Thoracic impedance detection with blood resistivity compensation
First Claim
1. A method comprising:
- detecting a thoracic impedance signal of a thorax of a subject;
detecting a blood resistivity signal; and
determining a thoracic fluid indication using the thoracic impedance signal, the determining the thoracic fluid indication including using the blood resistivity signal to reduce or eliminate an effect of a change in the blood resistivity on the thoracic fluid indication.
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Accused Products
Abstract
This document discusses, among other things, a cardiac rhythm management device or other implantable medical device that uses thoracic impedance to determine how much fluid is present in the thorax, such as for detecting or predicting congestive heart failure, pulmonary edema, pleural effusion, hypotension, or the like. The thoracic fluid amount determined from the thoracic impedance is compensated for changes in blood resistivity, which may result from changes in hematocrit level or other factors. The blood-resistivity-compensated thoracic fluid amount can be stored in the device or transmitted to an external device for storage or display. The blood-resistivity-compensated thoracic fluid amount can also be used to adjust a cardiac pacing, cardiac resynchronization, or other cardiac rhythm management or other therapy to the patient. This document also discusses applications of the devices and methods for predicting or indicating anemia.
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Citations
86 Claims
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1. A method comprising:
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detecting a thoracic impedance signal of a thorax of a subject;
detecting a blood resistivity signal; and
determining a thoracic fluid indication using the thoracic impedance signal, the determining the thoracic fluid indication including using the blood resistivity signal to reduce or eliminate an effect of a change in the blood resistivity on the thoracic fluid indication. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35)
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36. A method of using an implantable medical device, the method comprising:
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detecting a thoracic impedance signal of a thorax of a subject using implantable electrodes to deliver a test current and measure a responsive voltage;
detecting a blood resistivity signal, within a heart chamber or blood vessel, from a volume of blood that is substantially independent of a cardiac cycle and a respiratory cycle;
filtering the thoracic impedance signal to substantially remove frequency components above 0.05 Hz to obtain a near-DC thoracic impedance signal; and
determining a thoracic fluid indication using the thoracic impedance signal, the determining the thoracic fluid indication including compensating the thoracic impedance signal for changes in blood resistivity. - View Dependent Claims (37)
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38. The method of claim further comprising:
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storing a history of thoracic fluid measurements; and
determining whether at least one of heart failure decompensation, pulmonary edema, and pleural effusion is present using the history of thoracic fluid measurements to determine whether a change in thoracic fluid has occurred.
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39. A system comprising:
an implantable medical device, including;
a thoracic impedance measurement circuit, to provide a thoracic impedance signal;
a blood resistivity measurement circuit, to provide a blood resistivity signal; and
a controller, coupled to the blood resistivity measurement circuit, the controller operable to determine a thoracic fluid indication using the filtered thoracic impedance signal, including using the blood resistivity signal to reduce or eliminate an effect of a change in the blood resistivity on the thoracic fluid indication. - View Dependent Claims (40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73)
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74. A system comprising:
an implantable medical device, including;
a thoracic impedance measurement circuit, to provide a thoracic impedance signal;
a frequency-selective filter circuit, coupled to the thoracic impedance measurement circuit to receive the thoracic impedance signal, the frequency selective filter circuit including at least one lowpass pole providing a near-DC filtered thoracic impedance signal, the at least one lowpass pole substantially attenuating or removing at least one of a heart contraction component and a respiration component of the thoracic impedance signal;
a blood resistivity measurement circuit, to provide a blood resistivity signal from which a blood resistivity measurement is obtained, the blood resistivity measurement being substantially independent of a variation resulting from heart contractions, respiration, and degree of thoracic fluid; and
a controller, coupled to the filter circuit and the blood resistivity measurement circuit, the controller operable to determine a thoracic fluid indication using the filtered thoracic impedance signal, including using the blood resistivity signal to reduce or eliminate an effect of a change in the blood resistivity on the thoracic fluid indication, the thoracic fluid indication determined by multiplying a thoracic impedance signal value by a ratio of a baseline blood resistivity to a blood resistivity measured close in time to a time when the thoracic impedance signal value was measured. - View Dependent Claims (75)
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76. A system comprising:
an implantable medical device, including;
a thoracic impedance measurement circuit, to provide a thoracic impedance signal;
a frequency selective filter circuit, coupled to the thoracic impedance measurement circuit to receive the thoracic impedance signal, the frequency selective filter circuit providing a near-DC filtered thoracic impedance signal;
a blood resistivity measurement circuit, to provide a blood resistivity signal;
means for determining a thoracic fluid indication using the filtered thoracic impedance signal; and
means for reducing or eliminating an effect of a change in blood resistivity on the thoracic fluid indication. - View Dependent Claims (77)
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78. A method comprising:
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detecting a first blood resistivity at a first time using at least one implanted intravascular or intracardiac electrode in a patient;
detecting a second blood resistivity at a second time using the at least one implanted intravascular or intracardiac electrode;
comparing the second blood resistivity to the first blood resistivity; and
if the second blood resistivity is less than the first blood resistivity by at least a threshold value, then declaring an indication or prediction of anemia to be present in the patient. - View Dependent Claims (79, 80, 81)
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82. A system comprising:
an implantable medical device, including;
first and second electrodes located within the same blood vessel or heart chamber;
a blood resistivity measurement circuit, to provide a blood resistivity signal obtained between the first and second electrodes at different first and second times; and
a controller, coupled to the blood resistivity measurement circuit, the controller operable to determine an indication or prediction of anemia by comparing a current blood resistivity to a stored baseline blood resistivity value. - View Dependent Claims (83, 84, 85, 86)
Specification