Method and apparatus for electrode and transthoracic impedance estimation
First Claim
1. A method for estimating impedance, comprising the steps of:
- (1) applying a square wave input voltage, Vin (t), across a load impedance to be measured in series with a selected resistance;
(2) measuring a resulting output voltage, Vout (t);
(3) modeling the load impedance to be measured as a resistance component in series with a capacitance component;
(4) estimating a first transfer function between Vin (t) and Vout (t) based on circuit analysis;
(5) estimating a second transfer function between Vin (t) and Vout (t) based on a standard autoregressive moving average model; and
(6) equating said first and second estimated transfer functions to derive an estimation of the respective resistance and capacitance components of the load impedance.
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Abstract
Impedance across a load, such as a pair of face-to-face electrodes, or across electrodes in contact with a patient'"'"'s chest cavity, respectively, is modeled as a resistor in series with a capacitor, wherein the reactance component of the impedance equals 2π*frequency/capacitance. A reference square wave voltage is applied to the load in series with a selected load resistor, and a response voltage is measured across the load. Both the reference voltage and the response voltage are then used to estimate a transfer function between them. Equating this transfer function to a resistor-capacitor circuit model results in estimation of the actual resistance and capacitance components of the true impedance.
275 Citations
16 Claims
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1. A method for estimating impedance, comprising the steps of:
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(1) applying a square wave input voltage, Vin (t), across a load impedance to be measured in series with a selected resistance; (2) measuring a resulting output voltage, Vout (t); (3) modeling the load impedance to be measured as a resistance component in series with a capacitance component; (4) estimating a first transfer function between Vin (t) and Vout (t) based on circuit analysis; (5) estimating a second transfer function between Vin (t) and Vout (t) based on a standard autoregressive moving average model; and (6) equating said first and second estimated transfer functions to derive an estimation of the respective resistance and capacitance components of the load impedance.
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2. A method for estimating a load impedance, comprising the steps of:
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applying an input voltage Vin (t) across the load in series with a selected resistance to derive an output voltage Vout (t); estimating a first transfer function between Vin (t) and Vout (t) based on circuit analysis; estimating a second transfer function between Vin (t) and Vout (t) based on a modelling technique; and equating the first and second estimated transfer functions to derive respective resistance and reactance components of the load impedance. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10)
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9. The method of claim 6, wherein the reactance component of the load impedance is estimated by fitting a digitally sampled decay of Vout (t) to estimate a capacitance that is inversely proportional to the reactance component.
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10. The method of claim 9, wherein the capacitance is estimated by employing an optimization technique to minimize a squared error between observed and calculated decays of Vout (t).
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11. A method for selecting a defibrillation charge level to be delivered by a defibrillator to a patient over an electrode pair attached to the patient, comprising the following steps:
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applying an input voltage across the electrodes in series with a selected resistance and measuring the resulting output voltage; estimating a first transfer function between the input voltage and output voltage based on circuit analysis; estimating a second transfer function between the input voltage and output voltage based on a modelling technique; and equating the first and second estimated transfer functions to derive respective resistance and reactance components of the combined patient and electrode impedance. - View Dependent Claims (12, 13, 14, 15, 16)
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Specification