Tissue characterization using intracardiac impedances with an implantable lead system
First Claim
1. A method for use in an implantable device, comprising:
- generating pulses to apply to a bodily tissue via an electrode, wherein each pulse has an asymmetric amplitude waveform possessing alternating positive and negative phases that are charge-balanced and voltage-balanced, the asymmetric amplitude waveform having a duration less than a charging time constant of an electrode-electrolyte interface between the electrode and the bodily tissue;
applying the pulses having the waveform to the bodily tissue, wherein the pulses are applied at a frequency within a range of frequencies consisting of approximately 1 Hz to approximately 100 kHz; and
measuring an effect of the applied pulses to determine a physiological parameter.
1 Assignment
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Accused Products
Abstract
An implantable system acquires intracardiac impedance with an implantable lead system. In one implementation, the system generates frequency-rich, low energy, multi-phasic waveforms that provide a net-zero charge and a net-zero voltage. When applied to bodily tissues, current pulses or voltage pulses having the multi-phasic waveform provide increased specificity and sensitivity in probing tissue. The effects of the applied pulses are sensed as a corresponding waveform. The waveforms of the applied and sensed pulses can be integrated to obtain corresponding area values that represent the current and voltage across a spectrum of frequencies. These areas can be compared to obtain a reliable impedance value for the tissue. Frequency response, phase delay, and response to modulated pulse width can also be measured to determine a relative capacitance of the tissue, indicative of infarcted tissue, blood to tissue ratio, degree of edema, and other physiological parameters.
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Citations
28 Claims
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1. A method for use in an implantable device, comprising:
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generating pulses to apply to a bodily tissue via an electrode, wherein each pulse has an asymmetric amplitude waveform possessing alternating positive and negative phases that are charge-balanced and voltage-balanced, the asymmetric amplitude waveform having a duration less than a charging time constant of an electrode-electrolyte interface between the electrode and the bodily tissue; applying the pulses having the waveform to the bodily tissue, wherein the pulses are applied at a frequency within a range of frequencies consisting of approximately 1 Hz to approximately 100 kHz; and measuring an effect of the applied pulses to determine a physiological parameter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A method for use in an implantable device, comprising:
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generating pulses to apply to a bodily tissue via an electrode, wherein each pulse has a waveform possessing alternating positive and negative phases that are charge-balanced and voltage-balanced, the waveform having a duration less than a charging time constant of an electrode-electrolyte interface between the electrode and the bodily tissue, the waveform having a null segment having a duration sufficient to allow electronics in a processing circuit of the implantable device to settle intervenes between each positive phase and each negative phase; applying the pulses having the waveform to the bodily tissue; and measuring an effect of the applied pulses to determine a physiological parameter, wherein measuring an effect of the applied pulses includes; deriving an area of voltage waveforms resulting from applying current pulses having the waveform; and deriving an impedance value of the bodily tissue by dividing the area of the voltage waveforms by an area of the current pulses having the waveform. - View Dependent Claims (20, 21, 22, 23)
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24. A method for use in an implantable device, comprising:
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generating pulses to apply to a bodily tissue via an electrode, wherein each pulse has a waveform possessing alternating positive and negative phases that are charge-balanced and voltage-balanced, at least one negative phase having an absolute amplitude less than an absolute amplitude of one of the positive phases, the waveform having a duration less than a charging time constant of en electrode-electrolyte interface between the electrode and the bodily tissue; applying the pulses having the waveform to the bodily tissue; and measuring an effect of the applied pulses to determine a physiological parameter, wherein measuring an effect of the applied pulses includes; measuring a current waveform over time resulting from applying a voltage pulse having the waveform; deriving an area of each current waveform that results from applying the voltage pulses having the waveform; and deriving an impedance value of the bodily tissue by dividing the area of the voltage pulses having the waveform by an area of the current waveforms. - View Dependent Claims (25, 26, 27, 28)
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Specification