be based on at least two impedance values ​​measured by the IMD 10. In some instances, the at least two impedance values ​​may include one or more current impedance values ​​and / or one or more historical impedance values.

[0180] In some instances, the processing circuit system 50 can redetermine or modify the impedance score (130) when the fluid index value during the second time period meets an adaptive threshold multiplied by the corresponding weighting factor. Additionally, the processing circuit system 50 can redetermine or modify the impedance score when the average impedance meets an impedance threshold during the second time period.

[0181] In an illustrative example, the processing circuit system 50 may increase the impedance score by a point value equal to one in response to the following example conditions being met for a second time period: (1) the fluid index value for the most recent seven days is greater than or equal to the adaptive threshold (multiplied by 0.6) for one or more days; (2) the fluid index value for the most recent seven days is greater than or equal to the adaptive threshold (multiplied by 1.7) for one or more days; or (3) the fluid index value for the most recent seven days is greater than or equal to the adaptive threshold (multiplied by 1.5) for seven or more days. In this example, the processing circuit system 50 determines the weighting factors to be 0.6, 1.7, and 1.5. In this example, the second time period is the most recent seven days. However, as discussed herein, for example, the time period and weighting factors may vary depending on the specific circumstances associated with patient 4. Additionally, for the last condition, seven or more days may be consecutive days or cumulative seven days.

[0182] In another instance, the processing circuit system 50 may increase the impedance score by a point value greater than one (e.g., two points) in response to other example conditions being met with respect to a second time period: (1) the fluid index value for the most recent seven days is greater than or equal to an adaptive threshold (multiplied by 3.2) for one or more days; or (2) the average impedance for the most recent seven days is less than or equal to approximately 600 ohms. For the average impedance, the average impedance for the most recent seven days may refer to the set of daily average impedances for the most recent seven days. In other instances, the average impedance for the most recent seven days may refer to a single average of impedance values ​​measured over time. In other instances, the average impedance may refer to a single average of daily average impedance values ​​determined over time.

[0183] In some instances, where conditions overlap, only the higher point value is added to the impedance score to avoid any compounding effect on the modification of the impedance score. Consistent with the examples above, if both conditions are met (e.g., the average impedance over the last 7 days and the last 30 days is greater than or equal to approximately 600 ohms), the impedance score can only increase by two, not four. In other instances, if both conditions are met (e.g., the average impedance over the last 7 days and the last 30 days is greater than or equal to approximately 600 ohms), the processing circuit system 50 can increase the impedance score based on the satisfaction of both conditions.

[0184] Once the impedance score for a given date has been calculated, a processing circuitry, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can output the impedance score for further analysis (132). In one instance, processing circuitry system 50 of IMD 10 can output the impedance score to storage device 56. In other instances, processing circuitry system 50 can output the impedance score to external device 12 via communication circuitry system 54. In an instance where external device 12 calculates the impedance score, external device 12 can output the impedance score from processing circuitry system 80 to storage device 84. In some instances, external device 12 can output the impedance score to another device, such as one of IMD 10, computing device 100, or server 94, for further analysis. In an instance where server 94 calculates the impedance score, processing circuitry system 98 can output the impedance score from processing circuitry system 98 to storage device 96. In some instances, server 94 can output the impedance score to another device, such as IMD 10, computing device 100, or external device 12, for further analysis. For example, the impedance score can be used to determine the cardiac or health status of patient 4, such as... Figure 6 As described in [the text].

[0185] As previously mentioned Figure 6 As indicated, for reference Figure 7One or more of the various example techniques described can also be performed periodically. For example, the impedance score can be determined based on the resolution parameter settings of the IMD 10 (e.g., a resolution parameter used to represent the frequency at which the electrode 16 should detect impedance measurements). In other instances, the impedance score can be calculated without considering the resolution parameter, which may be used, for example, to determine the fluid index and / or the reference impedance value, but not to determine the impedance score. For example, the IMD 10 can calculate the impedance score daily at several time intervals (e.g., once in the morning, once in the afternoon, once in the evening, once after dinner, etc.). The IMD 10 can calculate the impedance score daily, weekly, bi-weekly, monthly, etc.

[0186] In some instances, IMD 10 may calculate an impedance score in response to a user command (e.g., from a physician, from a user interface) or in response to the fulfillment of another condition (e.g., based on activity level or other physiological parameters). For example, IMD 10 may determine the impedance score on a per-measurement basis, such as on a per-fluid index determination or on a per-impedance measurement basis. Those skilled in the art will understand that when IMD 10 or external device 12 can transmit, receive, or otherwise calculate the impedance score for subsequent analysis, there may be various time intervals.

[0187] Turn now Figure 8 , Figure 8 This is a flowchart illustrating an example method for determining a fluid index value. IMD 10 can determine the fluid index value using an impedance signal received from electrode 16. In some instances, IMD 10 can determine the fluid index value based on U.S. Applications Nos. 12 / 184,149 and 12 / 184,003 (both filed July 31, 2008) entitled “Using multiple diagnostic parameters for predicting heart failure events” and “Detecting worsening heart failure based on impedance measurements” by Sarkar et al. Although described as being performed by IMD 10, references... Figure 8 One or more of the various example technologies described may be executed by any one or more of the IMD 10, external device 12, or server 94, for example, by the processing circuitry system of any one or more of these devices.

[0188] In some instances, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can maintain buffers (140) for impedance values ​​and impedance statistics. For example, processing circuitry system 50 can calculate the fluid index over a finite time period, serving as a sliding window. Processing circuitry system 50 can calculate the fluid index daily over periods of several days, a week, or more. In such instances, processing circuitry system 50 can store a buffer of daily fluid index values ​​as fluid index values ​​in storage device 56. In some instances, the buffer stores previous daily fluid index values. In some instances, processing circuitry system 50 can maintain a buffer, such as a FIFO buffer, for the most recent predetermined number of days. Therefore, processing circuitry system 50 can maintain buffers of one or more subcutaneous tissue impedance signals that change relative to time.

[0189] In some instances, the processing circuitry 50 can perform a comparison of at least one second organizational impedance value with one or more reference impedance values. In some instances, the processing circuitry 50 can store the difference between the reference impedance value and the daily impedance value in a buffer. That is, the processing circuitry 50 can modify the buffer at least partially based on the comparison. In some instances, the buffer can contain the difference over the most recent twelve to fifteen days. For example, a FIFO buffer can contain the inter-day impedance difference over the most recent 12 days. In yet another instance, a FIFO buffer can contain the inter-day impedance difference over the most recent 15 days. The impedance difference refers to the difference from the corresponding reference impedance value.

[0190] In some instances, the processing circuitry, such as processing circuitry 50 of IMD 10, processing circuitry 80 of external device 12, or processing circuitry 98 of server 94, can begin calculating the fluid index after a predetermined number of days have elapsed since implantation of patient 4 from IMD 10. Therefore, processing circuitry 50 can determine whether a predetermined amount of time has elapsed (142) before calculating the fluid index. Until then, processing circuitry 50 can continue adding to the buffer and even after the predetermined number of days. In some cases, the predetermined number of days is 16 days, meaning that processing circuitry 50 may not determine the first reference impedance value until the 16th day after implantation. Therefore, processing circuitry 50 can determine the first fluid index value based on a comparison of the reference impedance value and the daily impedance value. While specific numbers of days (such as 16 days in this example) or ranges of days are used in some instances of this disclosure, the technology of this disclosure is not limited thereto, and other instances may include other suitable ranges or threshold numbers. For example, the processing circuitry 50 can estimate the first reference impedance value on day 6 post-implantation, or in another instance, it can wait longer than 16 days, such as 20 days, before estimating the first reference point. In some instances, the processing circuitry 50 can estimate the first reference impedance value as early as day 13 post-implantation. Figure 9 An example reference impedance value is shown.

[0191] Before a predetermined amount of time has elapsed, the processing circuitry 50 can analyze the change in impedance over time (144) before determining the first fluid index value. For example, the processing circuitry 50 can determine a statistical representation of the impedance value over time. In one instance, the processing circuitry 50 can calculate the difference between the currently measured impedance value and each value in a buffer of previously measured impedance values ​​from each day. Thus, the processing circuitry 50 can determine the median of these differences. This value is referred to as “MED_VAR” and can be stored as a variable value in the storage device 56.

[0192] In some instances, processing circuitry systems, such as processing circuitry system 50 of IMD 10, processing circuitry system 80 of external device 12, or processing circuitry system 98 of server 94, can determine a scaling factor and duration counter (146) for impedance variation over time. For example, processing circuitry system 50 can determine the variability value VAR_VAL based on a final average and impedance values ​​measured daily in the past. Processing circuitry system 50 can calculate the difference between the currently measured impedance value and each value in a buffer of impedance values ​​measured daily in previous days. In some instances, the variability value is time-independent; therefore, MED_VAR = VAR_VAL.

[0193] In some instances, the variability value can be time-dependent. In such instances, the time-dependent value VAR_FRAC can be determined using a piecewise linear function or any other mathematical function (e.g., exponential decay). The variability value can also be the product of the median difference between the daily impedance value (e.g., MED_VAR) stored in the buffer and the time-dependent value (VAR_FRAC), i.e., VAR_VAL = MED_VAR * VAR_FRAC.

[0194] An example piecewise linear function is:

[0195]

[0196] Where “x” represents the time measured in days since the current fluid index event began (e.g., the number of days the fluid index has been greater than 0 or the number of days since the daily average has been less than the daily reference value).

[0197] In some instances, the processing circuitry 50 may utilize a duration counter to track the number of days that have elapsed since the fluid index became greater than zero and store that value in storage device 56. Therefore, the processing circuitry 50 can access the time value from storage device 56 when calculating the variability value.

[0198] In one example, the processing circuitry 50 may implement a duration counter that counts the number of days since the fluid index began to be calculated. For example, the count reading of the duration counter may represent the number of days the fluid index has been above a fluid index threshold. In some examples, the fluid index threshold is zero. In such examples, the count reading of the duration counter may represent the number of days the fluid index has remained positive without being reset. The processing circuitry 50 may use running tally to calculate the duration count. In such examples, the processing circuitry 50 calculates the number of days since a self-measured impedance (or an average value or other value determined based on it) has been less than a reference impedance. When the fluid index is equal to zero, the processing circuitry 50 may reset the duration counter at any time (e.g., reset it to 0). In other examples, the duration counter may increment using a hysteresis function of the fluid index threshold, such that if the fluid index falls below a predetermined value, such as 1 or 2, the duration counter will reset. Alternatively, the duration counter may not begin incrementing until the fluid index is above the predetermined value for a specified amount of time.

[0199] In some instances, the processing circuitry 50 can determine the impedance difference and modify the buffer (148). For example, the processing circuitry 50 determines a reference impedance value associated with a measured impedance value (e.g., a historical impedance value). Specifically, the reference impedance value typically tracks the trend of the measured impedance value. For example, the processing circuitry 50 can calculate the reference impedance value by first retrieving the current impedance value and the reference impedance value (stored as the measured impedance value and the reference impedance value) from the storage device 56 and comparing these values ​​with each other. Because the reference impedance value tracks the measured impedance value, the comparison can be used to determine whether a new or current reference value should be calculated by increasing or decreasing the old or previous reference impedance value. The processing circuitry 50 can store the current reference value and the previous reference value in the storage device 56 as the reference impedance value.

[0200] Typically, the processing circuit system 50 can adjust the rate of change of the reference impedance over time. Specifically, this method allows the reference impedance to increase and decrease at different rates within the same time period, and at different rates over time. As previously described, this is achieved by storing pre-selected or predetermined groups of increment and decrement values. Each group of values ​​corresponds to a specific time period. The increment value of each group serves as a positive slope value, i.e., the value used to increase the reference impedance. The decrement value of each group serves as a negative slope value, i.e., the value used to decrease the reference impedance.

[0201] The processing circuit system 50 can also store multiple increment and decrement values, referred to as slope values, in the storage device 56. Example slope values ​​have been discussed above with reference to the upward and downward drift parameters. The slope values ​​are used to calculate the current reference impedance value based on a previous reference impedance value. Multiple slope values ​​comprise groups of multiple slope values. Each group of slope values ​​corresponds to a time period and includes predetermined increment and decrement values.

[0202] In some instances, the processing circuitry 50 can adjust the incremental and decremental parameters in a piecewise linear manner to accommodate the rapid rise in impedance over the months following implantation.

[0203] The processing circuit system 50 selects a specific group based on time and chooses a first or second slope value from the selected group based on a comparison between the currently measured impedance value and the corresponding reference impedance value. When the currently measured impedance value is greater than the reference impedance value, the processing circuit system 50 selects an increment value from the selected group. Similarly, when the currently measured impedance value is less than the reference impedance value, the processing circuit system 50 selects a decrement value from the selected group.

[0204] The processing circuitry system 50 can, for example, store two sets of slope values. The first set can be used during the first 34–60 days after IMD 10 implantation in patient 4. The second set can be used during the following 61–120 days. These time periods are merely examples, and other time periods and numbers of slope value sets are considered.

[0205] Choosing the slope value in this way allows for more accurate tracking of subcutaneous tissue impedance values ​​because the device bag dries out after IMD10 implantation. This is because fluid buildup in the device bag immediately after implantation causes impedance to be lower than normal. As the fluid dissipates, the impedance increases. The rate of fluid dissipation decreases over time, so it may be desirable for the reference impedance to change at a different rate immediately after implantation compared to after 60, 100, or 120 days. Similarly, it may be desirable to vary the rate at which the reference impedance changes over time.

[0206] When the processing circuitry system 50 determines that a predetermined amount of time has elapsed since implantation, it can calculate a fluid index (142). The processing circuitry system 50 uses measured impedance values ​​and reference impedance values ​​(i.e., a first impedance value and a second impedance value) stored in the storage device 56 to calculate the fluid index. The processing circuitry system 50 can store the calculated values ​​as one or more fluid index values ​​in the storage device 56. As previously described, the fluid index calculation technique can be performed by any one or more of the IMD 10, external device 12, or server 94, for example, by the processing circuitry system of any one or more of these devices.

[0207] For example, when the measured impedance value is less than the reference impedance value, the processing circuit system 50 can calculate the fluid index as a function of the difference between the measured impedance value and the reference impedance value. For example, when the measured impedance value is less than the reference impedance value, the processing circuit system 50 can simply calculate the fluid index as the difference between the measured impedance value and the reference impedance value.

[0208] In some instances, the processing circuitry 50 can determine the fluid index value by summing the buffer values. For example, the total fluid index value is the sum of all daily fluid index values ​​in the FIFO buffer. Because the size of the buffer is constant, the buffer operates as a time-sliding window for determining the fluid index; for example, when the current daily fluid index is added, the most recent value in the buffer is removed.

[0209] In some instances, the processing circuitry 50 can determine that a buffer reset condition has been met. For example, the processing circuitry 50 resets the fluid index buffer when the current impedance is greater than a reference impedance. For example, the processing circuitry 50 can reset the fluid index, i.e., reset the buffer, when the daily measured impedance value is greater than or equal to the reference impedance value. In some instances, the processing circuitry 50 can reset the fluid index, i.e., reset the buffer, when the daily average impedance value (e.g., the average of impedance values ​​measured over a 24-hour period) is greater than or equal to the daily reference impedance value. In any case, the processing circuitry 50 can reset the buffer in response to the meeting of the buffer reset condition.

[0210] The processing circuitry 50 can determine one or more fluid index values, at least in part, based on buffers. For example, the processing circuitry 50 determines the fluid index for any given day as the sum of the FIFO buffer values. In some instances, the processing circuitry 50 can determine time-dependent values ​​and adjust the fluid index values ​​(152). For example, time-dependent values ​​can be added to the fluid index based on the time it remains positive without being reset. The time-dependent values ​​can be increased as a linear, piecewise linear, exponential, or other function of the duration counter.

[0211] In some instances, the time-related value added on any given day is equal to the constant duration parameter multiplied by the duration counter minus 30, where this product can then be multiplied by the downward drift nominal value or another downward drift value. Consistent with the example above, with the downward drift nominal value equal to 0.05 and the constant duration parameter equal to 1.0, the time-related value would be equal to 1.0 multiplied by 0.05 (duration counter minus 30). The processing circuitry 50 can then add the time-related value to the fluid index value.

[0212] In some instances, the processing circuitry 50 can then store the fluid index value in storage device 56 (154). In other instances, the processing circuitry 50 can output the fluid index to external device 12 via communication circuitry 54. In instances where external device 12 calculates the fluid index based on data received from IMD 10, external device 12 can output the fluid index from processing circuitry 50 to storage device 84. In other instances, external device 12 can output the fluid index to another device, such as IMD 10, for further analysis. For example, IMD 10 or external device 12 can use the fluid index value to determine impedance score and / or the cardiac condition status of patient 4, such as... Figure 6 and 7 As described in [the text].

[0213] In some instances, the processing circuitry 50 may reset the reference impedance (156) in response to the identification of a fluid index reset condition. As part of a reference reset protocol, the processing circuitry 50 may reset the reference impedance value at any given time. For example, the processing circuitry 50 may identify a fluid index reset condition that causes at least one reference impedance value to be reset to a baseline value. In some instances, at least one reference impedance value includes the current reference impedance value most recently determined by the processing circuitry 50. In another instance, at least one reference impedance value includes a fluid index value that the processing circuitry 50 is determining, and therefore, while the processing circuitry 50 is performing the determination, it may set one or more reference impedance values ​​to the baseline value.

[0214] In some cases, the baseline value can be zero, causing the fluid index value to reset to zero. In some instances, the baseline value can be non-zero, such as positive or negative. In some instances, the processing circuitry 50 can reset the fluid index value to the baseline value by adjusting the reference impedance value to the reference impedance baseline value. That is, when the processing circuitry 50 performs a comparison between the reference impedance value and the fluid index, the processing circuitry 50 can make one or more reference impedance values ​​less than or equal to the daily average impedance value, causing all or part of the FIFO buffer to be cleared. In one instance, the processing circuitry 50 can adjust the up-drift or down-drift parameters used to calculate the reference slope to make the daily reference impedance value less than or equal to the daily average impedance value, thereby resetting the fluid index value to the baseline fluid index value.

[0215] In some instances, processing circuitry 50 may receive a reset signal indicating that the reference impedance value will be reset to the baseline value via communication circuitry 54. In response to receiving the reset signal, processing circuitry 50 may reset the reference impedance value. In some instances, processing circuitry 50 may receive a manual reset request from a doctor or patient via a user interface (e.g., the user interface of external device 12 or the user interface of one of the computing devices 100). For example, a doctor may determine that a patient has reached a new impedance equilibrium (or normal state) (e.g., after a new medication change). Therefore, the doctor may choose to transmit a manual reset request to a processing circuitry, such as processing circuitry 50 of IMD 10, processing circuitry 80 of external device 12, or processing circuitry 98 of server 94, thereby inducing a fluid index reset condition. In such instances, processing circuitry 50 may receive a manual reset request and identify a fluid index reset condition. In response to receiving a manual reset request, processing circuitry 50 may identify the fluid index reset condition and reset the reference impedance value to the baseline value. For example, the processing circuit system 50 can reset the reference impedance value to zero by clearing the FIFO buffer so that the accumulated value in the FIFO buffer is equal to zero.

[0216] In some instances, the processing circuitry 50 can identify fluid index reset conditions based on data received from the processing circuitry 50. For example, the processing circuitry 50 can automatically detect physiological or, in some cases, non-physiological impedance changes. In one example of a non-physiological change, the processing circuitry 50 can determine that the position or orientation of the IMD 10 has changed. In some instances, the processing circuitry 50 can determine whether the orientation of the IMD 10 has changed by more than a predetermined amount. For example, the processing circuitry 50 can use a measured change in impedance value to determine whether the IMD 10 has flipped or otherwise changed its orientation.

[0217] In some instances, the processing circuitry 50 can use accelerometer data to determine IMD orientation. For example, the processing circuitry 50 can identify relative changes between individual accelerometer values ​​to determine whether the IMD orientation meets a predefined IMD orientation threshold. The IMD orientation threshold can be set such that the threshold is met when the IMD 10 is oriented perpendicularly to the skin layer or perpendicularly to the muscle layer, etc. In another instance, the IMD orientation threshold can be set such that the threshold is met when the orientation of the IMD 10 indicates that the patient is upright, lying down, tilted, or lying face down, etc.

[0218] In some instances, the processing circuitry 50 can trigger a fluid index reset based on such a change in position or orientation, depending on the nature of the change. For example, if the IMD 10 changes position such that the electrode 16 now faces a different direction, such as towards the muscle layer 20 instead of outwards towards the skin 18, the processing circuitry 50 can reset the fluid index calculation by triggering a fluid index reset condition. Therefore, when the processing circuitry 50 determines that the orientation of the IMD 10 has changed by more than a predetermined amount, the processing circuitry 50 can identify a fluid index reset condition, such as indicating, for example, that the orientation of the IMD 10 is different from a previously recorded one. In such instances, the processing circuitry 50 can reset the fluid index to a baseline value upon identifying a change in the orientation of the IMD 10, where the change meets a threshold, such as a change of more than 45 degrees or 90 degrees clockwise or counterclockwise, or a change of 108 degrees, etc.

[0219] In one instance, the processing circuitry 50 can determine this positional change based on a specific impedance change or a change in the average impedance value. For example, the processing circuitry 50 can automatically detect a positional change in IMD 10 based on a daily impedance change exceeding a certain amount. In some instances, the processing circuitry 50 can determine this impedance value change based on a step function over X days before and after the average impedance value. In another instance, the processing circuitry 50 can detect that the position of IMD 10 has changed based on a signal received from a 3-axis accelerometer integrated as part of IMD 10. For example, the processing circuitry 50 can detect a change in the signal received from the accelerometer and determine that IMD 10 has flipped so that electrode 16 now faces a different orientation than before. Upon detecting such activity in IMD 10, the processing circuitry 50 can reset the fluid index value to a baseline value.

[0220] As previously mentioned Figure 6 and 7 As pointed out, for reference Figure 8 One or more of the various example techniques described can be performed periodically. For example, the fluid index value can be determined based on the resolution parameter settings of the processing circuit system 50 (e.g., a resolution parameter used to indicate the frequency at which the electrode 16 should detect impedance measurements). In other instances, the fluid index value can be calculated without considering the resolution parameter, which may be applied, for example, to the determination of impedance scores and / or reference impedance values, but not to the determination of the fluid index. For example, the processing circuit system 50 can calculate the fluid index value daily at several time intervals (e.g., once in the morning, once in the afternoon, once in the evening, once after meals, etc.). The processing circuit system 50 can calculate the fluid index value daily, weekly, bi-weekly, monthly, etc. In some instances, the processing circuit system 50 can also calculate the fluid index value in response to a user command (e.g., from a physician, from a user interface) or in response to the fulfillment of another condition (e.g., based on activity level or other physiological parameters). For example, the processing circuit system 50 can determine the fluid index value on a per-measurement basis, such as on a per-impedance score determination or on a per-impedance measurement basis. Those skilled in the art will understand that there may be various time periods when the processing circuit system 50 or external device 12 can transmit fluid index values, receive fluid index values ​​and / or otherwise calculate fluid index values ​​for subsequent analysis.

[0221] Figure 9 It is a time series diagram showing the use of a finite buffer to limit the accumulation of fluid exponents over time. Figure 9This demonstrates a sudden drop in the measured impedance value 920, followed by a trend of increasing impedance towards the baseline or reference impedance 922. Although the description of the processing circuit system 50 comparing the measured impedance result with the reference impedance measurement result to determine the difference is provided, the reference... Figure 9 One or more of the various example technologies described may relate to any one or more of the IMD 10, external device 12, or server 94, for example, to a processing circuit system relating to any one or more of these devices.

[0222] In instances where a finite buffer is not used, when the measured impedance is less than the reference impedance, all differences between the measured impedance and the reference impedance are summed, as shown in the lighter shaded area 950 between the measured impedance and the reference impedance. For example, the reference... Figure 9 The described non-finite buffer corresponds to the start of a fluid index event preceding time period 948. As a result, despite the increase in impedance, the corresponding fluid index 952 continues to increase, which may indicate an improvement in the patient's condition due to, for example, improved adherence to medication or diet. Therefore, the processing circuitry 50 or another device may provide an alert because the fluid index 952 exceeds a threshold, indicating that the patient's condition is actually improving, or the increasing fluid index 952 may be included in the determination of the impedance score, rather than restricting the fluid index to a finite buffer.

[0223] In instances using finite buffers, when the measured impedance is less than the reference impedance, a finite number of differences (e.g., a sliding window) between the measured and reference impedances are summed, as shown in the darker shaded area 954 between the measured and reference impedances. For example, a finite buffer (such as a reference...) Figure 9 The described example (a finite buffer) corresponds to a sliding time period 955, where the processing circuit system 50 does not encounter a buffer reset condition, so time period 955 continues to slide from left to right on the page. As a result, the corresponding fluid index 956 begins to decrease, while the measured impedance increases and the patient's condition improves. Therefore, the processing circuit system 50 or another device can avoid providing an alarm when the patient's condition actually improves.

[0224] Turn now Figure 10 External device 12 can receive the patient 4's cardiac or health status (1002) from IMD 10. In some instances, external device 12 can determine the cardiac status and receive other data, such as raw impedance values, from processing circuitry system 50. Although described as generally performed by IMD 10, references... Figure 10One or more of the various example technologies described may be executed by any one or more of the IMD 10, external device 12, or server 94, for example, by the processing circuitry system of any one or more of these devices.

[0225] External device 12 can determine instructions for medical intervention based on the patient 4's cardiac condition (1004). For example, if the impedance score is greater than a high-risk threshold, external device 12 can determine instructions for medical intervention based on the determination of high risk. In other instances, external device 12 can determine different instructions for different risk levels or categories. For example, external device 12 can determine a first set of instructions for high-risk patients and a second set of instructions for intermediate-risk patients. In some instances, external device 12 may not determine any instructions for low-risk patients (e.g., impedance score = 0). In some instances, external device 12 can provide alerts, such as text- or graphic-based notifications, visual notifications, etc. In some instances, external device 12 can issue auditory or tactile warnings to patient 4 to alert them to the determined risk level. In other instances, external device 12 can provide visible light indicators, such as red light for high risk or yellow light for intermediate risk. This alert can indicate possible or predicted heart failure decompensation events.

[0226] In some instances, external device 12 can transmit instructions for medical intervention to the user interface (1006). In other instances, external device 12 can transmit instructions to a caregiver's device, such as a pager. In an instance where the processing circuitry system 50 generates instructions based on the cardiac condition status, IMD 10 can transmit instructions for medical intervention to the user interface. The instructions may include an impedance score or a cardiac condition status determined based on the impedance score. In some cases, the physician or caregiver may not need to know the actual impedance score value and may only want to receive the cardiac condition status determined based on the impedance score. In some instances, external device 12, IMD 10, server 94, or computing device 100 may use impedance scoring to predict adverse health events using a comprehensive diagnostic approach, as described in a co-assigned and co-pending application filed on the same date by Sarkar et al. entitled “Determining Likelihood of Anadversive Health Event Based on Various Physiological Diagnostic States”.

[0227] Various examples have been described. However, those skilled in the art will understand that various modifications can be made to the described examples without departing from the scope of the claims. For example, although the description has been primarily based on subcutaneous impedance, in some examples, other physiological parameters may be considered in conjunction with subcutaneous impedance to detect worsening heart failure. Examples of other physiological parameters and techniques for detecting worsening heart failure based on these parameters in combination with impedance are described in co-assigned U.S. Applications No. 12 / 184,149 and No. 12 / 184,003, entitled “Using multiple diagnostic parameters for predicting heart failure events” and “Detecting worsening heart failure based on impedance measurements” (both filed July 31, 2008), by Sarkar et al.

[0228] This disclosure includes the following examples:

[0229] Example 1: A system for detecting cardiac condition status, the system comprising: an IMD including a plurality of electrodes and configured for subcutaneous implantation outside a patient's chest cavity, wherein the IMD is configured to receive one or more subcutaneous tissue impedance signals from the electrodes; and a processing circuit system configured to: determine at least one first tissue impedance value corresponding to a first time period based at least partially on the one or more subcutaneous tissue impedance signals; determine at least one second tissue impedance value corresponding to a second time period different from the first time period based at least partially on the one or more subcutaneous tissue impedance signals; determine one or more reference impedance values ​​based at least partially on the at least one first tissue impedance value; determine at least one of the following based at least partially on the one or more reference impedance values ​​and the at least one second tissue impedance value: an average impedance value of at least some impedance values, or one or more fluid index values; determine an impedance score based on at least one of the following: the one or more fluid index values ​​or the average impedance value; and determine the patient's cardiac condition status based at least partially on the impedance score.

[0230] Example 2: The system according to Example 1, wherein at least one of the electrodes is in contact with interstitial fluid in the subcutaneous space.

[0231] Example 3: The system according to any one of Examples 1 or 2, wherein the processing circuit system is configured to determine the one or more reference impedance values ​​by at least determining a statistical representation of the at least one first tissue impedance value corresponding to the first time period.

[0232] Example 4: According to the system described in Example 3, the statistical representation for determining the at least one first tissue impedance value includes determining at least one of the following: mean, mode, median, range, regression model, or standard deviation.

[0233] Example 5: A system according to any one or more of Examples 1 to 4, wherein the at least one first tissue impedance value comprises a plurality of historical tissue impedance values.

[0234] Example 6: A system according to any one or more of Examples 1 to 5, wherein the processing circuitry is configured to: maintain a buffer for the relative change of the one or more subcutaneous tissue impedance signals over time; and determine the one or more fluid index values ​​at least in part based on the buffer.

[0235] Example 7: The system according to Example 6, wherein the processing circuitry is configured to: perform a comparison of the at least one second tissue impedance value with the one or more reference impedance values; and modify the buffer at least in part based on the comparison.

[0236] Example 8: A system according to any one of Examples 6 or 7, wherein the processing circuitry is configured to: determine that a buffer reset condition has been met; and reset the buffer in response to the meeting of the buffer reset condition.

[0237] Example 9: A system according to any one or more of Examples 1 to 8, wherein the processing circuitry is configured to: identify at least a first subset of a first fluid index calculation to determine the one or more fluid index values; and identify at least a second subset of a second fluid index calculation to determine the one or more fluid index values, wherein the identification is based at least in part on a plurality of fluid index values ​​that have met a fluid index threshold over time.

[0238] Example 10: A system according to any one or more of Examples 1 to 9, wherein the processing circuitry is configured to modify the impedance score in response to the one or more fluid index values ​​satisfying one or more scoring thresholds in at least one of the following aspects: a predetermined amount of time or a predetermined number of time.

[0239] Example 11: The system according to Example 10, wherein the scoring threshold comprises an adaptive threshold scaled by one or more weighting factors, wherein the processing circuitry is configured to determine the adaptive threshold at least in part based on the median of the differences between one or more maximum tissue impedance values ​​and one or more minimum tissue impedance values.

[0240] Example 12: The system according to Example 11, wherein the one or more weighting factors range from 0.1 to 4.5.

[0241] Example 13: A system according to any one or more of Examples 1 to 12, wherein the processing circuitry is configured to: determine the average impedance value based on a subset of the at least one first tissue impedance value; and modify the impedance score in response to the average impedance value satisfying an impedance value threshold.

[0242] Example 14: A system according to any one or more of Examples 1 to 13, wherein the processing circuitry is configured to determine, with respect to one or more time windows, the satisfaction of at least one of the following: the scoring threshold or the impedance threshold.

[0243] Example 15: A system according to any one or more of Examples 1 to 14, wherein the processing circuitry is configured to: identify a resolution parameter for determining at least one of the following: the at least one first tissue impedance value, the one or more reference impedance values, or the at least one second tissue impedance value.

[0244] Example 16: The system according to Example 15, wherein the resolution parameter is implemented using a filter based on at least one of the following: time constraints or activity level.

[0245] Example 17: According to the system of Example 16, the processing circuitry is configured to: determine one or more sub-time periods, the one or more sub-time periods corresponding to at least one of the following: a first time period or a second time period; and apply the filter according to the one or more sub-time periods.

[0246] Example 18: A system according to any one of Examples 16 or 17, wherein the processing circuitry is configured to: determine that the patient’s activity level meets an activity threshold; and apply the filter at least based on the activity level meeting the activity threshold.

[0247] Example 19: A system according to any one or more of Examples 16 to 18, wherein the processing circuitry is configured to exclude a subset of tissue impedance signals from the one or more subcutaneous tissue impedance signals, in part based on the filter, when at least one of the following is determined: the at least one first tissue impedance value or the at least one second tissue impedance value.

[0248] Example 20: A system according to any one or more of Examples 1 to 19, wherein the processing circuitry is configured to: compare the impedance score with one or more risk thresholds; and generate an alarm in response to the impedance score satisfying at least one of the one or more risk thresholds.

[0249] Example 21: The system according to Example 20, wherein the alarm indicates a possible heart failure decompensation event.

[0250] Example 22: A system according to any one or more of Examples 1 to 20, wherein the IMD includes at least one of the following: a pacemaker, a cardioversion device, or a defibrillator.

[0251] Example 23: A method for detecting cardiac condition, the method comprising: determining at least one reference impedance value at least partially based on one or more subcutaneous tissue impedance signals received from at least one electrode disposed in the subcutaneous layer of a patient during a first time period; determining at least one additional impedance value at least partially based on the one or more impedance signals received from the at least one electrode during a second time period other than the first time period; determining at least one of the following at least partially based on the at least one reference impedance value and the at least one additional impedance value: one or more fluid index values ​​of the patient or a statistical representation of the one or more subcutaneous tissue impedance signals received from the at least one electrode; determining an impedance score at least partially based on the fluid index values ​​or the statistical representation of the one or more subcutaneous tissue impedance signals received from the at least one electrode; and determining the cardiac condition state of the patient at least partially based on the impedance score.

[0252] Example 24: According to the method of Example 23, wherein the at least one electrode is implanted outside the patient's chest cavity.

[0253] Example 25: The method according to any one of Examples 23 or 24, wherein the at least one electrode contacts interstitial fluid in the subcutaneous space.

[0254] Example 26: The method according to any one or more of Examples 23 to 25, wherein the at least one electrode comprises an outward-facing electrode.

[0255] Example 27: The method according to any one or more of Examples 23 to 26, wherein determining the one or more fluid index values ​​further includes determining a statistical representation of the at least one reference impedance value.

[0256] Example 28: The method according to any one or more of Examples 23 to 27, wherein determining the one or more fluid index values ​​further includes accessing a buffer, the buffer including the relative change of the one or more subcutaneous tissue impedance signals over time.

[0257] Example 29: The method according to Example 28 further includes: performing a comparison of the at least one reference impedance value with the at least one other impedance value; and modifying the buffer at least in part based on the comparison.

[0258] Example 30: The method according to any one or more of Examples 23 to 29 further comprises: modifying the impedance score in response to the one or more fluid index values ​​satisfying one or more scoring thresholds in at least one of the following aspects: a predetermined amount of time or a predetermined number of time.

[0259] Example 31: The method according to any one or more of Examples 23 to 30 further comprises: determining an adaptive threshold proportional to the absolute impedance value and intraday variation of the one or more subcutaneous tissue impedance signals; performing a comparison of the one or more fluid index values ​​with the adaptive threshold; and determining the cardiac condition state based at least in part on the comparison.

[0260] Example 32: The method according to Example 31 further includes: scaling the adaptive threshold using one or more weighting factors; and determining the cardiac condition state based at least in part on the scaled adaptive threshold.

[0261] Example 33: The method according to any one or more of Examples 23 to 32 further comprises: determining a statistical representation of at least one of the following: the at least one reference impedance value or the at least one other impedance value; and modifying the impedance score in response to the statistical representation satisfying an impedance threshold amount.

[0262] Example 34: The method according to Example 33, wherein the impedance threshold is approximately 600 ohms.

[0263] Example 35: The method according to any one or more of Examples 23 to 34 further includes: modifying the impedance score in response to determining a negative trend in the average impedance value over time.

[0264] Example 36: The method according to any one or more of Examples 23 to 35 further comprises: determining a time-related value to adjust the one or more fluid index values; determining the adjusted one or more fluid index values ​​based at least in part on the time-related value; and determining the patient's cardiac condition state based at least in part on the adjusted one or more fluid index values.

[0265] Example 37: The method according to any one or more of Examples 23 to 36 further comprises: determining the length of time since the at least one electrode was implanted in the patient; and determining the at least one reference impedance value based at least in part on the length of time.

[0266] Example 38: The method according to any one or more of Examples 23 to 37 further comprises: identifying a first fluid index calculation when at least a first subset of the one or more fluid index values ​​is determined; and identifying a second fluid index calculation when at least a second subset of the one or more fluid index values ​​is determined.

[0267] Example 39: The method according to any one or more of Examples 23 to 38, wherein determining the one or more fluid index values ​​includes determining a statistical representation of at least one of the following: the at least one reference impedance value or the at least one other impedance value.

[0268] Example 40: The method according to any one or more of Examples 23 to 39 further comprises: identifying a resolution parameter for determining at least one of the following: the at least one reference impedance value or the at least one other impedance value.

[0269] Example 41: According to the method of Example 40, the resolution parameter includes a filter based on at least one of the following: time constraint or activity level.

[0270] Example 42: The method according to Example 41 further includes: determining one or more sub-time periods, the one or more sub-time periods corresponding to at least one of the following: the first time period or the second time period; and applying the filter according to the one or more sub-time periods.

[0271] Example 43: The method according to any one of Examples 41 or 42 further comprises: determining that the patient's activity level meets an activity threshold; and applying the filter based at least in part on the activity level meeting the activity threshold.

[0272] Example 44: The method according to any one or more of Examples 41 to 43 further comprises: excluding a subset of the subcutaneous tissue impedance signals from the one or more subcutaneous tissue impedance signals, in part based on the filter, when at least one of the following is determined: the at least one reference impedance value or the at least one other impedance value.

[0273] Example 45: The method according to any one or more of Examples 23 to 44 further comprises: transmitting the cardiac condition status to another device when the heart failure state meets one or more risk thresholds.

[0274] Example 46: A non-transitory computer-readable storage medium having instructions stored thereon, which, when executed, cause one or more processors to perform at least the following operations: determining at least one reference impedance value based at least in part on one or more subcutaneous tissue impedance signals received from at least one electrode disposed in the subcutaneous layer of a patient during a first time period; determining at least one other impedance value based at least in part on the one or more subcutaneous tissue impedance signals received from the at least one electrode during a second time period other than the first time period; determining an impedance score of the patient based at least in part on the at least one reference impedance value and the at least one other impedance value; and outputting the patient's cardiac condition status based at least in part on the impedance score.

[0275] The techniques described in this disclosure can be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, aspects of these techniques can be implemented in one or more processors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic QRS circuit systems (such as QRS complexes) and any combination of such components embodied in external devices such as doctor or patient programmers, simulators, or other devices. The terms “processor” and “processing circuit system” can generally refer to any of the aforementioned logic circuit systems, alone or in combination with other logic circuit systems, or any other equivalent circuit system, alone or in combination with other digital or analog circuit systems.

[0276] For each aspect implemented in software, at least some of the functions of the systems and apparatus described in this disclosure can be embodied in instructions on a computer-readable storage medium, such as RAM, ROM, NVRAM, DRAM, SRAM, flash memory, magnetic disk, optical disk, flash memory, or various forms of EPROM or EEPROM. The instructions can be executed to support one or more aspects of the functions described in this disclosure.

[0277] Additionally, in some aspects, the functions described herein can be housed within dedicated hardware and / or software modules. Describing different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be implemented by separate hardware or software components. Rather, the functions associated with one or more modules or units can be performed by separate hardware or software components, or integrated into shared or separate hardware or software components. Moreover, the techniques can be fully implemented within one or more circuit or logic elements. The techniques disclosed herein can be implemented in a wide variety of devices or apparatuses comprising IMDs, external programmers, combinations of IMDs and external programmers, integrated circuits (ICs) or IC sets, and / or discrete circuit systems residing in IMDs and / or external programmers.

[0278] Furthermore, while examples of providing impedance scores to indicate worsening heart failure in response to detected changes in impedance have been described primarily with reference to such examples, other examples may additionally or alternatively automatically modify treatment in response to the detection of worsening heart failure in a patient. For example, treatment may be a substance delivered by an implantable pump, cardiac resynchronization therapy, refractory period stimulation, or cardiac enhancement therapy. These and other examples are within the scope of the following claims.

Claims

1. A system for detecting the state of a heart condition, the system comprising: An implantable medical device (IMD) includes a housing and a plurality of electrodes on the housing, the housing and the electrodes being configured for subcutaneous implantation, wherein the IMD is configured to receive one or more subcutaneous tissue impedance signals measured using only the plurality of electrodes on the housing; as well as Processing circuitry system, the processing circuitry system being configured to: At least one first tissue impedance value corresponding to the first time period is determined based at least in part on the one or more subcutaneous tissue impedance signals; At least one second tissue impedance value corresponding to a second time period different from the first time period is determined based at least in part on the one or more subcutaneous tissue impedance signals; One or more reference impedance values ​​are determined at least in part based on the at least one first tissue impedance value; One or more fluid index values ​​are determined, at least in part, based on the one or more reference impedance values ​​and the at least one second tissue impedance value; An adaptive threshold is determined based on the absolute impedance value of at least one of the one or more subcutaneous tissue impedance signals. Perform a comparison between the one or more fluid index values ​​and the adaptive threshold; The impedance score is determined at least in part based on the comparison. as well as The patient's cardiac condition is determined at least in part based on the impedance score.

2. The system according to claim 1, wherein at least one of the electrodes is in contact with the interstitial fluid.

3. The system of claim 1, wherein the processing circuitry is configured to: The one or more reference impedance values ​​are determined by at least determining a statistical representation of the at least one first tissue impedance value corresponding to the first time period.

4. The system of claim 1, wherein the processing circuitry is configured to: A buffer that maintains the relative change in the impedance signal of the one or more subcutaneous tissues over time; and The one or more fluid index values ​​are determined at least in part based on the buffer.

5. The system of claim 4, wherein the processing circuitry is configured to: Perform a comparison of the at least one second tissue impedance value with the one or more reference impedance values; and The buffer is modified at least in part based on the comparison.

6. The system of claim 1, wherein the processing circuitry is configured to: Identify at least a first subset of the values ​​of the first fluid index to determine the values ​​of the one or more fluid indexes; and Identify at least a second subset of the values ​​of the one or more fluid indices to determine the second fluid index calculation. The identification is based, at least in part, on multiple fluid index values ​​that have met the fluid index threshold over time.

7. The system of claim 1, wherein the processing circuitry is configured to: The impedance score is modified in response to the one or more fluid index values ​​satisfying one or more scoring thresholds in at least one of the following aspects: a predetermined amount of time or a predetermined number of time.

8. The system of claim 1, wherein the processing circuitry is configured to: An average impedance value is determined based on a subset of the at least one first tissue impedance value; and The impedance score is modified in response to the average impedance value meeting the impedance value threshold.

9. The system of claim 1, wherein the processing circuitry is configured to: Identify resolution parameters to determine at least one of the following: the at least one first tissue impedance value, the one or more reference impedance values, or the at least one second tissue impedance value.

10. The system of claim 1, wherein the processing circuitry is configured to: A subset of tissue impedance signals is excluded from the one or more subcutaneous tissue impedance signals when at least one of the following is determined: the at least one first tissue impedance value or the at least one second tissue impedance value.

11. The system of claim 1, wherein the processing circuitry is configured to: The impedance score is compared to one or more risk thresholds; and An alarm is generated in response to the impedance score satisfying at least one of the one or more risk thresholds.

12. A non-transitory computer-readable storage medium having instructions stored thereon, which, when executed, cause one or more processors to perform at least the following operations: At least one reference impedance value is determined, at least in part, based on one or more subcutaneous tissue impedance signals received from one or more electrodes disposed on the housing of the implantable medical device and implanted in the patient's subcutaneous layer, said one or more subcutaneous tissue impedance signals being measured using only said one or more electrodes disposed on said housing; In a second time period different from the first time period, at least one other impedance value is determined at least in part based on the one or more subcutaneous tissue impedance signals received from the plurality of electrodes; One or more fluid index values ​​are determined, at least in part, based on the at least one reference impedance value and the at least one other impedance value; An adaptive threshold is determined based on the absolute impedance value of at least one of the one or more subcutaneous tissue impedance signals. Perform a comparison between the one or more fluid index values ​​and the adaptive threshold; The patient's impedance score is determined at least in part based on the comparison. as well as The patient's cardiac condition is output at least in part based on the impedance score.

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