# US 11,298,547 B2 · Fluid status detection from a cardiac electrical signal and impedance signal > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,298,547 B2 - Document ID: US11298547B2 - Status: Granted - Kind: B2 - Application number: 16/521,963 - Filed: 2019-07-25 - Published: 2020-01-30 - Granted: 2022-04-12 - Earliest claimed: 2018-07-27 - Assignees: Medtronic, Inc. - Applicants: Medtronic, Inc. - Inventors: Zhendong Song; Todd M. Zielinski; Brian B. Lee - Web page: https://patentgrep.com/patent/US11298547B2 ## CPC - A61N 1/36585: {controlled by two or more physical parameters} - A61B 5/0031: {Implanted circuitry} - A61B 5/1116: {Determining posture transitions} - A61B 5/1118: {Determining activity level} - A61B 5/29: for permanent or long-term implantation - A61B 5/352: Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval - A61B 5/4875: {Hydration status, fluid retention of the body} - A61B 5/686: {Permanently implanted devices, e.g. pacemakers, other stimulators, biochips (A61B5/6861 takes precedence)} - A61B 5/6869: {Heart} - A61B 5/7221: {Determining signal validity, reliability or quality (preventing, reducing or removing noise induced by motion artefacts A61B5/7207; noise originating from a therapeutic or surgical apparatus A61B5/7217)} - A61B 5/746: {Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms} - A61N 1/3627: {for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy} - A61N 1/36521: {the parameter being derived from measurement of an electrical impedance} - A61N 1/36535: {controlled by body position or posture} - A61N 1/3702: {Physiological parameters (A61N1/365 takes precedence; evoked response A61N1/371)} - A61B 5/0537: Measuring body composition by impedance, e.g. tissue hydration or fat content - A61B 5/0538: invasively, e.g. using a catheter - A61B 5/7203: {for noise prevention, reduction or removal} - A61B 2560/0209: adapted for power saving - A61B 2560/0214: of power generation or supply - A61B 2560/0223: of calibration, e.g. protocols for calibrating sensors - A61N 1/37211: {Means for communicating with stimulators} - A61N 1/39622: {Pacing therapy} - A61N: ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY (measurement of bioelectric currents A61B; surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body A61B18/00; anaesthetic apparatus in general A61M; incandescent lamps H01K; infrared radiators for heating H05B) - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## Abstract A medical device is configured to generate fluid status signal data of a patient by determining impedance metrics from an impedance signal, determining cardiac electrical signal amplitudes from a cardiac electrical signal and determining a calibration relationship between the impedance metrics and cardiac electrical signal amplitudes. The medical device generates a fluid status signal data by adjusting cardiac electrical signal amplitudes according to the determined calibration relationship. The fluid status signal data may be displayed or monitored for detecting a change in the patient's fluid status. ## Claims ### Claim 1 A medical device, comprising: a sensing circuit configured to receive a cardiac electrical signal via electrodes coupled to the medical device; an impedance sensing circuit configured to apply a drive signal to electrodes coupled to the medical device and sense a resultant impedance signal; a telemetry circuit configured to transmit fluid status data to another medical device; and a control circuit coupled to the sensing circuit, the impedance sensing circuit and the telemetry circuit, the control circuit configured to: determine a plurality of impedance metrics from the impedance signal; determine a first plurality of amplitudes from the cardiac electrical signal; determine a first calibration relationship between the plurality of impedance metrics and the first plurality of amplitudes; determine a second plurality of amplitudes from the cardiac electrical signal; and generate fluid status signal data by adjusting the second plurality of amplitudes according to the determined first calibration relationship. ### Claim 2 (depends on 1) The device of claim 1, further comprising a power source coupled to the control circuit and the impedance sensing circuit for generating the drive signal, wherein the power source life is conserved by using the first calibration relationship compared to implantable medical devices that solely use the impedance signal to acquire fluid status signal data. ### Claim 3 (depends on 2) The device of claim 2, wherein the power source is a battery. ### Claim 4 (depends on 1) The device of claim 1, wherein the control circuit is further configured to control the telemetry circuit to transmit the fluid status signal data to another medical device for generating a display of the fluid status signal data. ### Claim 5 (depends on 1) The device of claim 1, wherein the control circuit is configured to determine each of the first plurality of amplitudes and each of the second plurality of amplitudes by determining an R-wave amplitude of the cardiac electrical signal. ### Claim 6 (depends on 1) The device of claim 1, wherein the control circuit is configured to determine each one of the first plurality of amplitudes by determining a cardiac event amplitude of the cardiac electrical signal during each one of a plurality of cardiac cycles. ### Claim 7 (depends on 1) The device of claim 1, wherein determining the first calibration relationship comprises determining at least one of a coefficient or a constant used for adjusting each of the second plurality of amplitudes. ### Claim 8 (depends on 1) The device of claim 1, wherein determining the first calibration relationship comprises generating a look-up table of calibrated cardiac electrical signal amplitudes. ### Claim 9 (depends on 1) The device of claim 1, wherein the control circuit is further configured to determine the calibration relationship by: determining the plurality of impedance metrics over a calibration time interval; determining the first plurality of cardiac electrical signal amplitudes during the calibration time interval; determining a range of the plurality of impedance metrics; extending the calibration time interval in response to the range of the plurality of impedance metrics being less than a minimum range; and determining the calibration relationship using the plurality of impedance metrics and the plurality of cardiac electrical signal amplitudes determined over the extended calibration time interval. ### Claim 10 (depends on 1) The device of claim 1, wherein the control circuit is further configured to generate a fluid status signal by: determining at least two impedance metrics from the impedance signal and spaced apart by a time interval; determining the second plurality of amplitudes of the cardiac electrical signal during the time interval; and generating a fluid status signal comprising at least one of the two impedance metrics and the adjusted second plurality of amplitudes of the cardiac electrical signal. ### Claim 11 (depends on 1) The device of claim 1, wherein the control circuit is further configured to: determine a verification impedance metric from the impedance signal after determining the second plurality of amplitudes from the cardiac electrical signal; determine a verification amplitude of the cardiac electrical signal corresponding in time to the verification impedance metric; adjust the verification amplitude of the cardiac electrical according to the first calibration relationship; compare the adjusted verification amplitude to the verification impedance metric; and re-determine the first calibration relationship in response to the adjusted verification amplitude being greater than a threshold difference from the verification impedance metric. ### Claim 12 (depends on 1) The device of claim 1, wherein the control circuit is further configured to: detect a threshold change in the adjusted second plurality of amplitudes; and re-determine the first calibration relationship in response to detecting the threshold change. ### Claim 13 (depends on 1) The device of claim 1, further comprising a posture sensor configured to produce a signal correlated to patient body posture and coupled to the control circuit; wherein the control circuit is further configured to: detect a change in patient body posture from the posture sensor signal, the change in patient body posture being from a first patient body posture corresponding to the first calibration relationship to a second patient body posture different than the first patient body posture; determine a second calibration relationship between the impedance signal and the cardiac electrical signal, the second calibration relationship corresponding to the second patient body posture; determine a third plurality of amplitudes of the cardiac electrical signal after the detected change in patient body posture; and generate the fluid status signal data by adjusting the third plurality of amplitudes according to the second calibration relationship. ### Claim 14 (depends on 13) The device of claim 13, wherein the control circuit is configured to determine the first calibration relationship using at least one impedance metric determined from the impedance signal after the detected change in patient body posture and an impedance metric determined from the impedance signal before the detected change in patient body posture. ### Claim 15 (depends on 13) The device of claim 13, wherein determining the first calibration relationship and the second calibration relationship by the control circuit comprises generating a look-up table comprising a first calibration parameter corresponding to the first patient body posture and a second calibration parameter corresponding to the second patient body posture. ### Claim 16 (depends on 13) The device of claim 13, wherein the control circuit is further configured to: generate a first fluid status signal comprising the adjusted second plurality of amplitudes corresponding to the first patient body posture; and generate a second fluid status signal comprising the adjusted third plurality of cardiac electrical signal amplitudes corresponding to the second patient body posture. ### Claim 17 (depends on 13) The device of claim 13, wherein the control circuit is further configured to generate the fluid status signal data by: updating the first calibration relationship each time the first patient body posture is detected; adjusting cardiac electrical signal amplitudes that are acquired while the first patient body posture is being detected according to the first calibration relationship; updating the second calibration relationship each time the second patient body posture is detected; adjusting cardiac electrical signal amplitudes that are acquired while the second patient body posture is being detected according to the second calibration relationship; generating a first fluid status signal by appending the cardiac electrical signal amplitudes adjusted according to the first calibration relationship; generating a second fluid status signal by appending the cardiac electrical signal amplitudes adjusted according to the second calibration relationship; wherein the first patient body posture comprises a plurality of upright patient body postures and the second patient body posture comprises a plurality of non-upright patient body postures. ### Claim 18 (depends on 1) The device of claim 1, further comprising a posture sensor configured to produce a signal correlated to patient body posture and coupled to the control circuit; wherein the control circuit is further configured to: detect a change in patient body posture from the posture sensor signal; determine that the change in patient body posture is a major change in a center of gravity of the patient; and responsive to the change in patient body posture being a major change, determine a second calibration relationship between a second plurality of impedance metrics determined from the impedance signal and a third plurality of amplitudes of the cardiac electrical signal. ### Claim 19 (depends on 1) The device of claim 1, further comprising a posture sensor configured to produce a signal correlated to patient body posture and coupled to the control circuit; wherein the control circuit is further configured to: detect a change in patient body posture from the posture sensor signal; determine whether the change in patient body posture is one of a major change in a center of gravity of the patient or a minor change in the center of gravity of the patient; in response to the change in patient body posture being a major change, determining a second calibration relationship between the impedance signal and the cardiac electrical signal; in response to the change in patient body posture being a minor change, determine when re-calibration criteria are met based on at least one of the impedance signal and the cardiac electrical signal; and determine a second calibration relationship between the impedance signal the cardiac electrical signal in response to the re-calibration criteria being met. ### Claim 20 (depends on 1) The device of claim 1, further comprising a posture sensor configured to produce a signal correlated to patient body posture and coupled to the control circuit; wherein the control circuit is further configured to: detect a change in patient body posture from the posture sensor signal; generate fluid status signal data from the cardiac electrical signal after detecting the posture change; and determine a time response of a change in the fluid status signal data generated after detecting the change in patient body posture. ### Claim 21 (depends on 20) The device of claim 20, wherein the control circuit is configured to detect the change in patient body posture by detecting a change in patient body posture between an upright and a non-upright position. ### Claim 22 (depends on 1) The device of claim 1, further comprising a therapy circuit coupled to the control circuit and configured to deliver a therapy: wherein the control circuit is further configured to: compare the fluid status signal data to criteria for detecting a fluid status condition; and control the therapy circuit to adjust delivery of the therapy in response to the criteria for detecting a fluid status condition being met. ### Claim 23 (depends on 1) The device of claim 1, wherein the control circuit is further configured to: compare the fluid status signal data to criteria for detecting a fluid status condition; and generate an alert in response to the criteria for detecting a fluid status condition being met. ### Claim 24 A method performed by an implantable medical device, the method comprising: determining a plurality of impedance metrics from an impedance signal resulting from a drive signal applied to electrodes coupled to the medical device; determining a first plurality of amplitudes from a cardiac electrical signal received by a sensing circuit via electrodes coupled to the medical device; determining a first calibration relationship between the plurality of impedance metrics and the first plurality of amplitudes; determining a second plurality of amplitudes from the cardiac electrical signal; generating fluid status signal data by adjusting the second plurality of amplitudes according to the determined first calibration relationship; and transmitting the fluid status signal data to another medical device for generating a display of the fluid status signal data. ### Claim 25 (depends on 24) The method of claim 24, further comprising generating the drive signal from a power source coupled to the control circuit and the impedance sensing circuit, wherein the power source life is conserved by using the first calibration relationship compared to implantable medical devices that solely use the impedance signal to acquire fluid status signal data. ### Claim 26 (depends on 24) The method of claim 24, wherein determining each of the first plurality of amplitudes and the second plurality of amplitudes comprises determining an R-wave amplitude of the cardiac electrical signal. ### Claim 27 (depends on 24) The method of claim 24, wherein determining each one of the first plurality of amplitudes comprises determining a cardiac event amplitude of the cardiac electrical signal during each one of a plurality of cardiac cycles. ### Claim 28 (depends on 24) The method of claim 24, wherein determining the first calibration relationship comprises determining at least one of a coefficient or a constant used for adjusting each of the second plurality of amplitudes. ### Claim 29 (depends on 24) The method of claim 24, wherein determining the first calibration relationship comprises generating a look-up table of calibrated cardiac electrical signal amplitudes. ### Claim 30 (depends on 24) The method of claim 24, wherein determining the calibration relationship comprises: determining the plurality of impedance metrics over a calibration time interval; determining the first plurality of cardiac electrical signal amplitudes during the calibration time interval; determining a range of the plurality of impedance metrics; extending the calibration time interval in response to the range of the plurality of impedance metrics being less than a minimum range; and determining the calibration relationship using the plurality of impedance metrics and the plurality of cardiac electrical signal amplitudes determined over the extended calibration time interval. ### Claim 31 (depends on 24) The method of claim 24, further comprising generating a fluid status signal by: determining at least two impedance metrics from the impedance signal and spaced apart by a time interval; determining the second plurality of amplitudes of the cardiac electrical signal during the time interval; and generating the fluid status signal comprising at least one of the two impedance metrics and the adjusted second plurality of amplitudes of the cardiac electrical signal. ### Claim 32 (depends on 24) The method of claim 24, further comprising: determining a verification impedance metric from the impedance signal after determining the second plurality of amplitudes from the cardiac electrical signal; determining a verification amplitude of the cardiac electrical signal corresponding in time to the verification impedance metric; adjusting the verification amplitude of the cardiac electrical according to the first calibration relationship; comparing the adjusted verification amplitude to the verification impedance metric; and re-determining the first calibration relationship in response to the adjusted verification amplitude being greater than a threshold difference from the verification impedance metric. ### Claim 33 (depends on 24) The method of claim 24, further comprising: detecting a threshold change in the adjusted second plurality of amplitudes; and re-determine the first calibration relationship in response to detecting the threshold change. ### Claim 34 (depends on 24) The method of claim 24, further comprising: detecting a change in patient body posture from a posture sensor signal, the change in patient body posture being from a first patient body posture corresponding to the first calibration relationship to a second patient body posture different than the first patient body posture; and determining a second calibration relationship between the impedance signal and the cardiac electrical signal, the second calibration relationship corresponding to the second patient body posture determining a third plurality of amplitudes of the cardiac electrical signal after the detected change in patient body posture; wherein generating the fluid status signal data comprises adjusting the third plurality of amplitudes according to the second calibration relationship. ### Claim 35 (depends on 34) The method of claim 34, wherein the control circuit is configured to determine the first calibration relationship using at least one impedance metric determined from the impedance signal after the detected change in patient body posture and an impedance metric determined from the impedance signal before the detected change in patient body posture. ### Claim 36 (depends on 34) The method of claim 34, wherein determining the first calibration relationship and the second calibration relationship comprises generating a look-up table comprising a first calibration parameter corresponding to the first patient body posture and a second calibration parameter corresponding to the second patient body posture. ### Claim 37 (depends on 34) The method of claim 34, further comprising: generating a first fluid status signal comprising the adjusted second plurality of amplitudes corresponding to the first patient body posture; and generating a second fluid status signal comprising the adjusted third plurality of cardiac electrical signal amplitudes corresponding to the second patient body posture. ### Claim 38 (depends on 34) The method of claim 34, wherein generating the fluid status signal data comprises: updating the first calibration relationship each time the first patient body posture is detected; adjusting cardiac electrical signal amplitudes that are acquired while the first patient body posture is being detected according to the first calibration relationship; updating the second calibration relationship each time the second patient body posture is detected; adjusting cardiac electrical signal amplitudes that are acquired while the second patient body posture is being detected according to the second calibration relationship; generate a first fluid status signal by appending the cardiac electrical signal amplitudes adjusted according to the first calibration relationship; generate a second fluid status signal by appending the cardiac electrical signal amplitudes adjusted according to the second calibration relationship; wherein the first patient body posture comprises a plurality of upright patient body postures and the second patient body posture comprises a plurality of non-upright patient body postures. ### Claim 39 (depends on 24) The method of claim 24, further comprising: detecting a change in patient body posture from a posture sensor signal; determining that the change in patient body posture is a major change in a center of gravity of the patient; and responsive to the change in patient body posture being a major change, determining a second calibration relationship between a second plurality of impedance metrics determined from the impedance signal and a third plurality of amplitudes of the cardiac electrical signal. ### Claim 40 (depends on 24) The method of any of claim 24, further comprising: detecting a change in patient body posture from a posture sensor signal; determining whether the change in patient body posture is one of a major change in a center of gravity of the patient or a minor change in the center of gravity of the patient; in response to the change in patient body posture being a major change, determining a second calibration relationship between the impedance signal and the cardiac electrical signal; in response to the change in patient body posture being a minor change, determine when re-calibration criteria are met based on at least one of the impedance signal and the cardiac electrical signal; and determine a second calibration relationship between the impedance signal the cardiac electrical signal in response to the re-calibration criteria being met. ### Claim 41 (depends on 24) The method of claim 24, further comprising: detecting a change in patient body posture from the posture sensor signal; generating fluid status signal data from the cardiac electrical signal after detecting the posture change; and determining a time response of a change in the fluid status signal data generated after detecting the change in patient body posture. ### Claim 42 (depends on 41) The method of claim 41, wherein detecting the change in patient body posture comprises detecting a change in patient body posture between an upright and a non-upright position. ### Claim 43 (depends on 24) The method of claim 24, further comprising: comparing the fluid status signal data to criteria for detecting a fluid status condition; and control a therapy circuit to adjust delivery of a therapy in response to the criteria for detecting a fluid status condition being met. ### Claim 44 (depends on 24) The method of claim 24, further comprising: comparing the fluid status signal data to criteria for detecting a fluid status condition; and generating an alert in response to the criteria for detecting a fluid status condition being met. ### Claim 45 A non-transitory computer-readable medium storing a set of instructions which when executed by a control circuit of a medical device, cause the medical device to: determine a plurality of impedance metrics from an impedance signal resulting from a drive signal applied to electrodes coupled to the medical device; determine a first plurality of amplitudes from a cardiac electrical signal received by a sensing circuit via electrodes coupled to the medical device; determine a calibration relationship between the plurality of impedance metrics and the first plurality of amplitudes; determine a second plurality of amplitudes from the cardiac electrical signal; generate fluid status signal data by adjusting the second plurality of amplitudes according to the determined first calibration relationship; and transmit the fluid status signal data to another medical device for displaying the fluid status signal data. ### Claim 46 A medical device, comprising: a telemetry circuit configured to receive fluid status data from another medical device, the fluid status data comprising a plurality of cardiac electrical signal amplitudes and a plurality of impedance metrics; and a control circuit coupled to the telemetry circuit and configured to: determine a calibration relationship between the plurality of impedance metrics and the plurality of cardiac signal amplitudes; adjust the plurality of cardiac electrical signal amplitudes according to the determined calibration relationship; and generate a fluid status signal comprising the adjusted cardiac electrical signal amplitudes; compare the fluid status signal to at least one threshold; determining a therapy adjustment command based on the comparison; and transmitting the therapy adjustment command to a therapy delivery device for delivering a therapy to a patient according to the therapy adjustment command.