Device for monitoring fluid status
First Claim
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1. A device, comprising:
- an exciter for outputting an excitation current waveform and impressing a current field between a pair of excitation current electrodes;
voltage sensing circuitry for sensing a voltage difference signal between a pair of voltage sense electrodes disposed in a patient'"'"'s blood and in the current field;
means for measuring an electrolyte concentration in the patient'"'"'s blood;
a controller interfaced to the voltage sensing circuitry which is programmed to estimate the patient'"'"'s hematocrit from the voltage difference signal and the measured electrolyte concentration; and
,wherein the controller is programmed to estimate the patient'"'"'s hematocrit with a mapping function which maps a capacitance value derived from the voltage difference signal to a hematocrit value and programmed to derive a capacitance value from the voltage difference signal by deriving a resistance value from the voltage difference signal at a first excitation frequency and measuring a phase angle between the excitation current waveform and the voltage difference signal at a second excitation frequency.
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Abstract
A technique for determining a patient'"'"'s hematocrit by an electrical impedance measurement is described. An implantable device may be configured to utilize the technique in order to assess a cardiac patient'"'"'s fluid status. In order to determine the hematocrit, the electrical impedance of the blood is measured and mapped by a mapping function to a corresponding hematocrit value.
42 Citations
15 Claims
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1. A device, comprising:
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an exciter for outputting an excitation current waveform and impressing a current field between a pair of excitation current electrodes; voltage sensing circuitry for sensing a voltage difference signal between a pair of voltage sense electrodes disposed in a patient'"'"'s blood and in the current field; means for measuring an electrolyte concentration in the patient'"'"'s blood; a controller interfaced to the voltage sensing circuitry which is programmed to estimate the patient'"'"'s hematocrit from the voltage difference signal and the measured electrolyte concentration; and
,wherein the controller is programmed to estimate the patient'"'"'s hematocrit with a mapping function which maps a capacitance value derived from the voltage difference signal to a hematocrit value and programmed to derive a capacitance value from the voltage difference signal by deriving a resistance value from the voltage difference signal at a first excitation frequency and measuring a phase angle between the excitation current waveform and the voltage difference signal at a second excitation frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for monitoring the fluid status of a patient, comprising:
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outputting an excitation current waveform and impressing a current field between a pair of excitation current electrodes; sensing a voltage difference signal between a pair of voltage sense electrodes disposed in the patient'"'"'s blood and in the current field; measuring an electrolyte concentration in the patient'"'"'s blood; estimating the patient'"'"'s hematocrit from the voltage difference signal and the measured electrolyte concentration; and
,estimating the patient'"'"'s hematocrit with a mapping function which maps a capacitance value derived from the voltage difference signal to a hematocrit value and deriving a capacitance value from the voltage difference signal by deriving a resistance value from the voltage difference signal at a first excitation frequency and measuring a phase angle between the excitation current waveform and the voltage difference signal at a second excitation frequency. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A device, comprising:
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an exciter for outputting an excitation current waveform and impressing a current field between a pair of excitation current electrodes; voltage sensing circuitry for sensing a voltage difference signal between a pair of voltage sense electrodes disposed in a patient'"'"'s blood and in the current field; means for measuring the electrolyte concentration in the patient'"'"'s blood; a controller interfaced to the voltage sensing circuitry which is programmed to estimate the patient'"'"'s hematocrit from the voltage difference signal and the measured electrolyte concentration; and
,wherein the controller is programmed to estimate the patient'"'"'s hematocrit with a mapping function which maps a capacitance value derived from the voltage difference signal to a hematocrit value and programmed to derive a capacitance value from the voltage difference signal by deriving a resistance value from the voltage difference signal at a first excitation frequency and measuring the amplitude of the voltage difference signal at a second excitation frequency.
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Specification