Method and apparatus for electrode and transthoracic impedance estimation
AssigneeCardiotronics, Inc.
InventorGail D. Baura
Life of this patent
Estimating the term…
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 2.pi.*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.
Claims16
A method for estimating impedance, comprising the steps of:
- (1) applying a square wave input voltage, V.sub.in (t), across a load impedance to be measured in series with a selected resistance;
- (2) measuring a resulting output voltage, V.sub.out (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 V.sub.in (t) and V.sub.out (t) based on circuit analysis;
- (5) estimating a second transfer function between V.sub.in (t) and V.sub.out (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.
A method for estimating a load impedance, comprising the steps of:
- applying an input voltage V.sub.in (t) across the load in series with a selected resistance to derive an output voltage V.sub.out (t);
- estimating a first transfer function between V.sub.in (t) and V.sub.out (t) based on circuit analysis;
- estimating a second transfer function between V.sub.in (t) and V.sub.out (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.
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:
- 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.
Dependencies are inferred from the claim text.