Multiple frequency impedance measurement system
First Claim
1. A cardiac pacemaker, comprising:
- pulse generator means for generating cardiac pacing pulses and for delivering said cardiac pacing pulses to a patient'"'"'s heart;
timing means coupled to said pulse generator means for controlling the rate at which said pacing pulses are generated;
means for monitoring said patient'"'"'s body tissue, said means for monitoring comprising a pair of electrodes adapted to be in contact with said tissue to be monitored, signal generator means for generating electrical signals at at least first and second frequencies for application to said pair of electrodes, measuring means responsive to signals at said first and second frequencies, for measuring the impedance between said pair of electrodes at said first and second frequencies, and means for detecting changes in the relationship of said measured impedances at said first and second frequencies; and
means coupled to said monitoring means and to said timing means for varying the rate at which said pacing pulses are generated in response to the detection of changes in said relationship of said impedances measured at said first and second frequencies.
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Accused Products
Abstract
A physiological monitoring system for monitoring the condition of a patient'"'"'s body tissue. The device includes electrodes for contacting the tissue to be monitored, circuitry for generating electrical signals at at least two frequencies for application to the tissue and circuitry for monitoring the impedance of the tissue, at the frequencies applied. The device includes in addition apparatus for detecting changes in the relationship of the measured impedances at the frequencies applied, and for processing the detected changes in impedance relationship to provide an indication of the condition of the tissue. The monitoring apparatus may be practiced in the context of an implantable stimulator, such as a cardiac pacemaker, in which the pulse frequency is varied as a function of the detected condition of the tissue.
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Citations
23 Claims
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1. A cardiac pacemaker, comprising:
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pulse generator means for generating cardiac pacing pulses and for delivering said cardiac pacing pulses to a patient'"'"'s heart; timing means coupled to said pulse generator means for controlling the rate at which said pacing pulses are generated; means for monitoring said patient'"'"'s body tissue, said means for monitoring comprising a pair of electrodes adapted to be in contact with said tissue to be monitored, signal generator means for generating electrical signals at at least first and second frequencies for application to said pair of electrodes, measuring means responsive to signals at said first and second frequencies, for measuring the impedance between said pair of electrodes at said first and second frequencies, and means for detecting changes in the relationship of said measured impedances at said first and second frequencies; and means coupled to said monitoring means and to said timing means for varying the rate at which said pacing pulses are generated in response to the detection of changes in said relationship of said impedances measured at said first and second frequencies. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A physiological monitoring device, comprising:
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means for monitoring the condition of a patient'"'"'s body tissue, said means for monitoring comprising a pair of electrodes adapted to be in contact with said tissue to be monitored, signal generator means for generating electrical signals at at least first and second frequencies for application to said pair of electrodes, measuring means responsive to signals at said first and second frequencies, for measuring the impedance between said pair of electrodes at said first and second frequencies, and means for detecting changes in the relationship of said measured impedances at said first and second frequencies, wherein said monitoring means comprises mean for calculating average values of said impedances measured at said first and second frequencies over predetermined periods of time and wherein said detecting means comprises means for comparing said average values to detect changes in said relationship of said measured impedances at said first and second frequencies; and means coupled to said monitoring means for providing indications of said detected changes in said relationship of said impedances measured at said first and second frequencies. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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19. A method of monitoring the condition of a patient'"'"'s tissue, comprising:
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determining a first frequency at which said tissue displays an impedance minimum and a second frequency at which said tissue displays an impedance maximum; locating a pair of electrodes in contact with said tissue; applying electrical signals at said first and second frequencies to said pair of electrodes; measuring the impedance between said pair of electrodes at said first and second frequencies; and measuring changes in the relationship of said measured impedances at said first an second frequencies. - View Dependent Claims (20, 21, 22, 23)
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Specification