Automatically configurable minute ventilation sensor
First Claim
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1. A minute ventilation sensing device, comprising:
- excitation current electrodes for imposing a current field in the thoracic cavity;
an exciter for supplying excitation current as an excitation current waveform at a specified excitation frequency and amplitude between the excitation current electrodes;
a plurality of selectable voltage sense electrodes for generating a voltage sense signal corresponding to a potential difference between two points in the thoracic cavity;
sampling circuitry for sampling the voltage sense signal during the excitation waveform at a specified sampling rate that corresponds to the excitation frequency;
circuitry for demodulating and filtering the voltage sense signal samples into a ventilation band to thereby generate a ventilation signal;
circuitry for deriving a signal proportional to minute ventilation from the ventilation signal;
circuitry for detecting noise when no excitation current is supplied by filtering the voltage sense signal when no excitation current is supplied into the ventilation band and for computing an average noise level;
a switch matrix with the capability of switching between different electrode configurations for use as voltage sense electrodes; and
,circuitry for operating the switch matrix to select a configuration of voltage sense electrodes for use by the device that result in the lowest average noise level.
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Abstract
A minute ventilation sensing device in which transthoracic impedance is measured with voltage sense electrodes during injection of current by excitation current electrodes. The device is capable of operating with different configurations of voltage sense and excitation current electrodes. By computing a signal and/or noise level for a number of available configurations, the electrodes resulting in the highest signal-to-noise ratio may be selected for use by the device.
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Citations
19 Claims
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1. A minute ventilation sensing device, comprising:
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excitation current electrodes for imposing a current field in the thoracic cavity; an exciter for supplying excitation current as an excitation current waveform at a specified excitation frequency and amplitude between the excitation current electrodes; a plurality of selectable voltage sense electrodes for generating a voltage sense signal corresponding to a potential difference between two points in the thoracic cavity; sampling circuitry for sampling the voltage sense signal during the excitation waveform at a specified sampling rate that corresponds to the excitation frequency; circuitry for demodulating and filtering the voltage sense signal samples into a ventilation band to thereby generate a ventilation signal; circuitry for deriving a signal proportional to minute ventilation from the ventilation signal; circuitry for detecting noise when no excitation current is supplied by filtering the voltage sense signal when no excitation current is supplied into the ventilation band and for computing an average noise level; a switch matrix with the capability of switching between different electrode configurations for use as voltage sense electrodes; and
,circuitry for operating the switch matrix to select a configuration of voltage sense electrodes for use by the device that result in the lowest average noise level. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A cardiac rhythm management device, comprising:
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a sensing channel for detecting intrinsic cardiac activity; a pacing channel for pacing the heart; a controller for delivering paces in accordance with a programmed mode as modulated by a minute ventilation sensor; a minute ventilation sensor, comprising; excitation current electrodes for imposing a current field in the thoracic cavity; an exciter for supplying excitation current as an excitation current waveform at a specified excitation frequency and amplitude between the excitation current electrodes; a plurality of selectable voltage sense electrodes for generating a voltage sense signal corresponding to a potential difference between two points in the thoracic cavity; sampling circuitry for sampling the voltage sense signal during the excitation waveform at a specified sampling rate that corresponds to the excitation frequency; circuitry for demodulating and filtering the voltage sense signal samples into a ventilation band to thereby generate a ventilation signal; circuitry for deriving a signal proportional to minute ventilation from the ventilation signal; a switch matrix with the capability of switching between different electrode configurations for use as voltage sense electrodes; circuitry for detecting noise when no excitation current is supplied by filtering the voltage sense signal when no excitation current is supplied into the ventilation band and for computing an average noise level; and
,circuitry for operating the switch matrix to select a configuration of voltage sense electrodes for use by the device that result in the lowest average noise level.
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12. A method for operating a minute ventilation sensing device, comprising:
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imposing a current field in the thoracic cavity as an excitation current waveform at a specified excitation frequency and amplitude; generating a voltage sense signal corresponding to a potential difference between two points in the thoracic cavity; sampling the voltage sense signal during the excitation waveform at a sampling rate that corresponds to the excitation frequency; demodulating and filtering the voltage sense signal samples into a ventilation band to thereby generate a ventilation signal; deriving a signal proportional to minute ventilation from the ventilation signal; and
,selecting a configuration of voltage sense electrodes for use by the device among a plurality of available configurations, wherein the plurality includes at least a first voltage sense electrode configuration and a second voltage sense electrode configuration, by; for each of the first and second voltage sense electrode configurations, detecting noise in the voltage sense signal while no excitation current is supplied by filtering the voltage sense signal when no excitation current is supplied into the ventilation band and computing an average noise level; and
,as between the first and second voltage sense electrode configurations, selecting the configuration of voltage sense electrodes that results in the lowest average noise level. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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Specification