Method and apparatus to measure bioelectric impedance of patient tissue
First Claim
1. A device for measuring an impedance of a tissue of a patient, the device comprising:
- calibration circuitry comprising an impedance;
at least four electrodes configured to couple to the tissue of the patient, the at least four electrodes comprising at least two measurement electrodes and at least two drive electrodes;
drive circuitry coupled to the at least two drive electrodes and the calibration circuitry to pass a current through the tissue and the calibration circuitry simultaneously, the drive circuitry configured to increase the current from a first current amount at a first frequency to a second current amount at a second frequency, the second frequency greater than the first frequency;
measurement circuitry configured to couple to the at least two measurement electrodes and the calibration circuitry, the measurement circuitry configured to measure a calibration signal from the calibration circuitry and a tissue impedance signal from the at least two measurement electrodes; and
processor circuitry comprising a tangible medium configured to determine the impedance of the tissue in response to the calibration signal and the tissue impedance signal.
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Accused Products
Abstract
A device to measure tissue impedance comprises drive circuitry coupled to calibration circuitry, such that a calibration signal from the calibration circuitry corresponds to the current delivered through the tissue. Measurement circuitry can be coupled to measurement electrodes and the calibration circuitry, such that the tissue impedance can be determined in response to the measured calibration signal from the calibration circuitry and the measured tissue impedance signal from the measurement electrodes. Processor circuitry comprising a tangible medium can be configured to determine a complex tissue impedance in response to the calibration signal and the tissue impedance signal. The processor can be configured to select a frequency for the drive current, and the amount of drive current at increased frequencies may exceed a safety threshold for the drive current at lower frequencies.
948 Citations
38 Claims
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1. A device for measuring an impedance of a tissue of a patient, the device comprising:
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calibration circuitry comprising an impedance; at least four electrodes configured to couple to the tissue of the patient, the at least four electrodes comprising at least two measurement electrodes and at least two drive electrodes; drive circuitry coupled to the at least two drive electrodes and the calibration circuitry to pass a current through the tissue and the calibration circuitry simultaneously, the drive circuitry configured to increase the current from a first current amount at a first frequency to a second current amount at a second frequency, the second frequency greater than the first frequency; measurement circuitry configured to couple to the at least two measurement electrodes and the calibration circuitry, the measurement circuitry configured to measure a calibration signal from the calibration circuitry and a tissue impedance signal from the at least two measurement electrodes; and processor circuitry comprising a tangible medium configured to determine the impedance of the tissue in response to the calibration signal and the tissue impedance signal. - 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, 37)
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24. A device for measuring an impedance of a tissue of a patient, the device comprising:
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at least four electrodes configured to couple to the tissue of the patient, the at least four electrodes comprising at least two drive electrodes and at least two measurement electrodes; drive circuitry coupled to the at least two drive electrodes to pass a variable current through the tissue to generate a tissue measurement signal, the drive circuitry configured to increase the current from a first current amount at a first frequency to a second current amount at a second frequency, the second frequency greater than the first frequency; and measurement circuitry coupled to the at least two measurement electrodes to determine the impedance of the tissue in response to the tissue measurement signal, the measurement circuitry comprising a variable gain of the measurement signal configured to decrease from a first gain at the first frequency to a second gain at the second frequency. - View Dependent Claims (25, 26, 27, 28, 29, 30)
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31. A method of measuring patient impedance, the method comprising:
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providing at least four electrodes comprising at least two drive electrodes and at least two measurement electrodes, the at least two drive electrodes connected in series to a calibration resistor; providing measurement circuitry to measure a tissue impedance signal from the measurement electrodes; passing a drive current through the patient impedance and the calibration resistor simultaneously with the drive circuitry, wherein the drive circuitry increases the drive current through the patient as a frequency of the drive current increases; measuring a current signal from the calibration resistor in response to the current through the calibration resistor; measuring the tissue impedance signal from the measurement electrodes; and determining the tissue impedance in response to the current signal and the tissue impedance signal. - View Dependent Claims (32, 33, 34, 35, 36, 38)
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Specification