Method and apparatus for high current electrode, transthoracic and transmyocardial impedance estimation
First Claim
1. A method for adjusting an output voltage level supplied by a defibrillator discharge capacitor to a patient over an electrode pair, comprising the following steps:
- delivering a first defibrillation voltage across the electrodes in series with a selected load resistance and measuring the resulting output voltage;
estimating a first transfer function between the first defibrillation voltage and output voltage based on circuit analysis;
estimating a second transfer function between the first defibrillation 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 patient and electrode impedance.
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Accused Products
Abstract
Impedance across a load, such as a pair of face-to-face electrodes and/or a patient'"'"'s transthoracic and transmyocardial impedance, 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. Alternately, the impedance may be measured with a high current load, such as during a defibrillator discharge. In this case, the voltage input and outputs are sampled at a much faster rate for the resistance component estimation, with the capacitance initialization adapted for the specific type of defibrillator waveform input.
47 Citations
13 Claims
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1. A method for adjusting an output voltage level supplied by a defibrillator discharge capacitor to a patient over an electrode pair, comprising the following steps:
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delivering a first defibrillation voltage across the electrodes in series with a selected load resistance and measuring the resulting output voltage;
estimating a first transfer function between the first defibrillation voltage and output voltage based on circuit analysis;
estimating a second transfer function between the first defibrillation 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 patient and electrode impedance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
and where Rd represents an internal resistance of the defibrillator, L represents an inductance of the defibrillator, Cd represents the capacitance of the defibrillator discharge capacitor, R represents the resistance component of the electrode and patient impedance, and R1 is the selected load resistance, respectively.
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9. A method for estimating a load impedance, comprising the steps of:
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applying a high current 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 (10, 11, 12, 13)
and where Rd represents an internal resistance of the defibrillator, L represents an inductance of the defibrillator, Cd represents the capacitance of the defibrillator discharge capacitor, R represents the resistance component of the electrode and patient impedance, and R1 is the selected load resistance, respectively.
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Specification