Method and apparatus for differential lead impedance comparison
First Claim
1. An appartus for use with devices employing electrodes that senses the integrity of lead connections comprising:
- (a) a first lead and a current source means coupled to said first lead and a current source means coupled to said first lead having a first lead impedance, a second lead having a second lead impedance and a reference lead having a reference lead impedance, wherein said current source means;
(i) produces a first AC current and applies said first AC current to said first lead;
(ii) produces a second AC current and applies said second AC current to said second lead; and
,(iii) produces a reference AC current and applies said reference AC current to said reference lead;
(b) a receiver coupled to said first and second leads for receiving a first voltage produced by said first AC current and said first lead impedance and a second voltage produced by said second AC current and said second lead impedance;
(c) differential amplifying means for differentially amplifying said first and second voltages to produce first and second differential impedance voltages, wherein said first differential impedance voltage is proportional to a first difference between said first and second lead impedances and wherein said second differential impedance voltage is proportional to a second difference between said first and second lead impedances;
(d) an output means coupled to said differential amplifying means for receiving said first and second differential impedance voltages and producing a leads-off output signal when one and only one of said first and second differential impedance voltages equals or exceeds a corresponding first or second threshold level.
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Accused Products
Abstract
A differential lead impedance comparison apparatus (10) senses lead impedance and compensates for patient-to-patient and electrode variability. A bridge circuit (12) is connected to one end of electrode conductors (22, 24 and 26) in an ECG Leads I configuration. The other end of the conductors (22, 24 and 26) are connected to a patient (18) via electrodes (RA, LA and LL). Leads formed in part by RA, LA and LL and the respective conductors (22, 24 and 26) have lead impedances (Rb, Ra, and Rc). Constant current sources (I1, I2 and I3) are connected to the conductors (22, 24, and 26) and supply constant AC currents (I1, I2 and I3). A first bridge output voltage (VM) is produced by I1 and a combination 32 of Ra, Rb, and Rc. A second bridge output voltage (VP) is produced by I2 and a combination 34 of Ra, Rb, and Rc. A differential amplifier circuit (14) differentially amplifies the VM and VP voltages to produce differential voltages (VOM and VOP). Demodulators (DM1 and DM2) demodulate VOM and VOP to produce differential impedance voltages (V1M and V1P). A first comparator (OA3) changes states and produces a high logic output when V1M equals or exceeds a first threshold level (VTH1). A second comparator (OA4) changes states and produces a high logic output when V1P equals or exceeds a second threshold level (VTH2). An exclusive OR gate (G1) produces a high logic output (VOUT) when one and only one of OA3 or OA4 produce a high logic output.
52 Citations
15 Claims
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1. An appartus for use with devices employing electrodes that senses the integrity of lead connections comprising:
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(a) a first lead and a current source means coupled to said first lead and a current source means coupled to said first lead having a first lead impedance, a second lead having a second lead impedance and a reference lead having a reference lead impedance, wherein said current source means; (i) produces a first AC current and applies said first AC current to said first lead; (ii) produces a second AC current and applies said second AC current to said second lead; and
,(iii) produces a reference AC current and applies said reference AC current to said reference lead; (b) a receiver coupled to said first and second leads for receiving a first voltage produced by said first AC current and said first lead impedance and a second voltage produced by said second AC current and said second lead impedance; (c) differential amplifying means for differentially amplifying said first and second voltages to produce first and second differential impedance voltages, wherein said first differential impedance voltage is proportional to a first difference between said first and second lead impedances and wherein said second differential impedance voltage is proportional to a second difference between said first and second lead impedances; (d) an output means coupled to said differential amplifying means for receiving said first and second differential impedance voltages and producing a leads-off output signal when one and only one of said first and second differential impedance voltages equals or exceeds a corresponding first or second threshold level. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for sensing the integrity of lead connections comprising the steps of:
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(a) producing first and second AC currents and a reference AC current; (b) applying said first AC current to a first lead having a first lead impedance, applying said second AC current to a second lead having a second lead impedance and applying said reference AC current to a reference lead having a reference lead impedance; (c) receiving a first voltage produced by said first current and said first lead impedance and receiving a second voltage produced by said second current and said second lead impedance; (d) differentially amplifying said first and second voltages to produce a first differential impedance voltage and a second differential impedance voltage, wherein said first differential impedance voltage is proportional to a first difference between said first and second lead impedances and said second differential impedance voltage is proportional to a second difference between said first and second lead impedances; and
,(e) producing a leads-off output signal when one and only one of said first or second differential impedance voltages equals or exceeds a corresponding first or second threshold level. - View Dependent Claims (14, 15)
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Specification