Cardiac rhythm management system with painless defribillation lead impedance measurement
First Claim
1. A method of determining an impedance between first and second defibrillation electrodes, the method comprising:
- delivering a first current, for a first time period, from the first defibrillation electrode to the second defibrillation electrode;
delivering a second current, for a second time period, from the second defibrillation electrode to the first defibrillation electrode, wherein a first charge delivered from the first defibrillation electrode during the first time period is approximately equal in magnitude to a second charge delivered from the second defibrillation electrode during the second time period; and
measuring a voltage associated with the first and second defibrillation electrodes while at least one of the first and second currents is being delivered.
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Abstract
A cardiac rhythm management system includes a defibrillation lead impedance measurement system by which defibrillation lead impedance is measured using a test current source different from the defibrillation output supply. A resulting voltage is measured to determine the defibrillation lead impedance. Using low amplitude test currents (e.g., 10-20 milliamperes) avoids patient discomfort. Charge-balanced test currents avoids charge build-up that may interfere with sensing and avoids electrode degeneration. Different current amplitudes and resulting measured voltages provide a differential defibrillation lead impedance measurement for canceling undesired effects. Bidirectional test currents account for polarity effects on the defibrillation lead impedance measurement. A calibration/correction technique uses measurements of known resistances to correct a measurement of an unknown defibrillation lead impedance measurement.
69 Citations
28 Claims
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1. A method of determining an impedance between first and second defibrillation electrodes, the method comprising:
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delivering a first current, for a first time period, from the first defibrillation electrode to the second defibrillation electrode;
delivering a second current, for a second time period, from the second defibrillation electrode to the first defibrillation electrode, wherein a first charge delivered from the first defibrillation electrode during the first time period is approximately equal in magnitude to a second charge delivered from the second defibrillation electrode during the second time period; and
measuring a voltage associated with the first and second defibrillation electrodes while at least one of the first and second currents is being delivered. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
measuring a first voltage associated with the first current level; and
measuring a second voltage associated with the second current level.
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6. The method of claim 5, further comprising obtaining a first indication of the impedance from a quotient of a difference between the first and second voltage measurements and a difference between the first and second current levels.
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7. The method of claim 6, in which delivering the second current includes delivering third and fourth current levels, and the third current level is different from the fourth current level.
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8. The method of claim 7, in which measuring the voltage further includes:
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measuring a third voltage associated with the third current level; and
measuring a fourth voltage associated with the fourth current level.
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9. The method of claim 8, further comprising obtaining a second indication of the impedance from a quotient of the difference between the third and fourth voltage measurements and a difference between the third and fourth current levels.
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10. The method of claim 9, further comprising obtaining a third indication of the impedance based on an average value of the first and second indications of the impedance.
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11. The method of claim 1, further comprising:
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measuring a first known impedance by delivering the first and second currents and measuring the voltage associated with the first and second defibrillation electrodes;
measuring a second known impedance, which is different in value from the first known impedance, by delivering the first and second currents and measuring the voltage associated with the first and second defibrillation electrodes;
measuring a third unknown impedance, by delivering the first and second currents and measuring the voltage associated with the first and second defibrillation electrodes; and
adjusting the third unknown impedance measurement based on the first and second known impedance measurements.
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12. A method of determining an impedance between first and second defibrillation electrodes, the method comprising:
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sourcing a first current, for a first time period, at the first defibrillation electrode;
sinking a second current, for a second time period, at the first defibrillation electrode, wherein a first charge sourced at the first defibrillation electrode during the first time period is approximately equal in magnitude to a second charge sunk at the first defibrillation electrode during the second time period; and
measuring a voltage associated with the first and second defibrillation electrodes while at least one of the first and second currents is being delivered.
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13. An apparatus for determining an impedance between first and second defibrillation electrodes, the apparatus comprising:
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means for delivering a first current, for a first time period, from the first defibrillation electrode to the second defibrillation electrode;
means for delivering a second current, for a second time period, from the second defibrillation electrode to the first defibrillation electrode, wherein a first charge delivered from the first defibrillation electrode during the first time period is approximately equal in magnitude to a second charge delivered from the second defibrillation electrode during the second time period; and
means for measuring a voltage associated with the first and second defibrillation electrodes while at least one of the first and second currents is being delivered.
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14. An apparatus for determining an impedance between first and second defibrillation electrodes, the apparatus comprising:
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a first current source/sink circuit coupled to the first defibrillation electrode;
a first voltage measurement circuit coupled to the first defibrillation electrode;
a second current source/sink circuit coupled to the second defibrillation electrode;
a controller, providing control signals to the first and second current source/sink circuits for sourcing a first charge at the first electrode and sinking a second charge at the first electrode, wherein the first and second charges are approximately equal in magnitude. - View Dependent Claims (15, 16, 17, 18, 19)
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20. An apparatus for determining an impedance between first and second defibrillation electrodes, the apparatus comprising:
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a first current source/sink circuit;
a first diode, coupling the first current source/sink circuit to the first defibrillation electrode;
a first voltage measurement circuit, coupled to the first defibrillation electrode through the first diode;
a second current source/sink circuit;
a second diode, coupling the second current source/sink circuit to the second defibrillation electrode; and
a second voltage measurement circuit, coupled to the second defibrillation electrode through the second diode. - View Dependent Claims (21, 22, 23)
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24. An apparatus for determining an impedance between first and second defibrillation electrodes, the apparatus comprising:
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a first diode, coupled to the first defibrillation electrode;
a second diode, coupled to the second defibrillation electrode;
a first current source/sink circuit;
a first voltage measurement circuit; and
a multiplexer circuit, coupling at least one of the first current source/sink circuit and the first voltage measurement circuit to each of the first and second defibrillation electrodes through the respective first and second diodes.
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25. An apparatus comprising:
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first and second defibrillation electrodes;
a first diode having an anode and a cathode, the cathode of the first diode coupled to the first defibrillation electrode;
a second diode having an anode and a cathode, the cathode of the second diode coupled to the second defibrillation electrode;
a first current source/sink circuit, coupled to the anode of the first diode;
a second current source/sink circuit, coupled to the anode of the second diode;
a controller, providing control signals to the first and second current source/sink circuits for sourcing a first charge at the first electrode and sinking a second charge at the first electrode, wherein the first and second charges are approximately equal in magnitude;
a first differential voltage measurement circuit, coupled to the anode of the first diode;
a first switching device, coupling the first defibrillation electrode to a ground node;
a second switching device, coupling the second defibrillation electrode to the ground node; and
a defibrillation output supply, coupled to the first defibrillation electrode through a third switching device, and coupled to the second defibrillation electrode through a fourth switching device. - View Dependent Claims (26, 27, 28)
a first zener diode, including an anode coupled to the ground node and a cathode coupled to the anode of the first diode; and
a second zener diode, including an anode coupled to the ground node and a cathode coupled to the anode of the second diode.
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27. The apparatus of claim 25, further comprising:
a multiplexer, coupling the first differential voltage measurement device to the anodes of each of the first and second diodes.
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28. The apparatus of claim 25, in which the first and second current source/sink circuits are the same circuit, and further comprising a multiplexer coupling the first and second current source/sink circuits to the anodes of each of the first and second diodes.
Specification