MINUTE VENTILATION SENSOR WITH AUTOMATIC HIGH PASS FILTER ADJUSTMENT
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;
voltage sense electrodes for generating an impedance signal corresponding to a potential difference between two points in the thoracic cavity when the excitation current is applied;
sampling circuitry for sampling the impedance signal;
circuitry for filtering the impedance signal samples into a ventilation band to thereby generate a ventilation signal, wherein the filtering circuitry includes a high pass filter with a variable pole frequency for removing a DC component from the impedance signal samples;
circuitry for calculating a signal variation parameter from a set of impedance signal samples;
circuitry for adjusting a frequency response of the high pass filter to compensate for changes in the calculated signal variation parameter; and
, circuitry for deriving a signal proportional to minute ventilation from the ventilation signal.
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Abstract
A minute ventilation sensing device in which transthoracic impedance is measured to generate an impedance signal from which a ventilation signal is derived, where the ventilation signal is proportional to minute ventilation. An adaptive high pass filter is used to filter the impedance signal into a ventilation band. The pole frequency of the high pass filter is adjusted in accordance with changes in a calculated signal variation parameter.
71 Citations
20 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;
voltage sense electrodes for generating an impedance signal corresponding to a potential difference between two points in the thoracic cavity when the excitation current is applied;
sampling circuitry for sampling the impedance signal;
circuitry for filtering the impedance signal samples into a ventilation band to thereby generate a ventilation signal, wherein the filtering circuitry includes a high pass filter with a variable pole frequency for removing a DC component from the impedance signal samples;
circuitry for calculating a signal variation parameter from a set of impedance signal samples;
circuitry for adjusting a frequency response of the high pass filter to compensate for changes in the calculated signal variation parameter; and
,circuitry for deriving a signal proportional to minute ventilation from the ventilation signal. - View Dependent Claims (2, 3, 4)
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5. 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;
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;
voltage sense electrodes for generating an impedance signal corresponding to a potential difference between two points in the thoracic cavity when the excitation current is applied;
sampling circuitry for sampling the impedance signal;
circuitry for filtering the impedance signal samples into a ventilation band to thereby generate a ventilation signal, wherein the filtering circuitry includes a high pass filter with a variable pole frequency for removing a DC component from the impedance signal samples;
circuitry for calculating a signal variation parameter from a set of impedance signal samples;
circuitry for adjusting a frequency response of the high pass filter to compensate for changes in the calculated signal variation parameter;
circuitry for deriving a signal proportional to minute ventilation from the ventilation signal; and
,circuitry for modulating a rate at which paces are delivered by the controller in accordance with the signal proportional to minute ventilation. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12)
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13. A method for measuring minute ventilation, comprising:
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imposing an excitation current field in the thoracic cavity;
generating an impedance signal corresponding to a potential difference between two points in the thoracic cavity when the excitation current field is imposed;
sampling the impedance signal;
filtering the impedance signal samples into a ventilation band to thereby generate a ventilation signal, including high pass filtering the impedance signal samples with a high pass filter having a variable pole frequency for removing a DC component from the impedance signal samples;
calculating a signal variation parameter from a set of impedance signal samples;
adjusting a frequency response of the high pass filter step to compensate for changes in the calculated signal variation parameter; and
,deriving a signal proportional to minute ventilation from the ventilation signal. - View Dependent Claims (14, 15, 16)
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17. A minute ventilation sensor, comprising:
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means for imposing an excitation current field in the thoracic cavity;
means for generating an impedance signal corresponding to a potential difference between two points in the thoracic cavity when the excitation current field is imposed;
means for sampling the impedance signal;
means for filtering the impedance signal samples into a ventilation band to thereby generate a ventilation signal, including high pass filtering the impedance signal samples with a high pass filter having a variable pole frequency for removing a DC component from the impedance signal samples;
means for calculating a signal variation parameter from a set of impedance signal samples;
means for adjusting a frequency response of the high pass filter step to compensate for changes in the calculated signal variation parameter; and
,means for deriving a signal proportional to minute ventilation from the ventilation signal. - View Dependent Claims (18, 19, 20)
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Specification