Detecting worsening heart failure based on impedance measurements
First Claim
1. A method comprising:
- periodically determining, using a medical device, an impedance of a patient based on measured impedances;
comparing each of the determined impedances to a respective reference impedance, wherein the respective reference impedance for each of the determined impedances is determined based on a plurality of previously determined impedances;
generating an index based on the comparisons between the determined impedances and the reference impedances;
determining a variability value based on the plurality of previously determined impedance values;
modifying the index over time based on the variability value and the comparisons between the determined impedances and the reference impedances;
comparing the index to at least one threshold; and
determining whether to provide an alert based on the comparison of the index to the at least one threshold.
1 Assignment
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Accused Products
Abstract
Techniques for processing impedance data to provide an early warning for heart failure decompensation are described. An example device may be configured to measure intrathoracic impedance values, and increment an index when a determined impedance is less than a reference impedance. The incrementing may be based on the difference between the reference impedances and the determined impedance. In some examples, the amount of incrementing is reduced based on a variability of the impedances, or increased over time so long as the index remains above a threshold, e.g., zero. In some examples, the manner is which the reference impedances are determined changes over time to, for example, address rapid changes in impedance after device or system implantation. In some examples, the index is compared to a threshold to determine whether to provide an alert. In some examples, two thresholds are used to provide hysteresis.
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Citations
33 Claims
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1. A method comprising:
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periodically determining, using a medical device, an impedance of a patient based on measured impedances; comparing each of the determined impedances to a respective reference impedance, wherein the respective reference impedance for each of the determined impedances is determined based on a plurality of previously determined impedances; generating an index based on the comparisons between the determined impedances and the reference impedances; determining a variability value based on the plurality of previously determined impedance values; modifying the index over time based on the variability value and the comparisons between the determined impedances and the reference impedances; comparing the index to at least one threshold; and determining whether to provide an alert based on the comparison of the index to the at least one threshold. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method comprising:
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periodically determining, using a medical device, an impedance of a patient based on a plurality of measured impedances; comparing each of the determined impedances to a respective reference impedance, wherein the respective reference impedance for each of the determined impedances is determined based on a plurality of previously determined impedances, and wherein comparing each of the determined impedances to a respective reference impedance comprises determining differences between the reference impedances and the determined impedances; determining an index based on the previous X or fewer comparisons, wherein determining the index based on the previous X or fewer comparisons comprises determining the index as a sum of the previous X or fewer differences so long as the determined impedance is less than the reference impedance, and wherein X is a predetermined constant value; comparing the index to at least one threshold; and determining whether to provide an alert based on the comparison of the index to the at least one threshold, wherein determining the index as a sum of the previous X or fewer differences comprises; storing the differences in a buffer with a limit of X differences; and summing the index values stored in the buffer. - View Dependent Claims (17)
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18. A method comprising:
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periodically determining, using a medical device, an impedance of a patient based on a plurality of measured impedances; comparing each of the determined impedances to a respective reference impedance, wherein the respective reference impedance for each of the determined impedances is determined based on a plurality of previously determined impedances; modifying an index over time based on the comparisons between the determined impedances and the reference impedances; comparing the index to a plurality of thresholds; and determining whether to provide an alert based on the comparison of the index to the plurality of thresholds, wherein comparing the index to a plurality of thresholds comprises comparing the index to a first threshold and a second threshold, wherein the first threshold is greater than the second threshold, and wherein determining whether to provide an alert based on the comparison of the index to the at least one threshold comprises; providing the alert when the index is at least one of greater than or equal to the first threshold; and stopping the alert when the index is subsequently at least one of less than or equal to the second threshold.
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19. A system comprising:
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a plurality of electrodes; a medical device coupled to the electrodes that periodically measures an impedance of the patient; and a processor that; periodically determines an impedance value based on a plurality of the measured impedances, compares each of the determined impedance values to a respective reference impedance, wherein the respective reference impedance for each of the determined impedance values is determined based on a plurality of previously determined impedance values, generates an index based on the comparisons between the determined impedances and the reference impedances, determines a variability value based on the plurality of previously determined impedance values, modifies the index over time based on the variability value and the comparisons between the determined impedance values and the reference impedances, compares the index to at least one threshold, and determines whether to provide an alert based on the comparison of the index to the at least one threshold. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A system comprising:
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a plurality of electrodes; a medical device coupled to the electrodes that periodically measures an impedance of a patient; a memory; and a processor that; periodically determines an impedance value based on a plurality of the measured impedances; compares each of the determined impedance values to a respective reference impedance to determine differences between the reference impedances and the determined impedance values, wherein the respective reference impedance for each of the determined impedance values is determined based on a plurality of previously determined impedance values; determines an index as a sum of the previous X or fewer differences so long as the measured impedance is less than the reference impedance, wherein X is a predetermined constant value; compares the index to at least one threshold; and determines whether to provide an alert based on the comparison of the index to the at least one threshold, wherein the processor stores the differences in a buffer with a limit of X differences in the memory and sums the index values stored in the buffer. - View Dependent Claims (31)
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32. A system comprising:
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a plurality of electrodes; a medical device coupled to the electrodes that periodically measures an impedance of a patient; and a processor that; periodically determines an impedance value based on a plurality of the measured impedances, compares each of the determined impedance values to a respective reference impedance, wherein the respective reference impedance for each of the determined impedance values is determined based on a plurality of previous measured impedances; modifies an index over time based on the comparisons between the determined impedance values and the reference impedances; compares the index to a plurality of thresholds; and determines whether to provide an alert based on the comparison of the index to the plurality of thresholds, wherein the processor compares the index to a first threshold and a second threshold, wherein the first threshold is greater than the second threshold, and wherein the processor provides the alert when the index is at least one of greater than or equal to the first threshold, and stops the alert when the index is subsequently at least one of less than or equal to the second threshold.
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33. A system comprising:
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means for periodically determining an impedance of a patient based on a plurality of measured impedances; means for comparing each of the determined impedances to a respective reference impedance, wherein the respective reference impedance for each of the determined impedances is determined based on a plurality of previous measured impedances; means for generating an index based on the comparisons between the determined impedances and the reference impedances; means for determining a variability value based on the plurality of previously determined impedance values; means for modifying the index over time based on the variability value and the comparisons between the determined impedances and the reference impedances; means for comparing the index to at least one threshold; and means for determining whether to provide an alert based on the comparison of the index to the at least one threshold.
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Specification