Minute ventilation sensor with dynamically adjusted excitation current
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 between the excitation current electrodes as a bipolar excitation current waveform at a specified excitation frequency and amplitude, wherein the excitation current waveform is output as a strobe made up of a specified number of excitation current waveform cycles with each strobe repeated at a specified strobing frequency;
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 strobe at a specified sampling rate that corresponds to the excitation frequency;
circuitry for initiating a noise detection operation wherein the voltage sense signal is sampled when no excitation current is supplied and the samples are then processed to detect a noise level; and
, circuitry for adjusting the excitation current in accordance with the detected noise level.
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Abstract
A minute ventilation sensing device in which transthoracic impedance is measured with a excitation current waveform at a specified amplitude and frequency. In order reduce interference with the impedance measurement from external noise sources, a noise detection operation may be performed with the amplitude and/or frequency of the excitation current waveform adjusted accordingly.
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Citations
23 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 between the excitation current electrodes as a bipolar excitation current waveform at a specified excitation frequency and amplitude, wherein the excitation current waveform is output as a strobe made up of a specified number of excitation current waveform cycles with each strobe repeated at a specified strobing frequency;
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 strobe at a specified sampling rate that corresponds to the excitation frequency;
circuitry for initiating a noise detection operation wherein the voltage sense signal is sampled when no excitation current is supplied and the samples are then processed to detect a noise level; and
,circuitry for adjusting the excitation current in accordance with the detected noise level. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. 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 between the excitation current electrodes as a bipolar excitation current waveform at a specified excitation frequency and amplitude, wherein the excitation current waveform is output as a strobe made up of a specified number of excitation current waveform cycles with each strobe repeated at a specified strobing frequency;
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 strobe at a specified sampling rate that corresponds to the excitation frequency;
a demodulator for generating a weighted average of the voltage sense signal samples of each strobe with a filter coefficient for each sample that is positive or negative in accordance with the polarity of the excitation current waveform such that an impedance portion of the voltage sense signal is low-pass filtered while an external field portion of the voltage sense signal is high-pass filtered;
circuitry for filtering the demodulated voltage sense signal samples into a ventilation band defined by an upper ventilation frequency and a lower ventilation frequency to thereby generate a ventilation signal;
circuitry for deriving a signal proportional to minute ventilation from the ventilation signal;
circuitry for initiating a noise detection operation wherein the voltage sense signal is sampled when no excitation current is supplied and the resulting samples are processed to detect a noise level; and
,circuitry for adjusting the excitation current in accordance with the detected noise level.
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15. A method for sensing minute ventilation, comprising:
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imposing a current field in the thoracic cavity as a bipolar excitation current waveform at a specified excitation frequency and amplitude, wherein the excitation current waveform is output as a strobe made up of a specified number of excitation current waveform cycles with each strobe repeated at a specified strobing frequency;
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 strobe at a sampling rate that corresponds to the excitation frequency;
initiating a noise detection operation wherein the voltage sense signal is sampled when no excitation current is supplied and the samples are then processed to detect a noise level; and
,adjusting the excitation current in accordance with the detected noise level. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23)
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Specification